Module 4 - RNA and protein synthesis

Question 1

Similarities and differences between RNA and DNA

Answer 1

Similarities
1. Polymers of nucleotides;
2. (Nucleotide has) pentose, (nitrogen-containing organic) base and a phosphate (group);
3. Cytosine, guanine and adenine (as bases);
4. Have phosphodiester bonds;

Differences
5. Deoxyribose v ribose;
6. Thymine v uracil;
7. Long v short;
8. Double helix/stranded v single stranded;

Question 2

6 marks

Desribe structure of DNA and chromosomes

Answer 2

DNA structure
* A nucleotide has a deoxyribose sugar, a phosphate and nitrogenuous base
* Backbone is joined by phosphodiester bonds
* Adenine, guanine, cytosine and thymine bases are joined by hydrogen bonds (A-T, G-C) - complementary base pairs
* Double helix formed (antiparallel)

Chromosome structure
* DNA associated with histone proteins
* 2 identical chromatids joined by a centromere

Question 3

5 marks

Starting with mRNA in the cytoplasm, describe how translation leads to the box production of a polypeptide.
Do not include descriptions of transcription and splicing in your answer.

Answer 3

1. mRNA molecule attaches to ribosome
2. Ribosome moves to the start codon
3. tRNA carries specific amino acid
4. Anticodon on tRNA complementary to codon on mRNA
5. Ribosome can fit two tRNAs
6. Amino acids join by peptide bonds in a condensation reaction to form a polypeptide using ATP

Question 4

2 marks

Describe how the production of messenger RNA (mRNA) in a eukaryote cell is
different from the production of mRNA in a prokaryote cell.

Answer 4

1. Pre-mRNA only produced in eukaryote cell
2. Splicing only occurs in eukaryote cell
3. Introns removed in eukaryote cell/ introns not present in prokaryote cell

Question 5

2 marks

Describe the role of ATP in the process of translation in protein synthesis.

Answer 5

1. Releases energy
2. So peptide bonds form between amino acids
   OR
   So amino acid joins to tRNA

Question 6

6 marks

Describe DNA transcription

Answer 6

1. Section of DNA unwinds using DNA helicase
2. Hydrogen bonds break
3. Single strand used as template
4. Free RNA nucleotide attach to exposed bases
5. Free RNA nucleotides join using complementary base pairings (A-U & G-C)
6. RNA polymerase joins RNA nucleotides in a condensation reaction, forming phosphodiester bonds
7. Until stop codon is reached
8. Pre- mRNA is spliced to remove introns

Question 7

2 marks

Scientists investigated the genetic diversity between several species 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.

Answer 7

1. DNA that does not code for polypeptides
2. Positioned between genes

Question 8

5 marks

Describe how mRNA is formed by transcription in eukaryotes.

Answer 8

1. Hydrogen bonds between DNA bases break
2. Only one DNA strand acts as a template
3. Free-floating RNA nucleotides align by complementary base pairing
4. In RNA Uracil base pairs with adenine on DNA
5. RNA polymerase joins adjacent RNA nucleotides
6. By phosphodiester bonds between adjacent nucleotides
7. Pre-mRNA is spliced to form mRNA. Introns are removed

Question 9

6 marks

Describe how a polypeptide is formed by translation of mRNA.

Answer 9

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
5. Amino acids join together with the use of ATP
6. tRNA released after amino acid joined to polypeptide
7. The ribosome moves along the mRNA to form the polypeptide

Question 10

2 marks

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule.

Answer 10

1. Condensation reaction–> loss of water
2. Between phosphate and deoxyribose
3. Catalysed by DNA polymerase