1. Cellular Metabolism Chapter 4
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2. Introduction
A living cell is the site of enzyme-catalyzed metabolic reactions that maintain life.
Metabolic processes – all chemical reactions that occur in the body
Many reactions form cycles or pathways

3. Metabolic Processes There are two (2) types of metabolic pathways:
Anabolism
Larger molecules are made from smaller ones
Requires energy
Catabolism
Larger molecules are broken down into smaller ones
Releases energy
The reactions of metabolism are often reversible

4. Anabolism
Anabolism provides the materials needed for cellular growth and repair
Example: Dehydration synthesis
Type of anabolic process
Used to make polysaccharides, triglycerides, and proteins
Produces water by joining two smaller molecules
CH2OH H OH O
Monosaccharide + HO
Disaccharide
H2O
Water

5. Anabolism + + H O H O H C OH HO C (CH2)14 CH3 H C O C (CH2)14 CH3 O O
Glycerol +
3 fatty acid molecules
Fat molecule (triglyceride) +
3 water
molecules
Peptide
bond H H H H H O O R R H O H O H H H O O N C C N C C N N C C C C N N C C C C OH OH
H2O H O H H O H H H R R R R H H H H
Amino acid +
Amino acid
Dipeptide molecule +
Water

6. Catabolism Catabolism breaks down larger molecules into smaller ones
Example: Hydrolysis
A catabolic process
Used to decompose carbohydrates, lipids, and proteins
Water is used to split the substances
Reverse of dehydration synthesis HO
CH2OH H OH O
Monosaccharide +
Disaccharide
H2O
Water

7. Catabolism + + H O H O H C OH HO C (CH2)14 CH3 H C O C (CH2)14 CH3 O O
Glycerol +
3 fatty acid molecules
Fat molecule (triglyceride) +
3 water
molecules
Peptide
bond H H H H H O O R R H O H O H H H O O N C C N C C N N C C C C N N C C C C OH OH
H2O H O H H O H H H R R R R H H H H
Amino acid +
Amino acid
Dipeptide molecule +
Water

8. Control of Metabolic Reactions
Enzymes
Metabolic reactions include hundreds of chemical changes that must occur in particular sequences.
Control rates of metabolic reactions
Lower activation energy needed to start reactions
Most are globular proteins with specific shapes
Not consumed in chemical reactions
Substrate specific
Shape of active site determines substrate
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Substrate molecules
Product molecule
Active site
Enzyme
molecule
Enzyme-substrate
complex
Unaltered
enzyme
molecule
(a)
(b)
(c)

9. Animation: How Enzymes Work
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10. 4.3: Control of Metabolic Reactions
Enzyme Action
4.3: Control of Metabolic Reactions
Enzymes (Catalysts)
Control rates of metabolic reactions
Lower activation energy needed to start reactions
Most are globular (complex) proteins with specific shapes
Not consumed in chemical reactions, recycled by the cell
Substrate specific
Shape of active site determines substrate
Speed depends on the number of enzyme/substrate molecules available.
Product molecule
Active site
(a)
(b)
(c)
Substrate molecules
Unaltered
enzyme
molecule
Enzyme-substrate
complex
Enzyme

11. Enzyme Action Metabolic pathways Enzyme names commonly:
Series of enzyme-controlled reactions leading to formation of a product
Each new substrate is the product of the previous reaction
Substrate 1
Enzyme A
Substrate 2
Enzyme B
Substrate 3
Enzyme C
Substrate 4
Enzyme D
Product
Enzyme names commonly:
Reflect the substrate
Have the suffix – ase
Examples: sucrase, lactase, protease, lipase

12. Regulation of Metabolic Pathways
Limited number of regulatory enzymes
Negative feedback
Inhibition
Rate-limiting
Enzyme A
Substrate 1
Substrate 2
Enzyme B
Substrate 3
Enzyme C
Substrate 4
Enzyme D
Product

13. Cofactors and Coenzymes
Make some enzymes active
Non-protein component
Ions or coenzymes
Coenzymes
Organic molecules that act as cofactors
Vitamins
Example: coenzyme A

14. Factors That Alter Enzymes
Factors that alter (denature) enzymes:
Heat
Radiation
Electricity
Chemicals
Changes in pH

15. Energy for Metabolic Reactions
Energy is the capacity to change something; it is the ability to do work
Common forms of energy:
Heat
Light
Sound
Electrical energy
Mechanical energy
Chemical energy
Energy can be changed from one form to another. Through cellular respiration, energy is transferred from molecules to make it available for cellular use.

16. Release of Chemical Energy
Chemical bonds are broken to release energy
We burn glucose in a process called oxidation
LEO says GER

17. ATP Molecules
Adenosine triphosphate (ATP) carries energy in a form that the cell can use
Each ATP molecule has three parts:
An adenine molecule
A ribose molecule
Three phosphate molecules in a chain P P P
Energy transferred
and utilized by metabolic reactions when phosphate bond
is broken
Energy transferred from cellular respiration used
to reattach phosphate P P P P