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Biology > Cell Cycle > Flashcards

Cell Cycle Flashcards

1
Q
  1. When a cell is not dividing, what form is the DNA in?
A

In a non-dividing cell, the DNA is uncoiled and thread-like and in the form of CHROMATIN

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2
Q
  1. When a cell is about to divide, what happens to the DNA?
A

The chromatin CONDENSES to form shorter, coiled DNA in rod-like structures called CHROMOSOMES

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3
Q
  1. In the nucleus of human cells, what do we mean by the DIPLOID number?
A

The diploid number refers to the fact that chromosomes are arranged as HOMOLOGOUS PAIRS; specifically 23 pairs in us, written as 2n = 46

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4
Q
  1. What do we mean by the HAPLOID number?
A

The haploid number refers to the fact that only one chromosome from each homologous pair is present; in us this is true of the sex cells, and it is written as n = 23

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5
Q
  1. What do we mean by the “karyotype” of an organism?
A

This is the number, appearance and arrangement of the homologous chromosome pairs

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6
Q
  1. What are “histones” and “nucleosomes”
A

Histones are the proteins that support the DNA and nucleosomes are made from stacks of histones around which the DNA is coiled.

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7
Q
  1. What is a HOMOLOGOUS PAIR of chromosomes?
A

In a homologous pair, each chromosome carries genes along their length, at the same loci.

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8
Q
  1. What is the “cell cycle”?
A

The cell cycle represents the entire life of a diploid cell and includes G1, S and G2 (Interphase), mitosis and cytokinesis.

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9
Q
  1. What does interphase consist of?
A

Interphase consists of growth phase one (G1), synthesis phase (S) and growth phase 2 (G2)

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9
Q
  1. What are the key events during G1?
A

G1 is the first growth phase: * Synthesis of new macromolecules including proteins and nucleotides. * Organelles are produced * Cell increases in size

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10
Q
  1. What happens in S phase?
A
  • DNA synthesis (by semi-conservative replication) occurs, resulting in each chromosome now consisting of 2 sister CHROMATIDS Histones are produced
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11
Q
  1. What are the key events in G2?
A
  • Synthesis of spindle proteins (tubulin) * Chromosomes are checked for errors and repaired * Energy stores are increased Cell continues to increase in size
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12
Q
  1. There are several CHECKPOINTS in the cell cycle. Why are they needed?
A

Checkpoints regulate the cycle by checking and monitoring each stage to ensure that no errors have occurred before the process continues

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12
Q
  1. Overall, what happens during mitosis?
A

Mitosis is the process of NUCLEAR DIVISION, during which the chromosomes are copied and then divided between two identical daughter cells

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13
Q
  1. What are the four stages of mitosis?
A

Prophase, Metaphase, Anaphase & Telophase

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14
Q
  1. What is cytokinesis?
A

The division of the cell into 2 separate daughter cells at the end of mitosis.

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15
Q
  1. Where are the main checkpoints in the cell cycle?
A
  1. At the end of G1, before the s phase begins (check made on nutrient levels, check for DNA damage, check on growth factors) 2. At the end of G2, before mitosis (check on cell size and that DNA replication has occurred correctly) 3. During the metaphase stage of mitosis (check that spindle fibres are attached properly to chromosomes)
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16
Q
  1. What is Go?
A

If a cell fails at the G1 checkpoint, it enters Go or the “resting state” until it is ready to enter S phase (where DNA is replicated by semi-conservative replication)

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17
Q
  1. What occurs in Go?
A
  • Some cells are very active carrying out normal cellular activities * Some cells remain permanently in G0 * Some cells will return back into the cell cycle when triggered
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18
Q
  1. What does the G2 checkpoint ensure before a cell can start mitosis?
A
  • That DNA replication is accurate * That there is no DNA damage
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19
Q
  1. What causes cancer?
A

Cancer is uncontrolled cell division (mitosis) due to the failure of the regulation mechanism at the checkpoints. The cells fail to enter Go when they should.

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20
Q
  1. What is chemotherapy?
A

Chemotherapy is using drugs to treat cancer, normally by disrupting the cell cycle and mitosis

20
Q
  1. In chemotherapy, how do mitotic poisons work?
A

Mitotic poisons e.g. vincristine, inhibit formation of spindle fibre microtubules, and therefore prevent anaphase from occurring

21
Q
  1. In chemotherapy, how do antimetabolites work?
A

Antimetabolites e.g. fluorouracil, inhibit S-Phase and therefore DNA replication/synthesis

22
Q
  1. What are the four stages of mitosis?
A

Prophase, Metaphase, Anaphase, Telophase

23
Q
  1. What is mitosis?
A

Mitosis is the process of nuclear division which occurs before a cell divides

24
Q
  1. What happens in prophase?
A
  • Chromatin condenses to form visible chromosomes (two chromatids joined via a centromere) * Centrioles move to opposite poles (animal cells only) * Spindle formation occurs * Nucleolus disappears * Nuclear membrane breaks down
24
Q
  1. What processes occur via mitosis?
A

Growth, tissue repair and asexual reproduction

25
Q
  1. What happens in metaphase?
A
  • Chromosomes align at equator * Spindle fibres attach to centromeres
26
Q
  1. What happens in anaphase?
A
  • Centromere splits * Chromatids are pulled apart by the contraction of spindle fibres and move towards the poles
27
Q
  1. What happens in telophase?
A
  • Sister chromatids arrive at opposite poles (and are once again referred to as being chromosomes) * Chromosomes decondense to form chromatin again The spindle breaks down and disappears The nucleolus reappears * Nuclear membrane reforms
28
Q
  1. Which process occurs immediately after mitosis?
A

Cytokinesis, the physical division of the cell form to two identical daughter cells

29
Q
  1. What is meiosis?
A

The type of cell division that produces haploid (n) and genetically different cells called gametes. It is reduction division.

29
Q
  1. How does cytokinesis occur in animal cells?
A

The cell surface membrane invaginates and a cleavage furrow forms which eventually splits the cell into two

30
Q
  1. How does cytokinesis occur in plant cells?
A

A cell plate is laid down in centre of cell and develops into a new cell wall

31
Q
  1. Where does meiosis occur?
A

In the sex organs - i.e. * testes and ovaries in mammals * pollen grains and ovules in plants - logous

32
Q
  1. What occurs in the two rounds of cell division by meiosis?
A
  • Meiosis 1 separates the homologous chromosomes * Meiosis 2 separates sister chromatids
33
Q
  1. When is the ploidy reduced from diploid to haploid?
A

During meiosis 1 - hence it known as the reduction division

34
Q
  1. What are bivalents and when are they formed?
A

Bivalents are the PAIRS OF HOMOLOGOUS CHROMOSOMES that form (during interphase, just before prophase 1 starts)

35
Q
  1. What are the key events in prophase 1?
A
  • Chromosomes condense, become visible and homologous chromosomes pair up to form bivalents * Each chromosome consists of 2 chromatids, which can break and exchange sections of DNA with another non-sister chromatid in “crossing over”. The points where they cross over are called chiasmata. * The nucleus and nucleolus break down and disappear
36
Q
  1. What are the key events in metaphase 1?
A
  • Pairs of homologous chromosomes (bivalents) align along the equator of the cell (independently assorted) * Spindle fibres attach to the centromere of each chromosome.
37
Q
  1. What are the key events in anaphase 1?
A

Spindle fibres contract to pull homologous chromosomes apart to opposite poles of the cell

38
Q
  1. What are the key events in telophase 1?
A
  • The chromosomes (consisting of 2 chromatids) reach the opposite poles. * Nuclear membrane reforms
39
Q
  1. At the end of telophase 1 of meiosis 1, cytokinesis occurs. Describe the cells formed.
A
  • 2 haploid daughter cells are formed * their chromosomes consist of two chromatids joined by a centromere
40
Q
  1. What are the key events in prophase 2?
A
  • The same events as prophase 1 occur i.e. chromosomes condense (each chromosome consists 2 chromatids but homologous pairs do not form), centrioles duplicate and move to poles, nuclear membrane starts to break down * The spindle fibres begin to form at right angles to the old spindle.
41
Q
  1. What happens during metaphase 2?
A
  • The spindle has now formed at right angles to the old one * Chromosomes (consisting of their two chromatids) align at equator and attach to the spindle via their centromeres
42
Q
  1. What happens during of Anaphase 2
A
  • The centromeres break and the chromatids are pulled apart to opposite poles when the spindle fibres contract
43
Q
  1. What are the key events of telophase 2?
A
  • The chromosomes (note they are now referred to as being CHROMOSOMES arrive at the poles * They decondense and the nuclear membrane reforms * Cytokinesis 2 occurs
44
Q
  1. What will the end result be after cytokinesis in meiosis 2?
A

Four, haploid, genetically different daughter cells

45
Q
  1. When does genetic variation arise in meiosis?
A

During meiosis 1: * Crossing over occurs in prophase 1 * Independent assortment of alleles occurs in metaphase 1

46
Q
  1. What is crossing over?
A
  • The non-sister chromatids of the bivalents entwine and swap section at points called chiasmata. * This results in a different combination of alleles in each chromosome. The two chromatids of each chromosome are no longer identical
47
Q
  1. What is a chiasma?
A

A point where chromatids of a bivalent entwine and exchange sections of genes.

48
Q
  1. What is independent assortment?
A
  • The homologous pairs of chromosomes line up at the equator randomly at the start of metaphase 1 * Which chromosome of each pair is closer to the poles is totally independent from how the other chromosome pairs line up * So, any one gamete can obtain either of the homologous chromosomes from any particular pair resulting in a huge number of combinations
49
Q
  1. What else adds to the genetic variation of offspring resulting from sexual reproduction?
A

Random fusion and fertilisation of the gametes

Biology (11 decks)

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