Cell division, Mitosis and Meiosis Flashcards
what happens when a cell is too big or too small
too small- cant contain organelles and molecules
too big- not adequate for exchange of materials
how long is the duration of the cell cycle in
a) Yeast
b) human
c) e. coli
a) 24 hours
b) 90 minutes
c) 60 minutes
what cells only divide occasionally
skin fibroblasts and liver cells
what are the three stages of the cell cycle
- Interphase
- Mitosis
- Cytokinesis
what parts is interphase composed of
- G1 (Gap1)
- S (Synthesis)
- G2 (Gap2)
what is the longest phase in the cell cycle
interphase
what happens during G1
• Cell doubles in size
• Cell produces all of the structures it needs to carry out its functions,
metabolically active
(cell living its normal life)
what happens during S phase
cell makes a copy of its DNA (to get directions for its function and survival)
what happens during G2 phase
• Cell prepares to divide
• Cell produces structures needed for cell division
(preparation checking phase)
what two processes are involved in M phase
Mitosis and cytokinesis
what happens during prophase of mitosis
- Chromosomes become visible (chromatids condense)
- Centrioles move to opposite poles
- spindle fibers grow from centrioles and radiate to centre
- Envelope breaks down and nucleolus disappears
what happens during Metaphase
- chromosomes thicken more
- line up at centre
- fibers attach
what happens during anaphase
spindle fibers pull sister chromatids apart, spindle fibers shorten, moving to opposite ends
what happens during telophase
- nuclear membrane forms around each end
- nucleolus reforms
- chromosomes become chromatids (less thick)
what can identify a cell in S phase
radioactive thymidine (3H Thymidine)
what else can be used to determine cellular
incubation of cells with a fluorescent dye that bind to DNA using flow cytometer
what occurs during cytokinesis
division of the cytoplasm
when does the start regulatory point occur in yeast
late in G1. it controls progression from G1 to S phase
what is the regulatory point in animals
restriction point (in late G1)
when does the cell enter the G0 stage
if growth factors are not available during G1. Cells are still metabolically active but have stopped growth and reduced rate of protein synthesis
until when are skin fibroblasts arrested in G0
until they are stimulated to divide as required to repair damage from a wound
what triggers proliferation of skin fibroblasts
platelet-derived growth factor
what are the functions of S phase checkpoint
- monitoring of integrity of DNA
2. quality control monitor to promote repair of errors during replication
what is the function of the G2 checkpoint
- prevents the initiation of mitosis until DNA replication is completed.
- prevents initiation of M before completion of S
what is the function of M phase checkpoint
monitor alignment of chromosomes on mitotic spindle
what are cyclins
most important core cell cycle regulatory proteins
what are the four basic types of cyclins found in most eukaryotes
G1 cyclins, G1/S cyclins, S cyclins, and M cyclins
what are CDKs
they are kinases (enzymes that phosphorylate specific target proteins)
what happens when a cyclin attaches to CDK
- activates CDK as a kinase
2. directs CDK to a specific set of proteins
what is Rb
a tumor suppressor gene whose inactivation leads to tumor development
describe what happens at the G1 checkpoint
if cyclin is absent, the tumor suppressor attaches to the gene group and represses transcription. if cyclin is present then the tumor suppressor is phosphorylated and cannot attach to the gene group and transcription occurs
what restricts DNA replication to once per cel cycle
MCM helicase proteins which binds to the ORC
what activates kinase activity of ATM
DNA damage caused by ionising radiation (double-strand DNA breaks)
what activates ATR kinase activity
in response to a different set of DNA lesions, including those caused by UV light
what does the Cdk1/cyclinB complex (MPF–maturation promoting factor) activate
- condensins,
- components of the nuclear envelop,
- Golgi matrix proteins and
- proteins associated with centrosomes and microtubules.
what is the function of the cortical granules
Makes the zona pellucida impenetrable to sperm (after fertilisation) to prevent polyspermy
what is the germinal epithelium
outer layer of cells in the ovary
what is the function of the primary follicles
contains the primary oocyte surrounded by a single layer of supporting follicle cells
what is the function of the mature follicle
contains the secondary oocyte, ready for ovulation
what is the medulla
central main body of the ovary (blood vessels, lymph and nerves)
once activated, what do ATM and ATR phosphorylate and activate
CHK1 and CHK2 kinases which then phosphorylate an inhibit the Cdc25A and Cdc25C protein phosphatases
what is the function of Cdc25A and Cdc25C
required to activate Cdk2 and Cdk1
what does inhibition of Cdc25A and Cdc25C cause
leads to arrest at the DNA damage checkpoints in G1, S and G2
