Download Chapter 9 - UC Canopy

8/7/2012
Chapter 9
Energy
Metabolism
Learning Objectives - Chapter 9
Upon completion the student will be able to:
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Explain the differences among metabolism, catabolism and
anabolism
Describe aerobic and anaerobic metabolism of glucose
Describe how energy is extracted from glucose, fatty acids,
amino acids, and alcohol by identifying/using metabolic
pathways, such as glycolysis, beta oxidation, transition
reaction, citric acid cycle, and the electron transport system
Describe the role that acetyl Co-A plays in cell metabolism
Identify the conditions that lead to ketogenesis and it’s
importance in survival during fasting
Describe the process of gluconeogenesis
Compare the fate of energy from macronutrients during the
fed and fasted state
Vocabulary
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Pathway - progression of metabolic chemical reactions
Intermediates - compounds formed from a pathway
Anabolic pathways - building of compounds with the use of
energy
Catabolic pathways - breaking down of compounds with the
release of energy
Aerobic Metabolism – refers to the process of energy
transport where oxygen is the final receptor of the electron
transport process.
Anaerobic Metabolism – refers to the process of energy
transport where oxygen not present
Photosynthesis – the process by which plants use energy
from the sun to produce energy yielding compounds such
as glucose
Respiration – The use/exchange of oxygen.
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Anabolism & Catabolism
Simplified Concept of
Metabolism
Adenosine Triphosphate (ATP)
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Energy used by the cell
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Oxidation-Reduction Reactions
Oxidation reduction reactions form a vital link between the energy
yielding nutrients and the formation of ATP.
 Oxidized
 Loses one or more electron or hydrogen
 Gains one or more oxygen
 Tend to be highly reactive
 Reduced
 Gains one or more electron or hydrogen
 Loses one or more oxygen
These two processes go together, you can not have one without the
other.
 Key to energy formation EX: (Zn is oxidized and Cu has been reduced)
Zn + Cu+2 
Zn+2 + Cu
The reduction of oxygen to form water is the ultimate driving force for
life as it is vital to the way cells synthesize ATP. Therefore oxidation –
reduction reactions are key to body survival.
Oxidation-Reduction Reactions
Controlled by Enzymes
Dehydrogenases are a class of enzymes that are able to
remove H from energy yielding nutrients or their
products
 Dehydrogenases then donate the removed hydrogen to
oxygen to form water
 Two B vitamins function as dehydrogenases/coenzymes
in this process: Niacin and Riboflavin
Niacin = Nicotinamide adenine dinucleotide (NAD)
Riboflavin = Flavin adinine dinucleotide (FAD)
These two compounds readily accept and donate electrons
and hydrogen ions in the metabolism of glucose to
oxygen in the metabolic pathways of the cell. Ex:
(oxidized)
NAD NADH+H (reduced)
(oxidized)
FAD  FADH2
(reduced)
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The 4 Phases/Steps of Energy
(ATP) Formation
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1.
This process can be aerobic or anaerobic.
Glycolysis = breaks glucose to pyruvate
2.
Transition Reaction = pyruvate is oxidized to
acetyl CoA
3.
Citric Acid Cycle = Acetyl CoA enters the cycle
and the end results are NADH+H, FADH2, ATP,
CO2
4.
Electron Transport Chain = NADH +H and
FADH2 are oxidized to O & H ions and combined
to form H2O
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Four Phases/Steps of Metabolism
Glycolysis - “Breaking Down
Glucose”
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Glycolysis (step 1) occurs in the cytosol portion of the cell.
Glycolysis takes glucose (a 6 carbon molecule) and breaks
it down to two 3-carbon molecules = pyruvate.
Requires 2 ATPs for metabolism. - Glycolysis produces 4
ATP. Net gain of 2 ATP.
This occurs under anaerobic conditions.
The Transition Reaction (step 2), which is the moving of
pyruvate into the mitochondria from the cytosol, occurs
next. (Pyruvate to Acetyl CoA)
Progression to this next step in the mitochondria, requires
presence of O.
Lactic Acid will form when NADH oxidation cannot keep
pace with the formation of pyruvate in glycolysis
32 ATP are formed from one molecule of glucose. - 2ATP
Glycolysis; 2 ATP Citric Acid Cycle; and 28 in the Electron
Transport Chain
Glycolysis – Step 1
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Transition Reaction – Step 2
Citric Acid Cycle – Step 3
Electron Transport Chain – Step 4
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Glycogen Metabolism
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Short-term storage of excess glucose is found in
liver and muscle cells. It is stored in the form of
Glycogen. Process is called Glycogenolysis
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Glycogen requires vitamin B-6 for the conversion
of glycogen back to glucose-phosphate, which
can then re-enter the glycolysis pathway at step
2.
This process is more energy efficient.
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There is a net gain of 3ATP rather than 2ATP.
Lipolysis - Breakdown of Fat
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The Break down of a stored fat molecule
(triglycerides) produces one glycerol and
three fatty acids
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Fatty acids are liberated from adipose cell
by hormone-sensitive lipase
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Fatty acids will be further broken down via
fatty acid oxidation
Lipolysis
Adipose cells
(Triglycerides)
Hormonesensitive lipase
Cytosol
Fatty Acid
Mitochondria
Beta Carnitine oxidation
Acetyl CoA
(2 Carbon Molecule)
ATP
Glycerol &
Fatty acid
Cell
Blood stream
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Energy Production from Fatty Acids
Fatty acids with an even number of
carbons (the majority) are
converted to 2 carbon fragments
and can enter the Citric Acid Cycle
as acetyl CoA.
Beta - Oxidation
Lipogenesis: Building of Fat
Amino Acids
Glucose
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Acetyl-CoA
2C
+ CoA
Excess glucose or
protein not
immediately used by
the body will be
converted into fat
(lipid)
16 C saturated fatty acid chain
Triglyceride
VLDL
Ketosis
Ketones are products of incomplete fat breakdown
Ketosis is the state of having elevated ketones levels in the
body
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Alcohol Metabolism
Gluconeogenesis
The production of new glucose by other
pathways in the cell
Ex: amino acids
 In order for the body to use amino acid as
fuel, the amino group must be removed
Deamination
Transamination
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Amino Acid
NH3
NH3
COOH
COOH
H C H
H C H
R
R
Amino Group Needs to be Excreted
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Catabolism (breakdown) of amino
acids yields an amino group (NH2)
Amino group will be converted to
ammonia
Build-up of ammonia is toxic to
cells/body.
The liver breaks down the amino
acid (to amine group & ammonia)
which are combined to form urea
(via urea cycle). Urea is released
via the kidneys.
After removal of the amine group
the remaining carbon skeleton
group can enter energy pathway
as acetyl CoA or other
intermediates in the Citric Acid
Cycle.
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Gluconeogenesis
Overview of Metabolism
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“Fasting and Feasting”
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Fasting encourages:
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Glycogen breakdown
Fat breakdown
Gluconeogenesis
Synthesis of ketone bodies
Feasting encourages:
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Glycogen synthesis
Fat synthesis
Protein synthesis
Urea synthesis
Energy State - Fasting
Energy State - Feasting
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