Mitosis and Meiosis

Question 1

What is the structure of DNA?

Answer 1

Double helix- coils around nucleosomes>supercoils>chromosomes.

Question 2

What are the complimentary base pairs?

Answer 2

Adenine-Thymine

Cytosine-Guanine

Question 3

How many chromosomes are there?

Answer 3

46 chromosomes:
22 pairs- autosomes (i.e. anything that isn’t sex determining).
1 pair of sex chromosomes (XY= male and XX= female).

Question 4

What is the karyotype?

Answer 4

The number and appearance of chromosomes in a cell.
The spreads are arranged in size order where the biggest is pair 1, the smallest pair is pair 22 and the sex pair is pair 23.

Question 5

How many base pairs in a chromosome and number of genes we have?

Answer 5

Each chromosome contains a continuous DNA duplex of roughly 10^7 base pairs and contains several hundred gene- we have approximately 30,000 genes.

Question 6

What is the structure of a chromosome?

Answer 6

Each chromosome has a long arm (q) and a short arm (p like ‘petite’) and is separated by a centromere.

Question 7

How many genes in humans?

Answer 7

22,000 genes in humans.

Question 8

What is mitosis?

Answer 8

Process to produce 2 daughter cells that are genetically identical to parent cells and is important for growth and to replace dead cells.

Question 9

In what context do you use chromatin, chromosomes and chromatids?

Answer 9

Chromatin is a long chain of DNA= when the cell is not in replication.
Chromosomes is rolled up DNA i.e. when the chromatin has condensed= during/when it is going through cell division.
Sister chromatids are the branches of the same chromosome= after

Question 10

What process must occur in order to enable mitosis?

Answer 10

Cell must be in the cell cycle and interphase must occur- the longest phase of the cycle.

Question 11

What are the 3 main parts of interphase?

Answer 11

1. G1- no visible activity.
2. S (synthesis).
3. G2.

Question 12

What occurs in G1 phase interphase?

Answer 12

G1= cell growth phase:

• Rapid growth.
• Normal metabolic function.
• New organelles produced.
• Protein synthesis of proteins involved in spindle formation.

Question 13

What occurs in the S/Synthesis phase of interphase?

Answer 13

S/synthesis= DNA synthesis:
- DNA doubles via DNA replication.
- Histone proteins double through protein synthesis.
- Centrosome replication.
N.B. At the end of S, there is x2 as much
DNA.

Question 14

What occurs in G2 phase interphase?

Answer 14

G2= cell growth:

• Chromosomes condense (coil up and become visible).
• Energy stores accumulate.
• Mitochondria and centrioles double.

Question 15

What are the different stages of the cell cycle?

Answer 15

1. Interphase:
   
   • G1
   • S
   • G2
2. Mitosis (PMAT):
   
   • Prophase (and prometaphase)
   • Metaphase
   • Anaphase
   • Telophase
3. Cytokinesis.

Question 16

What happens during prophase?

Answer 16

Chromatin condenses into chromosomes and the centrosomes nucleate microtubules and move to the opposite poles of the nucleus.

Question 17

What happens during prometaphase?

Answer 17

The nuclear membrane breaks down (chromosomes visible), microtubules/spindle fibres invade nuclear space, chromatids attach to the microtubules/spindle fibres and the cell no longer has a nucleus.

Question 18

What happens during metaphase?

Answer 18

Chromosomes line up along the equatorial plane (metaphase plate).

Question 19

What happens during anaphase?

Answer 19

As the spindle fibres contract, centromeres split in two and the sister chromatid separate and are pulled towards opposite poles of the cell (centromere first).

Question 20

What happens during telophase?

Answer 20

The nuclear membrane reforms, the chromosomes unfold into chromatin and cytokinesis begins.

Question 21

Steps of mitosis

Answer 21

I Prefer Milk And Tea:
I- Interphase.
P- Prophase.
M- Metaphase.
A- Anaphase.
T- Telophase.

Question 22

What happens during cytokinesis?

Answer 22

The cell organelles become evenly distributed around each nucleus.
Cell divides (cleavaging occurs?) into 2 daughter cells with a nucleus in each and 46 chromosomes.

Question 23

What is a clinical relevance of correct cell division process?

Answer 23

Down’s syndrome= 1 extra chromosome at 21 i.e. trisomy 21.

Question 24

How to identify a cell undergoing mitosis in histology?

Answer 24

If the nucleus is dark (i.e. the chromatin has condensed to chromosomes) and if the nuclei are not the same size.

Question 25

What appearance (in histology) may be defines as malignant?

Answer 25

If there are too many mitotic figures i.e. lots of dark nuclei of different sizes.
N.B. The number of mitotic figures may determine how bad a cancer is, the more there are=the worse.