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Flashcards in Chapter 2 Deck (45)
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1
Q

what is the function of chromatin?

A

functions of chromatin:

  1. packing DNA into smaller volumes
  2. strengthening DNA for meiosis and mitosis
  3. prevents damaging DNA
  4. controls gene expressio and replication
2
Q

what are two different types of chromatin?

A
  1. heterochromatin

> found in peripheral areas of nucleus

> responsible for gene regulation and protection of chromosomal integrity

  1. euchromatin

> less intense than heterochromatin

> tightly packed DNA, RNA and protein

> rich in gene expression and often under active transcription

3
Q

what is the centromere?

A

centromere:

> where sister chromatids are joined together

> essential for segregation during meiosis/mitosis

4
Q

what is the telomere?

A

telomere

> end of chromosomes

> long array of tandem repeats

>>> 5’- TTAAGGG-3’

5
Q

what is a problem during replication?

A

the final okazaki fragment cannot be printed

> there is no primer site to attach to

> DNA molecule would get shorter with every replication

> even if primer binds exactly at the end of the chromosome, there is no “replacement” of primer

6
Q

replication problem at telomeres

> solution?

A

solution:

> telomerase: used as a template to extend the 3’ end

> is only active in the early embryo and after birth in reproductive cells and stem cells

7
Q

what happens with cells that lack telomerase?

A

cells that lack telomerase activity undergo chromosome shortening every time they divide

> critical factor: maintain a protein cap

> cancerous cells are able to divide continously and often show overactive telomerase

8
Q

somatic cells are …?

germ cells are …?

A

somatic cells are diploid

> 2n chromosomes

germ cells are haploid

> n chromosomes

9
Q

what is the difference between mitosis and meiosis?

A

mitosis:

> normal cell division

meiosis

> cell division to form germ cells

> 4 haploid gametes are formed

10
Q

sex chromosomes men vs women

problem in men?

A

women: each chromosome has a fully homologous partner

> 22 autosomal pairs

> 2 x chr

men problem:

> X and Y are diferent

> they do pair however during prophase 1, due to short regions of homology between X and Y

11
Q

chr Y, how many base pairs?

how much of total DNA?

how many genes?

how many proteins?

A

chr Y

> 58 million bp

> 0.38% of total DNA

> 86 genes

> 23 distinct proteins

12
Q

what does gene SRY do?

A

gene SRY

> triggers testis development, determines sex

13
Q

chr Y cannot do what?

> exeption?

> implications?

A

chr Y cannot recombine with X

> exeption: short homologous regions

> rest are non-recombining regions

> SNPS in non recombining regions are used for tracing direct paternal ancestral lines

14
Q

what is X-inactivation?

why does it happen?

A

X-activation is a special form of imprinting

> one of the female X chr is silenced in every cell

> about 12 days after conception, half of female cells express paternal X and half maternal X -> genetic mosaics

> choice which X is random, but permanent

why:

> so females do not have twice as many X chr gene products as males (dosage compensation)

15
Q

how many basepairs in entire human genome?

A

entire genome:

> 3.146 billion bp

16
Q

what is a karyogram?

A

karyogram:

> set of chromosomes of an organism (banded appereance)

17
Q

what is a critical characteristics of heterochromatin?

A

in heterochromatin, transcription is limited

18
Q

what is the difference between

consitutional and somatic chromosomal abnormalities?

A

consitutional

> present in all cells of the body

> results of abnormal sperm or egg

somatic (acquired)

> present in only certain cells or tissues of an individual (mosaic)

19
Q

what are 2 categories of chromosomal abnormailites?

A

A. copy number is altered

B. structure of chromosome is abnormal

20
Q

what are 3 classes of numerical abnormalites?

A

numerical abnormalites

  1. polyploidy: more than two paired homologous sets of chromosomes
  2. aneuploidy: abnormal number of chr, e.g. 45/47 when 46 expected
  3. mixoploidy: two or more genetically different cell lineages within one individual

> from same zygote: mosaicism

> different zygotes: chimerism

21
Q

what is nondisjunction?

during

  1. meiosis I
  2. meiosis II/mitosis
A

nondisjunction:

meiosis I: failure of paired chr to separate

meoisis II/mitosis: failure of sister chromatids to disjoin

22
Q

consequences of nondisjunction

> during meiosis

> during mitosis

A

nondisjunction

meiosis: produces trisomic/monosomic individual
mitosis: produces a mosaic individual

23
Q

what is ploidy?

what are the general consequences of any ploidy higher than diploid?

A

almost any ploidy (extra copies of all chr) higher dan diploid results in early death in utero

24
Q

what is trisomy?

in which chr (partly) compatible with life?

A

trisomy: extra copy of a single chr

chr13/18/21

> 13/18 result in early death

> 21 result in down syndrome

25
Q

47, XXY: name?

45, X: name?

A

47, XXY: Kleinfelter syndrome

> trisomy of sex chr (at least one extra X)

45, X: Turner syndrome

> monosomic, one X is missing

26
Q

how do abnormalities in chromosomal structure develop?

A
  1. dmage to DNA due to radiation/chemicals etc
  2. errors in the recombination proces
27
Q

structural abnormalities

> 2 breaks in the same arm, consequences?

A

2 breaks in one arm

> deletion

> paracentric inversion (within arm)

28
Q

structural abnormalities

> breaks in 2 diff. arms, consequences?

A

breaks in 2 diff. arms

> join broken ends results in ring chr

> pericentric inversion (involving both centromere)

29
Q

what is reciprocal translocation?

A

reciprocal translocation

> exchange of fragments between two non-homologous chr

30
Q

robertsonian translocation

> which chr?

> results?

A

robertsonian translocation: centric and acentric fragments exchanges

> between chr 13,14,15,21,22 (acrocentric chr), short arm of those is very similar in DNA content

> result: 1 chr stable at mitosis

1 chr lost at mitosis

31
Q

result of translocation between chr 9 and chr 22?

association with cancer?

A

t(9;22)

  1. Der 9: chr9 longer than normal
  2. philadelphia: chr 22 shorter than normal

> creation of a fusion gene “bcr-abl”

> speeding up white blood cell divison

> philadelphia chr. is often found in leukemic cells of patients with chronic myelogenous leukemia

32
Q

what is chromosome condensation?

A

chromosome condensation

> long and fragile DNA strands resilient to breakage during cell division

> gene expression is impossible during this state

33
Q

what is a zygote?

A

zygote:

> first diploid cell, are cells are derived from this cell

34
Q

what is a spiral/solenoid arrangement?

A

spiral/solenoid:

> DNA is wrapped around nucleosomes, which are in turn wrapped in a spiral/solenoid structure

> 6-8 nucleosomes per turn

35
Q

which histone characteristics are associated with euchromatin DNA?

A

euchromatin

H1: weak binding

> extensive acetylation of all other histones

36
Q

what are two different types of heterochromatin?

A

consitutive heterochromatin

> repetative DNA, genetically inactive

facultative heterochromatin

> some times condensed - genetically inactive

> some times decondensed - genetically active

37
Q

in which phase of the cell cycle do the sister chromatids separate?

A

anaphase

38
Q

what are acentric chromosome fragments?

> what happens with those fragments during cell division?

> why?

A

acentric fragments: abnormal chromosome fragments that lack a centromere

> during cell division: those fragments cannot attach to the spindle and fail to be segregated correctly

39
Q

what happens with telomere length each life year?

A

telomere ~ 27bp shorter each year

40
Q

what are the 7 phases in a cell cycle

> what happens?

A
  1. interphase - normal cell activity
  2. prophase - centreoles form (first stage of mitosis)
  3. prometaphase - condensed chrom become attached to array of microtubules
  4. metaphase - chr aligned with mitotic spindle
  5. anaphase - sister chromatids separate
  6. telophase - nuclear envelope folds again, chr decondensate
  7. cytokinesis - final stage, two daughter cells produced
41
Q

why is meiosis called “reductive division”?

A

meiosis involves 2 cycles of cell division but only one cycle of DNA replication

42
Q

what is euploidy?

what is aneuploidy?

A

euploidy: having complete chromosome sets

> e.g. n, 2n, 3n etc.

aneuploidy: extra copies of single chrom.

43
Q

what are two general mechanisms that can lead to aneuploidy?

A
  1. nondisjunction
  2. anaphase lag

> chromosome/chromatid is delayed in movement during anaphase

44
Q

what happens with acentric/dicentric chrom. fragments during mitosis?

> are there exeptions?

A

acentric/dicentric chrom. fragments are typically unstable during cell division

> exeption: robertsonian translocation

45
Q

why are some chrom. fragments resulting from robertsonian translocation stable at cell division?

A

robertsonian translocation involved acrocentric chromosomes

> short arm of those chr. is very small and very similar in DNA content

> translocation results in two fragments

  1. acentric fragment which is lost in cell division
  2. dicentric fragment with two centromeres in close proximity which is stable at cell division