Metabolism

Cell Energetics Metabolism = total of all the chemical reactions taking place in an organism

Metabolism Anabolism = ‘ build up’ processes; ‘consume’ (store) energy by assembling macromolecules (photosynthesis) Catabolism = ‘break down’ reactions; release energy by breaking down (lyse) molecules (digestion)

Concept 8.1: An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics

Metabolism Energy - the ability to do work Closed Systems - system without energy input Open systems – system with energy input

Types Potential = capacity to do work –Caused by POSITION –Stored chemical energy; (glucose, glycogen) Kinetic – energy of motion Equilibrium = energy runs outEquilibrium = energy runs out

Thermodynamics Thermodynamics - the study of energy transformations 1 st Law of Thermodynamics - energy cannot be created nor destroyed transformed

2 nd Law of Thermodynamics - in a closed system, when energy is transformed, some is ‘lost’ as heat Entropy – decreasing available energy of the universe is increasing (disorder) Energy systems become more disordered/random; Total entropy increases; ‘stuff’ runs down

Free Energy The energy in a system available for work A spontaneous change can cause free energy to ‘flow’ –System becomes more stable –Less work capacity –Free energy decreases (entropy)

Biological Order and Disorder Organisms live at the expense of free energy Organisms are open systems with low entropy –Use free energy to maintain order and organization –Convert complex molecules into simpler ones; digestion –Trade organization for heat (increases randomness and entropy)

Types of Reactions Exergonic reaction - net release of free energy –Less stable, more work –Fire, respiration Endergonic reaction - energy-requiring reaction; energy is absorbed/stored –Photosynthesis

Concept 8.3: ATP Powers Cellular Work by Coupling Exergonic Reactions to Endergonic Reactions Cells do three main kinds of work –Mechanical - movement –Transport – of stuff –Chemical – polymerization, bioluminescence

Coupled Reactions Coupled Reactions - endergonic reactions are coupled with exergonic reactions Energy from an exergonic reaction (respiration) is stored in phosphate bonds Phosphate group is added to a molecule –Phosphorylation –Molecule ‘works’

ATP Adenine + ribose + phosphate group Phosphate bond is easily broken/formed Controlled by enzymes

Uses of Energy Mechanical - beating of cilia/flagella, muscle, cytoplasmic flow, movement of chromosomes (mitosis) Transport - H+ ‘pump’, receptors Chemical – polymerization, bioluminescence Figure 8.1

Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers

Enzymes - biological catalysts –Accelerate reactions without being changed –Proteins (700) Catabolic or anabolic All chemical reactions require activation energy –Activation energy, E A - the initial amount of energy needed to start a chemical reaction Often supplied as heat from the environment (spontaneous) Enzymes

Enzymes Cellular T needs to remain low, but metabolism is too slow at low T Enzymes reduce activation energy Transition state - reactants have absorbed energy

Enzymes Substrate = substance enzyme acts upon Active site = area on the enzyme which the substrate binds to (attaches) –Verryyy specific –Groove, pocket = 3d shape

2 mechanisms describe how enzymes function: –‘Lock and Key’ –Induced Fit - enzyme may change shape to allow better reaction on substrate Enzymes

Active site Induced fit Chemical bonds broken

Enzymatic action is reversible –E + S P + E –Enzyme unaffected by reaction –Dependent upon concentration of reactants vs products Reaction rate of 1000’s per second Speeding up enzyme reactions: –Add more substrate; until saturated with substrate… –Add more enzyme DNA controls cell’s activities by storing the code for protein synthesis (enzymes) Enzymes

Factors That Affect Enzyme Activity Temperature and pH Inorganic salts – disrupt H, ionic bonds, hydrophobic interactions Cofactors Inhibitors

Cofactors Cofactors - nonprotein enzyme helpers –Metals – Fe, Zn, Cu Coenzymes - organic –Vitamins Inhibitors = substances that inhibit the actions of enzymes (2 kinds:) –Competitive inhibitors –Noncompetitive inhibitors

Competitive inhibitors - resemble substrate, block active site Neurotoxin, Disulfiram

Noncompetitive inhibitors - causes enzyme to change shape –Destroys conformation (active site) –DDT, nerve gas (DSF) –May be allosteric regulation Enzymes

Concept 8.5: Regulation of enzyme activity helps control metabolism A cell’s metabolic pathways must be tightly regulated

Allosteric Regulation of Enzymes Allosteric regulation - a protein’s function at one site is affected by binding of a regulatory molecule at another site Receptor site located away from the active site (quaternary structure) Allosteric site has to be activated, (may be inhibited)

Allosteric activator

Allosteric inhibitor

Cooperativity - one substrate molecule can activate all other subunits of an enzyme Only requires a small concentration of substrate to activate enzyme –Hemoglobin Enzymes

Feedback Inhibition Metabolic pathways – series of enzymes creates small steps to a final product Controlling the enzymes (activity or production) controls the pathway and product(s) Feedback Inhibition - end product of the pathway inhibits the pathway Isoleucine – allosteric inhibitor

Feedback inhibition prevents cells from wasting resources –“don’t need gas if you don’t have a car.” Enzymes

Structure and Metabolism Cells are organized Enzymes are grouped into complexes or incorporated into membranes Multi-enzyme complex = enzymes are assembled in correct physical position for a sequence of events to happen –Mitochondria, chloroplasts