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principles of disease > chromosomes week 8 > Flashcards

chromosomes week 8 Flashcards

1
Q

what is euchromatin

A
  • open structure
  • active genes
  • the leg bits of chromosomes
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2
Q

what is heterochromatin

A
  • condensed structure
  • active genes
  • at ends and centre of chromosomes
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3
Q

what are telomeres

A

the bits at the end of chromosomes

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4
Q

what direction is DNA synthesised

A

5’ to 3’

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5
Q

what does DNA polymerase need to initiate DNA synthesis

A

RNA primer

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6
Q

what happens to the lagging strand in DNA replication

A

it is synthesised in fragments (Okazaki fragments) which are stitched together by ligase

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7
Q

why do telomeres get shorter as eukaryotes age

A

in the lagging strand the removal of the RNA primer causes a gap which is filled with repeats and is resynthisised by telomerase
- but telomerase is only expressed in certain cell types which is why telomeres shorten

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8
Q

what is the centromere

A
  • site of kinetochore which is the protein complex that binds to microtubules
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9
Q

what happens in S phase

A

DNA replication occurs

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10
Q

what percentage of our DNA is protein coding

A

2%

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11
Q

what are some extragenic sequences (non-coding)

A
  • tandomly repeated DNA sequences (satellite DNA and minisatellite DNA)
  • highly repeated interspersed DNA sequences (SINEs - short interspersed nuclear elements and LINEs - long)
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12
Q

what is a chromatin

A

DNA packaged with histone proteins forms chromatin

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13
Q

what charge do histone proteins have

A

positive charge

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14
Q

what are the unit packages in chromatins called

A

nucleosomes

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15
Q

what is at the core of the nucleosome

A

eight histone proteins collectively called octameric histone and DNA gets wrapped round this (146bp wrapped 1.8 turns)

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16
Q

what are the histone protein types in the octameric histone

A
  • histone H2A
  • histone H2B
  • histone 3
  • histone 4
    so two of each make the core
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17
Q

what does histone 1 do

A

binds to the base of the nucleosome and helps fix the DNA in place

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18
Q

what does the wrapping of nucleosomes form

A
  • solenoid strucure

- about 6 nucleosomes per turn

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19
Q

so what is each bit of the condensed chromatin structure

A
  1. nucleosome
  2. chromatin fibre
  3. fibre-scaffold complex
  4. chromosome
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20
Q

what is the purpose of packaging DNA

A
  • negatively charged DNA neutralised by positive charged histone proteins
  • DNA takes up less space
  • inactive DNA can be folded into inaccessible locations until required
  • inactive chromatin characterised by specific histone modification (e.g. methylation)
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21
Q

what is the shorter arm on a chromosome called

A

p or petite arm

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22
Q

what is the longer arm on a chromosome called

A

q arm

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23
Q

what is a metacentric chromosome

A

where centromere is close to being in the middle

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24
Q

what is a submetacentric chromosome

A

where centromere is displaced from centre

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25
Q

what is an acrocentric chromosome

A

the centromere is so far displaced that the petite arm contains no functional DNA

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26
Q

what is a karyotype

A

A karyotype is a preparation of the complete set of metaphase chromosomes sorted by length, centromere location and other features.

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27
Q

what is chromosome analysis

A
  • blood taken
  • remove red cells (no nucleus)
  • culture white cells
  • incubate
  • colchicine added (mitotic inhibitor)
  • separate off white cells
  • saline added
  • stain
  • photograph
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28
Q

what is fluorescent in situ hybridisation (FISH)

A

a more detailed way of looking at specific chromosome sequences
sequence of interest labelled with fluorescent dye

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29
Q

what is meiosis

A
  • cell division in germ cells
  • diploid cells (ovaries/testes) divide to form haploid cells
  • chromosome are passed on as re-arranged (recombined) copies
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30
Q

what is oogenesis

A

process of egg formation

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31
Q

what is spermatogenesis

A

process of sperm formation

32
Q

when does gametogenesis happen in males and females

A

females - early embryonic life cells arrive at meiosis 1 and then at puberty cells go through meiosis 2
males - puberty

33
Q

what is X inactivation

A

random inactivation of one X chromosome in females

34
Q

what are the different types of chromosomal abnormalities

A
  • numerical (wrong number)
  • structural (scale rearrangement that’s apparent from karyotype)
  • mutational (smaller scale - can range from small deletions to point mutations)
35
Q

what is the most common type of abnormality in first trimester miscarriages

A

trisomy (think tri=trimester)

36
Q

what is trisomy mutation

A

where there are three copies of a chromosome when there should only be two (so in total 47 chromosomes)

37
Q

what is monosomy X

A

there is only a single sex chromosome (so 45 chromosomes total)
- first trimester miscarriages

38
Q

what is triploidy mutation

A

where there are three whole copies of chromosomes (so 69 chromosomes)
- first trimester miscarriages

39
Q

what is tetraploidy mutation

A

there are four copies of chromosomes (so 92 total)

- first trimester miscarriages

40
Q

what are common chromosomal abnormalities in lovelorn infants

A
  • trisomy 13
  • trisomy 18
  • trisomy 21 (down’s)
  • 45 X
  • 47 XXY
  • 47 XYY
41
Q

what is trisomy 13

A

patua’s syndrome

- 47 XX

42
Q

what is trisomy 18

A

Edward’s syndrome

- 47 XY

43
Q

what is trisomy 21

A

Down’s syndrome

- 47 XX

44
Q

what is 47 XXY

A

Klinefelter

45
Q

what is monosomy 45X

A

turner

46
Q

what is an autosome

A

non-sex chromosome

47
Q

are sex chromosome abnormalities often from maternal or paternal origin

A

paternal

- 45X

48
Q

are autosomal abnormalities more often from maternal or paternal origin

A

maternal

- trisomy 21

49
Q

down’s syndrome

A
  • trisomy 21
  • 1 in 650
  • IQ can be less than 50
  • Alzheimer’s later in life
  • facial dysmorphologies
50
Q

patua syndrome

A
  • trisomy 13
  • 1 in 5000
  • multiple dysmorphic features and mental retardation
  • few survive beyond first year
51
Q

Edward’s syndrome

A
  • trisomy 18
  • 1 in 3000
  • severe developmental problems, most patients die within first year, many within first month
52
Q

turner syndrome

A
  • 45 X
  • 1 in 5000 to 1 in 10,000 (liveborn)
  • incidence at conception much greater but 97% result in spontaneous loss
  • female of short stature and infertile
  • neck webbing and wide spaced nipples
  • intelligence and lifespan normal
53
Q

klinefelter syndrome

A
  • 47 XXY
  • 1 in 1000
  • tall stature and long limbs
  • male but infertile
  • small testes
  • 50% gynaecomastia (man boobs)
  • mild learning difficulties
54
Q

what are the different types of structural abnormalities

A
  1. balanced or unbalanced rearrangements
  2. translocations (reciprocal or robertsonian)
  3. deletions
  4. insertions
  5. inversions
55
Q

what is a translocation mutation

A

where material is exchanged between two chromosomes

56
Q

what are the two types of translocation mutations

A
  1. reciprocal - involving breaks in two chromosomes, these broken segments swap and so info exchanged
  2. robertsonian - fusion of two Acrocentric chromosomes
57
Q

when is a reciprocal translocation said to be unbalanced

A

when there is additional DNA or DNA mission

  • so i.e. more from dad than mum when it should be equal
  • this can result in partial trisomy and partial monosomy in the same cell because only one and a half chromosomes from mum and two and a half from dad
58
Q

what happens in a robertsonian translocation

A
  • two Acrocentric chromosomes fuse
  • loss of short arms (which have no coding DNA anyway)
  • this can result in trisomy/monosomy
59
Q

who has a predisposition to having children with Down’s syndrome

A

individual with robertsonian translocation

60
Q

what is paracentric inversion

A

inversion of bit of chromosomal arm

61
Q

what is pericentric inversion

A

inversion of centromere

62
Q

what are some types of genetic mutations

A
  1. non-coding
  2. coding
    • silent - CGA (Arg) to CGC (Arg)
    • missense - CGA (Arg) to GGA (Gly)
    • nonsense - CGA (Arg) to TGA (stop)
    • frameshift (deletion/insertion)
63
Q

what is Cys64Arg

A

a cystine changed to an arginine at position 64

64
Q

what is M252X

A

methane 252 and X means stop codon

65
Q

what is 1294del40

A

amino acid 1294 deletion of 40

66
Q

what is 662-42C>T

A

the closest ending exon position is 662 and so 662-42 because it is 42 nucleotides before this

67
Q

what is IVS2+12insG

A

intervening sequence 2 so that will be the second intron in the +12 position within that intervening sequence and we have insertion of a G

68
Q

what techniques can you use to detect mutations

A
  • PCR
  • gel electrophoresis
  • restriction fragment length polymorphism (RFLP)
  • amplification refractory mutation system (ARMS)
  • DNA sequencing
69
Q

what do you need for PCR

A
  • sequence information
  • oligonucleotide primers
  • DNA
  • nucleotides
  • thermoresistant DNA polymerase
70
Q

what are the steps in PCR

A
  1. denature 93-95 degrees
  2. anneal (heat then cool) 50-70 degrees
  3. extend using DNA polymerase to add nucleotides
    70-75 degrees
71
Q

what is gel electrophoresis

A
  • separating DNA fragments by size by applying an electric field
  • you do this after PCR
72
Q

what is amplification refractory mutation system (ARMS)

A
  • type of PCR
  • if you use normal primer with normal nucleotide then DNA will be amplified with the help of a constitutive primer
  • if you use mutant primer with normal nucleotide no DNA amplification (e.g. A-G not work)
  • mutant primer with mutant nucleotide will work (e.g. A-T works)
73
Q

what are restriction endonucleases

A
  • enzymes from bacterial cells
  • protective mechanism
  • degrade DNA of invading viruses
  • recognise specific DNA sequences
  • usually recognises 4-8bp
  • always cuts DNA at same site
74
Q

what is RFLP analysis

A

so restriction enzyme can recognise and cut normal DNA but it cannot recognise mutant DNA
- simple and cheap

75
Q

what is DNA sequencing

A
  • chain termination method
  • use of dideoxynucleotides
  • there is a H group at the three prime position of the carbon ring instead of OH
  • expensive

principles of disease (19 decks)

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