Lecture 11 + DLA 11 Flashcards
What are the two broad stages of the cell cycle?
- Interphase
2. Mitosis
What are the stages of Interphase?
G1 (G0), S phase, G2 phase
What is the G0 phase?
They perform normal cell functions, but they are unable to divide
growth factors may enable the cell to reenter the cell cycle
What is the S phase?
Phase of DNA synthesis/ DNA replication
At the end of S phase, the DNA content doubles. Each chromosome has two sister chromatids
What happens in the G2 phase?
The DNA content is doubled
cell/ cytosol size is increased
genome is scanned for mistakes
What is the role of p53 in the cell cycle?
When DNA is damaged, the activity of p53 is increased which leads to
cell cycle arrest
activates DNA repair
may lead to apoptosis (if damage is severe)
What would happen if p53 is not active?
Will allow damaged cells to proliferate, this could lead to cancer development
What happens during prophase?
nuclear envelope dissolves
mitotic spindle forms
chromosomes condense and bind to spindle
Homologous chromosomes vs sister chromatids?
Homo - chromosomes of the same number, one paternal and one maternal
sister = copies joint at the centromere
What happens during metaphase?
chromosomes condense and are maximally visible
chromosomes align at the equator
Microtubules attach to centromere kinetochores
What happens during anaphase?
sister chromatids will move to the centrioles
separation of the sister chromatids
What happens during telophase?
sister chromatids move to opposite poles
chromosomes less condensed
nuclear envelope starts forming
What is it called when the sister chromatids fail to separate?
Aneuploidy (non-disjunction)
When does recombination occur during meiosis?
Prophase I; increases genetic diversity
The two stages of meiosis?
Meiosis I: Homologous chromosomes separate (reduction division)
Meiosis II: Sister chromatids separate
When does random segregation of the homo chromosomes occur?
anaphase I
non-dysjunction in meiosis I?
Homologous chromosomes do NOT separate
non-dysjunction during meiosis II?
Sister chromatids of a chromosome do NOT separate
Monosomy is only compatible with life when?
Only monosomy X compatible with life;
Autosomal monosomy or Y chromosome monosomy not compatible with life
No Y chromosome leads to what disease?
Turner’s syndrome (45X)
What disorder occurs when their is one cell with just X and the other cell has XY
Klinefelter syndrome (47,XXY)
Meiosis II non-dysjunctions?
Turner syndrome
47; XYY
47; XXX
Explain the G1 restriction checkpoint
critical for cell cycle regulation
mediated by the Rb protein
determine replication potential before S phase
Explain the G1 DNA-damage Checkpoint
monitors integrity of new synthesized DNA
Explain the S DNA-damage checkpoint
Monitors quality of replicating DNA
Explain the unreplicated DNA checkpoint
Prevents progression into mitosis before completion of DNA synthesis
Explain the G2 DNA-damage checkpoint
Monitor integrity of newly replicated DNA
Explain the Spindle-assembly checkpoint
Prevents premature entry into anaphase
Explain the Chromosome Segregation checkpoint
Prevents cytokinesis until separation of chromosomes
What happens during prometaphase?
Breakdown of nuclear envelope
Spindle microtubules bind to kinetochores
What filaments help in separation during cytokinesis?
Actin and myosin II
What does the Retinoblastoma Protein (Rb) do?
It is a tumor suppressor gene
prevents from G1 to S if DNA is not good
Cdc25C Phosphatase?
proto-oncogene
Triggers G2 to M progression
Phosphatase
Removes inhibitory phosphorylation of CDK1
CDK1 can then bind cyclin B
Cyclin B – CDK1 complex activates mitosis
What are proto-oncogenes?
Genes whose protein products control cell growth, proliferation and differentiation
Normal regulatory molecules
What are Oncogenes?
Mutated proto-oncogenes
