cell division

Question 1

Cell Cycle

Answer 1

the cell is an ordered set of events which culminates in the division of a cell into two daughter cells. It can be divided into two main phases (Interphase and M phase)

Question 2

Interphase

Answer 2

1) G1 - First intermediate gap stage in which the cell grows and prepares for DNA replication
2) S - synthesis stage in which DNA is replicated
3) G2 - second intermediate gap stage in which the cell finishes growing and prepares for cell division

Question 3

M phase

Answer 3

1) Mitosis - nuclear division, whereby DNA is separated into two identical nuclei
2) Cytokinesis - Cytoplasmic division, whereby cellular contents are segregated and the cell splits into two

Question 4

Events occuring in Interphase

Answer 4

1) DNA replication (DNA is copied during the S phase of interphase)
2) Organelle duplication (organelles duplicated for daughter cells)
3) Cell growth (Cytoplasmic volume increase prior to division)
4) Transcription/translation - proteins and enzymes synthesised
5) Obtain nutrients - vital cellular materials must be present
6) Respiration - ATP production is needed to drive division process

Question 5

Chromatin

Answer 5

Dna is usually loosely packed within the nucleus as a unravelled chromatin
in this unravelled form, the DNA is accessible to transcriptional machinate and so genetic information can be translated
DNA is organised as chromatin in all non - dividing cells and throughout the process of interphase

Question 6

Chromosome

Answer 6

DNA is temporarily tightly packed into a chromosome prior to division (via supercoiling)
In this form the DNA can be easily segregated yet is inaccessible to transcriptional machinery
DNA is organised as chromosomes during the process of mitosis

Question 7

Chromosome versus Chromatid

Answer 7

Chromosome = condensed form of DNA which is visible during mitosis. During the S phase the chromosomes contain two identical DNA strands

Chromatids = the identical strands (DNA) are called sister chromatids and are held together by the Centromere. when the Chromatids spereate during mitosis, independent chromosomes are formed with individual DNA

Question 8

Mitosis

Answer 8

Mitosis is the process of nuclear division whereby duplicated DNA molecules are arranged into two separate nuclei. It occurs during interphase and is divided into 4 stages: prophase, metaphase, anaphase, telophase

Question 9

Before Mitosis

Answer 9

1) DNA is present as uncondensed chromatin
2) DNA is contained within a clearly defined nucleus
3) Centrosomes and other organelles have been duplicated
4) Cell is enlarged in preparation for division

Question 10

Prophase

Answer 10

1) DNA supercoils and chromosomes condense (becoming visible under microscope)
2) Chromosomes are comprised of genetically identical sister chromatids (joined at a centromere)
3) Paired centrosomes move to the opposite poles of the cell and form microtubule spindle fibres
4) The nuclear membrane breaks down and the nucleus dissolves

Question 11

Metaphase

Answer 11

1)Microtubule spindle fibres from both centrosomes connect to the centromere of each chromosome
2) Microtubule depolymerisation causes spindle fibres to shorten in length and contract
3) This causes chromosomes to align along the centre of the cell (equatorial plane or metaphase plate)

Question 12

Anaphase

Answer 12

1) Continued contraction of the spindle fibres causes genetically identical sister chromatids to separate
2) Once the chromatids separate, they are each considered an individual chromosome in their own right
3) The genetically identical chromosomes move to the opposite poles of the cell

Question 13

telophase

Answer 13

1) Once the two chromosome sets arrive at the poles, spindle fibres dissolve
2) Chromosomes decondense (no longer visible under light microscope)
3) Nuclear membranes reform around each chromosome set
4) Cytokinesis occurs concurrently, splitting the cell into two

Question 14

Cytokinesis

Answer 14

Cytokinesis is the process of cytoplasmic division, where the cell splits into two identical daughter cells.
Cytokinesis occurs concurrently with the final stage of mitosis (telophase) and is different in plant and animal cells

Question 15

Animal cells (cytokinesis)

Answer 15

1) After anaphase microtubule filaments form a concentric ring around the cells centre
2) The microfilaments constrict to form a cleavage furrow, which deepens from the periphery towards the centre
3) When the furrow meets in the centre the cell is formed into two cells
4) Its describes as Centripetal (outside to centre)

Question 16

Plant cells (cytokinesis)

Answer 16

1) After anaphase carbohydrate rich vesicles form in a row at the centre of the cell
2) the vesicles fuse together and an early cell plate begins to form within the middle of the cell
3) the cell plate extends outwards and fuses with the cell wall dividing the cell into two distinct daughter cells
4) Its described as Centrifugal (centre to outside)

Question 17

Mitotic index

Answer 17

The mitotic index is a measure of the proliferation status of a cell population. It is an important prognostic tool for predicting the response of cancer cells to chemotherapy

Question 18

Identifying Mitotic cells

Answer 18

Cells undergoing mitosis will lack a clearly defined nucleus and possess visibly condensed chromosomes.

Prophase - Chromosomes condensed but still confined to a nuclear region
Metaphase - chromosomes aligned along the equator of the cell
Anaphase - two distinct clusters of chromosomes apparent at poles of the cell
Telophase - two nuclear regions present within a single cell

Question 19

Calculating Mitotic index

Answer 19

ratio between the number of cells in mitosis and the total number of cells

Question 20

Cyclins

Answer 20

Cyclins are a family of regulatory proteins that control the progression of the cell cycle.
Cylclins activate cyclin dependent kinases (CDKs) which control cell cycle processes through phosphorylation

Question 21

Mechanism of Cyclin action

Answer 21

1) Cyclin and CDK form a complex which will bind to a target protein and modify it via phosphorylation
2) The phosphorylated target protein will trigger a specific event
3) After the event, the cyclin is degraded and the CDK becomes inactive again

Question 22

Cyclin expression patterns

Answer 22

Different cyclins specifically bind to and activate different classes of cyclin dependent kinases. Cyclin levels will peak when their target protein is required

Question 23

Tumours

Answer 23

Tumours are abnormal cell growths resulting from uncontrolled cell division and can only occur in any tissue or organ.
Diseases caused by the growth of tumours are collectively known as cancers

Question 24

Mutagens

Answer 24

A mutagen is an agent that changes the genetic material of an organism

Question 25

Different Mutagens

Answer 25

1) Physical - Sources of radiation including X rays, ultraviolet light and radioactive decay
2) Chemical - DNA interacting substances including reactive oxygen species and metals
3) Biological - Viruses, certain bacteria and mobile genetic elements

Question 26

Mutagens leading to Cancer

Answer 26

Mutagens that lead to cancer are known as Carcinogens

Question 27

Oncogenes

Answer 27

An oncogene is a gene that has potential to cause cancer

Question 28

Proto-oncogene

Answer 28

Proto-oncongenes code for proteins that simulate the cell cycle and promote cell growth and proliferation.
When a Proto-oncogene is mutated or subjected to increased expression it becomes a cancer causing oncogene

Question 29

Tumour supressor

Answer 29

Tumour suppressor genes code for proteins that represent cell cycle progression and promote apoptosis.
Tumour supressor genes are sometimes referred to as anti-oncogenes as their normal function prevents cancer

Question 30

Metastasis

Answer 30

Metastasis is the spread of cancer from one location to another forming secondary tumour.
The spread cancer (secondary) is made up of the same type of cells as the primary tumour

Question 31

moving or remaining Cancer

Answer 31

Bengin - remain in their original location
Malignant - spread and invade neighbouring tissue

Question 32

Cigarette smoke

Answer 32

Cigarette smoke contains over 4,000 chemical compounds, over 60 are known to be carcinogenic (can cause cancer)

Question 33

correlation between smoking and cancer

Answer 33

90% of lung cancers attributed due to tobacco use
smoking also increases other cancers
high correlation between smoking and cancer