Lecture 20-22 Flashcards
Interphase
cell grows
3 phases
- G1
- S1
- G2
G1 phase
First gap. Cell grows and accumulates the substrates required for DNA replications. Movement of one centriole in the centrosome away from the other.
S1 phase
DNA synthesis. The amount of DNA present in the cell doubles as the DNA strands are replicated. Centrosome divides to give 2 daughter pairs.
G2 phase
Second gap. Cell continues to grow and produce the proteins and other molecules required for mitosis to occur.
G1 checkpoint
Here the cell either proceeds towards the S-phase or it leaves the cycle for the G0 phase
G2 checkpoint
This controls entry into the M-phase. There are checks to see if chromsomal DNA is damaged or poorly replicated.
M checkpoint
The presence of the correct signals at this point allows the chromatids to separate.
Cyclin-dependent kinases (CDK)
Kinase enzymes that are required for the cell cycle. They do not vary in concentration throughout the cycle. However, they are inactive until they bind with cyclins.
Cyclin
The concentrations of these proteins do vary throughout the cell cycle. Their rate of synthesis varies as the cell cycle progresses
Maturation (or M-phase)-promoting factor (MPF)
allows the cell to progress past the G2 checkpoint and enter mitosis.
It is formed when a cyclin binds to a CDK
It also initiates a sequence that leads to its separation back into a cyclin and the inactive cyclin-dependent kinase.
centriole
Paired microtubular structures found in some centrosomes that contribute to microtubule formation
centromere
The ‘waist’ of a chromosome. The structure where mitotic spindles attach to the kinetochores
centrosome
Organelle where microtubules are formed in some cells
chromatid
One of the paired structures that constitute a chromosome after DNA replication in the S phase
chromatin
‘Uncondensed’ DNA, which together with histone proteins is how DNA is packaged during G0 and interphase of the cell cycle (when cell is not dividing)
chromosome
The ‘condensed’ form of DNA seen during mitosis and meiosis (in dividing cells)
single strand
Can be a single structure or consist of 2 sister chromatids
kinetochore
centromere develops a kinetochore
which specialized microtubules attach and pull the chromosomes apart
Prophase
- sister chromatids
- kinetochores develop
- chromosomes visible
- polar microtubules extend from each centrosome in a formation called aster (will eventually be mitotic spindles)
Prometaphase
- chromosomes are tightly coiled
- nuclear lamina disintegrates and the nuclear envelope fragments to permit spindle microtubules to infiltrate the nuclear region.
- kinetochore microtubules start to attach to kinetochores
- start to push chromosomes to middle
Metaphase
- The kinetochores on each chromosome are:
attached to a kinetochore microtubule
aligned along the metaphase plate - The nuclear membrane and lamina has completely disintegrated.
- cohesions start to break down
Anaphase
NOW Daughter Chromosomes
- daughter chromosomes are pulled apart
- at end each pole has an Identical compliment of genetic material
Telophase
- separation of genetic info is COMPLETE
- chromatin begins to form again
- NEW nuclear membrane and nucleoli start to form
- lengthen non kinetochore
cytokinesis
2 complete daughter cells form
because of the formation of a barrier between the two cells
- animal = cleavage furrow (actin)
- plant = cell plate
Independent Assortment
Random arrangement of chromosomes at Metaphase 1
Crossing over
Prophase 1 of meiosis non sister chromatids of homologous chromosomes can exchange genetic material
- occurs at chiasmata b/w 2 non sister chromatids
random nature of fertilization
there are an insane amount of possible combinations so there genetic variation
3 Sources of Genetic Variation
- Independent Assortment
- Crossing Over
- Random Nature of Fertilization
