Protein Synthesis (Translation)

Question 1

What is translation? (1)

Answer 1

Translation is the process of mRNA being used to make a protein. Occurs in cytosol.

Question 2

How many codes in mRNA are read together for one amino acid? (1)

Answer 2

3 codes at once. E.g AUG = Met, UGG = Trp

Question 3

How many reading frames does the mRNA code have? (1)

Answer 3

3 reading frames. (as starts from first triplet code).

Question 4

How is mRNA interpreted by Ribosomes? (5)

Answer 4

1. mRNA translation occurs in Ribosomes using ATP.
2. The Ribosomes have Exit site, Pairing site and Acyl site. Ribosomes are made up of rRNA (large subunit 3rRNA, small subunit 1rRNA)
3. The tRNA which has Amnio acid attached arrives with a complementary anticodon to codon on mRNA. This first attaches on A-site.
4. The amino acid is paired on the P-site, the used tRNA leaves at E-site.
5. This process repeats and peptide bonds are made between amino acids that have been translated, making a polypeptide chain.
6. A series of ribosomes can work at the same time in a chain (polyribosome) to translate protein for same mRNA molecule.

Question 5

How do Antibiotics work in bacterial ribosomes?

Answer 5

1. Antibiotics bind to bacterial ribosome.

2. They exploit structural and functional differences between eukaryotic and prokaryotic ribosomes.

Question 6

Translation Mutation: What is Frameshift Mutation? (2)

Answer 6

When any nucleotides are deleted or inserted that isnt a multiple of 3.

This results in shorter amino acid sequence causing altered protein structure.

Question 7

What is an example of a condition caused by Frameshift mutation? How does it occur? (2)

Answer 7

1. Conginental deafness - mutation in GJB2 gene. It is an autosomal recessive disease.
2. Framshifted ribosome runs in a stop codon.

Question 8

Example of condition caused by Missense (substitution) mutation? (2)

Answer 8

1. Sickle Cell Anaemia. Mutation in Beta globin where codon for glutamic acid is changed to Valine.

Question 9

Example of mutation caused by non-sense mutation? (2)

Answer 9

Beta thelassemia - stop codon created near start of exon 2 via substitution.

Question 10

What are microRNAs? (2)

Answer 10

1. 21-22 nucleotides of non-coding RNAs.

2. Binds to mRNA and causes translational repression/degradation of mRNA.

Question 11

Example of condition that can occur due to lack of microRNA expression? (3)

Answer 11

1. Chronic lymphocytic leukemia due to deletion mutation.
2. Induces overexpression of BCL2 protein
3. Reduces apoptosis (cell death)

Question 12

What miRNA do we know that affects expression and regulation of metastasis and cancers?

Answer 12

1. miR-200 family can increases growth of primary tumour and colonisation of metastases.
2. miR-31 can inhibit movement and invasion of cancer cells to new location.
3. miR-21 over expressed in glioblastomas
4. miR-155 over-expressed in various forms of B-cell malignancy

Question 13

Why could miRNAs be excellent biomarkers? (5)

Answer 13

1. Circulating miRNAs are found in blood, urine, spinal fluid.
2. It is stable as pretected inside microvesicels and/or bound to proteins.
3. A lot of them >2200 in humans
4. Can be used using PCR on standard machines.
5. Can be used in combination with each other.