transcription & translation Flashcards
(17 cards)
describe the two stages of protein synthesis.
transcription - production of mRNA from DNA in the nucleus.
translation - production of polypeptides from the sequence of codons carried by mRNA or ribosomes.
what is a codon?
triplets of nucleotide bases that code for an amino acid.
describe the mature of the genetic code.
triplet code
universal
non-overlapping
degenerate
what is the triplet code on a codon?
a sequence of 3 bases that codes for a specific amino acid (to be added to the polypeptide chain)
what does it mean when genetic code is universal?
the same base triplets code for the same amino acids in all organisms.
what does it mean when genetic code is non-overlapping?
each base is part of only one triplet so each triplet is read as a discrete unit.
what does it mean when the triplet code is degenerate?
an amino acid can be coded for by more than one triplet.
what are non-coding base sequences and where are they found?
non coding base sequence - DNA that does not code for amino acid sequences, found between genes or within genes.
what are introns and exons?
intron - base sequence of a gene that doesn’t code for amino acids (non-coding DNA)
exon - base sequence of a gene coding for amino acid sequences (codes for proteins)
define genome.
the full range of DNA/genes in a cell .
define proteome.
the full range of proteins that a cell can produce.
what is splicing?
the editing of pre-mRNA, introns are removed and exons are joined together.
compare and contrast the structure of tRNA and mRNA.
- both single stranded.
- tRNA is folded into clover leaf shape, whereas mRNA is linear.
- tRNA has hydrogen bonds between bases, whereas mRNA doesn’t.
- tRNA is a shorter fixed length, whereas mRNA is a longer variable length.
- tRNA has anticodons, mRNA has codons.
- tRNA has an amino acid binding site, mRNA doesn’t.
describe the process of transcription.
- DNA helicase breaks hydrogen bonds between bases, causing strands to separate.
- RNA polymerase moves along DNA ‘template strand’.
- complementary RNA nucleotides join together (U-A C-G)
- RNA polymerase joins adjacent nucleotides by phosphodiester bonds.
- pre-mRNA is formed and this is spliced to remove introns, forming mRNA.
describe how the production of mRNA is different in a eukaryotic cell from a prokaryotic cell.
- pre-mRNA is produced in eukaryotic cells, whereas mRNA is directly produced in prokaryotic cells.
- because genes in prokaryotic cells do not contain introns so no splicing occurs.
describe the process of translation.
- ribosome attaches to starting codon on mRNA.
- tRNA molecule carries a specific amino acid to ribosome and tRNA anticodon binds to complementary mRNA codon.
- ribosome moves along, linking the amino acid on the next tRNA molecule so the amino acids on both tRNA molecules are joined together via condensation reaction, forming peptide bond.
- as this happens, the first tRNA is released from its amino acid.
- ribosome moves along mRNA to form a polypeptide until a stop codon is reached.
- ribosome, mRNA and tRNA separate and polypeptide chain is complete.
describe the role of ATP, tRNA and ribosomes in translation.
ATP: hydrolysis of ATP (to ADP and Pi) releases energy so amino acids are joined to tRNAs by peptide bonds.
tRNA: transports specific amino acid to ribosome and its anticodon binds to complementary mRNA codon.
- 2 tRNAs bring amino acids together forming peptide bonds.
ribosomes: attaches to starting codon on mRNA.
- allows tRNA with anticodons to bind
- catalyses formation of peptide bonds between amino acids.
