3.10 Protein Synthesis Flashcards
Where is DNA contained, in a eukaryotic cell (specifically)? (1 mark)
Within a double membrane called the nuclear envelope that encloses the nucleus.
Where does protein synthesis occur? (1 mark)
In the ribosomes
Why is transcription needed? (1 mark)
A DNA molecule is too large to leave the nucleus to supply the coding information needed to determine the protein’s amino acid sequence.
How does transcription work? (1 mark)
The sequences of genes are copied and transported to the site of protein synthesis.
What does transcription produce? (1 mark)
Shorter molecules of RNA.
What is the strand that contains the code for the protein called? (1 mark)
The sense strand.
Does the antisense strand code for the protein? (1 mark)
No.
What is the function of the antisense strand? (2 marks)
It acts as a template strand during transcription, so that the complementary RNA strand formed carries the same sequence as the sense strand.
Describe transcription. (5 marks)
- The section that contains the gene unwinds and unzips (RNA helicase).
- Free RNA nucleotides base pair with complementary bases on the antisense strand.
- Phosphodiester bonds form between the RNA nucleotides (RNA polymerase).
- The completed short strand of RNA is called messenger RNA (mRNA).
- mRNA detaches from template and leaves nucleus through a nuclear pore.
- The DNA helix reforms and the mRNA molecule travels to a ribosome.
What does RNA polymerase do? (1 mark)
Catalyses the formation of phosphodiester bonds between RNA nucleotides.
What is a short strand of RNA formed during transcription called? (1 mark)
mRNA
How does mRNA leave the nucleus? (1 mark)
Through a nuclear pore.
What are the two subunits in eukaryotic ribosomes composed of? (1 mark)
Protein and ribosomal RNA (rRNA).
Where does mRNA go after leaving the nucleus? (1 mark)
Travels to a ribosome and binds to a specific site on the small subunit.
What is translation? (1 mark)
The mRNA is decoded (translated) into a sequence of amino acids.
What is the anticodon? (1 mark)
Three bases on the end of a tRNA molecule.
What do tRNA molecules carry? (1 mark)
Carry an amino acid corresponding to the codon.
What happens when the tRNA anticodons bind to the complementary codons along the mRNA? (2 marks)
The amino acids are brought together in the correct sequence to form the primary structure of the protein, a polypeptide.
Describe the stages of translation. (5 marks)
- The mRNA attaches to ribosome
- A tRNA with the complementary anticodon binds to the mRNA start codon.
- Another tRNA then binds to the next codon on the mRNA.
- A peptide bond forms between the first and second amino acid (brought by the tRNA molecules)
- The ribosome then moves along the mRNA, releasing the first tRNA.
- This repeats, until the ribosome reaches the stop codon an the polypeptide chain is released.
When do the secondary and tertiary structures of the protein form? (1 mark)
As the amino acids are joined together forming the primary structure of the protein, they fold into secondary and tertiary structures.
Where may the protein undergo further modifications? (1 mark)
Golgi apparatus
Can multiple polypeptide chains be formed from the same mRNA molecule at once, why not/can they? (2 marks)
Yes, because many ribosomes can follow on the mRNA behind the first.
