Week 5

Question 1

Chemical reactions in a cell are accelerated by…?

Answer 1

chemical catalysts

Question 2

What is the rate of a chemical reaction defined as?

Answer 2

the amount of product formed (or reactant consumed) per unit of time

Question 3

What are catalysts?

Answer 3

substances that increase the rate of chemical reactions without being consumed themselves

Question 4

Most, but not all, catalysts are…?

Answer 4

proteins called enzymes

Question 5

exergonic reactions _____ free energy

Answer 5

release

Question 6

endogonic reactions ____ free energy

Answer 6

require

Question 7

All chemical reactions require….?

Answer 7

an input of energy to proceed

Question 8

Define transition state

Answer 8

the brief time in a chemical reaction in which chemical bonds in the reactants are broken and new bonds in the product are formed.

Question 9

the transition state is highly ____ and therefore has large amounts of…?

Answer 9

unstable

free energy

Question 10

negative ∆G means the reaction is _____

Answer 10

spontaneous

Question 11

Define activation energy (EA)

Answer 11

The energy input necessary to reach the transition state.

Question 12

The lower the energy barrier, the ____ the reaction

Answer 12

faster

Question 13

Enzymes work by ____ the transition state

Answer 13

stabilizing

Question 14

Does catalyzing a reaction change the value of ∆G?

Answer 14

No

Question 15

what is the sign on ∆G for non spontaneous reactions?

Answer 15

positive

Question 16

The higher the energy barrier, the ____ the reaction

Answer 16

slower

Question 17

Define substrate

Answer 17

A molecule acted upon by an enzyme.

Question 18

How does an enzyme speed up the rate of a reaction?

Answer 18

the enzymes forms a complex with the substrate and while the substrate is still part of the complex it is converted into the products. The complex then dissociates to leave you with your final product

Question 19

Define active site

Answer 19

The portion of the enzyme that binds substrate and converts it to product.

Question 20

Is the size of an active site big or small compared to the enzyme?

Answer 20

very small

Question 21

Why are enzymes specific?

Answer 21

• because they recognize either a unique substrate or class of substrates that share common chemical structures, and
• they catalyze only one reaction or a very limited number of reactions

Question 22

Define activator

Answer 22

A synthesized compound that increases the activity of an enzyme.

Question 23

Define inhibitor

Answer 23

A synthesized compound that decreases the activity of an enzyme.

Question 24

______ decrease the activity of enzymes

Answer 24

inhibitors

Question 25

____ increase the activity of enzymes

Answer 25

activators

Question 26

What are the two classes of inhibitors?

Answer 26

irreversible and reversible

Question 27

What is the difference between reversible and irreversible inhibitors?

Answer 27

irreversible inhibitors form covalent bonds with enzymes

reversible inhibitors form weak bonds with enzymes

Question 28

What are the two ways inhibitors work?

Answer 28

• an inhibitor with a structure similar to a substrate binds to the active site of an enzyme and therefore competes with substrates for active sites
• an inhibitor which is unlike a substrate binds to a site other than the active site and inhibits the activity of the enzyme

Question 29

define allosteric enzymes

Answer 29

An enzyme whose activity is affected by binding a molecule at a site other than the active site. Typically, allosteric enzymes change their shape on binding an activator or inhibitor.

Question 30

Define negative feedabck

Answer 30

Describes the effect in which the final product of a biochemical pathway inhibits the first step; the process in which a stimulus acts on a sensor that communicates with an effector, producing a response that opposes the initial stimulus. Negative feedback is used to maintain steady conditions, or homeostasis.