2. Bioenergetics
Bioenergetics is the quantitative study of the energy transductions
(conversions of one form of energy to another) that occur in living cells &
of the nature & function of the chemical processes underlying these
transductions.
Bioenergetics includes:
1) the radiant energy of sunlight used in photosynthesis
2) electrical energy of nerve impulses
3) mechanical energy of muscle contractions
4) heat energy liberated by chemical reactions within cells, and
5) potential energy stored in “energy-rich” chemical bonds.
The major source of biological energy is the chemical reactions occurring
inside cells.
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3. Chemical reactions in a cell are governed by thermodynamics
• Thermodynamically unfavorable chemical reactions can be driven forward by
coupling with thermodynamically favorable reactions
• The cell uses multistep chemical reactions to extract energy and atomic &
molecular components (catabolism) and to construct necessary molecular
building blocks (anabolism)
• Metabolic pathways are carefully regulated (using various methods) to fulfill
cellular needs while minimizing 'wasteful’ or energetically costly processes
• Cellular energy is manifested almost exclusively as phosphorylated organic
molecules (e.g., ATP) and reduced coenzymes (e.g., NADH; FADH2)
Fundamental features & themes in metabolism
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4. Metabolism
Catabolism Anabolism
• larger molecules
are broken down
• releases energy
• larger molecules
are made
• requires energy
The sum of all chemical reactions involved in maintaining the dynamic
state of a cell or organism.
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5. Metabolism
What are the fundamental questions in biochemical
metabolism?
• How do cells extract energy and reducing power from their
environment?
• How do cells synthesize the building blocks of their
macromolecules?
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6. Anabolism provides the substances needed for cellular
growth and repair
Dehydration synthesis
• type of anabolic process
• used to make polysaccharides, triglycerides, and proteins
• produces water
Anabolism
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8. Catabolism breaks down larger molecules into smaller ones
Hydrolysis
• a catabolic process
• used to decompose carbohydrates, lipids, and proteins
• water is used
• reverse of dehydration synthesis
Catabolism
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10. Metabolism is the sum of catabolism and anabolism
oxidation and the
release of energy
Triglycerides Proteins
Fatty acids
and glycerol
Amino
Acids
Small
molecules
Anabolism
of proteins
beakdown
of larger
molecules
to smaller
ones
Some nutrients and
products of catabolism
Products of anabolism,
including proteins and
nucleic acids
Catabolism Excretion
energy and
reducing
agents
Monosac-
charides
Polysac-
charides
Excretion Anabolism
Catabolism Anabolism
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11. CO2 , O2 , N2 cycling in the biosphere
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14. Cells and the Mitochondria
Animal cells have many components, each with specific functions.
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15. What is the first stage of catabolic process?
Digestion
• Food is broken down by hydrolysis of esters,
glycosides, and peptide in the digestive system
• Yields fatty acids, simple sugars, and amino acids
• Smaller molecules are degraded in cells to acetyl
groups attached to the large carrier molecule
coenzyme A
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16. Digestion of Carbohydrates
• Carbohydrates are the main source of energy in a diet; the
main dietary carbohydrates are:
▫ The polysaccharide starch.
▫ The disaccharides lactose and sucrose.
▫ The monosaccharides glucose and fructose.
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17. Digestion of Carbohydrates
Digestion of carbohydrates starts in the mouth:
• α-Amylase catalyzes the hydrolysis of α -1,4-glycosidic bonds
of starch and glycogen.
• β-Amylase catalyzes the hydrolysis of β-1,4-glycosidic bonds.
• Debranching enzymes catalyze the hydrolysis of β -1,6-
glycosidic bonds.
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19. Digestion of Fats
Fats are the most concentrated source of energy.
▫ Lipases, the enzymes that catalyze the hydrolysis of
lipids, are located in the small intestine.
▫ Bile salts, synthesized in the liver and stored in the
gallbladder, emulsify water-insoluble dietary fats so that
they can be acted upon by lipases.
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20. • Fats are hydrolyzed to fatty acids, and complex lipids to fatty
acids, alcohols (glycerol, ethanolamine, sphingosine), and
carbohydrates.
• The hydrolysis products are absorbed through the intestinal
walls.
Digestion of Fats
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21. Digestion of Proteins
Although dietary proteins can be used for energy, their
main use is to furnish amino acids from which the body
can synthesize its own proteins.
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22. Digestion of Proteins
• Digestion of proteins begins with cooking, which denatures
proteins and makes it easier for the digestive enzymes and
HCl of the stomach to hydrolyze them.
• Most protein digestion occurs in the small intestine.
• The 10 essential amino acids must be obtained from the diet.
• Complete protein: A dietary protein that contains all
essential amino acids.
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24. Common catabolic pathway
The two parts to the common catabolic pathway:
• The citric acid cycle, also called the tricarboxylic acid (TCA)
or Krebs cycle.
• Electron transport chain and phosphorylation, together
called oxidative phosphorylation.
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34. Four principal compounds participating in the
common catabolic pathway are:
• AMP, ADP, and ATP
• NAD+/NADH
• FAD/FADH2
• coenzyme A; abbreviated CoA or CoA-SH
Compounds in catabolic pathway
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35. Each ATP molecule has three parts:
• an adenine molecule
• a ribose molecule
• three phosphate molecules in a chain
Adenosine triphosphate (ATP)
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36. • third phosphate attached by high-energy bond
• when the bond is broken, energy is transferred
• when the bond is broken, ATP becomes ADP
• ADP becomes ATP through phosphorylation
• phosphorylation requires energy released from cellular
respiration
Adenosine triphosphate (ATP)
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38. ATP reactions often involve an
intermediate transfer step
ATP participation in a
reaction is often depicted
in a single step; the
mechanistic reality is
frequently a two-step
process
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40. What are the metabolic uses of ATP?
• An endergonic reaction has a thermodynamic barrier in
addition to a kinetic barrier
• Enzymes can cut kinetic barriers only
• Combining the reaction with an exergonic process (hydrolysis
of ATP) converts the energetics of the total process
• The endergonic reaction is "coupled" to an energetically
favorable reaction so that the overall free-energy change for
the two reactions together is favorable
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41. • The formation of glucose phosphate from glucose and HPO4
2− is
energetically unfavorable: ΔG°' = +13.8 kJ/mol (3.3 kcal/mol)
• The formation of glucose phosphate from ATP is energetically favorable
by 16.7 kJ/mol (4.0 kcal/mol)
Phosphorylation of glucose
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48. CoenzymeA
• Coenzyme A (CoA) is an acetyl-carrying group.
• CoA is often written CoA-SH to emphasize the fact that it contains a
sulfhydryl group.
• The acetyl group of acetyl CoA is bound as a high-energy thioester.
CH3 -C-S-CoA
O
Acetyl coenzyme A
(An acyl CoA)
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49. • Like NAD+ and FAD, coenzyme A contains a unit of ADP.
• The vitamin part of coenzyme A is pantothenic acid.
CoenzymeA
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50. • Oxidation-reduction or redox reactions
• Oxidation – removal of electrons
Decrease in potential energy
Dehydrogenation – removal of hydrogens
Liberated hydrogen transferred by coenzymes
Nicotinamide adenine dinucleotide (NAD)
Flavin adenine dinucleotide (FAD)
Glucose is oxidized
• Reduction – addition of electrons
Increase in potential energy
What happen during energy transfer?
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51. • Fate of glucose depends on needs of body cells
▫ ATP production or synthesis of amino acids, glycogen,
or triglycerides
• Glucose transporter (GluT) bring glucose into the cell
via facilitate diffusion
▫ Insulin causes insertion of more of these transporters,
increasing rate of entry into cells
▫ Glucose trapped in cells after being phosphorylated
Carbohydrate Metabolism
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52. Occurs in three series of reactions
1. Glycolysis
2. Citric acid cycle
3. Electron transport chain
Produces
• carbon dioxide
• water
• ATP (chemical energy)
• heat
Includes
• anaerobic reactions (without O2) - produce little ATP
• aerobic reactions (requires O2) - produce most ATP
Cellular Respiration
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53. 1
NADH + 2 H+
GLYCOLYSIS
+ 2 H+
NADH
CO2
FORMATION
OF ACETYL
COENZYME A
KREBS
CYCLE
+ 6 H+
CO2
FADH2
NADH
2
4
6
2
ELECTRON
TRANSPORT
CHAIN
e–
e–
e–
32 or 34
O2
6
6
2
2
2
2
H2O
Electrons
2 Acetyl
coenzyme A
2 Pyruvic acid
1 Glucose
ATP
ATP ATP
2
3
4
Overview of Cellular Respiration
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