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MGD > Session 9 > Flashcards

Session 9 Flashcards

0
Q

What does a change in the amino acid primary sequence of a polypeptide result in?

A
  • Change is shape and function of the protein
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1
Q

What can a change in the genetic base sequence result in?

A
  • Different amino acids being coded for
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2
Q

What types of mutational changes are there?

A
  • Point mutations

- Insertions/deletions

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3
Q

What are point mutations?

A
  • Base substitutions

- Also called Single Nucleotide Polymorphisms (SNPs)

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5
Q

What types of point mutations are there?

A
  • Transition: Purine to purine, Pyrimidine to pyrimidine (more common)
  • Transversion: purine to Pyrimidine, pyrimidine to purine
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6
Q

What types of point mutations are there that occur in coding regions of a protein?

A
  • Silent mutation
  • Missense mutation
  • Nonsense mutation
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7
Q

Can point mutations in non-coding regions or outside genes have a detrimental effect?

A
  • Yes

- Can alter binding sites, promoter sequence, splice sites

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8
Q

What type of mutations can insertions/deletions cause?

A
  • Frameshift mutations
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9
Q

What is an insertion or deletion mutation?

A
  • A sequence is added or removed from the nucleic acid
  • It can be a single nucleotide (single base mutation), a few nucleotides (eg triplet repeats) or millions of nucleotides (eg tandem duplications)
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10
Q

What is a silent mutation?

A
  • A point mutation that occurs in a coding region
  • Does not alter the amino acid specified
  • Most usually a single-base change at the third codon position
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11
Q

What is a missense mutation?

A
  • Occurs in a point mutation in a coding region

- A mutation that replaces one amino acid with another

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12
Q

What is a nonsense mutation?

A
  • A type of point mutation in a coding region

- Mutation changes an amino acid to a stop codon

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13
Q

What is a frameshift mutation?

A
  • Caused by an insertion/deletion
  • Addition or subtraction if nucleotides not in multiple of three
  • Causes all subsequent triplet codes to shift causing the amino acids to change
  • Stop codons are commonly found in alternative reading frames and cause termination of translation prematurely (premature termination codon (PTC)
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14
Q

How do mutations occur? What are the the 2 main types?

A
  • Spontaneous mutations

- Induced mutations

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15
Q

How do spontaneous mutations occur?

A
  • Not caused by exposure to a known mutagen
  • Caused by errors in DNA replication as DNA bases have a slight chemical instability
  • Each individual has multiple new mutations and by chance most are not in the coding regions
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16
Q

What does the differing rate of spontaneous mutations for different genes depend on?

A
  • Size

- Sequence

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17
Q

What are induced mutations?

A
  • Chemicals and radiation can cause mutations
  • Chemicals that cause a mutation are called mutagens (are mutagenic)
  • Chemicals that cause cancer are called carcinogens (are carcinogenic)
18
Q

What are some examples of mutagens?

A
  • Alkylating agents: remove a base
  • Acridine agents: add of remove a base
  • X Rays: break chromosomes/delete a few nucleotides
  • UV radiation: creates thymidine diners
19
Q

Define mutation

A
  • A change in a nucleic acid sequence, which can be the addition of one or more (or many) nucleotides [insertion], the removal of one or more (or many) nucleotides [deletions], or the rearrangement of several (or many) nucleotides
20
Q

Define wild-type

A
  • An individual within a population displaying a wild-type trait, which is the trait that is the most common in that population
21
Q

What phenotype can a mutation cause?

A
  • Mutant phenotype

- A phenotype that differs from the common or wild type phenotype in the population

22
Q

What type of allele can a mutation in a gene cause?

A
  • Mutant allele

- Allele that differs from the common or wild type allele in the population

23
Q

What are mutations that occur in the germline?

A
  • Germline mutations

- Can be passed on to offspring

24
Q

How often do mutations occur and what is done about them?

A
  • Very frequently

- Are recognised and repaired very frequently too

25
Q

How are mutations repaired?

A
  • Mismatch repair

- Excision repair

26
Q

What is mismatch repair?

A
  • Occurs when enzymes detect nucleotides that don’t pair in newly replicated DNA (eg A-C)
  • Incorrect base is excised and replaced
  • Detection of mismatches is called proofreading
27
Q

What is excision repair?

A
  • Damaged DNA is removed by excision of bases and replacement by DNA polymerase
  • Nucleotide excision repair: replaces up to 30 bases and is used in repair of UV damage and some carcinogens
  • Base excision repair: replaces 1-5 bases and repairs oxidative damage
28
Q

What happens if DNA repair fails?

A
  • Increased number of mutations will be present in the genome
  • The protein p53 (guardian of the genome) monitors repair damaged DNA and if the damage is too severe it promotes apoptosis
29
Q

What happens if there are mutations in the genes encoding DNA repair proteins?

A
  • Can be inherited

- Overall increase in mutations as errors/DNA damage isn’t repaired efficiently

30
Q

How are cancerous cells produced?

A
  • If apoptosis of cells that have damaged DNA promoted by p53 protein doesn’t occur or
  • Damage leads to uncontrolled growth
31
Q

What are tumours?

A
  • Derived from individual abnormal cells
  • Arise from lack of normal growth control
  • Generated by a multistep process
  • More likely to arise from cell types undergoing frequent cell division
  • All the cells of a tumour are of the same type
  • Behaviour of the tumour depends on the cell type
32
Q

What are oncogenes?

A
  • Genes involved in the control of cell division
  • Present in normal cells
  • Many different classes
  • May stimulate or inhibit growth
33
Q

What are tumour suppressor genes?

A
  • Genes involved in protecting the cells against one step of the path to cancer
34
Q

What is the difference between proto-oncogenes and oncogenes?

A
  • Proto-oncogenes are genes normally present in cells

- Oncogenes are genes after the proto-oncogene undergoes mutation or increased expression

35
Q

What can carry copies of oncogenes?

A
  • Viruses

- Presence of a virus means that the gene doesn’t function as normal eg HPV

36
Q

Why is PCR useful in the diagnosis of genetic disease?

A
  • Most human mutations are single base changes and therefore are hard to detect
37
Q

What is missing in sickle cell disease and how is this found?

A
  • Restriction site for the enzyme MstII is destroyed (single base change)
  • In gel electrophoresis/southern blotting the mutated gene will have fewer/one DNA fragment(s) if digested with MstII as it lack the site (so the DNA fragment will not be cut into 2)
38
Q

What is lost in cystic fibrosis and how is this found?

A
  • 3 base deletion (no frameshift) so loss of phenylalanine

- PCR amplification and southern blotting

39
Q

When is southern blotting used?

A
  • When larger segments of DNA within and around a gene needs to be analysed
  • Used to analyse triplet repeat disorders eg Huntington’s disease, Fragile X syndrome
40
Q

What is Array Comparative Genomic Hybridisation (Array CGH) used?

A
  • Screen for sub-microscopic chromosomal deletions for which the locus cannot be deduced from the patient’s phenotype
41
Q

How is Array CGH carried out?

A
  • An array of DNA probes covering the entire genome is applied to the surface of a solid matrix
  • Patient DNA and normal control DNA are labelled with different coloured fluorescent tags
  • Equal amount of the labelled DNA are then hybridised to the probe array and the hybridisation signals are detected and compared
  • For probes where the signal of the normal DNA exceeds that of the patients DNA, the patient has a deletion of the chromosomal region from which that probe was derived
42
Q

What happens to mRNA with a PTC?

A
  • Degraded by nonsense mediated decay (NMD)
  • Protective mechanism
  • Little or no protein is produced

MGD (9 decks)

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