Topic 4- Genes and variation Flashcards
(23 cards)
Describe 2 differences in the structures of a tRNA molecule and an mRNA molecule.
(2 marks)
1) tRNA is ‘clover leaf shaped’ whereas mRNA is linear
2) tRNA has hydrogen bonds whereas mRNA does not
3) tRNA has an amino acid binding site whereas mRNA does not
4) tRNA has anticodons whereas mRNA has codons
Describe the primary protein of all proteins.
(2 marks)
- Sequence/ order of amino acids
- Joined by peptide bonds
Describe the role of tRNA in translation.
(2 marks)
- Anticodon on tRNA binds to the complementary codon on mRNA
- tRNA brings/ carries specific amino acids to ribosomes
Describe how a gene is a code for the production of polypeptides.
Do not include information of transcription or translation.
(3 marks)
1) Because base/ nucleotide sequence
2) In triplets
3) Determines order/ sequence of amino acid sequence/ primary structure in polypeptide.
Describe how a gene is a code for the production of a polypeptide.
DO NOT include transcription or translocation in your answer.
(3 Marks)
- Because the base/ nucleotide sequence.
- In triplets.
- Determine order/ sequence of amino acid sequence/ primary structure in a polypeptide.
Name the fixed position occupied by a gene on a DNA molecule.
(1 Mark)
Loci/ locus
Define the term exon.
(1 Mark)
Base/ nucleotide/ triplet sequence coding for polypeptide/ sequence of amino acids/ primary structure.
Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule.
(2 Marks)
- Condensation reaction/ loss of water.
- Between phosphate and deoxyribose
- Catalysed by DNA polymerase.
Name the protein associated with DNA in a chromosome.
(1 Mark)
Histone
Scientists investigated the genetic diversity between several pieces of sweet potato. They studied non-coding multiple repeats of base sequences.
Define non-coding base sequences and describe where the non-coding multiple repeats are positioned in the genome.
(2 Marks)
- DNA that does not code for a protein/ polypeptide.
OR DNA that doesn’t code for tRNA/mRNA
OR DAN that doesn’t code for a sequence of amino acids. - Positioned between genes.
The nucleus and chloroplasts of a plant cell both contain DNA.
Give three ways that the DNA of a chloroplast differs from DNA in a nucleus.
(3 Marks)
In chloroplasts
1. DNA is shorter than in nucleus.
2. Fewer genes compared to nuclear DNA.
3. DNA is circular not linear.
4. Not associated with proteins/ histones, unlike nuclear DNA.
5. Introns absent but present in nuclear DNA.
Not all mutations in the nucleotide sequence of a gene caused a change in the structure of a polypeptide.
Give two reasons why.
(2 Marks)
- Triplets code for the same amino acid.
- Occurring in the introns/ non-coding sequence.
Compare and contrast the DNA in eukaryotic cells and the DNA in prokaryotic cells.
(5 marks)
Compare
1. Nucleotide structure is identical
2. Nucleotides joined by a phosphdiester bond
OR deoxyribose joined to a phosphate in sugar phosphate back bone.
3. DNA in mitochondria/ chloroplasts same/ Similar structure to DNA in prokaryotes.
Contrast
4. Eukaryotic DNA is longer
5. Eukaryotic DNA contains introns, prokaryotic DNA does not.
6. Eukaryotic DNA is linear, prokaryotic DNA is circular.
7. Eukaryotic DNA is associated with histones, prokaryotic DNA is not.
What is a homologous pair of chromosomes?
(1 Mark)
Two chromosomes that carry the same genes.
Describe and explain the difference in structure of pre-mRNA and mRNA.
(2 Marks)
- mRNA has fewer nucleotides
OR pre-mRNA has more nucleotides
OR mRNA has no introns only exons
or pre-mRNA has introns and exons - Because of splicing.
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome in translation.
(3 Marks)
- tRNA brings specific amino acid to ribosome.
- Anticodon on tRNA binds to codon on mRNA.
- Amino acids going by a condensation reaction using ATP.
OR amino acids join to form a peptide bond using ATP.
Describe how mRNA is produced from an exposed template strand of DNA.
DO NOT include DNA helicase or splicing.
- Free RNA nucleotide form complementary base pairings.
- Phosphdiester bond form.
- By action of RNA polymerase.
Describe how mRNA is formed by transcription in eukaryotes.
(5 Marks)
- Hydrogen bonds between DNA bases break.
2.Only one DNA strand acts as a template strand. - Free RNA nucleotides align by complementary case pairing.
- On RNA uracil 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 from mRNA.
Describe how a polypeptide is formed by translation of mRNA.
(6 Marks)
- mRNA attaches to ribosomes
OR mRNA attaches to RER. - tRNA anticodons bind to complementary mRNA codons.
- tRNA brings a specific amino acid.
- Amino acid joins by peptide bonds.
- Amino acids join together using ATP.
- tRNA releases after amino acid is joined to polypeptide.
- Ribosome moves along the mRNA to form the polypeptide.
Explain what is meant by the term semi-conservative replication.
(2 marks)
1) 2 identical copies
2) Each consisting of one new and old original strand.
Define genome.
(1 mark)
A complete set of genes in a cell/ organism
Define proteome.
(1 mark)
Range of proteins that a cell/ organism can produce.
OR range of proteins the genome/ DNA can code for.
The action of endopeptidases and exopeptidases can increase the rate of protein digestion. Describe how.
- Exopeptidases hydrolyse peptide bonds at the ends of a polypeptide
AND endopeptidases hydrolyse internal peptide bonds of a polypeptide. - More ‘ends’
