Topic 2.7 - Transcription and translation Flashcards
What is transcription and where does it occur ?
The synthesis of an RNA sequence from a DNA template. This process occurs within the nucleus of a cell
Which enzyme mediates transcription ?
RNA Polymerase
What happens after transcription ?
The RNA is released to the cytoplasm (for translation)
and the DNA remains within the nucleus and reforms a double helix
What are the three types of RNA ?
mRNA – Transcript used to make protein
tRNA – Transfers amino acid to ribosome
rRNA – Catalytic component of ribosome
What is the genetic code ?
The genetic code is the set of rules by which information encoded in mRNA sequences is converted into a polypeptide sequence
What is a codon ?
Codons: Triplets of bases which correspond to a particular amino acid
Give the characteristics of codons ?
The order of the codons determines the amino acid sequence for a protein. A coding sequence always begins with a start codon (AUG). A coding sequence is terminated with a stop codon.
What are the genetic code’s two key features ?
- Universality – All organisms use the same genetic code
- Degeneracy – Multiple codons may code for the same amino acid
What is translation ?
Translation is the process of polypeptide synthesis by the ribosome
Give the steps of translation
- Messenger RNA (mRNA) is transported to the ribosome
- A ribosome reads an mRNA sequence in base triplets called codons
- Each codon codes for a specific amino acid (as per the genetic code)
- Amino acids are transported to ribosomes by transfer RNA (tRNA)
- Each tRNA aligns opposite a codon via a complementary anticodon
- The ribosome moves along the mRNA sequence (5’ → 3’) and joins
amino acids together with peptide bonds (condensation reaction) - The synthesis of a polypeptide is initiated at a start codon (AUG)
and is completed when the ribosome reaches a STOP codon
What is a gene ?
A gene is a sequence of DNA which encodes a polypeptide sequence
* One gene = one polypeptide (proteins may have multiple polypeptides)
