3.8.1 Alteration of the sequence of bases in DNA can alter the structure of proteins

Question 1

Mutation

Definition

Answer 1

-a permanent change in the base sequence of DNA

Question 2

Gene mutation

Definition

Answer 2

-any change to one or more nucleotide bases, or any rearrangement of the bases

Question 3

Types of gene mutation

Answer 3

• base substitution
• base deletion (frameshift)
• addition of bases (normally frameshift)
• duplication of bases (frameshift)
• inversion of bases
• translocation of bases (frameshift)

Question 4

Gene mutation
Base substitution
definition

Answer 4

• one or more nucleotides are replaced by another nucleotide

└therefore a base is also replaced

Question 5

Gene mutation
Base substitution
effect

Answer 5

Silent mutation
-no effect on polypeptide produced
└ genetic code is degenerate
└amino acids are coded for by more than one triplet, may produce same amino acid

Mis-sense mutation
-produces a single different amino acid
└could affect tertiary structure
└may form a non-functional polypeptide

Nonsense mutation
-produces a stop codon
└protein synthesis stopped prematurely
└produces different/non-functional polypeptide

Question 6

Gene mutation
Base substitution
example

Answer 6

-causes sickle cell anaemia

Question 7

Gene mutation
Base deletion
definition

Answer 7

• one or more nucleotides are lost

└so base is also lost

Question 8

Gene mutation
Base deletion
effect

Answer 8

-produces non-functional protein
└causes frame shift to the left
└(all bases shifted left by one letter)
└all triplets are read differently downstream from mutation
-big effect on phenotype
-bigger effect near start of sequence

Question 9

Gene mutation
Base addition
definition

Answer 9

-one or more nucleotides are added

└so base is also added

Question 10

Gene mutation
Base addition
effect

Answer 10

-produces a different polypeptide
└ if 3 bases ,or any multiple of 3 bases, are added
└= no frameshift
└if between 2 codons
└polypeptide differs in 2 amino acids
└(the codon that was pushed out of the reading frame, and the added codon)
└if within codons
└polypeptide differs by 2/3 amino acids
└(the codon that was pushed out of the reading frame, and the 2 affected codons, though one of which could still code for the same amino acid)

-produces a non-functional polypeptide
└causes frameshift to right
└(all bases shifted to right by one letter)
└all triplets are read differently downstream from mutation.
└big effect on phenotype

Question 11

Gene mutation
Base duplication
Definition

Answer 11

-one or more nucleotides is repeated

└so one or more bases is repeated

Question 12

Gene mutation
Base duplication
effect

Answer 12

-produces a non-functional polypeptide
└causes frameshift to right
└(all bases shifted to right by one letter)
└all triplets are read differently downstream from mutation

Question 13

Gene mutation
Base inversion
definition

Answer 13

• a group of bases becomes separated from DNA

- rejoin at same position but in inverse order

Question 14

Gene mutation
Base inversion
effect

Answer 14

• produces a different polypeptide

└affects all codons that were inverted

Question 15

Gene mutation
Base translocation
definition

Answer 15

-a group of bases becomes separated from dna

└inserted into a different chromosome.

Question 16

Gene mutation
Base translocation
effect

Answer 16

• causes frameshift

- big effect on phenotype

Question 17

Gene mutation
Base translocation
Example

Answer 17

• can develop certain forms of cancer

- reduced fertility

Question 18

Causes of mutations

When they occur

Answer 18

• spontaneously during DNA replication
• during meiosis
• during transcription
• as a result of mutagens

Question 19

Spontaneous mutations

Definition

Answer 19

-mutations that occur in the DNA without any outside influence

Question 20

Mutagenic agent

Definition

Answer 20

-man-made agent (physical/chemical)

└which can alter the base sequence of DNA

Question 21

Mutagenic agent

Function

Answer 21

-increase the rate of mutation

Question 22

Mutagenic agent

Examples

Answer 22

-high energy ionising radiation
└ e.g. x-rays and UV light (short wavelength)
└ e.g. α and β particles

-chemicals
└that directly alter DNA structure or interfere w/transcription.
└e.g. nitrogen dioxide

Question 23

Which mutations do not affect the order of amino acids?

Answer 23

Substitution and inversion

Question 24

EQ: Mutation 1 leads to the production of a non-functional protein. Explain why.
(Single base deletion in the first exon )

Answer 24

-mutation changes triplets/codons after that point
  └causes frame shift
-changes amino acid sequence 
  └=codes for different amino acids 
-affects hydrogen/ionic/sulfur bond 
└=changes tertiary structure of protein 
  └=so nonfunctional

Question 25

EQ: What effect might mutation 2 have on the protein produced? Explain your answer.
(single base substitution in the intron)

Answer 25

-introns are non-coding
-so are not translated
└=no effect on amino acid sequence

Question 26

Not all mutations result in a change to the amino acid sequence of the encoded polypeptide. Explain why

Answer 26

• genetic code is degenerate

- the mutation could occur in an intron

Question 27

Types of mutations that affect the order of amino acids

Answer 27

addition, duplication and deletion

Question 28

Frameshift mutation

Definition

Answer 28

-a mutation that involves the insertion or deletion of a nucleotide in the DNA sequence

Question 29

How changing the sequence of DNA nucleotides could affect the final product the DNA codes for

Answer 29

How changing the sequence of DNA nucleotides could affect the final product the DNA codes for Different sequence of amino acids / primary structure
└=different tertiary structure
└=product is non-functional

Question 30

Benefits of mutations

Answer 30

-produce the genetic diversity

└necessary for natural selection and speciation

Question 31

Dangers of mutations

Answer 31

-can trigger disruption of normal cellular activities