Cell Division I and II Flashcards
what are the 3 discrete stages that cells reproduce?
- interphase
- mitosis
- cytokinesis
what is the longest stage in the cell cycle?
G1
**she asked a question about sampling 100 cells and what phase they would be found in
what occurs in G1 phase?
-prep for DNA synthesis
-active RNA and protein synthesis
-intracellular structures are duplicated
GROWTH
G 0 phase
- nondividing, differentiated stage
- Most human cells are in G0
- special examples liver (quiescent cells can be called out) and neurons
Synthesis of nuclear DNA occurs in ___ phase
S
which cell cycle phase ends with the formation of sister chromatids?
S phase
-takes about 6 hours
G2 phase
- Cell volume increases
- Synthesis of organelles and proteins necessary for spindle formation/division
M phase
- Duplicated chromosomes are distributed equally into a pair of daughter nuclei
- Prophase, prometaphase, metaphase, anaphase, telophase
Replication of DNA can be assessed by measuring the synthesis of new DNA. What molecule is used to assess new DNA??
- Metabolic labeling with 3H-thymidine
- Cells actively synthesizing DNA will accumulate radioactivity
Bromodeoxyuridine (BrdU)
-artificial thymidine analog used to identify S-phase
cells
CFSE
succinimidyl ester of carboxyfluorescein diacetate
FACs can measure the fluorescence of cells incubated with CFSE. Describe what we see from generation to generation
As cells divide, their fluorescently labeled cytoplasmic proteins are divided equally between the two daughter cells. Each daughter cell has half the fluorescence of the previous generation, which can be measured by flow cytometry
once can also assess cellular DNA content by flow cytometry. Describe how this graph works. What is on the x axis? what is on the yaxis
x-axis: relative amount of DNA per cell
y-axis: the number of cells
-Used to determine the lengths
of G1, S, and G2 + M phases
Quiescent (G0)
– cells that temporarily or reversibly stop dividing
-example liver cells
Senescent –
cells that permanently stop dividing due
to age or accumulated DNA damage
-examples: neurons
what are the 3 major checkpoints of the cell cycle?
- G1: (Restriction Point/Start) : commits cell to entering the cell-cycle and chromosome duplication
- G2 /M Checkpoint: triggers early mitotic events that lead to chromosome alignment on the spindle in metaphase
- Metaphase-to-Anaphase transition: stimulates sister chromatid separation, leading to the completion of mitosis and cytokinesis
T/F: Cyclins depend on the fluctuating levels of CDK to regulate their activity
False! CDK levels are relatively constant, but CDK activity is regulated by the fluctuating [ ] of cyclins
cyclin D complexes with which CDKs to perform which function?
- CDK-4 and CDK-6
- progress past the restriction point of G1 /S
cyclins E and A complex with which CDK to perform which function??
- CDK2
- initiate DNA synthesis in early S phase
cyclin B complex with which CDK to perform which function?
- CDK 1
- transition from G2 to mitosis
what is the function of CAK?
phosphorylate CDK to active state
-phosphorylates at the T loop
what enzyme is responsible for the 2nd inhibitory phorphorylation of CDK1?
-Wee1 kinase
what enzyme is the phophatase that is able to free CDK-1 to do its job?
cdc25 phosphatase
what is p27 and what is its relationship to cyclin-Cdk?
- p27 is a CKI
- CKI binding causes rearrangement in the CDK active site rendering it inactive
when/where do CKIs primarily regulate cell cycle progression?
-at G1/S and at S CDKs early on in the cell cycle
Who is APC/C?
-anaphase-promoting complex or cyclosome
what does APC/C do?
- ubiquitinates (tags for destruction) securin, s-cyclin, and m-cyclin
- initiates the separation of sister chromatids by destroying securin
what are the two steps required for chromosome duplication?
step 1: pre-replication complex (occurs late mitosis and early G1)
step-2: pre-initiation complex (occurs at onset of S)
where is DNA synthesis allowed to occur?
-at origins containing a pre-RC
what triggers the formation of the preinitiation complex initiating DNA synthesis??
-S-CDK activation
what stimulates pre-RC assembly?
-APC/C and Cdk inactivation
What are two major regulatory steps in mitosis?
- increase in M-CDK activity at G2/M checkpoint
- metaphase to anaphase transition when APC/C triggers the destruction of securin and cyclins
what are the two categories of cancer-critical mutations?
- ) overactivity mutation (gain of function) DOMINANT oncogene
- ) underactivity mutation (loss of function) (recessive) tumor suppressor gene
ras proto-oncogenes: what is the normal function of Ras?
-monomeric GTPases involved in signal transduction pathway from growth factor receptor to nucleus
what happens in ras oncogenes?
-point mutation to make overactive
what are the 3 ras mutants we learned about and where are their mutations?
-K-Ras: Arg at 12
-N-Ras: Arg at 61
H-Ras:val at 12
normal ras: gly at 12 and gln at 61
what specifically explains why mutated Ras remains active?
-mutated Ras cannot hydrolyze its bound GTP
take me through the Ras pathway
Ras –> Raf –> Mek –> Erk –> transcription factors –> genes turned on
what is the clinical presentation in someone who has nonhereditary retinoblastoma?
-unilateral RB
what is the clinical presentation in someone who has hereditary retinoblastoma
-bliateral RB
what is the normal function of Rb?
- controls entry into S phase
- nonphosphorylated version binds to transcription factors to STOP them
who is responsible for phophorylating Rb so cell can continue into S phase?
-cyclin D-CDK 4/6 complex
where in the cell cycle does p53 regulate?
G1
what happens to activated p53 levels if DNA is damaged or repair intermediates accumulate?
-p53 levels will rise
If DNA cannot be readily repaired, what will p53 do?
- turn on Bax gene, repress Bcl2 gene
- Bax homodimers activate process of cell destruction
Li-Fraumeni Syndrome
- autosomal dominant
- predisposition to cancer due to mutation in TP53 gene
how does HPV lead to cancer?
-viral protein E6 binds to p53
viral protein E7 binds to Rb
what is a surrogate marker of HPV-positive cancers?
-p16
describe the concept of synthetic lethality
-two genes are synthetically lethal if loss of function of BOTH leads to cell death. The idea is if tumors have a known loss of function of a gene with a buddy that can lead to synthetic lethality than we can target its buddy gene, kill the cell, and save normal cells
