Ch 4: Amino Acids and Proteins (Princeton Review) Flashcards
An individual amino acid is termed a _______ when it is part of a polypeptide chain.
residue
p. 71
In the polypeptide chain, the pattern is described by the following:
N-C-C-N-C-C-N-C-C
What does the N represent?
The amino terminus (or N-terminus), which by convention is always written first.
p. 71
In the polypeptide chain, the pattern is described by the following:
N-C-C-N-C-C-N-C-C
What does the C at the end represent?
The carboxy terminus (C-terminus), which by convention is always written last.
p. 71
Hydrolysis of a protein by another protein is called proteolysis or proteolytic cleavage, and the protein that does the cutting is known as a proteolytic enzyme or ________. This type of cleavage is a _______ means of cleaving peptide bonds.
protease
specific
p. 72
The disulfide bridge formed between two cysteine molecules plays an important role in stabilizing ________ protein structure. Once a cysteine residue becomes disulfide-bonded to another, it is called _______.
tertiary
cystine
p. 73
Whether 2 cysteine amino acids form a disulfide bridge will depend on….
….whether they are in an oxidizing environment, or a reducing environment.
p. 73
The inside of cells is known as a ________ environment because cells possess antioxidants (chemicals that prevent oxidation reactions).
reducing
p. 73
For the reason mentioned on the previous card, disulfide bridges btw cysteine molecules are found only in __________ polypeptides, where they will not be reduced.
extracellular
p. 73
Name two examples of protein complexes held together by disulfide bridges.
antibodies
insulin
p. 73
What is the term for a molecule with both positive and negative charges that balance?
a dipolar ion or zwitterion
p. 69
The pH at which a molecule is uncharged (zwitterionic) is referred to as its _________ (__). “Zwitter” is German for “hybrid”, implying that an amino acid at its pI has both (+) and (-) charges.
isoelectric point (pI)
p. 69
Acids with a low pKa tend to _________ easily.
deprotonate
p. 68
In its protonated, or acidic form, the amine of an amino acid is called an __________ group, and has a pKa between _ and __.
ammonium
9 and 10
p. 69
What will be the net charge on a glycine molecule at pH 12?
Since pH 12 represents a very low [H+], both groups will become deprotonated (COO- and NH2), creating a net charge of -1 per glycine molecule.
p. 69
The α-helices of proteins are always ____-handed, and _ angstroms in width.
right-handed
5 angstroms
In α-helices of proteins, the α-carbon of one amino acid residue hydrogen-bonded to….
….the α-amino proton of an amino acid 3 residues away (remember there are 3 whole amino acids between these 2 bonded atoms). It’s confusing, look at the picture. Really it’d be better to say it is bonded the the 4th amino acid away.
Enzymes cannot control the ________ in which a reaction proceeds. It is common to see an enzyme in a given class function in reverse.
direction
p. 78
Thermodynamically unfavorable reactions in the cell can be driven forward by ________ ________.
reaction coupling
p. 79
Enzymes have only a ______ role (influencing rate only), not a thermodynamic one.
kinetic
p. 80
The phosphate molecules in a nucleotide are assigned Greek letters. Which is the 3rd in the chain?
the gamma phosphate (γ)
What is the difference between a phosphorylase and a phosphatase?
A phosphatase removes a phosphate group from a molecule, utilizing water. A phosphorylase transfers, or adds, a phosphate group to a molecule from inorganic phosphate.
p. 79
What is the difference between what a kinase does and what a phosphorylase does?
A kinase transfers a phosphate group to a molecule from a high energy carrier, such as ATP.
A phosphorylase transfers, or adds, a phosphate group to a molecule from inorganic phosphate.
p. 79
What do ligases do? Name an example.
They form chemical bonds.
e. g. DNA ligase
p. 79
What does a lyase do?
Breaks chemical bonds by means other than oxidation or hydrolysis.
If an enzyme breaks breaks a chemical by means of hydrolysis, it is a hydrolase.
If it breaks a chemical bond by means of oxidation, it is an oxidoreductase.
p. 79
