Physiology 1, Fall 2008, LPC

Chapter 4 - Energy and Cellular Metabolism

I-Introduction

Everything but plants use plant products, +/- O2, to get energy. If use O2, -> CO2, = aerobic respiration.
Plants use CO2 + H2O + sun’s energy -> food

Energy = capacity to do work
            Use energy for:

Chemical work = making & breaking chemical bonds
Transport work = moves chemicals through membrane
Mechanical work = movement

Kinetic energy = energy of motion
Potential energy = stored energy

Kinetic energy <-> Potential energy

Potential energy in biological systems in concentration gradients & chemical bonds

Thermodynamics
            1st Law – the total amount of energy in the universe is constant
            2nd Law – disorder in universe increases = entropy increases

II-Chemical Reactions

Energy transfer between reactants (substrate) and products.
Reaction rate = speed reactants disappear or products appear
Free energy = potential energy in chemical.  More complex molecules usually have more stored energy.
Activation energy = energy to start reaction

Endergonic & Exergonic Reactions

Exergonic reactions power endergonic reactions, often via ATP

III-Enzymes

Name ends in “–ase”
Proteins that speed reactions = biological catalysts
Decrease activation energy.

Bind substrates & bring them together so can react easily

Isozymes – different forms of same enzyme, active in different tissues or conditions. Sometimes used to check for disease.

Control

Activation by proteolytic activation
Cofactors – bind to enzyme -> active
Coenzymes = organic cofactors
Inhibitors – bind to enzyme, change its shape -> inactive
Modulation – physical influence, like heat, pH

Rate determined by +/- enzyme or substrate concentration

If reaction reversible, obeys Law of Mass Action

Types of Reactions - four types.  Note enzyme names describing chemical group transfers.

IV – Metabolism = all reactions that take place in an organism.

Catabolism –breaks down molecules -> energy
Anabolism- build molecules, uses energy

Energy measured in kilocalories

Cellular energy stored in ATP, NADH, NADPH, FADH2 (low energy forms = ADP, NAD, NADP, FAD)

Regulation

1. control enzyme concentration           
2. modulators
3. use two different enzymes to catalyze reversible reaction  
4. isolate enzymes within intracellular organelles
5. control ATP:ADT, ie, readily available energy

V – ATP Production
   1.  Glycolysis = glycogen or glucose (C6) -> pyruvate (C3) + ATP

pyruvate -> Acetyl CoA (C2) + CO2

2. Citric Acid Cycle = Acetyl CoA -> ATP, NADH, FADH2 + CO2
3. Electron transport system = NADH + FADH2 + ADP + O2 -> ATP (lots)

Can be made from any food source, just enter reaction chain at different points

VI – Synthetic Pathways

Glucose stored as glycogen via dehydration
Glycerol and amino acids can -> glucose

Protein Synthesis
(Proteins – enzymes, transporters & pores, receptors/signal molecules, structure)

DNA -> RNA -> proteins
Codon = 3 bases code for an amino acid

Steps between DNA & functional protein

1. Gene Activation
2. Transcription = DNA -> mRNA   
3. mRNA processing -> introns & exons   (note different RNA product from same mRNA)
4. Translation – mRNA, rRNA, tRNA, amino acids, energy -> protein chain
5. Post-translational modification – folding, cross links, cleavage, add functional group(s), group together possible

Proteins have signal sequence or a target sequence to direct them to destination