Download bch2ibm: molecular biology end of semester 1 exam notes 2014

BCH2IBM: MOLECULAR BIOLOGY END OF SEMESTER 1 EXAM NOTES 2014 Qu. What is protein synthesis? -­‐ The process by which AAs are linearly arranged into proteins via peptide bonds through the involvement of ribosomal RNA, tRNA, mRNA and various enzymes. Qu. What is protein synthesis catalyzed by? -­‐ Ribosomes. They make covalent peptide bonds and ensure AAs are added in the correct order. Qu. Define translation. -­‐ It’s the process by which the nucleotide sequence of an mRNA is used as a
template to join the amino acids in a polypeptide chain in the correct order.
Qu. What are the 3 types of RNA molecules involved in translation and what do
they do?
1) Messenger RNA (mRNA)
-­‐ Carries genetic information from DNA in a linear form via the process of
transcription. It is read in sets of 3- nucleotide sequences called CODONS
which specify a particular amino acid.
2) Transfer RNA (tRNA)
-­‐ Deciphers the codons in mRNA.
-­‐ Each amino acid has its own set of tRNAs which bind to it. Each tRNA
contains a 3-nucletide sequence called the anticodon. ANTICODON. This is
complementary to the codon in mRNA
3) Ribosomal RNA
-­‐ Associates with protein to form the ‘ribosomes’. Ribosomes work together
with mRNA and tRNA molecules to catalyse the assembly of the assembly of
the amino acids into the polypeptide chain.
Qu. What was Crick’s adapter hypothesis? And what is the molecule now called? -­‐ Hypothesised that AAs don’t bind directly to mRNA but need an adaptor molecule that could match the mRNA with a corresponding AA. -­‐ One side of the adaptor could bind a specific AA to it, while the other side recognises the nucleotide sequence in mRNA. -­‐ Molecule now called tRNA Qu. If one/two/three bases correspond to an amino acid, how many potentially different amino acids could there be in a polypeptide? -­‐ 4^1 -­‐ 4^2 -­‐ 4^3 Qu. Why are codons groups of 3 nucleotides? -­‐ It’s the only way of ensuring there are enough codons for the 20 diff AAs. Qu. What is the AA sequence determined by? -­‐ The nucleotide sequence Qu. What are facts about the genetic code? -­‐ There are at least 20 AAs commonly found in proteins -­‐ The code is universal -­‐ Degenerate-­‐ Some AAs have more than one codon, but these codons are similar (only the 3rd base varies) -­‐ Some tRNAs can recognise more than one codon. Qu. What’s the ‘wobble base’? -­‐ -­‐ When several different codons specify more than one AA, usually with the first 2 bases are the same, and the third codon varies. This third codon is known as a wobble, and the bond formed between this third base on the tRNA and the ribosome is not as stable, thus its importance is diminished. Qu. How many bases do the following code for? -­‐ Methionine and tryptophan= 1 codon -­‐ Prolin = 4 codons -­‐ Serine = 6 codons Qu. What are start and stop codons? -­‐ Start codons= indicate where translation begins (AUG) -­‐ Stop codons= indicate where translation ends (UAA. UAG. UGA) Qu. What’s an open reading frame? -­‐ A segment in a nucleotide sequence that doesn’t have a termination codon for at least 50 codons. (There’s normally a stop codon for every 20 codons in a sequence) Qu. In theory, every mRNA has how many potential reading frames? -­‐ 3 possible reading frames because after 3 nucleotides, the codons are the same again… but in reality only 1 is used. Qu. What does the selection of the correct reading frame rely on? -­‐ Features upstream of the start codon (Shine-­‐Delgarno sequence) Qu. What is the Shine-­‐Delgarno sequence? -­‐ It’s a ribosomal binding site in mRNA, generally located 8 basepairs upstream of AUG -­‐ Exists only in prokaryotes -­‐ The six-­‐base consensus sequence is AGGAGGU –> this sequence helps recruit the ribosome to the mRNA to initiate protein synthesis by aligning it with the start codon AUG at the peptidyl (P-­‐site) on the ribosome.