Chapter 4, Metabolism

Section 1, Chapter 4

Cellular Metabolism

metabolism is the sum of all reactions in the body

AnabolismIn anabolic reactions energy is used to synthesize large molecules from smaller molecules.

Anabolic reactions create materials for growth and repair.

In catabolic reactions large molecules are decomposed into smaller molecules

Catabolic reactions release energy for cellular use

Catabolism

metabolic reactions are of two types

Amino acids are joined by dehydration synthesis

Dehydration SynthesisDehydration synthesis is a type of anabolic reaction.

triglycerides, polysaccharides, and proteins are synthesized through dehydration synthesis

A molecule of water is released from dehydration synthesis.

Dehydration Synthesis

Synthesizes

polysaccharides from monosaccharides

proteins from amino acids

nucleic acids from nucleotides

fats by joining fatty acids to glycerol

dehydration synthesis

Hydrolysis

hydrolysis is the reverse of dehydration synthesis

water is used to break apart molecules

hydrolysis releases energy from chemical bonds

hydrolysis

HydrolysisDecomposes Polysaccharides into monosaccharides & disaccharides

Decomposes proteins into amino acids

Decomposes Fats into fatty acids & glycerol

Decomposes Nucleic Acids into nucleotides

The critical amount of energy required for a reaction to occur is called the activation energy.

Enzymes are biological catalystsThey greatly reduce the activation energy required to start a reaction.

A substrate is the target molecule of an enzyme

Characteristics of enzymes

Most enzymes are Proteins

Enzymes lower the activation energy of a reaction

Enzymes catalyze reactions – they increase the rate of reactions, but are not consumed by the reaction

Enzymes are specific to one substrate.

Examples of enzymes:Lipase: decomposes lipidsProtease: decomposes proteinsNuclease: decomposes nucleic acidsATP Synthase: synthesizes ATP molecules

Enzyme NamesEnzymes are named for substrate they act upon and their name usually ends with _____ase.

The Active site of an enzyme is the region that binds to the substrate

The enzyme temporarily binds to the substrate forming an Enzyme-Substrate Complex

The Enzyme releases the product and enzyme is reused for a new reaction.

Enzymes

The rate of a reaction is limited by:

1. The concentration of substrate

2. The concentration of enzyme

3. The efficiency of enzymesSome enzymes handle 2-3 molecules per secondOther enzymes handle thousands per second

Rate of enzyme-catalyzed reactions

Example: The catabolic pathway for the breakdown of glucose is highly complex.

Metabolic PathwaysA metabolic pathway is a complex series of reactions leading to a product

Metabolic Pathways are controlled by several enzymes

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

Each step requires its own enzyme

The least efficient enzyme is the “Rate-Limiting Enzyme” Rate-limiting enzyme is usually first in sequence

• Enzyme A = Rate-limiting Enzyme

Metabolic Pathways

Negative feedback prevents too much product from being produced.

The product of the metabolic pathway often inhibits the rate-limiting enzyme.

Negative Feedback in Metabolic Pathway

Cofactorsubstance that increases the efficiency of an enzyme

Cofactors include ions (zinc, iron, copper) and coenzymes

Coenzymes are organic cofactors Coenzymes include Vitamins (Vitamin A, B, D)

Reusable – required in small amounts

Vitamins are essential organic molecules that humans cannot synthesize, so they must come from diet

Many vitamins are coenzymes

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

Example: Coenzyme A

Energy: is the capacity to change something, or ability to do work.

Common forms of energy: HeatLightSoundChemical energyMechanical energyElectrical energy

Energy for Metabolic Reactions

Energy cannot be created or destroyed, but it may be transferred from one form to another.

Fuel (chemical energy) +

Oxygen = Kinetic Energy + CO2 + H2O

example of energy transfer: combustion engine

The combustion of fuel converts chemical energy in the gasoline into kinetic energy, heat, sound. Water and CO2 are produced as waste.

Cellular Respiration

Cell Respiration is the transfer of energy from food molecules into a form the cells can use

Energy from foods such as glucose is used to make ATP for the cell.

End of Section 1, Chapter 4

Reaction of Cell Respiration

Initial fuel or energy source

ATP = Energy currency for cells