A Level Biology: Protein Synthesis Flashcards
What are the two stages of protein synthesis?
Transcription (DNA → mRNA) and Translation (mRNA → protein).
Where does transcription occur?
In the nucleus of eukaryotic cells.
Where does translation occur?
On ribosomes in the cytoplasm.
What are the three types of RNA involved in protein synthesis?
- mRNA (messenger RNA) – carries the genetic code from DNA to the ribosome.
- tRNA (transfer RNA) – carries amino acids to the ribosome.
- rRNA (ribosomal RNA) – makes up part of the ribosome and helps with translation.
What happens during transcription?
A section of DNA is copied into mRNA.
What enzyme is responsible for transcription?
RNA polymerase.
What is the role of RNA polymerase?
It binds to DNA, unzips the strands, and assembles a complementary mRNA strand.
What is complementary base pairing in transcription?
A (adenine) pairs with U (uracil), and C (cytosine) pairs with G (guanine).
What is pre-mRNA?
The initial RNA transcript that contains introns and exons.
What happens to pre-mRNA before it leaves the nucleus?
Splicing – Introns (non-coding regions) are removed, and exons (coding regions) are joined together.
Do prokaryotic cells perform splicing?
No, because prokaryotic DNA does not contain introns.
What happens during translation?
The mRNA sequence is used to assemble a polypeptide at the ribosome.
What is a codon?
A sequence of three bases on mRNA that codes for an amino acid.
What is an anticodon?
A sequence of three bases on tRNA that is complementary to an mRNA codon.
How does tRNA contribute to translation?
tRNA molecules carry specific amino acids to the ribosome.
What is the first codon in translation?
AUG (Start codon – codes for methionine).
What happens when the ribosome reaches a stop codon?
Translation ends, and the polypeptide is released.
What happens to the polypeptide after translation?
It folds into a functional protein and may undergo modifications in the Golgi apparatus.
What are the possible modifications to a polypeptide?
• Folding into secondary and tertiary structures.
• Adding functional groups (e.g., phosphate, carbohydrate).
• Combining with other polypeptides to form a quaternary structure.
What is the difference between a sense strand and an antisense strand?
• Sense strand: The coding strand (same sequence as mRNA, except T instead of U).
• Antisense strand: The template strand (used to make mRNA).
What is the difference between transcription in prokaryotes and eukaryotes?
• Prokaryotes: No splicing, transcription occurs in the cytoplasm.
• Eukaryotes: Splicing occurs, transcription happens in the nucleus.
Why is the genetic code described as degenerate?
Because more than one codon can code for the same amino acid.
Why is the genetic code non-overlapping?
Each base is read once and in triplets (codons) during translation.
Why is the genetic code universal?
The same codons code for the same amino acids in almost all organisms.
