2. Cell Cycle Flashcards
Diploid vs haploid
Two copies of each chromosome vs containing only one copy of each chromosome
Stages of interphase
G1, S, G2
What happens at G0 stage?
quiescence: Cell lives nml life, in stable state, performs reg cellular processes. Not part of interphase or cell cycle. Typically for non dividing cells (ex: neurons)
What happens at G1 stage?
Cells make organelles for energy and protein production like mito, ER, ribosomes; most cells = in this phase. Prepares for DNA replication too
How to transition from G1 stage to S stage?
Restriction point aka G1 checkpoint - checks for DNA damage, cell size, nutrients, growth factors. Are we ready to do S phase?
What happens at S stage?
Cell replicates chromosomes/chromatids into sister chromatids held by centromere
What happens at G2 stage?
Cell makes sure DNA is correctly replicated and there are enough organelles to make daughter cells; prepares for mitosis
What happens at M stage?
Mitosis
What happens at prophase?
Chromatin condense to chromosomes, centrioles move to opposite sides of cell and form spindle fibers; nuclear membrane dissolves
What happens at metaphase?
Chromosomes = attached to spindle fibers at kinetochores —> line up at metaphase/equatorial plate; involves kinesin
What happens at anaphase?
Centromeres split –> sister chromatids separate via 2 spindle fibers; involves kinesin.
What happens at telophase?
Spindle fibers disappear, nuclear envelopes reform, chrms relax (basically reverse prophase). Cleavage furrow initiates cytokinesis
What happens at cytokinesis?
Separation of cytoplasm and organelles. Initiated by cleavage furrow; occurs in telophase
Does meiosis occur in all cells?
No, only in gametocytes/germ cells
Other names for meiosis I and II
reductional division and equational division
Difference between meiosis I and II
Meiosis I separates homologous chrms to make haploid daughter cells; Meiosis II separates chrms similar to mitosis
What happens in prophase I?
Same as prophase + homologous chrms intertwine at held by synaptonemal complex => synapsis –> each synaptic pair contains 4 chromatids => tetrad; crossing over at chiasmata occurs
What happens at metaphase I?
Homologous pairs/tetrads line up at equatorial plate
What happens at anaphase I?
Homologous chrms separate (segregation) to opposite sides of cell via single spindle fiber (as opposed to 2 spindle fibers in mitosis) => disjunction
What happens at telophase I?
Nuclear membrane reforms, two sister chromatids still intact by centromere; interkinesis - chrms slightly uncoil
What happens at prophase II, metaphase II, anaphase II, and telophase II?
Same as mitosis
Purpose of G2 checkpoint?
Aka DNA damage checkpoint. Make sure DNA isn’t damaged and if DNA = replicated correctly; p53 = present. Are we ready to do M phase?
centrosome vs centrioles vs asters
creates mitotic spindles and microtubules, they’re the main microtubules organizing centers and they anchor microtubules at one end and make sure they don’t depolymerize, assembly site for kinetochores; consists of 2 centrioles vs 2 centrioles w/in a centrosome, make spindle fibers vs star shaped centrioles + their associated microtubules
How many times do somatic cells typically divide?
Enough till telomeres become too short to protect the DNA
Which protein controls progression of a cell thru cell cycle?
Cyclin and cyclin dependent kinases
What’s the mitotic spindle checkpoint?
Aka M checkpoint. In b/w metaphase and anaphase. Checks for chromosome attachment to spindle fibers at metaphase plate; are we ready to do anaphase?
p53 vs TP53
Protein that suppresses propagation of cells with damaged DNA; promotes apoptosis, cell cycle arrest, and DNA repair pathways; present in G2/DNA damage checkpoint vs mutated form of p53, causes cancer
What happens if cells can’t pass checkpoints?
If damaged DNA is the problem —> fix it np. Otherwise it can lead to apop, cancer - permanent activation of cell cycle, or senescence - permanent arrest of cell cycle (ie. Irreversible)
