4.2 DNA and protein synthesis Flashcards
What is mRNA?
- Made by transcription in the nucleus
- Acts as a template for translation in the cytoplasm
- Sequence of bases on RNA determines sequence of amino
acids in polypeptide chain - Straight chain molecule
- Sequence of bases on RNA determined by sequence of
bases on DNA (Triplet code = codon) - Chemically unstable
- So breaks down after a few days
What is tRNA?
- Carries an amino acid - amino acid binding site
- Anticodon = 3 bases
- Anticodon bases complementary to mRNA codon
- Each tRNA specific to one amino acid, in relation to its anticodon
- Single polynucleotide strand
- Folded – 3 hairpin loops = three-leafed clover shape
- Held together by hydrogen bonds
What is tRNA?
- Carries an amino acid - amino acid binding site
- Anticodon = 3 bases
- Anticodon bases complementary to mRNA codon
- Each tRNA specific to one amino acid, in relation to its anticodon
- Single polynucleotide strand
- Folded – 3 hairpin loops = three-leafed clover shape
- Held together by hydrogen bonds
What are the similarities and differences between the structure of mRNA and tRNA molecules?
Similarities
- Both single polynucleotide strand
Differences
- mRNA single helix / straight, whereas tRNA folded into clover shape
- mRNA is a longer, variable length, whereas tRNA is shorter
- mRNA contains no paired bases or hydrogen bonds, whereas tRNA has some paired bases and hydrogen bonds
Describe the process of transcription:
In nucleus
- DNA double helix unzipped / unwound by DNA helicase
- Hydrogen bonds broken
- Only one DNA strand acts as template
- RNA nucleotides align next to their complementary bases on the template strand by complementary base pairing
- Forming (temporary) hydrogen bonds
- RNA polymerase joins adjacent nucleotides - condensation reaction
- Forming phosphodiester bonds
- Pre-mRNA spliced to remove introns
What happens after transcription:
Whole gene transcribed to pre-mRNA (contains introns and exons)
SPLICING:
- Introns removed
- Exons spilced together
Prokaryotic DNA doesn’t contain introns - mRNA produced directly
Describe the process of translation:
- Sequence of mRNA codons determines sequence of amino acids
- tRNAs carry specific amino acids, in relation to their anticodon
- tRNA anticodon binds to complementary mRNA codon (hydrogen bonds formed)
- Two amino acids joined by condensation, forming a peptide bond (using energy from ATP)
- tRNA detaches, ribosome moves along mRNA to next codon
- Continues until stop codon (polypeptide released)
Describe the process of translation:
- Sequence of mRNA codons determines sequence of amino acids
- tRNAs carry specific amino acids, in relation to their anticodon
- tRNA anticodon binds to complementary mRNA codon (hydrogen bonds formed)
- Two amino acids joined by condensation, forming a peptide bond (using energy from ATP)
- tRNA detaches, ribosome moves along mRNA to next codon
- Continues until stop codon (polypeptide released)
What is the role of ATP in translation:
- Hydrolysis of ATP, to ADP + Pi, releases energy
- For the bond between the amino acid and its corresponding tRNA molecule
- Amino acid attaches at amino acid binding site
- For peptide bond formation between amino acids
