Protein synthesis and selection

Question 1

What is a mutation? (1)

Answer 1

Change to the DNA base sequence

Question 2

How and when do mutations occur? (2)

Answer 2

Randomly and spontaneously
During DNA replication

Question 3

Why might a mutation not lead to change in the amino acid sequence (2)

Answer 3

Genetic code is degenerate (mutation may end up coding for the same amino acid as the original triplet)
Mutation may occur in an intron

Question 4

What is a silent mutation?

Answer 4

Alters a base but does not change the amino acid coded for (the code is degenerate)

Question 5

What is a substitution mutation? (2)

Answer 5

One nucleotide takes place of another - usually leads to no change in the amino acid sequence

Question 6

What is an addition mutation? (1)

Answer 6

When one or more bases are added

Question 7

What is a deletion mutation? (2)

Answer 7

One nucleotide is removed from a gene or DNA sequence - harmful and significant because it leads to a frameshift which means the entire amino acid sequence will be different

Question 8

What does an addition/deletion mutation cause? (1)

Answer 8

Results in alteration of the base triplets from the mutation onwards and so is known as a frameshift

Question 9

How do mutations lead to non-functional proteins? (5)

Answer 9

Alter the primary structure of polypeptides
So alter the secondary structure and change the positions of the weak hydrogen bonds affecting alpha helixes and beta pleated sheets
Alter the tertiary structure (change positions of H-bonds, ionic bonds and disulphide)
Alter the binding site of proteins and make them non-functional

Question 10

What are mutations responsible for in the forces of natural selection and in speciation? (1)

Answer 10

Genetic diversity of populations

Question 11

What are mutagenic agents? (1)

Answer 11

Outside factors that increase the rate of spontaneous mutation

Question 12

Examples of mutagenic agents? (3)

Answer 12

High energy ionizing radiation (X-rays, UV light, gamma rays)
DNA reactive chemicals (benzene, hydrogen peroxide)
Biological agents such as some viruses and bacteria

Question 13

What is a chromosomal mutation and what does it cause? (2)

Answer 13

Mutations that produce changes in whole chromosomes
Causes chromosome non-disjunction

Question 14

What is chromosome non-disjunction? (2)

Answer 14

When chromosomes fail to separate correctly in meiosis, resulting in gametes with one more or less chromosome than normal.

Question 15

What is inversion mutation? (1)

Answer 15

When a segment of bases is reversed end to end

Question 16

What is duplication mutation? (2)

Answer 16

Doubling of a part of chromosome or of an entire chromosome or even the whole genome
When one or more bases are repeated

Question 17

What is translocation mutation? (1)

Answer 17

When groups of base pairs relocate from one area of the genome to another, usually between non-homologous chromosomes
Moves a segment from one chromosome to another, nonhomologous one

Question 18

What is a phenotype? (1)

Answer 18

The expression of the genetic constitution and its interaction with the environment

Question 19

What is a genotype? (1)

Answer 19

Genetic makeup of an organism (all the alleles an organism has)

Question 20

What is genetic diversity? (1)

Answer 20

The number of different alleles in a population

Question 21

What advantage does high genetic diversity provide? (2)

Answer 21

Ability to adapt to a change in environment
Allows natural selection to occur

Question 22

What are selection pressures? (1)

Answer 22

External agents which affect an organism’s ability to survive in a given environment

Question 23

Describe natural selection (6)

Answer 23

Variation due to mutation
Different environmental/selection pressures
Selection for advantageous allele
Differential reproductive success/(selected) organisms survive and reproduce
Leads to change in allelic frequency
Occurs over a long period of time

Question 24

When does stabilising selection occur? (1)

Answer 24

When environment is stable/the same

Question 25

What is stabilising selection? (2)

Answer 25

When the environment favours the average (most common characteristic - eliminates extremes)
Reduces diversity and reduces opportunity for evolutionary change

Question 26

What is directional selection and when does it occur? (2)

Answer 26

Favour an extreme phenotype
Occurs when environmental conditions change

Question 27

What does a mean in population represent? (1)

Answer 27

Optimum phenotype for existing conditions

Question 28

What is disruptive selection? (1)

Answer 28

Favours 2 extreme phenotypes

Question 29

What is evolution by natural selection? (1)

Answer 29

Change in allelic frequencies within a population

Question 30

What is the genome? (1)

Answer 30

Complete set of genetic information contained in the cell of an organism

Question 31

What is a proteome? (1)

Answer 31

Full range of proteins that a cell is able to produce

Question 32

What does loci mean? (1)

Answer 32

Position of a gene within the chromosome

Question 33

What is a gene? (1)

Answer 33

DNA base sequence coding for a single polypeptide

Question 34

What are exons and introns? (2)

Answer 34

Exons - sequence of nucleotides that code for the amino acid sequence
Introns - non-coding sequence of nucleotides

Question 35

Where are introns found? (1)

Answer 35

Between exons within genes

Question 36

Describe transcription (5)

Answer 36

DNA helicase breaks hydrogen bonds so that the strands separate
Only one strand acts as a template
RNA nucleotides attracted to exposed bases
Adenine - Uracil and Guanine - Cytosine
RNA polymerase joins adjacent nucleotides together forming phosphodiester bonds through condensation reaction
pre-mRNA spliced to remove introns

Question 37

Describe translation (8)

Answer 37

mRNA binds to ribosome
Ribosome finds the start codon
Only 2 codons can fit the ribosome at one time
tRNA with complementary anticodon binds to the codon on mRNA
tRNA brings a specific amino acid
Catalyses formation of peptide bonds between amino acids, held by tRNA, using energy from ATP
tRNA released as ribosomes move along
Ribosome releases polypeptide when the stop codon is reached

Question 38

What are ribosomes made of? (2)

Answer 38

rRNA and ribosomal proteins

Question 39

What is the genetic code? (2)

Answer 39

Order of bases on DNA
Consists of codons

Question 40

Identify and describe the features of the genetic code (3)

Answer 40

Non-overlapping - Each base is read once in a triplet
Degenerate - more than one triplet can code for the same amino acid
Universal - The same 3 bases on mRNA/DNA code for the same amino acids in all organisms

Question 41

What is a population? (1)

Answer 41

All the organisms of a particular species that live in the same habitat

Question 42

Give and explain an example of directional selection (3)

Answer 42

Antibiotic resistance
Bacteria with a mutation allowing them to survive in the presence of antibiotics will reproduce
Frequency of the allele will increase and the population will shift to have greater antibiotic resistance

Question 43

Give and explain an example of stabilising selection (2)

Answer 43

Birth weight
Babies that weigh around 3kg are more likely to survive than those at lower or higher weights

Question 44

Define a niche (1)

Answer 44

Role of a species within its environment
Species sharing the same niche will compete with each other

Question 45

What are the three types of adaptation and give an example of each (6)

Answer 45

Anatomical (changes to body structure) - oily fur
Physiological (changes to bodily processes) - venom production
Behavioural (changes to actions) - hibernation