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Biochemistry > 4. The Genetic Code, Mutations, and Translation > Flashcards

4. The Genetic Code, Mutations, and Translation Flashcards

1
Q

How many codons exist?

A

64

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2
Q

Stop codons

A

UAA, UGA, UAG

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3
Q

Start codon + amino acid

A

AUG, methionine (met in prokaryotes)

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4
Q

Code is unambiguous

A

1 codon = 1 amino acid

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5
Q

Code is degenerate, 2 exceptions

A

1 amino acid > 1 codon

Exceptions: Met and tryptophan (Trp)

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6
Q

Point mutations: transition and transversion

A

Transition: purine-pyrimidine bp -> purine-pyrimidine bp (AT->GC)
Transversion: purine-pyrimidine bp -> pyrimidine-purine bp (AT->TA or CG)

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7
Q

Missense mutation

A

New codon specifies different amino acid, variable effects

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8
Q

Nonsense mutation

A

Stop codon

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9
Q

Large segment deletions

A

Often during unequal crossover in meiosis

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10
Q

Recombination crossover when?

Examples of unequal crossover (2)

A

Normal in Meiosis I
Examples:
1. alfa-thalassemia (deletion of one or more alfa-globin genes from chromosome 16)
2. Cri-du-chat (mental retardation, microcephaly, wide-set eyes, kitten like cry), terminal deletion short arm chromosome 5

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11
Q

Examples (3) of splice site mutations

A

Beta-thalassemia, Gaucher disease, Tay-Sachs

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12
Q

Beta-thalassemia

  • Disease
  • Characteristics
  • Treatment
A

Many different types of mutations, deficiency of beta-globin compared to alfa-globin.
Mediterranean areas, splenomegaly, bone deformities (excessive activity bone marrow). Treatment: blood transfusions every 2-3 weeks, cave iron overload

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13
Q

Huntington disease

  • Type of disorder, age of onset
  • Symptoms
  • Normal vs diseased repeats
  • Amino acid involved
  • Juvenile
A
  • Autosomal dominant, 43-48
  • Mood disturbance, impaired memory, hyperreflexia, abnormal gait, chorea, dystonia, dementia, dysphagia
  • 5 vs >30
  • Glutamine (CAG)
  • Juvenile often paternal allele inherited
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14
Q

Trinucleotide repeat expansion diseases

  • 2 in coding region
  • 2 in untranslated region
A
  • Huntington (CAG), Spinobulbar muscular atrophy (CAG)

- Fragile X (CGG), Myotonic dystrophy (CTG), Friedreich’s ataxia (GAA)

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15
Q

Amino acid activation by..

Energy required from..

A

Aminoacyl tRNA synthetase (self-checking function)

Two high-energy bonds from ATP

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16
Q

Amino acid location on tRNA

A

3’ end

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17
Q

Amino acid linked to tRNA is a..

A

High energy bond, energy for peptide bond linking later

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18
Q

Formation of peptide bond between..

A

Carboxyl group (C) of growing peptide and amino group (NH3) of new amino acid

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19
Q

Where does translation occur?

A

In cytoplasm

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20
Q

Three stages of protein synthesis

A

Initiation, elongation and termination

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21
Q

What binds to mRNA during translation?

A

Small ribosomal subunit

  • Prokaryotes = 16S to Shine Dalgarno sequence in 5’ UTR
  • Eukaryotes = binds to 5’ cap
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22
Q

What happens after small subunit binds to mRNA?

A

(f)Met tRNA binds to AUG and large subunit binds to small subunit

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23
Q

What is P-site?

A

Peptidyl site: binding site for growing peptide chain

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24
Q

What is A-site?

A

Aminoacyl site: new incoming tRNA molecule

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25
Q

What are the three steps of elongation?

Energy required?

A
  1. Charged tRNA binds to A-site
  2. Peptidyl transferase (large subunit) forms peptide bond + break of bond to P-site
  3. Translocation: ribosome moves 3 nucleotides
    Energy: high energy bonds from tRNA-aminoacid (2) + GTP (2), in total 4
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26
Q

How do Pseudomonas and Diptheria toxins inhibit protein synthesis?

A

ADP-ribosylation of elongation factor-2 (used in translocation) in eukaryotes

27
Q

How do Shiga and Shiga-like toxins stop protein synthesis?

A

Clip adenine residue from 28S rRNA in the 60S subunit

28
Q

Termination (2 steps)

A
  1. Stop codon in A-site

2. Peptide transferase (+ release factors) hydrolyze the protein from final tRNA in P site

29
Q

Polysome

A

Several ribosomes on 1 mRNA

30
Q

Inhibitors of prokaryotic translation

A

Streptomycin, erythromycin, tetracyclin, chloramphenicol (also inhibits mitochondrial translation, because it resembles prokaryotic ribnosomes)

31
Q

Inhibitor of eukaryotic translation

A

Cycloheximide, Diphteria, Pseudomonas toxins

32
Q

Gray baby syndrome: drug, problem, symptoms

A

Chloramphenicol
UDP-glucuronyl transferase activity is insufficient (excretion)
Cyanosis, low blood pressure, death

33
Q

Characteristics of the four protein shapes

A

Primary: amino acid sequence
Secondary: alfa-helix, beta-pleated sheets (hydrogen bonds)
Tertiary: hydrogen, hydrophobic and ionic bonds, sometimes strong covalent disulfide bonds.
Quaternary: subunits interaction

34
Q

Proteins translated on RER ribosomes (3)

A

Secreted proteins
Proteins inserted into cell membrane
Lysosomal proteins

35
Q

Assistance in protein folding by..

A

Chaperones

36
Q

Incorrect folding:

  • Marked by
  • Where destructed?
A
  • Multiple copies of ubiquitin

- Proteasomes -> cytoplasmic complex, multiple proteases, play a role in producing antigenic peptides

37
Q

Cystic fibrosis

  • Genetic defect?
  • Abnormal protein?
A
  • Deletion Phe from 508, improper folding and post translational processing
  • Abnormal chloride channel protein is degraded
38
Q

Signal for RER translation

A

N-terminal hydrophobic signal (cleaved off in ER)

39
Q

Signal for directing protein to lysosome

- If defect, what disease?

A

Phosphorylation of mannose residues in N-linked oligosaccharide chains (by N-acetyl-glucosamine-1 phosphotransferase) -> Mannose-6-phosphate
- I-cell disease, lysosomal enzymes released in extracellular space, inclusion bodies accumulate in cell

40
Q

Glycoproteins are created in

A

ER and Golgi, proteins acquire oligosaccharide side chains

41
Q

N-glycosylation
What does it require?
Where?

A

Sugar chains to nitrogen of asparagine residues, requires dolichol phosphate
ER and Golgi

42
Q

O-glycosylation

Where?

A

Sugar chains to hydroxyl group of serine or threonine residues
Only in Golgi

43
Q

Alfa1-antitrypsin deficiency

  • Synthesized by
  • Normal function
  • Allelic variants associated with deficiency, type of mutation
A
  • Liver
  • Inhibits proteases released during inflammation
  • Z and S, point mutations
44
Q

I-cell disease

  • Symptoms (4)
  • Prognosis (1)
  • Diagnostics (1)
A

S. Coarse facial features, gingival hyperplasia, macroglossia
S. Joint immobility, clubfoot, claw-hand, scoliosis, growth retardation, bone fracture and deformities
S. Psychomotor retardation
S. Cardiorespiratory failure, mitral valve defect
P. Death in first decade
D. Secretion of active lysosomal enzymes into blood and extracellular fluid

45
Q

Glycosylation

A

Addition of oligosaccharide (ER, Golgi)

46
Q

Proteolysis

A

Cleavage of peptide bonds

Proinsulin, trypsinogen, prothrombin

47
Q

Phosphorylation

A

Addition of phosphate by protein kinases

48
Q

Gamma-carboxylation

A

Produces Ca2+ binding sites

49
Q

Prenylation

A

Addition of farnesyl or geranylgeranyl lipid groups to membrane-associated proteins

50
Q

Collagen structure

A

Gly-X-Y-Gly-X-Y

51
Q

Unique amino acid of collagen + how produced

A

Hydroxyproline

Hydroxylation propel residues Y positions in pro collagen

52
Q

Pro-alfa chains made by:

A

Prepro-alfa chain + cleaved hydrophobic signal

53
Q

Which vitamin is required for hydroxylation of prolines and lysines by propyl and lysyl hydroxylases?

A

Vitamin C (Ascorbate)

54
Q

Procollagen formation

A

Three pro-alfa chains, transferred to Golgi

55
Q

Tropocollagen

A

Procollagen secreted from cell, ends are cleaved by proteases

56
Q

Cross linking of collagen molecules

What does it require?

A

Fibrils, involves lysyl oxidase

Required O2 and copper

57
Q

Collagen type 1

A

High tensile strength
Bone, skin, tendons
Osteogenesis imperfecta, Ehlers-Danlos

58
Q

Collagen type 2

A

Thin fibrils, structural

Cartilage, vitreous humor

59
Q

Collagen type 3

A

Thin fibrils, pliable
Blood vessels, granulation tissue
Ehlers-Danlos IV, Keloid

60
Q

Collagen type 4

A

Amorphous (=lacking clear structure)
Basement membranes
Goodpasture, Alport disease, Epidermolysis bullosa

61
Q

Scurvy

  • Defect
  • Major symptoms (6)
A
  • Deficient hydroxylation due to ascorbate deficiency

- Petechiae, ecchymoses, loose teeth, bleeding gums, poor wound healing, poor bone development

62
Q

Osteogenesis imperfecta

  • Defect
  • Major symptoms (3)
A
  • Mutation in collagen genes

- Skeletal deformities, fractures, blue sclera

63
Q

Ehlers-Danlos syndromes

  • Defect
  • Major symptoms (6)
A
  • Mutations in collagen genes and proline and lysyl hydroxylases
  • Hyperextensible, fragile skin, hypermobile joints, dislocations, varicose veins, ecchymoses, arterial, intestinal ruptures
64
Q

Menkes diseases

  • Defect
  • Type of genetic defect
  • Major symptoms (6)
A
  • Deficient cross linking due to copper deficiency
  • X-linked recessive, ATP7A (ATP dependent copper efflux protein in intestine)
  • Depigmented (steely) hair, arterial turtuosity and rupture, cerebral degeneration, osteoporosis, anemia

Biochemistry (18 decks)

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