CK2: Genes and mutations Flashcards
How many genes are there in a fruit fly’s genome?
About 15,000
What causes an α-Wayne polypeptide to be five amino acids longer than an α-normal polypeptide?
A base deletion causing a frame shift
The stop codon is no longer in the frame
What are the two types of single base substitution? What is the difference between the two?
-
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)
Name a disease caused by fusion of chromosomes.
Leukaemia
What is the difference between inversion and translocation?
Inversion: when a part of a sequence is flipped
Translocation: when a part of a sequence is moved to another part of the gene
In which direction is mRNA synthesised during transcription?
5’ to 3’
How long is the β-chain of human haemoglobin?
146 amino acids
Why is the idea that ‘one gene codes for one polypeptide’ wrong?
Not all genes are expressed as protein — some are expressed as RNA they doesn’t code for protein, e.g. rRNA and tRNA
Define mutation
A heritable alteration in a gene or chromosome (i.e. a change in the sequence of nucleotides)
How many genes are there in the human genome?
About 25,000
Is heterochromatin tightly or loosely packaged?
Tightly packaged
How long is the α-chain of human haemoglobin?
141 amino acids
How can mutations change the amount of gene product?
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
How many chromosomes do humans have?
46
What does one gene code for?
(Hint: not one protein or one polypeptide)
One functional unit
(Either a sequence of amino acids in a polypeptide or a sequence of nucleotides in an untranslated RNA)
What are the three types of small-scale mutations?
Base substitutions
Base additions
Base deletions
What did Beadle and Tatum believe one gene coded for? Why is this wrong?
One protein
Wrong because haemoglobin is one protein but is coded for by two genes
In how many ways can a code be read?
Three — 0, +1, -1
What is the so-called ‘central dogma’?
DNA makes RNA makes protein
Define degenerate
More than one codon codes for an amino acid
What is the mutation that causes sickle cell anaemia?
Codon 7 of HBB (6th amino acid)
Base substitution mutation (missense)
Glu → Val
(GAG → GTG in DNA)
What are the three ways in which mutations can change the polypeptide chain length?
- Deletions and additions
- Chain-termination mutations (nonsense)
- Frameshift mutations
What is the genome?
The entire DNA sequence of an organism
What are the two types of large-scale mutation?
- Chromosome rearrangements
- Transposable element insertions
How can chain-termination mutations cause a change in the polypeptide chain length?
Changes a ‘sense’ codon into a nonsense (stop) codon
How would the symptoms of sickle cell anaemia differ for a physician, a cell biologist, and a biochemist?
Physician: susceptibility to infections, weakness, impaired growth, anaemia
Cell biologist: red blood cells ‘sickled’
Biochemist: Hb precipitates in low O2
What are them two types of transposable element insertions?
Movement of discrete DNA elements
Gene inactivation by insertion
Is euchromatin tightly or loosely packaged?
Loosely
What is another name for the non-overlapping triplet reading frame?
Commaless
(Code containing introns is said to ‘have commas’)
In which direction is DNA read during transcription?
3’ to 5’
When was the sequencing of the human genome completed?
2003
What are transposable elements?
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
Where are genes found?
On a chromosome at a specific location
What is an alternative definition of ‘mutation’ that is not commonly used?
The process that produces the alteration (the source of most alleles)
How many chromosomes are in the human genome?
24 — 22 autosomes plus 2 allosomes (X and Y)
How many genes are there in the genome of E. coli?
About 4,500
What are the genes that code for human haemoglobin‘s subunits? On which chromosomes are they found?
α-chain — HBA1 gene on chr 16
β-chain — HBB chain on chr 11
Define ‘genotype’
The genetic make-up
How much shorter/longer than normal haemoglobin is:
- Hb Leiden
- Hb Lyon
- Hb Gun-Hill?
Hb Leiden — β-chain 1aa shorter
Hb Lyon — β-chain 2aa shorter
Hb Gun-Hill — β-chain 5aa shorter
Are genes expressed in heterochromatin or euchromatin?
Euchromatin
What are the four types of chromosome rearrangements?
- Insertion
- Deletion
- Inversion
- Translocation
What are the four types of single nucleotide changes?
- Mutations that change gene products
- Mutations that change the amount of gene product
- Mutations that change the polypeptide length
- Mutations that have no effect
Define ‘phenotype’
The form/trait/characteristic that you can see
What are human haemoglobin‘s subunits?
α2β2
How many chromosome pairs do humans have?
23
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?
Both codons code for Glu so there is no change to the polypeptide
It is a silent/neutral mutation with no phenotypic change
In which direction is a polypeptide synthesised during translation?
N-terminus to C-terminus
In which direction is mRNA read during translation?
5’ to 3’
