Term
| How does the intended purpose of glycogen in muscles differ from that of the liver |
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Definition
Muscles - purely for local use
Liver - mainly for export via the bloodstream to other locations such as the brain |
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Term
| Explain the alpha and beta orientation hydroxyl groups on anomeric carbons and the role they play in metabolism |
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Definition
Alpha - hydroxyl group points down
Beta - hydroxyl group points up
Our enzymes are specific enough to distinguish between alpha and beta orientations. Starch and glucose, for instance, are alpha orientations whereas cellulose, a waste product we cannot digest, is a beta orientation |
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Term
| Which end of the carbon chain is the reducing end? |
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Definition
| Number 1 carbon (when it has a free oxygen to it, its capable of reducing metals, which based on his description hasnt been useful in the last 20 years, sweet fact, bro) |
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Term
| Describe the 2 types of linkage bonds in glycogen |
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Definition
1. 1-4 linkages of alpha hydroxyl groups to join adjacent rings
2. 1-6 glycosidic linkages joining the alpha hydroxyl of one glucose ring to the carboxyl group of another by elimination of water |
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Term
| What end of the glucose ring do subsequent glucose rings add on to in glycogen formation? |
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Definition
| They join to the hydroxyl group of the anomeric carbon (the reducing end of the ring) |
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Term
| What are the advantages of storing glucose as glycogen as opposed to fat or just glucose? |
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Definition
1. Storing as glucose would increase osmotic pressure in blood
2. Fat cannot be mobilized for energy use as quickly as glycogen
3. Fat use requires oxygen, which is not always available in muscles
4. There is trouble making glucose for the brain from fat |
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Term
| What protein initiates glycogen synthesis? |
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Definition
Glycogenin
A small piece of glycogen is made while bound to the reducing end of this protein prior to elongation and branching |
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Term
| How does glucose get modified to the inital building block (UDP-glucose) for glycogen synthesis? |
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Definition
1. Glucose goes to Glucose 6-Phosphate (hexokinase)
2. G6P goes to G1P (phosphoglucomutase)
3. G1P reacts with UTP (uridine tri phosphate, energy rich molecule) to make UDP-glucose (uridylyltransferase catalyzes the release of 2 phosphates from UTP in this process)
4. This UDP-glucose molecule is the donor of glucose molecules for glycogen synthesis |
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Term
| Why does the branching of glycogen make it a more efficient molecule for energy storage? |
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Definition
1. Increased branching leads to increased solubility (better storage)
2. More non reducing ends leads to a rapid response time when it must be converted back to glucose |
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Term
| How does glycogen cleave to reform glucose? Why does it not simply hydrolyze the glycogenic bond? |
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Definition
Phosphorylase using inorganic phosphate to cleave the 1-4 bonds to make glucose 1-phosphate
It does not use water because if you used water, additional energy expenditure would be necessary to rephosphorylate glucose to G6P (the phorphorylase way is more energy efficient) |
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Term
| How are 1-6 branching bonds broken in glycogen? |
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Definition
1. Phosphorlyase breaks off glucose rings until about 4 glucoses are left branching off
2. Debranching enzyme removes all the remaining glucose except 1 and attaches them to the non reducing end of the branch
3. Debranching enzyme removes the last glucose in the branch
Note: The difference in phosphorylaze and debranching is the type of bond they cleave. Phosphorylaze cleaves 1-4 linkages. Debranching cleaves 1-4 to remove "stump" glucose molecules, but also cleaves 1-6 at the branch point |
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Term
| Explain the pathway by which glucagon and epinephrine affect glycogen synthesis and metabolism in the liver. |
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Definition
Note: Glycogen and Epinephrine are beta adregenic receptors. Their presence ALWAYS signals release glucose into the bloodstream, do NOT store it in cells.
1. Glucagon/ Epinephrine bind to beta-adregenic receptros and simulate the release of cAMP
2. cAMP activates protein kinase A
3. Protein kinase A simultaneously stimulates phorphorylase (break down glycogen) and inhibit glycogen synthase (store glucose as glycogen)
Note: As learned earlier, these two hormones will ALSO inhibit glycolysis once the glucose becomes available by inhibiting PFK-1, so the glucose can be released from the cell. |
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Term
| How does glycogen synthesis and metabolism response differ in muscles then in the liver? |
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Definition
Note: This is all in response to ALPHA receptors, not BETA
1. The protein kinase activated is protein kinase C, not protein kinase A
2. Muscles cannot make glucose from glucose 6-phosphate, so all the G6P released from these signals is made for local use to undergo glycolysis |
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Term
| How does insulin affect glycogen synthesis/metabolism? |
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Definition
Increases synthesis, decreases metabolism.
Insulin creates a signal cascade leading to increased glycogen synthase activity and decreases phosphorylase activity |
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Term
| How does insulin affect muscles differently from the liver for glycogen synthesis? |
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Definition
| Muscles have the GLUT4 receptor, so insulins presence also increases the uptake of glucose in muscle cells, leading to an increased glycogen synthesizing response relative to the liver, whose transporters are not affected by insulin |
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Term
| What is Von Gierke's disease? |
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Definition
A deficiency in glucose-6-phosphatase (turns G6P into glucose)
Outcome: Liver cannot release glucose because it cannot convert the broken down G6P (from glycogen) to a form that can be transported. Leads to hypoglycemia between meals. |
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Term
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Definition
| A defect in alpha 1,4-glucosidase, which uses water to cleave the 1-4 bonds in glycogen (as opposed to phosphorylase, which uses phosphate), leads to accumulation of glycogen granules in the lysosome |
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Term
| What are some of the problems associated with high levels of fructose consumption? |
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Definition
1. Heart disease
2. Obesity (fructose is more easily converted to fat then other sugars)
3. Contributes to insulin resistance in pre diabetics |
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Term
| How is fructose more easily converted to fat then other sugars? |
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Definition
1. Bypasses PFK-1 (you do not need to form fructose 6-phosphate in this pathway) so this pathway is unresponsive to changes in insulin and glucagon
2. Fructose goes to fructose 1-phosphate instead of 6-phosphate in the liver. F1P reacts with F1P aldolase to make glyceraldehyde, which is easily converted to glycerol (building blocks for fats) |
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Term
| How is galactose metabolized? |
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Definition
1. Galactose converted to Galactose-1-phosphate
2. Reacts with UDP-glucose to form UDP-galactose and G1P
3. UDP-galactose can be converted back to UDP-glucose |
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Term
| How is mannose metabolized? |
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Definition
1. Mannose goes to mannose 6-phosphate (via hexokinse)
2. Mannose 6 phosphate goes to fructose 6-phosphate |
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Term
| What is the purpose of the pentose phosphate pathway and what processes are the products useful for? |
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Definition
Pentose phosphate pathway metabolizes glucose all the way to CO2 and H2O anaerboically but DOES NOT make ATP.
It makes NADPH instead, which is the reducing equivalent in ANABOLIC processes (2 per glucose) as well as Ribose 5-phosphate, the building block for RNA synthesis and DNA (very important molecule) |
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Term
| What enzyme (in the pentose phosphate pathway) is one of the most commonly occurring enzymatic defects known and what is its outcome? |
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Definition
1. glucose 6-phosphate dehydrogenase
2. Red blood cells cannot make NADPH, making them very labile to hemolysis |
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