Chapter 2 - Protein Composition and Structure Flashcards
Proteins are linear polymers built of monomer units called
amino acids.
Primary structure of a protein
The sequence of amino acids linked end to end.
Secondary structure of a protein
The 3d structure formed by hydrogen bonds between amino acids near one another.
Tertiary structure of a protein
Formed by long-range interactions between amino acids.
Enzymes
The proteins that catalyze specific chemical reactions in biological systems.
Zwitterions
A molecule or ion having separate positively and negatively charged groups.
The R group of an amino acid is often referred to as the
side chain.
Which isomer of amino acids are constituents of proteins?
L amino acids
For all amino acids, the L isomer has ___ absolute configuration.
S
In acidic solution the amino group of an amino acid is
protonated (-NH3+).
In acidic solution, the carboxyl group of the amino acid is
not dissociated (-COOH).
As the pH is raised, the first group to give up a proton in an amino acid is the
carboxylic acid.
The protonated amino group in an amino acid loses a proton around pH
9
The only achiral amino acid is
glycine.
Which amino acids have more than 1 chiral center?
Isoleucine and threonine.
How many amino acids have readily ionizable side chains?
7
Peptide bond (or amide bond)
Formed by linking the alpha-carboxyl group of one amino acid to the alpha-amino group of another amino-acid.
The formation of a dipeptide is accompanied by the loss of a
water molecule.
The lifetime of a peptide bond in aqueous solution in the absence of a catalyst approaches ______ years.
1000
Each amino acid unit in a polypeptide is called a
residue.
Main chain (or backbone)
Regularly repeating part of a polypeptide chain.
The polypeptide backbone is rich in ______ bonding potential.
Hydrogen
The largest known polypeptide is ______ which consists of more than ______ amino acids.
Titin; 27000
Oligopeptides
Peptide chains made of small numbers of amino acids.
The most common cross links are
disulfide bonds.
Disulfide bonds form by
the oxidation of a pair of cysteine residues.
Cystine
The result of two linked cysteines.
The amino acid sequences of proteins are determined by
the nucleotide sequences of genes.
A peptide bond is essentially planar or nonplanar?
planar
A peptide bond cannot rotate because
the bond resonates between a single and double bond with the C=O group.
Almost all peptide bonds are (cis or trans)
trans.
The most common cis peptide bonds are
X-Pro linkages
phi
The angle of rotation about the bond between the nitrogen and the alpha-carbon atoms.
psi
The angle of rotation about the bond between the alpha-carbon and the carbonyl carbon atoms.
The phi and psi angles determine
the path of the polypeptide chain.
Some diseases resulting from improperly folded proteins.
- Parkinson disease
- Huntington disease
- transmissible spongiform encephalopathies (prion disease)
Alpha helices, beta strands, and turns are formed by
a regular patter of hydrogen bonds between the peptide N-H and C=O groups of amino acids near each other in the linear sequence.
The alpha helix is stabilized by
hydrogen bonds between the NH and CO groups of the main chain.
The CO group of each amino acid forms a hydrogen bond with the NH group of the amino acid that is ______ residues ahead in the sequence.
four
Number of amino acids residues per turn in an alpha helix.
3.6
The pitch of the alpha helix is the
length of one complete turn along the helix axis.
The pitch of the alpha helix is equal to
the product of the rise (1.5 A) and the number of residues per turn (3.6), or 5.4 Angstroms.
Essentially, all alpha helixes formed in proteins are ______ handed.
right
Beta sheets are stabilized by
hydrogen bonding between polypeptide strands.
A beta sheet is formed by
linking two or more beta strands lying next to one another through hydrogen bonds.
