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Biology > 7. Cell Division > Flashcards

7. Cell Division Flashcards

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1
Q

What is mitosis?

A

A type of nuclear division that produces daughter cells genetically identical to each other and to the parent cell.

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2
Q

What is cytokinesis?

A

Cytoplasmic division following nuclear division, resulting in two new daughter cells

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3
Q

What is interphase?

A

Phase of the cell cycle when the cell is not dividing.

It is subdivided into cell growth and DNA synthesis phases.

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4
Q

What is the purpose of checkpoints?

A

There are two main checkpoints the G1/S checkpoint and the G2/M checkpoint
They prevent uncontrolled division that would lead to tumours (cancer), they ensure the cell cycle cannot be reversed, they allow the detection and repair of damage to DNA and ensure that DNA is only duplicated once each cell cycle.

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5
Q

What are the 5 phases of the cell cycle (in order)?

A

M phase, G0 phase, G1 phase (also called the growth phase), S (synthesis) phase of interphase, G2 phase of interphase

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6
Q

What happens in the M phase?

A

A checkpoint chemical triggers condensation of chromatin, cell growth stops, nuclear division (mitosis) happens and cytokinesis happens

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7
Q

What happens in the G0 phase?

A 
Some cells (e.g. epithelial cells) do not have this phase.
Cells may undergo differentiation and some cells remain in this phase for a long time or indefinitely.
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8
Q

What happens in the G1 phase?

A 
Ensures that the cell is ready to enter the S phase and begin DNA synthesis.
All cell contents except the chromosomes are duplicated.
P 53 (tumour suppressor) gene controls this phase
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9
Q

What happens in the S phase of interphase?

A

DNA replicates, each chromosome now consists of a pair of identical sister chromatids, this phase is rapid as DNA base pares are more susceptible to mutations.

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10
Q

What happens in the G2 phase of interphase?

A

The cell grows and stimulates proteins involved in making chromatin condense.

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11
Q

Why do all living organisms need to divide by mitosis?

A

For asexual reproduction, growth and tissue repair.

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12
Q

What is asexual reproduction?

A

when organisms divide by mitosis to produce new individuals

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13
Q

What are the four main stages of mitosis?

A

Prophase, metaphase, anaphase and telophase

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14
Q

What happens during prophase?

A

The chromosomes shorten and thicken as DNA super coils (they become visible).
Nuclear envelope breaks down
The centriole found in the centrosome divides and the two daughter centrioles move to opposite poles of the cell.
Tubulin threads form a spindle between the centrioles.

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15
Q

What happens during metaphase?

A

Pairs of chromatids attach to the spindle treads at the equator region by their centromeres.

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16
Q

What happens during anaphase?

A

The centromere of each chromosome splits
Motor proteins pull each sister chromatid in opposite directions towards the opposite poles
The chromatids are now called chromosomes.

17
Q

What happens during telophase?

A

The separated chromosomes reach the poles
A new nuclear envelope forms around each set of chromosomes
The cell now contains two nuclei each genetically identical to each other and to their parent cell

18
Q

What happens during cytokinesis?

A

The cells’ cytoplasm splits into two.

Each new cell contains a nucleus.

19
Q

Why is genetic variation important?

A

Genetic variation within a population increases its chances of survival when the environment changes, as some individuals will have characteristics that enable them to be better adapted to the change.

20
Q

How many chromosomes do haploid and diploid cells in humans have?

A 
Haploid= 23
Diploid= 46
21
Q

What are homologous chromosomes?

A

Matching chromosomes, containing the same genes in the same places.
One is paternal and one is maternal.

22
Q

What happens before meiosis?

A

Each chromosome is duplicated and its DNA replicated.
Each chromosome consists of two sister chromatids.
The chromosomes pair up in their homologous pairs.

23
Q

What are the stages of meiosis?

A

In the first division, there are 4 stages…
Prophase 1, metaphase 1, anaphase 1, and telophase 1
The cell may enter a short interphase.
The second meiotic division also has four stages…
Prophase 2, metaphase 2, anaphase 2, and telophase 2
This takes place at a right angle to that of the first division.
Then cytokinesis may occur.

24
Q

What happens during prophase 1?

A

Chromosomes condense as DNA super coils.
Crossing over occurs.
The nuclear envelope breaks down.
Spindle threads of tubulin protein form between the centrioles.

25
Q

What happens during metaphase 1?

A

Pairs of homologous chromosomes, still crossed over, attach along the equator of the spindle by their centromeres
Homologous pairs are arranged randomly, this arrangement determines how they will segregate once pulled apart

26
Q

What happens during Anaphase 1?

A

The homologous chromosome pairs are pulled apart by their centromere.
The crossed over areas separate from each other.
Each chromosome consists of two chromatids.

27
Q

What happens during telophase 1?

A

Nuclear envelopes may form around the new chromosomes sets
The cell divides by cytokinesis and there’s a short interphase when chromosomes uncoil.
Plant cells go straight to prophase 2

28
Q

What happens during prophase 2?

A

If nuclear envelopes have re-formed, they now break down
The chromosomes coil and condense each one consisting of two chromatids
The chromatids of each chromosome and no longer identical, due to crossing over in prophase 1
Spindles form

29
Q

What happens during metaphase 2?

A

The chromosomes attach by their centromere to the equator of the spindle
Again, the chromatids of each chromosome are randomly arranged.

30
Q

What happens during anaphase 2?

A

The centromeres divide
The chromatids of each chromosome and are pulled apart by motor proteins towards opposite poles
The chromatids are randomly segregated

31
Q

What happens in telophase 2?

A

Nuclear envelopes form around each of the four haploid nuclei
In animals the two cells now divide to give four haploid cells.
In plants a tetrad of four haploid cells is formed

32
Q

Give 4 ways that meiosis produces genetic variation?

A

Crossing over during prophase 1 shuffles alleles.
Independent assortment of chromosomes in metaphase 1 and 2 leads to a random distribution of chromosomes.
The haploid gametes produced can undergo fertilisation with gametes derived from another organism.

33
Q

What is differentiation?

A

The process by which stem cells become specialised into different types of cells.

34
Q

Which types of organisms require specialised cells?

A

Single-cell organisms are small and have a large SA:V ratio. Oxygen can diffuse across the plasma membrane and throughout the cell.
However, multicellular organisms have smaller SA:V ratios, most of their cells are not in contact with the external environment.
They need specialised cells to carry out specific functions.

35
Q

How are specialised cells made in animals?

A

A zygote is produced after fertilisation.
After several mitotic divisions, many embryonic stem cells are formed.
These have the ability to differentiate to produce any type of cell (pluripotent).
Each cell is specialised for a particular function.

36
Q

How large is the average cell?

A

10–20 μm

37
Q

What is crossing over?

A

Where two non-sister chromatids wrap around each other, forming a bivalent, and swap sections so that alleles are shuffled.
Where the chromosomes touch is called the chiasma.

38
Q

How do you calculate the number of possible combinations of genes in the gametes after meiosis?

A

Calculate 2 to the power of n

Where n is the haploid number of the cell.

39
Q

How do you calculate the number of mitotic divisions needed to produce a certain number of cells?

A

Use the formula
2 to the power of n= number of cells made
Where n is the number of mitotic divisions.

Biology (13 decks)

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