Transcript Ch.23Pt.1_001

Biochemical Energy
Production
Metabolism
– Sum of all the chemical activities taking place in
an organism
– Catabolism
• Larger molecules broken down into smaller ones
– Stages 1-4 (Digestion; Formation of Acetyl CoA; Citric Acid Cycle;
Electron Transport Chain & Oxidative Phosphorylation)
• Releases energy (may be stored temporarily as ATP)
– Anabolism
• Complex molecules synthesized from simpler substances
• Absorbs energy & stores it as chemical bonds
Enzymes play a key role in
metabolic pathways
• Series of small reactions are run with help of enzymes
• Free energy differences between reactants & products is
low
• Concentration differences keep enzyme-run reactions
going in one direction
• How?
• Products are constantly removed so no build up at the end.
Concentration stays low for products
Enzymes catalyze oxidation via series of small steps –
Free E transferred to carrier molecules (e.g. ATP & NADH). Enzymes
(∆G)
reduce activation energy barrier.
Total free energy released is the same in (A) and (B).
Eukaryotic cell with organelles
In eukaryotic cells,
the mighty
mitochondrion
is where the majority
of our energy is
grabbed from our
food molecules in
a process called
aerobic cellular
respiration
Cellular respiration
Anaerobic respiration
•Fermentation
•Does not require oxygen
Aerobic respiration
•Requires molecular oxygen
•Includes redox reactions
All are exergonic (occur spontaneously)
Use a lot of coupled reactions
• A pyramid of production reveals the flow of
energy from producers to primary
consumers and to higher trophic levels
Tertiary
consumers
10 kcal
Secondary
consumers
Primary
consumers
Producers
100 kcal
1,000
kcal
10,000 kcal
1,000,000 kcal of sunlight
Most biochemical pathways
involve coupled reactions
• ATP is the most common “energy carrier”
• This is why examinations of metabolic
products focus on ATP production
• Other molecules can also act as exergonic
energy carriers to help drive an endergonic
biochemical reaction
– Examples: NADH and FADH2 will become
familiar to you as energy carriers
– GTP, UTP, etc.
Reaction Coupling:
released energy drives an endergonic reaction
1) ATP Hydrolysis reaction:
Exergonic (spontaneous)
ATP + H2O  ADP + Pi + H+
∆G = ~ -30 kJ
2) Phosphorylation of Glucose reaction: Endergonic (nonspontaneous)
Glucose + Pi + H+  Glucose-Phosphate + H2O
∆G = ~ +14 kJ
3) Coupled Reaction (showing just the key reactants & products):
Glucose + ATP  Glucose-Phosphate + ADP
net ∆G = ~ -16 kJ
Coupled reaction has a net Exergonic effect,
so will occur “spontaneously”
Structural relationships among
AMP, ADP, and ATP molecules.
ATP links exergonic and
endergonic reactions
High Energy Phosphate Compounds
• High energy compounds
have greater free energies of
hydrolysis than typical
compounds
• They contain very reactive
(strained) bonds - represented
by a squiggle (~)
Redox reactions (oxidation/reduction)
oxidized species can gain O or lose H. Substance
that becomes oxidized gives up energy
reduced species can gain H or lose O. Substance
that becomes reduced receives energy
Essential part of cellular respiration
Many metabolic pathways use
a series of small Redox reactions
to minimize energy loss.
Energy is transferred in the form of electrons (e-)
Summary of RedOx Reactions
• FAD + 2H+ + 2e- <==> FADH2
• NAD+ + 2H+ + 2e- <==> NADH + H+
energy transfer agent:
In reduced state has more
free energy;
less in its oxidized state.
Structural formula for coenzyme A
• The active portion of CoA is the sulfhydryl group
• An acetyl group bonds to CoA through a thioester
bond
Classification of metabolic intermediate
compounds according to function
Four stages of aerobic respiration
Note location of each stage & amount of ATP formed
Product of one stage becomes reactant of next stage
the Four
Stages of
Biochemical
Energy
Production
Stages 1 & 2
• Both stages are specific to the type of
food
• Related to metabolism of:
– Carbohydrates
– Lipids
– Proteins