Protein Synthesis

Question 1

Stages of protein synthesis

Answer 1

Stage 1- Transcription

Stage 2- Translation

Question 2

What is transcription?

Answer 2

The process of making mRNA from the template provided on DNA

Question 3

What does transcription require?

Answer 3

• DNA to act as a template
• Free RNA nucleotides
• Enzymes including RNA polymerase
• ATP for energy

Question 4

Transcription step 1

Answer 4

Weak hydrogen bonds between DNA bases break and DNA unwnds

Question 5

Transcription step 2

Answer 5

Transcription of a gene starts from a region of a gene known as the promoter. The molecule elongates until it reaches the terminator sequence, the molecule produced is called the primary transcript.

Question 6

Transcription step 3

Answer 6

RNA splicing occurs and produces the mature transcript

Question 7

RNA splicing

Answer 7

The introns (non-coding) are removed to produce the primary transcript and then the exons (coding) are spliced together to form a continuous sequence called the mature transcript. The mature transcript then leaves the nucleus to travel to the cytoplasm.

Question 8

RNA Polymerase

Answer 8

• The enzyme responsible for transcription
• Binds at the promoter and unwinds the DNA
• Adds nucleotides onto the 3’ end of the growing mRNA molecule

Question 9

What is translation?

Answer 9

Translation is the changing of the code on mRNA into a sequence of amino acids. It occurs in the cytoplasm and involves ribosomes.

Question 10

Translation step 1

Answer 10

The mRNA passes through the ribosomes and the ribosome binds to the mRNA so that the start codon is in place

Question 11

Translation step 2

Answer 11

The codons are recognised by tRNA, each carrying a particular amino acid. The appropriate tRNA brings its amino acid to the ribosome as it moves along the mRNA

Question 12

Translation step 3

Answer 12

Adjacent amino acids join together with a peptide bond and the tRNA then leaves the ribosome. This process continues until a stop codon is reached and the polypeptide is released.

Question 13

Genes and proteins

Answer 13

The same gene can be used to make several different proteins by alternative RNA splicing and post-translational modification

Question 14

Alternative RNA Splicing

Answer 14

Under certain conditions alternative segments of RNA may be treated as exons and introns during RNA splicing. One gene can produce several different mature mRNA transcripts and several different proteins