3.4.2 DNA and protein synthesis ( 3.4 Genetic information , variation and relatoonships between organisms) Flashcards
Define ‘genome’.
The complete set of genes in a cell (including those in mitochondria and/or chloroplasts).
Define ‘proteome’.
The full range of proteins that a cell can produce (coded for by the cell’s DNA/genome).
What are the two stages of protein synthesis?
- Transcription
- Translation
What happens during transcription?
Production of messenger RNA (mRNA) from DNA, in the nucleus.
What happens during translation?
Production of polypeptides from the sequence of codons carried by mRNA, at ribosomes.
Compare the structure of tRNA and mRNA.
Both are single polynucleotide strands.
Contrast the structure of tRNA and mRNA.
tRNA is folded into a ‘clover leaf shape’, whereas mRNA is linear/straight.
tRNA has hydrogen bonds between paired bases, mRNA doesn’t.
tRNA is a shorter, fixed length, whereas mRNA is longer, variable length (more nucleotides).
tRNA has an anticodon, mRNA has codons.
tRNA has an amino acid binding site, mRNA doesn’t.
How is mRNA formed by transcription in eukaryotic cells?
- Hydrogen bonds between DNA bases break.
- Only one DNA strand acts as template.
- Free RNA nucleotides align next to their complementary bases on the template strand.
- RNA polymerase joins adjacent RNA nucleotides.
- This forms phosphodiester bonds via condensation reactions.
- Pre-mRNA is formed and this is spliced to remove introns, forming (mature) mRNA.
What is used in place of thymine in RNA?
In RNA, uracil is used in place of thymine (pairing with adenine in DNA).
How does the production of mRNA differ in eukaryotic and prokaryotic cells?
Pre-mRNA is produced in eukaryotic cells whereas mRNA is produced directly in prokaryotic cells.
Because genes in prokaryotic cells don’t contain introns so no splicing in prokaryotic cells.
What are the steps of translation leading to the production of a polypeptide?
- mRNA attaches to a ribosome and the ribosome moves to a start codon.
- tRNA brings a specific amino acid.
- tRNA anticodon binds to complementary mRNA codon.
- Ribosome moves along to next codon and another tRNA binds so 2 amino acids can be joined by a condensation reaction forming a peptide bond.
- tRNA released after amino acid joined polypeptide.
- Ribosome moves along mRNA to form the polypeptide, until a stop codon is reached.
What energy source is used during translation?
Using energy from hydrolysis of ATP.
What is the role of ATP in translation?
Hydrolysis of ATP to ADP + Pi releases energy, allowing amino acids to join to tRNAs and form peptide bonds.
What is the function of tRNA in translation?
tRNA attaches to and transports a specific amino acid, in relation to its anticodon.
tRNA anticodon forms complementary base pairs with mRNA codon, creating hydrogen bonds.
How do ribosomes function in translation?
mRNA binds to ribosome, allowing tRNA with anticodons to bind and catalyzing the formation of peptide bonds between amino acids. Ribosomes move along mRNA during translocation.
