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Biology A-Level > The Mitotic Cell Cycle + Chromosomes (Chapter 5) > Flashcards

The Mitotic Cell Cycle + Chromosomes (Chapter 5) Flashcards

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1
Q

What is a chromosome?

A

A thread-like structure made up of DNA

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2
Q

What is the structure of the chromosome during interphase?

A

The chromosome is a double structure made of two identical structures called chromatids, joined together
- the two chromatids are held together by a narrow region called the centromere which can be found anywhere along the length of the chromosome

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3
Q

Why is a chromosome made up of two identical chromatids during interphase?

A

Because during this period, each DNA molecule in a nucleus makes an identical copy of itself
- each chromatid contains one of these DNA copies

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4
Q

How many DNA molecule does each chromosome contain?

A

ONEEEE

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5
Q

What is DNA?

A

The molecule of inheritance made up of a series of genes

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6
Q

What is a gene?

A

A section of a DNA molecule that codes for a particular polypeptide

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7
Q

What happens when cells divide?

A

One chromatid goes into one daughter cell and the other chromatid goes into the other daughter cell, making the daughter cells genetically identical (bc chromatids, therefore DNA, therefore genes are identical)

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8
Q

How is DNA stored?

A

It is wound around the outside of basic protein molecules called histones which prevent knots in DNA

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9
Q

Why is DNA wrapped around histones?

A

Because DNA is a very long molecule (total length in cell = 1.8m) and has to be packed into the nucleus (6μm diameter)

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10
Q

Why do histones interact easily with DNA?

A

Because they are basic and DNA is acidic

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11
Q

What is chromatin?

A

The mixture combination of DNA and histones, which is very highly condensed by coiling

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12
Q

What are chromosomes made of?

A

Chromatin

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13
Q

What is mitosis?

A

Nuclear division that produces two genetically identical daughter nuclei, each containing the same number of chromosomes as the parent nucleus

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14
Q

What is the cell cycle?

A

The regular sequence of events that takes place between one cell division and the next

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15
Q

What are the three phases of the cell cycle?

A

Interphase
Nuclear division
Cell division

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16
Q

What happens during interphase?

A

The cell grows to its normal size after cell division and carries out its normal functions, synthesising many substances (esp proteins) in the process

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17
Q

What are the phases of interphase?

A

G1, S and G2

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18
Q

What happens during the S (synthesis) phase of interphase?

A

1) At some point during interphase, a signal may be received that the cell should divide again
2) If this happens, the DNA in the nucleus replicates so that each chromosome consists of two identical chromatids - relatively short phase

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19
Q

What happens during the G1 phase?

A

1) During G1, cells make the RNA, enzymes and other proteins needed for growth
2) At the end of G1, the cell becomes committed to dividing or not dividing (restriction point)

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20
Q

What happens during the G2 phase?

A

1) The cell continues to grow and new DNA is checked and any errors are usually repaired
2) Preparations are made to begin the process of division e.g. there is a sharp increase in production of the protein tubulin which is needed to make microtubules for the mitotic spindle and centrioles are doubled

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21
Q

What phase follows interphase?

A

Nuclear division (M phase, M=mitosis)

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22
Q

What happens to growth during mitosis?

A

It stops temporarily

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23
Q

What happens after the M phase?

A

The whole cell divides to create two genetically identical cells

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24
Q

How does cell division occur in animal cells?

A

By cytokinesis

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25
Q

How does cell division occur in plant cells?

A

It involves the formation of a new cell wall between the two new nuclei

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26
Q

How long does the cell cycle last?

A

It is very variable, depending on environmental conditions and cell type (but normally hours)

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27
Q

Even though mitosis is continuous, what are the four main stages?

A

Prophase
Metaphase
Anaphase
Telophase

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28
Q

Although the behaviour of chromosomes is identical to animal cells, how is nuclear/cell division different?

A

1) Plant cells do not contain centrosomes (or centrioles)

2) A new cell wall must form between the daughter nuclei

29
Q

What happens during early prophase?

A

(Centrosomes replicate just before prophase)
1) Chromosomes start to appear as the chromatin condenses (coils up), becoming shorter and thicker
(The nucleolus and nuclear envelope are intact)

30
Q

What happens during late prophase?

A

1) The nuclear envelope and nucleolus disappear (disaggregate), making more space
2) Chromosomes are formed, made of twin chromatids
3) Centrosomes move to the opposite ends of the nucleus where they form the poles of the mitotic spindle, which is formed at the end of prophase

31
Q

What is the mitotic spindle made of?

A

Microtubules

32
Q

What happens during metaphase?

A

1) Chromosomes line up across the equator of the mitotic spindle - they are attached by their centromeres, each to a separate spindle fibre
2) Each centrosome reaches a pole - centrosomes help to organise the production of the spindle microtubules

33
Q

What happens during anaphase?

A

1) The centromere of each chromosome splits
2) Each chromatid is pulled away from its twin, centromeres first, towards opposite poles, by the mitotic spindle - each chromatid is now called a chromosome

34
Q

What happens during telophase?

A

1) Chromosomes (ex-chromatids) have reached the poles of the spindle - they will now uncoil again, reforming chromatin
2) Cytokinesis occurs
3) The nucleolus and nuclear envelope reform
4) The mitotic spindle breaks down and disappears
- Each chromosome contains one DNA molecule, which will replicate itself during interphase before the next division

35
Q

What is cytokinesis?

A

The division of the cytoplasm and cell into two by constriction from the edges of the cell between the two nuclei

36
Q

How is the centromere visible?

A

As a constriction

37
Q

What is the role of the centromere?

A

It is needed for the separation of chromatids during mitosis and is the site of attachment of the spindle (more specifically, the spindle binds to kinetochores on the centromeres)

38
Q

What do centrosomes consist of?

A

A pair of centrioles surrounded by a large number of proteins - these proteins control production of microtubules, not the centrioles

39
Q

Where are the centrosomes located?

A

At the poles of the spindle, one at each pole

40
Q

What are the roles of mitosis that are biologically significant?

A

1) Growth
2) Replacement of cells and repair of tissues
3) Asexual reproduction
4) Immune response

41
Q

Explain the biological significance of mitosis in growth

A
  • The two daughter cells formed have the same number of chromosomes as the parent cell and are genetically identical (clones)
  • This allows growth of multicellular organisms from unicellular zygotes
  • Growth may occur over the entire body or confined to certain regions e.g. meristems in plants
42
Q

Explain the biological significance of mitosis in the replacement of cells and repair of tissues

A

This is possible using mitosis followed by cell division

  • Cells are constantly dying and being replaced by identical cells e.g. in the skin and gut
  • Some animals are able to regenerate whole parts of the body e.g. starfish can regenerate new arms
43
Q

Explain the biological significance of mitosis in asexual reproduction in unicellular and multicellular organisms

A

Mitosis is the basis of asexual reproduction

  • Offspring are genetically identical to the parent
  • Unicellular organism: cell division inevitably results in reproduction
  • Multicellular organism: new individuals may be produced which bud off from the parent in various ways e.g. in plants a bud on a part of the stem can grow a new plant (vegetative propagation) which will eventually become detached and independent e.g. tuber or bulb
  • Important in biotechnology
44
Q

Explain the biological significance of mitosis in the immune response

A

The cloning of B and T lymphocytes during the immune response is dependent on mitosis

45
Q

What are the ends of chromosomes ‘sealed’ by?

A

Telomeres

46
Q

What are telomeres?

A

Structures made of DNA with short base sequences that are repeated many times (multiple repeat sequences)

47
Q

Why are telomeres needed?

A
  • The copying enzyme cannot run to the end of the DNA and complete the replication - it stops a little short of the end
  • If part of the DNA is not copied, that piece of information is lost
  • At each subsequent division, another small section of information would be lost - eventually the lost of vital genes would lead to cell death
48
Q

How do telomeres work?

A
  • They make DNA longer by adding some more bases (telomeres)
  • They have no useful information, but allow the copying enzyme to complete copying the meaningful DNA
  • As long as extra bases are added during each cell cycle, no vital information will be lost and the cell will be able to continue dividing successfully
  • This ensures that when DNA is replicated, the ends of the molecule are included in the replication and not left out
49
Q

What is the enzyme that adds on the telomeres?

A

Telomerase

50
Q

What is the function of telomeres?

A

To prevent the loss of genes during cell division and to allow continued replication of a cell
- they protect chromosomes from damage and degradation during DNA replication

51
Q

What happens to cells that do not top of telomeres at each division?

A

The telomeres get shorter until vital DNA is no longer protected and the cell dies
- could be one of the mechanisms of ageing

52
Q

What is a stem cell?

A

A cell that can divide an unlimited number of times (by mitosis)

53
Q

What happens when a stem cell divides?

A

Each new cell has the potential to remain a stem cell or to develop (differentiate) into a specialised cell

54
Q

What is the stem cell’s potency?

A

The extent of the power of a stem cell to produce different cell types

55
Q

What are cells that can differentiate into any type of cell called?

A

Totipotent e.g. zygotes

56
Q

Why is essential that small populations of stem cells remain which can produce new cells remain in an adult?

A

1) For growth and repair

2) Because mature blood cells have a relatively short life span

57
Q

What are multipotent stem cells?

A

Stem cells that can replicate any number of times, but can only produce one type of cell e.g. blood cells from stem cells in the bone marrow

58
Q

What is stem cell therapy?

A

The introduction of new adult stem cells into damaged tissue to treat disease/injury

59
Q

What is stem cell therapy used for?

A

1) Bone marrow transplantation for blood cancers
2) Could be used to treat conditions like diabetes and brain disorders as stem cells are found in many places in the body

60
Q

How do cancer cells form a tumour?

A

Cancerous cells divide repeatedly and uncontrollably

61
Q

What is a tumour?

A

An irregular mass of cells

62
Q

What is an oncogene?

A

A mutated cancer-causing gene (a gene that controls cell division)

63
Q

What is any agent that causes cancer called?

A

A carcinogen and is carcinogenic

64
Q

What can uncontrolled cell division result in?

A

The formation of a tumour

65
Q

What is the difference between normal mutated cells and cancerous cells?

A
  • Most mutated cells are either affected in some way that results in their early death or destroyed by the immune system
  • Cancerous cells mange to escape both of these, so the mutation is passed on when the cell divides
66
Q

How many chromosomes does a human have?

A

46 (2n=46)

67
Q

What is the function of the spindle during mitosis?

A

To arrange the chromosomes and determine where they move during mitosis

68
Q

What is the function of the centromere during mitosis?

A

It attaches to the spindle and keeps the twin chromatids together

Biology A-Level (44 decks)

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