Lecture 2 - asexual cell cycle

Question 1

What does cell division give in the asexual cell cycle?

Answer 1

identical daughter cells

Question 2

What type of products come from asexual cell division?

Answer 2

mitotic nuclear division gives clonal products in eukaryotes

Question 3

What does mitosis of single-celled organisms lead to?

Answer 3

clones, derived from a single ancestral cell

Question 4

What does mitosis of multicellular organisms lead to?

Answer 4

genetically identical cells derived from a single fertilised egg

Question 5

What are the 2 types of cells that can be found in a multicellular organism?

Answer 5

soma (body) cells
gametes (stemming from the germline)

Question 6

What is a semidiscontinuous DNA replication?

Answer 6

• a double-stranded chromosome which is copied to give 2 identical daughter molecules.
• leading & lagging strand
• complimentary DNA meaning it ends up identical

Question 7

How do bacteria replicate?

Answer 7

binary fission

Question 8

Describe the steps in binary fission

Answer 8

1. DNA duplicates - cell gets bigger
2. Replicated chromosomes move apart
3. Protein called FtsZ marks the middle
4. New cell wall
5. 2 daughter cells

Question 9

What is the structure of the cell cycle?

Answer 9

Interphase:
- G1
- S phase
- G2
Mitosis:
- PPMAT (prophase, prometaphase, metaphase, anaphase, telophase) *cytokinesis

Question 10

In what stage of the cell cycle does the cell spend most of its time?

Answer 10

Interphase

Question 11

What occurs during G1 phase?

Answer 11

• cell increases in size
• ribosomes, RNA produced
• preparation for DNA synthesis

Question 12

What occurs during S phase?

Answer 12

• DNA synthesised (chromosomes duplicated)

Question 13

What occurs during G2 phase?

Answer 13

• cell checks fidelity (accuracy) of DNA
• preparation for nuclear division

Question 14

What occurs during G0 phase?

Answer 14

cell steps out of the cell cycle - inactive (quiescent) - don’t divide

Question 15

What is the overall purpose of gap phases?

Answer 15

cell growth, protein synthesis, etc.

Question 16

What are sister chromatids?

Answer 16

identical copied versions of chromosomes, which segregate during mitosis into new nuclei, meaning the overall amount of DNA ends up the same.

Question 17

How many sister chromatids are present between interphase & mitosis?

Answer 17

2

Question 18

What occurs during prophase?

Answer 18

chromosomes condense so they are now visible (thread-like structures), with each chromosome compromised of 2 sister chromatids and a single centromere

Question 19

What holds sister chromatids together?

Answer 19

Cohesin

Question 19

During what phase does the nuclear membrane break down?

Answer 19

prometaphase

Question 20

What is the mitotic spindle made of?

Answer 20

cytoskeleton structure - microtubules (polymers of small tubulin protein subunits)

Question 21

What is the role of the mitotic spindle?

Answer 21

to separate sister chromatids to different daughter cells

Question 22

How does the mitotic spindle separate the sister chromatids?

Answer 22

the microtubules get shorter - pulling chromosomes towards the poles

Question 23

What are centromeres?

Answer 23

specialised chromosome regions that direct the equal segregation of chromosomes during mitosis (& meiosis)

Question 24

What joins to sister chromatids together?

Answer 24

centromeres

Question 25

Where can centromeres be found?

Answer 25

at any point along the chromosome

Question 26

What connects centromeres to the microtubules?

Answer 26

a large protein complex - kinetochore

Question 27

What occurs during metaphase?

Answer 27

- centromeres align at spindle equator (midway between the 2 poles) - microtubules attach to each pole - tension between these keep chromosomes in the centre

Question 28

What occurs during anaphase?

Answer 28

- sister chromatid cohesion breaks down, separating chromatids to become separate chromosomes - centromeres start moving to opposite poles - depending on position of the centromere - each chromosome can form a V shape as it's dragged behind the centromere

Question 29

What occurs during telophase?

Answer 29

- chromosomes arrive at the cell poles and decondense - no longer recognisable thread structures - before the daughter nuclei then reform

Question 30

What occurs during cytokinesis?

Answer 30

division of the rest of the cell - cleavage furrow (animals) or cell plate (plants) forms in-between the 2 poles, creating 2 daughter cells

Question 30

What is a bridge chromosome?

Answer 30

a chromosome that erroneously has 2 centromeres is pulled towards both poles at once - ends up being broken

Question 30

What are 2 examples of mitosis going wrong?

Answer 30

- bridge chromosome - acentric chromosome

Question 31

What is an acentric chromosome?

Answer 31

lacking a centromere, unable to segregate properly