Quan's study guide Exam 1

Question 1

The most critical function of an enzyme

Answer 1

are the catalysts of biological reactions, and speeds up a reaction. LOWERS THE ACTIVATION ENERGY NEEDED FOR A REACTION TO OCCUR.

Question 2

Common features of enzymes

Answer 2

Catalyze only thermodynamically possible rxns

Are not used or changed during a reaction (are not used up by the rxn)

Don’t change the position or direction of equilibrium

Usually act by forming a transient complex with the reaction

Question 3

Influence of temperature and PH on enzyme

Answer 3

Inorganic catalyst- rxn rate increases with temperature

Temp- function best at ambient or body temp. Can increase activity at slightly higher temps, but because they contain proteins, they eventually denature (45-50 C)

pH- affects the ionic charge of the amino acid side chains (most optimum pH =7)

Question 4

Pepsin is optimal at what pH?

Answer 4

At a pH of 3

Question 5

Composition of complex enzyme

Answer 5

protein + non protein

Protein- Apoenzyme
Non protein- Cofactor (Either prosthetic group or coenzyme)

Prosthetic – small inorganic and tightly bound to apoenzyme

Coenzyme- Large and loosely bound to apoenzyme

Question 6

Prosthetic Cofactor

Answer 6

small inorganic and tightly bound to apoenzyme

Question 7

Coenzyme cofactor

Answer 7

Large and loosely bound to apoenzyme

Question 8

oxidoreductase

Answer 8

Catalyze oxidation-reduction reactions

Question 9

Transferase

Answer 9

Catalyzed group transfer reactions

Question 10

Hydrolase

Answer 10

Add an OH from an H2O group

Question 11

Isomerase

Answer 11

Isomerization- turning a left handed molecule into a right handed molecule

Question 12

Ligase

Answer 12

Joining two substrates together

Question 13

Active site(s) of enzymes

Answer 13

The specific region in the enzyme to which the substrate molecule is bound

■ Small three dimensional region of the protein. Substrate interacts with only three to five amino acid residues. Residues can be far apart in sequence

■ Binds substrates through multiple weak interactions (noncovalent bonds)

■ There are contact and catalytic regions in the active site

Question 14

Absolute specificities of enzymes

Answer 14

Absolute: Only one enzyme acts on one substrate

Question 15

Definition of enzyme activity

Answer 15

The specific activiy of an enzyme is a measure of the number of IU/mg protein

One IU of substrate catalyzes the conversion of 1 umol of substrate per minute

Question 16

Relative specificities of enzymes

Answer 16

Relative: One enzyme acts on different substrates which have the same bond type

Question 17

Km, Vmax

Answer 17

Km is the concentration of substrate {s} where reaction speed of substrate is ½ of Vmax (Constant)

○ Vmax - maximum velocity

○ Vo = Vmax[S] / (Km + [S])

Question 18

Reversible inhibition

Answer 18

After combining with enzyme (EI complex is formed) can rapidly dissociate

Enzyme is inactive only when bound to inhibitor

EI complex is held together by weak, noncovalent interactions

Question 19

3 types of Reversible inhibition

Answer 19

Competitive

UNcompetitive

NONcompetitive

Question 20

Competitive

Answer 20

Inhibitor has a structure similar to the substrate thus can bind to the same active
site
■ The enzyme cannot differentiate between the two compounds
■ When inhibitor binds, prevents the substrate from binding
■ ~Inhibitor can be released by increasing substrate concentration~***

Question 21

UNcompetitive

Answer 21

Uncompetitive inhibitors bind to ES not to free E

■ This type of inhibition usually only occurs in multisubstrate reactions

Question 22

NONcompetitive

Answer 22

Binds to an enzyme site different from the active site
■ Inhibitor and substrate can bind enzyme at the same time
■ Cannot be overcome by increasing the substrate concentration
Changes confirmation of the enzyme so the enzyme no longer can carry out its function

Question 23

irreversible inhibition

Answer 23

very slow dissociation of EI complex

Tightly bound through covalent or noncovalent interactions

Question 24

Types of irreversible inhibition

Answer 24

■ Group-specific reagents
■ Substrate analogs
■ Suicide inhibitors

Question 25

Group-specific reagents inhibition

Answer 25

react with specific R groups of amino acids

Question 26

Substrate analogs inhibition

Answer 26

structurally similar to the substrate for the enzyme

● covalently modify active site residues

Question 27

Suicide inhibitors inhibition

Answer 27

Inhibitor binds as a substrate and is initially processed by the normal catalytic mechanism

● It then generates a chemically reactive intermediate that inactivates the enzyme through covalent modification

● Suicide because enzyme participates in its own irreversible inhibition

Question 28

Inhibitor

Answer 28

Binds to an enzyme complex and prevents the formation of ES complex or breakdown to E + P

Question 29

Types of regulation of enzyme activity

Answer 29

allosteric
reversible covalent
isoenzymes
proteolytic

Question 30

Where does the TCA cycle occur?

Answer 30

In the mitochondrial matrix

Question 31

2 major functions of the TCA cycle

Answer 31

Energy production and biosynthesis

Question 32

Aliphatic Amino Acids

Answer 32

Glycine, Alanine, Valine, Leucine, Isoleucine

Question 33

Aromatic Amino Acids

Answer 33

Phenylalanine, Tyrosine, Tryptophan

Question 34

Sulfur Containing Amino Acids

Answer 34

Cysteine, Methionine

Question 35

Aliphatic Hydroxyl Amino Acids

Answer 35

proline

Question 36

Basic Amino Acids

Answer 36

Histidine, Lysine, Arginine

Question 37

Acidic Amino Acids

Answer 37

Aspartic Acid, Glutamic Acid

Question 38

Amide Derivative Amino Acids

Answer 38

Asparagine, Glutamine, Threonine, Serine

Question 39

Cyclic

Answer 39

Proline