KAAP221 Lecture Notes - Lecture 20: Anabolism, Protein Catabolism, Net Energy Gain
11 May 2018
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Lecture 20
• Chapter 23 - metabolism, nutrition, and energetics
• Metabolism = sum of all chemical reactions that occur in body tissues; includes catabolism and
anabolism
• Catabolism - breakdown of organic substrates; larger to smaller; releases energy
• Anabolism - synthesis of new organic molecules; allows cells to continuously replace cellular
components; uses energy to convert small molecules into larger ones
• Metabolic turnover - process where there’s a continual breakdown and replacement of all cellular
organic components (except DNA)
• Cells get building blocks from - catabolic reactions and absorption of organic molecules from
interstitial fluid
• Nutrient pool - formed from cell’s organic building blocks; it’s the accessible source of organic
substrates
• Aerobic metabolism - nutrient pool can be used to generate ATP through aerobic metabolism
• Happens in mitochondria; nutrient pool is used to “feed” mitochondria
• Produces energy in form of ATP from ADP and Pi (inorganic phosphate)
• 40% of energy is captured - ATP is used for anabolism and other cellular function
• 60% of energy escapes as heat - warms interior of cell and surrounding tissue
• Nutrient pool
• Source of organic substrates for catabolic and anabolic reactions
• Anabolism is necessary as things break down to replace membranes, organelles, enzymes, and
structural proteins
• Catabolism is required for - converting substrates to 2C molecule that can be utilized by
mitochondria to produce ATP; mitochondria must have a continuous supply of 2C molecules
• Mobilization/movement of metabolic reserves
• Use reserves in between meals or when it’s been awhile since we last ate
• Mobilize reserves to maintain levels in different tissues
• Reserves are mobilized when absorption across the GI tract is insufficient to maintain normal
nutrient levels
• Liver breaks down triglycerides and glycogen —> fatty acids and glucose are released into the
blood
• Adipocytes break down triglycerides —> into fatty acids
• Skeletal muscle breaks down contractile proteins —> AA’s are released
• Reserves are filled when absorption by GI tract is greater than immediate nutrient needs (after
you’ve eaten a meal)
• Liver stores triglycerides and glycogen
• Adipocytes convert excess fatty acids to triglycerides
• Skeletal muscle store glucose as glycogen; use AA’s to increase myofibril number and
metabolize fatty acids at rest
• Glycolysis
• 1st step in glucose metabolism
• Anaerobic - doesn’t require oxygen
• Occurs in cytosol of cell
• Breaks down 6C glucose molecule to 2 3C molecules of pyruvate
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• Energy is used in 1st 2 steps resulting in loss of 2 ATP
• 4 ATP are generated in lower part of the pathway; since glycolysis required 2 ATP molecules at the
beginning (loss of 2 ATP in 1st 2 steps), there’s a net gain of 2 ATP for each glucose molecule
• Cytosolic NAD accepts H atoms to generate 2 NADH (a coenzyme) molecules - NADH then
transports those H atoms and their respective electrons to the mitochondria
• In lower portion of pathway, releases 2 H2O
• Total - formed 2 3C pyruvates, produced net gain of 2 ATP, released 2 H2O
• Citric acid cycle (CAC) = TCA cycle = Krebs cycle - circular pathway
• Overall function - remove H atoms from specific organic molecules and transfer them to
coenzymes, such as NAD
• Cycle turns twice for every glucose molecule - because 1 glucose is split into 2 pyruvate molecules
in glycolysis
• 8 reactions in total
• Aerobic process
• Occurs in mitochondria
• Prior to CAC, pyruvate is broken down to acetyl CoA
• Steps
• Pyruvate (3-C) enters the mitochondrial matrix
• Converted to 2-C acetate ion (NAD picks up a hydrogen electron and CO2 is generated) —> 1
NADH and 1 CO2 produced
• Now have formed acetate; through the action of coenzyme A it donates a CoA molecule to the
acetate ion and it becomes acetyl-CoA, and acetyl-CoA is part of the first step in citric acid
cycle
• Need to have a constant supply of acetyl CoA to keep the cycle running
• When NAD picks up an electron and becomes NADH it then travels to the ETC
• CoA added to form acetyl-coA
• Acetyl group from acetyl coA attach to 4-C molecule to form citric acid - coenzyme A released
• Coenzymes - each is derived from B vitamins
• Deliver H atoms to ETC
• NAD - nicotinamide adenine dinucleotide (contains niacin)
• Each NAD can carry 1 H atom as NADH
• In the citric acid cycle, 3 NADH are generated
• FAD - flavin adenine dinucleotide (contains riboflavin)
• Each FAD can carry 2 H atoms as FADH2
• In the citric acid cycle, 1 FADH2 is generated
• Summary
• For each acetyl-CoA molecule entering CAC
• 5 H atoms removed and transferred to coenzymes - 3 NADH and 1 FADH2
• 2 molecules of CO2 produced
• 2 molecules of H2O consumed
• Net energy gain of 1 ATP - GTP formed from GDP; transfers phosphate group to ADP,
forming ATP
• Electron transport chain - ETC
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find more resources at oneclass.com
Document Summary
Use reserves in between meals or when it"s been awhile since we last ate: mobilization/movement of metabolic reserves, mobilize reserves to maintain levels in different tissues. Reserves are mobilized when absorption across the gi tract is insufficient to maintain normal nutrient levels. Liver breaks down triglycerides and glycogen > fatty acids and glucose are released into the blood. Adipocytes break down triglycerides > into fatty acids. Skeletal muscle breaks down contractile proteins > aa"s are released. Reserves are filled when absorption by gi tract is greater than immediate nutrient needs (after you"ve eaten a meal) Converted to 2-c acetate ion (nad picks up a hydrogen electron and co2 is generated) > 1. Now have formed acetate; through the action of coenzyme a it donates a coa molecule to the acetate ion and it becomes acetyl-coa, and acetyl-coa is part of the first step in citric acid cycle.
