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BIOL2202 Genetics > Module 1--Genes & Mutations > Flashcards

Module 1--Genes & Mutations Flashcards

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1
Q

What are the two levels of specificity that tRNA exhibit?

A

Aminoacyl-tRNA synthesise specificity (specify the correct amino acid to be added) and codon specificity (specify if the right tRNA is used during translation)

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2
Q

What are the interactions between codon and anticodon?

A

Hydrogen bonds

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3
Q

How are the abnormal bases in tRNAs created?

A

Post-transcriptional modification

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4
Q

What is the best-know abnormal base in tRNA?

A

Inosine

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5
Q

What bases does inosine forms hydrogen bonds with?

A

C, A and U, but not G

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6
Q

List the components of a cell-free protein synthesising system

A
  • amino acids + tRNA
  • ribosomes + ATP + GTP
  • amino acids
  • synthetic RNA
  • one 14C amino acid
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7
Q

What are the alternative start codons do prokaryotes use?

A

GUG and UUG (only at start)

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8
Q

In Candida species, what codon encodes serine instead of leucine?

A

CUG

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9
Q

According to Wobble Rules, what bases does U in 1st position in anticodon binds to?

A

A or G

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10
Q

According to Wobble Rules, what bases does G in 1st position in anticodon binds to?

A

U or C

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11
Q

According to Wobble Rules, what bases does I in 1st position in anticodon binds to?

A

U, C or A

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12
Q

What is RNA polymerase reading?

A

RNA polymerase creates an RNA molecule complementary to the template strand

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13
Q

What is reading frame?

A

Refers to the position at which you start reading nucleic acid in 3 nucleotide codons

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14
Q

What is open reading frame (ORF)?

A

A region in any reading frame that begins with a start codon (ATG) and ends with a stop codon

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15
Q

Why mutation is inevitable?

A

DNA is not totally chemically stable:

  • Spontaneous deamination of cytosine to uracil
  • Spontaneous hydrolysis of purines
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16
Q

What is spontaneous mutation?

A

It occurs due to inherent metabolic errors or unknown agents in environment

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17
Q

What is induced mutation?

A

It results from exposure of organisms to mutagens

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18
Q

What is germinal mutation?

A

It occurs in germ-line cells and will be transmitted through the gametes to the progeny

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19
Q

What is somatic mutation?

A

It occurs in somatic cells; the mutant phenotype will occur only in that cell and its direct descendent

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20
Q

Does environmental stress cause specific mutations?

A

No, environmental stress selects for mutants that are best adapted to the environmental stress; mutation does not occur in response to specific needs

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21
Q

What is stationary-phase mutagenesis?

A

A process that increases spontaneous mutation rate in a cell, potentially creating a mutant with a selective advantage in a certain environment

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22
Q

When does stationary-phase mutagenesis occur?

A

It occurs when populations of bacteria of fungi stop growing

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23
Q

What is a forward mutation?

A

A mutation of a wild-type allele to a mutant allele

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24
Q

What is a reverse mutation?

A

A second mutation that restores to the original phenotype

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25
Q

What is a back mutation?

A

A kind of reverse mutation with a second mutation at the same site

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26
Q

What is suppressor mutation?

A

A kind of reverse mutation when a second mutation at a different location in the genome overcomes the deleterious effect of the first mutation

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27
Q

What is isoallele?

A

It has no effect on phenotype or small effects that can be recognised only by special techniques

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28
Q

What is null allele?

A

It results in no gene product or totally nonfunctional gene products

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29
Q

What is neutral mutation?

A

It has no effect on phenotype and produces isoalleles

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30
Q

What is recessive lethal mutation?

A

It is lethal in homozygous state

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31
Q

What is conditional lethal mutation?

A

It is lethal in restrictive condition and viable in permissive condition

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32
Q

What is auxotroph?

A

Mutant organism that is unable to synthesise an essential metabolite that is synthesised by prototrophs, and can grow only when it is supplied in the medium

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33
Q

What is temperature-sensitive mutant?

A

It grows at one temperature but not at another

34
Q

What is suppressor-sensitive mutant?

A

It is viable only when a second genetic factor (a suppressor) is present

35
Q

What are the major classes of mutation?

A

Substitution, inversion, insertion and deletion

36
Q

What is silent mutation?

A

It does not change the gene product expressed by an organism

37
Q

What is synonymous mutation?

A

A kind of point mutation that causes change in codon, but no amino acid change

38
Q

What is non-synonymous, conservative substitution?

A

A kind of point mutation in which the new amino acid that has similar physical properties to the old one

39
Q

What is non-synonymous, non-conservative substitution?

A

A kind of point mutation in which the new amino acid that has very different physical properties to the old one

40
Q

Which amino acids are non-polar and aliphatic?

A

Glycine, Alanine, Proline, Valine, Leucine, Isoleucine, Methionine

41
Q

Which amino acids are polar and uncharged?

A

Serine, Threonine, Cysteine, Asparagine, Glutamine

42
Q

Which amino acids are aromatic?

A

Phenylalanine, Tyrosine, Tryptophan

43
Q

Which amino acids are positively charged?

A

Lysine, Arginine, Histidine

44
Q

Which amino acids are negatively charged?

A

Aspartate, Glutamate

45
Q

What is missense mutation?

A

Amino acid substitution leads to protein being defective

46
Q

What is nonsense mutation?

A

It creates a stop codon, prematurely ending the codon, often loss of function

47
Q

How tautomeric shifts affect base pairing?

A

A:C base pair and G:T base pair

48
Q

What are the types of substitution?

A
  • Transitions: pyrimidine pyrimidine; purine purine

- Transversions: pyrimidine purine

49
Q

What is the effect of nitrous acid?

A

Oxidative Deamination of bases

50
Q

What mutagenesis is caused by ultraviolet radiation?

A
  • Hydrolysis of cytosine may cause misfiring during replication
  • Cross-linking of adjacent thymine forms thymine dimers, which block DNA replication and activate error-prone DNA repair mechanism
51
Q

What can cause frameshift mutations?

A

Insertions or deletions in an ORF

52
Q

What are the effects of ionising radiation?

A

It breaks chromosomes and can cause deletions, duplications, inversions, and translocations

53
Q

What is the effect of hydroxylamine agent?

A

It hydroxylates the amino group of cytosine and leads to G:C –> A:T transitions

54
Q

What is the effect of alkylating agent?

A

It donates alkyl groups to other molecules, causing transitions, transversions, frameshift, and chromosome aberrations

55
Q

What are the two mechanisms of suppressor mutation occurs within the original codon?

A
  • Reversion to original amino acid

- Change to a different amino acid but with similar property

56
Q

What is intragenic suppressor mutation?

A

When a second mutation occurs within the same gene but in different codon

57
Q

What is intergenic suppressor mutation?

A

When a second mutation occurs in a different gene

58
Q

What is the mechanism of tRNA intergenic suppressor mutation?

A

First mutation in ORF is deleterious to bacterium; second (suppressor) mutation in anticodon region of a tRNA gene restores full ORF function

59
Q

What is amber mutation?

A

Tyr codon is converted to stop codon, UAC or UAU –> UAG (stop)

60
Q

What is ochre codon?

A

TAA

61
Q

What is opal codon?

A

TGA

62
Q

What is the Ames test?

A

It screen chemicals for mutagenicity with histidine auxotrophic mutants of Salmonella

63
Q

How can thymine dimers be removed?

A

By photoreactivation, a light dependent repair, or by postreplication repair

64
Q

What is the mechanism of photoreactivation?

A

Photolyase absorbs blue light for energy, cleaves thymine dimers restoring original state

65
Q

What is the function of a DNA repair endonuclease or endonuclease-containing complex?

A

It recognises, binds to, and excises the damaged base or bases

66
Q

What are the two kinds of excision repair?

A
  • Base excision repair: remove abnormal or chemically modified bases
  • Nucleotide excision repair: remove larger defects
67
Q

What is the general mechanism of excision repair?

A
  • DNA repair endonuclease or endonuclease containing complex recognises, binds to, and excises the damaged base or bases
  • DNA polymerase fills in the gap
  • DNA ligase seals the break left by DNA polymerase
68
Q

What is the mechanism of mismatch repair?

A
  • MutS recognises mismatches and binds to them to initiate the repair process
  • MutH and MutL join the complex
  • MutH cleaves the unmethylated strand at hemimethylated GATC sequences on either side of the mismatch
  • Excision require DNA helices II and an exonuclease
  • DNA polymerase III fills in the gap and DNA ligase seals the nick
69
Q

What is the mechanism of post replication repair?

A
  • DNA polymerase III restarts DNA synthesis past the dimer, leaving a gap in the nascent strand
  • RecA binds to the single strand of DNA at the gap and mediates base pairing
  • DNA polymerase fills the gap and DNA ligase seals the nick
70
Q

When is SOS response activated in E. coli?

A

When DNA is heavily damaged by mutagenic agents

71
Q

What is the mechanism of SOS response?

A
  • DNA polymerase V replicates DNA in damaged regions
  • LexA normally binds to and represses DNA regions that regulate transcription of SOS response genes
  • When extensive DNA damage occurs, RecA binds to single-stranded regions of DNA in damaged regions
  • This activates RecA, which stimulates LexA to inactivate itself, turning on SOS
72
Q

What is the Holliday Model?

A

1) Pairing of homologous chromosomes
2) Formation of single-strand breaks
3) Strand displacement
4) Strand exchange
5) Formation of covalent single-strand bridge
6) 3-D structure (chi structure)
7) Equivalent 3-D structure
8) Resolution of single-strand bridge
9) 2-D view
10) Recombinant chromosomes

73
Q

Garrod’s concept regarding the relationship between gene and metabolism can best be described as:

A

One gene - one metabolic block

74
Q

George W. Beadle and Edward L. Tatum refined the concept of the gene to state which original idea?

A

One gene - one enzyme

75
Q

What is the modern concept of the gene?

A
  • Gene controls synthesis of one polypeptide chain or RNA molecule
  • Nucleotide pair is the smallest unit that can be mutated; it cannot be subdivided by recombination
76
Q

What are the purposes of complementation test or trans test?

A
  • Provides an operational definition of the gene when used with recessive mutations
  • Determines whether mutations are in the same gene or different gene
77
Q

How is the complementation test constructed?

A
  • Geneticists construct trans heterozygotes:
  • If the trans heterozygote has a mutant phenotype, the two mutations are in the same gene
  • If the trans heterozygote has a wild-type phenotype, the two mutations are in different genes
78
Q

When the two mutations are on the same chromosome, the arrangement is called:

A

Coupling configuration and cis configuration

79
Q

When the two mutations are on different chromosome, the arrangement is called:

A

Coupling configuration and trans configuration

80
Q

What is complementation test?

A

Introduction of two recessive mutations into the same cell to determine whether they are alleles of the same gene

BIOL2202 Genetics (6 decks)

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