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50 Cards in this Set

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what are enzymes?
proteins that act as catalysts
what is the location where catalytic change occurs (where the substrate is converted into product) called?
the substrate binding site is often a portion of this site.
active site
Affinity of the enzyme to the transition state is (greater, lesser, or equal) to/than the substrate.
greater
What are these?
-proximity and orientation
-bond strain or distortion
-acid-base catalysis/proton donors and acceptors
-electrostatic catalysis
-covalent intermediate
the 5 main strategies that an enzyme can use to catalyze a reaction
What is the residue that is often involved in the acid/base enzyme strategy? Why?
Histidine
Because it's pKa is close to neutral pH and can therefore accept and donate protons
What is this?
-employs all 5 of the catalytic strategies
-a digestive serine protease enzyme released into the intestines that catalyzes the hydrolysis of specific peptide bonds in proteins.
-contains the catalytic triad which is...
chymotrypsin

serine
aspartate
histidine
what are complex, nonprotein organic molecules that participate in catalysis by providing functional groups that are otherwise not available in the active site of an enzyme?
Most are synthesized or derived from vitamins.
Coenzymes
What are the 2 main classes of coenzymes in catalysis?
activation-transfer coenzymes

oxidation-reduction coenzymes
oxidation involves ... of electrons and reduction involves ... of electrons.
loss
gain

(OIL RIG)
what is the optimal pH range for enzyme activity?
7.2-8.5
what is the optimal temperature for enzyme activity?
37 degrees Celcius (in Canada)

98.6 degrees F
What class of enzyme is this?
-transfer of electrons from donor to acceptor
-many require metal ions as cofactors
Oxidoreductases
What class of enzyme is this?
-transfer of functional groups from one molecule to another.
transferases
what class of enzyme is this?
-C-O, C-N, C-S bonds cleaved by addition of H20
-names specify what group is being cleaved
Hydrolases
what class of enzyme is this?
-C-C, C-O, and C-N bonds cleaved by means other than hydrolysis or oxidation (no H20 or O2 involved)
Lyases
what class of enzymes is this?
-simply rearrange existing atoms and bond structure
isomerases
what class of enzymes is this?
-synthesize C-C, C-S, C-O, and C-N bonds in reactions coupled to cleavage of high-energy phosphate bonds
-requires ATP to form new bonds
Ligases
What are the 6 classes of enzymes?
-Oxidoreductases
-transferases
-hydrolases
-lyases
-isomerases
-ligases
enzyme kinetics involves the study of the ... of chemical reactions that are catalyzed by enzymes.
rates
The michaelis-menten equation applies only to simple, ... substrate enzymatic reactions
single
what is the concentration of substrate required to reach 1/2 Vmax?
Km
In a Michaelis-Menten graph, ... is plotted versus ...
substrate concentration [S]
initial reaction velocity (Vi)
The higher the Vmax, the ... the reaction occurs. If comparing two enzymes, the one with the ... Vmax works more quickly and efficiently
faster
higher
A ... Km value means the enzyme has a lower affinity for its substrate. In other words, a ... Km means the enzyme needs more substrate to achieve 1/2 the Vmax. If comparing 2 enzymes, the one with the ... Km has the greater affinity for its substrate
higher
higher
lower
High Km --> ... affinity
low
In the lineweaver-burk plot, the y-intercept is equivalent to ... and the x-intercept of the graph represents ...
1/Vmax
1/Km
2 examples of multi-substrate reactions are the ... (where both substrates bind enzyme at the same time (random or ordered), and the ... (where the first substrate must be released before the second substrate can bind)
ternary-complex mechanism

ping-pong mechanism
Which type of inhibition increases Km, but has no effect on Vmax?

ex. methanol poisoning
competitive inhibition
Which type of inhibition decreases Vmax, but has no effect on Km? (2 types)
non-competitive inhibition

irriversible inhibition
which type of inhibition decreases Vmax and decreases Km?
Uncompetitive Inhibition
which type of inhibition decreases Vmax and increases Km?
mixed inhibition
Changes in the rate of a metabolic pathway can occur because of 2 things, which are
-(activity) at least 1 enzyme (regulatory enzyme) has been activated or inhibited
-(amount) the amount of enzyme has been increased or decreased
the ... enzyme usually catalyzes the rate-limiting step
regulatory
what can this cause?
-reversible binding to active site
-changing conformation of active site
activation or inhibition of at least one enzyme
if you increase substrate concentration, the rate will...
increase
if you increase product concentration, the rate will ...

This is called ...

This prevents one enzyme from generating product faster than it can be used by the next enzyme in the sequence
decrease

feedback or end product inhibition
The 4 types of regulation that can result in conformational change of the enzyme are
-allosteric regulation
-covalent modification (i.e. phosphrylation)
-protein-protein interactions
-proteolytic cleavage
allosteric enzymes usually contain 2 or more subunits and exibit ... (binding of substrate to one unit facilitates binding of substrate to another subunit)
positive cooperativity
The main advantage in allosteric regulation is that ...
a small increase in substrate concentration can result in a large increase in catalytic rate (Vmax)
an allosteric activator will ... Km

an allosteric inhibitor will ... Km and slow the overal reaction rate
decrease

increase
what is phosphorylation?
the addition of phosphate group to a protein
kinase (adds or removes) PO4?
adds
phosphorylase (adds or removes) PO4?
removes
What is an example of activation through phosphorylation and allosteric activation through AMP binding?
muscle glycogen phosphorylase
what are 2 examples of conformational changes from protein-protein interactions?
Ca2+-Calmodulin family

Monomeric G Proteins (regulation of cell activity)
The inactive precursor form of the enzyme is called a ...
proenzyme
The precursor of proteases (enzymes that cleave specific peptide bonds in proteins) are called ...

An example of this is ..., which is synthesized by pancreatic acinar cells and later activated in the duodenum of the small intestines by the protease trypsin
zymogens

chymotrypsinogen
The synthesis of an inactive precursor in a cell helps to protect the cell against...
auto-digestion or auto-lysis.
The rate of a chemical reaction can be altered by either increasing or decreasing the amount of enzyme available, which involves induction (...) and repression (...) of mRNA transcription and/or translation into a protein.
upregulation
downregulation
The concentration of enzyme can also be reduced in the cell through increased ... by lysosomes, proteosomes, and caspases.
degradation