Cellular Metabolism

• Metabolism = Sum of all reactions in the body

Anabolism• Synthesizes smaller molecules into larger molecules

• Provides materials for growth and repair

• Consumes energy

Metabolic reactions are of two types

Catabolism• Large molecules decompose into smaller molecules

• Releases energy for cellular use

ATP = energy

Dehydration SynthesisDehydration Synthesis

• Type of anabolic reaction

• Joins triglycerides, polysaccharides, and proteins

• Water is formed from dehydration synthesis

Dehydration synthesis joining

amino acids together

Dehydration Synthesis

• Synthesizes polysaccharides from monosaccharides• Synthesizes polysaccharides from monosaccharides

• Synthesizes proteins from amino acids

• Joins fatty acids to glycerol, forming form fats

• Synthesizes nucleic acids from nucleotides

CatabolismCatabolism

• Reverse of Anabolism• Reverse of Anabolism

• Breaks down molecules

• Releases energy from chemical bonds

• Example: Hydrolysis

HydrolysisHydrolysis

• Type of Catabolic reaction

• Reverse of dehydration synthesis

• Requires water to break bonds• Requires water to break bonds

Hydrolysis

• Decomposes Polysaccharides into monosaccharides & disaccharides

• Decomposes proteins into amino acids• Decomposes proteins into amino acids

• Decomposes Fats into fatty acids & glycerol

• Decomposes Nucleic Acids into nucleotides

Anabolism & Catabolism are reversible reactions

Enzymes control direction & rate of reactions

Enzyme Actions

Enzymes

• Are biological catalyst

• They greatly reduce the activation energy required to start a reaction.

Substrate

• Target molecule of an enzyme

• Each enzyme acts on a specific substrate

a reaction.

Enzyme Characteristics

• Most all are Proteins

• Catalyze reactions - Increases the rate of reactions

• Reusable - Not consumed by reaction

• Specificity – Able to “recognize” a specific substrate

Enzyme Names

• Named for substrate they act upon

• Usually end with ____ ase.

• Examples:

• Lipase: decomposes lipids

• Protease: decomposes proteins

• Nuclease: decomposes nucleic acids

• ATP Synthase: synthesizes ATP molecules

a. Active site

• Region of enzyme that binds to substrate

b. Enzyme-Substrate Complex

• Enzyme temporarily binds to substrate

Enzyme releases product

• Enzyme is reused to join new substrates

Rates of reactions are limited by:

• The concentration of substrate

• The concentration of enzyme• The concentration of enzyme

• The efficiency of enzymes

• Some enzymes handle 2-3 molecules per second

• Other enzymes handle thousands per second

Metabolic Pathways

• Complex series of reactions leading to a product

• Pathways are controlled by several enzymes

Example: Catabolic pathway for

the breakdown of glucose

• The product of each reaction becomes the substrate of next reaction.

• Each step requires its own enzyme

Metabolic Pathways

• “Rate-Limiting Enzyme”

• Least efficient enzyme in group

• Rate-limiting enzyme is usually first in sequence

• Enzyme A = Rate-limiting Enzyme

Negative Feedback in Metabolic Pathway

• Product of reaction often inhibits the rate-limiting enzyme.

• Negative feedback prevents the overproduction of a product.

Cofactor

• Combines with and activates some enzymes

• Exposes the active site of enzyme to substrate

• Cofactors are non-proteins

• Include ions (zinc, iron, copper) and coenzymes

Coenzymes = organic cofactors

• Coenzymes include Vitamins (Vitamin A, B, D)

• Reusable – required in small amounts

Vitamins

• Essential organic molecules that humans cannot synthesize - must come from diet

• Many vitamins are coenzymes

• Vitamins can function repeatedly, so can be used in • Vitamins can function repeatedly, so can be used in small amounts.

• Example: Coenzyme A

Energy for Metabolic ReactionsEnergy for Metabolic Reactions

Energy: is the capacity to change something, or

ability to do work.

Common forms of energy:

Heat

Light

Sound

Chemical energy

Mechanical energy

Electrical energy

Energy cannot be created or destroyed.

Only transferred from one form to another

Think of a combustion engine

Fuel (chemical energy)

+

Oxygen

= Kinetic Energy + CO2 + H2O

Cellular RespirationCellular Respiration

• Cell Respiration: is the transfer of energy from food to make available for cellular use

• Energy is stored in the electrons of food molecules• Energy is stored in the electrons of food molecules

• Oxidation: “controlled burning” of food molecules to release their energy

• Cellular respiration requires enzymes

Cellular RespirationCellular Respiration

Glucose (C6H12O6) + 6O2 → Energy for ATP + H2O + CO2Glucose (C6H12O6) + 6O2 → Energy for ATP + H2O + CO2

ATP

Energy from foods such as glucose is used to make ATP

End of Section 1, Chapter 4