Protein Synthesis

Question 1

What is protein synthesis?

Answer 1

The process whereby proteins are made

Question 2

Where does protein synthesis occur?

Answer 2

Protein synthesis occurs on ribosomes in the cytoplasm

First stage = nucleus
Second stage = ribosomes

Question 3

What are the two main stages in protein synthesis?

Answer 3

Transcription and Translation

Question 3

How many stages are there in protein synthesis?

Answer 3

There are two main stages in protein synthesis

Question 3

What is transcription?

Question 3

Where does transcription occur?

Question 3

What is the first process in protein synthesis

Question 4

What is pre - mRNA?

Answer 4

mRNA molecules containing introns and exons of a certain gene

Question 4

What is the step by step process of protein synthesis at transcription?

Answer 4

1. DNA helix unwinds and hydrogen bonds between bases break by the use of DNA helicase
2. The bases are exposed and one chain of the DNA acts as a template (mRNA is single stranded)
3. Free mRNA nucleotides in the nucleus align opposite any exposed complementary DNA bases
4. The enzyme RNA polymerase bonds together the RNA nucleotides to create a new RNA polymer chain (entire gene has been copied)
5. Once copied, mRNA is modified, leaves nucleus through nuclear envelope pores

Question 5

What isa complementary mRNA copy of a gene made?

Answer 5

1. The DNA is too big to leave the nucleus and attach to a ribosome
2. DNA should not leave the nucleus as there are enzymes in the cytoplasm that could cause damage to the DNA
3. mRNA is shorter in size as it is only one gene (instead of 23 000 genes like DNA) so can fit through
   the nuclear pores in the nuclear envelope and move through the cytoplasm to attach to the ribosomes

Question 6

What happens to pre - mRNA before it is ready to leave the nucleus?

Answer 6

Pre - mRNA needs to be modified after transcription to become mRNA, ready to leave the nucleus and partake in translation

Question 7

What occurs during the splicing of mRNA?

Answer 7

Introns are spliced out by a protein called a splicesome, leaving only the coding sequences of the gene, exons

Question 8

What is the protein that splices introns out of the pre - mRNA?

Answer 8

Splicesome

Question 9

What is translation?

Answer 9

Translation is the stage where the polypeptide chain is created using both the mRNA base sequence and the tRNA

Question 10

After translation, what is formed?

Answer 10

The polypeptide chain is now formed and will enter the golgi body for folding and modification

Question 10

Where does the translation of proteins occur?

Answer 10

Translation occurs in the cytoplasm

Question 11

What is the step by step process of translation?

Answer 11

1. Modified mRNA leave the nucleus , then attach to ribosomes in the cytoplasm
2. The ribosomes attach to mRNA’s start codon
3. The tRNA molecule with the complementary anticodon to the start codon aligns opposite the mRNA, held in place by ribosomes
4. Ribosomes will move along the mRNA molecule, to allow other complementary tRNA to attach to the next codon on the mRNA
5. Whilst ribosomes hold tRNA molecule anticodon in place with the codon of the mRNA. Amino acids that have been delivered by the tRNA molecule join together through a peptide bond. This reaction is catalysed by an enzyme and requires ATP
6. This motion continues until the ribosomes reach a stop codon at end of mRNA molecule

The stop codon will not code for an amino acid, meaning the ribosome will detach, ending translation

Question 12

Outline the steps of the transcription part of protein synthesis with key words:

Answer 12

1. DNA helicase
2. Template
3. Alignment
4. RNA polymerase
5. Modification

Question 13

Outline the process of translation during protein synthesis using key words:

Answer 13

1. Modified mRNA
2. Ribosome
3. tRNA molecule
4. Movement
5. Amino acids
6. Stop codon