Chapter 4 (genetic Code, Mutations And Translation) Flashcards
Proteins start with which amino acid
Methionine in eukaryotes and formylmethionine in prokaryotes
Code for methionine ?
AUG
Types of DNA mutations ?
Silent Missense Nonsense Frameshift ( deletion or insertion ) Trinucleotide repeat expansion 5’ splice site or 3’ splice site
Example for missense mutation
Sickle cell anemia : glutamine into valein
Example for nonsense mutation ?
Hemophilia : factor 8 mutation
Example for single nucleotide deletion ?
Duchenne
Example for deletion not causing frame shift ?
Cystic fibrosis ( CFTR protein ) delta F508
Example for insertion causing frame shift ?
Tay sachs disease ( hexosaminadase A gene mutation )
Example for insertion not causing frame shift ?
Huntington’s disease ( huntingtin )
Examples for mutations in splice sites ?
Beta thalassemia , Gaucher disease and Tay-Sachs
Examples for trinucleotide repeat expansion ?
Huntington disease Spinobulbar muscular dystrophy Fragile X syndrome Myotonic dystrophy Friedreich’s ataxia
In which direction are the proteins synthesized ?
From the amino to the carboxyl terminus
Aminoglycosides mechanism ?
Preventing the 30 S subunit of ribosome from recognizing Shine-Dalgarno on the mRNA in the initiation phase of translation
Linezolid mechanism ?
Binds to 50 S subunit and prevents initiation phase
Tetracycline mechanism ?
Prevent aminoacyl-tRNA from binding to A site in the ribosome in the elongation phase of translation
Chloramphenicol mechanism ?
Inhibition of peptidyl transferase in the elongation phase of translation
Macrolides ( erythromycin ) and clindamycin mechanism ?
Bind to 50 S subunit and prevent translocation in elongation phase of translation
Pseudomonas and diphtheria toxins mechanism ?
Inactivation of eEF-2 by ADP-ribosylation in the elongation phase of translation
Grey baby syndrome ?
Newborns
Given chloramphenicol
Showing blue lips , nails and skin
With low BP and finally death
Genetic defect in cystic fibrosis ?
Deletion of phenyalanine at position 508 which interferes with proper protein folding and the posttranslational processing of oligosaccharide side chains
How the enzymes are directed to the lysosomes ?
By phosphorylation of mannose residues
N-terminal hydrophobic signal sequence in the proteins function ?
To ensure translation on the RER
Proteins in blood that aren’t glycosylated ?
Albumin
Insulin
Glucagon
Protein solely N-glycosylated ?
Transferin
Protein solely O-glycosylated ?
Heparin
Protein both N and O-glycosylated ?
LDL receptor
Alpha 1 antitrypsin deficiency defect ?
Z mutation which causes the alpha 1 antitrypsin protein to misfold and aggregate in the ER where it damages cells
Presents by micronodular cirrhosis and prominent fibrosis
I-Cell disease ?
Genetic defect of phosphorylation of lysosomal enzymes leading to their release into the extracellular space and inclusion bodies accumulate in the cell Symptoms : coarse facial features Gingival hyperplasia Psychomotor and growth retardation Bone deformities Mittal valve defect
Scurvy ? (Vitamin C deficiency )
Defect : deficient hydroxylation of prolines and lysines during collagen synthesis
Symptoms : Petechiae
Loose teeth
Bleeding gums
Osteogenesis imperfecta ?
Defect : mutation in collagen l gene
Symptoms : skeletal deformities
Blue sclera
Ehlers-Danlos syndrome ?
Defect : mutations in collagen genes and proline and lysyl hydroxylases
Symptoms : hyperextensible fragile skin
Hypermobile joints
Arterial and intestinal ruptures
Menkes disease ? ( Ehlers-Danlos type lX) ( kinky hair syndrome )
Defect : deficient cross linking in collagen synthesis due to functional copper deficiency du to mutation of ATP7A gene that encodes ATP-dependent copper efflux protein in the intestine
Symptoms : kinky hypopigmented hair
Arterial turtuosity and rupture
Cerebral degeneration ( mentally retarded ) , subdural hematoma
Bladder diverticula
Alport syndrome ?
Mutation in collagen Vl gene
Amino acids that have 1 codon only ?
Methionine and Tryptophan
Example for large segment deletion ?
Alpha thalassemia in which unequal cross over has deleted one or more alpha globin genes from chromosome 16
Which amino acid is unique to collagen ?
Hydroxyproline
Alpha thalassemia mutation ?
Unequal cross over has deleted one or more alpha globin genes from chromosome 16
Functions of proteasomes ?
1- digesting damaged proteins to peptides 2- play a role in producing antigenic peptides for presentation by class l MHC molecules
