Updated: 2/24/2018

Protein Synthesis

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Ribosome
  •  Structure
    • eukaryotes
      • small subunit (40S)
        • synthesized in the nucleus
      • large subunit (60S)
        • synthesized in the nucleolus
      • total = 80S
        • S = sedimentation
    • prokaryotes
      • small subunit (30S) + large subunit (50S) → 70S
  • Catalytic sites 
    • A (acceptor) site
      • accepts charged aa-tRNA 
    • P (peptidyl) site 
      • holds the growing peptide chain and transfers to the aa-tRNA in the A site 
    • E (exit) site
      • allows tRNA to exit the ribosome after releasing its amino acid to the aa-peptide chain
  • Forms
    • polysomes
      • single mRNA being translated simultaneously by several ribosomes
      • can be
        • free
          • proteins for nucleus or mitochondria
        • membrane bound
          • found on rough ER 
          • proteins for secretion or membrane insertion
Steps
  • Initiation 
    • initiation complex generated from
      • small ribosomal subunit
      • mRNA
        • 5'-cap (eukaryotes)
        • Shine-Dalgarno sequence (prokaryotes) 
      • initiation aa-tRNA
        • met-tRNA (eukaryotes)
        • fmet-tRNA (prokaryotes)
      • initiation factors (IFs)
        • help in assembly
        • released when mRNA joins the ribosomal subunit
    • once assembled, recruits the large ribosomal subunit
      • initiation aa-tRNA occupies the P-site
        • all other aa-tRNAs bind the A-site
      • the A-site is empty
  • Elongation
    • aminoacyl-tRNA binds to A site
      • consumes 1 GTP
    • peptidyl-bond formation
      • peptidyl transferase reaction catalyzed by ribosomal rRNA ("ribozyme")
      • transfers growing polypeptide to amino acid in the A site
    • translocation 
      • ribosome moves 3 nucleotides at a time in a 5' to 3' direction
      • moves peptidyl RNA from A site to P site
      • moves empty tRNA from P site to E site for exit
      • A site now empty and ready to accept next aa-tRNA
      • catalyzed by elongation factor-2 (eEF-2)
        • inactivated via ADP-ribosylation by bacterial toxins (Pseudomonas and Diphtheria)
      • consumes 1 GTP
    • cycle is repeated for each amino acid addition to the polypeptide
    • Wobble phenomenon
      • The anticodon of certain tRNA molecules can bind to multiple codons
      • The first two nucleotides of the codon adequately specify which tRNA (and amino acid) binds the codon, thereby permitting multiple nucleotides in the third position to bind the same tRNA. 
  • Termination
    • stop codon reached in mRNA
    • release factor binds mRNA
    • peptide bond is hydrolyzed and completed protein is released
    • ribosomal complex dissociates
  • Overall energy requirement
    • 4 high energy bonds
      • ATP to AMP for tRNA charging (2)
      • 2 GTP to GDP for elongation (2)
Pharmacologic Inhibition of Prokaryotic Protein Synthesis
  • Bind 30S
    • aminoglycosides
      • inhibit formation of the initiation complex
      • promotes misreading of mRNA
  • Bind 50S
    • chloramphenicol
      • inhibits peptidyl transferase
    • macrolides
      • inhibits translocation
    • clindamycin
      • inhibits translocation

References

 

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Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.BC.70) The ribosome is an essential organelle that plays an important role in the synthesis of new proteins. The location of the ribosome within the cell can vary and provides a clue to the function of the particular cell. What ribosome location is essential for protein-secreting cells? Review Topic

QID: 106487
1

Rough endoplasmic reticulum

100%

(18/18)

2

Smooth endoplasmic reticulum

0%

(0/18)

3

Cytosol

0%

(0/18)

4

Cell membrane

0%

(0/18)

5

Nucleus

0%

(0/18)

M1

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PREFERRED RESPONSE 1

(M1.BC.4) In translation, the wobble phenomenon is best illustrated by the fact that: Review Topic

QID: 100069
1

A tRNA with the UUU anticodon can bind to either AAA or AAG codons

58%

(154/264)

2

There are more amino acids than possible codons

13%

(34/264)

3

The last nucleotide provides specificity for the given amino acid

16%

(42/264)

4

The genetic code is preserved without mutations

7%

(18/264)

5

Charged tRNA contains energy needed for peptide bonds to form

4%

(11/264)

M1

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PREFERRED RESPONSE 1
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