Protein synthesis Flashcards
What are the 2 steps involved in protein synthesis
- Transcription
- Translation
Define transcription
Where one gene of the DNA is copied into mRNA
Define translation
Where the mRNA joins with a ribosome, and corresponding tRNA molecules brings the specific amino acid the codon codes for
Where does transcription happen within the cell
Inside the nucleus
Why do we have the create a copy of the gene of interest on the DNA for protein synthesis (2 reasons)
- Because DNA is too big to leave the nucleus
- There are enzymes in the cytoplasm that could damage the DNA
How come mRNA is small enough to leave the nucleus but DNA isn’t
Because mRNA carries the code for one gene whereas DNA carries the code for all the genes
What is the first step in transcription, and name the enzyme
The DNA HELIX UNWINDS to expose the bases to act as a template - unwinding is catalysed by DNA HELICASE
During transcription, how many chains of DNA act as a template, and why is this
Only one because mRNA is single stranded
What type of bonds does DNA helicase break between the bases
Hydrogen bonds
Once DNA helicase has unzipped the DNA strand, what do the free mRNA nucleotides do
They align opposite exposed complementary DNA bases
What is the name of the enzyme that bonds together RNA nucleotides to create a new RNA polymer chain
RNA polymerase
What bonds form between the RNA nucleotides uses the enzyme RNA polymerase
Phosphodiester bonds
What process occurs to change pre-mRNA to mRNA
Splicing
What happens during splicing
The introns are removed
What are introns
The sequences of bases in the DNA which don’t code for amino acids
What is the name of the enzyme involved in splicing
Splicesome
What bonds does the splicesome break
The phosphodiester bonds
Does mRNA contain any introns
No, it only contains exons- the coding part of DNA
What happens during translation
The polypeptide chain is created using both the mRNA base sequence and the tRNA
Once the mRNA has left the nucleus where does it go
It attaches to a ribosome in the cytoplasm
What does the tRNA molecule with the complementary anticodon to the start codon do
It aligns opposite the mRNA, held in place by the ribosome
What is the role of the ribosome during translation
To hold the mRNA and tRNA molecules in place
Once the tRNA that has complementary anticodon to the codon on mRNA has aligned, what does the ribosome do
It moves along the mRNA, so another tRNA molecule can align
How many tRNA molecules can the ribosome hold at one time during translation
Two
When there are 2 tRNA molecule aligned with the mRNA molecule, what happens to their amino acids before the ribosome releases it, and what is required for this to happen
The amino acids are joined by a peptide bond- this is catalysed by an enzyme and requires ATP
Can tRNA molecules be reused
Yes, after they have detached from the ribosome than enter the cytoplasm again and can be reused
What codon is required at the end of the mRNA molecule to stop translation
The stop codon
How does the stop codon end translation
Because it doesn’t code for an amino acid and therefore the ribosome detaches since there isn’t a corresponding anticodon on a tRNA molecule
After translation, where does the polypeptide chain go and what happens
It enters the Golgi body for folding and modification
When reading a base sequence wheel, what sequence does it read for; DNA, mRNA, or tRNA
mRNA
Describe 2 differences between the structure of a tRNA molecule and the structure of an mRNA molecule
- tRNA is clover leaf shape, mRNA is linear
- tRNA has hydrogen bonds, mRNA does not
- tRNA has an amino acid binding site, mRNA does not
- tRNA has anticodon, mRNA has codon
Describe and explain the difference in the structure of pre-mRNA and mRNA (2 marks)
- mRNA has fewer nucleotides
- Because of splicing
Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation (3 marks)
- tRNA brings specific amino acid to ribosome
- Anticodon on tRNA binds to codon on mRNA
- Amino acids join by condensation reaction/ join by forming a peptide bond
Describe how mRNA is produced from an exposed template strand of DNA, not including DNA helicase or splicing (3 marks)
- Free RNA nucleotides form complementary base pairs
- Phosphodiester bonds form
- By action of RNA polymerase
Describe how mRNA is formed by transcription in eukaryotes (5 marks)
- Hydrogen bonds between DNA bases break
- Only one strand acts as a template
- Free RNA nucleotides align by complementary base pairing
- In RNA uracil base pairs with adenine
- RNA polymerase joins adjacent RNA nucleotides
- By phosphodiester bonds
- Pre-mRNA is spliced
Describe how a polypeptide is formed by translation of mRNA (6 marks)
- mRNA attaches to ribosomes
- tRNA anticodon binds to complementary mRNA codon
- tRNA brings specific amino acid
- Amino acid joins by peptide bond
- Amino acids join together with the use of ATP
- tRNA released
- The ribosome moves along the mRNA to form the polypeptide
What is the proteome of a cell
Range of different proteins that a cell is able to produce
Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide (5 marks)
- mRNA associates with a ribosome
- Ribosome moves to the start codon
- tRNA brings specific amino acid
- Anticodon to codon
- Ribosome moves along to next codon
- Amino acids join by peptide bonds
Describe the role of a ribosome in the production of a polypeptide (3 marks)
- mRNA binds to ribosome
- 2 codons
- tRNA with anticodons to bind
- Formation of peptide bonds between 2 amino acids
- Moves along mRNA to next codon
