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FBS1 > Cellular Genetics and Cell Cycle > Flashcards

Cellular Genetics and Cell Cycle Flashcards

1
Q

What are examples of monogenic disorders?

A

Cystic fibrosis, sickle cell anemia

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2
Q

What are examples of polygenic disorders?

A

type II diabetes, rheumatoid arthritis, schizophrenia

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3
Q

What is the function of herceptin?

A

Block HER2 receptors in tumors that overexpress it

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4
Q

What is cytogenetics?

A

the study of the genetic components of a cell through the visualisation and analysis of chromosomes

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5
Q

In which categories does the location of the centromere organise chromosomes?

A

metacentric, submetacentric, acrocentric

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6
Q

What is the structure of a Y chromosome?

A 
Pseudoautosomal regions (PARs) at both ends
Male specific region (MSY): contains sex determining region of Y (SRY)
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7
Q

What does SRY encode?

A

A protein that acts as a testis determining factor (TDF)

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8
Q

What are trisomy 21, 13, 18

A

Trisomy 21: Down syndrome
Trisomy 13: Patau syndrome
Trisomy 18: Edward’s syndrome

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9
Q

Which syndrome is XXY, X and XYY?

A

XXY: Klinefelter’s syndrome (infertility)
X: Turner’s syndrome (monosomy), infertility, short stature and amenorrhea
XYY: asymptomatic

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10
Q

What causes aneuploidy?

A

Non-disjunction: failure of homologous chromosomes to separate properly during meiosis

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11
Q

What is the timeline of oogenesis?

A

Before birth: oogonium undergoes mitosis to become primary oocyte arrested in prophase I
After birth: meiosis continues and secondary oocyte is arrested in metaphase II
After fertilization: meiosis II is completed

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12
Q

What type of disorder is cystic fibrosis?

A

Autosomal recessive; CFTR on chromosome 7

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13
Q

What defines pedigrees of autosomal recessive diseases?

A

Trait is rare, often skips generations, affects females and males equally, transmitted by either sex

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14
Q

What type of disorder is Huntington’s?

A

Autosomal dominant, HD locus has > 36 repeats of CAG codon as compared to 28

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15
Q

What defines pedigrees of autosomal dominant diseases?

A

trait is frequent, in each generation, males and females are affected equally, transmitted by either sex

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16
Q

What type of disorder is haemophilia A?

A

X-linked recessive, mutation of gene for blood clotting factor VIII on X chromosome

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17
Q

What defines pedigrees of X-linked recessive diseases?

A

Usually affects males, cannot be passed from father to son, all daughters of affected fathers are carriers, half the sons of a carrier will be affected and half her daughters will be carriers.

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18
Q

What are multifactorial traits?

A

Polygenic and influenced by the environment (cardiovascular diseases, obesity, diabetes mellitus, mental illness)

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19
Q

Which nucleic acids are purines and which are pyrimidines?

A

Purines: G, A
Pyrimidines: C, T

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20
Q

What are the side groups of nucleic acids?

A

Amine, methyl or carbonyl

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21
Q

What is a nucleoside?

A

Sugar + base

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22
Q

What bonds are present in DNA?

A

Phosphodiester bonds

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23
Q

In which direction does DNA replication occur?

A

5’ to 3’ end

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24
Q

How many nucleotides are needed for one turn of DNA, and what is the diameter of the helix?

A

10; 2 nm

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25
Q

What is the composition of protein coding genes in the human genome?

A

1.1%

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26
Q

What are transposon based repeats?

A

Retrotransposable elements; move to randomly selected new location through mechanism involving RNA intermediate.
LINEs (e.g. haemophilia) and SINEs

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27
Q

What is heterochromatin?

A

satellite DNA, transcriptionally inactive, composed of long arrays of high copy number tandemly repeated sequences –> genetic fingerprint

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28
Q

What are message processing non-coding RNAs?

A

Small nuclear RNAs (snRNAs); forms complex with protein –> small ribonucleoprotein particles (snRNPs) required for splicing of pre-mRNAs

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29
Q

What is decoding RNA?

A

rRNA and tRNA

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30
Q

What is Xist?

A

Long non-coding RNA that controls mammalian X inactivation

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31
Q

What are miRNA

A

micro RNA; control gene expression
hairpin stem-loop precursor of miRNA –> exported to cytoplasm and processed by nucleases –> translational repression and deadenylation (mRNA instability)

32
Q

What does mtDNA encode?

A

13 polypeptides + rRNA and tRNA

33
Q

What are examples of mitochondrial cytopathies?

A

MELAS: myopathy, encephalopathy, lactic acidosis, stroke-like episodes
LHON: leber’s hereditary optic neuropathy

34
Q

How does DNA replication happen?

A

DNA helix is unwound by helicase;
single strand binding proteins prevent re-formation;
topoisomerase breaks phosphodiester bond ahead of replication fork to allow freedom of movement;
DNA polymerase synthesises new strand in 5’ to 3’ direction from existing RNA primer synthesised by primase (RNA polymerase)
*Lagging strand: exonuclease degrades primer, DNA polymerase continues synthesis, DNA ligase forms last phosphodiester bond between okazaki fragments

35
Q

What is the distance between origins of replications in humans

A

around 150 kb

36
Q

What are telomeres and how are they formed?

A

hundreds of copies of 5’ TTAGGG 3’

Formed by telomerase (carries its own template, a stretch of RNA)

37
Q

What are the different types of mutations?

A

Point mutations: silent, missense, nonsense
Indels: CFTR (multiple of 3), HD
Inversions
Deletions: cri du chat (chromosome 5)
Duplications
Translocations: chronic myelogenous leukemia (pieces on chromosome 9 and 22 swap)

38
Q

How do mutations appear in the genome?

A

SPONTANEOUS:
Errors in DNA replication
Replication slippage: reverse or forward
Deamination
INDUCED MUTATIONS:
Physical: ionising radiation (DNA single or double strand breaks), UV light (UV-B, thymine dimers)
Chemical: nitrous acid, alkylating agents, free radicals

39
Q

How is DNA damage repaired?

A

Direct repair: dealkylation enzymes

Removal of damaged region followed by re-synthesis: nucleotide excision repair (NER)

40
Q

What are the three steps of transcription?

A

Initiation, elongation and termination

41
Q

How does transcription in prokaryotes occur?

A

initiation: sigma factor binds to prinbow box (TATA box) and guides RNA polymerase to transcription start site
elongation: 5’ UTR region, protein coding region, 3’ UTR region
termination: reaching of transcriptional termination site (GC rich stem loop + AU weak pairing)

42
Q

What are the types of mRNA processing in eukaryotes?

A

Splicing
Capping: formation of 7-methylguanosine cap at 5’ end
Adenylation: addition of adenosine tail to 3’ end of RNA

43
Q

What are the functions of RNA polymerase I, II and III?

A

polymerase I: rRNAs (long)
polymerase II: mRNAs and microRNAs
polymerase III: rRNA (5S) and tRNA

44
Q

When is transcription of chromatin possible?

A

active open chromatin, unmethylated cytosines, acetylated histones

45
Q

What is Rett syndrome?

A

X-linked dominant; mutation in methyl CpG binding protein 2 –> responsible for silencing gene expression especially in neurons

46
Q

What is the structure of tRNA?

A

75-90 nucleotides; CCA-OH sequence at 3’ end; anticodon on central loop, wobble mechanism of pairing;
aminoacyl-tRNA-synthetases load tRNA molecules with amino acids (require ATP)

47
Q

What are the components of prokaryotic ribosomes?

A 
70S complex:
Large subunit (50S): 23S rRNA + 5S rRNA + 34 proteins
Small subunit (30S): 16S rRNA + 21 proteins
48
Q

What is the initiation step of translation in prokaryotes?

A

formation of initiation complex comprising ribosome, mRNA and initiator tRNA (met); IF1,2,3 are required; IF2 is activated by binding to GTP

  1. 30S subunit binds to IF1, 3 and mRNA
  2. fmet-tRNA binds GTP-IF2 and enters P site of 30S
  3. Alignment of anticodon with mRNA codon
  4. Large subunit binds and releases GDP + Pi
    * Shine-dalgarno sequence ensures in-frame translation
49
Q

What is the elongation step of translation in prokaryotes?

A
  1. aminoacyl-tRNA binds to EF-Tu-GTP and enters A site
  2. proof reading through GTP hydrolysis
  3. peptidyl-transferase forms dipeptidyl-tRNA
  4. translocation through Ef-G-GTP hydrolysis
  5. release of discharged tRNA
50
Q

What is the termination step of translation in prokaryotes?

A
  1. Stop codon presented to A site
  2. release factor (RF1, 2) binds
  3. hydrolysis of protein from tRNA
  4. ribosome disassembles, requires IF3, ribosomal recycling factor and GTP hydrolysis
51
Q

What are the components of eukaryotic ribosomes?

A

40S + 60S = 80S

52
Q

What are the differences between prokaryotic and eukaryotic translation?

A 
Eukaryotes:
interaction btw 5' cap and ribosome
initiator tRNA is met-tRNA
mRNA codes for one protein (non-polycistronic)
polyribosomes are free or bound
53
Q

Why can prokaryotic antibiotics be used without harming the eukaryotic host despite the interference with mitochondrial protein synthesis?

A

Few drugs can cross the inner mitochondrial membrane

Mitochondria have a very low rate of transcription

54
Q

Actinomycin

A

Binds to transcription initiation complex and prevents elongation by RNA polymerase

55
Q

Rifamycin

A

Inhibition of DNA-dependent RNA synthesis through binding to prokaryotic RNA polymerase

56
Q

Streptomycin

A

Affects initiation (30S) and causes misreading of codons

57
Q

Erythromycin

A

Binds to 50S subunit and prevents translocation

58
Q

Chloramphenicol

A

Inhibits peptidyl transferase by binding to 50S subunit

59
Q

Tetracyclines

A

Inhibit binding of aminoacyl-tRNAs to ribosome

60
Q

Puromycin

A

Premature chain termination during translation (pro and eu)

61
Q

alpha-aminitin

A

inhibitor of RNA polymerase II (pro and eu)

62
Q

Cycloheximide

A

inhibits protein biosynthesis in eukaryotes by interfering with translocation step

63
Q

Diphteria toxin

A

RNA translational inhibitor by inactivating eukaryotic elongation factor-2

64
Q

What are restriction enzymes?

A

Recognize specific nucleotide sequences in the DNA and cuts both strands of the sugar phosphate backbone
The sequence forms a palindrome
Cleavage leaves cohesive or blunt ends

65
Q

What is cDNA?

A

copy of an mRNA produced using reverse transcriptase

66
Q

How does DNA sequencing work?

A

DNA polymerase copies single stranded DNA using dideoxy nucleotides, gel electrophoresis is used to distinguish length, laser determines different fluorescence wavelengths

67
Q

How does PCR work?

A

Three steps: denaturation, primer annealing and extension (thermostable DNA polymerases: Taq or Pfu are used)
Thermocycler used to amplify: doubles each cycle (30 cycles will yield 2^30)

68
Q

What are DNA microarrays?

A

Use nucleic acid hybridisation to rapidly measure which genes are expressed in a tissue sample

69
Q

What are the types of genetic variations?

A

Single nucleotide polymorphisms, tandem repeat polymorphisms, structural variation (copy number variant, CNV; inversions)

70
Q

What are haplotypes?

A

Series of SNP alleles along a single chromosome

71
Q

What is meant by linkage disequilibrium?

A

SNPs in the same genetic region may be correlated –> knowing the allele at SNP1 gives information on allele at SNP2

72
Q

What is used in forensic investigations for identity matching?

A

Microsatellite DNA

73
Q

What are examples of diseases that involve tandem repeat polymorphisms?

A

Huntington disease

ALS: hexanucleotide repeat on chromosome 9

74
Q

What is heritability?

A

proportion of phenotypic variation that is due to genetic differences among individuals

75
Q

Define epigenetics

A

The study of heritable changes in gene expression that do not involve changes to the underlying DNA sequence

FBS1 (5 decks)

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