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);
