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Biology > Cell Division > Flashcards

Cell Division Flashcards

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1
Q

What are the two main checkpoints within the cell cycle?

A

The G1/S checkpoint (the restriction point)

The G2/M checkpoint

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2
Q

What is the purpose of the checkpoints?

A

To prevent uncontrolled division that would lead to tumours

To detect and repair damage to DNA

To ensure that the cycle happens in the correct sequence and cannot be reversed

To ensure the DNA is only duplicated once each cell cycle

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3
Q

Name the phases of the cell cycle

A

M phase

Gap 0 (G0) phase

Gap 1 (G1) phase

Synthesis (S) phase

Gap 2 (G2) phase

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4
Q

What happens during the M phase?

A

Cell growth stops

Nuclear division (mitosis) - prophase, metaphase, anaphase and telophase

Cytokinesis

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5
Q

What happens during the G0 phase?

A

Cells may undergo apoptosis, differentiation or senescence

Cells may remain in this phase indefinitely or for a very long time

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6
Q

What happens during the G1 phase?

A

Cells grow and increase in size

Transcription of genes to make RNA occurs

Organelles duplicate

Biosynthesis e.g. protein synthesis

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7
Q

What happens during the S phase of interphase?

A

DNA replicates and when all chromosomes have been duplicated, each one consists of a pair of identical sister chromatids

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8
Q

Why is the S phase of interphase quick?

A

The exposed DNA base pairs are more susceptible to mutagenic agents so the speed reduces the chances of spontaneous mutations

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9
Q

What happens during the G2 phase of interphase?

A

Cells grow

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10
Q

What are chromatids?

A

Replicates of chromosomes

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11
Q

What is mitosis?

A

A type of nuclear division that maintains the chromosome number; each new daughter cell contains the same genetic information as the parent cell (they are genetically identical)

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12
Q

Why do all living organisms need to undergo mitosis?

A

Asexual reproduction

Growth

Tissue repair

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13
Q

What are the main stages of mitosis?

A

Prophase

Metaphase

Anaphase

Telophase

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14
Q

What are the events that occur during prophase?

A

Chromosomes that have replicated during the S phase of interphase, now shorten and thicken

Nuclear envelope breaks down

The centriole divides and two new daughter centrioles move to oppose poles of the cell

Tubulin threads form a spindle between the two centrioles

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15
Q

What are the events that occur during metaphase?

A

The pairs of chromatids attach to the spindle threads at the equator region

They attach by their centromeres

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16
Q

What are the events that occur during anaphase?

A

The centromere of each pair of chromatids splits

Motor proteins pull each sister chromatid of a pair, in opposite directions, towards opposite poles

Because their centromere goes first, the chromatids, now called chromosomes, assume a V shape

17
Q

What are the events that occur 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 the parent cell from which they arose

18
Q

What process happens once mitosis is complete?

A

Cytokinesis - division of cell cytoplasm so two cells are produced

19
Q

How does cytokinesis differ in plant and animal cells?

A

In animal cells, the plasma membrane folds inwards and ‘nips in’ the cytoplasm

In plant cells, an end plate forms where the equator of the spindle was, and new plasma membrane and cellulose cell wall material are laid down on either side along this plate

20
Q

What is meiosis?

A

A type of nuclear division that results in the formation of cells containing half the number of chromosomes of the parent cell (haploid gametes)

Diploid (two complete sets of chromosomes) to haploid (one set of chromosomes)

21
Q

What is the significance of meiosis in life cycles?

A

It increases genetic variation as it involves the combining of genetic material from two unrelated individuals from the same species by fertilisation. This variation within a population increases its chance of survival when the environment changes.

22
Q

What are homologous chromosomes?

A

Matching pairs of chromosomes, one maternal and one paternal, that contain the same genes at the same gene loci

May contain different alleles

23
Q

How many divisions take place during meiosis?

A

Two

24
Q

What are the stages that occur during meiosis?

A

In the first meiotic division, the four stages are prophase 1, metaphase 1, anaphase 1 and telophase 1

In the second meiotic division, the four stages are prophase 2, metaphase 2, anaphase 2 and telophase 2

Cytokinesis occurs at the end of the second division

25
Q

What events occur during prophase 1?

A

The chromatin condenses and each chromosome supercoils

The nuclear envelope breaks down and spindle threads of tubulin protein form from the centriole in animal cells

The chromosomes come together in their homologous pairs - each member of the pair consists of two chromatids

Crossing over occurs where non-sister chromatids wrap around each other and may swap sections so alleles are shuffled

26
Q

What events occur during metaphase 1?

A

The pairs of homologous chromosomes, still in their crossed over state, attach along the equator of the spindle by their centromeres

The homologous pairs are arranged randomly, with the members of each pair facing opposite poles (independent assortment)

The way they line up in metaphase determines how they will segregate independently when pulled apart in anaphase

27
Q

What events occur during anaphase 1?

A

The members of each pair of homologous chromosomes are pulled apart by motor proteins that drag them along the tubulin threads of the spindle

The centromeres do not divide, and each chromosome consists of two chromatids

The crossed-over areas separate from each other, resulting in swapped areas of chromosome and allele shuffling

28
Q

What events occur during telophase 1?

A

In most animal cells, two new nuclear envelopes from around each set of chromosomes, and the cell divides by cytokinesis

Each new nucleus contains half the original number of chromosomes, but each chromosome consist of two chromatids

In plant cells, the cell goes straight from anaphase 1 into prophase 2

29
Q

What events occur during prophase 2?

A

If the nuclear envelopes have reformed, then they now break down

The chromosomes coil and condense, each one consisting of two chromatids

The chromatids of each chromosome are no longer identical, due to crossing over in prophase 1

Spindles form

30
Q

What events occur during metaphase 2?

A

The chromosomes attach by their centromere to the equator or the spindle

The chromatids of each chromosome are randomly arranged

The way that they are arranged will determine how the chromatids separate during anaphase

31
Q

What events occur during anaphase 2?

A

The centromeres divide

The chromatids of each chromosome are pulled apart by motor proteins that drag them along the tubulin threads of the spindle, towards opposite poles

The chromatids are therefore randomly segregated

32
Q

What events occur during 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 tetras of four haploid cells in formed

33
Q

How does meiosis produce genetic variation?

A

Crossing over during prophase 1 shuffles alleles

Independent assortment of chromosomes in anaphase 1 leads to random distribution of maternal and paternal chromosomes of each pair

Independent assortment of chromatids in anaphase 2 leads to further random distribution of genetic material

Haploid gametes are produced, which can undergo random fusion with gametes derived from another organism of the same species

Biology (7 decks)

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