Topic 2.3- Eukaryotic cell division

Question 1

State what the cell cycle is and outline its stages

Answer 1

The cell cycle is a regulated cycle of division with intermediate growth periods.

1. interphase
2. mitosis/meiosis
3. cytokinesis

Question 2

Outline what happens during interphase

Answer 2

G1. cell synthesises proteins for replication e.g. tubulin for spindle fibres + cell size doubles
S. DNA replicates, chromosomes consist of 2 sister chromatids joined at a centromere
G2. organelles divide so there is 2 of everything

Question 3

What is the purpose of mitosis?

Answer 3

Produces 2 genetically identical daughter cells for:

• growth
• cell replacement/ tissue repair
• asexual reproduction

Question 4

Name the stages of mitosis

Answer 4

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Question 5

Outline what happens during prophase

Answer 5

1. Chromosomes condense, becoming visible. (X-shaped: 2 sister chromatids joined at centromere)
2. Centrioles move to opposite poles of cell (animal cells) + mitotic spindle fibres form
3. Nuclear envelope and nucleolus break down= chromosomes free in cytoplasm

Question 6

Outline what happens during metaphase

Answer 6

sister chromatids line up at cell equator, attached to the mitotic spindle by their centromeres

Question 7

Outline what happens during anaphase

Answer 7

(requires energy from ATP hydrolysis)

1. Spindle fibres contract=centromeres divide
2. Sister chromatids separate into 2 distinct chromosomes + are pulled to opposite poles of cells
3. Spindle fibres break down

Question 8

Outline what happens during telophase

Answer 8

1. Chromosomes decondense, becoming invisible again

2. New nuclear envelopes form around each set of chromosomes= 2 new nuclei, each with a copy of each chromosome

Question 9

What happens during cytokinesis?

Answer 9

1. Cell membrane cleavage furrow forms

2. Contractile division of cytoplasm

Question 10

Explain how to prepare a temporary root tip squash

Answer 10

1. place root in HCL to halt cell division and hydrolyse middle lamella
2. stain root tip with a dye that binds to chromosomes
3. macerate tissue in water using mounted needle
4. use mounted needle at 45 degrees to press down coverslip + obtain a single layer of cells. avoid trapping air bubbles

Question 11

Explain the procedure for a root tip squash experiment

Answer 11

1. prepare a temporary mount of foot tissue
2. focus an optical microscope on the slide. count total number of cells in field of view and how many are in a stage of mitosis
3. calculate mitotic index (proportion of cells undergoing mitosis)

Question 12

Name 2 dyes that bind to chromosomes

Answer 12

1. Toulidine blue

2. Acetin orcein (purple-red)

Question 13

Why is only the root tip used when calculating a mitotic index?

Answer 13

• meristematic cells at root tip are actively undergoing mitosis
• cells further from the root tip are elongating not dividing

Question 14

What is mitosis?

Answer 14

the process by which a cell divides to produce 2 genetically identical daughter cells

Question 15

What is asexual reproduction?

Answer 15

the production of genetically identical offspring from a single parent or organism

Question 16

What is sexual reporoduction?

Answer 16

the production of genetically different offspring from the parent organism or organisms by the fusing of 2 sex cells

Question 17

What is meiosis?

Answer 17

a form of cell division where the chromosome number of the original cell is halved, leading to the formation of gametes

Question 18

What are histones?

Answer 18

positively charged proteins involved in the coiling of DNA to form dense chromosomes in cell division

Question 19

What are nucleosomes?

Answer 19

dense clusters of DNA wound round histones

Question 20

What is a karyotype?

Answer 20

a way of displaying chromosome images of a cell to show the autosomes and sex chromosomes

Question 21

What is the cell cycle?

Answer 21

a regulated process of 3 stages (interphase, mitosis, cytokinesis) in which cells divide into 2 genetically identical daughter cells

Question 22

What is a chromatid?

Answer 22

one strand of the replicated chromosome pair that is joined to the other chromatid at the centromere