The Celly Cycle Flashcards

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1
Q

What two main parts does the cell cycle consist of ?

A

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

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2
Q

What three stages can interphase be divided into?

A

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

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3
Q

What happens during the G1 phase?

A

•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

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4
Q

What happens in the S (synthesis) phase?

A

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

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5
Q

What happens in the G2 phase?

A

•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

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6
Q

What happens in the M (mitotic) phase ?

A

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

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7
Q

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

A

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 G
o permanently)
•some cells enter G*o temporarily eg B memory cells, they can be triggered to reenter the cell during an infection

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8
Q

How is the cell cycle tightly regulated?

A

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

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9
Q

What happens is a cell fails the checkpoint?

A

It will leave the cell cycle and enter G*o

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10
Q

Where are the three checkpoints?

A

• 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

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11
Q

How many pairs of chromosomes in human cells?

A

23 pairs

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12
Q

Diploid cells

A

When cells contain chromosomes with pairs of

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13
Q

What is formed when each chromosome is copied during interphase?

A

Sister chromatids, joined at the centromere

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14
Q

What are the four phases of mitosis?

A

Prophase
Metaphase
Anaphase
Telophase

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15
Q

What happens during phrophase?

A
  • 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
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16
Q

What happens at metaphase?

A

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

17
Q

What happens during anaphase?

A

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

18
Q

What happens during telophase?

A

•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

19
Q

What happens during cytokinesis ?

A

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

20
Q

What is the difference with cell division in plants?

A

•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

21
Q

When is meiosis used?

A

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

22
Q

What is the process of meiosis?

A

•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)

23
Q

Differences between meiosis and mitosis?

A

•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

24
Q

What do u start and end up with for meiosis

A

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

25
Q

What do u start and end up with for mitosis?

A

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

26
Q

Why is it important that gametes are haploid cells?

A

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