Cell Cycle And Cell Division

Question 1

What protein is DNA made up of?

Answer 1

Histone

Question 2

When do chromosomes become visible?

Answer 2

Chromatin condenses prior to cell division

Question 3

What does haploid mean and what symbol is associated with it?

Answer 3

Having one complete set of chromosomes. Symbol= n

Question 4

What does Diploid mean and what is the symbol associated with it?

Answer 4

Having two complete sets of chromosomes. Symbol= 2n

Question 5

What is used to describe the number of complete sets of chromosomes in an organism?

Answer 5

The Ploidy level

Question 6

How are organisms with more than two complete set of chromosome described as?

Answer 6

Polyploid

Question 7

What are the 3 steps to the cell cycle?

Answer 7

Interphase
Mitosis
Cytokinesis

Question 8

Describe the process of Prophase:

Answer 8

The chromosomes condense-> becoming distinguishable as pairs of chromatids

Centrioles separate and move to opposite ends of the cell-> As they move they organise a partner so by the time they reach the poles their in pairs again

Protein microtubules form-> Making the spindle. Spindle fibres extend from pole to pole and from pole to the centromere of each chromosome

Nuclear envelope disintegrates-> The nucleolus disappears (late prophase)

Question 9

Describe what happens at Metaphase:

Answer 9

The centromere attaches to the spindle fibres so that the chromosomes are aligned on the equator. The chromosomes line up.

Question 10

How do chromosomes in metaphase look like when viewed from different points?

Answer 10

From the poles= spread out
From the side= in a line

Question 11

Describe what happens at anaphase:

Answer 11

The spindle fibres shorten and the centromeres separate. Pulling the now separated chromatids to the poles, centromere first.

Question 12

Describe what happens at telophase:

Answer 12

Chromatids are referred to as chromosome again.

• Chromosomes uncoil and lengthen
• The spindle fibres break down
• The nuclear envelope reforms
• The nucleolus reappears

Question 13

Describe cytokinesis and how it differs in animal and plant cells:

Answer 13

Cytokinesis= the division of the cytoplasm to make new cells

Animal cells= Occurs by constriction of the parent cell around the equator, from outside inwards

Plant cells= a cell plate form across the equator of the parent cell from the centre outwards and they extend and join to form the new cell wall

Question 14

Name some key differences between mitosis in animal cells and plant cells:

Answer 14

Shape= animal cell becomes rounded before mitosis, where’s in plant there is no change

Centriole= in animal is present, in plant absent from higher plant cells

Cytokinesis= Cleavage furrow, Cell plate. Cleavage furrow develops from outside inwards, Cell plate develops from the centre outwards

Spindle= in animal degenerates at telophase, in plant it remains throughout new cell wall formation

Occurrence= bone marrow/hair follicles/ sites of tissue repair, in meristems

Question 15

The significance of mitosis:

Answer 15

Produces cells that are genetically identical to the parent (same number of chromosomes)

Growth- can repair tissue and replace dead cells. Some tissues are constantly worn away and need replacing like the gut lining.

Asexual reproduction- produces complete offspring that is genetically identical to the parent

Question 16

What is the name given to the genes that prevents the cell cycle from repeating continually?

Answer 16

Tumour suppressing genes

Question 17

When a gene is mutated but does not cause cancer what is it called?

Answer 17

Porto-oncogenes

Question 18

When a gene is mutated and does cause cancer what is it called?

Answer 18

oncogenes

Question 19

Where does DNA replication occur?

Answer 19

Within interphase before mitosis/meiosis

Question 20

Describe what happens at prophase I of meiosis I:

Answer 20

• Paternal and maternal chromosomes come together in homologous pairs (synapsis), each chromosome pair is a bivalent
• The centrioles move to opposite poles and form the spindle fibres
• Chiasmata occurs when the chromatids wrap around each other

-Crossing over happens as DNA from one chromatid may be exchanged causing a source of variation

-This allows ‘genetic recombination’ which produces new combinations of alleles, single cross over in meisosis one can result in four haploid gametes having a different genetic composition

• By the end of prophase I, the nuclear envelope disintegrated and the nucleolus has disappeared

Question 21

Describe what happens at metaphase I:

Answer 21

• Pairs of homologous chromosomes arrange themselves at the equator of the spindle.
• Independent assortment happens, each combination of paternal and maternal chromosomes faces each pole, so the combination of chromosomes that enters each daughter cell at meiosis 1 is random

Question 22

With 3 pairs of chromosomes, how many possible combinations are there of maternal and paternal chromosomes?

Answer 22

2 to the power of 3 = 8 possible combinations

Question 23

Describe what happens at anaphase I:

Answer 23

• Spindle fibres shorten which separates each chromosome in the bivalent resulting in each pole receiving only one of each homologous pair of chromosome.

Question 24

Describe what happens at telophase I:

Answer 24

In some species the nuclear envelope reforms around the haploid group of chromosomes and the chromosomes decondense making them no longer visible, but in many species the chromosomes stay in their condensed form.