Chapter 11: How Cells Reproduce By: Ryan Bihasa

The Cell Cycle

The cell cycle - a series of events from the time a cell forms until its cytoplasm

- includes all phases (interphase) and mitosis

- all single cells of multicellular organisms go through the cell cycle

- cells multiply through division


Interphase - the interval between mitotic division when a cell grows

- a typical cell spends most of its life in this phase

- a cell doubles the number of its cytoplasmic components and replicates its DNA

- 3 stages of interphase

— G1: metabolic activities - cell growth and everything is doubled but DNA

— S: DNA Synthesis - DNA is doubled

— G2: protein synthesis needed for cell division - checkpoints to see if a cell is ready for mitosis


Mitosis - the process of nuclear division that maintains chromosome number

- every cell does this but sperm and egg cells

- when a cell divides by mitosis, it produces two descendant cells

- Mechanism of gene expression control determine whether or not a cell divides

- There are four stages of Mitosis: Prophase, Metaphase, Anaphase and Telophase/Cytokinesis

Prophase: 1st Stage of Mitosis

Prophase - the first stage of cell division where the chromosomes become paired chromatids and the nuclear envelope disappears

- one of two centrosomes move to the opposite end of the cell

- microtubules assemble and lengthen forming spindles

- sister chromatids are attached to opposite centrosomes

Metaphase: 2nd Stage of Mitosis

Metaphase - the second stage of cell division where chromosomes attach to the spindle fibers

Anaphase: 3rd Stage of Mitosis

Anaphase - the stage of cell division where the chromosomes move away from one another to opposite poles of the spindle

- near the end of this phase, cytokinesis or the actual cytoplasmic cell division may occur in most eukaryotes

—cytokinesis differs among plant and animal cells

Telophase and Cytokinesis: The Final Stage of Mitosis

Telophase - the final phase of cell division where the chromatids or chromosomes move to opposite ends of the cell and two nuclei are formed

- near the end of this phase, cytokinesis or the actual cytoplasmic cell divison may occur in most eukaryotes


Telomeres - a region of repetitive nucleotide sequences at each end of a chromosome, which protects the end of the chromosome from deterioration or from fusion with nearby chromosomes

- in other words, it's function is to contain the chromosome to itself

- They are non coding repeat DNA sequences

- telomere buffers are important


Mutations - some mutations can affect the cell cycle

- can cause loss of gene function and their protein products

- controls that limit gene expression may fail

—when enough checkpoint mechanism fail, a cell loses control over its cell cycle

—neoplasm - accumulation of abnormally dividing cells


Cancer - disease where abnormal cells divide uncontrollably and destroy body tissue - a malignant neoplasms that gets progressively worse and is dangerous to health

- there is no known cure, there are only methods of controlling and containing it.

— Such as chemotherapy

- Causes 15-20% of deaths in developing countries

- mutations in checkpoint genes are required to make a normal cell into a malignant one

—lifestyle can reduce the risk of requiring these mutations

- some neoplasm can be detected beforehand with periodic screenings

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