Enzymes

1
Enzymes
2
Review

• Energy coupling
• Is a key way cells manage their energy resources
  to do this work

3
Energy is released from ATP When the terminal
phosphate bond is broken
4
ATP hydrolysisCan be coupled to other reactions
5
How ATP Performs Work

• ATP drives endergonic reactions
• By phosphorylation, transferring a phosphate to
  other molecules
• The molecule is said to be phosphorylated

6
(No Transcript)
7
Why enzymes?

• Spontaneous reactions may still occur very
  slowly.
• Example sucrose ? glucose and fructose
• ?G -7, but could take years!
• With an enzyme, seconds.

8
Enzymes

• Enzymes speed up metabolic reactions by lowering
  activation energy barriers
• A catalyst
• Is a chemical agent that speeds up a reaction
  without being consumed by the reaction
• An enzyme
• Is a catalytic protein

9
Activation Energy

• When a reaction proceeds there is usually an
  unstable intermediate
• Because of this energy is required to start a
  reaction activation energy
• The activation energy, EA
• Is the initial amount of energy needed to start a
  chemical reaction
• Is often supplied in the form of heat from the
  surroundings in a system

10
(No Transcript)
11
Substrate Specificity of Enzymes

• The substrate
• Is the reactant an enzyme acts on
• The enzyme
• Binds to its substrate, forming an
  enzyme-substrate complex
• Enzyme Enzyme- Enzyme
• Substrate(s) Substrate Product(s)
• Complex
• When the reaction is complete the enzyme can be
  used again and products are released.

12
How enzymes work

• Animation

13

• The active site
• Is the region on the enzyme where the substrate
  binds

14

• Induced fit of a substrate
• Brings chemical groups of the active site into
  positions that enhance their ability to catalyze
  the chemical reaction

15
The catalytic cycle of an enzyme
16
How do enzymes lower EA?

• The active site can lower an EA barrier by
• Orienting substrates correctly
• Straining substrate bonds
• Providing a favorable microenvironment
• Covalently bonding to the substrate

17

• The activity of an enzyme is affected by general
  environmental factors
• Each enzyme
• Has an optimal temperature in which it can
  function

18

• Each enzyme
• Has an optimal pH in which it can function

19
Enzyme helpers

• Cofactors
• Are nonprotein enzyme helpers
• Zinc, iron, copper
• Coenzymes
• Are organic cofactors
• Most vitamins are necessary because they are
  coenzymes

20
Enzyme Inhibitors

• Competitive inhibitors
• Bind to the active site
• of an enzyme,
• competing with the
• substrate

21
Noncompetitive inhibitors

• Bind to another part of an enzyme, changing the
  function

22
Allosteric Regulation of Enzymes

• any case in which a proteins function at one
  site is affected by binding of a regulatory
  molecule at another site
• Many enzymes are allosterically regulated
• Regulation of enzyme activity helps control
  metabolism

23

• The enzyme changes shape when regulatory
  molecules bind to specific sites, affecting
  function

24

• Cooperativity
• Is a form of allosteric regulation that can
  amplify enzyme activity

25
Feedback Inhibition

• In feedback inhibition
• The end product of a metabolic pathway shuts down
  the pathway

26
Feedback inhibition
27
Specific Localization of Enzymes

• Within the cell, enzymes may be
• Grouped into complexes
• Incorporated into membranes
• Contained inside organelles