Protein Control of Cell Division Flashcards
What is apoptosis?
Programmed cell death triggered by cell-death signals
What are caspases?
Degradation enzymes which help to achieve apoptosis
Describe the EXTRINSIC pathway involved in apoptosis.
Cell death signals come from outside the cell. Ligands bind to a surface receptor protein, causing a conformational change. This triggers a PROTEIN CASCADE
Describe the INTRINSIC pathway involved in apoptosis.
Cell death signals come from within the cell. If DNA damage occurs, the p53 protein can activate a CASPASE CASCADE. A lack of growth factors may also trigger cell death.
Explain what a caspase cascade is.
Includes a series of post-translational modifications, these allow rapid responses and involve cleavage.
State the definition of the term cleavage.
Subunits are removed and can be reassembled to form active caspases .
What does the term fragmentation of the cell refer to?
Remaining small vesicle fragments of cell are engulfed and digested by phagoctic white blood cells
Describe interphase
Period of time where the cell appears to be doing nothing but is actually undergoing an active period of growth and metabolism. Interphase includes three stages; G1, S and G2
State the definition of the spindle fibres.
Part of the cytoskeleton; responsible for the movement of chromosomes.
Describe prophase
Stage 1 of mitosis- chromosomes condense; microtubules disassemble; spindle fibres form and attach to chromosome’s centromeres; nuclear membrane disintegrates.
Describe metaphase
Stage 2 of mitosis - chromosomes line up along the equator of the cell, known as the metaphase plate
Describe Anaphase
Stage 3 of mitosis - spindle fibres pull sister chromatids apart.
Describe Telophase
Stage 4 of mitosis - separated chromosomes pulled to opposite poles of the cell; daughter nuclei form; chromosomes uncoil; nuclear membrane is made again
Describe cytokinesis
Membrane of cell in pulled in by actin and myosin, separating the cytoplasm. Daughter cells are formed.
The cell cycle must be tightly controlled. Explain why.
A reduction in the rate of the cycle leads to degenerative diseases.
An increase in the rate of the cycle will lead to tumour formation.
What is the purpose of cell cycle checkpoints?
They regulate the cycle by giving ‘stop’ and ‘go’ signals.
What is the purpose of the G1 checkpoint
monitors cell size; cell has to have enough mass to proceed to S phase.
What is the purpose of the G2 checkpoint
assesses the success of DNA replication
What is the purpose of the M checkpoint?
monitors the alignment of chromosomes to ensure each daughter cell receives only one chromatid from each chromosome. This triggers the exit from mitosis and the start of cytokinesis.
What is cyclin-dependent kinase?
Regulatory proteins that bind to cyclin to form a mistosis-promoting factor. Active CDKs cause the phosphorylation of target proteins, if successful this will activate the cell cycle.
Describe the three phases of interphase
G1 phase - growth stage (cell produces proteins and copies of organelles)
S phase - DNA replication occurs
G2 phase - cell growth (preparation for mitosis)
Retinoblastoma protein
Transcription factor inhibitor - inhibits transcription of genes needed in S phase. If CDKs are sufficient, Rb can no longer bind to transcription factors
What is the role of the p53 Protein
Transcription factor that can stimulate DNA repair, arrest the cell cycle or trigger cell death.
