1.6 CELL DIVISION

Question 1

Before Mitosis can occur

Answer 1

All the DNA in the nucleus must be replicated

= INTERPHASE

Question 2

Role of mitosis

Answer 2

Each chromo is converted from single DNA M into 2 identical DNA M: chromatids

During mitosis, 1 chromatid passes to each daughter cell

Question 3

Mitosis def

Answer 3

Mitosis is the division of the nucleus into 2 genetically identical daughter cells

Question 4

Mitosis is a X process

Answer 4

CONTINUOUS process

4 phases –> PMAT

Question 5

CYCLINS AND THE CONTROL OF THE CELL CYCLE

Answer 5

CYCLINS, group of proteins, bins to enzymes “cyclin-dependent kinases” which become active and attach phosphate groups to other proteins in the cell

The attachment triggers the other protein to become active/ carry out tasks specific to one cell cycle phase

4 main type of cyclin in human cells

Unless these CYCLINS reach threshold concentration, the cell does not progress to the next stage

Question 6

INTERPHASE overview

Answer 6

Very active phase of the cell cycle with many processes occurring in the nucleus/ cytoplasm

DNA rep in the nucleus and protein synthesis in cytoplasm only happens here

Number of mitochondria in cytoplasm increases due to growth/ division of mitochondria

In plant cells n. of chromo increase too

Question 7

INTERPHASE PHASES

Answer 7

G1: all content but chromosome is duplicated

Some cells never go beyond G1: never going to be divided so they don’t need to prepare for mitosis

They enter G0: temp or permanent

S PHASE: replicates all genetic material/ each chromo is duplicated so that after mitosis new cells have a complete set of genes

Question 8

SUPERCOILING

Answer 8

Chromosomes condense by supercoiling

DNA is immensely long: 50 000 um
Human nuclei: <5 um diameter

Essential to pack chromo= condensation of chromo

1st stage of mitosis: repeated coiling of DNA M–> shorter/wider = SUPERCOILING

Histone proteins associated with DNA in eukaryotes + enzyme help

Question 9

PROPHASE

Answer 9

SUPERCOILING: chromo become shorter/ wider repeatedly

Nucleolus breaks down

Microtubules grow from MTOC “microtubules organising centre” to form spindle shapers array: links cell poles

Nuclear membrane breaks down

Question 10

METAPHASE

Answer 10

MicroT still grows and attached to centromeres on chromo

Spindle microT put under tension to test it attachment is correct by shortening microT at centromere

It attachment is correct, chromo remains on equator

Question 11

ANAPHASE

Answer 11

Each centromere divides
Pairs of sister chromatid can separate

By shortening of Spindle microT that pulls them to separate polls

Mitosis produces 2 gen identical nuclei because sister chromatids are pulled to opposite poles

Question 12

TELOPHASE

Answer 12

Chromatids have reached the poles and are now called chromosomes

At each pole chromo are pulled tight in groups near MTOC and nuclear membrane reforms around them

Chromo uncoils and nucleus is formed

By now cell has divided and 2 daughter cells enter interphase

Question 13

Mitotic index

Answer 13

Number of cell in mitosis
Divided by
Total number of cells

Question 14

TUMOUR FORMATION AND CANCER overview

Answer 14

Mutagens, oncogenes and metastasis are involved in the development of primary/ secondary tumours

Question 15

Tumour?

Answer 15

Group of abnormal cells

Question 16

Benign

Answer 16

Cells adhere to each other and don’t invade nearby tissue or move thus they are unlikely to cause harm

Question 17

Malignant

Answer 17

Detached tumour cells which can develop into secondary tumours and lead to death

Question 18

Carcinomas

Answer 18

Malignant tumours

Question 19

Cancer

Answer 19

Disease due to malignant tumour

Question 20

Cause of cancer

Answer 20

Carcinogens: chemical/ agents that cause gene mutation and eventually cancer (radiation)

Question 21

Mutation

Answer 21

Random changes to base sequence of genes

Yet most genes don’t cause cancer if they mutate

Question 22

Cancer causing genes

Answer 22

Oncogenes

In a normal cell oncogenes control the cell cycle and division

Thus a mutation of an oncogene= uncontrolled cell division= tumour

Question 23

Tumour cell

Answer 23

Several mutations are needed
V. Small chances but because of large n. Of cells the chance
Of having a tumour in a lifetime is significant

Question 24

Metastasis

Answer 24

Movement of 1 tumour to a 2 nd one

Question 25

CYCLINS

Answer 25

Proteins that ensure tasks are done at the right time

Control when cell moves to the next stage of cycle

Question 26

Cytokinesis

Answer 26

Occurs during mitosis and if different in plant and animal cells

Cell can divide after mitosis with 2 genetically identical nuclei

Question 27

Cytokines in animal cells

Answer 27

Plasma membrane is pulled inward around equator of the cell to form cleavage furrow

Using ring of contractile protein: actin and myosin

When cleavage furrow reaches centre, the cell is pinched apart into 2 daughter cells

Question 28

Cytokinesis in plant cells

Answer 28

Vesicles move to equator where they fuse together

–> forms cell plate in the middle: lamella which fuses with the cell wall

diving the cell into two distinct daughter cell

Daughter cells bring in cellulose to equator be exocytosis