THE CELL CYCLE

Question 1

Why do cells need to divide?

Answer 1

Single celled organisms- mutliplu
Mutlicellualr organisms- growth and repair
To produce gametes
Cells have a limited size- if too big then SA:V ratio is inefficient

Question 2

What is interphase

Answer 2

Cells do not divide continuously
Long periods of growth and nromal working seperate divisions
ACtive phase of the cell

Question 3

What things happen in interphase?

Answer 3

Dna is replicated and checked for errors
Protein synthesis occurs in cytoplasm
Mitachondria grow and divide, increasing in number in the cytoplasm
Chloroplasts grow and divide in plant and agal cell cytoplasm
Norma, metabolic processes occur

Question 4

What are the 3 phases of interphase

Answer 4

G1- First growth stage
S- Synthesis
G2- 2nd grwoth phase

Question 5

What is g1

Answer 5

Cells grow and increase in size
Organelles duplicated
Making DNA replication enzyme
Transcription for genes to make RNA

Question 6

What is S

Answer 6

Synthesis
Replication of DNA
Specific sequence of the replication of genes; these that are active in all types of cells are duplicated first
Genes shat are normally inactive in specific types of cell are replicated last
Rapid, exposed DNA base pairs are more susceptible to mutagenic agents- reduces chance of spontaneous mutations

Question 7

g2

Answer 7

Cell grows more in size
Energy stores increased
DNA checked for errors
Special chemicals ensure the cells are read for mitosis by stimulating proteins that will be involved in makign chromosome condense and in formation for the spindle

Question 8

g0

Answer 8

Cell leaves the cycle, temporarily or permanently
Triggered during early g1, at the restriction point by a checkpoint chemical
Some cells e..g epithelial in gut don’t have this phase

Question 9

REASONS for G0

Answer 9

Differentiation - A cell that becomes specialized wont enter the cell cycle again

DNA may be damaged- Enters period of permanent cell arrest

Question 10

Control of cell cycle?

Answer 10

Vital to ensure the 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

Ensures fidelity of the cell division

Checkpoints are the control mechanism of the cycle- monitor and verify whether the processes at each stage of the ell cycle has been accurately completed before the cell is allowed to progress into next phase

Question 11

G1 checkpoint

Answer 11

• Check for cell size, nutrients , growth factors and DNA damage
• Ensures cell is ready to enter S phase
• If satisfies requirements- triggered to begin DNA replication, and if not- enters g0

Question 12

What is the gene that helps to control G1

Answer 12

p53- tumor suppressor

Question 13

g2 checkpoint

Answer 13

Check for cell size, DNA replication and damage

If checkpoint is passed - cell initiates the molecular process that signal beginning of mitosis

Question 14

Spindle assembly checkpoint

Answer 14

Metaphase

Chromosomes should be attached to spindles and aligned

Question 15

Importance of mitosis - growth

Answer 15

All cells produced enable a zygote to become an adult

Must be genetically identical

All cells wihtin a tissue must have the same structure and perform the same function

Question 16

Importance of mitosis - repair

Answer 16

-If cells become damaged or lost, repair cells used have to be exact copies otherwise the tissue wouldn’t function

Question 17

Importance of mitosis - Asexual reproduction

Answer 17

• Parents that have survived - well suited to that environment
  Genetically identical offspring should also succeed in the same environment
• Most common in plants

Question 18

Structure of a chromsome

Answer 18

DNA molecule
2 molecules called chromatids
chromatids joined in centromere
Necessary to keep chromatids together in mitosis so they can be precisely maneuvered and segregated eqaully - 1 each into the 2 new daughter cells

Question 19

PROPHASE

Answer 19

Chromatin fibres coil and condense
Nucelolus dissapears
Nucelar membrane breaks down
Protein microtubules form spindle shaped structures linked to the poles of the cell
Spindles( fibre forming) are necessary to move chromosomes into correct positiions before cell division
2 centrioles migrate to opposite poles of cell
Spindle fibres attach to specific areas of centromeres and move chromosomes to center of cell

Question 20

METAPHASE

Answer 20

Chromsomes align in the middle of the cell
Metaphase plate
Attached to the spindle by centromere
Metaphase checkpoint

Question 21

Anaphase

Answer 21

The centromeres holding rogerher he pairs of chromatids in each chromosome divide
Chromatids separates and pulled to hte poles by shortening spindel fibres
V shape of chromatids moving towards pole = result of being dragged through liquid cytosol by centromers

Question 22

Telophase

Answer 22

Chromatids reach opposite poles - now called chromosomes
2 new sets of chromosomes assemble around each pole and nuclear envelope reforms around them
Chromosomes uncoil and nucleoulus forms

Question 23

Cytokinesis

Answer 23

Cytoplasm divides

Now 2 genetically identical daughter cells

Question 24

Cytokinesis - animals

Answer 24

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

Question 25

Cyokinesis - plants

Answer 25

• Vesicles from the golgi begin to assemble in the same place where the meta phase plate was formed

The vesicles fuse together and with teh cell surface membrane,, dividing the cell in 2

New sections of cell wall then form along the new sections of membrane( if dividing cell wall were formed before the daughter cells separated they would immediately undergo osmotic lysis from surrounding water)