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SLE111 Cells And Genes > Module 8: Cell Reproduction > Flashcards

Module 8: Cell Reproduction Flashcards

1
Q

What are the phases of mitosis in order?

A
  1. Interphase.
  2. Prophase.
  3. Metaphase.
  4. Anaphase.
  5. Telophase & cytokinesis.
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2
Q

What are the three main phases of a fertilised egg?

A

Zygote → Embryo → Fetus

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3
Q

What is a genome?

A

All the genetic information in a cell, including DNA: the complete nucleotide sequences that make up chromosomes.

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4
Q

What is characteristic of a genome in prokaryotes?

A

A single double-stranded DNA molecule in a loop or circle.

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5
Q

Where are prokaryotic genomes found?

A

A region called the nucleoid.

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6
Q

How is antibiotic resistance spread through bacterial colonies?

A

Often, it is spread through plasmid exchange from resistant donors to recipient cells.

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7
Q

What are plasmids?

A

Smaller loops of DNA found in prokaryotes that are not essential for normal growth.
Bacteria can exchange plasmids with other bacteria.

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8
Q

What is characteristic of a genome in eukaryotes?

A

Several double-stranded linear DNA molecules.

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9
Q

How many chromosomes do human somatic cells have?

A

46

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10
Q

How many chromosomes do human gametes have?

A

23

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11
Q

What is a homologous set of chromosomes called?

A

Diploid.
Represented as 2n

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12
Q

What are single set chromosomes called?

A

Haploid.
Represented as 1n

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13
Q

What is a locus (in genetics)?

A

A specific, fixed position on a chromosome where a particular gene or genetic marker is located.

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14
Q

What are genes?

A

A hereditary unit containing a sequence of DNA that occupies a specific location on a chromosome.
Determines specific characteristics by coding for specific proteins.

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15
Q

What are traits (in genetics)?

A

Variations of specific characteristics coded for by genes.
E.g. hair colour is a characteristic with traits that are blond, brown, black, etc.

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16
Q

What are alleles?

A

Alternative forms of a gene that can have the same place on homologous chromosomes and are responsible for alternate traits.

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17
Q

What is chromatin?

A

Packed nucleosomes.

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18
Q

What is a nucleosome?

A

A sub-unit of chromatin.
DNA-histone complex.
Formed by DNA double helix wrapped around eight histone proteins at intervals along the length of the chromosome.

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19
Q

What is a chromatid?

A

Half of a chromosome.
Two sister chromatids are identical and joined by a centromere.

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20
Q

What is a centromere?

A

The structure in a chromosome that holds the sister chromatids together.
Also, the point of attachment of the kinetochore.

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21
Q

What are the levels of compacting DNA into chromosomes?

A
  1. DNA wraps around histone proteins, forming nucleosome.
  2. Nucleosome and linker DNA coil into chromatin fibre.
  3. Fibrous proteins pack the chromarin.
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22
Q

On what phase does DNA replicate?

A

The S phase of interphase, which precedes mitosis.

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23
Q

What binds chromatids into chromosomes?

A

Cohesin proteins.

24
Q

What are the 3 stages of interphase?

A
  1. G1
  2. S
  3. G2
25
Q

What is karyokinesis?

A

The division of the cell nucleus in the M phase of the cell cycle. The first stage of mitosis.
Also known as nuclear division.

26
Q

What is cytokinesis?

A

The division of the cytoplasm during the M phase of the cell cycle.

27
Q

What occurs in interphase?

A

The growth of the cell and the replication of its DNA.

28
Q

What occurs during G1 phase?

A

G1 phase, also known as first gap phase, is the first stage of interphase.
The cell accumulates chromosomal DNA and associated proteins. Energy reserves are also accumulated.

29
Q

What occurs during S Phase?

A

S Phase, also known as the synthesis of DNA phase, is the 2nd stage of interphase.
DNA replication resulting in two sister chromatids attached to the centromeric region. The centrosome is also duplicated.
The two centrosomes will give rise to the mitotic spindle.

30
Q

What are centrioles?

A

Rod-like objects that are part of the centrosome and help cell division by anchoring microtubules.

Not present in all eukaryotes.

31
Q

What happens in the G2 phase?

A

The G2 phase, also known as the second gap, is the 3rd and final stage of interphase.
The cell replenishes energy stores and synthesises additional proteins. Some cell organelles are duplicated, and the cytoskeleton is dismantled. Possible additional cell growth occurs.
The final preparations for mitosis.

32
Q

What occurs during Prophase?

A

The first phase of mitosis/karyokinesis.
Nuclear envelope dissociates, membrane organelles fragment, and disperse.
Microtubules forming the mitotic spindle extend between centrosomes, pushing them apart.
Sister chromatids coil with the aid of condensing proteins.

33
Q

What occurs during Prometaphase?

A

The ‘first change phase’ in mitosis/karyokinesis.
Processes in prophase continue to advance.
Further fragmentation of nuclear envelope.
Mitotic spindle continues to develop and stretch.
Each sister chromatid develops a protein structure called a kinetochore in its centromeric region. This structure connects to the miotic spindle.

34
Q

What is a kinetochore?

A

A disc-shaped protein structure found at the centre of the centromere of each chromatid.
Moves chromosomes during mitosis and meiosis.
like a knot, connecting the chromatids to rope

35
Q

What occurs in Metaphase?

A

The 2nd phase of mitosis/karyokinesis.
All chromosomes are aligned in a plane called the metaphase plate or the equatorial plane.
The sister chromatids are still tightly attached together by cohesion proteins.
Chromosomes are maximally condensed.

36
Q

What occurs in Anaphase?

A

The 3rd phase of mitosis/karyokinesis.
Cohesion proteins degrade, separating chromatids at the centromere.
The chromatids become chromsomes on each side of the cell.
The cell is visibly elongated.

37
Q

What occurs in Telophase?

A

The 4th phase of mitosis/karyokinesis
The chromosomes reach the opposite poles and begin to decondense (unravel).
The mitotic spindles depolymerises into tubulin monomers that will assemble the cytoskeleton.
Nuclear envelopes form around the chromosomes.

38
Q

What is cytokinesis?

A

cell motion
Sometimes viewed as the second stage of the mitosis phase. May or may not take place after mitosis.
Different depending on cell type: plant cells vs. animal cells.

39
Q

Cytokinesis in animal cells?

A

Starts during late anaphase.
Actin filament forms at former metaphase plate and pulls the equatorial of the cell inward, forming a fissure. This is called the cleavage furrow.
The furrow deepens as the actin ring contracts, and eventual the membrane is cleaved in two.

40
Q

Cytokinesis in plant cells?

A

During interphase, the Golgi Apparatus accumulates enzymes, structural proteins, and glucose molecules.
During telophase, these Golgi vesicles form a phragmoplast (vesicular structure) at the metaphase plate.
More vesicles fuse from the centre towards the cell walls, forming a cell plate. This cell plate enlarges until it merges with the cell walls.
Enzymes use the glucose to build a new cell wall.
Golgi membranes become part of the plasma membrane on either side of the new cell wall.

41
Q

What is G0 phase?

A

Cells in G0 are not actively preparing to divide. This is an inactive stage.

Some cells are in G0 temporarily due to environmental conditions, while other cells (such as nerve cells) remain permanently in G0.

42
Q

Define quiescent

A

Inactive or still.

G0 is a quiescent phase.

43
Q

How can the cell cycle be regulated?

A
  1. External events.
    e.g. human growth hormone (HGH or hGH), crowding of cells, cell size SA/V ratio, death of nearby cells
  2. Internal checkpoints.
    there are 3 main checkpoints in the cell cycle
44
Q

What does the G1 checkpoint do?

A

Also called the restriction point (in yeast).
Determines if conditions are favourable for cell division. The point of irreversibly committing to cell division.
Checks against external factors (e.g. cell size, growth factors) as well as for genomic DNA damage.
Can halt the cycle and attempt to remedy the problem, or the cell can advance to G0 and wait until conditions improve.

45
Q

What does the G2 checkpoint do?

A

Guards entry point into miotic phase.
Ensures all chromosomes have been replicated and no damaged DNA.
If DNA isn’t good, the cell cycle halts and the cell either attempts to complete DNA replication or repair the damaged DNA.

46
Q

What does the M checkpoint do?

A

Occurs near the end of metaphase.
Also known as spindel checkpoint: checks if sister chromatids are correctly attached to spindel microtubules.
The cycle will not proceed until the kinetochores of each pair of sister chromatids are anchored to at least 2 spindle fibres from opposite poles of the cell.

47
Q

What are the positive regulators of the cell cycle?

A

Cyclin and cyclin-dependent kinases (Cdks).
Proteins.

48
Q

How does positive regulation regulate the cell?

A

The Cdk/cyclin complex must be phosphorylated in specific locations to activate.
In turn, the Cdks phosphorylates other proteins, activating them.
The proteins phosphorylated by Cdks are involved in advancing the cell through the checkpoint.

49
Q

What determines Cdk/cyclin complex formation?

A

Cyclin concentration - levels fluctuate based on timing of the cell cycle.

50
Q

What are the two types of cell regulation?

A
  1. Positive cell regulation - allowing cell progression.
  2. Negative cell regulation - stopping the cell cycle.
51
Q

What are the best understood negative regulators of the cell cycle?

A

Retinoblastma proteins (Rb), p53, and p21.

52
Q

What are retinoblastoma proteins?

A

A group of tumour-suppressor proteins common in many cells.

53
Q

How does p53 operate?

A

p53 is a multi-functional protein that acts at the G1 checkpoint.
If damaged DNA is detected, p53 halts the cell cycle and recruits specific enzymes to repair the DNA.
If it cannot be repaired, p53 can trigger apoptosis.

54
Q

What is apoptosis?

A

Cell suicide.

55
Q

How does p21 work?

A

As p53 levels rise, production of p21 is triggered.
p21 enforced a halt in the cell cycle by binding to and inhibiting the Cdk/cyclin complexes.

56
Q

How does Rb regulation work?

A

Rb acts primarily at the G1 checkpoint.
Rb (retinoblastma protein) binds to transcription factors.
This prevents transcription factors from ‘turning on’ genes and transitioning through the cell cycle.
After being phosphorylated, Rb is inactivated and releases the transcription factors.

57
Q

In order for a cell to move past a checkpoint…?

A

All positive regulators must be turned on.
All negative regulators must be turned off.

SLE111 Cells And Genes (17 decks)

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