Fain 53

HMP Shunt- hexose monophosphate shunt or pentose phosphate pathway
Glycogen Metabolism
3: Know what the pentose phosphate pathway does. Purpose- give 5-carbon sugars for DNA and RNA synthesis. Need NADPH for biosynthesis. In glycolytic pathway, you get NADH for catbolism. NADPH is needed to hydrogenate double bonds- does not come from glycolysis. NADPH is needed for fatty acid biosynthesis.
For NADPH, recycle 5-C to get 6-C sugar. Intermediates formed are summarized on the slide.
Know it is HMP or PP pathway.
6: 6-phosphogluconate dehydrogenase produces NADPH and CO2, converting glucose to D-ribulose 5 phosphate in fed state. (Cells want to grow and divide when well fed)
7: difference isomerase and epimerase: Isomerase changes aldehyde to ketone (or vice versa- reaction is reversible). Epimerase moves OH to other side of same carbon. Moved from one plane to another.
8: 5+5 (ribose-5-phosphate+xylulose-5-phosphate)=7+3(sedoheptulose-7-phosphate+glygeraldehyde-3-phosphate)
11: fructose 6 phosphate can be isomerized to glucose 6- phosphate. Know this figure. When glucose enters, has 3 possible pathways (glycolysis, pentose phosphate pathway, or glycogen synthesis). The arrows between fructose-6-phosphate and fructose 1,6 bisphosphate should not be doubled.
12: another depiction.
13: If you want ribose and not reducing equivalents, you can go directly from glyceraldehyde 3 phosphate.
14: Red blood cells have no nucleus and no mitochondria. they use the pentose phosphate pathway for NADPH. Red cells need NADPH to prevent oxidative damage to red blood cells. This deficiency reduces the half life of red blood cells. Causes hemolytic anemia.
16: processing of fructose. Muscle and fat have hexokinase to phosphorylate fructose, but it is difficult for fructose to get into them. Fructose messes up metabolism- has to be converted in liver.
17: Milk sugar is made of glucose and galactose. Galactose 6-p – get UDP galactose. UDP galactose is conv to UDP glucose. Get Glucose 1-phosphate.
18: Galactosemia is rare enzymatic defect. To treat the deficiency, reduce exposure to lactose until teenage years when alternate pathway becomes available.
19: Summary for galactose, fructose, and mannose. UDP glucose is used to make glycogen.
20: We store glucose in liver and muscle as glycogen.
22: Chain elongation requires UDP-glucose.
25: once you get 10 glucose linked, you need a branch point.
27: breakdown.
31: In test tube, you can make glycogen with glycogen phosphorylase with large amounts of glucose-1-phosphate(G-1-P), glucose, and limit dextrin. Not in vivo- not high enough concentration G-1P. In vitro they forced the enzyme to run backward.
33: We have receptors (in liver and muscle) in the cell membrane. Epinephrine added to membranes made cAMP that was heat stable. Added to liver extract, got second messenger to induce glycogen breakdown.
34: Phosphorylation activates phosphorylase kinase and inactivates glycogen synthase.
Review:
from 1-26 on exam review sheet.
17. basic pathway.
18. Why is virtually all fructose utilization in liver in humans? Liver ‘s function is to interconvert metabolic intermediates.
20. How do you make glycogen from glucose? Rapid Hydrolysis of pyrophosphate makes it reversible. Why need both enzymes? Linear polymer can get twisted and tangled. Branching works better. Less osmotic effect.
21. what does glycogenolysis require? debranching enzyme and phosphorylase, regulated by phosphorylase kinase.
Phosphorylate serine and/or threonine residues. Catecholamines regulate cAMP to cause covalent modification.
23-26: forget. His mistake. From other lectures. Not on test.
He has 3 questions, one for each lecture.
If you do not know A in a question on the test, do B and C for 6 pts instead of 10.