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IMMS > Mitosis And Meiosis > Flashcards

Mitosis And Meiosis Flashcards

1
Q

During mitosis, chromosomes attach themselves to microtubules that propagate from centrosomes.

What are these microtubules made of?

A

Tubulin

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2
Q

Examining a histological section, a pathologist sees a cell undergoing mitosis. The chromosomes are moving towards opposite poles of the cell and there are no nuclear membranes.

Which phase of mitosis is this?

A

Anaphase

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3
Q

Where is DNA inside the cell?

A

Nucleus

Mitochondria

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4
Q

Structure of DNA

A

• Double helix

•Complimentary base pairs:
•A T (two bonds)
•G C (three bonds)

•Coils around nucleosomes
•Coils again into supercoils
•And again into chromosomes

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5
Q

DNA structure and organisation: chromosomes

A

• There are 46 chromosomes in the human genome (22 autosomal pairs + sex chromosomes (XY))

• Each human chromosome contains a continuous DNA duplex of ~107 bp and contain several hundred genes

• Each has a long arm (q) and a short arm (p) separated by the centromere

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6
Q

Staining of chromosomes

A

• Chromosomes can be characteristically stained for identification and analysis with dyes (Giemsa: G banding, Quinacrine: Q banding)

• G banding gives ~ 400-500 bands/haploid human chromosome set

• Each band ~6-8 Mbp

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7
Q

What is mitosis for?

A

•Producing two daughter cells

•Genetically identical to parent cell

•Growth

•Replace dead cells

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8
Q

The steps of mitosis

A

•Cell must be in cell cycle – interphase

•In S-phase:
•DNA replication
•Centrosome replication

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9
Q

Prophase

A

•Chromatin condenses into chromosomes

•Centrosomes nucleate microtubles and move to opposite poles of nucleus

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10
Q

Prometaphase

A

• Nuclear membrane breaks down

•Microtubules invade nuclear space

•Chromatids attach to microtubules

• Cell no longer has a nucleus

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11
Q

Metaphase

A

Chromosomes line up along equatorial plane (metaphase plate)

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12
Q

Anaphase

A

•Sister chromatids separate and are pushed to opposite poles of the cell, centromere first, as spindle fibres contract

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13
Q

Telophase

A

•Nuclear membranes reform

•Chromosomes unfold into chromatin

•Cytokinesis begins

  • To remember mitosis: I Prefer Milk And Tea (Interphase, Prophase, Metaphase, Anaphase and Telophase)
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14
Q

Clinical relevance

A

Categorising tumours as benign or malignant

Grading malignant tumours

  • In histology can tell if cell undergoing mitosis if its nucleus is dark (i.e. chromatin has condensed to chromosomes) and if the nuclei are not the same size
  • Something is defined as malignant if there are too many mitotic figure i.e. lots of dark nuclei of different sizes
  • Number of mitotic figures determine how bad cancer is, the more there are, the worse it is

Downs syndrome, 1 extra chromosome at 21 [trisomy 21]

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15
Q

Drugs for prevention of cells replication

A

Prevent/slow down/stop certain parts of mitosis

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16
Q

Mitotic spindle

A

• Taxol
• Vinca alkaloids – vinblastine, vincristine

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17
Q

Anaphase

A

Colchicine-like drugs

18
Q

Spindle poles

A

Ispinesib

19
Q

Meiosis

A

Similar to mitosis but key differences:
• Only in gametes
• Recombination of genetic material generates diversity
• Two cell divisions
• 4 haploid daughter cells (HALF number of chromosomes i.e. 23) cells produced, which are genetically distinct from each other and the parent cell
• MEIOSIS IS NOT A CYCLE

20
Q

Cross over

A

In prophase 1

In prophase 2

21
Q

Sperm production (gametogenesis)

A

•Primordial germ cells → lots of mitoses →Spermatogonia (mature sperm)

•Meiotic divisions commence at puberty and continues throughout life
• Some mitosis occurs in embryonic stages to produce primary spermatocytes present at birth

•The cytoplasm divides evenly

•After meiosis II four equal gametes

•Millions of mature sperm continuously produced
•Process takes 60-65 days
•100-200 million sperm/ejaculate

22
Q

Eggs (gametogenesis)

A

• Primordial germ cell → 30 mitoses → oogonia
•Oogonia enter prophase of meiosis I by 8th month of intrauterine life

•Process suspended
•Cells enter ovulation 10-50 years later
•Cytoplasm divides unequally – 1 egg and 3 polar bodies (that apoptose- go onto die)

•Meiosis I is completed at ovulation
(then cells remain in suspended animation) - at this point there is 1 big cell, 1 small cell each with diploid DNA. Then go on to divide again each (after fertilisation) to form 1 big cell (egg) and 3 small cells (polar bodies)

•Meiosis II only completed if fertilisation occurs

23
Q

Non-disjunction

A

Failure of chromosome pairs to separate in Meiosis I or sister chromatids to separate properly in meiosis II

24
Q

Down syndrome

A

Most cases result from regular trisomy 21

~75% maternal meiosis I
~25% maternal meiosis II
~3-5% paternal non disjunction

likelihood of this happening increases with age of both men and females

25
Q

Gonadal mosaicism

A

•Occurs when precursor germline cells to ova or spermatozoa are a mixture of two or more genetically different cell lines (due to errors in mitosis)

•One cell line is normal, the other mutated

•Incidence increases with advancing paternalage

•Parent is healthy (since genetic change is only in the germline so all the other cells are unaffected - have usual genetic components), but the fetus may have a genetic disease

26
Q

Where can Gonadal mosaicism be observed?

A

Can be observed with any inheritance pattern, but most commonly autosomal dominant and X-linked

Observed in a number of conditions, including osteogenesis imperfecta and Duchenne muscular dystrophy

More common in males

27
Q

Summary

A

•Mitosis allows faithful cell replication and the production of 2 daughter cells

•Meiosis produces 4 genetically different daughter cells

•The structure of DNA is essential to successful mitosis and meiosis

•Mitosis and meiosis are clinically relevant, in terms of disease causation, diagnosis and treatment!

28
Q

Autosomes

A

Anything that isn’t sex determining

29
Q

Karyotype

A

Number and appearance of an individual’s complete set og chromosomes in a cell. Spreads are arranged
in size order, biggest is pair 1 and smallest is pair 22, sex pair is 23

30
Q

Chromosome structure

A
  • Each chromosome contains a continuous DNA duplex of roughly 107 base pairs and contain several hundred genes - we have around 30,000 genes
  • Each chromosome has a long arm (q) and a short arm (p - can remember p as petit) separated by a centromere
  • 22,000 genes in humans
31
Q

Chromatin

A

Chromosomes when the Cell is not in replication

DNA associated with his tone proteins

32
Q

Chromosomes

A

Referred to chromosomes DURING cell replication

When the DNA is short and condensed

33
Q

Chromatids

A

Chromosomes are called chromatids after cells have replicated

Diffuse and uncondensed form of chromosomes

34
Q

For a cell to undergo mitosis…

A

The cell must be in the cell cycle interphase

35
Q

Interphase

A

Longest phase

G1, S, G2

36
Q

G1

A

no visible activity but the following occurs

• Rapid growth
• Normal metabolic function
• New organelles produced
• Protein synthesis of proteins involved in spindle formation

37
Q

S (synthesis)

A

• DNA doubles through DNA replication

• Histone proteins double through protein synthesis ( 2 x as much DNA at end of S)

• Centrosome replication

38
Q

G2

A

• Energy stores accumulate

• Mitochondria and centrioles double

39
Q

CYTOKINESIS

A

• Cell organelle become evenly distributed around each nucleus

• Cell divides into two daughter cells with a nucleus in each and 46 chromosomes

40
Q

Meiosis 1

A

• Chromosome number is halved

• In Prophase 1, crossing over occurs between non-sister chromatids [genes sort independently thus if 1 gene switches over, doesn’t mean another one will], resulting in genetic diversity

• In Metaphase 1, random assortment occurs on the metaphase plate - also resulting in genetic diversity

41
Q

Meiosis 2

A

• Sister chromatids separate

• Haploid cells produced

42
Q

GAMETOGENESIS

A

• The first stage is the proliferation of primordial (undifferentiated) germ cells (developing gametes) by mitosis

• The timing of mitosis in germ cells differs greatly in males and females

IMMS (29 decks)

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