Lecture 20-22

Question 1

Interphase

Answer 1

cell grows
3 phases
- G1
- S1
- G2

Question 2

G1 phase

Answer 2

First gap. Cell grows and accumulates the substrates required for DNA replications. Movement of one centriole in the centrosome away from the other.

Question 3

S1 phase

Answer 3

DNA synthesis. The amount of DNA present in the cell doubles as the DNA strands are replicated. Centrosome divides to give 2 daughter pairs.

Question 4

G2 phase

Answer 4

Second gap. Cell continues to grow and produce the proteins and other molecules required for mitosis to occur.

Question 5

G1 checkpoint

Answer 5

Here the cell either proceeds towards the S-phase or it leaves the cycle for the G0 phase

Question 6

G2 checkpoint

Answer 6

This controls entry into the M-phase. There are checks to see if chromsomal DNA is damaged or poorly replicated.

Question 7

M checkpoint

Answer 7

The presence of the correct signals at this point allows the chromatids to separate.

Question 8

Cyclin-dependent kinases (CDK)

Answer 8

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.

Question 9

Cyclin

Answer 9

The concentrations of these proteins do vary throughout the cell cycle. Their rate of synthesis varies as the cell cycle progresses

Question 10

Maturation (or M-phase)-promoting factor (MPF)

Answer 10

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.

Question 11

centriole

Answer 11

Paired microtubular structures found in some centrosomes that contribute to microtubule formation

Question 12

centromere

Answer 12

The ‘waist’ of a chromosome. The structure where mitotic spindles attach to the kinetochores

Question 13

centrosome

Answer 13

Organelle where microtubules are formed in some cells

Question 14

chromatid

Answer 14

One of the paired structures that constitute a chromosome after DNA replication in the S phase

Question 15

chromatin

Answer 15

‘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)

Question 16

chromosome

Answer 16

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

Question 17

kinetochore

Answer 17

centromere develops a kinetochore
which specialized microtubules attach and pull the chromosomes apart

Question 18

Prophase

Answer 18

• sister chromatids
• kinetochores develop
• chromosomes visible
• polar microtubules extend from each centrosome in a formation called aster (will eventually be mitotic spindles)

Question 19

Prometaphase

Answer 19

• 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

Question 20

Metaphase

Answer 20

• 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

Question 21

Anaphase

Answer 21

NOW Daughter Chromosomes
- daughter chromosomes are pulled apart
- at end each pole has an Identical compliment of genetic material

Question 22

Telophase

Answer 22

• separation of genetic info is COMPLETE
• chromatin begins to form again
• NEW nuclear membrane and nucleoli start to form
• lengthen non kinetochore

Question 23

cytokinesis

Answer 23

2 complete daughter cells form
because of the formation of a barrier between the two cells
- animal = cleavage furrow (actin)
- plant = cell plate

Question 24

Independent Assortment

Answer 24

Random arrangement of chromosomes at Metaphase 1

Question 25

Crossing over

Answer 25

Prophase 1 of meiosis non sister chromatids of homologous chromosomes can exchange genetic material
- occurs at chiasmata b/w 2 non sister chromatids

Question 26

random nature of fertilization

Answer 26

there are an insane amount of possible combinations so there genetic variation

Question 27

3 Sources of Genetic Variation

Answer 27

1. Independent Assortment
2. Crossing Over
3. Random Nature of Fertilization