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BIO 211 Chapter 11
The Cell Cycle
29
Biology
Undergraduate 2
12/14/2010

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Term
meiosis
Definition
• occurs only in reproductive cells
• results in cells that have half the chromosomes of the parent cell
• one diploid parent cell makes four haploid gametes
• occurs only prior to formation of gametes
• basis of sexual reproduction
• physical basis for eukaryotic genetics
Term
mitosis
Definition
• happens in somatic cells
• results in daughter cells that are genetically identical to parent cell
• usually accompanied by cytokinesis
• responsible for growth, wound repair and reproduction
• purpose: distribute parent cell's genetic material to daughter cels during cell division
• prior to mitosis, each chromosome is copied
• at end of mitosis, one chromosome distributed to each daughter cell
Term
chromosome
Definition
• single, long DNA double helix that is wrapped around in proteins in a highly organized manner
• can only be stained and observed during M phase
Term
chromatid
Definition
• each of the DNA copies in a replicated chromosome
• joined along entire length and at centromere
• one continuous DNA molecule wrapped around proteins
Term
centromere
Definition
where each set of chromatids is joined
Term
sister chromatids
Definition
chromatids from same chromosome
Term
histones
Definition
protein associated with DNA in the chromatin of eukaryotic cells
Term
mitotic spindle
Definition
structure that produces mechanical forces that pull chromosomes into daughter cells during mitosis
• made of microtubules, which are made of α-tubulin and β-tubulin dimers
• length of microtubule determined by how many dimers it contains
• microtubules are asymmetric and grow at plus end
• spindle fibers grow from centrosome until plus end attaches to kinetochore
Term
centrosome
Definition
o microtubule organizing center
• contains pair of centrioles
• kinetochore: where spindle fibers and chromatids attach
• located at centromere
• each chromosome has two kinetochores where spindle fibers attach, one on each side
Term
kinetochore
Definition
thought to have a base that attaches to centromere region of chromosome and crown of fibrous proteins projecting outward
• contains dyneins and other motor proteins
• attached to crown
• capable of walking down microtubules from plus to minus
• proteins in kinetochore catalyze loss of tubulin subunits at plus end while dyneins and other motor proteins walk toward minus end
Term
karyotype
Definition
depiction of complete set of chromosomes
Term
C-value
Definition
measure of total DNA a cell has, measured in base pairs of DNA – think about it as chromatids
Term
heterochromatic
Definition
some chromosomes coil on a different cycle; short and think instead of long and thin
Term
growth factors
Definition
o polypeptides or small proteins responsible for stimulating cell division
• also stimulates production of key regulatory protein, E2F
• when cells are in G0, arrival of growth factors stimulates production of cyclins (analogous to MPF)
• triggers expression of genes needed for S phase
• when first produced, binds to a tumor suppressor protein (Rb)
• when E2F bound to Rb, in off position (can’t activate S phase)
Term
if growth factors continue to arrive
Definition
• production of cyclins and therefore cyclin-cdk complexes continues
o cyclins are specific to G1 checkpoint
• when activated, being phosphorylation of Rb, which means it can’t bind to E2F anymore
• E2F now free to activate target genes and S phase starts
Term
Rb protein
Definition
one of key molecules that enforces G1 checkpoint
Term
interphase
Definition
o phase of cell cycle in which cell is not dividing, everything other than mitosis (where cells spend most of their time)
o three parts
• S phase: time during which DNA is replicated
• G1: busiest time for cell metabolism and growth
• G2: allows cell to build protein machinery necessary to mitosis
o gap phases exist so cells can replicated organelles and manufacture additional cytoplasm and grow large enough
Term
M phase (mitosis)
Definition
o phase of cell cycle in which cell division occurs
o at start, each chromosome consists of two sister chromatids attached to one another at centromere
o divided into stages (IPPMAT)
Term
prophase of mitosis
Definition
step 1 of mitosis
DNA gets packaged and ready for movement
• chromosomes already replicated from interphase
• DNA is complex with proteins (histones) into chromatin
• chromatin condenses (first becomes visible)
• marked by formation of mitotic spindle
Term
prometaphase of mitosis
Definition
step 2 of mitosis
• nuclear envelope breaks down and nucleolus disappears
• spindle fibers from each centromere attach to one of two sister chromatids at kinetochore
• centrosomes begin moving to opposite poles
• spindle fibers attached to kinetochores begin to move chromosomes to middle of cell
Term
metaphase of mitosis
Definition
step 3 of mitosis
• chromosomes line up at metaphase plate
• mitotic spindle is fully formed
• each chromosome is held by kinetochores reaching to opposite poles and exerting same amount of tension (tug of war)
Term
anaphase of mitosis
Definition
step 4 of mitosis
• separating duplicated chromosomes
• become full-fledged chromosomes
• spindle fibers attached to kinetochores shorten, pulling sister chromatids apart via motor proteins
• spindle fibers not attached to kinetochores begin to push against each other via motor proteins that connect them, causing poles of cell to be separated even more
• chromatids pull to opposite poles so that each daughter cells gets identical sets of chromosomes
• kinetochore microtubules remain stationary during anaphase
o microtubules shorten at kinetochore because tubulin subunits are lost from plus ends
Term
telophase of mitosis
Definition
step 5 of mitosis
• nuclear envelope re-forms and mitotic spindle disappears
• chromosomes begin to de-condense
• once two independent nuclei have formed, mitosis is complete
Term
cytokinesis
Definition
• division of cytoplasm to form two daughter cells
• usually occurs immediately after mitosis
Term
cytokinesis in animals
Definition
cleavage furrow forms between two new nuclei
o made from ring of actin and myosin microfibrils that surround inside circumference of cell
o microfilaments contract, causing cell membrane to constrict and pinch cell in two
Term
cytokinesis in plants
Definition
• a cell plate forms
o vesicles from Golgi apparatus carrying cell-wall material migrate to middle of cell between two new nuclei
o vesicles build up and fuse, forming new cell membrane and cell wall
Term
length of cell cycle various enormously, mostly due to___________
Definition
variation in length of G1

in rapidly dividing cells, practically no G1
Term
non-diving cells stay in ________
Definition
o a G1-like phase (G0) indefinitely
• sometimes referred to as post-mitotic
• nerve and muscle cells
Term
cyclin/cdks serve as ________
Definition
switches that push cell from one cell-cycle phase to next
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