Highlights Lecture #26 Spring 2017

Highlights Energy

1. Oxidation produces energy for cells to make ATP. ATP is the energy currency of cells and is used in anabolic reactions to synthesize things.

2. ATP has high energy due to the mutual repulsion of the phosphates it contains.

3. NADH and FADH2 must readily be converted back to NAD+ and FAD in the cell or oxidative reactions will have no molecule to transfer electrons to.

Highlights Glycolysis

1. Glycolysis is a metabolic pathway for the breakdown (catabolism) of glucose and related sugars. The pathway requires two ATPs to start the process and generates 4 ATPS (for a net of two ATPs) per glucose. Also generated during glycolysis are two NADHs.

2. The two NADHs produced in glycolysis are a factor in determining which pathways is taken after pyruvate is produced in glycolysis.

3. The video lecture contains info needed to know for the exam regarding structures, names, and enzymes. Hexokinase (need to know) is an enzyme that catalyzes the first step in glycolysis. It uses an ATP to put a phosphate onto glucose, making glucose-6-phosphate (G6P) and ADP.

4. G6P is converted to fructose-6-phosphate (F6P) in the next step of the pathway.

5. Conversion of F6P to fructose-1,6-bisphosphate is catalyzed by the enzyme phoshofructokinase (PFK) (need to know). This reaction also requires ATP.

6. In the next step of glycolysis, the six carbon F1,6BP is split into two three carbon pieces (DHAP and G3P) catalyzed by the enzyme aldolase (need to know). The deltaGzeroprime for this reaction is very positive, meaning that there is an energy barrier to get over.

7. The two three carbon pieces are then converted into the same form – glyceraldehyde-3-phosphate (G3P).

8. Reaction 6 of glycolysis involves the only oxidation. The enzyme responsible is glyceraldehyde-3-phosphate dehydrogenase (G3PDH – need to know). In the reaction, the aldehyde of G3P is converted to an acid group, which is subsequently linked to a phosphate. Note that the energy of the oxidation provides the necessary energy to put the phosphate on. ATP is not required.

9. In reaction 7, ATP is generated. Since there are two three carbon molecules per six carbon glucose, two ATPs are produced per starting glucose. This reaction is referred to as a substrate level phosphorylation (ATP being made directly from ADP by transfer of a phosphate from another molecule with phosphate). Substrate level phosphorylation is one of three types of phosphorylation in cells. The other two are oxidative phosphorylation in mitochondria and photophosphorylation of photosynthesis in chloroplasts.

10. Reaction 8 is a simple isomerization. An intermediate in the process is 2,3 BPG. Reaction nine involves removal of a water molecule from each three carbon intermediate to form the high energy molecule called phosphoenolpyruvate (PEP).

11. Reaction 10 is the “big bang” reaction of glycolysis. It produces another ATP for each PEP (by substrate level phosphorylation) and in turn, each PEP is converted to pyruvate, the end product of glycolysis. The enzyme, pyruvate kinase, is an important one, as it provides yet another control point for glycolysis. Pyruvate kinase is controlled by both allosteric and covalent modifications. This reaction is VERY energetically favorable and helps to “pull” earlier reactions that are not so favorable.

12. Glycolysis is regulated by three enzymes – hexokinase, phosphofructokinase, and pyruvate kinase.

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