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2 Cell Basics > Chromosomes, the Cell Cycle and an Intro to its Regulation > Flashcards

Chromosomes, the Cell Cycle and an Intro to its Regulation Flashcards

1
Q

In eukaryotic cells, what is a chromatin?

A

chromosomal DNA in a complex wtih RNA and proteins

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2
Q

Histones

A

highly alkaline proteins which package and order DNA into structural units called nucleosomes
chief protein of chromatin, acting as spools around which DNA winds, and playing a role in gene regulation.

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3
Q

What makes up a nucleosome?

A

2 loops of DNA double helix wrapped around a cluster of 8 histones

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4
Q

How are chromosomes formed?

A

supercoiling and condensation of chromatin

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5
Q

What are genes in relation to chromosomes?

A

specialised functional sites arranged along the choromosomes

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6
Q

Forms of chromatin

A

in interphase nuclei:
heterochromatin
euchromatin

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7
Q

Heterochromatin

A

more condensely and densely staining
tends to be found near nuclear envelope
represents genes that are switched off
two types: constitutive and facultative

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8
Q

Euchromatin

A

less condensed and lightly staining
more central location
represents genes that are switched on

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9
Q

How are tissues of the body divided in relation to cell turnover?

A
  1. continuously renewing: epidermis of skin, intestinal epithelium, blood-forming tissues
  2. conditionally renewing: liver, kidney, endocrine glands
  3. static/non-proliferative: cardiac, nerve cells
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10
Q

Cell cycle

A

G1 phase - S phase - G2 - M phase - cytokinesis - G1/G0

G0 = doing function, no division

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11
Q

Mitosis

A

prophase - prometaphase - metaphase - anaphase - telophase

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12
Q

G1-S phase transition importance

A

control point to deermine whether cells enter S phase

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13
Q

S phase

A

replication of DNA and RNA and protein

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14
Q

G2 phase

A

final prep for mitosis

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15
Q

M phase

A

division of 2 sister chromatids of each chromosome into separate nucleoli and division of the parent cell into 2 daughter cells

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16
Q

Prophase

A

chromatin condenses to form visible chromosomes
each chromosome comprises 2 sister chromatids joined at the centromere
centrioles duplicate
centrioles move apart to form 2 poles and act as microtubule-organising centres
microtubules form the mitotic spindle apparatus between the centrioles

17
Q

Prometaphase

A

nucleoli regress and nuclear membranes disassemble
chromosomes move towards the equator and interact with microtubules
each pair of sister chromatids has an attachment site - kinetochore, which attaches to spindle

18
Q

Metaphase

A

central region of cell forms a metaphase plate
chromosomes arrange themselves on this plate, 2 sister chromatids joined at centromeres
spindle consists of microtubules running from pole to pole or pole to chromosome
latter microtubules run to centromeres of sister chromatids and attach at kinetochores

19
Q

Anaphase

A

sister chromatids of each pair move apart to opposite poles of the cell - elongation of polar microtubules, shortened kinetochore microtubule
these chromosomes are pulled along by the microtubules

20
Q

Telophase

A

chromosomes reach poles and start to become less condensed
nuclear membrane reassembles
a cleavage furrow begins around the equator
spindle disappears
nucleoli reappear

21
Q

Cytokinesis

A

actin-myosin belt

cells separate to form 2 daughter cells

22
Q

Interphase

A

G0, G1, S and G2

23
Q

How is the cell cycle regulated?

A

cyclins and cyclin-dependent kinases

24
Q

What are cyclins and CDK?

A

regulatory proteins
determine cell’s progress through the cell cycle
coordinate cell’s entry into the next phase of the ceel cycle

25
Q

How do cyclin and CDKs regulate the cell cycle?

A

CDKs activated when they bind to cyclin
activated CDKs cause phosphorylation to activate or inactivate target proteins
these proteins coordinate cell’s entry into next phase

26
Q

Clinical relevance of cell cycle regulation

A

inhibitors of cyclin/CDK complexes: 2 families of genes prevent the progression of the cell cycle
can be used as anticancer agents - tumour suppressors

27
Q

Difference in cell cycle of cells undergoing mitosis and meiosis

A

in S phase of meiosis, DNA is duplicated (4c), therefore there must be 2 separate reduction divisions to achieve 1c amount in gamete

28
Q

Meiosis I

A

prophase, metaphase, anaphase, telophase

29
Q

Prophase I

A

recombination and pairing
Leptotene - chromatin condenses -> chromosomes, chromomeres visible
Zygotene - homologous chromosomes pair to form bivalents, split into sister chromatids, synapsis develop between sister chromatids of homo pairs
Pachytene - synapsis completed and chiasma formed, where genetic info is exchanged
Diplotene - chromatids held together by chiasmata and centromeres
Diakinesis - chiasmata appear to move towards the ends of chromatids

30
Q

Metaphase I

A

each bivalent has 2 centromeres and arrange themselves by chance on opposite sides of the metaphase plate
independent assortment results in genetic variation

31
Q

Anaphase I

A

chromosomes move to opposite poles of cell

each pole mix of maternal and paternal chromosomes - source of genetiv variation

32
Q

Telophase I

A

each daughter cell has half diploid number of chromosomes

nuclear envelope may reassemble before prophase II of the 2nd meiotic division

33
Q

Meiosis II

A

similar to mitosis

centromeres split at kinetochores and sister chromatids move to opposite poles

34
Q

Gametogenesis and meiosis

A

4 daughter cells formed at end of meiosis II in spermatogenesis but not in oogenesis
oogenesis: ovum and 3 polar bodies

35
Q

Genetic variation in meiosis

A

pachytene of prophase I: genetic info exchanged bewtween homo pairs of chromosomes at chiasmata
anaphase I: each pole has mixture of maternal and paternal chromosomes
fertilisation

36
Q

Monosomy

A

individual missing chromosome from a pair

eg. Turner’s syndrome (XO)

37
Q

Trisomy

A

individual has more than 2 chromosomes of a pair

eg. Down’s syndrome (trisomy 21), Patau’s syndrome (trisomy 13), Edward’s syndrome (trisomy 18), Kleinfelter’s (XXY)

38
Q

How does aneuploidy occur?

A

homo chromosomes in meiosis I do not separate properly, one has 24, other has 22 = non-disjunction

2 Cell Basics (6 decks)

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