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108 Terms
What is myoglobin?
An oxygen-storage protein in muscle.
How many subunits does hemoglobin have?
Four.
What is the largest human protein?
Titin.
What is a conjugated protein?
A protein containing a non-amino-acid prosthetic group.
What are lipoproteins?
Proteins containing lipids.
What are glycoproteins?
Proteins containing carbohydrates.
What are phosphoproteins?
Proteins containing phosphate groups.
What are hemoproteins?
Proteins containing heme.
What protein stores iron?
Ferritin.
What metal is found in alcohol dehydrogenase?
Zinc.
What protein contains heme and transports oxygen?
Hemoglobin.
What is protein purification?
The process of isolating a protein from a mixture.
Why are proteins separable?
They differ in size, charge, shape, and binding properties.
What is chromatography?
A method used to separate molecules based on physical or chemical properties.
What is the mobile phase?
The moving liquid in chromatography.
What is the stationary phase?
The solid matrix inside a chromatography column.
What is a crude extract?
The mixture obtained after cells are lysed.
What is fractionation?
The process of separating proteins into groups.
What is salting out?
Protein precipitation caused by increasing salt concentration.
What salt is commonly used for salting out?
Ammonium sulfate.
What is dialysis?
Removal of small molecules through a semipermeable membrane.
What passes through a dialysis membrane?
Small molecules and salts.
What remains inside a dialysis membrane?
Proteins.
What is ion-exchange chromatography?
Chromatography that separates proteins based on charge.
What does a cation exchanger bind?
Positively charged proteins.
What does an anion exchanger bind?
Negatively charged proteins.
In cation exchange chromatography, which proteins elute first?
Most negatively charged proteins.
How are proteins eluted from ion-exchange columns?
By changing salt concentration or pH.
What is size-exclusion chromatography?
A method that separates proteins by size.
What is another name for size-exclusion chromatography?
Gel filtration chromatography.
Why do large proteins elute first?
They cannot enter bead pores and take a shorter path.
What is affinity chromatography?
A method that separates proteins based on specific binding interactions.
What is attached to the affinity column?
A ligand that binds the target protein.
Why is affinity chromatography highly selective?
It exploits specific biological interactions.
What is HPLC?
High-Performance Liquid Chromatography.
Why is HPLC better than conventional chromatography?
It provides higher resolution and faster separation.
What does resolution mean in chromatography?
The ability to distinguish similar molecules.
What does increasing specific activity indicate?
Increasing purity.
What generally happens to yield during purification?
It decreases.
What is electrophoresis?
Separation of proteins in an electric field.
What determines protein migration in PAGE?
Charge, size, and shape.
What does PAGE stand for?
Polyacrylamide Gel Electrophoresis.
What can electrophoresis estimate?
Purity, molecular weight, pI, and number of proteins in a sample.
What is electrophoretic mobility?
The rate at which a protein migrates in an electric field.
What increases electrophoretic mobility?
Higher charge.
What decreases electrophoretic mobility?
Greater friction due to size or shape.
What is SDS?
Sodium dodecyl sulfate, a detergent used in protein electrophoresis.
What does SDS do to proteins?
Denatures and coats them with negative charge.
Why is SDS used?
To eliminate differences in charge
What determines migration in SDS-PAGE?
Molecular weight only.
Which proteins move faster in SDS-PAGE?
Smaller proteins.
What law relates absorbance to concentration?
Beer-Lambert Law.
Beer-Lambert equation?
A = εlc.
What does A represent in Beer-Lambert law?
Absorbance.
What does ε represent in Beer-Lambert law?
Extinction coefficient.
What does l represent in Beer-Lambert law?
Path length.
What does c represent in Beer-Lambert law?
Concentration.
What are the four major functions of proteins?
Catalysis, transport, structure, and motion.
What are proteins made of?
Linear polymers of amino acids.
What is a heteropolymer?
A polymer made from different types of monomers.
What are the four groups attached to the α-carbon of an amino acid?
Amino group, carboxyl group, hydrogen atom, and R group.
What determines the identity of an amino acid?
The R group (side chain).
What is the α-carbon?
The central carbon atom in amino acids.
What is chirality?
The property of a molecule existing as non-superimposable mirror images.
What amino acid is achiral?
Glycine.
Why is glycine achiral?
Its R group is a hydrogen, giving it two identical substituents.
Which amino acid stereoisomer is found in proteins?
L-amino acids.
What are enantiomers?
Non-superimposable mirror-image molecules.
What is phosphorylation?
Addition of a phosphate group to a protein.
Why is phosphorylation important?
It regulates protein activity.
What is ionization?
Gain or loss of protons by a molecule.
Which amino acid group acts as an acid?
The carboxyl group.
Which amino acid group acts as a base?
The amino group.
What is a zwitterion?
A molecule containing both positive and negative charges but with net charge zero.
What is the predominant form of amino acids at physiological pH?
The zwitterionic form.
What is the net charge of an amino acid at very low pH?
Positive (+1).
What is the net charge of an amino acid at very high pH?
Negative (-1).
How does amino acid charge change as pH increases?
It becomes progressively more negative.
What is pKa?
The pH at which 50% of a group is protonated and 50% is deprotonated.
What is a titration curve?
A graph showing pH changes as acid or base is added.
What are buffer regions?
Regions where pH changes slowly near a pKa value.
What is the isoelectric point (pI)?
The pH at which net charge equals zero.
What is special about proteins at their pI?
They have no net charge and minimal mobility in an electric field.
How do you calculate pI for amino acids with ionizable side chains?
Average the two pKa values surrounding the neutral form.
What is a peptide?
A chain of amino acids connected by peptide bonds.
What reaction forms peptide bonds?
A condensation (dehydration) reaction.
What is removed during peptide bond formation?
Water.
What is a peptide bond?
An amide bond linking amino acids.
Why is the peptide bond rigid?
It has partial double-bond character.
What is an oligopeptide?
A short chain of amino acids.
What is a polypeptide?
A long chain of amino acids.
How many peptide bonds exist in a chain of n amino acids?
n - 1.
What are the two ends of a peptide?
N-terminus and C-terminus.
What is the N-terminus?
The amino end of a peptide.
What is the C-terminus?
The carboxyl end of a peptide.
In what direction are peptides written?
N-terminus to C-terminus.
How are peptides named?
Starting from the N-terminus.
What neuropeptide is involved in pain transmission?
Substance P.
What antibiotic peptide targets Gram-negative bacteria?
Polymyxin B.
What antibiotic peptide targets Gram-positive bacteria?
Bacitracin.