Notes on Cellular Respiration/Photosynthesis

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Chapter 6-Intro to Metabolism
METABOLISM= all the chemical reactions in an organism
CATABOLIC PATHWAY (CATABOLISM)• release of energy by the breakdown of complex molecules to simpler compounds

EX: digestive enzymes break down food
• consumes energy to build complicated molecules from simpler ones

EX: linking amino acids to form proteins
ENERGY- capacity to do work
KINETIC ENERGY- energy of moving objects
POTENTIAL ENERGY- energy stored as a result of position or structure CHEMICAL ENERGY- form of potential energy stored in chemical bonds in molecules THERMODYNAMICS- study of energy transformations that occur in matter 1st LAW OF THERMODYNAMICS = Conservation of energy

• energy of universe is constant; energy CAN BE transferred and transformed, but NEVER created or destroyed

• every energy transfer or transformation increases the entropy (disorder or randomness) in universe

Equation that describes energy of system;

G= H-T S
- change in free energy is represented by  G
G = FREE ENERGY of a system
(energy that is able to perform work when the temperature is uniform) H = Total energy in system
T = Absolute temperature in °Kelvin

You don’t need to be able to
do G problems; just know
that there is an equation;

EXERGONIC REACTION- releases energy and occurs spontaneously Energy of products is lower than energy of reactants (negative G) ENDERGONIC REACTION- requires energy; absorbs free energy from system; not spontaneous Energy of products is higher than energy of reactants (positive G) SPONTANEOUS REACTION

- can occur without outside help
- can be harnessed to do work (objects moving down their power gradient) Cells manage their energy resources and do work by ENERGY COUPLING (use energy from exergonic reactions to drive endergonic ones) Key role of ATP = ENERGY COUPLING

= primary source of energy in all living things
ADP (adenosine diphosphate) + Pi → ATP;
-adding phosphate group stores energy;
-removing it releases energy

ACTIVATION ENERGY = amount of energy required to get chemical reaction started CATALYST- substance that changes the rate of a chemical reaction without being altered ENZYMES = biological catalysts; most enzymes are PROTEINS (Ch 17 & 26: RNA enzymes = RIBOZYMES) ENZYMES work by LOWERING ACTIVATION ENERGY; Don’t change the FREE ENERGY of reaction SUBSTRATE= Reactant enzyme acts on

ACTIVE SITE = region on enzyme that binds to substrate
Substrate held in active site by WEAK interactions (ie. hydrogen and ionic bonds) SUBSTRATE(S) + enzyme → Enzyme-substrate complex → enzyme + PRODUCT(S) ENZYMES are UNCHANGED & REUSABLE
LOCK-AND-KEY MODEL: enzyme fits substrate like “lock and key” -only specific substrate will fit
INDUCED FIT MODEL: once substrate binds to active site, enzyme changes shape slightly to bind the substrate more firmly placing a strain on the existing bonds in substrate lowering act energy Enzymes have OPTIMAL TEMPERATURE for activity

Higher temperatures = more collisions among the molecules so increase rate of a reaction BUT. . .
above a certain temperature, activity begins to decline because the enzyme begins to DENATURE
So rate of chemical reaction increases with temperature
up to optimum, then decreases.

Enzymes have own OPTIMAL pH
Different enzymes have different pH curves
Extremes in pH and temp can DENATURE enzymes
-causing them to unwind/lose their 3-D TERTIARY structure
-breaks hydrogen, ionic bonds; NOT covalent peptide bonds
Many enzymes require helpers:
(zinc, iron, and copper)

Ex: vitamins
-part of NAD+, NADP, FADH2,
Coenzyme A molecules

- reversible
- compete with substrate for active site

- bind another spot on enzyme
- cause shape change making...
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