The Cell Cycle

Question 1

Why do cells need to divide ?

Answer 1

Cells have limited size - if too big SA: V ratio is inefficient

Produce gametes

Multicellular organisms - growth and repair

Asexual reproduction

Question 2

What is Interphase

Answer 2

Cells do not divide continuously
Long periods of growth and normal working separate divisions

Active phase of the cell cycle - cell is carrying out major functions liek producing enzymes and hormones while actively preparing for cell division

Question 3

What things happen in interphase speicifically?

Answer 3

Dna is replicates an checked for errors in the nucleus

Protein synthesis occurs in cytoplasm

Mitachondria grow and divide increasing in number in the cytoplasm

Chloroplasts grow and divide, in agal cell cytoplasm

Normal cell metabolic processes occur ( some e.g. reputation also occur throughout cell division ! T

Question 4

3 phases of interphase

Answer 4

G1- first growth phase , proteins from which organelles are synthesised are produced + organelles replicate , cell increases in size

S- synthesis phase, DNA replicated

G2- 2nd growth the cell continues to increase in size, energy stores increased and the duplicated DNA is checked for errors

Question 5

The cell cycle

Answer 5

A series of events when a parent cell divides to form 2 daughter cells

Daughter cells can function as parent cells - EXACT copy of dna

Question 6

G1 phase

Answer 6

Cells grow and increase in size

Transcription for genes to make rna

Organelles duplicate

Making DNA replication enzyme

P53( tumour suppressor) gene helps to control this phase

Question 7

S phase

Answer 7

Replication of DNA

Chromosomes are unwound and DNA Is replicated

Specific sequence of the replication of genes - these rhat are active in all types of cells are duplicated first

Genes that are normally inactive in specific types of cell are replicated LAST

rapjd and because exposed DNA base pairs are more susceptible to mutagenic agents, reduces chance of spontaneous mutations

Question 8

G2

Answer 8

Special chemicals ensure the cells are ready for mitosis by stimulating proteins that will be infolved in making chromosomes condense and in formation for be spindle

Cells growth

Question 9

Miotic phase

Answer 9

MITOSIS

Question 10

Cytokinesis

Answer 10

Cytoplasm divides and 2 new cells produced

Question 11

G0

Answer 11

The cell leaves the cycle, temporarily or permenantly

Triggered during early g1 at the restriction point by a checkpoint chemical

Some cells e.g. epithelial in gut DONT have this phase

Question 12

Reasons for g0

Answer 12

Differentiation

The dna May be damaged - enters period of permenant cell arrest

Question 13

Control of cell cycle?

Answer 13

Viral to ensure he cell only divides when it has grown to the right size , the replicated dna is error free/ repaired and the Chromosomes are in correct positions during mitosis

This is to ensure fidelity of cell division

Checkpoints are the control mechanisms of the cycle

Monitor or verify whether the processes at each stage of the cell cycle has been accurately completed before cell is allowed to progress into next phase

Question 14

G1 checkpoint

Answer 14

Check for cell size, nutrients, growth factors and DNA damage

Ensures cell is ready to enter Sphase

If it satisfies requirements - triggered to begin DNA replication , If not it enters G 0

Question 15

G2 checkpoint

Answer 15

Check for all size , dna replication and damage

if checkpoint is passed, cell initates the molecular process that signal beginning of mitosis

Question 16

Spindle assembly checkpoint

Answer 16

(metaphase) at the point is mitosis where all the chromosomes should be attatched to spindles and have aligned
mitosis CANNOT proceed until this checkpoint is passed

Question 17

Importance of mitosis - GROWTH

Answer 17

All cells produced enable a zygote to become an adult
Must be genetically identical
All cells within a tissue must have the same structure and perform the same function

Question 18

Importance of mitosis- REPAIR

Answer 18

If cells become damaged o lost- repair cells used have to be exact copies otherwise the tissue wouldnt function

Question 19

Importance of mitosis- ASEXUAL REPRODUCTION

Answer 19

Parents that have survived- well suited to that environemnt,
Genetically identical offspring shoudl also succeed in the same environment
Moat common in plants( vegetitive propagation and natural cloning)

Question 20

Chromosome

Answer 20

Each DNA molecule is converted into 2 identical DNA molecules called chromatids in interphase
The chromatids are joined at the CENTROMERE - necessary to keep them together so they can be precisely maneuvered and segregated equally = 1 each inot the 2 new daughter cells

Question 21

prophase

Answer 21

Chromatin fibres coil and condense
nucleolus disappears
Protein microtubules form spindle-shaped structures linked to the poles of the cell. Spindles(fibres forming)are necessary to move chromosomes into correct positions before cell division.
2 centrioles migrate to opposite poles of the cell
spindle fibres attatch to specific areas of centromeres and move chromsomes to centre

Question 22

Metaphase

Answer 22

Chromsomes align in the middle f the cell
METAPHASE plate
Attatched to spindle by centromere
Metaphase checkpoint

Question 23

Anaphase

Answer 23

The centromeres holding together the pairs of chromatids in each chromsome divide

• Chromatids seperated and pulled to poles by shortening spindle fibres
• V shape of chromatids, moving towards pole = result in being dragged through liquid cytosol by centromeres

Question 24

Telophase

Answer 24

Chromatids reach opposite poles- now called CHROMOSOMES
2 new sets of chromosomes assemble around each pole and nuclear envelope reforms around them
chromosomes uncoil adn nucleolus formed

Question 25

Cytokenisis

Answer 25

Cytoplasm divides

There are now 2 genetically identical daughter cells

Question 26

Cytokinesis - ANIMALS

Answer 26

Cleavage furrow forms around the middle of the cell, the cell surface mebrane is pulled inwards by the cytoplasm until its close enough to fuse aorund the middle, forming 2 cells

Question 27

cytokinesis in PLANTS

Answer 27

Vesicles from the golgi begin to assmeble in the same place where the metaphase plate was formed
The vesicles fuse together and the cell surface membrane, dividing the cell in 2
New sections of cell wall then form along hte new sections of the membrane ( if the dividing cell wall were formed before the daughter cells separated , they would immediately undergo osmatic lysis from surrounding water)