Topic 4---A: DNA, RNA and Protein Synthesis- 4. Transcription and translation Flashcards
1
Q
What happens during transcription?
A
An mRNA copy is made from DNA
2
Q
Where does transcription take place in eukaryotic cells?
A
In the nucleus
3
Q
Where does transcription take place in prokaryotic cells?
A
In the cytoplasm
4
Q
Transcription (stages)
A
- Specific region of the DNA molecule unwinds and unzips- hydrogen bonds between base pairs are broken which is catalysed by the enzyme DNA helicase
- 1 strand of DNA acts as a template strand for complementary mRNA nucleotides to line up at (known as coding/sense strand) by their base pairing.
- RNA polymerase moves along the DNA strand adding 1 complementary RNA nucleotide at a time to the mRNA strand to make a polynucleotide
chain. - RNA polymerase catalyses the formation of phosphodiester bonds between phosphate group and neighbouring ribose sugars
5
Q
What happens when RNA polymerase reaches stop signal?
A
- It stops making mRNA and detatches from DNA
- In eukaryotes mRNA moves out of the nucleus through a nuclear pore and attaches to a ribosome in the cytoplasm.
6
Q
Why do eukaryotic mRNA gets spliced?
A
Eukaryotic DNA contains introns so they get transcribed into pre-mRNA along with the exons
Splicing removes the introns from pre-mRNA and joins together the exons
7
Q
What happens during translation?
A
Amino acids are joined together to make a polypeptide chain following the sequence of codons carried by the mRNA
8
Q
Translation (stages)
A
- Ribosome moves along the mRNA strand reading the information one codon at a time (group of 3 mRNA bases)
- Each codon of mRNA bases attracts a tRNA molecule with the corresponding complementary anti-codons
- As each tRNA carries a specific amino acid this brings amino acids to the ribosome in a specific order and amino acids are joined by peptide bonds.
9
Q
Where does translation occur?
A
At the ribosomes in the cytoplasm
