Biochemically Small PeptidesㅡQuarternary Structure Of Proteins Flashcards
The two best-known peptide hormones, both produced by the pituitary gland, are
___________ and __________. Each hormone is a nonapeptide (nine amino acid residues) with six of the residues held in the form of a loop by a disulfi de bond formed from the interaction of two cysteine residues.
oxytocin
vasopressin
Another name for vasopressin is _____________.
antidiuretic hormone (ADH)
____________ are pentapeptide neurotransmitters produced by the brain itself that bind at receptor sites in the brain to reduce pain.
The pain-reducing effects of ____________ action play a role in the “high” reported by long-distance runners, in the competitive athlete’s managing to finish the game despite being injured, and in the pain-relieving effects of acupuncture.
Enkephalins
The two best-known enkephalins are ___________ and ____________, whose structures differ only in the amino acid residue present at the C-terminal end of the peptide.
Met-enkephalin: Tyr–Gly–Gly–Phe–Met
Leu-enkephalin: Tyr–Gly–Gly–Phe–Leu
The tripeptide __________ is present in signifi cant concentrations in most cells and is of considerable physiological importance as a regulator of oxidation–reduction reactions. Specifically, ____ functions as an antioxidant, protecting cellular contents from oxidizing agents such as peroxides and superoxides (highly reactive forms of oxygen often generated within the cell in response to bacterial invasion).
glutathione (Glu–Cys–Gly)
A __________ is a protein in which only one peptide chain is present.
monomeric protein
A _____________ is a protein in which more than one peptide chain is present.
multimeric protein
The peptide chains present in multimeric proteins are called __________.
protein subunits
A ____________ is a protein in which only amino acid residues are present.
More than one protein subunit may be present in a _________, but all subunits contain only amino acids.
simple protein
A _____________ is a protein that has one or more non-amino acid entities present in its structure in addition to one or more peptide chains. These non-amino acid components, which may be organic or inorganic, are called prosthetic groups.
conjugated protein
A __________ is a non-amino acid group present in a conjugated protein.
prosthetic group
___________ is the order in which amino acids are linked together in a protein.
Primary protein structure
The British biochemist _______________ (1918– )
determined the primary structure of the protein hormone insulin in 1953.
Frederick Sanger
____________ is the arrangement in space adopted by the backbone
portion of a protein.
Secondary protein structure
The two most common types of secondary structure are the
_____________ and the ______________.
a. alpha helix (a helix)
b. beta pleated sheet (b pleated sheet)
An _____________ is a protein secondary structure in which a single protein
chain adopts a shape that resembles a coiled spring (helix), with the coil configuration
maintained by hydrogen bond.
alpha helix structure
A ___________ is a protein secondary structure in which two fully
extended protein chain segments in the same or different molecules are held together
by hydrogen bonds.
beta pleated sheet structure
This “_____________” is the most frequently encountered type of b pleated sheet
structure.
U-turn structure
An _________________ is a protein secondary structure that is neither an
a helix nor a b pleated sheet.
unstructured protein segment
_____________ is the overall three-dimensional shape of a protein that results from the interactions between amino acid side chains (R groups) that are
widely separated from each other within a peptide chain.
Tertiary protein structure
Four types of stabilizing interactions contribute to the tertiary structure of a protein:
(1) covalent disulfide bonds
(2) electrostatic attractions (salt bridges)
(3) hydrogen
bonds and
(4) hydrophobic attractions
__________, the strongest of the tertiary-structure interactions, result from
the ㅡSH groups of two cysteine residues reacting with each other to form a covalent disulfide bond. This type of interaction is the only one of the four
tertiary-structure interactions that involves a covalent bond.
Disulfide bonds
___________, also called salt bridges, always involve the interaction
between an acidic side chain (R group) and a basic side chain (R group). The side
chains of acidic and basic amino acids, at the appropriate pH, carry charges, with
the acidic side chain being negatively charged and the basic side chain being positively charged.
Electrostatic interactions
___________ can occur between amino acids with polar R groups. They are relatively weak and are easily disrupted by changes in pH and temperature.
Hydrogen bonds
