Ch 4

Question 1

Enzymes Definition

Answer 1

A class of proteins (exception – ribozymes are made of RNA) that serve as biological catalysts

Question 2

What do enzymes do?

Answer 2

• Increase the rate of a reaction
• Are not changed by the reaction (so can be used again)
• Do not change the nature of the reaction – the reaction could have occurred without the enzyme, just much slower
• Lowers the activation energy of the reaction

Question 3

What is activation energy?

Answer 3

the energy required for reactants to engage in a reaction (energy barrier we have to overcome)

• Most molecules lack the activation energy for a reaction.

• -> Adding heat increases the likelihood of are action occurring. This increases the rate of reactions, however, heat has some negative effects on cells.
• -> Catalysts help the reaction occur at lower temperatures.

Question 4

Enzyme Activity

Answer 4

• structure dictates function
• characteristic 3D shape w/active sites
• reactants: substrates
• Measured by the rate at which substrate is converted to product

Question 5

What are substrates?

Answer 5

fit into the active site like a key to a lock (“lock-and-key model”)

Question 6

Induced-Fit Model

Answer 6

Sometimes the initial fit is not exact but will change as the substrate moves into the active site

Question 7

Enzyme Nomenclature

Answer 7

• suffix: -ase

- first part of the name apply to the function

Question 8

Phosphatases

Answer 8

remove phosphate groups

Question 9

Synthetases/synthases

Answer 9

catalyze dehydration synthesis

Question 10

Hydrolases

Answer 10

promote hydrolysis

Question 11

Dehydrogenases

Answer 11

remove hydrogen atoms

Question 12

Kinases

Answer 12

add phosphate groups

Question 13

Isomerases

Answer 13

rearrange the atoms

Question 14

Isoenzymes

Answer 14

-same name for enzymes w/same function in diff locations

molecules may be slightly different (in areas outside the active site) = isoenzyme

Question 15

Enzyme activity influenced by….

Answer 15

• Temperature
• pH
• Cofactors and coenzymes
• Enzyme activation
• Substrate concentration
• Possible stimulatory or inhibitory effects of products on enzyme function

Question 16

Enzymes and pH

Answer 16

• exhibit peak activity within a narrow pH range
• changes will result in enzyme conformational changes (like temp)
• Optimum pH reflects the pH of the fluid the enzyme is found in (ex. stomach vs. saliva vs. small intestine)

Question 17

Coenzymes

Answer 17

organic molecules derived from water-soluble vitamins

• transport H/small molecules between enzymes
• larger
• required

Question 18

Cofactors

Answer 18

help form the active site through a conformational change of the enzyme or help in enzyme-substrate binding

• Cofactors are metal ions such as, Ca2+, Mg2+, Mn2+,Cu2+, Zn2+
• smaller, help form active site

Question 19

Enzyme Activation

Answer 19

zymogen: inactive form of enzyme that is activated when needed (stored so don’t have to make again –> pepsinogen to pepsin)
-often requires additional enzymes to phosphorylate or
dephosphorylate the molecule
-inhibition can be controlled through turnover, by which enzymes are degraded

Question 20

Substrate Concentration

Answer 20

• as substrate concentration increases, so will rate of enzyme saturation
• Adding more substrate will NOT increase the rate of the reaction

Question 21

saturated

Answer 21

every enzyme in the solution is being used

Question 22

Reversible Reactions

Answer 22

-enzyme can drive reaction in two different directions depending of concentration of substrate/product

Question 23

the law of mass action

Answer 23

one side gets higher, the other reaction reverses

Question 24

Metabolic Pathways

Answer 24

-reactions linked together in chains
-begin with an initial substrate and end with a final product,
–> w/many steps along the way
BRANCHED: where several products can be produced

Question 25

End Product Inhibition

Answer 25

• Branch points are often inhibited by a form of negative feedback in which one of the final products inhibits the branch point enzyme
• allosteric inhibition
• keeps final product from accumulating

Question 26

allosteric inhibition

Answer 26

the product binds to the enzyme at a location away from the active site and changes the 3D conformation of the enzyme

Question 27

Endergonic Reactions

Answer 27

Chemical reactions that require an INPUT of energy

• products contain more free energy than the reactants
  ex. glucose -> glycogen (synthesis reaction)
• STORED energy

Question 28

Exergonic Reactions

Answer 28

Chemical reactions that produce energy

• products will have less free energy than the reactants
• -> ex. breaking glucose down into carbon dioxide and water produces energy
• -> Energy is used to make ATP for use in other endergonic reactions in the body

Question 29

Coupled Reactions

Answer 29

Energy from the environment (food) is broken down in exergonic reactions to drive the endergonic reactions in our bodies

• energy must be stored in a usable form = ATP
• -> production of ATP is actually an endergonic reaction that is coupled to an exergonic reaction to drive it
• -> ATP molecule stores energy in its bonds to be used elsewhere

Question 30

how is ATP made?

Answer 30

adenosine diphosphate (ADP) + inorganic phosphate = adenosine triphosphate (ATP)