Exam 1 - Enzymes

Front 1

what are enzymes?

Back 1

proteins that act as catalysts

Front 2

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.

Back 2

active site

Front 3

Affinity of the enzyme to the transition state is (greater, lesser, or equal) to/than the substrate.

Back 3

greater

Front 4

What are these?
-proximity and orientation
-bond strain or distortion
-acid-base catalysis/proton donors and acceptors
-electrostatic catalysis
-covalent intermediate

Back 4

the 5 main strategies that an enzyme can use to catalyze a reaction

Front 5

What is the residue that is often involved in the acid/base enzyme strategy? Why?

Back 5

Histidine
Because it's pKa is close to neutral pH and can therefore accept and donate protons

Front 6

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...

Back 6

chymotrypsin

serine
aspartate
histidine

Front 7

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.

Back 7

Coenzymes

Front 8

What are the 2 main classes of coenzymes in catalysis?

Back 8

activation-transfer coenzymes

oxidation-reduction coenzymes

Front 9

oxidation involves ... of electrons and reduction involves ... of electrons.

Back 9

loss
gain

(OIL RIG)

Front 10

what is the optimal pH range for enzyme activity?

Back 10

7.2-8.5

Front 11

what is the optimal temperature for enzyme activity?

Back 11

37 degrees Celcius (in Canada)

98.6 degrees F

Front 12

What class of enzyme is this?
-transfer of electrons from donor to acceptor
-many require metal ions as cofactors

Back 12

Oxidoreductases

Front 13

What class of enzyme is this?
-transfer of functional groups from one molecule to another.

Back 13

transferases

Front 14

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

Back 14

Hydrolases

Front 15

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)

Back 15

Lyases

Front 16

what class of enzymes is this?
-simply rearrange existing atoms and bond structure

Back 16

isomerases

Front 17

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

Back 17

Ligases

Front 18

What are the 6 classes of enzymes?

Back 18

-Oxidoreductases
-transferases
-hydrolases
-lyases
-isomerases
-ligases

Front 19

enzyme kinetics involves the study of the ... of chemical reactions that are catalyzed by enzymes.

Back 19

rates

Front 20

The michaelis-menten equation applies only to simple, ... substrate enzymatic reactions

Back 20

single

Front 21

what is the concentration of substrate required to reach 1/2 Vmax?

Back 21

Km

Front 22

In a Michaelis-Menten graph, ... is plotted versus ...

Back 22

substrate concentration [S]
initial reaction velocity (Vi)

Front 23

The higher the Vmax, the ... the reaction occurs. If comparing two enzymes, the one with the ... Vmax works more quickly and efficiently

Back 23

faster
higher

Front 24

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

Back 24

higher
higher
lower

Front 25

High Km --> ... affinity

Back 25

low

Front 26

In the lineweaver-burk plot, the y-intercept is equivalent to ... and the x-intercept of the graph represents ...

Back 26

1/Vmax
1/Km

Front 27

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)

Back 27

ternary-complex mechanism

ping-pong mechanism

Front 28

Which type of inhibition increases Km, but has no effect on Vmax?

ex. methanol poisoning

Back 28

competitive inhibition

Front 29

Which type of inhibition decreases Vmax, but has no effect on Km? (2 types)

Back 29

non-competitive inhibition

irriversible inhibition

Front 30

which type of inhibition decreases Vmax and decreases Km?

Back 30

Uncompetitive Inhibition

Front 31

which type of inhibition decreases Vmax and increases Km?

Back 31

mixed inhibition

Front 32

Changes in the rate of a metabolic pathway can occur because of 2 things, which are

Back 32

-(activity) at least 1 enzyme (regulatory enzyme) has been activated or inhibited
-(amount) the amount of enzyme has been increased or decreased

Front 33

the ... enzyme usually catalyzes the rate-limiting step

Back 33

regulatory

Front 34

what can this cause?
-reversible binding to active site
-changing conformation of active site

Back 34

activation or inhibition of at least one enzyme

Front 35

if you increase substrate concentration, the rate will...

Back 35

increase

Front 36

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

Back 36

decrease

feedback or end product inhibition

Front 37

The 4 types of regulation that can result in conformational change of the enzyme are

Back 37

-allosteric regulation
-covalent modification (i.e. phosphrylation)
-protein-protein interactions
-proteolytic cleavage

Front 38

allosteric enzymes usually contain 2 or more subunits and exibit ... (binding of substrate to one unit facilitates binding of substrate to another subunit)

Back 38

positive cooperativity

Front 39

The main advantage in allosteric regulation is that ...

Back 39

a small increase in substrate concentration can result in a large increase in catalytic rate (Vmax)

Front 40

an allosteric activator will ... Km

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

Back 40

decrease

increase

Front 41

what is phosphorylation?

Back 41

the addition of phosphate group to a protein

Front 42

kinase (adds or removes) PO4?

Back 42

adds

Front 43

phosphorylase (adds or removes) PO4?

Back 43

removes

Front 44

What is an example of activation through phosphorylation and allosteric activation through AMP binding?

Back 44

muscle glycogen phosphorylase

Front 45

what are 2 examples of conformational changes from protein-protein interactions?

Back 45

Ca2+-Calmodulin family

Monomeric G Proteins (regulation of cell activity)

Front 46

The inactive precursor form of the enzyme is called a ...

Back 46

proenzyme

Front 47

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

Back 47

zymogens

chymotrypsinogen

Front 48

The synthesis of an inactive precursor in a cell helps to protect the cell against...

Back 48

auto-digestion or auto-lysis.

Front 49

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.

Back 49

upregulation
downregulation

Front 50

The concentration of enzyme can also be reduced in the cell through increased ... by lysosomes, proteosomes, and caspases.

Back 50

degradation