Chapter 4 (genetic Code, Mutations And Translation)

Question 1

Proteins start with which amino acid

Answer 1

Methionine in eukaryotes and formylmethionine in prokaryotes

Question 2

Code for methionine ?

Answer 2

AUG

Question 3

Types of DNA mutations ?

Answer 3

Silent
Missense 
Nonsense 
Frameshift ( deletion or insertion ) 
Trinucleotide repeat expansion 
5’ splice site or 3’ splice site

Question 4

Example for missense mutation

Answer 4

Sickle cell anemia : glutamine into valein

Question 5

Example for nonsense mutation ?

Answer 5

Hemophilia : factor 8 mutation

Question 6

Example for single nucleotide deletion ?

Answer 6

Duchenne

Question 7

Example for deletion not causing frame shift ?

Answer 7

Cystic fibrosis ( CFTR protein ) delta F508

Question 8

Example for insertion causing frame shift ?

Answer 8

Tay sachs disease ( hexosaminadase A gene mutation )

Question 9

Example for insertion not causing frame shift ?

Answer 9

Huntington’s disease ( huntingtin )

Question 10

Examples for mutations in splice sites ?

Answer 10

Beta thalassemia , Gaucher disease and Tay-Sachs

Question 11

Examples for trinucleotide repeat expansion ?

Answer 11

Huntington disease 
Spinobulbar muscular dystrophy 
Fragile X syndrome 
Myotonic dystrophy
Friedreich’s ataxia

Question 12

In which direction are the proteins synthesized ?

Answer 12

From the amino to the carboxyl terminus

Question 13

Aminoglycosides mechanism ?

Answer 13

Preventing the 30 S subunit of ribosome from recognizing Shine-Dalgarno on the mRNA in the initiation phase of translation

Question 14

Linezolid mechanism ?

Answer 14

Binds to 50 S subunit and prevents initiation phase

Question 15

Tetracycline mechanism ?

Answer 15

Prevent aminoacyl-tRNA from binding to A site in the ribosome in the elongation phase of translation

Question 16

Chloramphenicol mechanism ?

Answer 16

Inhibition of peptidyl transferase in the elongation phase of translation

Question 17

Macrolides ( erythromycin ) and clindamycin mechanism ?

Answer 17

Bind to 50 S subunit and prevent translocation in elongation phase of translation

Question 18

Pseudomonas and diphtheria toxins mechanism ?

Answer 18

Inactivation of eEF-2 by ADP-ribosylation in the elongation phase of translation

Question 19

Grey baby syndrome ?

Answer 19

Newborns
Given chloramphenicol
Showing blue lips , nails and skin
With low BP and finally death

Question 20

Genetic defect in cystic fibrosis ?

Answer 20

Deletion of phenyalanine at position 508 which interferes with proper protein folding and the posttranslational processing of oligosaccharide side chains

Question 21

How the enzymes are directed to the lysosomes ?

Answer 21

By phosphorylation of mannose residues

Question 22

N-terminal hydrophobic signal sequence in the proteins function ?

Answer 22

To ensure translation on the RER

Question 23

Proteins in blood that aren’t glycosylated ?

Answer 23

Albumin
Insulin
Glucagon

Question 24

Protein solely N-glycosylated ?

Answer 24

Transferin

Question 25

Protein solely O-glycosylated ?

Answer 25

Heparin

Question 26

Protein both N and O-glycosylated ?

Answer 26

LDL receptor

Question 27

Alpha 1 antitrypsin deficiency defect ?

Answer 27

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

Question 28

I-Cell disease ?

Answer 28

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

Question 29

Scurvy ? (Vitamin C deficiency )

Answer 29

Defect : deficient hydroxylation of prolines and lysines during collagen synthesis
Symptoms : Petechiae
Loose teeth
Bleeding gums

Question 30

Osteogenesis imperfecta ?

Answer 30

Defect : mutation in collagen l gene
Symptoms : skeletal deformities
Blue sclera

Question 31

Ehlers-Danlos syndrome ?

Answer 31

Defect : mutations in collagen genes and proline and lysyl hydroxylases
Symptoms : hyperextensible fragile skin
Hypermobile joints
Arterial and intestinal ruptures

Question 32

Menkes disease ? ( Ehlers-Danlos type lX) ( kinky hair syndrome )

Answer 32

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

Question 33

Alport syndrome ?

Answer 33

Mutation in collagen Vl gene

Question 34

Amino acids that have 1 codon only ?

Answer 34

Methionine and Tryptophan

Question 35

Example for large segment deletion ?

Answer 35

Alpha thalassemia in which unequal cross over has deleted one or more alpha globin genes from chromosome 16

Question 36

Which amino acid is unique to collagen ?

Answer 36

Hydroxyproline

Question 37

Alpha thalassemia mutation ?

Answer 37

Unequal cross over has deleted one or more alpha globin genes from chromosome 16

Question 38

Functions of proteasomes ?

Answer 38

1- digesting damaged proteins to peptides 
2- play a role in producing antigenic peptides for presentation by class l MHC molecules