Topic 2: Mutations

Question 1

Mutations happen {randomly/spontaneously} by _______.

There are many lifestyle factors which can increase the risk of a mutation taking place.

Examples:
Ionising radiation (like UV)
Carcinogens in tobacco smoke

Answer 1

chance

Question 2

Key Summary: Define mutation

1 point

Answer 2

1. A CHANGE IN THE BASE SEQUENCE of DNA

Question 3

Key Summary: Define gene mutation

1 point

Answer 3

1. A change in the base sequence of the DNA IN A GENE which codes for a protein

Question 4

During semi-conservative DNA replication, errors can be made when DNA is copied.

Explain how these errors can occur (1 point)

Answer 4

1. As mononucleotides line up along both template strands, the wrong nucleotide base may complementary base pair with a nucleotide in the template

Question 5

Any change in the base sequence of DNA is a _________.

Answer 5

mutation

Question 6

What are the 3 types of gene mutations?

Answer 6

1. Base substitution (the correct {base/bases} may be substituted for incorrect {one/ones})
   eg. ACTATC could be changed to AGTATC
2. Base deletion (a base is missed out)
   eg. ACTATC changes to ATATC
3. Base insertion (an extra base is added)
   eg. ACTATC changes to AACTATC

Question 7

________ and ________ mutations (apart from multiples of 3 bases) tend to have a huge effect on the ______ made from the gene as they cause a _______ ______ – all {triplets/codons/amino acids} after mutation are changed.

Answer 7

Addition

deletion

protein

frame shift

Question 8

Substitution mutations which change only one amino acid may have ____ of an effect - unless the changed amino
acid was involved in _______ or the mutation leads to a _____ ______ being created.

If one base is substituted this may change one {triplet/codon/amino acid}, but not the ones that _________.

Answer 8

less

bonding

stop codon

follow

Question 9

Due to the genetic code being ___________, a substitution usually has _____ of an effect if it changes the ____ ____ in a DNA triplet (but more of an effect if it changes the first base in a triplet).

Answer 9

degenerate

less

last base

Question 10

Some mutations DO NOT change proteins because…

3 points

Answer 10

1. When the mutated DNA triplet is transcribed to form an mRNA codon, the codon may still code for the SAME amino acid, due to the DEGENERATIVE NATURE OF THE GENETIC CODE.
2. If the amino acid sequence of the polypeptide (primary structure) is changed, this may not affect the {bonding/folding} of the protein into its functional 3D shape.
3. Mutations in {non-coding DNA/‘junk’ DNA/DNA INTRONS} are not in genes, so no proteins are made from this DNA

Question 11

Some mutations DO change proteins because…

3 points

Answer 11

1. Mutations are in genes which direct the synthesis of proteins

2 (this point is important). When the mutated DNA triplet is transcribed to form an mRNA codon, the codon may code for a different amino acid which may be involved in bonding and folding (affects 3D shape), an enzyme active site, a binding site (eg. for ATP)

3. the mutated DNA triplet may change a start or stop codon, which results in no protein or a {shorter/longer} polypeptide.

Question 12

Key Summary: How does a substitution mutation affect the protein?
(4 points)

Answer 12

1. Substitution mutations only usually change {ONE DNA triplet /ONE mRNA codon}
2. and this new codon may code for the same amino acid, due to the DEGENERATE NATURE OF THE GENETIC CODE, so the amino acid sequence may not change, especially if 3rd base.
3. If one amino acid does change it still may not have an effect on the protein as it may not {be involved in/affect} bonding or folding.
4. Number of amino acids remains the same.

Question 13

Key Summary: How does a {deletion/insertion} mutation affect the protein?
(4 points)

Answer 13

1. Deletion and insertion mutations may change {every DNA triplet/every mRNA codon} which follows the mutation due to a FRAMESHIFT
2. so will result in a different sequence of amino acids in the primary structure and a DIFFERENT NON-FUNCTIONAL PROTEIN BEING PRODUCED.
3. The position of a stop codon is also likely to change or a stop codon may be created, which may result in a shorter polypeptide chain and a non-functional protein.

Question 14

Key Summary: How does a gene mutation affect a protein?

8 steps

Answer 14

1. gene mutation is a change in the base sequence of DNA in a gene
2. changes mRNA codon(s)
3. {{different/wrong/no amino acid} included/stop codon created}
4. different sequence of amino acids/primary structure
5. different R groups
6. changed bonding between R groups in {protein/named bond}
7. protein forms different {secondary/tertiary/quaternary} structure (as appropriate for given protein)
8. {different/incorrect} 3D SHAPE so cannot function – then state function that cannot be carried out – read question

Question 15

The CF gene (which codes for the CFTR protein) is a section of DNA found on __________ ___.

Hundreds of different mutations of the CF gene have been identified, which give rise to cystic fibrosis.

Answer 15

chromosome 7

Question 16

How can mutations affect the CFTR protein?

3 different ways

Answer 16

1. CFTR protein is not made at all
2. CFTR protein is {mis-folded/incorrect shape}, so does not function properly (eg. faulty opening/ATP binding site not present)
3. Shortened {polypeptide/protein} produced ( Possible reason – mutation produces a stop codon earlier in mRNA)

NOTE: These mutations are passed on to offspring (CF is an inherited disease)

Question 17

In a mutation, the CFTR protein is not made at all

State the 3 possible reasons why

Answer 17

1. Base insertion or deletion changes the sequence of bases so all DNA triplets that follow are changed (frameshift), so a different protein would be made (so no CFTR protein)
2. Due to base insertion or deletion, start codon could be different – ribosome cannot attach to mRNA – no CFTR protein made
3. Due to base insertion or deletion, stop codon could be created earlier in mRNA, so shorter polypeptide chain – no CFTR protein made

Question 18

In a mutation, the CFTR protein is misfolded, so does not function properly (eg. {faulty opening/ATP binding side not present})
State the possible reasons why (6 steps)

Answer 18

1. Due to base substitution there is a change in the DNA base sequence for one triplet, OR due to base deletion of 3 bases a triplet is not present
2. This {changes/removes} one amino acid in the sequence
3. So there is a {changed/missing} R group, so different bonding
4. This causes a mis-folding which changes the 3D shape of the CFTR protein
5. Due to this, if ATP can’t bind then channel may not open,
6. so chloride ions do not (or less of them) pass through channel protein

Question 19

In a mutation, a shortened CFTR protein was produced

State 1 possible reason why

State 2 possible effects of this mutation

Answer 19

1. Insertion/deletion/substitution mutation produces a stop codon earlier in the DNA than it should appear
2. CFTR protein is made in smaller quantities than normal
3. CFTR protein breaks down quickly after it is made

Question 20

Channel protein could be the incorrect _____, so cannot function or has a reduced function – so cannot transport ______ ions or cannot transport as many ions.

Answer 20

shape

chloride

Question 21

Mutation in DNA – causes non-functional CFTR protein,

So ________ ions cannot be transported, so mucus thickness cannot be regulated – this causes ________ mucus

________ mucus blocks lung bronchioles, pancreatic duct, cervix, sperm ducts

Therefore, impairing the function of:

1. the _________ system (poor digestion and absorption),
2. ________ system (poor gas exchange, lung damage and recurring lung infections)
3. and _________ systems (reduced chance of pregnancy)

Answer 21

chloride

thicker

thicker

digestive

respiratory

reproductive

Question 22

Germ line mutations occur in cells of the _____ or ______ which form ovum or sperm.

Mutation is passed on to future ___________ (present in every cell produced from the zygote)

Answer 22

ovary

testes

generations

Question 23

Somatic mutations occur in _______ _____ after _________ (zygote onwards) and may cause a problem for the individual.

NOTE: Some mutations have no effect on the individual eg. neutral mutations (extra finger)

Mutation is NOT passed on to future ___________.

Answer 23

somatic (body) cells

conception

generations

Question 24

There can also be mistakes made during transcription of protein synthesis (NOT MUTATIONS):

1. _____ is made with one or more incorrect codons
2. faulty _______ or no _______ produced
3. as the mistake is in the _____, it would ONLY affect the proteins produced from that one faulty _____ molecule, in that cell, at that time
4. The next time ______ is made, the base sequence should be correct.

Answer 24

mRNA

protein or no protein

mRNA

mRNA

mRNA