BioChem Final Flashcards
How is Gluconeogenesis regulated?
- Turned on when needed
2. Reciprocally regulated with glycolysis
When does Gluconeogenesis need to be turned on?
- High levels of LACATE = Exercise;
- High levels of GLYCEROL = High fat diet;
- High levels of AMINO ACIDS = Starvation (not enough cards) or Diabetes (inhibits glucose to cells) ; Liver will produce glucose for Brain with starvation and DM
What is Reciprocal Regulation?
Regulation of enzymes in opposing pathways by the same of similar compounds;
- One reaction turned ON, while opposing reaction is turned OFF;
- Prevents futile cycling (going in circles)
How is Gluconeogenesis reciprocally regulated with Glycolysis?
- PFK (glyco) inhibited by ATP/citrate and activated by AMP/Fructose2-6-bisPO4….while Fructose-1-6-bisphosphatase (gluconeo) is oppositely affected;
- Pyruvate Kinase (glyco) is inhibited by Acetyl-CoA…while Pyruvate Carboxylase (glucoeneo) is activated by Acetyl-CoA;
- Pyruvate Dehydrogenase Complex (glyco) is also inhibited by Acetyl-CoA
Why does increased Acetyl-CoA INHIBIT Pyruvate Kinase and the Pyruvate Dehydrogenase Complex of GLYCOLYSIS?
- Because there is enough Acetyl-CoA, so pyruvate does not need to be converted to make more, which would be the commitment AWAY from carb synthesis;
- So Acetyl-CoA is used to direct away from forming more and allow pyruvate to be used in another way
Why does increase Acetyl-CoA ACTIVATE Pyruvate Carboxylase of Gluconeogenesis?
-Lots of Acetyl-CoA needs a lot of OAA, so wants to make more OAA to bind and be able to continue into the TCA cycle;
What is the Energy Concern with Gluconeogenesis?
- Very energy expensive process!;
- Requires 6 ATP (4 ATP + 2 GTP) and 2 NADH to synthesize ONE glucose from TWO pyruvate;
- Spend MORE to make Glucose with gluconeogenesis than to Breakdown with glycolysis
What must the Sum of the Delta G values be?
-Delta G must be NEGATIVE for Glycolysis and Gluconeogenesis for each pathway to be able to occur
What is the Alternative to Hexokinase of glycolysis?
Glucose-6-Phosphatase of gluconeogenesis =
-Converts Glucose-6-PO4 back to Glucose
What is the alternative to PFK (phosphofructokinase) of Glycolysis?
Fructose-1,6-bisphosphatase of gluconeogenesis =
-Converts Fructose-1,6-bisPO4 back to Fructose-6-PO4
What is the alternative to Pyruvate Kinase of glycolysis?
-Pyruvate Decarboxylase (pyruvate to OAA) and then PEP Carboxykinase (OAA to PEP) of gluconeogenesis
What is Glycogen?
- Animal storage form of Glucose;
- Highly branched polyglucose;
- Found in the Liver and Muscle
What are the 2 paths of Glycogen Metabolism?
- Glycogenesis = Synthesis of glycogen from Glucose-6-PO4 (of glycolysis) in times of storage;
- Glycogenolysis = Breakdown of Glycogen back into Glucose-6-PO4 to provide glucose in times of need
What is the enzyme for Glycogen SYNTHESIS with Glycogenesis?
Glycogen Synthetase = STORES
How is Glucose-6-PO4 from glycolysis converted to GLYCOGEN for storage?
GLYCOGEN SYNTHETASE=
- Reversible conversion/isomerization to Glucose-1-PO4;
- Glucose-1-PO4 undergoes activation to be UDP~glucose;
- Converted to Glycogen
2nd step in Glycogen synthesis: Glucose-1-PO4 to UDP~glucose
- UTP REMOVES 2Pi (pyrophosphate) from Glucose-1-PO4 to leave activated UDP~glucose;
- Removing 2Pi expends ALOT of energy
What is UTP?
- High energy compound that is dedicated for use ONLY in polysaccharide synthesis;
- Contain Uridine (found in RNA)
Why does a diphosphate (UDP) still remain after removing 2Pi with UTP?
For UDP~glucose, the glucose is attached at C1m making a di-PO4 remain, just moved around;
-Still two TOTAL glucose remaining in the molecule
3rd step in Glycogen synthesis: UDP~glucose to Glycogen
- UDP molecule is REMOVED from the glucose, breaking the high energy bond;
- Remaining glucose molecule is ADDED to the at the C4 on the NONREDUCING ending of the Glycogen chain to added another branch (C1 already activate);
- C1 and C4 come from the Alpha-1,4 links of glycogen
What is the enzyme for Glycogen BREAKDOWN with Glycogenolysis?
-Glycogen Phosphorylase = BREAKS off a glucose at C1 and adds a PO4
How is Glycogen from storage converted back into Glucose-6-PO4?
GLYCOGEN PHOSPHORYLASE=
- Breaks glycogen chain off at C1 to take a glucose molecule and adds a Pi from the cytoplasm to created GLUCOSE-1-PO4;
- Reversible conversion/isomerization to Glucose-6-PO4
What happens one the Glucose-6-PO4 has been created from the breakdown of Glycogen?
- Liver = Glucose-6-Phosohatase converts to GLUCOSE and sends to blood to raise levels and supply for the Brain;
- Muscle = Undergoes GLYCOLYSIS to provide its own energy (CANNOT send back to the Blood)
Why can’t the Muscle supply the blood with glucose?
-Doesn’t have the enzyme Glucose-6-Phosphatase to converted the Glucose-6-PO4 back into the just glucose
How is Glycogen Synthetase of Glycogen STORAGE controlled ALLOSTERICALLY?
- Glycogen Synthetase 1 (active) INHIBITED by AMP;
- Glycogen Synthetase D (inactive) ACTIVATED by Glucose-6-PO4
How is Glycogen Phosphorylase of Glycogen BREAKDOWN controlled ALLOSTERICALLY?
- Phosphorylase A (active) INHIBITED by glucose (liver);
- Phosphorylase B (inactive) INHIBITED by Glucose-6-PO4 and ATP; ACTIVATED by AMP (muscle)
How do LOW ENERGY LEVELS affect the Glycogen Metabolism and its substrates?
HIGH concentration of Pi (during high ATP breakdown) when energy levels are LOW = ACTIVATE Glycogen Phosphorylase to breakdown Glycogen
How do HIGH ENERGY LEVELS affect the Glycogen Metabolism and its substrates?
HIGH concentration of UTP when energy levels are HIGH = ACTIVATE Glycogen Synthetase to store as Glycogen
What Hormones affect Glycogen Metabolism?
- Glucagon;
- Epinephrine;
- Insulin
How do Glucagon and Epinephrine control Glycogen Metabolism?
-GLUCAGON (Liver)= Lowers blood glucose;
=EPINEPHRINE (Muscle) = Provides energy with glucose;
*Both INCREASE breakdown and INHIBIT synthesis of Glycogen
How does Insulin control Glycogen Metabolism?
- Allows glucose to enter cells;
- Released when HIGH BLOOD glucose concentration;
- INCREASES synthesis and INHIBITS breakdown of Glycogen
How does Glucagon and Epinephrine act on the cell?
- Peptide Hormones that DO NOT enter the cells, just act on the SURFACE;
- Bind to receptor which sends signal across the cell membrane = SIGNAL TRANSDUCTION
How does Signal Transduction work?
- Peptide hormones DON’T enter cells;
- Bind to specific receptor proteins in cell membrane of the outer surface of target cells;
- Cause a conformational change in receptor protein ;
- Then, causes a conformational change in ADENYL CYCLASE on the inner surface of the membrane making it ACTIVE
What occurs when Adenyl Cyclase is ACTIVATED?
-Catalyzes the conversion of ATP to CYCLIC AMP by the removal of 2Pi (pyrophosphate)
What is the “Cascade Mechanism” of Signal Transduction?
- The amplification of small amounts of message to bring about a large amount of results in a short amount of time;
- Adenyl cycles enzyme works over and over again increasing the amplifying the number of responses each time
What is the mechanism for Covalent Modification?
- Add PO4 to enzyme;
- Conformational change occurs;
- Increase or decreases enzyme activity (totally on or off)
What happens to the Cyclic AMP to continue glycogen breakdown?
-Protein Kinase covalently modifies it by adding the Regulatory molecule to CAMP and leaving the catalytic molecule free
What is the free Catalytic Subunit then used for in glycogen breakdown?
- Activates Phosphorylase Kinase by adding PO4 ;
AND - Inactivates Glycogen Synthetase (the glycogen storage enzyme) by adding a PO4;
=RECIPROCAL REGULATION
What is the next step with Activated Phosphorylase Kinase in Glycogen breakdown?
-Phosphorylase Kinase then ACTIVATES Glycogen Phosphorylase by adding a PO4 (major breakdown enzyme)
What is the final step with Activated Glycogen Phosphorylase (has a PO4)?
- Catalyzes the Addition of a Pi from the cytoplasm to the NON-Reducing end of glycogen to create Glucose-1-PO4 which will then isomerize into Glucose-6-PO4;
- Now can be used by the Liver or the Muscle
Why does Glycogen Breakdown use Reciprocal Regulation to INACTIVE Glycogen Synthetase?
- Active Glycogen Synthetase STORES glycogen;
- During times of Glucose need, glycogen does NOT NEED to be stored, so using the sam enzyme to activate breakdown and inactivate storage is highly efficient
What are Phosphatases?
- Allosteric controls that RETURN Covalently Modified enzymes back to their ORIGINAL form by removing the PO4;
- Can either be returning it to active or inactive, whatever is the normal state
Why can Glycogen be broken down so quickly to provide glucose in sudden need?
-The molecule is highly branched allowing it to be broken down at all the branches and quickly catabolized back to glucose as the cascade mechanism amplifies the enzymatic reaction at each point
What happens when the breakdown of CAMP is inhibited by Caffeine?
-More energy will released in at once because the CAMP will hang around longer activating more enzymes than normal
Where does GALACTOSE enter carb metabolism?
-Through UDP-Glucose and into the Glycogen pathway to become Glucose-1-PO4 and onto Glucose-6-Phosphate to be used in Glycolysis
Where does MANNOSE enter carb metabolism?
-Through Fructose-6-Phosphate into the Glycolysis pathway
Where does FRUCTOSE enter carb metabolism?
-Through DHAP and Glyceraldehyde to Glyceraldehyde-3-PO4 and into the Glycolysis pathway
What is the Pentose Phosphate Pathway?
Where does the Pentose Phosphate pathway occur?
- In the liver, mammary glands, testes, and adrenal cortex in animals;
- Tissues that carry out ALOT of biosynthesis, so need a lot of NADPH and the accompanying electrons
What are the FUNCTIONS of the Pentose Phosphate Pathway?
- Alternative route for glucose oxidation to CO2 and H2O (another form of complete breakdown);
- Energy released in oxidation is used to make NADPH (12 NADPH/glucose);
- Allows interconversion of 3,4,5,6,7 C sugars to inter into glycolysis (transaldolases and transketolases);
- Biosynthesis of ribose-5-PO4 from glucose-6-PO4;
- In plants, many some type of enzymes used for photosynthesis
Why is the Pentose Phosphate pathway important for the generation of NADPH?
- Traps the energy as needed electrons in the needed Redox coenzyme for SYNTHETIC pathways (NADPH);
- Can be used to generate NADH;
- NADPH is used by antioxidant enzymes
How can NADH be used to create NADH with the Pentose Phosphate Pathway?
-Remove electrons from NADPH and give them to NAD+;
-Generates NADH and NADP+;
(NEVER move Phosphate, just electrons)
How many ATP could come from the Pentose Phosphate Pathway?
-12 NADPH produced per glucose;
= ~36 ATP if converted to NADH and sent to ETC;
(3 ATP generated per NADH)
What are Lipids?
Variety of biological molecules that are soluble in NON-POLAR solvents, but NOT in water;
-Either Saponifiable or Non-sapinofiable
What are Saponifiable Lipids?
Can be broken down to at least one fatty acid + an alcohol
What lipids are Saponifiable?
- Fatty acids and derivatives (building blocks)
- Triaclglycerols (storage)
- Phosphoacylglycerolds (membranes)
- Sphingolipids (nerve tissue)
- Glycolipids (carb conjugates)
- Wax esters (lubricants, coatings)
What lipids are Non-Saponifiable?
- Isoprenoids (Terpenes, Steroids) = 5-C
2. Derivatives of Arachidonic acid (Prostaglandins, Leuokotrienes, Thromboxanes)
What are Fatty Acids?
Long, chain monocarboxylic acids; -Long carbon chain is HYDROPHOBIC; -Carboxylic acid group is HYDROPHILIC due to separation of charge =AMPHIPHILIC overall ; -Saturated or Unsaturated
What are Saturated Fatty Acids?
- Contain NO double bonds;
- Saturated with Hydrogens;
- Lack of double bonds allows them to stack together very closely making them SOLID at room temp