3.4.2 Protein synthesis

Question 1

What is transcription?

Answer 1

Where DNA is copied into a molecule of mRNA

Question 2

What is translation?

Answer 2

Where mRNA joins with ribosomes and the sequence of bases is used to synthesise a protein

Question 3

What is protein synthesis?

Answer 3

Production of from a cell’s genes

Question 4

What happens in the process of transcription?

Answer 4

1. RNA Polymerase (enzyme) attaches to DNA double helix, unzips it (hydrogen bonds between bases broken with DNA helices attached to the RNA polymerase)
2. Complementary pre-mRNA is formed as free bases attach to exposed complementary bases. RNA Polymerase then catalyses the formation of phosodiester bonds in newly formed pre-mRNA
3. RNA Polymerase moves down the DNA strand and assembles pre-mRNA strand. Hydrogen bonds reform between uncoiled strands of DNA and coils back into double helix
4. RNA Polymerase reaches stop codon. Production of mRNA ends and RNA polymerase detaches from the DNA
5. Pre-mRNA will be spliced into mRNA. Introns are removed by forming a spliceosome and be cut off, the exons join together. mRNA then move out of the nucleus though nuclear pores into the cytoplasm

Question 5

What happens in the process of translation?

Answer 5

1. mRNA attaches itself to a ribosome and amino acids are activated - combined with tRNA
2. ATP is hydrolysed in the process of joining amino acid with tRNA
3. tRNA molecule has an anticodon that’s complementary to codon on mRNA
4. tRNA with the start codon will attach to the mRNA and start the process of translation, mRNA is located in between subunits of ribosomes
5. Ribosome moves along mRNA, one codon at a time, more tRNA attach on mRNA
6. Peptide bonds are formed between amino acids brought by tRNA, catalysed by enzymes found in ribosomes
7. As ribosomes move along, tRNA that are no longer between ribosomes are released back into the rest of the cytoplasm and will activate more amino acids
8. Process of translation continues until there’s a stop signal
9. Polypeptide chain then moves away from the ribosome as translation is complete
10. mRNA strand could be translated by thousands of ribosomes, producing a lot of proteins

Question 6

What is the structure and function of mRNA?

Answer 6

Made during transcription
Carries genetic code from DNA to ribosome for protein synthesis

A single polypeptide strand
Chain of codons

Question 7

What is the structure and function of tRNA?

Answer 7

Carries amino acids to mRNA during translation

A single polypeptide chain that is folded into clover shape
Amino acids binding site at the top
Anti-codon loop at the bottom