Chapter 4: The Genetic Code, Mutations, and Translation

Question 1

What amino acid is a start codon in Eukaryotes and Prokaryotes?

Answer 1

Eu: Methionine / Pro: formylmethionine

Question 2

Point mutation could be classified with a chages of base type. What are two types of base chages?

Answer 2

transition(purine to pyrimidine) & transversion(purine-pyrimidine becomes other purine-pyrimidine)

Question 3

Point mutation could be classified with changes of amino acid product. What are four types?

Answer 3

Silent mutation, Missense mutation, nonsense mutation, frameshift mutation

Question 4

What is the cause of a-thalassemia?

Answer 4

unequal crossover deleted one or more a-globin genes from chromosome 16

Question 5

What is the cause of Cri-du-chat syndrome and what are the symptoms?

Answer 5

Terminal deletion of the short arm of chromosome 5.
Sx) microcephaly, intellectual disability, wide-set eyes, characteristic kitten-like cry

Question 6

A 9-month old infant of Greek descent was brought to the hospital by ihs parents because he became pale, listless, and frequently irritable. The atending physician noted that the spleen was enlarged and that the infant was severly anemic. His face ahd unusual features with large cheekbones due to deformities in the skull.
What’s the Dx), Sx), Tx)?

Answer 6

Dx) b-thalassemia
Note: Mediterranean area
Sx) Splenomegaly(due to abnormality of red blood cells), bone deformities(excessive activity of the bone marrow for making more blood), long bones of the arms and legs are abnormally weak and fracture easilty
Tx) blood transfusion every 2-3 weeks.

Question 7

What is a major clinical manifestation of the trinucleotide repeat expansion disorders?

Answer 7

Neurodegeneration of specific neurons

Question 8

What are the symptoms of Huntington disease?
(What is the repeating code?)

Answer 8

Sx) Mood disturbance, hyperreflexia, abnormal gait, chorea, dystonia, dementia, dysphagia.
(CAG)

Question 9

During translation initiation phase, which part of the gene does ribosome bind to?(Eu & Pro)

Answer 9

Eu: 5’cap structure and slides down the message to the first AUG
Pro: Shine-Dalgarno sequence in the 5’ untraslated region of the mRNA

Question 10

Inhibitors of prokaryotic translation(Protein synthesis)?

Answer 10

Streptomycin, erythromycin, tetracycline, chloramphenicol

Question 11

Inhibitors of eukaryotic translation(protein synthesis)?

Answer 11

cycloheximide and Diphtheria and Pseudomonas toxins, Shiga and Shiga-like toxins

Question 12

What is the major cause of Gray baby syndrome? and what are the symptoms?

Answer 12

Cholramphenicol(prokaryotic protein synthesis inhibitor) which might also inhibit mitochondrial protein synthesis. Babies might not have sufficient enzyme activity to allow excretion of this drug.
Sx) cyanosis(blue lips, skin), Death, low blood pressure.

Question 13

Every translation of Eu gene begins on free ribosomes but it differs later by their roles(rER or free cytoplasmic ribosomes). What are the roles that are synthesized in rER?

Answer 13

1. Secreted proteins
2. Proteins inserted in to the cell membrane
3. Lysosomal enzymes

Question 14

There is a class of specilized proteins whose function is to assist in the protein folding in the final synthesis of the protien. What is the name of this specific protein?

Answer 14

Chaperones.

Question 15

What is the signal for pre-proteins to be synthesized in the rER?

Answer 15

N-Terminal Hydrophobic Signal Sequence is found on proteins destined to be secred, cell membrane, directed to the lysosome.

Question 16

A 70-year-old woman with elevated liver function tests was being evaluated for cirrhosis. Ehr serum a-antitrypsin level was 25mg/dL(normal 90-225 mg/dL). A liver biopsy showed micronodular cirrhosis and prominent fribrosis. Immunohistochemical studies showed intense staining with a-antitrypsin antibody. The patient was tested for likely mutations in the a-antitrypsin gene and found to be homozygous for the Z mutation. This mutation causes the a-antitrypsin protein to misfold and aggregate in the endoplastic reticulum, where it dagmages cells, eventually leading to cirrhosis.

Answer 16

Dx) a-antitrypsin deficiency
- a-antitrypsin is a protein synthesized primarily by the liver
- its function is to protect cells by serving as an inbitor of proteases released during a normal inflammatory response.

Question 17

A child aged 5 months was referred to a specialist. The child had been born with dislocated hips and a coarse featured face. He had been suffering repeated upper respiratory tract infections and did not seem to be developing his motor abilities. Clinical examination revealed hyperplasia of the gums, restriction of joint mobility and hepatosplenomegaly. On listening to the heart a mitral valve murmur could be detected. Further investigation involved cell culture of the child’s fibroblasts obtained from a skin biopsy. Examination of the fibroblasts under the microscope revealed the presence of numerous intracellular inclusions, which on electron microscopy were revealed to be large lysosomes. Biochemical analysis showed decreased levels of the lysosomal hydrolase b-glucuronidase witin the fibroblasts, but elevated levels of this enzyme within the culture medium.

Answer 17

Dx) I-Cell disease
Sx) coarse facial features, gingival hyperplasia, macroglossia, Craniofacial abnormalities, growth retardation, Cardiorespiratory failure, bone fracture and deformities, Mitral valve defect, Secretion of active lysosomal enzymes into blood and extracellular fluid

Question 18

What is the amino acid unique to collagen?

Answer 18

Hydroxyproline(proline with -OH), produced by hydroxylation of prolyl residues at the Y positions in procollagen chains as they pass through the RER

Question 19

During procollagen syntheisis, prolines and hysines are hydroxylated which needs X. Deficiency of X leads to disease Y. What is X & Y

Answer 19

X: Vitamin C(ascorbate)
Y: scurvy

Question 20

Collagen Type 1 Functions, associated diseases?

Answer 20

Most abundant in bone & skin & tendons, Osteogenesis imperfecta, Ehlers-Danlos

Question 21

Collagen Type III functions, associated diseases?

Answer 21

Blood vessels / Ehlers-Danlos type IV

Question 22

Deficient hydroxylation
Sx) Petechiae, ecchymoses loose teeth, bleeding gums, Poor would healing, Poor bone development

Answer 22

Scurvy

Question 23

Mutations in collagen genes
Skeletal deformities, Fractures, Blue sclera

Answer 23

Osteogenesis imperfecta

Question 24

Mutations in collagen genes and proline and lysyl hydroxylases
Sx) Hyperextensible, fragile skin Hypermobile joints, disloctions, varicose veins, ecchymoses(피하에 생긴 1cm 이상의 멍), ruptures

Answer 24

Ehlers-Danlos syndromes

Question 25

A 4-month-old infant who failed to grow and appeared intellectually disabled was seen at the clinic. An arteriogram showed elongation and tortuosity(뒤틀림) of the major arteries. Additional tests revealed bladder diverticula and subdural hematomas, plus low serum cerulopla smin and only 10% of normal serum copper. The child’s hair is also noted to be abnormally kinky and hypopigmented.

Answer 25

Dx) Menkes disease
- deficient cross-linking secondary to functional copper deficiency.
Sx) depigmented hair, arterial tortuosity, rupture, cerebral degeneration, osteoporosis, anemia
- mutations in the gene ATP7A
- lysyl oxidase requires copper and plays a direct role in collagen formation by catalzing the cross-linking of collagen fibrils.

Question 26

Collagen consist of three major AAs. what are they?

Answer 26

GLy-X-Y(Glysine, hydroxyproline, lysine)