DNA, Mutations, Genes & Chromosomes 4.1

Question 1

What is a mutation? (1)

Answer 1

An alteration to the DNA base sequence
Arises spontaneously during DNA replication

Question 2

What are addition and deletion mutations? (1)

Answer 2

One or more nucleotides (bases) are inserted OR deleted from DNA base sequence

Question 3

What is a substitution mutation? (1)

Answer 3

Where one nucleotide base is replaced by another in DNA base sequence

Question 4

What is a duplication mutation? (1)

Answer 4

One or more nucleotides (bases) duplicate and repeat

Question 5

What is an inversion mutation? (1)

Answer 5

A group of nucleotide bases separate from the DNA sequence and rejoin in reverse order/are flipped

Question 6

What is a translocation mutation? (1)

Answer 6

A group of nucleotide bases separate from DNA sequence and are inserted into DNA on a different chromosome

Question 7

Which DNA base mutations are most likely to have a significant impact & why? (2)

Answer 7

Insertion, Deletion, Duplication, Translocation
- All produce a frameshift, entire amino acid sequence produced will be different

Question 8

Which mutations are most likely to have a smaller impact and why? (2)

Answer 8

Substitution and Inversion
- Only alter a few DNA triplets, so amino acid sequence may not be affected as degenerate (more than one codon/triplet for each amino acid)

Question 9

Is mutation resulting in a change to amino acid sequence always harmful? (2)

Answer 9

No; may be no change in protein produced /protein has little effect
May be beneficial - basis for evolution and natural selection

Question 10

What is a mutagenic agent? Give examples

Answer 10

Factors that increase the rate of gene mutation.

Ionising radiation = GAMMA, UV and X-RAY
Chemical mutagens = alcohol and benzene

Question 11

What are the three components of nucleic acids?

Answer 11

a pentose sugar, a phosphate group, an organic base

Question 12

Describe the structure of DNA

Answer 12

Deoxyribose sugar
Phosphate group
Organic bases (A-T, C-G)
- Double stranded
- Hydrogen bonds between bases form helix shape

Question 13

Describe the role of DNA (1)

Answer 13

Carries an organism’s genetic material, determines inherited characteristics

Question 14

Describe the structure of RNA

Answer 14

Single stranded
Ribose sugar
Phosphate group
Organic bases (A-URACIL, C-G)

Question 15

Describe the role of RNA (1)

Answer 15

Transfers genetic information from DNA to ribosomes for protein synthesis.

Question 16

Which bases are purine and which are pyrimidine?

Answer 16

Purine (double ring) = adenine + guanine
Pyrimidine (single ring) = cytosine + thymine/uracil

Question 17

What are the features of the genetic code? (3)

Answer 17

Non-overlapping = Each codon is only read once

Universal = same bases and sequences used by all species

Degenerate = more than one triplet codes for the same amino acid (64 combinations to 20 amino acids)

Question 18

What is a gene?

Answer 18

A sequence of bases on a DNA molecule that codes for a specific sequence of amino acids to make a polypeptide
(also codes for functional RNA)

Question 19

What is an allele?

Answer 19

Different versions of the same gene, found at the same locus of a chromosome (position of gene on DNA molecule)

Question 20

What are exons and introns?

Answer 20

Exons = Regions of DNA that code for amino acid sequences
Introns = Do not code for anything

Question 21

Where are introns found?

Answer 21

Between exons within genes