Protein Synthesis

Question 1

Protein Translation

• Conversion of a ___ code to an____ code
• Occurs in___ on ____
• mRNA is read from ___
• Amino acids are the building blocks of proteins
• N-terminus (amino-terminus) translated ___, extend toward C-terminus (carboxy terminus)
• Amino acids are joined by peptide bonds
• Occurs in 3 stages: Initiation, elongation, termination

Answer 1

• Conversion of a nucleotide code to an amino acid code
• Occurs in cytoplasm on ribosomes
• mRNA is read from 5’ to 3’
• Amino acids are the building blocks of proteins
• N-terminus (amino-terminus) translated 1st, extend toward C-terminus (carboxy terminus)
• Amino acids are joined by peptide bonds
• Occurs in 3 stages: Initiation, elongation, termination

Question 2

Ribosomes

• •Protein Factory
• _________ particles
• •Contain ___ and ___
• •Prokaryotes—___S
• •Small (__S)-___proteins + ___ rRNA
• •Large (__S)- ___ proteins + ____ rRNA
• •Eukaryotes—__S
• •Small (___S)__proteins + ___ rRNA
• •Large (___S)- ___proteins ____ rRNA
• •Many lines of evidence indicate___ essential, ___ less so.

Answer 2

• Protein Factory
• Ribonucleoprotein particles
• Contain protein and rRNA’s
• Prokaryotes—70S
• Small (30S)-21 proteins + 16S rRNA
• Large (50S)- 34 proteins + 23S & 5S rRNA
• Eukaryotes—80S
• Small (40S)-33proteins + 18S rRNA
• Large (60S)- 49 proteins 28S, 5S,5.8S rRNA
• Many lines of evidence indicate rRNA essential, protein less so.

Question 4

Ribosome contains 3 tRNA Binding Sites

Question 5

tRNA

____molecules
___ distinct loops + ___ ___ ___ (Site of amino acid attachment)
•Each amino acid is carried by a tRNA molecule to the ribosome as _____________

Answer 5

• Adaptor molecules
• 4 distinct loops + amino acid arm (Site of amino acid attachment)
• Each amino acid is carried by a tRNA molecule to the ribosome as aminoacyl-tRNA complex.

Question 6

Activation of tRNA

•Amino acid ____ are activated intermediates in protein synthesis.
________is a ____ ____
•Enzyme involved is a____aminoacyl tRNA synthetase
•One for each amino acid -______ tRNA synthetase

Answer 6

• Amino acid esters are activated intermediates in protein synthesis.
• Aminoacyl-tRNA is a charged tRNA
• Enzyme involved is a specific aminoacyl tRNA synthetase
• One for each amino acid -Alanine tRNA synthetase

Question 7

Proofreading by Aminoacyl-tRNA Synthetases

•Increases ____ of protein synthesis
___ ____ in recognition of amino acid
•Specific tRNA synthetase corrects its ___ ___ by ___ ___ ______-____
•

Answer 7

•Increases fidelity of protein synthesis
•Highly selective in recognition of amino acid
•Specific tRNA synthetase corrects its own errors by hydrolyzing incorrect aminoacyl-adenylate
•

Question 8

Codon Recognition

____ ___ ___ interactions between the codon on the mRNA strand and the anticodon of the tRNA.
•
•Amino acid ___ ___ ___ role in selecting codon

Answer 8

•Complementary base pairing interactions between the codon on the mRNA strand and the anticodon of the tRNA.
•
•Amino acid does not play role in selecting codon

Question 9

Wobble

__ than ___ ___ for each ___ ___
•1 tRNA can recognize ___ than ___ ___
•Wobble = ___ in ___ ___ of ____

Answer 9

• More than 1 codon for each aa
• 1 tRNA can recognize more than 1 codon
• Wobble = imprecision in 3rd base of codon

Question 10

Stages of Protein Synthesis

Answer 10

• Initiation
• Elongation
• Translocation
• Termination

Question 11

Initiation of Protein synthesis (Comparison between Eukaryotes and Prokaryotes)

mRNA binding to small ribosomal subunit

1st aa

Initiation Factors

Answer 11

eIF – Eukaryotic initiation factors

IF – Initiation factors

Question 12

Initiation of Protein Synthesis

•Methionyl-tRNA binds to___ and ___
•This complex interacts with the ___ subunit of the ribosome.
•___ complex binds to the _____of the mRNA strand. (_________)
•The _________________ complex interacts with the ____ complex and moves along mRNA strand until it finds the start of translation ____
•GTP is ____, eIFs are ____ and the large ribosomal subunits ____. Methionyl-tRNA binds to _ site.

Answer 12

• Methionyl-tRNA binds to elF and GTP.
• This complex interacts with the small subunit of the ribosome.
• elF4 complex binds to the 5’ Cap of the mRNA strand. (ATP is required)
• The ribosome-methionyl-tRNA complex interacts with the cap complex and moves along mRNA strand until it finds the start of translation AUG.
• GTP is hydrolyzed, eIFs are released and the large ribosomal subunits binds. Methionyl-tRNA binds to P site.

Question 13

Elongation

•Incoming aminoacyl-tRNA binds ___ and ____
•GTP is____ and the EF (Elongation factor) is ____ when the aminoacyl-tRNA binds to the _-site.
____ _____ activity catalyzed by the____of the ____ subunit results in the formation of the peptide bond between the amino acids.

Answer 13

• Incoming aminoacyl-tRNA binds GTP and EF1A.
• GTP is hydrolyzed and the EF (Elongation factor) is released when the aminoacyl-tRNA binds to the A-site.
• Peptidyl transferase activity catalyzed by the RNA of the large subunit results in the formation of the peptide bond between the amino acids.

Question 14

Translocation
•Peptidyl-tRNA must be moved out of the “___” site so a new aminoacyl-tRNA can enter
•Catalyzed by ____ (________)
•mRNA moved __ nucleotides to allow new tRNA into now open “A” site
•Peptidyl-tRNA moved to “_” site
•Next codon enters “_” site
•Uncharged tRNA dissociation through “_” site

Answer 14

• Peptidyl-tRNA must be moved out of the “A” site so a new aminoacyl-tRNA can enter
• Catalyzed by eEF-2 (translocase)
• mRNA moved 3 nucleotides to allow new tRNA into now open “A” site
• Peptidyl-tRNA moved to “P” site
• Next codon enters “A” site
• Uncharged tRNA dissociation through “E” site

Question 15

Termination

___ ___ read stop codons
•No ____ for stop codons
•When stop codon (UAA, UGA, UAG) in “A” site they are recognized by release factors. ___ rRNA also plays role in termination
•Release factor alters_____ of peptidyl transferase
__________________
•Protein is released along with tRNA and mRNA
•Ribosome dissociates into 2 subunits.

Answer 15

• Release factors read stop codons
• No tRNA for stop codons
• When stop codon (UAA, UGA, UAG) in “A” site they are recognized by release factors. 16S rRNA also plays role in termination
• Release factor alters specificity of peptidyl transferase
• Water used as acceptor
• Protein is released along with tRNA and mRNA
• Ribosome dissociates into 2 subunits.

Question 16

Polysomes

Answer 16

• Many ribosomes simultaneously translate 1 mRNA
• Move 5’à3’

Question 17

Inhibitors of Protein Synthesis

• Antibiotics
• Puromycin- Causes____ ___ _____ by acting as an ____ of ____ _____
• Streptomycin- Inhibits ____ and causes ____ of ____ in prokaryotes
• Diphtheria toxin
• Inhibits ____
• A fragment catalyzes the ___________of ____ blocking its capacity to act in _____ of polypeptide chain being synthesized
• Protein synthesis is ___ ____

Answer 17

•Antibiotics
•Puromycin- Causes premature chain termination by acting as an analog of aminoacyl-tRNA
•Streptomycin- Inhibits initiation and causes misreading of mRNA in prokaryotes
•
•Diphtheria toxin
•Inhibits translocation
•A fragment catalyzes the ADP-ribosylation of EF2 blocking its capacity to act in translocation of polypeptide chain being synthesized
•Protein synthesis is completely inhibited

Question 18

Summary

___ ___ and ____are required for translation.
•Protein synthesis occurs in ___ stages.
___ ____ exist between the process of translation in prokaryotic and eukaryotic organisms.
•Many inhibitors of proteins synthesis are important ___ used in medicine and dentistry.
•
•

Answer 18

•An RNA template, tRNA and ribosomes are required for translation.
•Protein synthesis occurs in four stages.
•Several difference exist between the process of translation in prokaryotic and eukaryotic organisms.
•Many inhibitors of proteins synthesis are important antibiotics used in medicine and dentistry.
•
•

Question 19

Protein Targeting in Eukaryotic Cells

•Proteins are made in the_____
•
•How do they end up in different cellular compartments?

Answer 19

•Proteins are made in the cytoplasm
•
•How do they end up in different cellular compartments?

Question 20

Protein Targeting to Endoplasmic Reticulum (ER)

•All proteins destined for____and all proteins destined for the ____, the____, the ___, the ____, and the _______are first imported into the ___ from the ____
•In the ER lumen, the proteins ___ and ____ ____(Ex – N – linked glycosylation)
___ ___ ______ indicates the ___ of ___ ____
•Only proteins that are ___ ____ leave the endoplasmic reticulum to other organelles.

Answer 20

• All proteins destined for secretion and all proteins destined for the ER itself, the Golgi apparatus, the lysosomes, the endosomes, and the plasma membrane are first imported into the ER from the cytosol
• In the ER lumen, the proteins fold and processed further. (Ex – N – linked glycosylation)
• N – linked glycosylation indicates the extent of protein folding
• Only proteins that are properly folded leave the endoplasmic reticulum to other organelles.

Question 21

Signal Sequence

• Directs proteins to the ___ ___
• Found near ___ ___ of ___
• __-___ amino acids
• Many are ____ amino acids•

Interacts with the ___ ____ ____
–_____ complex
•
___ ____ (enzyme) removes signal peptide

Answer 21

•Directs proteins to the endoplasmic reticulum (ER)
•
•Found near N-terminus of protein
•13-36 amino acids
•Many are hydrophobic amino acids•Interacts with the signal recognition particle (SRP)
–ribonucleoprotein complex
•
•Signal peptidase (enzyme) removes signal peptide

Question 22

Protein Targeting to the ER

• The SRP binds to the __ ____ of the polypeptide, thereby ___ translation.
• The SRP bound to the ___ - _____ complex interacts with the ___ ____ located on the ___ ____
• The nascent (new) polypeptide chains is directed ___ a ___ (___ ____) which leads into the lumen of the ER.
• ___ ____ from the ribosome complex and____ ____ until termination.
• Once the polypeptide chain is completely in the lumen of the ER, __ ___ ____ ____ are ____by a signal peptidase on the ___ side of the ER membrane.

Answer 22

• The SRP binds to the signal sequence of the polypeptide, thereby stalling translation.
• The SRP bound to the ribosome-polypeptide complex interacts with the SRP receptor located on the ER membrane.
• The nascent (new) polypeptide chains is directed into a channel (protein translocator) which leads into the lumen of the ER.
• SRP dissociates from the ribosome complex and translation continues until termination.
• Once the polypeptide chain is completely in the lumen of the ER, N-terminal signal sequences are removed by a signal peptidase on the lumenal side of the ER membrane.

Question 23

Protein Glycosylation

• Occurs on many ____ and ____proteins
• Occurs initially in___
• Core oligosaccharide added to _____ (for N-linked glycosylation)
• Further glycosylation occurs in the____

Answer 23

• Occurs on many secretory and lysosomal proteins
• Occurs initially in ER
• Core oligosaccharide added to asparagine (for N-linked glycosylation)
• Further glycosylation occurs in the Golgi

Question 25

N-linked glycosylation of proteins in the lumen of the ER
•___ ___ oligosaccharide is transferred to an ____ residue of proteins
•The transfer of the precursor oligosaccharide to the protein is catalyzed by ___ ____enzyme ___ ____

Answer 25

• Preformed precursor oligosaccharide is transferred to an asparagine residue of proteins
• The transfer of the precursor oligosaccharide to the protein is catalyzed by membrane bound enzyme oligosaccharyl transferase

Question 26

Transport of Proteins from the ER Through the Golgi Apparatus

•The Golgi apparatus ____ the many proteins and lipids that it receives from the ER.
•_-linked oligosaccharides that are added to proteins in the ER are often initially ____ by the removal of ____
•_-linked _____ occurs as well as _______chains are added to ___ ___ to form _____
•The finished new protein are packaged into ___ ____and dispatched to various destinations.

Answer 26

• The Golgi apparatus distributes the many proteins and lipids that it receives from the ER.
• N-linked oligosaccharides that are added to proteins in the ER are often initially trimmed by the removal of mannoses.
• O-linked glycosylation occurs as well as glycosaminoglycan chains are added to core proteins to form proteoglycans.
• The finished new protein are packaged into transport vesicles and dispatched to various destinations.

Question 27

Summary

•Protein directed to ___ ____ or ____are first directed to____ for _____
•
•The signal recognition particle facilitates the____ of translated proteins into the ___ of the ___
•
•Glycosylation of ___ and ____ proteins occurs in the lumen of the ER.
•
•Proteins translocated to the ___ are further processed by ____ and by the addition of _____
•
•

Answer 27

•Protein directed to other organelles or secreted are first directed to ER for processing.
•
•The signal recognition particle facilitates the targeting of translated proteins into the lumen of the ER.
•
•Glycosylation of lysosomal and secreted proteins occurs in the lumen of the ER.
•
•Proteins translocated to the golgi are further processed by glycosylation and by the addition of glycosaminoglycans.
•
•