Biology 6

Chapter 6: Energy and Metabolism

The flow of Energy:

The flow of energy:

Thermodynamic

• Branch of chemistry concerned with energy change

• Cells govern by physic and chem

Energy:

Capacity to do work

2 states: kinetic (energy of motion) and potential (stored energy)

•1 calorie = heat required to raise 1 gram of water 1° C.

•Calorie on food labels (with a capital C) is actually a kilocalorie (1000 calories).

Energy flow 

energy flows the biological world of the sun

Photosynthetic organisms capture energy

(Opposite of photosynthesis is cellular respiration)

Stored as potential energy in chemical bonds

Redox Reaction

Oxidation = loss of electron

Reduction = gain of an electron

First Law of thermodynamic

Energy can not be created nor destroyed

Can only change form to another

Durning conversion some energy is lost as heat

Second law 

Entropy (disorder) continuously increase

Energy transformations proceed spontaneously to convert matter from a more ordered/less stable form to a less ordered/more stable form (ex like a messy room)

Free energy

G = Energy available to do work

G = H−TS

• H = enthalpy, energy in a molecule’s chemical bonds.

• T = absolute temperature.

• S = entropy, unavailable energy

A+b.             -)            c

G reactant          G product

∆G = ∆H − TS

∆G = change in free energy

Positive ∆G

•Products have more free energy than reactants.

•H is higher or S is lower.

•Not spontaneous, requires input of energy.

•Endergonic. (Means require Input of energy won’t happen spontaneously)

Negative ∆G

•Products have less free energy than reactants.

•H is lower or S is higher or both.

•Spontaneous (may not be instantaneous). (ex: ice melting)

•Exergonic. (opposite of endergonic) (release of energy)

Activation energy

The extra energy required to destabilize to existing bond and initiate chemical reactions

The rate of exergonic reaction depends on the activation energy required

•Larger activation energy proceeds more slowly.

The rate can be increased two ways:

1. Increasing energy of reacting molecules (heating) 

      2.  Lowering activation energy (enzymes and lower)

Speed is the height with enzyme ( lower the reacting barrier)

Catalysts

Substances that influence chemical bonds in a way that lowers the activation energy

Cannot violate laws of thermodynamics

•Cannot make an endergonic reaction spontaneous.

Do not alter the proportion of reactant turned into a product

ATP

Primary energy “currency” used by cells

Composed of:

•Ribose – five carbon sugar.

•Adenine.

•Chain of three phosphates.

    •Key to energy storage.

    •Bonds are unstable, release energy when broken.

    •ADP − adenosine diphosphate = two phosphates.

     AMP − adenosine monophosphate = one phosphate − lowest energy form

 Cycle ATP
ATP hydrolysis drives endergonic reactions

•Coupled reaction results in the net –G (exergonic and spontaneous).

ATP not suitable for long-term energy storage

•Phosphate bonds are too unstable.

•Fats and carbohydrates better.

•Cells store only a few seconds worth of ATP.

* burns glucose to make ATP

Enzyme: Biological catalysts

99% of enzymes are proteins very few enzymes are RNA

A+B ->C need only small amount to make enzyme ( reuse the rest)

Substrate means reactant

Shape of enzyme stabilizes a temporary association between substrates

Induced fit theory - Enzymes  changes shape to perfectly bind to the  substrate

Forms of enzymes

Multienzyme complexes – subunits work together to form molecular machine

•Product can be delivered easily to next enzyme.

•Unwanted side reactions prevented.

•All reactions can be controlled as a unit.

Biochemical pathway a become e. (listen 1 hour)

Nonprotein enzyme

Ribozymes

1981 discovery that certain reactions catalyzed in cells by RNA molecule itself

Two kinds:

1. Intramolecular catalysis – catalyze reaction on RNA molecule itself

2. Intermolecular catalysis – RNA acts on another molecule

Enzyme function

The rate of enzyme-catalyzed reaction depends on concentrations of substrate and enzyme

Any chemical or physical condition that affects the enzyme’s three-dimensional shape can change rate

•Optimum temperature.

•Optimum pH.

H202 = hydrogen proxide

-> H20 +O2 

Inhibitors

substance that binds to enzyme and decrease its activity

competitive inhibitor - competes with substrate to active site (concentration of inhibitor matter)

noncompetitive inhimbiter - bind to enzyme at site other than active site, cause shape change that enzyme unable to bind substrate  (not matching so cant react) (concentration doesn't matter, a little is enough) 

Allosteric enzyme

Allosteric enzymes – enzymes exist in active and inactive forms

Most noncompetitive inhibitors bind to allosteric site – chemical on/off switch

Allosteric inhibitor – binds to allosteric site and reduces enzyme activity

Allosteric activator – binds to allosteric site and increases enzyme activity

enzyme needs to be controlled so we us activator an inhibiter

listen to 24

Metabolism

two parts of metabolism

anabolic reaction - expand energy to build up molecules

catabolic reaction - harvest energy by breaking down molecule

Biochemical pathway

reaction occur in sequence

steps may take place in specific organells

ex: glucose is make in citocal and mitochondria

Feedback inhibition

End-product of pathway increases in concentration as it is synthesized

More product increases probability that it binds to an allosteric site on an enzyme in the pathway and causes it to change so it cannot bind normal substrates

Shuts down pathway so raw materials and energy are not wasted