DNA and protein synthesis Flashcards
1
Q
What is messenger RNA (mRNA)? [4]
A
- Made by transcription in the nucleus
- Acts as a template for translation in the cytoplasm
- Sequence of bases on RNA determined by sequence of bases on DNA
- Chemically unstable, so breaks down after a few days
2
Q
What is a transfer RNA (tRNA)? [4]
A
- Carries an amino acid at the amino acid binding site
- Each tRNA specific to one amino acid, in relation to its anticodon
- Anticodon bases complementary to mRNA
codon - Single, folded polynucleotide strand, held together by hydrogen bonds
3
Q
Give 1 similarity and 3 differences in the structure of mRNA and tRNA molecules
A
SIMILARITIES
Both single polynucleotide strand
DIFFERENCES
mRNA a single straight helix
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
4
Q
Transcription [9]
A
- Takes place in nucleus
- DNA double helix unzipped by DNA helicase
- Hydrogen bonds broken
- RNA nucleotides align next to their complementary bases on the template strand
- Forming (temporary) hydrogen bonds
- Uracil replaces thymine in RNA
- RNA polymerase joins adjacent nucleotides in a condensation reaction, forming phosphodiester bonds
- When RNA polymerase reaches stop codon, mRNA (prokaryotes) or pre-mRNA (eukaryotes) detaches from DNA, breaking temporary hydrogen bonds
- mRNA leaves nucleus via nuclear pore
5
Q
Post Transcriptional Modification [4]
A
- Eukaryotic genes contain exons (coding regions) + introns (non-coding regions)
- Whole gene transcribed to pre-mRNA, containing both exons and introns
- Splicing takes place, where introns are removed and exons spliced together
- Exons spliced together in different combos for different proteins
6
Q
Why is mRNA produced directly from DNA in prokaryotic cells? [3]
A
- Prokaryotic DNA doesn’t contain introns
- mRNA produced directly from DNA
- No splicing necessary
7
Q
Translation [7]
A
- Sequence of mRNA codons determines sequence of amino acids
- tRNAs carry specific amino acids, in relation to their anticodon
- At the ribosome, tRNA anticodon binds to complementary mRNA codon, forming hydrogen bonds
- Two amino acids joined by condensation, forming a peptide bond, using energy from ATP
- tRNA detaches leaving its amino acid behind
- ribosome moves along mRNA to next codon
- Continues until stop codon and polypeptide released
8
Q
Describe the role of ATP in Translation [4]
A
- Allows hydrolysis of ATP, to ADP + Pi, releasing energy
- Allows the bond between the amino acid and its corresponding tRNA molecule to form
- Allows amino acid to attach at amino acid binding site
- Allows for peptide bond formation between amino acids
9
Q
Describe the role of tRNA in Translation [4]
A
- tRNA attaches to and transports a specific amino acid, in relation to its anticodon
- tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds
- Two tRNAs bring amino acids together for the formation of a peptide bonds
- About 60 types of tRNAs to carry 20 different amino acids as the genetic code is degenerate
10
Q
Describe the role of ribosomes in Translation [2]
A
- Attaches to mRNA and houses tRNA, allowing codon-anticodon complementary base pairing
- Allows peptide bonds to form between amino acids
