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Biology > D2.1 (Cell and nuclear division) > Flashcards

D2.1 (Cell and nuclear division) Flashcards

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1
Q

What does the cell theory state about the formation of new cells?

A

The cell theory states that new cells are produced from pre-existing cells.

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2
Q

What is cytokinesis?

A

Cytokinesis is the division of the cytoplasm following nuclear division, resulting in two daughter cells.q

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3
Q

What is nuclear division?

A

Nuclear division is the process by which the nucleus divides into two nuclei before cytokinesis occurs.

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4
Q

How does cytokinesis differ between animal and plant cells?

A

In animal cells, a cleavage furrow forms and separates the cells, while in plant cells, a cell plate forms and develops into a new cell wall.

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5
Q

What is a cleavage furrow?

A

A cleavage furrow is the indentation that forms during cytokinesis in animal cells, leading to the separation of the two daughter cells.

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6
Q

What is a cell plate?

A

A cell plate is the precursor to a new cell wall that forms during cytokinesis in plant cells.

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7
Q

What happens during cytokinesis in animal cells?

A

A contractile ring of actin and myosin proteins forms at the cell’s equator, pulling the plasma membrane inward to create two separate cells.

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8
Q

What is the role of vesicles in plant cell cytokinesis?

A

Vesicles carry carbohydrates, lipids, proteins, pectin, and cellulose to form the new cell wall between the two daughter cells.

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9
Q

What is equal cytokinesis?

A

Equal cytokinesis is when the cytoplasm divides evenly between two daughter cells, resulting in cells of similar size.

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10
Q

Why is it important that each daughter cell receives at least one mitochondrion or chloroplast?

A

Mitochondria are needed for cellular respiration, and chloroplasts are needed for photosynthesis in plant cells. A cell (or whole organism) could not function without these two processes.

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11
Q

What is unequal cytokinesis?

A

Unequal cytokinesis occurs when the cytoplasm divides unevenly, resulting in daughter cells of different sizes.

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12
Q

Give an example of unequal cytokinesis.

A

Oogenesis in humans and budding in yeast are examples of unequal cytokinesis.

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13
Q

What happens during oogenesis in humans?

A

During oogenesis, a primary oocyte divides to form a secondary oocyte and a polar body, followed by another division to form an ovum and a second polar body.

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14
Q

What happens to polar bodies formed during oogenesis?

A

Polar bodies degenerate and become part of the final ovum during oogenesis.

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15
Q

What are the two processes by which the nucleus of a eukaryotic cell can divide?

A

Two processes by which the nucleus of a eukaryotic cell can divide are mitosis and meiosis.

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16
Q

Why must the nucleus divide before cell division?

A

The nucleus must divide before cell division to avoid the production of anucleate cells, which are cells without a nucleus.

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17
Q

What is the role of mitosis in eukaryotic cells?

A

Mitosis gives rise to genetically identical cells and is used for growth, repair of damaged tissues, replacement of cells, and asexual reproduction.

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18
Q

How does mitosis maintain chromosome number?

A

Mitosis maintains the chromosome number by producing daughter cells that are diploid (2n) and genetically identical to the parent cell.

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19
Q

What is the role of meiosis in eukaryotic cells?

A

Meiosis gives rise to genetically different cells and is used to produce gametes (sex cells).

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20
Q

How does meiosis contribute to genetic diversity?

A

Meiosis produces haploid (n) daughter cells with half the chromosome number of the parent cell, leading to genetic variation.

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21
Q

What must occur before mitosis and meiosis?

A

DNA replication, during interphase, must occur to create two identical strands of DNA called chromatids. This must happen before mitosis and meiosis.

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22
Q

What happens to chromatids during anaphase?

A

During anaphase one chromatid from each chromosome is pulled to opposite poles of the cell, eventually becoming individual chromosomes.

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23
Q

Why is DNA condensation necessary before mitosis?

A

DNA condensation is necessary to fit the long DNA molecules into the small nuclei of cells.

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24
Q

How does supercoiling aid in chromosome condensation?

A

Supercoiling, aided by histone proteins and enzymes, repeatedly coils the DNA molecule to condense it into chromosomes.

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25
What is the role of microtubules during cell division?
Microtubules are responsible for the movement of chromosomes by lengthening and shortening to facilitate their movement.
26
What are microtubule motors?
Microtubule motors are motor proteins that carry chromosomes along the microtubules to the equator of the cell in preparation for nuclear division.
27
How many main stages are there in mitosis?
There are four main stages of mitosis: prophase, metaphase, anaphase, and telophase.
28
What happens to chromosomes during prophase?
During prophase chromosomes condense and become visible. Each chromosome consists of two identical sister chromatids joined at the centromere.
29
What role do centrosomes play during prophase?
During prophase the two centrosomes move toward opposite poles of the nucleus, and spindle fibers begin to emerge from them.
30
What happens to the nuclear envelope and nucleolus during prophase?
During prophase, the nuclear envelope breaks down into small vesicles, and the nucleolus disappears.
31
Where do chromosomes align during metaphase?
During metaphase chromosomes line up at the equator of the spindle, also known as the metaphase plate.
32
How do spindle fibers interact with chromosomes during metaphase?
During metaphase, spindle fibres attach to the centromeres of the chromosomes via kinetochores. Each sister chromatid is connected to a spindle fibre from opposite poles.
33
What is the key event of anaphase?
The key event of anaphase is when the sister chromatids separate at the centromere and are pulled to opposite poles by the shortening spindle fibres.
34
What happens to chromosomes during telophase?
During telophase, chromosomes arrive at opposite poles and begin to de-condense.
35
How does the nucleus reform during telophase?
Nuclear envelopes reform around each set of chromosomes, spindle fibres break down, and new nucleoli form within each nucleus.
36
What is the purpose of meiosis in sexual reproduction?
Meiosis produces haploid gametes, reducing the chromosome number by half, which is essential for maintaining the species' chromosome number across generations during sexual reproduction.
37
What happens during Meiosis I?
During Meiosis I, homologous chromosomes are separated, resulting in two haploid nuclei, each still containing chromosomes with two chromatids.
38
What is a bivalent?
A bivalent is a pair of homologous chromosomes that come together during prophase I of meiosis.
39
Why is Meiosis I called reduction division?
Meiosis I is called reduction division because it reduces the chromosome number by half, from diploid (2n) to haploid (n).
40
What occurs during Meiosis II?
During Meiosis II, the chromatids of each chromosome are separated, resulting in four haploid nuclei, each containing chromosomes with a single chromatid.
41
True or False? Chromosome replication occurs between Meiosis I and Meiosis II?
False. There is no chromosome replication between Meiosis I and Meiosis II.
42
What role does crossing over play in meiosis?
Crossing over results in the exchange of genetic material between homologous chromosomes, creating recombinant chromosomes and increasing genetic variation.
43
How does the random orientation of bivalents contribute to genetic variation?
The random orientation of bivalents during metaphase I leads to the independent assortment of chromosomes, which generates a variety of possible genetic combinations in gametes.
44
What is the significance of genetic variation in populations?
Genetic variation is important for natural selection and increases a species' ability to adapt and survive in changing environments.
45
What is non-disjunction?
Non-disjunction occurs when chromosomes fail to separate properly during meiosis, leading to gametes with an abnormal number of chromosomes.
46
How does non-disjunction lead to Down Syndrome?
Down Syndrome, also known as Trisomy 21, occurs when non-disjunction results in an extra copy of chromosome 21, leading to a total of 47 chromosomes in the affected individual, instead of 46.
47
What increases the risk of non-disjunction?
The risk of non-disjunction increases with the age of the mother, older ova are more likely to undergo incorrect chromosome separation.
48
What is cell proliferation?
Cell proliferation is the process of cells dividing to promote growth, replace cells, and repair tissues.
49
Define interphase in the cell cycle.
Interphase is a metabolically active phase in which the cell grows, synthesises DNA, and prepares for mitosis.
50
What are the main stages of interphase?
The main stages of interphase are G1, S, and G2 phases.
51
State the purpose of cyclins in the cell cycle.
Cyclins regulate the cell cycle by increasing and decreasing in concentration, ensuring checkpoints are met.
52
What happens in the S phase of interphase?
In the S phase, DNA is replicated to ensure each daughter cell has a full set of genetic information.
53
True or False? Cyclins must reach a threshold concentration to proceed through cell cycle checkpoints.
True. Cyclins must reach a threshold concentration to ensure cell cycle checkpoints are passed.
54
Define cytokinesis.
Cytokinesis is the process where the cell's cytoplasm divides, resulting in two daughter cells.
55
What role does cell proliferation play in wound healing?
Cell proliferation replaces damaged cells in the skin, promoting tissue repair and wound healing.
56
True or False? Cytokines are protein molecules that control the cell cycle.
False. Cyclins are protein molecules that control the cell cycle. When a threshold concentration is reached, the next stage of the cell cycle can begin. Cytokines are protein molecules involved in cell signalling within the immune system.
57
What is the consequence of a mutation in a proto-oncogene?
A proto-oncogene normally regulates cell growth and division. A mutation in a proto-oncogene converts it into an oncogene, leading to uncontrolled cell division.
58
Define tumour suppressor gene.
A tumour suppressor gene is a gene that regulates cell division and prevents uncontrolled growth.
59
What is the difference between benign and malignant tumours?
Benign tumours do not invade other tissues or spread, while malignant tumours can invade tissues and cause cancer.
60
Define metastasis.
Metastasis is the spread of cancer cells from a primary tumour to form secondary tumours in other parts of the body.
61
What is a secondary tumour?
A secondary tumour forms when cancer cells from a primary tumour break off and spread to another location in the body via the blood or lymphatic system.
62
Define oncogene.
An oncogene is a mutated proto-oncogene. It is permanently activated and therefore causes uncontrolled cell division and tumour formation.
63
True or False? Benign tumours cause cancer.
False. Benign tumours do not invade tissues and do not cause cancer.
64
What characteristic distinguishes malignant tumours?
Malignant tumours have the capacity for invasion and metastasis, spreading cancer to other tissues.
65
Describe the role of a proto-oncogene.
Proto-oncogenes regulate cell growth and division.
66
What information is required to calculate the mitotic index of a population of cells?
In order to calculate the mitotic index of a sample of cells, we need to know... * The number of cells with visible chromosomes (undergoing mitosis) * The total number of cells in the sample
67
Give the formula used to calculate the mitotic index.
Mitotic index = of cells with visible chromosomes / total number of cells in the sample

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