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LQB186: Human Cell and Molecular Biology > 5 - Meiosis, mitosis and the cell cycle > Flashcards

5 - Meiosis, mitosis and the cell cycle Flashcards

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1
Q

What is the locus

A

A gene’s specific location on a chromosome

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2
Q

Explain diploid

A

Each diploid organism has two of each chromosome and therefore 2 alleles of each gene

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3
Q

Describe homo/heterozygous alleles

A

Homozygous (AA): alleles are the same for that gene
Heterozygous (Aa): different alleles for that gene

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4
Q

Compare and contrast mitosis and meiosis

A
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5
Q

Explain how humans are diploid

A
  • Two copies of each of 22 autosomes and 1 pair sex chromosomes = XX, XY, X0 etc
  • Each is a pair of homologous chromosomes
  • One copy is via egg (maternal line) and other is from sperm (paternal line)
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6
Q

Define mitosis

A

a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus

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7
Q

What are the stages of the cell cycle

A
  1. Interphase: G1, S, G2
  2. Mitosis: prophase, metaphase, anaphase, telophase
  3. Cytokinesis
  4. Resting phase (G0)
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8
Q

Explain interphase

A

G1: growth and metabolic roles
S: replication of DNA
G2: Growth and more preperation

G roles: Increases mass of cells, growth and preperation for chromosome seperation

Nucleolus and nuclear envelope are distinct
Chromosomes are in the form of threadlike chromatin

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9
Q

Explain prophase

A
  • Chromosomes begin to condense and become visible
  • Nuclear envelope breaks down
  • Centrioles move to opposite sides of cell
  • Mitotic spindle begins to form (microtubules)
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10
Q

Explain prometaphase

A
  • Chromosomes continue to condense
  • Chromosomes begin to attach to the spingle at centromeres via kinetochores
  • Centrosomes form the spindle poles
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11
Q

What are kinetochores

A

Connect chromosomes to microtubules

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12
Q

Explain metaphase

A
  • Chromosomes are now tightly coiled
  • Each has 2 chromatids that are lined up on the metaphase plate
  • Each sister chromatid is attached to a spindle fibre from opposite pole
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13
Q

Explain Anaphase

A
  • Centromeres split in 2
  • Sister chromatids (chromosomes) are pulled towards opposite poles
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14
Q

Explain telophase and cytokinesis

A

Telophase
- Chromosomes are at the poles and decondense (become more diffuse)
- Nuclear envelope and nucleolus reform
- Mitotic spindle breaks down
- Spindle fibres continue to push the poles apart
- Cytoplasm begins to divide
Cytokinesis
- Cleavage furrow seperates daughter cells
- Division into 2 identical daughter cells is completed

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15
Q

How is the cell cycle regulated?

A
  • Timing of events are controlled (each process can be turned on and off at certain times)
  • Events occur in the correct order in a linear, irreversible direction
  • Each event is triggered only once per cycle
  • Redundancy (back ups) to ensure the cycle functions properly even when some parts are malfunctioning
  • Adaptable systems so that it can be modified for different cell types and environmental conditions
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16
Q

Why is the cell cycle highly regulated?

A

ensures that a dividing cell’s DNA is copied properly, any errors in the DNA are repaired, and each daughter cell receives a full set of chromosomes.

17
Q

What are the 3 important cell cycle checkpoints?

A

G1 checkpoint
- cell size
- nutrients
- growth factors
- DNA damage
- If cells don’t meet the conditions, move to G0 (resting phase)
G2 Checkpoint
- Cell size
- DNA replication
- DNA damage
Metaphase checkpoint
- Chromosome attachment to spindle

18
Q

Why do we need cell cycle checkpoints?

A
  • ensure that the processes have occurred, to enable cell cycle to move to next stage
  • Unregulated cell cycles usually result in cancerous cells
19
Q

What proteins help regulate cell cycle?

A
  • Cyclins
  • Cyclin-dependent kinases (CDKs)
20
Q

What are cyclins?

A
  • different ones increase during the cell cycle
  • Activate CDKs
21
Q

Describe how CDKs control the cell cycle

A
  • CDKs are always there, but most are inactive, waiting for cyclins
  • Kinases are proteins that activate/inactivate via phosphorylation
  • Attached phosphate group acts like a switch (making the target protein more or less active)
  • Target proteins control functions like: proteins that make nuclear membrane break down or promote DNA replication
  • Threshold of cyclin-CDK activation = cell moves past “restriction point”
22
Q

What is cancer and how is the cell cycle related to it?

A
  • Cancer: disease of abnormal gene expression that allows for inappropriate cell division
  • Cancer cells are in an unregulated cell cycle (loss of control)
  • Develops in a multi-step process (multiple mechanisms must fail for cells to become cancerous)
  • Most cancers arise as cells acquire a series DNA mutations that make them divide more quickly, escape internal and external controls on division, and avoid programmed cell death
23
Q

Describe homologous chromosomes

A
  • Sister chromatid from each parent
    Not identical but have:
  • Genes controlling the same specific characteristics
  • Genes are in the same order
  • Gene sequences may change through mutation (=alleles)
  • Diploid cells have 2 alleles for each gene
24
Q

What is a karyotype?

A
  • Display of homologous chromosomes for visual comparison
  • Cell must be in metaphase of meiosis to see diploid human chromosomes
  • Each chromosome has been copied into 2 sister chromatids and condensed so its ready for division
25
Q

How are different alleles created

A
  • Mutations in genes create different alleles
    New alleles can:
  • Can be passed onto offspring
  • Introduce genetic variation to population
  • May increase ability of population to adapt to environmental change
26
Q

How do genes show different genetic characteristics

A

Locus: position of gene on chromosome
Gene: confers trait (eye colour)
Allele: form of trait (specific colour)

27
Q

First stage of meiosis

A

Interphase (G1 - cell grows; S - copies all of its chromosomes; G2 - prepares for division)

28
Q

Describe prophase 1

A
  • Occupies 90% of meiosis
  • Chromosomes condense and become visible
  • Homologous chromosomes (tetrads) pair up at the metaphase plates
  • Synapsis and crossing over occur (1 sister chromatid of each pair of homologous chromosomes exchanges DNA)
29
Q

Describe crossing over

A
  • Produces genetic variation in offspring
  • Produces new chromosomes that contain genes from both parents
  • Homologous portions of 2 non-sister chromatids in a tetrad trade places
  • 2-3 crossover events per chromosome pair in humans
  • Increases genetic diversity of gametes
30
Q

Describe Anaphase I

A
  • Homologous chromosomes move apart to
    opposite sides of the cell
  • Guided by spindle apparatus
  • Sister chromatidsr emain attached at the centromere
31
Q

Describe telophase I and cytokinesis I

A
  • New nuclei form
  • Cytoplasm of cell divides
  • Haploid chromosome number (n)
  • Chromosomes still as sister chromatids
  • cytokinesis
32
Q

Explain prophase II

A
  • Each chromosome consists of 2 sister chromatids
  • Chromosomes move towards metaphase plate
33
Q

Explain metaphase II

A

chromosomes align on metaphase plate

34
Q

Explain anaphase II

A
  • Replicated chromosomes seperate
  • Sister chromatids move towards opposite poles of cell
35
Q

Explain telophase II

A
  • Nuclei form at opposite poles of the cel
  • Chromosomes unravel to form chromatin
36
Q

Explain cytokinesis II

A
  • Both cells split into 2
  • Result: 4 daughter cells with haploid chromosome complement
  • males: 4 sperm develop
  • females: 1 egg + 3 polar bodies
37
Q

What is independent assortment

A
38
Q

What is reshuffling of genes?

A

LQB186: Human Cell and Molecular Biology (5 decks)

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