IPHY 3430 8-25-11

If you missed class on Tuesday, please pick up a syllabus from Dr. Carey

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Clicker question:What are your future plans?A. med schoolB. dental schoolC. physical therapyD. nursingE. other

Energetics

Energy is the ability to produce change or an effect by doing work.

Energy comes in several forms:heat, chemical, radiant, etc.

What is work in a human system?

1. Synthesis of macromolecules2. Maintenance of ionic disequilibria3. Muscle contraction4. Transmission of information5. Many others

Chemical energy is the only form of energy that can be used to work in the human body.

Bonds between C, H, N, S, O, etc. contain energy.

Heat energy cannot be used to do work in the human body.

Where does energy for use in the human body come from?

Chemical energy in food (carbohydrates, proteins, and fats)

Carbohydratescomplex carbohydrates (glycogen, starch) --> simple sugars (glucose, galactose, fructose) ---> once absorbed into the body can be stored temporarily as glycogen or immediately catabolized

-->energy released by enzymatic breakage of bonds ---> some work done and the rest lost as heat

ProteinsComplex proteins in diet --->broken down toamino acids--->

once absorbed into body, amino acids can be used temporarily to make new proteins or immediately catabolized--->

energy released by enzymatic breakage of bonds--> some work done and the rest lost as heat

FatsTriglycerides broken down to monoglyceride and two fatty acids-->

Once absorbed into body, can be stored temporarily as triglycerides or split into glycerol and three fatty acids which then are catabolized-->energy released by enzymatic breakage of bonds --> some work done and the rest lost as heat

Summary:

Chemical bonds in carbohydrates, proteins and fats are enzymatically broken, with the result that most chemical energy is lost as heat energy but some is conserved in chemical form to do work.

Heat energy is lost as chemical bonds are broken since products of cellular reactions frequently, but not always, have a lower energy content than the original moleculeA---> B + C

In living cells, chemical bonds must be broken in a step-by-step sequence, not all at once.

1. Cell can’t use heat to do work2. Heat liberation would cause a lethal rise in cell temperature

Most of the energy in food is lost immediately as heat, but a small amount is used to form a few high energy bonds

Adenosine triphosphate

ATP is the intermediary between the energy content of the food and the need to have chemical energy to do work.

Anaerobic conditions can occurin periods of high energy demand;lactate lactic acid is formed, increasing acidity in the tissue.Figure 3-42

ATP ProductionGlycolysis

1. Converts one 6-carbon molecule (glucose) into two three carbon molecules (pyruvate)2. Requires 2 ATP to start, generates 4 ATP, so produces a net 2 ATP3. H+ transferred to NAD+---> NADH4. If no Oxygen present, NADH loses H to pyruvate, forming lactate and regenerating NAD+

Each transition of pyruvate to acetyl coenzyme A yields one NADH and one CO2. The acetyl coenzyme A then enters the Krebs cycle.

In aerobic conditions,two spins of the Krebs cycle occur for each glucose that enters glycolysis.

ATP ProductionCitric Acid Cycle

1. Requires that oxygen be available2. 2 GTP ---> 2 ATP synthesized3. All 6 carbons and 6 oxygens from original glucose lost as CO24. The rest of all the original H+ on glucose transferred to NAD and FAD

Glucose catabolism “powers” ATP synthesis via a combination of substrate and oxidative phosphorylation.

For each NADH, 3 ATPs are formed.For each FADH2, 2 ATPs are formed.

ATP ProductionOxidative Phosphorylation

1. NADH and FADH2 oxidized to NAD+ and FAD+2. H separated into proton H+ and e-3. Electrons passed from cytochrome to cytochrome, with large energy drops at 3 steps, at which ATP made4. H+ combined with e-, O2 split, forming water 5. 34 ATP made during this process

1 molecule of glucose produces2 ATP in glycolysis2 ATP in citric acid cycle22-34 ATP in oxidative phosphorylation

Total = 26-38 ATP --energy conversion is 38-44 % efficient

electric motor or gasoline engine is 10-20% efficient

Fats are catabolized to make ATP

1. Fatty acids broken down into 2-C fragments, enter as acetyl-CoA2. Glycerol enters glycolysis as 3-C

1 molecule of palmitate (16 C fatty acid) = 84 ATP

Amino Acids are catabolized to make ATP

HOOC - C - NH2 R (one or more carbons)

Enter as pyruvate, acetyl CoA or intermediate in citric acid cycle.