Paper 1 (Practice based)

Question 1

Describe how mRNA is formed by transcription in eukaryotes

Answer 1

1. Hydrogen bonds between DNA between DNA bases break
2. Only one DNA strand acts as template
3. Free RNA nucleotides align by complementary base pairing
4. Uracil base pairs with adenine in RNA
5. RNA polymerase joins adjacent RNA nucleotides in a condensation reaction forming phosphodiester bonds
6. Pre-mRNA is spliced to form mRNA

Question 2

Describe how a polypeptide is formed by translation of mRNA

Answer 2

1. mRNA attaches to ribosomes
2. tRNA anticodons bind to complementary mRNA codons
3. tRNA brings a specific amino acid
4. Amino acids join by peptide bonds with the use of ATP
5. tRNA released after amino acid joined to polypeptide
6. The ribosome moves along the mRNA to form the polypeptide

Question 3

Define gene mutation, explain how it can have a positive effect or no effect

Answer 3

1. A gene mutation is the change in the base sequence of DNA
2. Results in the formation of new alleles
3. Has no effect because genetic code is degenerate so the amino acid sequence may not change
4. Or the new allele is recessive so it doesn’t influence the phenotype
5. Has a positive effect if it results in changes in the polypeptide which positively changes the properties
6. Or it results in increased reproductive success

Question 4

Describe and explain features found in a cell specialised for absorption

Answer 4

1. Microvilli so there is a large surface area for absorption
2. Large number of carrier proteins so fast rate of absorption
3. Large number of mitochondria so makes more ATP by respiration
4. Membrane-bound digestive enzymes so maintains concentration gradient for fast absorption

Question 5

Describe the role of micelles in the absorption of fats into the cells lining the ileum

Answer 5

1. Micelles include bile salts and fatty acids
2. Makes the fatty acids more soluble in water
3. Release fatty acids to lining of the ileum
4. Maintains higher concentration of fatty acids to the lining of the ileum
5. Fatty acids absorbed by diffusion

Question 6

Describe a method to prepare a colour standard and how this could be used

Answer 6

1. Use known concentration of extract
2. Prepare dilution series
3. Compare results with colour standards to give score

Question 7

Describe the role of DNA polymerase in the semi-conservative replication of DNA

Answer 7

1. Joins adjacent DNA nucleotides
2. Catalyses condensation reactions
3. Forms phosphodiester bonds between adjacent nucleotides

Question 8

Differences between DNA in plant cell and DNA in prokaryotic cell

Answer 8

1. Plant associated with histones, prokaryotes not associated
2. Plant linear, prokaryotes circular
3. Plant no plasmids, prokaryotes has plasmids
4. Plants have introns, prokaryotes don’t
5. Plant DNA is longer, prokaryote DNA is shorter