4.2 DNA and Protein Synthesis 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)
describe the two stages of protein synthesis
-transcription= production of messenger RNA (mRNA) from DNA, in the nucleus
-translation= production of polypeptides from the sequence of codons carried by mRNA, at ribosomes
compare similarities between the structure of tRNA and mRNA
-both single polynucleotide strand
contrast differences between 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 a longer, variable length (more nucleotides)
● tRNA has an anticodon, mRNA has codons
● tRNA has an amino acid binding site, mRNA doesn’t
describe how mRNA is formed by transcription in eukaryotic cells
- hydrogen bonds between DNA bases break
- only one DNA strand acts as a template
- free RNA nucleotides align next to their complementary bases on the template strand
○ in RNA, uracil is used in place of thymine (pairing with adenine in DNA) - 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
describe how production of messenger RNA (mRNA) in a eukaryotic cell is different from the production of mRNA in a prokaryotic cell
● pre-mRNA 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
describe how translation leads 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
○ using energy from hydrolysis of ATP - tRNA released after amino acid joined polypeptide
- ribosome moves along mRNA to form the polypeptide, until a stop codon is reached
describe the role of ATP in translation
- hydrolysis of ATP to ADP + Pi releases energy
- so amino acids join to tRNAs and peptide bonds form between amino acids
describe the role of tRNA in translation
-attaches to / transports a specific amino acid, in relation to its anticodon
-tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds
-2 tRNAs bring amino acids together so peptide bond can form
describe the role of ribosomes in translation
-mRNA binds to ribosome, with space for 2 codons
-allows tRNA with anticodons to bind
-catalyses formation of peptide bond between amino acids (held by tRNA molecules)
-moves along (mRNA to the next codon) / translocation
describe how the base sequence of nucleic acids can be related to the amino acid sequence of polypeptides when provided with suitable data
● you may be provided with a genetic code to identify which
triplets / codons produce which amino acids (example shown)
● tRNA anticodons are complementary to mRNA codons
○ eg. mRNA codon = ACG → tRNA anticodon = UGC
● sequence of codons on mRNA are complementary to sequence
of triplets on DNA template strand
○ eg. mRNA base sequence = ACG UAG AAC → DNA base sequence = TGC ATC TTG
● in RNA, uracil replaces thymine
