TOPIC 4 MARK SCHEME SHIT Flashcards
Suggest how the change in the anticodon of a tRNA leads to mitochondrial disease (3)
- Change to tRNA leads to wrong amino acid being incorporated into protein
- Tertiary structure changed
- Protein required for oxidative phosphorylation/Krebs cycle, so less/no ATP made
Describe how a gene is a code for the production of a polypeptide. DO NOT INCLUDE INFO ABOUT TRANSCRIPTION OR TRANSLATION (3)
- Base/nucleotide sequence
- (In) triplet(s)
- (Determines) order/sequence of amino acids/primary structure (in polypeptide)
Define an exon (1)
Base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure
NOTICE HOW “PROTEIN” ISN’T ALLOWED
Define ‘non-coding base sequences’ and describe where the non-coding multiple repeats are positioned in the genome (2)
- DNA that doesn’t code for protein/polypeptides/(sequences of) amino acids/tRNA/rRNA
- (Positioned) between genes
Give 2 reasons why not all mutations in the nucleotide sequence of a gene causes a change in the structure of a polypeptide (2)
- Triplets code for same amino acid
Accept: DNA/code/triplets are degenerate - Occurs in introns/non-coding sequence
Suggest how a mutation can lead to the production of a protein with one missing amino acid (2)
Loss of codon/3 bases/triplet
Describe how mRNA is produced in the nucleus of a cell
- Helicase
- Breaks hydrogen bonds
- Only one DNA strand acts as template
- RNA nucleotides attracted to exposed bases
- (Attraction) according to complementary base pair rule
- RNA polymerase joins (RNA) nucleotides together via phosphodiester bonds
- Pre-mRNA spliced to remove introns
Describe how a polypeptide is formed by translation of mRNA
- (mRNA attaches to) ribosomes/rough endoplasmic reticulum
- ribosome moves to start codon
- (tRNA) anticodons (bind to) complementary (mRNA) codons
- tRNA brings a specific amino acid
- Amino acids join by peptide bonds
- (Amino acids join together) using ATP
- tRNA released (after amino acid joined to polypeptide)
- The ribosome moves along the mRNA to form the polypeptide
Suggest why the scientist took his sample from the population at random (1)
- Avoids bias
- Results (likely to be) reliable/repeatable
Describe how to make a 1 in 10 dilution and then use this to make a 1 in 1000 dilution of the original liquid culture of bacteria (3)
- Add 1 part culture to 9 parts liquid
- Mix
- Repeat using 9 parts fresh liquid and 1 part of 10^-1 and 10^-2 dilutions to make 10^-3 dilution
Suggest why student decided not to use 1 in 10 dilution for determining the number of cells in the undiluted liquid culture (2)
- COUNT unlikely to be accurate/reproducible/repeatable/reliable
- Because too many cells/cells overlapping/not spread out
Suggest & explain one reason why bacteria resistant to A are more common than bacteria resistant to B in farm animals (2)
- A used more often/in higher doses
- Resistant bacteria more likely to pass on allele/gene for resistance
- More/higher frequency of mutations
- Gene passed on to more bacteria
- A used over longer time period
- More time for (chance) mutation to occur/for selection to occur
Explain what is meant by a hierarchy (2)
- Groups within groups
- No overlap
Explain what is meant by a phylogenetic group (1)
(Grouped according to) evolutionary links/history/relationships/common ancestry
Explain why having fewer differences in amino acid sequences compared with humans shows that it’s the most closely related to humans (2)
- Similar primary structure
- So similar DNA sequence/base sequence
Explain why diversity of insects in the area decreased after the forest was cleared (3)
- Fewer niches
- Fewer food sources
- Fewer plant species
Explain the role of independent segregation in meiosis (2)
- Genetic variation
- Different combinations of maternal and paternal chromosomes/alleles
Suggest why an animal crossed from a zebra (32 chromosomes) and a donkey (62 chromosomes) is infertile (2)
- 47/odd/uneven number of chromosomes
- Chromosomes cannot pair/are not homologous/chromosome number can’t be halved/meiosis can’t occur/sex cells/haploid cells aren’t produced
Define genetic diversity (1)
Number of different alleles OF EACH GENE
Give 3 ways in which courtship behaviour increases probability of successful mating (3)
- Recognise/identify/attract same species
- Stimulates/synchronises mating/production/release of gametes
- Recognition/attraction of mate/opposite sex
- Indication of maturity/fertility/readiness to mate
- Formation of a pair bond
Describe 2 differences between the structure of a tRNA molecule and the structure of a mRNA molecule (2)
- tRNA is clover-leaf shaped, mRNA is linear
- tRNA has H bonds, mRNA doesn’t
- tRNA has an amino acid binding site, mRNA doesn’t
- tRNA has anticodon, mRNA has codon
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation (3)
- tRNA bring specific amino acid (to ribosome)
- anticodon (on tRNA) binds to codon (on mRNA)
- amino acids join by condensation reaction/join to form a peptide bond (using ATP)
Describe the role of a ribosome in the production of a polypeptide. DO NOT INCLUDE TRANSCRIPTION (3)
- mRNA binds to ribosome
- idea of TWO codons/binding sites
- (allows) tRNA with ANTICODONS to bind/associate
- (catalyses) formation of peptide bond between amino acids
- moves along (mRNA to the next codon)
EXPLAIN one other way genetic variation within a species is increased apart from mutation (2)
- Random fertilisation
- Produces new allele combinations
Define ‘gene mutation’ and explain how a gene mutation can have
• no effect on an individual
• a positive effect on an individual (4)
- Change in the base/nucleotide (sequence of DNA)
- Results in the formation of a new ALLELE
- Genetic code is degenerate/mutation is in an intron
- Changes AA but no effect on 3º structure
- (New allele) is recessive so doesn’t influence phenotype
- Results in change in polypeptide that positively changes the properties (of the protein)
- May result in increased survival/reproductive success
Describe crossing over and explain how it increases genetic diversity (4)
- Homologous pairs of chromosomes associate/form a bivalent
- Chiasma(ta) form
- (Equal) lengths of (non-sister) chromatids/alleles are exchanged
- Producing new combinations of alleles
Explain why it is more useful to calculate index of diversity than to record species richness (2)
- Measures abundance/number/population of EACH species
- May be many/few of some species
Give one way in which sampling procedures could be standardised
Same size of area
Size size net/mesh
Same sampling time
Samples taken at same time of day/on the same day
