Lecture 3

Question 1

3 reasons cells need to divide?

Answer 1

Now organisms,
Growth,
Cell replacement (either wear and tear, or programmed cell death).

Question 2

3 basic requirements for a cell to divide efficiently?

Answer 2

DNA of parent cell must be duplicated.
Chromosomes containing replicated DNA must be physically segregated into 2 daughter cells.
Daughter cells must physically divide from each other.

Question 3

4 steps in binary fission?

Answer 3

Chromosome replication begins, before one copy of origin moves to the other end of the cell.
Replication continues, with one copy of the origin now at the other end of the cell.
Replication finishes, plasma membrane grows inward, and new cell wall is deposited.
Two daughter cells result.

Question 4

What is binary fission?

Answer 4

Process by which bacteria duplicate DNA and segregate their chromosome into two daughter cells.

Question 5

4 pain stages of cell cycle? What happens at each?

Answer 5

G1 - Gap - Cell grows, preparing to replicate DNA.
S - Synthesis - Cell grows, synthesis of duplicate DNA.
G2 - Gap - Cell grows, prepares for mitosis.
M - Mitotic phase - Mitosis and Cytokinesis.

Question 6

Define mitosis.

Answer 6

The physical process of segregating chromosomes into daughter cells.

Question 7

How many chromosomes before the beginning of mitosis?

Answer 7

23 pairs.

Question 8

Are body cells haploid or diploid?

Answer 8

Diploid.

Question 9

What does interphase consist of?

Answer 9

G1, S, G2.

Question 10

What is found in G2 as preparation for mitosis?

Answer 10

Intact nuclear envelope,
Chromosomes replicated, indistinct loosely packed chromatin fibres.
Centrosome replicated,
Microtubules extend, radically forming asters.

Question 11

4 things that happen in prophase?

Answer 11

Chromatin fibres condense - form discrete chromosomes.
Nucleoli disappear.
Centrosomes move away from each other.
Mitotic spindle begins to form.

Question 12

3 things that happen in pro metaphase?

Answer 12

Breakdown of nuclear envelope.
Some microtubules attach to chromosomes at kinetochores.
Other microtubules interact with those at opposite poles.

Question 13

3 things that happen in metaphase?

Answer 13

Centrosomes at opposite poles.
Chromosomes align at metaphase plate.
Sister kinetochores attached to microtubules from opposite poles.

Question 14

4 things that occur in anaphase?

Answer 14

Separation of centromeres.
Sister chromatids move to opposite poles.
Each chromatid becomes new chromosome.
Poles move further apart.

Question 15

4 things that happen in telophase?

Answer 15

Elongation of cell by polar microtubules.
Daughter nucleoli begin to form at poles of cell.
Nuclear envelopes form.
Chromatin decondenses.

Question 16

3 parts of the mitotic spindle?

Answer 16

Tubules, centrosomes, chromatid pairs on metaphase plate.

Question 17

3 types of tubule?

Answer 17

Astral, kinetochore, Non-kinetochore/polar.

Question 18

What is the function of the mitotic spindle?

Answer 18

To organise chromatids along metaphase plate, and then pull sister chromatids apart.

Question 19

What 3 things do the astral motors (dynein) do?

Answer 19

Pull astral microtubules towards poles during prophase.
Cause microtubules to de-polymerise and shorten.
Hold astral microtubules in place during metaphase and later.

Question 20

What 3 things do kinetochore motors (dynein) do?

Answer 20

Attach chromosomes to microtubules.
Pull on microtubules during anaphase - chromosomes move towards centrosomes.
Causes microtubules to de-polymerise and shorten.

Question 21

What 4 things do non-kinetochore/polar motors (kinesin) do?

Answer 21

Motors attached to microtubule from either side at the place where they overlap.
Motors push microtubules away in opposite directions during metaphase and anaphase.
Microtubules polymerise and get longer.
Cell elongates, aiding telophase/cytokinesis.

Question 22

What 3 things occur during cytokinesis in animal cells?

Answer 22

Microfilaments form ring at the furrow.
Ring contracts, due to interaction between actin and myosin filaments.
Furrow deepens until cell is pinched in two.

Question 23

What 2 things occur during cytokinesis in plant cells?

Answer 23

Cell plate forms at equatorial plane of the cell.

Cell wall forms - from plate contents.