1. Chapter 5 Cell Respiration and Metabolism
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2. Metabolism
Is all reactions in body that involve energy transformations
Divided into 2 categories:
Catabolism breaks down molecules and releases energy
Is primary source of energy for making ATP
Anabolism makes larger molecules and requires energy
Source of body’s large energy-storage compounds
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3. Metabolism continued
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4. Glycolysis
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5. Glycolysis
Is metabolic pathway by which glucose is converted into 2 pyruvates
Does not require oxygen
Overall net equation is:
glucose + 2NAD + 2ADP + 2Pi  2 pyruvates + 2NADH + 2 ATP
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6. Glycolysis continued
Glycolysis is exergonic - produces net of 2ATPs and 2NADHs
However, glucose must be activated with 2ATPs (phosphorylation) before energy can be obtained
Phosphorylation traps glucose inside cell
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7. Lactic Acid Pathway
To avoid end-product inhibition NADHs produced in glycolysis need to give Hs away
In absence of O2 NADH gives its Hs to pyruvate creating lactic acid (anaerobic respiration or fermentation)
Makes muscles feel fatigued
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8. Lactic Acid Pathway continued
Only yields a net gain of 2 ATPs per glucose
RBCs don’t have mitochondria; use only lactic acid pathway
Occurs in skeletal and heart muscle when oxygen supply falls below critical level
During heavy exercise or vascular blockage
Only in skeletal and heart muscle
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9. Glycogenesis and Glycogenolysis
For osmotic reasons cells can’t store many free glucoses
Instead store glucose as glycogen (glycogenesis)
Skeletal muscle and liver store lots of glycogen
Glycogenolysis clips glucose out of glycogen as glucose 6-phosphate. Breaking down of glycogen
Phosphate groups trap molecules in cells
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10. Glycogenesis and Glycogenolysis continued
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11. Glycogenesis and Glycogenolysis continued
Skeletal muscles use trapped glucose-6-phosphate for own energy needs
Only liver has glucose-6-phosphatase that removes phosphate groups
So it can secrete glucose
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12. Aerobic Respiration
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13. Aerobic Respiration
Begins when pyruvate formed by glycolysis enters mitochondria
CO2 is clipped off pyruvate forming acetyl CoA (coenzyme A is a carrier for acetic acid)
CO2 goes to lungs
Energy in acetyl CoA is extracted during aerobic respiration in mitochondria
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14. Krebs Cycle
Begins with acetyl CoA combining with oxaloacetic acid to form citric acid
In a series of reactions citric acid converted back to oxaloacetic acid to complete the pathway
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15. Krebs Cycle continued
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16. Fat and Protein Metabolism
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17. Fats and Proteins as Energy Sources
Fats can be hydrolyzed to glycerol and fatty acids
These can be modified to run through Kreb’s
Proteins can be broken down to amino acids
Which can be deaminated and run through Kreb’s
These pathways can be used to interconvert carbohydrates, fats, and proteins
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18. Energy Storage
When more energy is taken in than consumed, ATP synthesis is inhibited
Glucose converted into glycogen and fat
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19. Acetyl CoA Is a common substrate for energy and synthetic pathways
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20. Fat Synthesis (Lipogenesis)
Acetyl CoAs can be linked together to form fatty acids
Fatty acids + glycerol = Fat (triglycerides)
Occurs mainly in adipose and liver tissues
Fat is major form of energy storage in body
Yields 9 kilocalories/g
Carbos and proteins yield only 4/g
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21. Lipolysis Is breakdown of fat into fatty acids and glycerol
Via hydrolysis by lipase
Acetyl CoAs from free fatty acids serve as major energy source for many tissues
Found in the liver
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22. Brown Fat Amount of brown fat greatest at time of birth
Is major site for thermogenesis in the newborn
Brown fat produces an uncoupling protein, causing H+ to leak out of inner mitochondrial membrane
Less ATP is produced, causing electron transport system to be more active
Heat produced instead of ATP
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23. Ketone Bodies
Triglycerides are continually broken down and resynthesized
Ensures blood will contain fatty acids for aerobic respiration
During fasting and diabetes lots of fat is broken down
Causes high levels of ketone bodies
Which are fat metabolites
Gives breath an acetone smell
Cells cannot have big storages of glycogen
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24. Amino Acid Metabolism Nitrogen (N) is ingested primarily as protein
Which is used in body as amino acids
Excess is excreted mainly as urea
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25. Nitrogen (N) Balance Nitrogen balance = N ingested minus N excreted
Positive N balance: more Nitrogen ingested than excreted
Negative N balance: less Nitrogen ingested than excreted
In healthy adults amount of N excreted = amount ingested
-if this is not happening, diet is not balanced
Excess amino acids can be converted into carbos and fat
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26. Essential and Non-essential Amino Acids
20 amino acids are used to build proteins
12 can be produced by body
8 must come from diet (= essential amino acids)
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27. Gluconeogenesis
Occurs when amino acids or other non-carbos are converted to Keto acids, then pyruvate, then glucose
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28. Uses of Different Energy Sources
Different cells have different preferred energy substrates
Brain uses glucose as its major source of energy
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29. Summary of Metabolic Conversions of Nutrients
Figure 22-2: Summary of metabolism