dna genes and protein synthesis

Question 1

define genome

Answer 1

as the complete set of genes in a cell

Question 2

define proteome

Answer 2

as the full range of proteins that a cell is able to produce.

Question 3

describe how a gene is a code for the production of a polypeptide

Answer 3

1. (Because) base/nucleotide sequence;
2. (In) triplet(s);
3. (Determines) order/sequence of amino acid sequence/primary
   structure (in polypeptide);

Question 4

define the term exon

Answer 4

/triplet sequence coding for polypeptide

Question 5

an intron is a non coding sequence of dna, where is it positioned in the genome

Answer 5

positioned between genes

Question 6

differences between dna in nucleus of plant cell and dna in prokaryotic cell

Answer 6

1. (Associated with) histones/proteins v no histones/proteins;
2. Linear v circular;
3. No plasmids v plasmids;
   4, Introns v no introns;
4. Long(er) v short(er);

Question 7

not all mutations in nucleotide sequence of a gene cause change in structure of polypeptide. why?

Answer 7

Triplets code for same amino acid
Occurs in introns /non-coding sequence;

Question 8

compare and contrast dna in pro vs eu cells

Answer 8

compare:
Nucleotide structure is identical;
Nucleotides joined by phosphodiester bond;
DNA in mitochondria / chloroplasts same / similar (structure) to DNA
in prokaryotes;
contrast:
Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones,
prokaryotic DNA is not;

Question 9

what is a homologous pair of chromosomes

Answer 9

(Two chromosomes that) carry the same genes;

Question 10

explain how number of chromosones is halved during meiosis

Answer 10

1. Homologous chromosomes (pair);
2. One of each (pair) goes to each (daughter)
   cell / to opposite poles;

Question 11

crossing over increases genetic diveristy explain how

Answer 11

1. Homologous pairs of chromosomes associate
   / form a bivalent;
2. Chiasma(ta) form;
3. (Equal) lengths of (non-sister) chromatids /
   alleles are exchanged;
4. Producing new combinations of alleles;

Question 12

Explain the meaning of
Degenerate
Non overlapping

Answer 12

Degenerate : more than one base triplet can code for the same amino acid
Non overlapping: each base is part of only one triplet

Question 13

mRNA is used during translation to form polypeptides.
Describe how mRNA is produced in the nucleus of a cell.

Answer 13

1. Helicase;
2. Breaks hydrogen bonds;
3. Only one DNA strand acts as template;
4. RNA nucleotides attracted to exposed bases;
5. (Attraction) according to base pairing rule;
6. RNA polymerase joins (RNA) nucleotides together;
7. Pre-mRNA spliced to remove introns.

Question 14

Contrast the structures of mRNA and DNA

Answer 14

1. DNA double
   stranded/double helix and mRNA single-stranded;
   Contrast requires both parts of the statement
2. DNA (very) long and RNA short;
   Accept ‛RNA shorter’ or ‛DNA bigger/longer’
3. Thymine/T in DNA and uracil/U in RNA;
4. Deoxyribose in DNA and ribose in RNA;
   R Deoxyribonucleic/ ribonucleic acid
   Ignore ref. to histones
   Ignore ref. to helix and straight chain alone
5. DNA has base pairing and mRNA doesn’t/ DNA has hydrogen
   bonding and mRNA doesn’t;
6. DNA has introns/non-coding sequences and mRNA doesn’t;

Question 15

Single base deletion can lead to a non func protein
Why

Answer 15

Mutation) changes triplets / codons after that point / causes frame shift;
Accept changes splicing site
Ignore changes in sequence of nucleotides / bases
2. Changes amino acid sequence (after this) / codes for different amino
acids (after this);
Accept changes primary structure
Reject changes amino acid formed / one amino acid changed
3. Affects hydrogen / ionic / sulfur bond (not peptide bond);
4. Changes tertiary structure of protein (so non-functional);

Question 16

Mutation in intron causes whag

Answer 16

Intron non- coding (DNA) / only exons coding;
Context is the intron
Do not mix and match from alternatives
Neutral references to introns removed during splicing
1. and 2. Ignore ref. to code degenerate and get same / different
amino acid in sequence
2. (So) not translated / no change in mRNA produced / no effect (on protein)
/ no effect on amino acid sequence;
Accept does not code for amino acids
OR
3. Prevents / changes splicing;
4. (So) faulty mRNA formed;
Accept exons not joined together / introns not removed
5. Get different amino acid sequence;

Question 17

Explain how the structure of DNA is related to its function

Answer 17

Sugar-phosphate (backbone) / double stranded / helix so provides strength / stability
/ protects bases / protects hydrogen bonds;
Must be a direct link / obvious to get the mark
Neutral: reference to histones
2. Long / large molecule so can store lots of information;
3. Helix / coiled so compact;
Accept: can store in a small amount of space for ‘compact’
4. Base sequence allows information to be stored / base sequence codes for
amino acids / protein;
Accept: base sequence allows transcription
5. Double stranded so replication can occur semi-conservatively / strands can act
as templates / complementary base pairing / A-T and G-C so accurate
replication / identical copies can be made;
6. (Weak) hydrogen bonds for replication / unzipping / strand separation / many
hydrogen bonds so stable / strong;
Accept: ‘H-bonds’ for ‘hydrogen bonds’

Question 18

differences in primary structure in haemoglobin molecules can provide evidence of phylogenic (evolutionary relationships between species
explain how (5)

Answer 18

1. Mutations change base / nucleotide (sequence);
   Reject if mutation in amino acid
2. (Causing) change in amino acid sequence;
3. Mutations build up over time;
4. More mutations / more differences (in amino acid / base / nucleotide sequence / primary structure) between distantly related species;
   OR
   Few(er) mutations / differences (in amino acid / base / nucleotide sequence / primary structure) in closely related species;
5. Distantly related species have earlier common ancestor;
   OR
   Closely related species have recent common ancestor;
   Accept “order” for “sequence”

Question 19

compare and contrast DNA structure (5)

Answer 19

Comparisons
1. Nucleotide structure is identical;
Accept labelled diagram or description of nucleotide as phosphate, deoxyribose and base
2. Nucleotides joined by phosphodiester bond;
OR
Deoxyribose joined to phosphate (in sugar, phosphate backbone);
3. DNA in mitochondria / chloroplasts same / similar (structure) to DNA in prokaryotes;
Accept shorter than nuclear DNA/is circular not linear/is not associated with protein/histones unlike nuclear DNA;
Contrasts
4. Eukaryotic DNA is longer;
5. Eukaryotic DNA contain introns, prokaryotic DNA does not;
6. Eukaryotic DNA is linear, prokaryotic DNA is circular;
7. Eukaryotic DNA is associated with / bound to protein / histones, prokaryotic DNA is not;

Question 20

describe the role of a ribosome in the production of polypeptide

Answer 20

1. mRNA binds to ribosome;
2. Idea of two codons / binding sites;
3. (Allows) tRNA with anticodons to bind / associate;
4. (Catalyses) formation of peptide bond between amino acids (held by tRNA molecules);
5. Moves along (mRNA to the next codon)