The Endomembrane System By Katie Reed Period F

~Nucleus~

All eukaryotic cells contain nuclei, however prokaryotic cells do not.

Structure:

  • It is a membrane-bound structure that contains a nuclear envelope, chromosomes, and a nucleolus
  • The nuclear envelope is a double membrane that separates the inside of the nucleus from the cytoplasm
  • The nuclear envelope is a phospholipid bilayer that keeps the shape of the nucleus together and controls the transport of molecules into and out of the nucleus through nuclear pores
  • The chromosomes (DNA) are found inside the nucleus and are long, entangled structures called chromatin when the cell isn't dividing
  • The nucleolus is found inside the nucleus and is made of RNA and proteins, which helps make ribosomes for the cell (and therefore proteins)
Nuclei are not prolific in certain organisms because each eukaryotic cell only contains one nucleus, however there are some slime molds that contain millions of nuclei in their cells.

Function:

  • Regulation of protein synthesis- DNA holds the genetic information needed for proteins
  • The nucleus makes mRNA which is transported to the cytoplasm through the nuclear pores on the nuclear envelope
  • Once in the cytoplasm, the mRNA is translated by the ribosomes and tRNA to make the proteins

Associated Disease: Emery-Dreifuss Muscular Dystrophy

  • A mutation in a protein in the inner membrane of the nuclear membrane
  • The protein is either emerin or lamin A/C
  • This disease includes types of cardiomyopathies, neuropathies, and weaknesses in cardiac and skeletal muscles

The nucleus is the largest organelle of the cell, and it occupies 10% of the cell's volume! Also, each of our cells contains nearly 6 feet of DNA that is organized and tightly packed inside the nucleus!

~Ribosomes~

Ribosomes are found in both prokaryotic and eukaryotic cells, however, they are much smaller in prokaryotic cells.

Structure

  • Mainly made of RNA and proteins
  • Consist of two subunits
  • In eukaryotes, the ribsomes are 80S , with the smaller unit being 40S and the larger being 60S
  • In prokaryotes, the ribosomes are 70S, with the smaller unit being 30S and the larger being 50S
  • They either float free in the cytoplasm or are found attached to the rough ER
The small subunit works with the mRNA during translation and the large subunit is where the peptide bond begins to form.

Function:

  • They put together amino acids to make proteins for the cell
  • The two subunits become bound to the polymers of the mRNA in the cytoplasm and they work with the tRNA to produce proteins
  • The proteins made by free ribosomes in the cytoplasm are used in the cytoplasm
  • The proteins made in the ribosomes attached to the rough ER are transported outside the cell

Associated Diseases:

  • Diamond-Blackfan Anemia: a mutation in genes that give instructions for ribosomal proteins; makes bone marrow unable to make enough red blood cells
  • Cartilage Hair Hypoplasia: a mutation in the gene that makes enzymes that build rRNA; makes people have underdeveloped and thin hair
  • Dyskeratosis Congenita: a mutation in a gene that builds ribosomes; makes the bone marrow unable to make red blood cells, white blood cells, and platelets

Ribosomes are prolific in bacteria cells- one cell has 10,000 ribosomes, and they make up 30% of the weight of the cell.

Ribosomes are pretty hardcore organelles- after they create a protein, its two subunits are separated and either broken down or recycled. Also, because prokaryotic ribosomes are smaller than eukaryotic ones, antibiotics are able to harm bacterial cells without harming our cells!

~Rough ER~
All eukaryotic cells contain rough ER, however prokaryotic cells do not. Rough ER is found in plant and animal cells and is not a prolific organelle.

Structure:

  • A network of flattened sacs and membranous tubules
  • The tubules and discs are hollow- the inside of them is called the lumen
  • Ribosomes are attached to its cytoplasmic surface
The small black dots on the picture represent the ribosomes attached to the rough ER.

Function:

  • The ribosomes attached to its surface produce proteins
  • The proteins being formed are fed into the lumen- some get used by the ER, others get attached to the membrane
  • The proteins inside the rough ER fold and get modified- they either become part of the ER or they are transported out of the cell
  • The proteins that don't stay inside the rough ER form vesicles that get sent to the Golgi apparatus
  • The rough ER also makes phospholipids that get transported by vesicles and are used in other membranes in the cell

Associated Diseases:

  • Proteins that are misfolded can cause the ER stress response to activate in the rough ER
  • If too many proteins are misfolded, the ER stress response over-activates and can cause Alzheimer's, ALS, Huntington's disease, and Parkinson's disease
  • If the ER stress response does not work properly, type 2 diabetes can also occur

Rough ER helps prevent us from health issues because after proteins are produced, it checks the quality of the protein and rejects ones that are not up to code. This prevents us from conditions like cystic fibrosis and emphysema.

~Smooth ER~

Smooth ER is also only present in eukaryotes, mainly plant and animal cells. They are also not prolific in organisms.

Structure:

  • A network of membranes and flattened discs- same as the rough ER
  • The smooth ER is continuous with the rough ER
  • It does not have ribosomes attached to its cytoplasmic surface
Smooth ER is built off of rough ER (continuous)

Function:

  • It produces steroid hormones, lipids, and carbohydrates
  • It detoxifies/breaks down toxins and medications
  • It can store calcium ions- muscle cells have a special type of smooth ER called sarcoplasmic reticulum that stores calcium ions that make the cell contract
  • There are small areas of smooth ER on the rough ER that allow vesicles from the rough ER to exit the ER- these areas are called transitional ER

Diseases Associated:

  • Similar to the rough ER, the misfolding of proteins causes the ER stress response, which can lead to diseases like Alzheimer's and ALS
  • Smooth ER helps detoxify toxins, so if the smooth ER in liver cells can't break down chemicals, liver diseases can occur
  • Diabetes can also occur if the smooth ER in pancreatic cells is unable to produce insulin
The structure and network of the smooth ER allows it to have a large surface area that is perfect for storing valuable enzymes, proteins, and other molecules produced!
~Golgi Apparatus~

The Golgi apparatus can be found in eukaryotic cells. They are prolific in salivary glands because they need to release digestive enzymes, like amylase. They are also prolific in immune system cells because they release antibodies.

Structure:

  • Stacks of flattened membrane discs
  • The inside surface of the discs is called the lumen
  • The Golgi apparatus is two-faced: the receiving side is the cis face and the opposite side is the trans face

Function:

  • Sort, tag, and package lipids and proteins in vesicles sent by the rough ER
  • The vesicles from the ER go to the cis face- they combine with it and send its contents into the lumen
  • The lipids and proteins from the vesicle are modified , sorted based on identifying markers (such as chemical tags) and packaged into vesicles that come from the trans face
  • Some of the vesicles are transported to other organelles (such as lysosomes or vacuoles) while other vesicles merge with the cell membrane to transport proteins

Diseases Associated:

  • Achondrogenesis is a group of diseases that causes disorders in cartilage and bone devlopment
  • It is caused by a mutation in the microtubules of the Golgi apparatus
  • The three types of Achondrongenesis are Type 1, 1B, and II
  • Other symptoms of the diseases include small limbs, a narrow chest, and a short trunk- results from the body not producing enough growth hormone

When animal cells undergo mitosis, the Golgi apparatus disintegrates at the beginning and then gets re-formed during telophase. This process does not occur in the Golgi apparatus of plant cells.

~Mitochondria~
Mitochondria are only found in eukaryotic cells. They are prolific in fat and muscle cells that require a lot of energy in the form of ATP to function.

Structure:

  • Double membrane (inner and outer) that divide the organelle into compartments
  • The outer membrane is a phospholipid bilayer with porins- allow the membrane to be permeable to molecules like ions, ATP, nutrients, and ADP
  • The inner membrane is only permeable to water, carbon dioxide, and oxygen, includes an electron transport system, transport proteins, and an ATP synthetase complex
  • The inner membrane also has folds that divide it into layers (lamillae) called cristae
  • The compartments are broken into intermembrane space and a matrix
  • The intermembrane space is the space between the inner and outer membranes- allows for oxidative phosphorylation
  • The matrix includes enzymes and dissolved oxygen, carbon dioxide, and water molecules

Function:

  • Oxidative phosphorylation: nutrients sent into the mitochondria are processed and produce charged molecules that combine with oxygen to produce ATP (energy) for the cell
  • The ATP produced in oxidative phosphorylation is the energy source for cellular respiration
  • It helps the cell maintain a proper concentration of calcium ions
  • The formation of specific parts of blood and hormones are aided by mitochondria
  • Mitochondria also plays a role in apoptosis (programmed cell death)

Disease Associated: Mitochondrial Disease

  • Caused by malfunctions of the mitochondria or mutations that affect the proteins/RNA in mitochondria
  • The diseases cause insuffecient amounts of energy to be produced
  • The diseases cause the most harm to the heart, liver, brain, kidney, skeletal muscles, the endocrine system and the respiratory system
  • Symptoms: muscle pain/weakness, liver disease, cardiac disease, seizures, poor growth, respiratory complications, diabetes, and infection

Mitochondria can reproduce quickly by binary fission (growing larger and dividing) in order to produce more energy as the cell needs it. If the cell does not need anymore energy, mitochondria are able to become inactive or die.

~Chloroplasts~

Chloroplasts are found in eukaryotic cells, however they are only in plant cells and some autotropic algae cells. They are prolific in plant cells because the cells are complex, however they aren't prolific in algae cells because they are simpler.

Structure:

  • Oval-shaped with an envelope, a stroma, thylakoids, a grana, photosystems, and a peripheral reticulum
  • Envelope: a double-membrane structure made of phospholipid bilayers - the space in between the membranes is called the intermembrane space
  • Stroma: a liquid matrix inside the envelope- contains internal parts of the chloroplasts, dispersed solutes, proteins, enzymes, ribosomes, DNA, and starch
  • Thylakoids: internal membrane-bound sections enclosed by thylakoid membranes- the space inside is called the thylakoid lumen and it contains plastocyanins and other molecules needed for the transport of electrons
  • Grana: discs of thylakoids stacked on top of one another - the thylakoids are connected to each other through stroma thylakoids or intergrana thylakoids
  • Photosystems: located inside thylakoid membranes; used to get solar energy- they are reaction systems that have antennas that have chlorophyll, carotenoids, proteins, and pigments for photosynthesis
  • Peripheral reticulum: another network of membranous tubules that come from the envelope

Function

  • Photosynthesis, photorespiration, and other regulatory processes
  • The envelope is semi-permeable and controls what molecules enter and leave the cell
  • Lipids and pigments used in capturing light energy are produced in the envelope
  • Light-dependent reactions: pigments like chlorophyll take in light energy and use it to break down water molecules and produce ATP and oxygen
  • Light-independent reactions: enzymes break down carbon dioxide and ATP to make sugar and starch molecules-process is called carbon dioxide fixation
  • Photorespiration (light-dependent oxygen fixation) protects the cell during droughts or excessive radiation

Disease Associated: Tobacco Mosaic Virus (TMV)

  • TMV affects the proteins in the chloroplasts of tobacco leaves
  • TMV reduces the levels of chloroplast proteins so they can't function- causes the tobacco leaves to undergo a hypersensitive reaction
  • As a result of the TMV infection, the cells with the affected chloroplasts die because they can no longer function
Chloroplasts can actually move themselves within the cell in order to position themselves in the best spot to absorb the most sunlight!
~Flagellum~

Flagella are found in both prokaryotic and eukaryotic cells. They are prolific organelles because some cells contain many flagella in order to help the cell move, however other cells only contain one.

Structure:

  • Hairlike structure
  • Eukaryotes: they move in a whip-like fashion, they are composed of nine pairs of microtubules surrounding two central pairs of microtubules, and their base is connected to the cell by a basal body
  • Prokaryotes: helically-shaped, contains the protein flagellin, rotates clockwise or counterclockwise, and the base of it is near the cell surface and is attached to the basal body in the cell envelope
The left diagram shows a prokaryotic cell with a flagellum, and the right diagram shows the structure of the flagella in eukaryotes.

Function:

  • Allows for cell movement
  • Flagella allow motile bacteria to move
  • The movement of eukaryotes relies on ATP as a source of energy- prokaryotes obtain their energy for movement from a proton-motive force, or ion gradient, across the cell membrane
  • The movement of the flagella results in water currents that are necessary for sponges and coelenterates to undergo respiration and circulation

Diseases Associated:

  • Spirochetes are bacteria that have an endocellular flagellum and are human pathogens
  • They are found in watery environments, such as blood, lymph, water, and mud
  • They can cause relapsing fever, Lyme disease, syphilis, and yaws
  • T. pallidum pallidum causes syphilis
  • T. pallidum pertenue causes yaws
  • Borrelia includes pathogens that are spread by ticks and lice
When bacterial flagella rotate counterclockwise, the bacteria can move straight, however when they rotate clockwise, it causes the bacteria to "tumble" and move in a random direction.
~Cilia~

Cilia are only found projecting from eukaryotic cells. They are prolific in organs like the larynx that need to move materials (such as mucus) through the cell/body.

Structure:

  • Small appendages that extend from eukaryotic cells
  • They are whip-like and move back and forth
  • They are very small and are composed of tubulin
  • They are attached to the cell by a basal body
This diagram shows how cilia are more abundant and smaller compared to flagella within the cell.

Function:

  • There are two kinds of cilia- motile cilia and primary cilia
  • Motile Cilia: they are used in intraflagellar transport-they always move in one direction to move the cell around fluids and move fluids past the cell; typically found in groups
  • Primary Cilia: they are non-motile and are used to sense the environment surrounding the cell- each cell only has one non-motile cilium

Disease Associated: Polycistic Kidney Disease (PKD)

  • PKD is caused by the mutation of a gene that causes cilia to become malformed or nonexistent
  • Several fluid-filled sacs cause people with the disease to have clogged kidneys- prevents blood from getting filtered
  • The cysts that form in the kidneys cause renal failure
  • Over 12.5 million people worldwide suffer from PKD

Humans are able to breathe because we have cilia in our lungs that help move dirt and mucus out of the way and keep our airways clean!

~Lysosome~

Lysosomes are only found in eukaryotic cells, specifically animal cells. They are prolific in cells that undergo many reactions using enzymes, such as white blood cells, liver cells, and pancreatic cells.

Structure:

  • Spherical-shaped
  • Tiny sac that contains fluid and enzymes
  • The outer surface has a single membrane made of a phospholipid bilayer
  • The interior is acidic because it has many enzymes that function best in acidic environments

Function:

  • Plays role in exocystosis- releasing enzymes outside of the cell
  • Autophagy: breaking down materials inside the cell; usually worn-out organelles because the chemicals in their structures can be used again by the cell
  • Heterophagy:¬†breaking down materials from outside the cell (examples are phagocytosis and pinocytosis)
  • Biosynthesis:¬†recycling the products of biochemical reactions in the cell (such as materials brought in through endocytosis)
  • Autolysis:¬†completely breaking down cells that have died
  • The main function of lysosomes is to break down, process, and eliminate harmful and useless materials

Disease Associated: Tay-Sachs Disease

  • This disease is caused when a lysosome can't break down waste materials and they begin to build up in the cell
  • Materials cannot be broken down as a result of a missing enzyme known as glucocerebrosidase
  • Symptoms: deafness, blindness, seizures, irritability, and paralysis
  • Symptoms occur in infants, and they usually die by the age of 5

Lysosomes protect us from bacteria because they are present in our white blood cells, which engulf the bacteria through phagocytosis and break it down before it can harm our cells.

~Food Vacuole~

Food vacuoles are found in eukaryotic cells. There are some in animal, paramecium, amoeba, and protozoa cells, however they are mainly found in plant cells. They are not prolific organelles, however there are more in plant cells than other types of cells.

Structure:

  • A sac enclosed by a membrane made up of a phospholipid bilayer
  • It is created when food comes into contact with the cell membrane- the membrane pinches off what needs to be stored or destroyed in the vacuole

Function:

  • Phagocytosis: they encircle food particles when they are brought into the cell, and once the particles are inside the vacuole, they are processed and used as energy
  • They play a role in the digestion of food particles
  • They mainly store food and other nutrients that the cell needs in order to survive
  • They also store waste products of the cell

Disease Associated: Danon's Disease

  • Caused by a mutation in the LAMP 2 gene- affects the autophagic vacuoles and lysosomes- causes them to fuse slowly
  • The disease causes skeletal muscles and cardiac muscles to become weaker (known as myopathy and cardiomyopathy)
  • It also causes intellectual disabilities
  • Males show symptoms of the disease earlier than females do- usually begin in early childhood
  • Males with the disease usually live to be 19 years old while females usually live to be 34

Vacuoles in plants can store toxins such as nicotine, so they are able to protect the cell from harmful chemicals/contamination and they can use the toxins to protect the plant from predators.

~Central Vacuole~

Central vacuoles are found in eukaryotic cells, specifically only in plant cells. They are not prolific because each plant cell only contains one central vacuole.

Structure:

  • Tonoplast: the membrane that surrounds the vacuole; separates it from the cytoplasm- it includes transport proteins that help move molecules into and out of the cell
  • Cell Sap: the inside of a vacuole; it is a solution of chemicals and molecules- contains water, salts, sugars, lipids, amino acids, storage proteins, waste products, enzymes, and some toxins that can protect against predators

Function:

  • Regulate normal levels of turgor (pressure) in the cell
  • The amount of water inside the vacuole determines the turgor of the cell (osmotic pressure)
  • If there is a lot of water in the cell, the turgor pressure increases and the cell swells- normal for plant cells
  • If there isn't enough water in the vacuoles, the turgor pressure will decrease and the cell will shrink
  • They temporarily store some materials and they are permanent storage units for waste products
  • The central vacuole contains transport proteins that regulate ions entering/exiting the cell- helps adjust the solute concentration in the cell and maintain normal osmotic pressure/turgor
  • The ions that are transported also help the vacuole maintain pH levels so that the enzymes inside can function

Diseases Associated:

  • Central vacuoles function in order to protect plant cells from diseases and pathogens
  • They contain hydrolytic enzymes and antimicrobial compounds to get rid of pathogens
  • With the help of the central vacuole, plants have developed an immune system in their cells to fight disease
  • The membranes of the vacuoles are able to collapse to prevent pathogens from spreading throughout the cell
  • The membranes can also fuse with the plasma membrane of the cell to prevent bacteria and other pathogens from accumulating/becoming more abundant in the cell

Since the central vacuole can occupy up to 80% of the volume of a plant cell, it is able to push the parts of the cytoplasm closer to the cell membrane, which allows the chloroplasts to have more access to light energy and makes photosynthesis more efficient.

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Katie Reed
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