topic 4 exam style questions Flashcards
Describe how a gene is a code for the production of a polypeptide. Do not
include information about transcription or translation in your answer.
(Because) base/nucleotide sequence;
(In) triplet(s);
(Determines) order/sequence of amino acid sequence/primary
structure (in polypeptide);
Define the term exon.
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.
Condensation (reaction)/loss of water;
(Between) phosphate and deoxyribose;
(Catalysed by) DNA polymerase;
Complete Table 1 to show three differences between DNA in the nucleus
of a plant cell and DNA in a prokaryotic cell.
Associated with) histones/proteins v no histones/proteins;
Linear v circular;
No plasmids v plasmids;
Do not credit if suggestion that prokaryotic DNA
only exists as plasmids.
Introns v no introns;
Long(er) v short(er);
Define ‘non-coding base sequences’ and describe where the non-coding
multiple repeats are positioned in the genome.
1.DNA that does not code for protein/polypeptides
Or
DNA that does not code for (sequences of) amino acids
2.(Positioned) between genes;
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
Accept: DNA/code/triplets are degenerate
Reject: codons (as question states within genes)
Occurs in introns /non-coding sequence;
Reject: codons (as question states within genes)
Compare and contrast the DNA in eukaryotic cells with the DNA in
prokaryotic cells
Comparisons:
Nucleotide structure is identical;
Nucleotides joined by phosphodiester bond;
Deoxyribose joined to phosphate (in sugar, phosphate backbone);
DNA in mitochondria / chloroplasts same / similar (structure) to DNA
in prokaryotes;
Contrasts
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 / bound to protein / histones,
prokaryotic DNA is not;
In Figure 2 the chromosomes are arranged in homologous pairs.
What is a homologous pair of chromosomes?
Two chromosomes that) carry the same genes;
Describe how one amino acid is added to a polypeptide that is being
formed at a ribosome during translation.
tRNA brings specific amino acid (to ribosome);
Anticodon (on tRNA) binds to codon (on mRNA);
Amino acids join by 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 in your answer.
(Free RNA) nucleotides form complementary base pairs;
Accept A-U, G-C OR combination of those pairs
Phosphodiester bonds form;
Accept linkages for ‘bonds’
By (action of) RNA polymerase;
Describe how mRNA is formed by transcription in eukaryotes.
- Hydrogen bonds (between DNA bases) break;
Ignore DNA helicase.
Reject hydrolysing hydrogen bonds.
(Only) one DNA strand acts as a template;
(Free) RNA nucleotides align by complementary base pairing;
For ‘align by complementary base pairing’, accept
‘align to complementary bases’ or ‘align by base
pairing’.
(In RNA) Uracil base pairs with adenine (on DNA)
OR
(In RNA) Uracil is used in place of thymine;
Do not credit use of letters alone for bases.
RNA polymerase joins (adjacent RNA) nucleotides;
Reject suggestions that RNA polymerase forms
hydrogen bonds or joins complementary bases.
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3
1
(By) phosphodiester bonds (between adjacent nucleotides);
Describe how a polypeptide is formed by translation of mRNA.
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 how mRNA is produced in a plant cell.
The DNA strands separate by breaking the H bonds;
OR
H bonds broken between (complementary) (DNA) bases;
(Only) one of the strands/template strand is used (to make
mRNA/is transcribed);
(Complementary) base pairing so A ⟶ U, T ⟶ A, C ⟶ G, G
⟶ C;
(RNA) nucleotides joined by RNA polymerase;
pre-mRNA formed;
Splicing / introns removed to form mRNA;
Describe the role of a ribosome in the production of a polypeptide. Do not
include transcription in your answer
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
(held by tRNA molecules);
Moves along (mRNA to the next codon) / translocation
described;
