Superior Cell Cycle

Chapter 12 notes

I. Purpose

A. Reproduction

1. Unicellular organisms use the cell cycle to make offspring

2. Multicellular organisms use the cell cycle for Growth (1 cell to many), Repair (after injury) and Renewal (replacing cells that die from normal wear and tear)

II. Genome - total amount of a cell’s DNA

A. prokaryotes - single, circular strandB. eukaryotes - DNA packaged into chromosomes. Each species has a characteristic number

1. humans somatic (body) cells - 46 chromosomes

2. humans gametes (sex) cells - 23 chromosomes

III. Vocabulary

A. chromatin - linear strand of DNA along with proteins that help it maintain it’s structure and control activity of genes

III. Vocabulary

B. chromosome - (after DNA duplicates) -when cell is preparing to divide - chromatin coils and folds and becomes thickened

III. Vocabulary

C. sister chromatids - each

strand of the chromosome

contains identical DNA to

the other strand

D. centromere - place

where 2 sister chromatids

are attached

III. Vocabulary

E. mitosis - division of the nucleus of the cell

F. cytokinesis - division of the cytoplasm (rest of the cell)

G. meiosis - division to make gametes (more next chpt)

IV. Cell Cycle for Somatic Cells

A. Interphase - 90% of cell cycle

1. G1 phase - cell grows by producing proteins and organelles

2. S phase – Synthesis DNA/ chromosomes make exact copy (replicates)

3. G2 phase - cell grows more and prepares for division

IV. Cell Cycle for Somatic Cells

B. Mitosis - series of steps to divide nucleus of cell1. Prophase a. chromatin becomes coiled into chromosomesb. nucleolus disappearc. centrosomes (centrioles) move to opposite polesd. spindle (made of microtubules) begins to form

2. Prometaphase

a. nuclear envelope (membrane) disappears

b. microtubules extend across cell

c. kinetechore (near centromere) becomes visible

3. Metaphase

a. chromosomes line up on metaphase plate

b. centromeres aligned with each other

C. Kinetochores of the sister chromatids attach to kinetochore microtubules

4. Anaphase

a. centromeres separate, pulling sister chromatids apart

b. chromosomes move to opposite ends of cell as microtubules shorten

c. Cell elongates

d. end with identical chromosomes at each side

5. Telophase

a. “daughter” nuclei form at each end of cell

b. nuclear envelopes re-form (from ER and nuclear fragments)

c. chromosomes uncoil and become chromatin

d. nucleolus reforms in each new nucleus

END OF MITOSIS

6. Cytokinesis

a. Animal Cell

1. cytoplasm splits by formation of a cleavage furrow between cells

2. cells splits in two “daughter cells”

b. Plant cell

1. Vesicles move along center of cell carrying cell wall materials

2. materials are deposited across the cell forming a cell plate

V. Binary Fission

1. Cell division (making whole new organism) for prokaryotic cells

2. Circular DNA replicates, as membrane pinches, it splits 1 organism into 2

3. Most likely evolved into eukaryotic mitosis

VI. Cell cycle for plant cells

1. Similar to animals except:

a. spindle forms directly from cell wall (no centrioles)

b. Cell plate forms instead of cleavage furrow

Cell Cycle Control System

set of operating molecules that triggers and coordinates key events in the cell cycle

*System will proceed on it’s own but can also be controlled by external and internal signals

A. Checkpoint

critical control point where stop and go signals can regulate the cycle

1. Animal cells - have built in “stop” signals that stop the cycle until a go-ahead signal comes

a. G1 checkpoint - “restriction point” - if it receives a go ahead signal here, it will continue and divide. If it does not, it will enter a non dividing state called G0.

ex. human nerve and muscle cells are permanently in G0. Liver cells are usually in G0 unless there is an injury

B. Cell Cycle Control molecules

pace the events of the cycle

1. Protein kinases - enzymes that activate or inactivate other proteins by phosphorylating them.

*They are always present in a growing cell but are “inactive’.

Protein Kinases

*Cyclin - a protein that has a cyclically fluctuating concentration. This will activate protein kinases at specific times.

Cyclin-dependent kinases (Cdk’s)- proteins whose activity rises and falls due to changes in amount of cyclin

*MPF - M-phase promoting factor - Signals transition from G2 to M (mitosis) phase

-cyclins build up during G-2 and become associated with Cdk’s.

-this initiates mitosis to begin by phosphorylating proteins in the nuclear membrane and stimulating other molecules

-MPF switches itself off by destroying cyclin using enzymes

C. Internal signals

still under investigation but they know of one for sure1. Anaphase will not begin until all chromosomes are properly lined up*Signal comes from kinetochores that have not yet attached*When all kinetochores are attached, the wait signal is released and anaphase begins

D. External signals

1. Growth factor - protein released by certain body cells that stimulates others to divide

a. PDGF - platelet derived growth factor - made by platelets in blood

*PDGF is needed for division of fibroblasts which are used in blood clotting

D. External signals

2. Density dependent inhibition of cell division - crowded cells stop dividing - due to amount of growth factors and nutrients available to each cell

3. Anchorage dependence - In order to divide, animal cells must be attached to a substratum (extra-cellular matrix)

E. Cancer cells

do not respond to body’s control mechanisms - divide excessively and invade other tissuesa. Cancer cells do not exhibit density dependent inhibition - they will continue to divide even if there is not enough growth factorb. Cancer cells (if they do stop) stop at random points in cell cycle - normal cells in a lab divide 20-50 times, but they have cancer cells that have been dividing since 1951

c. Transformation - single cell in a tissue converts from a normal cell to a cancer cell. Normally, this is taken care of by the immune system, but if the cell somehow avoids destruction, it can begin dividing*Tumor - mass of abnormal cells -benign tumor - mass stays at original site

-malignant tumor - impairs the functions of one or more organs = Cancer*may have unusual # of chromosomes*can lose attachment to tissue and spread*can enter blood stream and invade body = metastasis