Protein synthesis Flashcards
The ribosomes involved in Eukaryote protein synthesis
40 and 60S subunits –> 80S ribosome.
Prokaryote ribosome subunits are
30 and 50S –> 70S ribosomes.
Describe intiation of protein synthesis
GTP hydrolysis and initiation factors assemble 40S ribsome subunits with tRNA and the 60S subunit with mRNA.
Describe elongation of protien
Aminoacyl-tRNA binds to A site in the ribosome complex.
rRNA catalyzes the peptide bond formation binding the polypeptide to the new aminoacid in A-site.
Ribosome advances 3nucleotides along the mRNA (5’ –3’) with the peptidyl tRNA moving into the P-site
Describe termination of protein synthesis
Stop codon (UAA/UGA/UAG) recognised and polypeptide is released.
Describe the A, P and E sites of the ribosome
A site accomodates the incoming aminoacyle-tRNA (TRNA plus amino acid for protein synthesis)
P-site - Accomodates the growing peptide
E-site hold the empty/used tRNA as it exits.
Describe post-translational modifications of Proteins
Happen in the Golgi Apparatus.
Trimming - removal of N-/C- terminus
Covalent alterations - phosphorylation, glycosylation, hydroxylation, methylation, acetylation and ubiquitination
Describe what the Rough endoplastic reticulum does?
Has many ribosomes present.
Site of synthesis of secretory protiens and the addition of N-linked oligiosaccharides to proteins.
Mucous secreting cells and plasma cells are rich in RER.
What is a Nissl body?
RER in neurones that synthesise neurotransmitters.
Describe Smooth Endoplasmic reticulum
No ribosomes and is the site of steroid synthesis in adrenal cortex and gonads
Detoxification of drugs and poisons in hepatocytes.
Describe the function of the Golgi apparatus.
involved in cell trafficking and distrubution of proteins and lipids from ER to vesicles and the plasma membrane.
modifies proteins for packaging.
Endosomes sort incoming material and can send it to lysosomes for destruction or to the Golgi for use.
What is I cell disease
Inclusion cell disease is an inherited lysosomal storage disorder.
defect in N-acetylglucosaminyl-1-phosphotransferase leads to the Golgi unale to phosphorylate mannose residues (low mannose-6-phosphate) on glycoproteins leading to excretion rather than lysosome packaging.
What are the characteristics of I-cell disease
Coarse facial features, Clouded corneas, Restricted joint movement high plasma levels of lysosomal enzymes. Often fatal in childhood.
What are Peroxisomes and Proteasomes
Peroxisome - membrane enclosed organella involved in catabolism of very-long-chain fatty acids, amino acids and other branched fatty acids.
Proteasome - Protein comple that degrades damaged or ubiquitin-tagged proteins.
Problems in this system has been indicated in Parkinson’s disease.
