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BS1050: Genes > CK2: Genes and mutations > Flashcards

CK2: Genes and mutations Flashcards

1
Q

How many genes are there in a fruit fly’s genome?

A

About 15,000

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2
Q

What causes an α-Wayne polypeptide to be five amino acids longer than an α-normal polypeptide?

A

A base deletion causing a frame shift

The stop codon is no longer in the frame

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3
Q

What are the two types of single base substitution? What is the difference between the two?

A
  • Transition = change to the same type of base
    • Purine to purine (A⇌G)
    • Pyrimidine to pyrimidine (T⇌C)
  • Transversion = change to a different type of base
    • Purine to pyrimidine or vice versa (A/G⇌C/T)
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4
Q

Name a disease caused by fusion of chromosomes.

A

Leukaemia

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5
Q

What is the difference between inversion and translocation?

A

Inversion: when a part of a sequence is flipped

Translocation: when a part of a sequence is moved to another part of the gene

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6
Q

In which direction is mRNA synthesised during transcription?

A

5’ to 3’

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7
Q

How long is the β-chain of human haemoglobin?

A

146 amino acids

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8
Q

Why is the idea that ‘one gene codes for one polypeptide’ wrong?

A

Not all genes are expressed as protein — some are expressed as RNA they doesn’t code for protein, e.g. rRNA and tRNA

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9
Q

Define mutation

A

A heritable alteration in a gene or chromosome (i.e. a change in the sequence of nucleotides)

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10
Q

How many genes are there in the human genome?

A

About 25,000

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11
Q

Is heterochromatin tightly or loosely packaged?

A

Tightly packaged

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12
Q

How long is the α-chain of human haemoglobin?

A

141 amino acids

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13
Q

How can mutations change the amount of gene product?

A

They can affect transcription or translation:

  • Alter promoter activity — specificity may change
  • Alter translation initiation at AUG
  • Prevent mRNA splicing
  • Reduce mRNA stability — 5’ or 3’ UTR
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14
Q

How many chromosomes do humans have?

A

46

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15
Q

What does one gene code for?

(Hint: not one protein or one polypeptide)

A

One functional unit

(Either a sequence of amino acids in a polypeptide or a sequence of nucleotides in an untranslated RNA)

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16
Q

What are the three types of small-scale mutations?

A

Base substitutions

Base additions

Base deletions

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17
Q

What did Beadle and Tatum believe one gene coded for? Why is this wrong?

A

One protein

Wrong because haemoglobin is one protein but is coded for by two genes

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18
Q

In how many ways can a code be read?

A

Three — 0, +1, -1

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19
Q

What is the so-called ‘central dogma’?

A

DNA makes RNA makes protein

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20
Q

Define degenerate

A

More than one codon codes for an amino acid

21
Q

What is the mutation that causes sickle cell anaemia?

A

Codon 7 of HBB (6th amino acid)

Base substitution mutation (missense)

Glu → Val
(GAG → GTG in DNA)

22
Q

What are the three ways in which mutations can change the polypeptide chain length?

A
  • Deletions and additions
  • Chain-termination mutations (nonsense)
  • Frameshift mutations
23
Q

What is the genome?

A

The entire DNA sequence of an organism

24
Q

What are the two types of large-scale mutation?

A
  • Chromosome rearrangements
  • Transposable element insertions
25
Q

How can chain-termination mutations cause a change in the polypeptide chain length?

A

Changes a ‘sense’ codon into a nonsense (stop) codon

26
Q

How would the symptoms of sickle cell anaemia differ for a physician, a cell biologist, and a biochemist?

A

Physician: susceptibility to infections, weakness, impaired growth, anaemia

Cell biologist: red blood cells ‘sickled’

Biochemist: Hb precipitates in low O2

27
Q

What are them two types of transposable element insertions?

A

Movement of discrete DNA elements

Gene inactivation by insertion

28
Q

Is euchromatin tightly or loosely packaged?

A

Loosely

29
Q

What is another name for the non-overlapping triplet reading frame?

A

Commaless

(Code containing introns is said to ‘have commas’)

30
Q

In which direction is DNA read during transcription?

A

3’ to 5’

31
Q

When was the sequencing of the human genome completed?

A

2003

32
Q

What are transposable elements?

A

Also known as ‘jumping genes’ and ‘transposons’

They are specific DNA sequences that transpose as a discrete unit to random sites

They can inactivate a gene by inserting themselves into it

33
Q

Where are genes found?

A

On a chromosome at a specific location

34
Q

What is an alternative definition of ‘mutation’ that is not commonly used?

A

The process that produces the alteration (the source of most alleles)

35
Q

How many chromosomes are in the human genome?

A

24 — 22 autosomes plus 2 allosomes (X and Y)

36
Q

How many genes are there in the genome of E. coli?

A

About 4,500

37
Q

What are the genes that code for human haemoglobin‘s subunits? On which chromosomes are they found?

A

α-chain — HBA1 gene on chr 16

β-chain — HBB chain on chr 11

38
Q

Define ‘genotype’

A

The genetic make-up

39
Q

How much shorter/longer than normal haemoglobin is:

  • Hb Leiden
  • Hb Lyon
  • Hb Gun-Hill?
A

Hb Leiden — β-chain 1aa shorter

Hb Lyon — β-chain 2aa shorter

Hb Gun-Hill — β-chain 5aa shorter

40
Q

Are genes expressed in heterochromatin or euchromatin?

A

Euchromatin

41
Q

What are the four types of chromosome rearrangements?

A
  • Insertion
  • Deletion
  • Inversion
  • Translocation
42
Q

What are the four types of single nucleotide changes?

A
  • Mutations that change gene products
  • Mutations that change the amount of gene product
  • Mutations that change the polypeptide length
  • Mutations that have no effect
43
Q

Define ‘phenotype’

A

The form/trait/characteristic that you can see

44
Q

What are human haemoglobin‘s subunits?

A

α2β2

45
Q

How many chromosome pairs do humans have?

A

23

46
Q

Why does the mutation GAG to GAA of codon 7 of human haemoglobin not cause a disease?

What is the name for this type of mutation?

A

Both codons code for Glu so there is no change to the polypeptide

It is a silent/neutral mutation with no phenotypic change

47
Q

In which direction is a polypeptide synthesised during translation?

A

N-terminus to C-terminus

48
Q

In which direction is mRNA read during translation?

A

5’ to 3’

BS1050: Genes (26 decks)

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