Term
| List six examples of covalent modification of proteins |
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Definition
1. Disulfide crosslinks
2. Amino and carboxyl terminal modifications
3. Individual AA modifications
4. Attachment of carbohydrate side chains
5. Addition of hydrophobic and prosthetic groups
6. Proteolysis |
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Term
| List four common physiological products that result from post-translational amino acid modifications |
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Definition
| Collagen (hydroxyproline), Blood clotting and calcium binding (carboxyglutamate), enzyme/receptor activation (phosphoserine and phosphotyrosine) |
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Term
| What membrane soluble phosphate, sugar derivatives and amino acid residue on a polypeptide are required for N-linked glycoside synthesis? |
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Definition
a) Dolichol phosphate
b) UDP-N-acetyl glucosamine
c) GDP-mannose
d) UDP-glucose
e) Asparagine residue |
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Term
| Where does N-linked glycoside synthesis take place? |
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Definition
| Mostly in the endoplasmic reticulum |
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Term
| What causes ribosomes to become attached to the rough endoplasmic reticulum? |
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Definition
| Presence of an N-terminal consensus sequence (signal peptide) that attaches to a signal recognition particle (SRP composed of scRNA) and moves the ribosome to a ribosomal receptor in the ER membrane |
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Term
| What is the result of a ribosome attaching to rough ER? |
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Definition
| The N-terminal region of the growing polypeptide is moved into the ER by an SRPmediated translocation before much of the polypeptide is synthesized |
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Term
| All eukaryotic proteins have methionine as their N-terminus, but when secreted proteins are purified they usually do not begin with methionine. Why not? |
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Definition
Secreted proteins have an N-terminal signal sequence that is cleaved on secretion.
Thus, only intracellular proteins, for example hemoglobin, retain methionine at the N-terminus. |
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Term
| The term translocation occurs at four steps during protein synthesis and processing. What are these steps and what cofactor does each use? |
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Definition
a) Amino acid elongation on the ribosome using EF-G•GDP after peptide bond formation
b) Polypeptide release
c) Secretion into the ER using Signal Recognition Particle during peptide synthesis
d) Asparagine (N) -linked oligosaccharide synthesis using dolichol phosphate after adding Nacetylglucosamine & mannose residues
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Term
| Where do proteins become targeted to lysosomes? |
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Definition
| In the Golgi where a phosphate residue is added to a terminal mannose residue on an asparagine-linked glycan on the enzyme |
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Term
| What are the similarities between chaperones and chaperonins? Which act first? |
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Definition
They both bind unfolded protein along with ATP and release the correctly folded protein
when ATP is hydrolyzed.
Both types of proteins are known as ‘heat shock
proteins’
Chaperones act first |
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Term
| What is the function of lysosome-targeted proteins and how does this function differ from proteasomes? |
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Definition
| Lysosomal proteins hydrolyze extracellular proteins and dead cells. Proteasomes remove dysfunctional intracellular proteins within living cells |
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Term
How many enzymes are used to ubiquinate a protein?
What are they called? |
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Definition
| Three- Ubiquitin ligases E1, E2 and E3 |
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Term
| What are the functions of Ubiquitin ligases E1, E2 and E3? |
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Definition
E1: activates ubiquitin by attaching cysteine to ubiquitin's C-terminal. Then EI transfers the attached ubiquitin to a corresponding cysteine residue on one of a few E2 ligases.
E2: Binds activated ubiquitin on a cysteine thiol ester
E3: ligases and transfers the
ubiquitin from the E2 to the ε-amino group of an internal lysine residue on the target (isopeptide bond). Lysine residues within the attached ubiquitin undergo poly-ubiquitination |
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Term
| What feature of ubiquitination determines the alternative fates of proteins that have been ubiquinated? |
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Definition
| The fate of ubiquitinated proteins depends on whether their lysine has received more or less than 4 ubiquitin residues. If less than 4, the target is activated to some function and if more than 4, the target is moved to the proteasome and destroyed. |
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Term
| What enzyme is the initial target of transcription coupled repair and what does it do? |
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Definition
a) RNA PolII stalled by a DNA mutation during transcript elongation
b) Targets enzyme to proteasome and recruits repair enzymes to the DNA substrate
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Term
| What is the mediator of transcription coupled repair? |
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Definition
| Covalent ubiquitin binding to PolII |
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Term
| What does covalent ubiquitin binding in transcription coupled repair replace? |
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Definition
| Phosphate residues on the CTD (C-terminal Domain of PolII). |
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Term
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Definition
| An RNA protein particle on which protein are synthesized |
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Term
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Definition
| A protein particle (26s) that digests ubiquitinylated proteins in the cytosol |
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Term
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Definition
| An snRNA particle that removes introns as eukaryotic mRNA is being synthesized |
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Term
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Definition
| Protein exonuclease particle that digests all types of RNA from 3' →5'. In eukaryotes, the mRNA cap and tail are removed by endonucleases and the fragments by exonucleases, mostly in exosomes |
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Term
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Definition
A large section of DNA bound to histones and not transcribed unless an
activator first removes the histones |
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Term
| What is the function of tunicamycin? |
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Definition
| It is an anti-cancer drug that inhibits N-linked oligosaccharide synthesis via competitive inhibition (also causes lysosome enzyme secretion) |
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Term
| Briefly describe the steps of synthesis of core oligosaccharide of glycoproteins |
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Definition
Step 1: 2 UDP-GlcNAc -> UMP and UDP (adds a phosphate and glucose)
Step 2: 5 GDP-Man-> 5 Man (adds 5 mannose)
Step 3: translocation into ER lumen
Step 4: Attach more sugars
Etc: Growing polypeptide gets into ER and binds to oligosacharide
9: The glycoprotein moves to golgi, dolichol phosphate recycled |
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Term
| Describe nuclear protein targeting |
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Definition
Importins get proteins through nuclear pores, then the carriers are removed
Involves GTP |
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