The Celly Cycle

Question 1

What two main parts does the cell cycle consist of ?

Answer 1

•The M phase (mitotic phase) - when mitosis takes place and the cell then divides into two
•interphase

Question 2

What three stages can interphase be divided into?

Answer 2

• First stage in called the G1 phase
•Second stage is the S (synthesis) phase
•Third stage is the G2 phase

Question 3

What happens during the G1 phase?

Answer 3

•The cell replicates organelles such as mitochondria (demand a great deal of proteins) so a high level of transcription and translation take place
•Size of the cell also increases—> ensures that when the cells divide the two daughter cells are the correct size

Question 4

What happens in the S (synthesis) phase?

Answer 4

•All of the chromosomes are replicated, this requires a great deal pf DNA

Question 5

What happens in the G2 phase?

Answer 5

•cell replaces the energy stores used during S phase
•continues to carry out transcription and translation
•repaire any damaged chromosomes
•cell continues to grow in size

Question 6

What happens in the M (mitotic) phase ?

Answer 6

• the first part, during mitosis, the chromosomes are separated into two nuclei
•the second part is called cytokinesis, the cell divides into two

Question 7

What is G*o (gap 0) phase? And what 3 reasons can they enter G1 for?

Answer 7

A resting phase triggered during early G1 by a checkpoint chemical. Cells can enter G1…
•fully differentiated cells enter Go to stay there for the rest of their lives eg neurones in adults
• over time the DNA in cells can be damaged so no longer be able to divide (senescent cells) (enters Go permanently)
•some cells enter G*o temporarily eg B memory cells, they can be triggered to reenter the cell during an infection

Question 8

How is the cell cycle tightly regulated?

Answer 8

At certain key points of the cell cycle, the cell checks that the cell cycle should continue, called checkpoints

Question 9

What happens is a cell fails the checkpoint?

Answer 9

It will leave the cell cycle and enter G*o

Question 10

Where are the three checkpoints?

Answer 10

• before the S phase , the G1 checkpoint, here the cell checks that it has grown to the correct size, and also checks for dna damage
• checkpoint at the end of G2, same checks as g1
•metaphase checkpoint, checks that the chromosomes are assembled correctly on the mitotic spindle

Question 11

How many pairs of chromosomes in human cells?

Answer 11

23 pairs

Question 12

Diploid cells

Answer 12

When cells contain chromosomes with pairs of

Question 13

What is formed when each chromosome is copied during interphase?

Answer 13

Sister chromatids, joined at the centromere

Question 14

What are the four phases of mitosis?

Answer 14

Prophase
Metaphase
Anaphase
Telophase

Question 15

What happens during phrophase?

Answer 15

• chromosomes condense and become visible in the nucleus
• nucleolus disappears and nuclear membrane starts to break down
  *a pair of centrioles move to either side of the cell
  *proteins begin to form spindle fibres which attach to the centromere of each chromosome, these spindle fibres move the chromosomes towards the centre of the cell

Question 16

What happens at metaphase?

Answer 16

•The spindle apparatus has completely formed
•The chromosomes are lined up at the centre or equator of the cell

Question 17

What happens during anaphase?

Answer 17

The centromeres divide into two and the spindle fibres begin to shorten
-this pulls the sister chromatids towards opposite poles of the cell

Question 18

What happens during telophase?

Answer 18

•The chromatids have reached the poles of the cell so they r now chromosomes again
•The spindle apparatus breaks down and the nuclear membrane reform
•chromosomes uncoil back to their chromatin state and the nucleolus
reappears in each nucleus

Then cytokinesis occurs

Question 19

What happens during cytokinesis ?

Answer 19

The central membrane is pulled inwards by the cytoskeleton, this creates a groove which gradually deepens
• eventually the membranes fuse to form two independent cells

Question 20

What is the difference with cell division in plants?

Answer 20

•Centrioles do not play a role in forming the spindle apparatus
•when plant cells undergo cytokinesis, the cell membrane cannot form a groove as in animal cells, instead vesicles from the Golgi apparatus form membrane structures down the centre of the cell which then fuse together to form a central cell membrane, dividing the cytoplasm into two, a new cellulose cell wall also forms in the centre

Question 21

When is meiosis used?

Answer 21

To produces gametes eg sperm and eggs in mammals and pollen and eggs in plants

Question 22

What is the process of meiosis?

Answer 22

•DNA replicates to make copies of genetic information
•cell divides twice
• forming 4 cells called gametes:
- each whith a single set of chromosomes, half the number of the original cell
-All genetically different from each other (receive different combinations of chromosomes)

Question 23

Differences between meiosis and mitosis?

Answer 23

•Mitosis has one cell division where meiosis has two cell divisions
•mitosis produces 2 cells where meiosis produces 4 gametes
•mitosis produces genetically identical cells where meiosis produces genetically different cells
•mitosis happens in body cells ehere meiosis happens in reproductive organs

Question 24

What do u start and end up with for meiosis

Answer 24

Start with a diploid cell and end up with four haploid gametes ( these cells contain individual chromosomes not pairs)

Question 25

What do u start and end up with for mitosis?

Answer 25

Start with a diploid cell and end up with 2 identical diploid cells

Question 26

Why is it important that gametes are haploid cells?

Answer 26

During fertilisation gametes fuse together to produce a fertilised egg pr zygote