2.3 EUKARYOTIC CELL CYCLE AND DIVISION

Question 1

What is cell theory?

(part of biological molecules)

but its all relevant

Answer 1

cells are the basic unit of life
all living things are made up of cells
and all cells come from other cells

Question 2

What is the process of cell division in prokaryotic cells?

Answer 2

binary fission

Question 3

What is the process of cell division in eukaryotic cells?

Answer 3

Cell division is part of a regulated process called the cell cycle. It conists of three main stages: Interphase, mitosis, cytokinesis
It produces two identical duaghter cells for growth, repair and aesxual reproduction.

Question 4

What is interphase?

Answer 4

• Interphase is always the longest part of the cell cycle (but is variable in length)
• There are 3 stages that occur in interphase

Question 5

What are the three stages of interphases?

Answer 5

• G1 (the first growth phase)
• S (synthesis)
• G2 (second growth phase)

Question 6

cell cycle

What happens in G1 (Interphase)

Answer 6

• in the nucleus some genes are ‘switched on’ and their base seuquence is transcribed to pre-mRNA molecules

- The cytoplasm increases in volume (grows) by producing new proteins and cell organelles, including mitochondria and endoplasmic reticulum.

Question 7

cell cycle

What happens in synthesis?

Answer 7

• In the nucleus, the semi-conservative replication of DNA occurs.
• New histones are syntehsised and attatch to the replicated DNA in the nucleus.
• Each chromosome becomes two chromatids attatched at the centromere.

Question 8

cell cycle

What happens in G2?

Answer 8

• In the nucleus, replicated DNA is ‘double checked’ for errors and corrected if any errors are found
• If correction is not possible, the cell is normally halted at this G2 phase.
• Cell growth continues by further synthesis of proteins and cell organelles.

Question 9

What are the stages of mitosis?

Answer 9

• Prophase
• Metaphase
• Anaphase
• Telophase

Question 10

Mitosis

What happens in prophase?

Answer 10

• chromosomes increasingly shorten and thicken
• chromosomes become visible (towards the end of prophase)
• centrioles divide and move to opposite ends of the cell
• spindle fibres form

Question 11

note on cell structure (TOPIC 1)

What is cytosol?

Answer 11

the aqueous component of the cytoplasm of a cell, within which various organelles and particles are suspended.

Question 12

Is the cytosol structureless?

Answer 12

No.
Microtubules of a globular protein called tubulin are often present.
Form a network of unbranched hollow cylinders

Question 13

What do microtubules do?

Answer 13

• involved in moving organellles around the cytoplasm
• form the centrioles found in animal cells

Question 14

Desribe the structure and location of centrioles
+what happens to them in mitosis

Answer 14

• occur in pairs
• normally lie at right angles to each other
• just outside cell’s nucleus
• each centriole is composed of nine bundles of microtubules
• during cell division the centrioles move apart creating a network of micrtubules called the spindle.

Question 15

What is a centromere?
3 points

Answer 15

• A narrow region occupying a specific position on each chromosomes.
• This is the only site on each chromosome to which the microfibres of the spindle can attatch in mitosis.
• Following DNA replication it temproarily holds together two copies of each chromosome (the chromatids)

Question 16

What happens in metaphase?

Answer 16

Chromosomes line up on the equator

Question 17

What happens in anaphase?

Answer 17

• The spindle fibres contract and shorten
• Results in the two chromatids being pulled apart by their centromeres to opposite poles of the spindle.

Question 18

What happens in telophase?

Answer 18

• Nuclear membrane reforms
• Chrosomes de-condense
• spindle disappears

Question 19

What happens in cytokinesis?

Answer 19

cytoplasm divides, forming two identical duaghter cells (clones)

Question 20

Where is mitosis commonly observed?

give an example in mammals and in plants

Answer 20

tissues of multicellular organisms that are actively growing.
in mammals: epithelial tissues (skin, intestine lining)
in plants: meristems

Question 21

Define ‘meristems’

Answer 21

A group of plant cells that is able to divide by mitosis.
Primary meristems are found at tips of growing shoots and roots.
Secondary meristems are found in woody plants leading to an increased diameter of roots and shoots.

Question 22

CP 3

How could you investigate mitosis?

Answer 22

Making a temporary squash preparation of a root tip to investigate the stages of mitosis under a microscope.

Question 23

What is meiosis?

Answer 23

A type of cell division that produces four non-identical daughter cells that each have half the number of chromosomes of the parent cell.

Question 24

What is a diploid cell?

Answer 24

• A eukaryotic cell that contains two copies of each chromosome.
• Is represnted as 2n
• In sexually reproducing organisms one copy comes from each parent

Question 25

What is a haploid cell?

Answer 25

- A euakaryotic cell that contains only one chromosome from each of its homologous pairs - is represented as n

Question 26

What are homolgous chromosomes?

Answer 26

A pair of chromosomes in a diploid cell that have the same shape and size and **carry the same genes in the same order**, although not necessarily the same alleles of each gene.

Question 27

How many divisions are there in meiosis?

Answer 27

2

Question 28

Overview of meiosis | Figure 5.8

Answer 28

Question 29

What is meiosis?

Answer 29

a type of cell division that results in four non identical daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes.

Question 30

An overview of mitosis

Answer 30

Question 31

What happens in prophase I

Answer 31

- chromosomes shorten and thicken - homologous chromosomes pair up to form bivalents - centrioles duplicate - chromosomes become visible - crossing over occurs- visible as chiasmata

Question 32

What happens in metaphase I

Answer 32

- nuclear membrane breaks down - spindle forms - bivalents line up on the equator - independent assortment* | *random alignment of homologous pairs along the equator

Question 33

What happens in anaphase I

Answer 33

- Homologous chromosomes (pairs) seperate - spindle fibres shorten and contact pulling whole chromosomes by their centromeres to opposite ends of the cell | forms n cells

Question 34

What happens in telophase I

Answer 34

- Nuclear membrane reforms around daughter nuclei - chromosomes start to decondense

Question 35

What happens in prophase II

Answer 35

- The chromosomes condense - centrioles duplicate

Question 36

What happens in metaphase II

Answer 36

- Nuclear membrane breaks down - spindle forms - chromosomes attatch by their centromere to the spindle fibres at the equator of the spindle

Question 37

What happens in anaphase II

Answer 37

- The chromatids seperate at their centromere - pulled to opposite poles of the cell

Question 38

What happens in telophase II

Answer 38

Chromatids (now called chromosomes) decondense. The nuclear membrane reforms.

Question 39

What is chromosome translocation?

Answer 39

part of the chromsomes breaks and rejoins a completely different chromosomes.

Question 40

What is chromosome non-disjunction?

Answer 40

The failure of homologous chromosomes to seperate properly during the first division of meiosis. It results in daughter cells (gametes) with too many or too few chromosomes.

Question 41

Polysomy | + name an example

Answer 41

A term used to describe a diploid cell or organism with more than two copies of a particular chromosome. eg: Downs Syndrome - three copies of chrosome 21 (trisomy)

Question 42

Monosomy | + name an example

Answer 42

A term used to describe a diploid cell or organism with only one copy of a particular chromosome. eg: Turner's Syndrome- monosomy of the sex chromosome (only one X)