12.4 - Protein Synthesis + Selection

Question 1

What is the difference between eukaryotic and prokaryotic DNA? 1+2+3

4) chloroplasts and mitochondria contain DNA that is…

Answer 1

1) Linear (has ends) V circular (no ends)
2) Associated with histone proteins V not associated with histone proteins
3) Contains introns V doesn’t contain introns.

4) similar to the DNA found in prokaryotes. (70S ribosomes as well)

Question 2

mRNA (formed in transcription)

1) This is a single-….
2) It is a complementary copy of a single gene from…
3) It is much shorter…
4) Three bases are a…

GIVE 6 ways DNA is different to mRNA (6)

Answer 2

1) stranded polynucleotide chain
2) the template strand of DNA
3) than DNA
4) codon.

1) Double stranded v single stranded
2) longer v shorter
3) thymine v uracil
4) deoxyribose v ribose
5) hydrogen bonds v no hydrogen bonds
6) introns v no introns

Question 3

Give two structural differences between a molecule of mRna and a molecule of tRNA. (5)

tRNA (involved in translation)

1) The role of tRNA molecules is to carry..
2) tRNA anticodon is complementary to…

Answer 3

1) mRNA = no H bonds, tRNA does
2) mRNA = linear, tRNA = cloverleaf structure
3) mRNA = no AA binding site, tRNA does.
4) mRNA has more nucleotides
5) Different mRNAs have different lengths, all tRNA have the same length
6) mRNA = codons, tRNA = anticodons

1) A specific AA to the ribosome (site of protein synthesis)
2) the codon on mRNA.

Question 4

DEFINITIONS

1) Define the term exon.
2) What is an intron?
3) What is a gene?
4) What is an allele?
5) What is a genome?
6) What is a proteome?
7) What is a Loci?

Answer 4

1) Base sequence within a gene of DNA coding for an AA/polypeptide/primary structure
2) Non-coding base sequences within a gene of DNA
3) A sequence of DNA nucleotides that codes for a polypeptide
4) Different version / form of a gene.
5) Complete set of genes in a cell
6) full range of proteins that a cell is able to produce
7) position of a gene within a chromosome.

Question 5

Describe transcription in eukaryotes. (7)

Answer 5

1) Hydrogen bonds between DNA bases break
2) One DNA strand acts as a template
3) Free RNA nucleotides align by complementary base pairing
4) In RNA - U pairs with A on DNA.
5) RNA polymerase joins adjacent RNA nucleotides
6) By phosphodiester bonds
7) pre-mRNA is spliced to form mRNA (introns are removed)

[then mRNA passes out the nucleus via nuclear pore to the ribosome]

Question 6

Describe translation. (7)

Answer 6

1) mRNA attaches to ribosome
2) tRNA anticodons bind to complementary mRNA codons
3) tRNA brings a specific AA
4) AAs join by peptide bonds
5) With the use of ATP
6) tRNA is released (after AA is joined to the pp)
7) ribosome moves along the mRNA to form the polypeptide.

Question 7

Describe the role of ATP in the process of translation in protein synthesis. (2)

Answer 7

1) Releases energy
2) So peptide bonds form between AAs (or AA joins to tRNA)

Question 8

THE GENETIC CODE

1) What are 3 bases on DNA, mRNA and tRNA?
2) What is meant by the genetic code being UNIVERSAL?
3) Explain what the term non-overlapping DNA means.
4) Define degenerate code.

Answer 8

1) triplet, codon, anticodon.
2) The same 3 bases code for the same AAs in all organisms. [the mechanism of transcription + translation are universal throughout all organisms.]
3) A base from one triplet cannot be used in an adjacent triplet (each base belongs to only one triplet/codon)
4) More than one codon codes for an AA. (e.g proline coded by 4 triplets)

Question 9

A mutation in a gene coding for an enzyme could lead to the production of a non-functional enzyme. Explain how. (5)

Answer 9

1) Change in base sequence
2) Change in AA sequence
3) Change in H/ionic/diS bonds
4) Change in tertiary structure - active site of enzyme
5) Substrate no longer complementary to enzyme / no ESC.

Question 10

1) What is meant by a substitution mutation? A silent mutation?

2) What is an addition/deletion mutation?

Answer 10

1) One base is substituted for another. A silent mutation means that the mutation doesn’t change the AA coded for, as code is degenerate - glycine is coded for by CCT, CCG, CCA and CCC. So a mutation in the 3rd base would make no difference.

2) 1 full DNA base is gained or lost - results in an alteration of base triplets. The frame has shifted to the right/left by one base - frame shift.

Question 11

Not all mutations in the nucleotide sequence of a gene cause a change in the structure of a polypeptide. Give two reasons why. (2)

Answer 11

1) Triplets code for the same AA.
OR
2) Occurs in introns (non-coding base sequences)

Question 12

Define gene mutation and explain how a gene mutation can have:
-no effect
-positive effect
(7)

Answer 12

1) G.M = change in the base sequence of DNA
2) Results in formation of new allele.

3) Genetic code is degenerate OR mutation is in an intron.
4) Does change AA but no effect on tertiary structure
5) New allele is recessive so no effect on phenotype

6) Results in change in pp that positively changes the properties of the protein
7) May result in increased reproductive success or survival chances.

Question 13

MUTAGENIC AGENTS

1) Mutations occur..
2) Mutagenic agents increase the rate..
3) What are the three mutagenic agents?

Answer 13

1) spontaneously, natural and random.
2) of spontaneous mutation
3)
- High energy ionising radiation (X rays, gamma rays) - damage DNA molecule
- DNA reactive chemicals. (nitrous acid can change cytosine to uracil)
- Biological agents (viruses and bacteria)

Question 14

1) What is a chromosomal mutation?
2 What is an inversion mutation?
3 What is a duplication mutation?
4 What is a translocation mutation?

Answer 14

1) When daughter cells produced contain too many chromosomes, e.g pair of homologous chromosomes could failed to separate (chromosome non-disjunction)
2) Where a segment of bases is reversed end to end. (taken out, flipped, put back in.)
3) A doubling of a part of a chromosome, an entire chromosome, or the full genome.
4) When groups of base pairs relocate from one area of the genome to another, usually between non-homologous chromosomes.

Question 15

SELECTION

1) An organism’s characteristics (phenotype) is determined by…
2) What is genetic diversity?
3) What is meant by natural selection?
4) What are three things that can result in differential survival success? (selective pressures)
5) What is stabilising selection?
6) What is directional selection? E.g

Answer 15

1) the genotype (the alleles an organism has) and its interaction with the environment
2) The number of different alleles of genes in a population.
3) Process by which organisms that are better adapted to the environment survive and reproduce in greater numbers, resulting in the increase of the frequency of the advantageous allele in the population.
4) Predation, disease, competition,
5) Where selection is against both extremes.
6) Where there is selection for only one extreme. (e.g. antibiotic resistance in bacteria)

Question 16

Explain how selection occurs in living organisms. (6)

Answer 16

1) Variation due to mutation
2) Different env/biotic/abiotic conditions / selection pressures
3) Selection for advantageous allele
4) Different reproductive success (those with it survive + reproduce)
5) Leads to a change in allele frequency
6) Occurs over a long period of time.

Question 17

Describe two aseptic techniques she would have used when transferring a sample of broth culture onto an agar plate. Explain why each was important. (3)

Answer 17

1) Keep lid on petri dish -> to prevent unwanted bacteria contaminating dish
2)Wear gloves -> Prevent contamination of bacteria on hands
3) Use sterile pipette -> To maintain a pure culture of bacteria.