Chapter 13 - How Cells Obtain Energy from Food

The breakdown of sugar requires lots of energy, all of which is released as heat. Enzymes help reduce the amount of energy this requires, and sugars are oxidated over time and will keep decreasing the energy within the sugar molecule

Catabolism has different steps, including glycolysis, beta-oxidation of fatty acids, the TCA cycle, and the electron transport chain (ETC). The overall equation is Food + O2 → ATP + NADH + CO2 + H2O. Without oxygen, glycolysis can only happen. The citric acid cycle uses oxygen. NADH plays a large role, as demonstrated above. Ultimately, oxygen takes up the protons that are created by reactions, with the energy from electrons going to be stored in ATP

Stage 1 is without oxygen, and breaks down large food molecules into smaller subunits (protein → amino acid, polysaccharide → simple sugars, fats → fatty acids/glycerol)

Stage 2 only occurs with oxygen, and breaks down these subunits into acetyl CoA, and produces a limited amount of ATP and NADH

Step 3 is also only done without oxygen, and oxidates the acetyl group from acetyl CoA into CO2 and H2O, which produces large amount of ATP on the inner mitochondrial membrane

Many catabolic pathways intersect, such as carbohydrate metabolism and fatty acid metabolism, along with amino acid metabolism all leading to acetyl CoA

Glycogen is how animals store sugar, it is a large branching molecule with individual units of glucose

A given polymer of glycogen may interact with glycogen phosphorylase, to either add too or remove a glucose molecule. If one is removed, it then goes through glycolysis

Glycolysis takes glucose and breaks it into pyruvate, ATP, and NADH. The process requires 2 ATP but produces 4 ATP. A kinase phosphorylates a phosphate from ATP to a substrate. Other kinases transfer a phosphate to ADP to form ATP. Isomerase prepares molecules for future chemical alterations. Dehydrogenases generate NADH, and mutases move the phosphate to help prepare the substrate to transfer the group to ADP to produce ATP

Steps of Glycolysis:

1. Glucose is phosphorylated by ATP to form a sugar phosphate, the negative charge traps it in the cell

   

2. ?

3. A new hydroxyl group in C1 is phosphorylated by ATP, to prepare for the formation of two 3 carbon sugar phosphates. This step regulates the entry of sugars into glycolysis, via phosphofructokinase

   

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5. ?

6. (7) The oxidation of an aldehyde to a carboxylic acid releases energy, much of which is captured and carried by ATP and NADH. Forms a high energy intermediate, which can be done in the absence of oxygen

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8. ?

9. (10) A high energy intermediate is formed, allowing for it to be done without oxygen

   

10. A high energy phosphate group is transferred to ADP, forming ATP and completing glycolysis.

    

The high energy bonds broken to form ATP typically come from anhydrides, either anhydrides using carbon or other phosphates (like in ATP)

In the presence of oxygen (aerobic), oxidative phosphorylation is done in the mitochondrion. Without oxygen (anabolic), fermentation is done in the cytosol

Fermentation only occurs without the presence of oxygen. In yeast, there is an additional step

Pyruvate dehydrogenase complex (PDH) is located within the mitochondrial matrix, and is the irreversible link between glycolysis and the TCA cycle

Beta oxidation is the step that converts fatty acids into acetyl-groups, and is done in the mitochondrial matrix

Acetyl CoC production from sugar and fat follow this

The TCA cycle is the central catabolic pathways in the cell

Amino acid degeneration and anaplerotic reactions can be glucogenic or ketogenic

Catabolic pathways provide building blocks for the cell, after breaking them down from macromolecules. The process is amphibolic

Oxidative phosphorylation releases CO2 and consumes O2

Without oxygen pyruvate, the cell will go through an 11th step of glycolysis, or it will lactate