Cell Cycle and Cancer

exam 3

What is cell division?

new cells are formed by splitting of pre-existing cells

What is cancer a result of?

out of control cell division

What is a chromosome?

A single long piece of DNA with associated proteins

What is a chromatid?

one of two identical halves of a chromosome

What is a sister chromatid

Two identical halves of the same replicated chromosome that are joined together

What are two attached sister chromatids still considered as?

a single chromosome

what proteins attach sister chromatids along their entire length?

cohesins

What are the two phases of cell division in eukaryotic cells?

M phase and interphase

what is the M phase?

the dividing phase, cells in process of separating their chromosomes

What is Interphase?

non-dividing phase, cells are growing and preparing to divide

What phase do cells spend most of their time in?

interphase

What is interphase not a part of?

Mitosis

What are the four phases of the cell cycle?

M phase, interphase (G₁, S, and G₂)

What does the G₁ phase do?

begins replication and transitions to S phase

What happens in the S phase?

DNA synthesis

What does the G₂ phase do?

prepares for the M phase

When does mitosis begin?

when chromatin condenses

what happens to the sister chromatids during mitosis?

the two sister chromatids separate to form independent daughter chromosomes, one copy of each chromosome goes to each of the two daughter cells

What are the 5 subphases of mitosis? (M phase)

prophase, prometaphase, metaphase, anaphase, telophase

what happens during prophase?

Chromosomes condense and become visible, spindle apparatus forms, centrosome has been duplicated and migrates to opposite sides of cell

what does the spindle apparatus do?

moves replicated chromosomes during early mitosis, pull chromatids apart in late mitosis

what is the spindle apparatus made of?

Microtubules, centrosome

What happens during prometaphase?

Nuclear envelope breaks down, microtubules attach to chromosomes at kinetochores, chromosomes are pushed and pulled by microtubules until they reach middle of spindle

What is a kinetochore

a protein structure that acts as the primary attachment point where spindle fibers connect to pull the chromosomes apart

What happens during metaphase?

Chromosomes are lined up on metaphase plate, each chromosome is held by kinetochore microtubules from opposite poles

what is the metaphase plate?

the imaginary plane between two spindle poles, usually in middle of cell

What happens during anaphase?

sister chromatids are pulled by spindle fibers toward opposite poles of the cell, creates two identical sets of daughter chromosomes

What happens during telophase?

chromosomes are on opposite sides of the cell and begin to decondense, new nuclear envelope begins to form around each set of chromosomes

When is mitosis considered complete?

When two independent nuclei have formed

What happens during cytokinesis in plants?

Vesicles from golgi apparatus brings membrane and cell wall components to middle of cell, vesicles fuse to form cell plate

What happens during cytokinesis in animals and other eukaryotes?

rind of actin and myosin filaments contracts inside cell membrane, pinches inward to form cleavage furrow, ring shrinks and tightens until division is complete

What is cytokinesis?

The final stage of cell division where the cell divides to create two distinct daughter cells

How do bacteria replicate their cells?

divides via binary fission

What happens during binary fission?

Chromosomes are replicated, protein filaments attach to replicated chromosomes, filaments pull chromosomes apart, other proteins divide cytoplasm

What phase do nondividing cells get stuck in?

The G₁ state

What is the arrested state called when nondividing cells get stuck in G₁ phase?

G₀ state

What phase is essentially eliminated from rapidly dividing cells?

G₁ phase

What protein is responsible for cell cycle activity?

M phase-promoting factor (MPF)

What polypeptide subunits make up MPF?

protein kinase, cyclin

what does protein kinase do?

catalyzes transfer of phosphate group from ATP to target protein

What is cyclin responsible for?

activate kinase, the activity of the protein kinase depends on cyclin protein levels

How is MPF activated?

When one of the phosphate groups attached to the cyclin dependent kinase (Cdk) is removed

what removes the phosphate group from Cdk?

the protein phosphatase

when is Cdk phosphorylated?

after the cyclin binds to the Cdk

How is MPF deactivated?

cyclin is degraded by the ubiquitin-proteasome system which deactivates the Cdk and the MPF

what are cell-cycle checkpoints?

regulatory molecules present at each checkpoint that allow the cell to “decide” whether to proceed with division

What can cells that divide without control form?

a tumor

Where are the four cell-cycle checkpoints?

G₁ checkpoint, G₂ checkpoint, M-phase checkpoint(s)

What does the G1 checkpoint go?

most important checkpoint, establishes if cell will continue through cycle and divide or exit cycle and enter G₀

What factors affect the G₁ checkpoint?

size, availability of nutrients, social signals from other cells, damage to DNA

what happens if the DNA is physically damaged in the G₁ checkpoint?

p53 protein either activates proteins that pause cell cycle until damage can be repaired, or initiates apoptosis

What is apoptosis?

programmed cell death

When does the G₂ checkpoint occur?

Between G₂ and M phases

what happens if chromosome replication has not proceeded properly or if DNA is damaged in G₂ phase?

phosphate is not removed from MPF, MPF is not activated and cells remain in G₂ phase

When does the first M-phase checkpoint occur?

between metaphase and anaphase

What does the first M-phase checkpoint do?

ensures that sister chromatids do not split until all kinetochores are attached to the spindle apparatus

When does the second M-phase checkpoint occur?

between anaphase and telophase

What does the second M-phase checkpoint do?

Ensures that chromosomes have fully separated before nuclear envelope begins to re-form