Lipincott Chapter 31 Flashcards
T or F. Huntington’s and Fragile x syndrome are examples of trinucleotide repeat expansion.
True. Huntington is CAG repeats (glutamine), and fragile X repeats in the UTR of a gene, decreasing protein produced.
When the genetic code is said to have: specificity, universality, degeneracy and nonoverlapping, what does that mean?
Specificity: particular codon always codes for the same AA.
Universality: same code, save for mitochondria
Degeneracy: redundant codes for one AA
Nonoverlapping: code is read from fixed point.
What enzymes are required to attach amino acids to their corresponding tRNAs?
Aminoacyl tRNA synthetases.
What does the APE sites in a ribosome do, respectively?
A: binds incoming aminoacyl tRNA
P: peptidyl tRNA, this tRNA carries chain of amino acids already synthesized
E: empty tRNA exiting ribosome
T or F. Mitochondria have their own DNA and ribosomes, and make most of their own proteins.
False. Most mitochondrial proteins are encoded by nuclear DNA, made by ribosomes in the cytosol and post translationally targeted to mitochondria.
How much energy is required to add one aa to a growing polypeptide chain?
- two from ATP for the aminoacyl tRNA synthetase reaction
two from GTP for the binding of tRNA to the A site, and the translocation step.
What is the wobble hypothesis?
codon anticodon pairing follows the traditional CG AT rule for the first two bases of the codon but can be less stringent for the last base.
What is the Shine Dalgarno sequence?
in E. coli mRNA, a purine rich sequence 6-10 bases upstream of AUG where the rRNA component of a ribosomal subunit complements, attaches.
What is the 5’ cap?
the eukaryotic equivalent of the shine dalgarno sequence. 5’ cap binds to small 40s subunit and moves down sequence until it hits AUG. scanning process requires ATP.
Describe the process of initiation in translation.
AUG recognition is facilitated by (e)IF2-GTP. Initiator tRNA enters P site directly. Large ribosomal subunit joins complex. N terminal Met usually removed before translation completes.
Describe elongation of amino acid chain.
tRNAs delivered to A site, facilitated by elongation factors. peptide bond formed by the peptidyltransferase activity of an rRNA of the large ribosomal subunit. the aa on the tRNA in the P site bonds with the aa of the tRNA in the A site. Translocation moves APE down 3 nucleotides (costs GTP to GDP)
Describe aa termination.
Termination codons enter A site, recognized by termination factors RF1 and RF2 (eRF). This hydrolyzes the bond between the peptide and tRNA in the P site. RF3 (eRF3) releases RF1/2 (eRF).
eIF, which helps bring initiator tRNA to P site, when phosphorylated, is ______.
Inactive.
T or F. NLS and mitochondrial entry sequence are examples of protein targeting sequences.
True.
What is protein trimming?
many proteins destined for secretion are made as large precursors that are cleaved via endoproteases in the ER, golgi, or secretory vesicle.
