Why is it important that enzymes in lysosomes are more active at acidic pH than at neutral pH?
It prevents them from accidentally degrading the macromolecules in the cytosol.
Proteins in biological membranes maybe________.
spanning the membrane, porous, and attached to surface of the membrane.
Which of the following developed during the revolution of eukaryotic cells from prokaryotic cells?
What is the only cell in the human body that is capable of motility and posses a flagellum?
What is the approcimate pka of a weak acid HA if a soln of 0.1 M HA and 0.3 MA A- has a pH of 6.5?
pka = pH + log (base/acid), 6.0
the capacity of a buffer to resist changes in pH upon addition of protons or hydroxide ions depends on ______.
pka of weak acid in buffer soln, pH of the buffer, total concn of the weak acid and its conjugate base in the buffer.
about half of the amino acids are called essential, because ____.
our bodies cannot synthesize them in sufficient quantity to meet synthetic needs if hey need to be present in the diet
what is osmosis?
the movement of solvent molecules from a less concentrated soln to an adjacent, more concentrated solns.
how do plants and animals prevent the effects of incubation in a cell at a soln of low osmotic pressure?
storing of glucose like a polymer (glycogen) which reduces the effect of the influx of water needed to dissolve glucose molecules (what causes cell to burst) or surround cell with isotonic soln negating a net efflux or influx of water.
The isoelectronic point of an amino acid is the point where ______.
the amino acid carries no net electrical charge
Ribosomes use L amino acids to synthesize proteins. these amino acids are called "L" because _____.
they turn polarized light to the left
Which of the following has the most dramatic influence on the characteristics of an individual protein?
Amino acid sequence
A fast and common method for determining the protein concn in column effluent is ___.
measuring light absorption at 280 nm
Proline is not often found in an alpha-helices of proteins because ____.
lacks a free hydrogen atom on its amide nitrogen
Loops and turns in protein are ______.
stretches of non-repeating 3-D structures in proteins, regions that let a polypeptide chain fold back on itself, and regions causing direction change in the polypeptide backbone.
Name facts about polypeptide bond
peptide bond has a partial double-bond character, the carbonyl oxygen and the amide hydrogen are most often in a trans configuration with respect to one another, rotation is restricted about the peptide bond
Chaperones are proteins which _____.
renature any denatured proteins, help cells repair damage due to heat shock, use ATP to fold proteins, and assist protein self assembly.
Tertiary structure of proteins describe _____.
stabilizing protein structure by non-covalent interaxn, bringing amino acids far apart in primary structure close together, disulfide bridges, and polypeptide folding.
what are facts about globular protein that performs its biological function as a single independent polypeptide chain?
could contain alpha-helices that are stabilized by hydrogen bonding, non-covalent forces are the primary src of stability for the secondary and tertiary structure, and its tertiary structure is likely stabilized by the interaxn of amino acid side chains in non-neighboring regions of the polypeptide chain
structure proteins that typically assemble into large cables or threads to provide mechanical support to cells or organisms are classified as ____.
Proteins with alpha helix regions called leucine zippers are ____.
part of pairs of helices that are wrapped around each other, often found in DNA binding proteins, amphipathic helices
Supersecondary structures that contain recognizable combinations of alpha-helices, beta-strands and loops (e.g the Greek key) are called ____.
in a multienzyme complex the process of directly transferring a product of one reaction to the next active site without allowing it to enter the bulk solvent is termed ____.
what is true about covalent modification?
it is slightly lower than allosteric regulation, and it is reversible
What are correlated with allosteric enzymes that do not follow typical Michaelis-Menten kinetics?
sigmoidal curves of velocity S is varied, cooperative binding of the substrate, and changes in conformation of the enzyme when S binds
An enzyme is irreversibly inhibited by diisopropylfluorophosphate (DFP). what does this show?
Serine is likely an important residue in the active site
In ____ inhibition the inhibitor binds at a site other than the active site, but alters the active site to prevent binding of the normal substrate.
in a ping-pong rxn what occurs?
enzyme covalently binds to a portion of the first substrate, a group is transferred from one substrate to another, one product is released before a second substrate is bound.
the Km valus for an enzyme rxn such as
A + B--->C+D
can be determined by holding (A or B) at high concn, while varying the concn of the other substrate
A detailed description of a chemical rxn in terms of molecular, atomic or subatomic events is called the rxn ______.
When the concn of a substrate inside a cell falls below the substrate concn at half maximal velocity, _____.
ES dissociates to E + S
a chemical group that has a negative charge or an unshared electron pair may act as a ____.
The product(s) of lactate and dehydrogenase under anaerobic conditions in the muscle is (are)
NADH and pyruvic acid
A rxn that occurs with every collision between the reactant molecules is called a(n) ____.
what is the role of magnesium ion in kinases that require magnesium ATP complex to donate phosphoryl groups?
shield the charged phosphate groups of ATP
ATP is involved in ____.
transfer of its AMP moiety to another compound, forming S-adenosylmethionine, transferring a phosphate group to other compounds
the active site of a certain enzyme contains a serine residue. When the enzyme is incubated for a short time with its substrate, a form of the enzyme which the active site is acetylated can be isolated and purified. in the native protein the serine is never found to be acetylated. this information supports ____..
covalent catalysis mode
unlike the coenzymes that are prosthetic groups, ____ are altered in the course of an enzyme rxn and dissociate from the active site.
What are true about alph-helix?
stabilized by hydrogen bonding, its is a type of secondary structure, its usually right-handed
chaperones are proteins which___.
use ATP to fold proteins, renature and denature proteins, help cells repair damages due to heat shock, assist protein self assembly
What is true about the determination of protein structures?
its often difficult to produce quality protein crystals for X-ray analysis, NMR spectroscopy exposes proteins solns to a magnetic field, and NMR can generate sets of structures which may represent proteins fluctuations
proteins with very high Tm values are generally stable at ___.
temps below 50 degrees Celsius and above 60 degrees Celsius, between 50 and 60 and also room temp
the trans configuration of most peptide groups is adopted in cells because it ___.
minimizes steric hindrance of R group, and favored by protein synthesis
What does it mean to say a protein is oligomeric?
the active protein involves the association of 2 or more polypeptide chains
Many proteins have multiple subunits because ___.
they are more stable and flexible in movement, an active site is shared by different subunits, and different combos can perform diff functions
Conditions in the tissue which enhance the delivery of oxygen by hemoglobin are the presence of
2,3 BPG, CO2, protons
pyranose rings are more stable when the ring adopts a ___ conformation with the bulkiest ring substituents in ___ positions.
polysaccharides structure can be varied by difference in ___.
kinds of sugar in each polysaccharides, presence of branching, chain length (# of sugar in each polysaccharide)
Chitin is ___.
composed of linear fibrils like cellulose, composed of N-acetylglucosamine subunits, found in fungi cell walls, found in insect and crustacean shells
(T/F) the large number of possible oligosaccharide structures in glycoproteins is limited in cells by the kinds of enzymes available for their synthesis
which type of membrane protein might be dissociated from the membrane by changing the pH or the ionic strength?
peripheral membrane protein
Determination of the tertiary structure of a membrane protein finds the outer surface is composed primarily of hydrophobic residues. What can be concluded from this?
it is an integral protein
A deficiency in synthesis of sphingomyelins or cerebrosides will most likely result in the improper formation of ___.
A fatty acid designated 20:0 is ___ while one that is designated 20:3 D5, 8, 11 is ___.
What are functions of cholesterol in mammals?
modulate fluidity of membranes, precursor of steroid hormones, precursor of bile salts
Cholesterol is converted to cholestryl esters for ___ in cells and are ___ (more, less) hydrophobic than glycerophospholipids.
polar heads of glycerophospholipids may be __.
+ charge, - charge, a mixture of + and -, neutral but polar
what are the similarities between active transport proteins and enzymes?
both susceptible to inhibition, both can reach a saturation limit, both undergo conformational changes upon binding a substrate
Mitochondria differ from other cellular structures such as lysozomes or nuclei by having ____.
a double membrane