Mitosis

Question 1

How is mitochondrial DNA inherited?

Answer 1

Inherited from mother only.

Question 2

What is the structure of DNA?

Answer 2

Double helix of nucleotide strands.

Base pairs are complementary and hydrogen bonds form between them.

Question 3

Hydrogen bonds form between which base pairs?

Answer 3

A and T (2 H bonds)

C and G (3 H bonds)

Question 4

How does DNA form chromosomes?

Answer 4

• coils around histones, forming nucleosomes
• nucleosomes coil into supercoils
• supercoils coil further around a protein scaffold, into chromosomes

Question 5

What is a nucleosome?

Answer 5

DNA coiled around 8 histone proteins.

Question 6

How coiled is chromatin?

Answer 6

Supercoiled but not coiled into chromosomes.

Question 7

What joins a pair of chromosomes?

Answer 7

Centromere.

Question 8

How many chromosomes are there in the human genome?

Answer 8

46 chromosomes (23 pairs)

Question 9

What are autosomes?

Answer 9

Pairs of chromosomes that are NOT sex chromosomes.

Question 10

How many genes per chromosome?

Answer 10

Several hundred

Question 11

How long is the DNA in a chromosome?

Answer 11

Around 10^7 bp long

Question 12

What are the long and short arms of a chromosome called?

Answer 12

Long arm - q

Short arm - p

Question 13

What dyes stain chromosomes?

Why do we stain chromosomes?

Answer 13

Giemsa (shows G banding)
Quinacrine (shows Q banding)

Chromosomes are stained for identification and analysis.

Question 14

How are chromosome bands numbered?

Answer 14

Numbered moving out from the centromere.

Question 15

How many bands does Giemsa staining typically give?

Answer 15

400 - 500 bands.

Question 16

How many bp in length is each G band?

Answer 16

Around 6-8 Mbp

Question 17

What is the purpose of mitosis?

Answer 17

Producing two daughter cells that are genetically identical to the parent cell, for growth and to replace dead cells.

Question 18

What are the 3 phases of interphase?

Answer 18

G1 (growth phase 1)
S (synthesis phase)
G2 (growth phase 2)

Question 19

How long does interphase last?

Answer 19

Around 23 hours

Question 20

What happens during G1? How long does G1 last?

Answer 20

• cell increases in size
• organelles are replicated

Lasts 11-12 hrs

Question 21

What happens between G1 and S?

Answer 21

Checkpoint for mutations in DNA before it is replicated.

Question 22

What happens in S phase?

Answer 22

• DNA replication

- centrosome duplication

Question 23

What happens in G2?

Answer 23

• further cell growth
• production of proteins and additional organelles
• organisation of cell contents in preparation for mitosis.

Question 24

What are labiles?

Answer 24

Cells which readily undergo mitosis.

Question 25

How long does mitosis last on average?

Answer 25

1 hr

Question 26

What are permanent cells?

Answer 26

Cells which do not divide, so they exist permanently outside the cell cycle. - cardiac myocytes, neurons

Question 27

What is G0?

Answer 27

Stable cells are in G0 when they are outside the cell cycle. They can enter the cell cycle when necessary. - liver cells.

Question 28

What happens during prophase?

Answer 28

- chromatin condenses into chromosomes - centrosomes propagate microtubules and move to opposite poles of the nucleus - a scaffold of tubulin filaments (microtubules) forms between the centrosomes.

Question 29

What is the telomere?

Answer 29

Region at the end of a chromosome which consists of a repetitive DNA sequence (TTAGGG) Telomere protects the internal regions of the chromosome, it is worn away a little with every cell replication.

Question 30

What happens during prometaphase?

Answer 30

- nuclear membrane breaks down - microtubules invade the nuclear space - chromatids attach to microtubules in a haphazard arrangement.

Question 31

What happens in metaphase?

Answer 31

Chromosomes line up along the equatorial plane.

Question 32

What happens in anaphase?

Answer 32

- sister chromatids separate | - they are pushed to opposite poles of the cell by microtubule scaffold.

Question 33

What happens during telophase?

Answer 33

- nuclear membranes reform - chromosomes unfold into chromatin - cytokinesis

Question 34

What is the clinical relevance of staining chromosomes and viewing mitoses under a microscope?

Answer 34

- detecting chromosomal abnormalities - categorising tumours as benign or malignant - grading malignant tumours

Question 35

Which drugs prevent formation of the mitotic spindle?

Answer 35

- taxol | - vinca alkaloids (vinblastine, vincristine)

Question 36

Which drug targets spindle poles?

Answer 36

- ispinesib

Question 37

Which drugs stop anaphase?

Answer 37

Colchicine-like drugs

Question 38

What are some indicators of malignancy in cells?

Answer 38

- ring mitoses - varied sizes of nuclei - varied degrees of staining of nuclei