Genetic information, variation & relationships Flashcards
Define the term exon.
Base/nucleotide/triplet sequence coding for polypeptide/sequence of amino acids/primary structure;
Give two structural differences between a molecule of messenger RNA (mRNA) and a molecule of transfer RNA (tRNA). [2]
- mRNA does not have hydrogen bonds / base pairing, tRNA does; OR mRNA is linear / straight chain, tRNA is cloverleaf;
- mRNA does not have an amino acid binding site, tRNA does;
- mRNA has more nucleotides;
- (Different) mRNAs have different lengths, all tRNAs are similar / same length;
- mRNA has codons, tRNA has an anticodon;
What is an allele?
- (Different) form/type/version of a gene
OR
- different base sequence of a gene;
What is a gene?
- A sequence of DNA (nucleotide) bases that codes for a (specific) polypeptide;
- ‘codes for a functional RNA’
- ‘codes for rRNA/tRNAs’
- ‘codes for a sequence of amino acids/primary structure’
What is a TRIPLET?
A sequence of 3 DNA (nucleotide) bases
What is a CODON?
A sequence of 3 mRNA (nucleotide) bases
What is an ANTICODON?
A sequence of 3 tRNA (nucleotide) bases that is complementary to a specific codon.
If a DNA sequence is:
TAG.GCG.AAT.CCG
What is the mRNA sequence?
AUC.CGC.UUA.GGC
Describe the structure of DNA and the structure of a chromosome. [5]
- Polymer of nucleotides; Accept ‘polynucleotide’
- (Nucleotide) consists of deoxyribose, phosphate and an organic/nitrogenous base;
- Phosphodiester bonds (between nucleotides);
- DNA double helix held by H bonds OR 2 strands held by H bonds;
- (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine;
Reject adenosine and cysteine
- DNA is associated with histones/proteins;
- (During mitosis/when visible) chromosome consists of two chromatids joined at a centromere;
Describe Transcription in Eukaryotes [5]
- Hydrogen bonds (between DNA bases) break;
- (Only) one DNA strand acts as a template;
- (Free) RNA nucleotides align by complementary base pairing;
- (In RNA) Uracil base pairs with adenine (on DNA) OR (In RNA) Uracil is used in place of thymine;
- RNA polymerase joins (adjacent RNA) nucleotides;
- (By) phosphodiester bonds (between adjacent nucleotides);
- Pre-mRNA is spliced (to form mRNA) OR Introns are removed (to form mature mRNA);
Describe Translation [5]
- (mRNA attaches) to ribosomes OR (mRNA attaches) to rough endoplasmic reticulum;
- (tRNA) anticodons (bind to) complementary (mRNA) codons;
- tRNA brings a specific amino acid;
- Amino acids join by peptide bonds;
- (Amino acids join together) with the use of ATP;
- tRNA released (after amino acid joined to polypeptide);
- The ribosome moves along the mRNA to form the polypeptide;
Describe the role of ATP in the process of translation in protein synthesis. [2]
- Releases energy;
- (So) peptide bonds form between amino acids OR (So) amino acid joins to tRNA;
A mutation in a gene coding for an enzyme
could lead to the production of a non-functional enzyme. Explain how [3]
- Change in base sequence (of DNA/gene);
- Change in amino acid sequence / primary structure (of enzyme);
- Change in hydrogen/ionic/ disulphide bonds;
- Change in the tertiary structure/active site (of enzyme);
- Substrate not complementary/cannot bind (to enzyme / active site) / no enzyme-substrate complexes form;
Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why.
- Triplets code for same amino acid
- Occurs in introns /non-coding sequence;
Define ‘gene mutation’ and explain how a gene mutation can have:
* no effect on an individual
* a positive effect on an individual.
- (Definition of gene mutation)
- Change in the base/nucleotide (sequence of chromosomes/DNA);
- Results in the formation of new allele;
- (Has no effect because)
- Genetic code is degenerate (so amino acid sequence may not change); OR
- Mutation is in an intron (so amino acid sequence may not change);
- Accept description of ‘degenerate’, eg some amino acids have more than one triplet/codon.
- Does change amino acid but no effect on tertiary structure;
- (New allele) is recessive so does not influence phenotype;
- (Has positive effect because)
- Results in change in polypeptide that positively changes the properties (of the protein) OR Results in change in polypeptide that positively changes a named protein; For ‘polypeptide’ accept ‘amino acid sequence’ or ‘protein’.
- May result in increased reproductive success OR May result in increased survival (chances);
Name the type of gene mutation that has no effect on the Primary structure of a polypeptide.
Substitution (Silent)
Explain how natural selection produces changes within a species. [5]
- Variation between members of population / species is caused by mutation;
- Predation / disease / competition results in differential survival;
- Some have adaptations that favour survival;
- Differential reproductive success / survive to reproduce/ have more offspring;
- Pass on their advantageous alleles;
- Changes allelic frequencies
Name 3 types of single point gene mutation.
- Addition
- Deletion
- Substitution
Name 4 types of chromosomal mutation
- Duplication
- Inversion
- Translocation
- Non-disjunction
When do most mutations occur?
DNA replication;
S phase of Interphase
Which process may lead to:
- Inversion and Translocation mutations
- Non-disjunction mutations?
- Meiosis 1
- Meiosis 2
State 3 factors that affect reproductive success or survival?
- Competition (Inter or Intraspecific)
- Predation
- Pathogens
Name 4 selection pressures
Any 4 Biotic or Abiotic factors
Why is a Log scale graph used?
There is a large range in ……….(y axis label)
If the T value is 15 and the critical value is 3.4. What can you conclude?
Use the words probability and chance in your answer.
The probability that the difference is due to chance is less than 5%.
The difference is significant.
Reject the Null hypothesis.
When would you use the Student’s T test?
Comparing the difference between TWO means
