USMLE step 1 biochemistry
Ribosomes are made of proteins and rRNA
- Eukaryotes  60 and 40s = 80s
- Prokaryotes  50 s and 30 s = 70 s
Have 23s in 50s
- Have 23s in 50s
Translation
- Initiation
IF1, IF2, If3
Assist in assembly of smaller ribosomal subunit to first trna molecule
Methionine is always the start
f-Methionine in prokaryotes
IF-2 first binds to 30s and then to methionine tRNA. Then when 50s comes along, it hydrolyzes GTP on IF2 and allows 50s to attach to 30s
A site  Incoming aminoacyl TRNA binds
P site  Polypeptide binds (Growing chain)
First tRNA binds here
E site  Free tRNA (exit)
- IF1, IF2, If3
Assist in assembly of smaller ribosomal subunit to first trna molecule
Methionine is always the start
f-Methionine in prokaryotes
IF-2 first binds to 30s and then to methionine tRNA. Then when 50s comes along, it hydrolyzes GTP on IF2 and allows 50s to attach to 30s
- Assist in assembly of smaller ribosomal subunit to first trna molecule
- Methionine is always the start
- f-Methionine in prokaryotes
- IF-2 first binds to 30s and then to methionine tRNA. Then when 50s comes along, it hydrolyzes GTP on IF2 and allows 50s to attach to 30s
- A site  Incoming aminoacyl TRNA binds
- P site  Polypeptide binds (Growing chain)
First tRNA binds here
- First tRNA binds here
- E site  Free tRNA (exit)
- Elongation
Incoming charged aminoacyl TRNA binds to A site
Elongation factor help incoming trna to bind to A site (Uses GTP)
50s has peptidyl transferase transfers AA from p site to A site
In prokaryotes, activity is in 23s subunit of 50s rRNA
Translocation
Ribosome complex moves 3 nucleotides
tRNA + Peptide is moved from A site to P site
Newly uncharged tRNA from P side to E side
EF-G   Eukaryotes
EF-2 in eukaryotes
Diptheria and exotoxin (Pseudomonas) inhibit this
- Incoming charged aminoacyl TRNA binds to A site
- Elongation factor help incoming trna to bind to A site (Uses GTP)
- 50s has peptidyl transferase transfers AA from p site to A site
In prokaryotes, activity is in 23s subunit of 50s rRNA
- In prokaryotes, activity is in 23s subunit of 50s rRNA
- Translocation
Ribosome complex moves 3 nucleotides
tRNA + Peptide is moved from A site to P site
Newly uncharged tRNA from P side to E side
EF-G   Eukaryotes
EF-2 in eukaryotes
Diptheria and exotoxin (Pseudomonas) inhibit this
- Ribosome complex moves 3 nucleotides
- tRNA + Peptide is moved from A site to P site
- Newly uncharged tRNA from P side to E side
- EF-G   Eukaryotes
- EF-2 in eukaryotes
Diptheria and exotoxin (Pseudomonas) inhibit this
- Diptheria and exotoxin (Pseudomonas) inhibit this
- Termination
Stop codons
UGA, UAA and UAG
Signal to STOP
No new TRNA coming
Release factor binds to MRNA and hydrolyzes GTP and new polypeptide is released.
- Stop codons
UGA, UAA and UAG
Signal to STOP
No new TRNA coming
Release factor binds to MRNA and hydrolyzes GTP and new polypeptide is released.
- UGA, UAA and UAG
- Signal to STOP
- No new TRNA coming
- Release factor binds to MRNA and hydrolyzes GTP and new polypeptide is released.
- Antibiotics
Aminoglycosides  Inhibit 30s subunit before initiation (No pairing with TRNA)
Linezolid  Inhibits initiation by binding to 50s subunit
Tetracycline
Bind to 30s subunit
Prevent aminoacyl TRNA from binding to A site
Chloramphenicol
Inhibits peptidyl transferase
Binds to 50s
Macrolides
Inhibits translocation by binding to 50s subunit
Clindamycin
Same as macrolides
Lincamycin
Bind to 50s and inhibit translocation
Streptrogranin
Bind to 50s and inhibit translocation
Buy AT 30 ,CCELL at 50
- Aminoglycosides  Inhibit 30s subunit before initiation (No pairing with TRNA)
- Linezolid  Inhibits initiation by binding to 50s subunit
- Tetracycline
Bind to 30s subunit
Prevent aminoacyl TRNA from binding to A site
- Bind to 30s subunit
- Prevent aminoacyl TRNA from binding to A site
- Chloramphenicol
Inhibits peptidyl transferase
Binds to 50s
- Inhibits peptidyl transferase
- Binds to 50s
- Macrolides
Inhibits translocation by binding to 50s subunit
- Inhibits translocation by binding to 50s subunit
- Clindamycin
Same as macrolides
- Same as macrolides
- Lincamycin
Bind to 50s and inhibit translocation
- Bind to 50s and inhibit translocation
- Streptrogranin
Bind to 50s and inhibit translocation
- Bind to 50s and inhibit translocation
- Buy AT 30 ,CCELL at 50
- Post translational modification
Trim terminals
Covalent modification
Glycosylation, hydroxylation, phosphorylation
Collagen  Hydroxylation of proline and lysine
Disulfide bonds
Protein folding
Primary structure  Chain
Secondary structure  Beta and alpha pleated
Tertiary structure
- Trim terminals
- Covalent modification
Glycosylation, hydroxylation, phosphorylation
Collagen  Hydroxylation of proline and lysine
- Glycosylation, hydroxylation, phosphorylation
- Collagen  Hydroxylation of proline and lysine
- Disulfide bonds
- Protein folding
Primary structure  Chain
Secondary structure  Beta and alpha pleated
Tertiary structure
- Primary structure  Chain
- Secondary structure  Beta and alpha pleated
- Tertiary structure