topic 4 protien synthesis/variation/diversity

Question 1

Define the term exon {1}

Answer 1

. base sequence region of DNA coding for amino acid

Question 2

Desc how a gene is a code for the production of a polypeptide {3}

Answer 2

. base sequence
. (forming) triplets
. determines order of amino acid sequence/primary
structure of polypeptide

Question 3

Desc how a phosphodiester bond is formed betw 2 nucleotides {2}

Answer 3

. condensation reac, losing water
. betw phosphate and deoxyribose
.catalysed by DNA polymerase

Question 4

Define ‘non-coding base sequences’ & desc where non-coding
multiple repeats are positioned in the genome {2}

Answer 4

. DNA that does not code for polypeptides
. positioned between genes

Question 5

Not all mutations in nucleotide sequence of a gene cause change in structure of a polypeptide.

Give 2 reasons why {2}

Answer 5

. degenerate - triplets code for same amino acid
. mutations can occur in introns

Question 6

Compare & contrast the DNA in eukaryotic cells with the DNA in
prokaryotic cells {5}

Answer 6

. nucleotide structure is identical;
. nucleotides joined by phosdiester bond
. Eukaryotic DNA is longer;
. Eukaryotic DNA contain introns, prokaryotic DNA does not
. Eukaryotic DNA is linear, prokaryotic DNA is circular
. Eukaryotic DNA is associated with histones

Question 7

What is a homologous pair of chromosomes? {1}

Answer 7

. 2 chrmzn that carry same genes

Question 8

Desc 2 diff between the structure of tRNA & mRNA {2}

Answer 8

1. tRNA clover leaf shape, mRNA is linear
2. tRNA has hydrogen bonds, mRNA does not;
3. tRNA has an amino acid binding site, mRNA does not
4. tRNA has anticodon, mRNA has codon;

Question 9

Desc how 1 amino acid is added to a polypeptide thats being formed at a ribosome during translation {3}

Answer 9

. tRNA brings specific amino acid to ribosome
. Anticodon binds to codon
3. Amino acids join by condensation reaction usi

Question 10

Describe how a polypeptide is formed by translation of mRNA. {6}

Answer 10

. mRNA attaches to ribosomes on RER
. ribosome moves to find the start codon
. anticodons bind to complementary codons
. tRNA brings specific amino acid to mRNA
. Amino acids join by peptide bonds
. with the use of ATP
. tRNA released after amino acid joined to polypeptide
. The ribosome moves along the mRNA to form the polypeptide

Question 11

Give the 2 types of molecule from which a ribosome is made {1}

Answer 11

. rRNA
. polypeptide

Question 12

Define the term mutagenic agent {1}

Answer 12

. a factor that increases the rate of mutations

Question 13

Apart from mutation, explain one other way genetic variation within a
species is increased. {2}

Answer 13

. random fertilisation
. produces new allele combinations
OR
produces new maternal and paternal chromosome combinations;

Question 14

Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual
{4}

Answer 14

. Change in the base sequence of DNA
. Results in the formation of new allele;
(Has no effect because)
. genetic code is degenerate
. does change amino acid but no effect on tertiary structure;
. new allele is recessive so does not influence phenotype;
(Has positive effect because)
6. Results in change in polypeptide that positively changes properties of protein

Question 15

Give two differences between mitosis and meiosis {2}

Answer 15

. 1 division, two divisions in meiosis;
. daughter cells genetically identical,
daughter cells genetically different in
meiosis
. 2 cells produced, four cells produced in meiosis;
. diploid to diploid/haploid to haploid, diploid to haploid in
meiosis
. crossing over only in meiosis;
. independent segregation only in meiosis;

Question 16

Explain how the chromosome number is halved during meiosis {2}

Answer 16

. homologous chromosomes pair
. 1 of each pair goes to each daughter cell / to opposite
poles;

Question 17

Suggest why the scientist took his sample from the population at random {1}

Answer 17

. avoid bias

Question 18

Alcohol is toxic to fruit flies. Suggest and explain why the frequency of the ADF allele (allele that breaks down alcohol) increased after the 45 generations. {4}

Answer 18

. flies with ADF have selective advantage in presence of
alcohol
. so insects w ADF more likely to reproduce
. pass on ADF allele
. allele frequency increases;

Question 19

organism is identified by referring to species name & genus name.

What term is used to describe this method of naming organisms {1}

Answer 19

. binomial

Question 20

Explain how a hierachy of species in shown in a diagram {2}-

Answer 20

. large groups containing smaller groups
. With no overlap (between groups);

Question 21

Describe how breeding experiments could determine whether 2
populations are from the same species. {2}

Answer 21

. breed the two mice together
. same species produce fertile offspring.

Question 22

besides hunting, suggest 2 reasons why populations might show low levels of genetic diversity. {2}

Answer 22

. genetic bottleneck e.g natural disater
. founder effect; e.g migration f small group-amish
. Inbreeding

Question 23

Explain why its more useful to calculate index of diversity than species richness {2}

Answer 23

. also measures population of each species
. some species present in small numbers

Question 24

Suggest & explain 1 advantage & 1 disadvantage to farmer of replanting hedges on her farmland {2}

Answer 24

. adv- more biodiversity so theres more predators for pest
. dis- more pests so less yield

Question 25

Index of diversity of insects was higher in hedge than in barley field. Suggest why {3}

Answer 25

. more plant species
. more food sources
. more habitats