What is the start codon for translation?
AUG
What amino acid does AUG code for?
Methionine
What does the initiator tRNA do?
It carries methionine and recognizes the AUG start codon during translation initiation.
What is eIF2's role in translation initiation?
It helps bring the initiator tRNA to the small ribosomal subunit.
What does eIF4E bind to?
The 5' cap of mRNA.
What is the function of the 5' cap?
It helps the ribosome recognize and bind to the mRNA during translation initiation.
What does the small ribosomal subunit do during initiation?
It binds to mRNA and scans for the AUG start codon.
What happens when the ribosome recognizes AUG?
Initiation factors leave and the large ribosomal subunit binds.
What are the 3 major stages of translation?
Initiation, elongation, and termination.
What happens during translation elongation?
Amino acids are repeatedly added to the growing polypeptide.
Where does the incoming tRNA enter the ribosome?
The A site.
What is the A site?
The ribosomal site where incoming aminoacyl tRNAs bind.
What forms the peptide bond during translation?
The peptidyl transferase activity of the large ribosomal subunit.
What is a peptide bond?
A bond connecting two amino acids.
What happens after a peptide bond forms?
The growing polypeptide is transferred to the tRNA in the A site and the ribosome translocates.
What does translocation mean?
Movement of the ribosome/tRNAs along the mRNA during translation.
What are the stop codons?
UAA, UAG, and UGA.
What do stop codons do?
Signal the end of translation.
What recognizes a stop codon?
A release factor.
What does a release factor do?
Binds to the A site and causes the completed polypeptide to be released.
What is translation termination?
The stage of translation when a stop codon is reached and the polypeptide is released.
What are molecular chaperones?
Proteins that help newly synthesized or misfolded proteins fold correctly.
What do molecular chaperones recognize on misfolded proteins?
Exposed hydrophobic regions.
Why are exposed hydrophobic regions a sign of misfolding?
Hydrophobic residues are normally buried inside a properly folded protein.
What is Hsp60?
A molecular chaperone that helps fully translated proteins fold inside an isolation chamber.
What is the Hsp60 isolation chamber?
A chamber that encloses a protein and provides an environment for proper folding.
Does Hsp60 require ATP?
Yes.
What is Hsp70?
A molecular chaperone that repeatedly binds exposed hydrophobic regions of proteins.
When does Hsp70 often interact with proteins?
As proteins emerge from the ribosome.
Does Hsp70 use ATP?
Yes.
What is one major difference between Hsp60 and Hsp70?
Hsp60 encloses fully translated proteins in an isolation chamber, while Hsp70 repeatedly binds exposed hydrophobic regions.
What is one similarity between Hsp60 and Hsp70?
Both are molecular chaperones that help proteins fold correctly.
What happens to a protein that cannot be properly folded?
It can be marked for degradation through ubiquitination.
What is ubiquitination?
The attachment of ubiquitin molecules to a target protein, usually on lysine residues.
What is the purpose of ubiquitination?
To mark a protein for destruction by the proteasome.
What amino acid residue is ubiquitin commonly attached to?
Lysine.
What are the 3 enzymes involved in ubiquitination?
E1, E2, and E3.
What does E1 do?
Uses ATP to activate and bind ubiquitin.
What does E2 do?
Receives/transfers ubiquitin from E1 toward the target protein.
What does E3 do?
Recognizes the target protein and determines substrate specificity.
Which ubiquitination enzyme determines substrate specificity?
E3 ubiquitin protein ligase.
What is a polyubiquitin chain?
A chain of ubiquitin molecules attached to a target protein.
What does a polyubiquitin chain signal?
Degradation by the proteasome.
What is the correct order of ubiquitination enzymes?
E1 → E2 → E3.
What does E1 use to activate ubiquitin?
ATP.
What is the proteasome?
A large protein complex that recognizes and degrades ubiquitinated proteins.
What does the proteasome recognize?
A polyubiquitin chain on a target protein.
Where are the proteases located in the proteasome?
Inside the central cylindrical region.
What is the main function of the proteasome?
To degrade proteins marked with ubiquitin.
What happens first when a protein is targeted for proteasomal degradation?
The proteasome recognizes the ubiquitinated protein.
What happens after the proteasome recognizes the target protein?
The protein is fed into the proteasome cylinder.
What happens inside the proteasome?
Proteases cleave and degrade the protein.
What are membrane lipids?
Lipids that make up the cell membrane and form the lipid bilayer.
What does amphipathic mean?
Having both hydrophilic and hydrophobic regions.
Which part of a membrane lipid is hydrophilic?
The polar head.
Which part of a membrane lipid is hydrophobic?
The fatty acid tails.
What is the most prevalent type of lipid in the membrane?
Phospholipids.
What are the 4 major parts of a phospholipid?
Polar head group, phosphate, bridge molecule, and fatty acid tails.
What is the function of the fatty acid tails?
They form the hydrophobic interior of the membrane.
What are the two major types of phospholipids?
Phosphoglycerides and sphingolipids.
What backbone do phosphoglycerides contain?
A glycerol backbone.
What backbone do sphingolipids contain?
A sphingosine backbone.
What is a glycolipid?
A lipid with a carbohydrate attached.
What is a transmembrane protein?
A protein that crosses completely through the lipid bilayer.
What is an integral membrane protein?
A protein that is embedded partially or completely in the membrane.
What is a peripheral membrane protein?
A protein associated with the membrane surface but not embedded through the bilayer.
Are all transmembrane proteins integral membrane proteins?
Yes.
Are all integral membrane proteins transmembrane proteins?
No.
What is a single
pass transmembrane protein? A protein that crosses the membrane one time.
What is a multipass transmembrane protein?
A protein that crosses the membrane multiple times.
What structure can membrane proteins form to create pores?
Beta barrels.
What is a protein dimer?
A complex made of two protein subunits.
What is a protein trimer?
A complex made of three protein subunits.
What is the difference between phosphoglycerides and sphingolipids?
Phosphoglycerides have a glycerol backbone, while sphingolipids have a sphingosine backbone.
What is the difference between phospholipids and glycolipids?
Phospholipids contain phosphate, while glycolipids have carbohydrates attached.
Where are glycolipids primarily found?
On the outside/extracellular leaflet of the membrane.
What is cholesterol's role in the membrane?
It regulates membrane fluidity and permeability.
How does cholesterol affect membrane permeability?
it decreases membrane permeability.
How does cholesterol affect fatty acid chains?
It makes them more rigid.
What does cholesterol prevent?
It prevents hydrocarbon chains from crystallizing/packing too tightly.
Why is cholesterol important for membrane fluidity?
It prevents the membrane from becoming too rigid by preventing hydrocarbon chains from crystallizing.
What is a micelle?
A closed structure made from a single layer of lipids.
How are lipids arranged in a micelle?
Polar heads face outward toward water and nonpolar tails face inward.
What is a lipid bilayer?
A membrane made of two layers of lipids.
How are lipids arranged in a bilayer?
Polar heads face outward toward water while nonpolar tails face inward toward each other.
What is the main difference between a micelle and a lipid bilayer?
A micelle has one lipid layer, while a bilayer has two lipid layers.
Are membrane lipids stationary?
No, they are constantly moving/diffusing.
What is lateral diffusion?
Side to side movement of a lipid within the same leaflet.
Is lateral diffusion common?
Yes, it occurs frequently.
What is flipflop?
Movement of a lipid from one leaflet of the membrane to the other.
Is flipflop common?
No, it is rare.
Why is flipflop rare?
The polar head would have to cross the hydrophobic interior of the membrane.
What enzyme helps move lipids between membrane leaflets?
Flippases.
What is scramblase?
A type of enzyme that promotes movement of lipids between membrane leaflets.
What type of lipid movement is most common?
Lateral diffusion.
What type of lipid movement is rare?
Flipflop.
What are the two main components of a membrane lipid?
A hydrophilic head and hydrophobic tails.
What happens to hydrophobic tails in water?
They avoid water and point toward the interior of the membrane structure.
What happens to hydrophilic heads in water?
They face the water.