Cell Cycle Flashcards
Why do cells divide?
Problems happen when they get too big (DNA overload and inefficient transport)
What are the stages of interphase?
G1-cell grows, builds organelles, proteins, enzymes, etc.
S-DNA is synthesized and replicated, preparing for division
G2-cell finishes growth and preparation to dovide
What are the phases of mitosis? (In order)
Prophase, metaphase, anaphase, telophase
What happens during prophase?
Chromatin condenses into chromosomes, nuclear envelope breaks down, spindle fibres develop, centrioles start moving to the poles
What happens during metaphase?
Chromosomes line up single file in centre of cell, spindle fibres attach to chromosomes
What happens during anaphase?
Sister chromatids are pulled to opposite ends of the cell
What happens during telophase?
Chromosomes have arrived at poles, nuclear envelopes reform, chromosomes start to unwind
What is cytokinesis?
Separation of the cytoplasm, cleavage furrows form during telophase, though it’s not part of mitosis. Plant cell cytokinesis involves formation of a cell plate between new cells.
What is the result of mitosis?
Two, genetically identical, diploid cells
What is the purpose of meiosis?
To form gametes, or sex cells
What are homologous chromosomes?
Chromosomes pairs similar in length, gene position, and centromere position
What happens during prophase I?
Chromatin condenses, nuclear membrane breaks down, formation of tetrads, cross-over, spindle fibre development
What happens during metaphase I?
Tetrads line up 2 by 2 in the centre of the cell, spindle fibres attach
What happens during anaphase I?
Tetrads are pulled apart
What happens during telophase I?
Chromosomes arrive at their destinations, with n at each pole
What happens during Meiosis II?
The events are essentially the same as mitosis, just with half the normal number of chromosomes.
What is a karyotype?
An image of a person’s chromosomes organized into homologous pairs
What are autosomes?
Chromosome pairs 1-23, they code for most of our bodies
What are sex chromosomes?
Pair 23, determine an organism’s sex. X has functions outside of sex determination, Y does not
What is nondisjunction?
When homologous chromosomes fail to separate during anaphase I, results in two gametes having an extra chromosome, and two missing one
What causes Down Syndrome?
Trisomy 21, or three chromosomes in the 21st pair, instead of the normal two
What are some examples of sex chromosome disorders?
Turner’s syndrome in females, only one X can’t do meiosis. Klinefelter’s in males, XXY, extra x interferes with meiosis, usually sterile
What are the four checkpoints of the cell cycle?
G1/S, S, G2/M, Metaphase/anaphase
What are the stimulating proteins of the G1/S checkpoint?
Growth factors stimulate G1 cyclin release, which mind with CDKs to move the cell to S
What are the inhibiting proteins of the G1/S checkpoint?
p53 checks for DNA damage, and can stall the cell for repairs or initiate apoptosis if the damage is too much. Rb prevents entering S phase without signals from growth factors
What are the stimulating proteins of the S phase checkpoint?
S-phase cyclins activate CDKs which stimulate the replication of DNA
What are the inhibiting proteins of the S checkpoint?
Ataxia telangiectasia mutated (ATM) checks for breaks in the replicated DNA strands, and can activate BRCA1 to repair those strands, or initiate apoptosis
What are the stimulating proteins of the G2/M checkpoint?
M-phase cyclins bind to their CDKs and send the cell into mitosis
What are the inhibiting proteins of the G2/M checkpoint?
p53 comes back!
What are the stimulating proteins of the M-check checkpoint?
Anaphase-promoting complex/cyclosome (APC/C) activates once all chromosomes are attached to the spindle fibres, and stimulates destruction of the proteins holding sister chromatids together to allow anaphase to occur
What are the inhibiting proteins of the M-check checkpoint?
Mitotic arrest deficient (MAD) proteins inhibit APC/C from activating if chromosomes are not properly attached to the spindle, stopping anaphase from occuring
How do CDKs work?
Cyclin-dependant kinases are proteins that must bind to cyclins do function. Once activated, they stimulate various stages of the cell cycle by activating other proteins.
How do cyclin levels contribute to cell cycle regulation?
Cyclin levels rise and fall cyclically, controlling the number of CDKs that can be active at a time. CDK thresholds must be met for them to influence the progression through stages of the cell cycle
