A Tour of the Cell exploring the organelles of cells

The cell is life's fundamental unit of structure and function

All Living Things are Composed of Cells

"A cell is regarded as the true biological atom"

-George Henry Lewes

  • The Cell Theory states that all living things are made up of cells, the cell is the basic unit of living things, and all cells arise from pre-existing cells
  • The cell is fundamental in biology- it is the simplest collection of matter that can live
  • Organisms can be simple, single celled organisms or they can be very complex and multicellular
  • There are many different kinds of cells that perform specialized, life functioning processes for organisms, in humans alone there are over 200 different cells
Top Row: Plant Cells, Nerve Cells, Animal Cells ~ Bottom Row: Red Blood Cells, Bacteria Cells

Two Types of Cells

Prokaryotic and Eukaryotic Cells

What is the main difference between the two?

Presence of a NUCLEUS and membrane bound ORGANELLES
  • Eukaryotic cells have a nucleus and have membrane bound organelles (ex. plant cells and animal cells)
  • Prokaryotes are cells that lack a nucleus and do not have membrane-bound organelles (ex. bacteria cells)
  • Organelles in Eukaryotic cells allow these cells to carry out many of life's necessary functions at once- they can even specialize a cell to perform certain tasks in the cells of organisms
  • Organelles compartmentalize certain parts of the cell by a cell membrane and allow for specialization
Eukaryotic vs. Prokaryotic Cell

Organelles in Different Types of Cells

  • Plant Cells and Animal Cells do not have all the same organelles and structures as each other
  • Both consist of some organelles they both share, but there are some organelles that only plants or animals have
  • Prokaryotes do not have membrane-bound organelles but they do have some of the same non-membrane organelle structures that Eukaryotes have
Animal Cells (Top) and Plant Cells (Bottom) have different organelles and structures
Lets explore the microscopic but powerful organelles of cells

Key Organelles

We will be focusing on:
  • Nucleus
  • Ribosomes
  • Rough Endoplasmic Reticulum
  • Smooth Endoplasmic Reticulum
  • Golgi Apparatus
  • Mitochondria
  • Chloroplast
  • Flagellum
  • Cillia
  • Lysosome
  • Food Vacuole
  • Central Vacuole

Nucleus

STRUCTURE:

  • The structure of a nucleus contains a nuclear membrane, chromosomes, nucleolus and cytoplasm
  • It is usually a spherical structure found towards the center of the cell
  • The cell nucleus is bound by a double membrane called the nuclear envelope: helps maintain the shape of the nucleus and act as a semipermeable membrane
  • The nuclear envelope is lined by the nuclear lamina
  • The envelope is perforated by pores called nuclear pores that help regulate the flow of molecules across the nuclear membrane
  • Within the nucleus the DNA is organized into small units called chromosomes which are arranged into long entangled structures called chromatin (DNA and its associated proteins) when the cell is not dividing
  • A permanent structure within the nucleus is the nucleolus: a dense structure composed of RNA and proteins
  • The nucleoplasm is the cytoplasmic liquid that fills the inside of the nucleus
Nucleus Diagrams

FUNCTION:

  • Control center of a cell as it contains all the cells instructions
  • The nucleus contains most of the genes in a eukaryotic cell- it houses most of the cell's DNA
  • The hereditary information stored in the nucleus controls the cell's growth, reproduction, intermediary metabolism and protein synthesis
  • DNA is able to replicate in the nucleus in order for a cell to divide
  • The nucleus directs protein synthesis by transcribing the information stored in DNA into messenger RNA (mRNA) to be transported out of the cell and into the cytoplasm where it is translated by ribosomes into proteins
  • The nucleolus synthesizes ribosomal RNA (rRNA) from instructions in the DNA
  • Also in the nucleolus, proteins imported from the cytoplasm are assembled with rRNA into large and small ribosomal subunits which are then exported out of the nucleus into the cytoplasm where they are assembled into ribosomes
  • Because it directs the synthesis of rRNA, ribosomes, and mRNA the nucleus is the control center of the cell also because it is responsible for the making of proteins which carry out the cell's actions encoded in the DNA

ORGANISMS THAT HAVE NUCLEUS:

  • All eukaryotic cells have a nucleus, so all animals, plants, fungi, and protists have a nucleus

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • A nucleus can be found in all eukaryotic cells, but some may have more than one nucleus- this is called multinucleated cells
  • Some common organs cells that have many cells with multiple nuclei are muscle cells, skeletal cells, liver cells, and some immune white blood cells
  • Osteoclasts are multinucleated cells which are found commonly in the human body that aid in the maintenance and repair of the bones
  • Certain types of fungi and protists have multinucleated cells
Multinucleated skeletal muscles (left) and osteoclasts (right)

DISEASES ASSOCIATED:

  • Emery-Dreifuss muscular dystrophy (EDMD) is a type of degenerative muscular disorder that affects muscles used for movement and heart muscles
  • Mutations in the EMD and LMNA genes cause EDMD: provide instructions for making proteins in the nuclear envelope
  • Nuclear envelope may play a role in regulating the activity of certain genes
  • Mutations in the EMD gene: normally provides instructions for making a protein called emerin- essential for the normal function of skeletal and cardiac muscle
  • Lack of emerin is believed to interfere with the reorganization of the nuclear membrane after a cell has divided: this leads to weak or dying cells
  • Muutations in LMNA gene: normally provides instructions for making two proteins, lamin A and lamin C
  • Nuclear membrane may become unstable when lamin proteins are abnormal leading to muscle breakdown

INTERESTING FACT:

  • Each human cell contains about 6 feet of DNA which is tightly packed and organized with proteins into 26 chromosomes

Ribosome

STRUCTURE:

  • Ribosomes are particles made of ribosomal RNA and proteins and are not surrounded by a membrane
  • Ribosomes are composed of two different subunits, called the large subunit and the small subunit- Both subunits are composed of rRNA and proteins
  • The large and small subunits assemble to form a ribosome
  • The smaller subunit binds to the larger subunit and mRNA, and the larger subunit binds to the tRNA, the amino acids, and the smaller subunit
  • Ribosomes can be found floating in the cytoplasm, called free ribosomes, or attached to the outside of the rough endoplasmic reticulum or the nuclear envelope, called bound ribosomes
  • Bound ribosomes and free ribosomes are structurally the same and ribosomes can alternate between the two roles
  • Prokaryotic ribosomes are smaller than eukaryotic ribosomes
Basic Diagram of Ribosome
Free vs. Bound Ribosomes

FUNCTION:

  • Ribosomes are the organelles that carry out protein synthesis
  • Ribosomes assemble amino acids to form specific proteins which are needed to carry out cellular activities
  • DNA information to build specific proteins are transcribed into mRNA which is then transported into the cytoplasm and binds to ribosomes which translates the mRNA with it's corresponding amino acids to build polypeptide chain with the help of transfer RNA (tRNA)
  • tRNA is bound to an amino acid and matches it's base pairs with the mRNA to add the amino acid to a growing polypeptide chain to make a protein
  • Most free ribosomes make proteins that function within the cytosol
  • Most bound ribosomes make proteins that are either inserted into membranes, packaged within certain organelles, or secreted from the cell
Protein Synthesis in Ribosomes

ORGANISMS THAT HAVE RIBOSOMES:

  • Ribosomes are found in both Eukaryotic and Prokaryotic cells
  • Plants, Animals, Fungi, Protists, and Bacteria all have ribosomes
  • Prokaryotic ribosomes are smaller than eukaryotic ribosomes- this is what allows antibiotics to only effect prokaryotic (bacterial) ribosomes
  • Prokaryotes, which do not have a nucleus, build their ribosomes in the cytosol

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • Cells that have high rates of protein synthesis need a lot of ribosomes such as those in the human pancreas which must make many enzymes
  • Stomach cells often have many ribosomes as they must produce many digestive enzymes
  • Cells that specialize in protein secretion have a large number of bound ribosomes such as cells in the pancreas (secretes digestive enzymes)

DISEASES ASSOCIATED:

  • Mutations in the proteins that make ribosomes cause disorders are called ribosomopathies
  • Ribosomopathies are a collection of disorders in which genetic abnormalities in proteins cause impaired ribosome synthesis and function
  • Characterized by bone marrow failure and anemia early in life, followed by elevated cancer risk in middle age
  • Alzheimer's has been found to have ribosomal function impairments
  • Impaired ribosomes have a decreased rate of protein synthesis and decreased levels of ribosomal RNA and transfer RNA
  • Tau protein important in Alzheimer’s disease- normally functions to help maintain cell structure and transport nutrients throughout the cell
  • Abnormally modified tau binds to ribosomes in nerve cells more strongly than usual and can disrupting ribosome function

INTERESTING FACT:

  • tRNAs move through the ribosome protein synthesis through tunnel and are moved along with the mRNA f
  • The movement of tRNA and mRNA through the ribosome are due to proteins EF-G in prokaryotes or EF-2 in eukaryotes: these bind to the ribosome and uses the energy stored in guanosine triphosphate to move the tRNAs and mRNA along
  • This also moves parts of the ribosome which is believed to allow ribosomes to make sure sure that correct amino acids are added to the protein at the right point along the mRNA

Endoplasmic Reticulum

  • The endoplasmic reticulum is an extensive network of membranes and consists of membranous tubules and sacs called cisternae
  • The ER membrane separates the internal compartment of the ER, the ER lumen, from the cytosol
  • Plays a major role in the production, processing, and transport of proteins and lipids- it is active in membrane synthesis and other synthetic and metabolic processes
  • The ER produces transmembrane proteins and lipids for its membrane and for other cell components including lysosomes, secretory vesicles, the Golgi appatatus, the cell membrane, and plant cell vacuoles
  • Two different but connected types of ER: Rough ER and Smooth ER

ROUGH ENDOPLASMIC RETICULUM

STRUCTURE:

  • The Rough ER has millions of ribosomes that stud he outer surface of the membrane giving it a rough appearance- these are called membrane bound ribosomes
  • Mainly consists of convoluted membranous sacs
  • The rough ER is attached to the nuclear envelope that surrounds the nucleus and therefore allows for movement between the two membranes
  • Rough ER is found throughout the cell but the density is higher near the nucleus and the Golgi apparatus

FUNCTION:

  • Compartmentalizes the cell, provides structural support, and is active in protein synthesis
  • Ribosomes on the rough ER produce secretory proteins
  • Rough ER lumen where the ER assists in polypeptide folding
  • Glycoproteins produced by the rough ER have carbohydrate molecules attached to the protein in the ER by molecules built into the ER membrane
  • Secretory proteins will be released from the ER in vesicles that bud from the transitional ER
  • The rough ER also is a membrane factory for the cell: it grows in place by adding membrane proteins that are made from its ribosomes and phospholipids to its own membrane
  • Enzymes built into the ER membrane assemble phospholipids
  • The ER membrane can be transferred in transport vesicles to other membranous parts of the cell

ORGANISMS THAT HAVE ROUGH ER:

  • All eukaryotes have rough ER, including plant cells, animal cells, fungi cells, and protist cells

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • Cells that specialize in protein secretion have a lot of rough ER
  • Pancreatic cells have a high concentration of rough ER as they function in producing secretory digestive enzymes such as insulin in large quantities
  • Stomach cells also have a lot of rough ER as they produce many digestive enzymes
  • Plasma cells, white blood cells that secrete immune proteins called antibodies, are very crowded with rough ER

DISEASES ASSOCIATED:

  • Endoplasmic reticulum (ER) stress involved in neurodegenerative disorders such as Alzheimer's and Parkinson’s disease
  • Environmental and genetic factors that disrupt ER function cause a build up of misfolded proteins
  • ER stress leads to the accumulation of unfolded or misfolded proteins
  • In Alzheimer’s disease, an accumulation of amyloid β-peptide results in activation of ER stress- contributes to neurodegeneration

INTERESTING FACT:

  • It is in the rough ER that hemoglobin, the protein responisble for transporting oxygen in the blood, is made
  • Four polypeptide chains are brought together to form hemoglobin and a metal group is added to the protein

SMOOTH ENDOPLASMIC RETICULUM

STRUCTURE:

  • Smooth ER is more tubular than rough ER and forms a connected sub compartment of the ER
  • It is found fairly evenly distributed throughout the cytoplasm
  • It is not studded with ribosomes, so it is referred to as smooth

FUNCTION:

  • The smooth ER synthesizes lipids for the cell (like cell membranes), detoxifies drugs and poisons, and metabolizes carbohydrates
  • The smooth ER is involved in many metabolic processes
  • Enzymes of the smooth ER aid in the synthesis of lipids (oils, phospholipids, steroids)
  • Other enzymes in the smooth ER help detoxify drugs and poisons which involves adding hydroxyl groups to drugs making them more soluble and easier to flush out of the body
  • The smooth ER stores calcium ions

ORGANISMS THAT HAVE SMOOTH ER:

  • All eukaryotes have smooth ER, which includes plant, animal, fungi, and protist cells

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • Cells in the testes and ovaries of animal cells that synthesize and release steroid hormones such as testosterone are rich in smooth ER
  • Smooth ER is especially common in liver cells as liver cells are involved in the detoxification of the blood
  • Muscle cells have specialized smooth ER membranes that pump calcium ions from the cytosol into the ER which triggers the contraction of the muscle cell

DISEASES ASSOCIATED:

  • Malfunctions in the smooth ER are involved in liver diseases
  • ER stress often leads to an unfolding protein response which prevents the cells from being able to detoxify alcohol and drugs

INTERESTING FACT:

  • The smooth ER can double its surface area in a few days when it needs to detoxify a chemical such as alcohol
  • The smooth ER creates and releases whatever it needs to depending on where it is located in the cell such as calcium ions in muscle cells and hormones in the endocrine glands

Golgi Apparatus

STRUCTURE:

  • The Golgi Apparatus consists of flattened membranous sacs called cisternae- A cell may have many or even hundreds of these stacks- the space within the Golgi membrane is called the lumen
  • The cisternae sacks are not connected but are held together by matrix proteins, and the whole of the Golgi apparatus is supported by cytoplasmic microtubules
  • It is located in the cytoplasm next to the endoplasmic reticulum and near the cell nucleus
  • The apparatus has three compartments: the cis (cisternae nearest the endoplasmic reticulum), medial (central layers of cisternae), and trans (cisternae farthest from the endoplasmic reticulum)
  • The Golgi stack has membranes of cisternae on opposite sides of the stack differing in thickness and molecular composition: the two poles of the apparatus are the cis face and the trans face which act as shipping and receiving ports respectively
  • Vesicles nearby engaged in the transfer of material between the parts of the Golgi and to and from other structures

FUNCTION:

  • Synthesis, modification, and packaging of molecules- products from the ER are modified and stored and then sent to their proper destinations
  • Transport vesicles moving materials from the ER to the apparatus move towards the cis face of the apparatus nearest the ER
  • A vesicle that buds from the ER adds its membrane contents within its own lumen to the cis face by fusing with the Golgi membrane
  • The trans face creates vesicles which pinch off and travel to other parts of the cell
  • Products from the ER are modified during their transition fro the cis region to the trans region- proteins and phospholipids may be altered by Golgi enzymes- The most frequent modification is the addition of short chains of sugar molecules
  • The Golgi sorts and packages products and targets and marks them to be transported to specific intracellular and extracellular locations before it is released in vesicles from the trans face: the newly-modified proteins and lipids are tagged with phosphate groups or other small molecules to get them to their proper destinations
  • The Golgi apparatus also manufactures some macromolecules on its own-many polysaccharides secreted by cells are from the Golgi and are secreted from the trans face inside transport vesicles that will fuse with the plasma membrane-in plants it can serve as the site where polysaccharides for the cell wall are synthesized
  • The Golgi Apparatus helps build lysosomes

ORGANISMS THAT HAVE GOLGI APPARATUS:

  • All eukaryotes have the Golgi apparatus
  • Animal cells tend to have fewer and larger Golgi apparatus. Plant cells can contain as many as several hundred smaller versions

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • The Golgi apparatus is especially extensive in cells specialized for secretion
  • In specialist secretory cells the Golgi complex is responsible for the sorting and packing of such well-known items as insulin, digestive enzymes and pectin
  • Pancreatic cells producing digestive enzymes often have many Golgi apparatus organelles
  • Cells in the salivary glands that secrete digestive enzymes as well and have many Golgi bodies
  • Stomach cells have many Golgi bodies- food nutrients that are digested in the stomach must be absorbed by stomach cells and sorted and sent to specific parts of the cell
  • The antibody-secreting plasma B cells of the immune system have prominent Golgi complexes

DISEASES ASSOCIATED:

  • Achondrogenesis type 1A is a newborn lethal skeletal disorder associated with the Golgi Apparatus
  • Newborns affected with this disease have severe shortening of all bones and have absent mineralization in the skull and the vertebral column
  • Usually involves extreme shortening of the arms and legs, abnormal development of ribs, vertebra and other skeletal abnormalities
  • Caused by mutations in the gene TRIP11 which encodes the protein GMAP210, a protein involved in the trafficking of proteins inside a cell
  • The protein GMAP210 is on the cis side of the Golgi apparatus: it captures transport vesicles arriving from the Endoplasmic reticulum and helps with the fusion of these vesicles with the Golgi apparatus
  • Without the GMAP210, protein trafficking from the ER malfunctions: this disturbance results in the accumulation of proteins inside the ER of skeletal cells and causes cell death
Achondrogenesis Causes Skeletal Shortening

INTERESTING FACT:

  • Until recently the Golgi Apparatus was thought to be a static structure with products in various stages of processing transferred between cisternae by vesicles
  • Recent research suggests that the Golgi Apparatus is more dynamic: the cisternal maturation model
  • This theory says that the cisternae of the Golgi progress forward from the cis face to the trans face, carrying and modifying the protein products as they go

Mitochondria

STRUCTURE:

  • Mitochondria is a rod shaped structure enclosed by two membranes, each a phospholipid bilayer with associated proteins
  • The outer membrane of the mitochondria is smooth but the inside is complex with infoldings called cristae- this gives the mitochondria a high surface area
  • The outer membrane has special proteins known as the porins- integral membrane proteins that regulate the movement of molecules
  • The inner membrane divides the mitochondria into two internal compartments: the intermembrane space, the narrow region between the inner and outer membranes and the mitochondrial matrix, enclosed within the inner membrane
  • The mitochondrial matrix contains different enzymes and mitochondrial DNA and ribosomes
  • The matrix fluid is where most of the chemical reactions of the cellular respiration process happens due to the many enzymes
  • Mitochondrion have their own DNA (circular DNA like bacteria) and ribosomes so they are able to replicate by fission and make their own proteins
  • Some cells have a single large mitochondrion, but usually a cell has hundreds to thousands of mitochondria
Anatomy of a Mitochondrion

FUNCTION:

  • The mitochondria is often referred to as the powerhouse of the cell
  • Mitochondria are the sites of cellular respiration, the metabolic process that generates ATP by extracting energy from sugars, fats, and other fuels with the help of oxygen
  • Mitochondria are responsible for regulating the metabolic activity of cells as ATP is the chemical energy of the cell that powers all the metabolic activities of the cell
  • The mitochondria also helps in regulating the concentration of calcium ions and plays a role in programmed cell death

ORGANISMS THAT HAVE MITOCHONDRIA:

  • Nearly all Eukaryotes have mitochondria, including plant, animal (except for red blood cells), protist, and fungi cells

PROLIFIC IN CERTAIN ORGANS/ ORGANELLES:

  • The number of mitochondria present in a cell is correlated with the cell's level of metabolic activity- motile and contractile cells have many mitochondria
  • Cells that need to perform high amounts of work, such as muscle cells in the heart and legs, fat cells and liver cells, have a high amount of mitochondria
  • Sperm cells also have many mitochondria to provide ATP for motility
  • Nerve cells need many mitochondria because they use ATP to maintain distribution of ions needed in generating action potentials

DISEASES ASSOCIATED:

  • Mitochondrial diseases result from failures of the mitochondria
  • Due to mutations in mtDNA or nDNA which lead to altered functions of the proteins or RNA molecules in mitochondria
  • When mitochondria fail less and less energy is generated within the cell
  • This causes cell injury and even cell death
  • If this process is repeated throughout the body, whole organ systems can fail: the heart, brain, muscles and lungs which recquire the most energy, are the most affected

INTERESTING FACT:

  • When a cell needs more energy the mitochondria can reproduce by growing larger and then dividing, and when a cell needs less energy, some of the mitochondria will die
  • Mitochondria are able to change shape and move around the cell when needed along the cytoskeleton which is very important in neurons

Chloroplasts

STRUCTURE:

  • Chloroplasts are lens-shaped organelles that are found in the leaves and other green organs of plants and in algae
  • Chloroplasts contain the green pigment chlorophyll, along with enzymes and other molecules that function in the photosynthetic production of sugar
  • The contents of the chloroplasts are separated from the cytosol by an envelope consisting of at least two membranes separated by a small intermembrane space
  • Inside the chloroplasts is a membraneous system of flattened, connected sacs called thylakoids- thylakoids can have different structures, in some regions they are stacked, each stack is called a granum
  • Chlorophyll molecules sit on the surface of each thylakoid and capture light energy from the Sun
  • The stacks of thylakoid sacs are connected by stroma lamellae. The lamellae act like the skeleton of the chloroplast, keeping all of the sacs an appropriate distance from each other and maximizing the efficiency of the organelle
  • The fluid outside the thylakoids is called the stroma, which contains the chloroplasts DNA and ribosomes and many enzymes
  • The membranes divide the inner chloroplast space into 3 compartments: the intermembrane space, the stroma, and the thylakoid space

FUNCTION:

  • The chloroplast makes food by the process of photosynthesis. During photosynthesis sugar and oxygen are made using light energy, water, and carbon dioxide
  • Chloroplasts absorb sunlight through photosynthesis and use it with the water and carbon dioxide absorbed through other parts of the plant to create food for the plant to grow and survive
  • The sugars made through photosynthesis feed the cell’s machinery and provide it with energy
  • Light energy is converted into chemical energy (such as the chemical energy in ATP and NADPH) when the energy from the sun hits a chloroplast and the chlorophyll molecules

ORGANISMS THAT HAVE CHLOROPLASTS:

  • Some Eukaryotes contain chloroplasts- not animal cells or fungi cells
  • All plant cells contain chloroplasts and algae contains chloroplasts
  • Some protists may contain chloroplasts

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • Chloroplasts are found in all plant cells- they can contain hundreds of chloroplasts
  • Plant cells need chloroplasts because they are not able to consume carbohydrates physically, so they must use photosynthesis to make carbohydrates from the sun energy

DISEASES ASSOCIATED:

  • Problems with chloroplasts in plants can lead to mineral deficiencies and cause plant cells to die as they are not able to get enough nutrients through photosynthesis
  • Chlorosis is a yellowing of leaf tissue due to a lack of chlorophyll in chloroplasts
  • Chlorosis causes include poor drainage, damaged roots, and nutrient deficiencies in the plant which can prevent chloroplast function
Wilted Plant

INTERESTING FACT:

  • Chloroplasts can degrade their thylakoid membrane and convert into chromoplasts, structures filled with colorful pigments found in plants such as flowers and fruits: this is why fruit changes color as it ripens
  • Leaves change color during the winter because there is not enough light during the winter
  • Trees will rest and live off the food they stored during the summer: this shuts down chloroplasts and the green chlorophyll found in chloroplasts fades away leaving yellow, red, and orange colors

Flagellum

STRUCTURE:

  • Flagellum are long locomotive extensions from cells
  • The structure of flagellum is different in prokaryotes and eukaryotes

EUKARYOTES:

  • Eukaryotes have one to many flagella which move in a whiplike motion
  • The core of Eukaryotic flagellum is a bundle of nine pairs of microtubules in a ring surrounding two central pairs of microtubules (9 + 2 pattern) composed of the protein tubulin all sheathed in an extension of the plasma membrane
  • The coordinated sliding of these microtubules confers movement- a flagellum has a wave like motion that generates force in the same direction as the flagellum's axis
  • The base of the flagellum in Eukaryotes is anchored to the cell by a basal body
  • The motor protein extending from one microtubule pair to the other is called dyenein- these dyenein arms responsible for the bending movement of flagella
  • Moving eukaryotic flagella require adenosine triphosphate (ATP)
  • Usually limited to one or a few flagella per cell

PROKARYOTES:

  • Bacterial flagella are helically shaped structures containing the protein flagellin
  • Prokaryotic flagella are much thinner than eukaryotic flagella, and they lack the typical "9 + 2" arrangement of microtubules
  • The base of the flagellum called the hook is attached to the basal body enclosed in the cell envelope
  • The flagellum rotates in a clockwise or counterclockwise direction by the hook rotating
  • Prokaryotes use energy from the proton-motive force, which is the ion gradient that lies across the cell membranes.
  • Flagella may be scattered over the entire surface or concentrated one or both ends

FUNCTION:

  • Flagella are used by cells and unicellular organisms for movement, sensation and signal transduction
  • Flagella are locomotor appendages from cells that allow many unicellular eukaryotic cells and prokaryotic cells to move and propel through water
  • The primary role of the flagellum is locomotion, but it also functions as a sensory organelle being sensitive to chemicals and temperatures outside the cell

ORGANISMS THAT HAVE FLAGELLUM:

  • They are found in all three domains: bacteria, archaea, and eukaryota
  • Nearly all prokaryotes (bacteria) have at least one flagellum
  • Many unicellular eukaryotic cells have flagella: protists are propelled by flagella
  • Sperm of animals, algae, and some plants have flagella

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • Protists, which are single celled organisms, often use flagella to move and propel themselves
  • Prokaryotes, such as bacteria, also often have flagella that allow for bacterial movement
  • Human sperm cells have flagella are needed in order for them to swim toward the egg for fertilization
Sperm Cells Swimming Towards Egg

DISEASES ASSOCIATED:

  • Primary ciliary dyskinesia is a infertility disease caused by abnormal or disfuncional flagella
  • Movements of the flagella are necessary to propel the sperm cells forward to the female egg cell
  • Because their sperm do not move properly due to abnormalities such as shortened, absent, or disformed flagella, males with this disease are usually fertile

INTERESTING FACT:

  • Environmental factors can greatly influence the stability of the flagella structure: an acidic pH will cause flagella to fall off and very cold temperatures will lead to disassembly of the flagella proteins
  • Flagella will reassemble with a change back to a suitable environment with a neutral pH or normal temperature

Cillia

STRUCTURE:

  • Cilia are short, hair like appendages extending from the surface of a living cell- they are around the same width as flagella but much shorter
  • Structurally very similar to flagellum but differ in beating patterns: cilia have alternating power and recovery strokes that generate movement perpendicular to the cilium's axis
  • Cilia usually occur in very large numbers, such as hundreds, on the cell surface
  • Often divided into two different types: motile and non-motile
  • Motile cilia are always moving in a single direction- they help the cell move around in the cellular fluids and help move fluids past the cell. Motile cilia are found together on cells and coordinate their movements to be most effective, making up for their small size.
  • Non-motile cilia, or primary cilia, are responsible for sensing the surrounding environment.
Cilia Anatomy

FUNCTION:

  • The primary purpose of cilia in many cells is to move fluid, mucous, or cells over their surface
  • Motile cilia functions to either to move the cell itself or to move substances over or around the cell
  • Non-motile cilia act as a sensory antenna for the cell receiving signals from other cells or fluids

ORGANISMS THAT HAVE CILLIA:

  • Cilia are found in eukaryotic cells
  • Most animal cells and protists have cilia
  • Not found in plant cells or fungi cells

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • Motile cilia is common in sperm cells of eukaryotes as it helps propel sperm cells towards the egg
  • Motile cilia are found in the lining of the trachea where they sweep mucus and dirt out of the lungs
  • In a woman's reproductive tract cilia lining the oviducts help move the egg toward the uterus
  • Primary cilia in the kidney bend with urine flow and send a signal to alert the cells

DISEASES ASSOCIATED:

  • Primary Ciliary Dyskinesia is a rare disease that affects cilia lining the respiratory tract that normally move out bacteria and mucus from airways
  • PCD is caused by having two abnormal copies of the PCD gene: this prevents them from making some of the proteins that allow cilia to beat normally
  • Bacteria will stay in airways if cilia does not work properly: causes breathing problems, infections, and other disorders mainly with the sinuses, ears, and lungs
  • In men who have PCD cilia structures on sperm do not work well which causes infertility
  • Women who have PCD can have problems with the cilia in fallopian tubes which may cause infertility

INTERESTING FACT:

  • Cilia cells in the respiratory system are the primary cells affected by the common cold and most flu viruse
  • Viruses work by killing the cell completely or by paralyzing the cilia which can cause mucus and bacteria to back up and accumulate

Lysosome

STRUCTURE:

  • A lysosome is a membranous sac of hydrolytic enzymes- they are single-membrane organelles
  • The hydrolytic enzymes are created in the rough endoplasmic reticulum, then packaged in a vesicle and sent to the Golgi apparatus for further processing- this then creates the digestive enzymes and the Golgi apparatus pinches off a small, very specific vesicle, a lysosome
  • Lysosomes are surrounded by a membrane composed of phospholipids that separate the inside of the lysosomes from the membrane's external environment
  • Enzymes only work within a specific pH range which protects the rest of the cell
  • The external membrane allows molecules inside of the lysosome without allowing the digestive enzymes to escape into the cell
  • Lysosomes have an acidic environment that allows its enzymes to work well and properly
  • The proteins embedded in the lysosome membrane and the digestive enzymes within the lysosome have three dimensional conformations that protect it from enzyme activity

FUNCTION:

  • Lysosomes are digestive membranous compartments that uses it's enzymes and proteins to hydrolyze and digest macromolecules- it is an important structure for digestion and removal of wastes from the cell
  • Lysosomes also repair cell membranes and respond to foreign substances such as bacteria, viruses and other antigens
  • Lysosomes carry out intracellular digestion and digest excess or worn out organelles, food particles, and engulfed viruses or bacteria
  • Cells that engulf smaller cells through phagocytosis use lysosomes to digest the food it has ingested
  • Waste products in the lysosome are released back into the cell in the form of a vesicle that can be transported out of the cell
  • Programmed for cell death (autolysis) to digest the cell

ORGANISMS THAT HAVE LYSOSOMES:

  • Lysosomes are found in nearly every animal eukaryotic cell because animals need the enzymes found in lysosomes in order to digest and use the food for energy that they eat
  • Lysosomes are very important in phagocytic unicellular eukaryotes and protists
  • Lysosomes are sometimes but not usually found in plant cells

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • Macrophages are specialized phagocytic cells with many lysosomes
  • Phagocytic cells, such as white blood cells in the immune system, contain many lysosomes to break down and destroy foreign substances
  • Organs that contain many macrophages have cells with a lot of lysosomes such as the lungs, liver, and spleen

DISEASES ASSOCIATED:

  • The lysosomal storage diseases (LSD) are a group of around 50 genetic disorders caused by the absence of one or more lysosomal enzymes
  • This results in the accumulation of undigested molecules causing cell damage
  • Tay-Sachs disease is a lysosome storage disease
  • Mutations in the HEXA gene cause Tay-Sachs disease- normally provides instructions for making part of an enzyme called beta-hexosaminidase A: important in the brain and spinal cord
  • Enzyme is in lysosomes and helps break down a fatty substance called GM2 ganglioside
  • Mutated HEXA gene disrupts activity of enzyme and GM2 ganglioside accumulates to toxic levels- causes destruction of neurons

INTERESTING FACT:

  • All of the digestive enzymes found in the lysosome require an acidic environment to function properly: called acid hydrolases
  • Low pH of the lysosome maintained by membrane proteins that pump protons from the cytosol into the lysosome
  • If enzymes were to leak out of the lysosome they would not function in the neutral pH of the cytosol

Vacuole

  • Vacuoles are membrane bound structures that are filled with inorganic and organic molecules, water, enzymes, and occasionally solid substances that have been engulfed
  • Functions in isolating harmful materials, storing waste products, storing water in plant cells, maintaining pressure, balancing the pH of a cell, exporting products out of the cell, and storing proteins

FOOD VACUOLE

STRUCTURE:

  • Food vacuoles are formed by phagocytosis- they are not concrete organelles as they form and disappear regularly
  • Formed when food comes into contact with the cellular membrane
  • Membrane enclosed sacs containing the material taken up in by phagocytosis

FUNCTION:

  • Participate in exocytosis and endocytosis within a cell
  • Food vacuoles store injested food in a cell until it is eventually digested when it is fused with a lysosome whose enzymes digest the food
  • Digestion products then pass into the cytosol and become nutrients for the cell, and waste products are expelled from the cell in the vacuole

ORGANISMS THAT HAVE FOOD VACUOLES:

  • Eukaryotic cells have food vacuoles- they can be found in plant, animal, protist, and fungi cells
  • Food vacuoles are commonly found in protists that get their nutrients through phagocytosis

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • Protists and single celled eukaryotes commonly have many food vacuoles as they engulf their food through phagocytosis
  • Amoebas use food vacuoles to store the prey they have engulfed

DISEASES ASSOCIATED:

  • Danon disease can be the result of malfunctions in vacuoles
  • Caused by mutations in the LAMP 2 gene: normally helps with the fusion of vacuoles and lysosomes
  • Mutations with this gene cause the lysosomes and the food vacuoles to fuse very slowly: number of food vacuoles increases
  • Large amount of vacuoles can lead to the breakdown of muscles cells

INTERESTING FACT:

  • Vacuoles play a huge role in autophagy, the degradation of the cell's components, to balance synthesis and destruction of cell structures and substances

CENTRAL VACUOLE

STRUCTURE:

  • The central vacuole is a very large vacuole enclosed by a membrane called the tonoplast which is selective in transporting solutes
  • The central vacuole is formed by the combining of smaller vacuoles formed from the endoplasmic reticulum and the Golgi apparatus
  • The solution inside the vacuole is called cell sap and is a solution of chemicals and molecules that fill the vacuole
  • Cell sap is made up of water, enzymes, salts and also stores many macromolecules, pigments, waste, and toxins
Central Vacuole in a Plant Cell

FUNCTION:

  • Primary function of the central vacuole is to maintain proper turgor (pressure) of the plant cell: absorbing more water increases the pressure on the cell wall- this provides structural support for the cell
  • The central vacuole stores food, wastes, pigment, and toxic materials
  • The central vacuole holds many important organic compounds, proteins, and enzymes that help with digestion
  • Plant cells main storage location of inorganic ions such as potassium and chloride
  • Many plant cells use the central vacuole as a deposit site for toxic by-products of metabolic processes that would endanger the cell if it built up in the cytosol
  • Vacuole plays a role in the growth of plant cells: as vacuoles absorb more water it makes the cell larger

ORGANISMS THAT HAVE CENTRAL VACUOLES:

  • Plant and fungi cells have one large central vacuole

PROLIFIC IN CERTAIN ORGANS/ ORGANISMS:

  • The central vacuole is found in all plant and fungi organisms

DISEASES ASSOCIATED:

  • In plants, central vacuoles are important to maintaining the structure and health of the plant
  • When the plant has enough water collects in cell vacuoles producing rigidity in the plant making it firm and healthy
  • Without sufficient water there is not much pressure in the vacuole and the plant will wilt

INTERESTING FACT:

  • Toxins stored in the central vacuole can help plants against predators- vacuoles may contain substances that animals cannot eat
  • Central vacuoles that contain pigments color the cells to help attract pollinating insects to flowers for example

Works Cited

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Created By
Emily Michaud
Appreciate

Credits:

Created with images by qimono - "blood cells red" • NIAID - "Mycobacterium tuberculosis Bacteria" • kaibara87 - "Onion cells 2" • ZEISS Microscopy - "Indian Muntjac fibroblast cells" • eLife - the journal - "Multi-coloured representation of the Plasmodium falciparum 80S ribosome bound to emetine (in cyan spheres)" • Swallowtail Garden Seeds - "Honey Bee on Gaillardia Flower" • kaibara87 - "Rose Petal"

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