Exam #2 Prep Flashcards
Which cells can/do perform glycolysis? Why?
Any tissues, because it DOES NOT REQUIRE mitochondria, i.e. it is an ANAEROBIC PROCESS (no O2). Some cells in which it is performed do not have mitochondria, e.g. erythrocytes.
What energy source provides 50% of the calories in most diets?
Carbohydrates
What is the major carbohydrate?
Glucose
What are the end products of anaerobic glycolysis?
Lactate and 2 ATP. NO NADH.
What are the products of aerobic glycolysis?
1 glucose = 2 pyruvate, 2 NADH, 2 net ATP (4 ATP total, but 2 invested)
What does arsenic poisoning do? 3 things
- )Inhibits LIPOIC ACID containing enzymes, which is one of the 5 cofactors needed for the PDHC. It is also needed for the TCA (via alpha-ketoglutarate DH for AA metabolism). Thus, leads to an increase in pyruvate –> LACTATE = LACTIC ACIDOSIS.
- ) Forms a complex that bypasses 1,3-BPG = DECREASED ATP.
Name the enzymes involved in the CAC, what they catalyze, and how many carbons are involved at that point. Note the rate-limiting step.
mnemonic: Our City Is Kept Safe And Sound From Malice.
1. ) Citrate synthase (6C): Forms citrate. Basically irreversible, and highly exergonic.
- ) Aconitase: Forms isocitrate.
- ) Isocitrate Dehydrogenase**: Forms alpha-ketoglutarate (5C). NADH formed!!!. CO2 released. RATE LIMITING REACTION (EXERGONIC). Activated by ADP, inhibited by ATP/NADH.
- ) Alpha-ketoglutarate dehydrogenase (alpha-KGDH): Forms Succinyl-CoA (4C)–> high-energy thioester. EXERGONIC. A complex of 3 enzymes and 5 cofactors (SIMILAR TO PDHC). NADH FORMED! CO2 released.
- ) Succinate thiokinase (Succinyl-CoA synthetase): Forms succinate (4C). Cleaves high-energy Succinyl-CoA. RELEASE ENERGY AS GTP (interconvertible to ATP…substrate-level phosphorylation) s quick removal from the cycle.
- ) Succinate DH: Forms fumarate. Releases FADH2.
- ) Fumarase: Forms malate.
- ) Malate DH: Forms OAA. Releases NADH.
What are the products of one turn of CAC? Give the sources.
One turn from ONE ACETYL-CoA, but 2 ACETYL-CoA from Glucose. So 1 Glucose = TWO TURNS
Oxidative phosphorylation: 1 NADH = 3 ATP in ETC –> 3 NADH from CAC, so 9 ATP. SOURCES OF NADH: 1.) isocitrate DH 2.) alpha-ketoglutarate DH 3.) Malate DH
1 FADH2 (succinyl DH) = 2 ATP 11 running tally (22 from one glucose)
Substrate level: 1 GTP (from succinyl-CoA thioester) = 1 ATP TWO GTP from ONE glucose. So 2 ATP in total from substrate level
12 ATP in TOTAL for ONE TURN, 24 TOTAL with TWO TURNS of CAC FROM ONE GLUCOSE
3 NADH + 1 FADH2. 1 GTP. OR… 6 NADH + 2 FADH2 and 2GTP.
Isocitrate dehydrogenase is inhibited by ______? Thus, _____ and _____ accumulate.
High [ATP] and [NADH]. Citrate and isocitrate accumulate.
If the amino group from Glutamate is shed, what is the product? What enzyme catalyzes this reaction?
Alpha-ketoglutarate. Catalyzed by GLUTAMATE DEHYDROGENASE.
This is the CAC connection to protein
What are the reactants and products for the reaction involving the enzyme ALT?
Glutamate + pyruvate –>
What is the importance of Succinyl-CoA?
It is a high-energy thioester.
Produces GTP when hydrolyzed.
Which compounds make Propionyl-CoA? What is the fate of Propionyl-CoA? What else can it make (not energy related)?
Odd-chain fatty acids (5, 7, 9, etc.) and branched amino acids (valine, isoleucine, etc.).
It feeds the CAC. It is also a precursor in making heme.
What is the source for FADH2 in the CAC? What enzyme catalyzes the reaction?
Succinate, via succinate dehydrogenase.
Where else, besides the CAC, is Fumarate created (2 places)?
- ) The urea cycle. It can then feed into the CAC.
2. ) During catabolism of Phr and Tyr
What is the only reversible rxn in the CAC? What is the catalyzing enzyme and cofactors?
Malate –> oxaloacetate, via Malate DH. NADH is the cofactor.
What reaction IN ITS REVERSE can be used for gluconeogenesis in the cytosol?
Malate –> oxaloacetate (in its reverse, forming malate via NADH). Causes OAA levels to drop, thus indicating low energy and the need for glucose.
What intermediate from the CAC can be used to make pyruvate and NADPH? How?
Malate. Forms PYRUVATE and NADPH (used for fatty acid synthesis) via MALIC ENZYME.
What is the precursor to citrate in the CAC?
Oxaloacetate.
Give two important points about oxaloacetate
- ) Limiting concentration for the CAC
2. ) Precursor for gluconeogenesis (OAA –> Glucose)
What is the total ATP production from glucose? Show sources.
38 ATP MAX
The CAC: 24 ATP
PDH: 2NADH = 6 ATP
Glycolysis: 2NADH = 6 ATP, Substrate level = 2 ATP.
Where does gluconeogenesis take place?
The majority of reactions occur in the cytosol and mitochondria of LIVER CELLS, but it needs tissue with mitochondria, so NO RBC’s.
What is the purpose of gluconeogenesis?
Synthesis of glucose in order to maintain blood glucose within normal fasting range
- ) What is the normal fasting blood glucose range?
2. ) Postprandial?
- ) 70-100 mg/dL (approx. 5mM). Average is 83 mg/dL (4.6 mmol/L).
- ) <100 mg/dL (5.5 mmol/L) 2 hrs postprandial.
What are the main and secondary organs where gluconeogenesis takes place?
Main organ: LIVER. Kidney cortex during periods of severe hypoglycemia (fasting).
What is a prediabetes/diabetes FBS (i.e. hyperglycemia)?
> 126mg/dL
What is the average time it takes normal people to return to normal FBS after a meal?
2 hours
What serves as the major carbon source for gluconeogenesis?
Glycerol from triacylglycerides. It DOES NOT USE THE FATTY ACID PORTION because fatty acids are used for acetyl-CoA, which is KETOGENIC, not GLUCONEOGENIC. Glycerol is the 3 CARBON BACKBONE to fatty acids.
How is glycerol used in gluconeogenesis?
Glycerol is phosphorylated to glycerol 3-phosphate, and is then oxidized to Dihydroxyacetone phosphate (DHAP), then to G3-P in gluconeogenesis.
Which product of glycolysis is used in gluconeogenesis? How?
Lactate, a product of anaerobic glucose metabolism in the exercising muscles and RBC’s, is oxidized with lactate dehydrogenase to PYRUVATE (gluconeogenic).
How does lactate, from anaerobic glucose metabolism, get from its place of origin (exercising muscles and RBC’s) to the liver?
The Cori Cycle. Lactic acid from muscles is sent to liver, where it is converted to glucose and sent back to target tissues.
What is the major precursor to gluconeogenesis during prolonged periods of fasting? Where is it acquired? How does it get to the liver?
Gluconeogenic amino acids, e.g. Alanine, Glycine. They come from the hydrolysis of tissue proteins (muscle). It gets to the liver via the GLUCOSE-ALANINE CYCLE.
Why is alanine considered gluconeogenic? How?
Alanine can easily be converted to pyruvate using ALT (alanine aminotransferase). ALANINE IS THE CARBON SKELETON FOR PYRUVATE, i.e. alanine minus its amino group is pyruvate.
What two gluconeogenic precursors are most prevalent in the blood and can be measured at high levels?
Lactic acid, from the Cori Cycle. Alanine from the Glucose-Alanine Cycle.
How many reactions do gluconeogenesis and glycolysis share? Which reactions of glycolysis need to be bypassed for gluconeogenesis to occur?
They share 7/10 reactions.
- ) Glucokinase
- ) PFK-1
- ) Pyruvate kinase –> All 3 have large negative delta G
How many reactions/enzymes in gluconeogenesis are needed to bypass the irreversible glycolysis steps/enzymes? What are they?
4 reactions in gluconeogenesis are needed to bypass glycolysis.
- ) Pyruvate carboxylase and 2.) PEP carboxykinase are needed to bypass Pyruvate kinase of glycolysis.
- ) Fructose-1,6 bisphosphatase is needed to bypass PFK-1 of glycolysis.
- ) Glucose-6-phosphatase (ER membrane) is needed to bypass Hexokinase of glycolysis.
Describe the first bypass step and the enzyme used in gluconeogenesis, where does it occur? What coenzyme(s) is required? How is reaction/step regulated?
It occurs in the MITOCHONDRIA. Two new enzymes: pyruvate carboxylase (requires coenzyme BIOTIN, like all carboxylases) PEPCK.
Bypass pyruvate kinase: 1.) Pyruvate to oxaloacetate (carboxylation via pyruvate carboxylase REQUIRES BIOTIN AND 2 ATP), but oxaloacetate cannot exit mitochondrial membrane so… 2.) Oxaloacetate is converted to malate via cytoplasmic malatedehydrogenase (NADH used, opposite of CAC reaction). 3.) Malate exits membrane, converted BACK TO OXACLOACETATE (precursor to gluconeogenesis) via malate dehydrogenase (NADH made). 4.) Oxaloacetate to PHOSPHOENOLPYRUVATE (PEP) via PEPCK (PEP carboxykinase).
This step is regulated ALLOSTERICALLY by Acetyl-CoA, because increased Acetyl-CoA in the mitochondria indicate a metabolic state in which increased OAA is required. (HOW? Sort this out!)
What class of reaction replenishes oxaloacetate?
ANAPLEUROTIC reaction.
What can the replenishment of OAA during gluconeogenesis be used for?
1.) For gluconeogenesis, or 2.) To replenish the CAC.
What is the second enzyme used in the first bypass step of gluconeogenesis? What type of reaction is it? Where does it occur? What is required?
Enzyme #2 (PEPCK) for bypass step #1 of gluconeogenesis.
OAA to PEP via PEP Carboxykinase (PEPCK). It is a decarboxylation reaction (lose CO2) that forms HIGH ENERGY PEP, thus, it REQUIRES GTP. It can occur in the cytoplasm and mitochondria
What is the second bypass step of gluconeogenesis? What new enzyme is introduced? Describe its action. How is it regulated
i.e. what inhibits (2) and stimulates (2)?
Bypass of the IRREVERSIBLE PFK-1 reaction via HYDROLYSIS of Fructose 1,6-bisphosphate to Fructose 6-phosphate, using the enzyme Fructose 1,6-bisphosphaTASE (new enzyme). Pi (inorganic phosphate) is released.
This is an IMPORTANT REGULATORY SITE for gluconeogenesis.
It is INHIBITED BY 1.) HIGH AMP (low energy, the opposite of PFK-1), and 2.) INHIBITED by Fructose 2,6-bisphosphate (opposite of PFK-1).
Stimulated by 1.) GLUCAGON, and 2.) HIGH ATP.
What is the third bypass step in gluconeogenesis? What enzyme/type of enzyme is used? Where does the enzyme originate, i.e. which cells and which part of cells?
Bypass of hexokinase/glucokinase. Glucose 6-phosphate to Glucose + Pi, via enzyme Glucose 6-phosphaTASE (new enzyme). This reaction RELEASES FREE GLUCOSE INTO THE BLOOD.
Enzyme Glucose 6-phosphatase originates in the ER of LIVER cells.
How does glucose 6-phosphate get to ER of liver cell, where enzyme glucose 6-phosphatase converts it to glucose, and then into the blood stream as free glucose?
p. 231
1. ) Glucose 6-phosphate transported to lumen of ER by a translocase.
- ) Glucose 6-phosphate is dephosphorylated to free glucose by enzyme glucose 6-phosphatase in the membrane of liver cell ER.
- ) Glucose transported out of ER to cytosol by GLUT-7.
- ) Glucose transported out of liver to blood as FREE BLOOD GLUCOSE by GLUT-2
It terms of energy usage, what kind of reaction is gluconeogenesis? How much, if any, energy is needed for gluconeogenesis?
It is an ENDERGONIC reaction. It requires 2 ATP for pyruvate carboxylase, 2 ATP for glycerate kinase, 2 GTP for PEPCK, and 2 NADH for G-3-PDH. TOTAL requirements: 2 pyruvate, 4 ATP, 2 GTP, 2 NADH, and 4 H2O.
What is the delta G sign of gluconeogenesis? Why?
Negative delta G (spontaneous in the forward direction), because the enzymes used in the bypass steps have a negative delta G.
What are the regulators of gluconeogenesis?
- ) Hormonal regulation (insulin:glucagon ratio).
- ) Availability of gluconeogenic precursors.
- ) Allosteric activation enzymes.
- ) Energy availability.
How does glucagon regulate gluconeogenesis?
- ) Glucagon activates ADENYLATE CYCLASE which increases cAMP.
- ) Increased cAMP leads to INCREASE IN PROTEIN KINASE A activity.
- )Protein Kinase A (PKA) phosphorylates PFK-2, which decreases the activity of PFK-2.
- ) Phosphorylated PFK-2 IS INACTIVE (FAVORS GLUCONEOGENESIS).
- ) PFK-2 is bifunctional, when it is phosphorylated the PHOSPHATASE function (FBP-2, fructose bisphosphatase) is INCREASED.
- ) Activated FBP-2 decreases fructose 2,6-bisphosphate (at lower levels of fructose 2,6-BP, glycolysis is inhibited and gluconeogenesis is favored).
How does the availability of substrates/precursors regulate gluconeogenesis?
- ) High protein diet = glucogenic amino acids (Glycine and alanine) *While fasting, insulin decreases and, thus, INCREASES release of amino acids from muscle.
- ) Odd-chain fats (3, 5, 7, 9 carbons or greater) can be converted to succinyl-CoA, and then to OAA (which is gluconeogenic).
_____ -chain fats are not gluconeogenic, but do provide what? What else can the end product of fat metabolism (what is it?) be used for?
EVEN-chain fats are not gluconeogenic. But they provide the ATP needed for glucose synthesis.
Acetyl-CoA, the end product of fat metabolism, is NOT gluconeogenic, but can be used in the CAC to make gluconeogenic precursors, e.g. OAA.
What activates/inhibits the ALLOSTERIC controllers of gluconeogenesis? p.234
- ) Pyruvate carboxylase: Activated by increased [Acetyl-CoA] (occurs during fasting).
- ) Fructose 1,6-bisphosphatase: Inhibited by AMP (which activates PFK-1) and Fructose 2,6-bisphosphate. Thus, AMP stimulates pathways that oxidize nutrients to provide energy for the cell.
Under fasting conditions, where is most of the energy for gluconeogenesis derived from?
Fatty acid oxidation. It leads to Acetyl-CoA –> the CAC –> ETC –> ATP REMEMBER: 6 ATP needed for gluconeogenesis.
Describe Von-Gierke’s Disease, i.e. Glycogen storage disease Type 1a. Give nature of disease, symptoms, and treatments.
It is a deficiency of LIVER Glucose 6-Phosphatase, which allows the liver TO RELEASE SYNTHESIZE AND RELEASE GLUCOSE.
It increases LIVER GLYCOGEN STORAGE.
Pt’s present with: Hepatomegaly (enlarged liver), Severe fasting HYPOGLYCEMIA (lethargy, seizures, brain damage), hyperlipidemia and hyperuricemia (high uric acid).
Treatment: Frequent meals and nighttime glucose infusion.
Describe the effect of ethanol on gluconeogenesis. Where is ethanol metabolized and how?
95% of ethanol is metabolized in the liver. It is oxidized to acid-aldehyde using Alcohol DH, then to a carboxylic acid using Aldehyde DH (both using NADH as a cofactor), and then finally to Acetyl-CoA using Acetyl-CoA synthetase. LARGE AMOUNTS OF NADH IS REQUIRED.
LARGE AMOUNTS OF NADH INHIBITS GLUCONEOGENESIS.
How does ethanol inhibit gluconeogenesis? Symptoms?
Causes decrease in precursors to gluconeogenesis.
Large amounts of NADH (required for alcohol metabolism) causes Lactate dehydrogenase (LDH) to convert pyruvate to lactate, and OAA to Malate via malate DH. This is a loss of TWO important precursors to gluconeogenesis
Symptoms include: Low blood glucose–>rapid heartbeat. Increase in lactate = metabolic acidosis (compensated by rapid breathing).
Why is drinking methanol bad?
Methanol is converted to formaldehyde, which can cause blindness and can be fatal.
What are effects of alcohol metabolism and subsequent increased NADH/NAD+ ratio? (5 things)
- ) Inhibition of fatty acid oxidation cycle = Fatty liver and increased triglycerides.
- ) Increased triglycerides increases VLDL = hyperlipidemia
- ) Decreased CAC = increased acetyl-CoA = increased ketone bodies
- ) Increase in lactic acid = acidosis = decrease in uric acid excretion (i.e. increased uric acid) = GOUT.
- ) Increased risk of Hypoglycemia (risk increased in those taking insulin).
Describe the bonding in glycogen polymers
Alpha-1,4 linkages linearly. Alpha-1,6 linkages branching.
Is gluconeogenesis slow or fast to respond?
Slow to respond, but sustainable.
What is the bodies first source of blood glucose during fasting? Describe its response time and duration.
LIVER glycogen. Quick to respond, but limited in quantity. Usually lasts 16-18 hours.
Compare and contrast the two types of glycogen storage: A.) Liver B.) Muscle
Liver distributes to maintain blood glucose homeostasis, muscle keeps for self as energy for contraction
A.) Liver:
- )Largest single [glycogen] site, about 100g glycogen.
- ) LIVER glycogen used for blood glucose homeostasis.
- ) Regulated by insulin/glucagon, blood glucose, epinephrine.
- ) Usually lasts 16-18 hours fasting
B.) Muscle glycogen:
- ) More TOTAL muscle glycogen, must liver largest SINGLE storage site.
- ) Used ONLY by muscles for energy for contraction.
- ) Glycogenolysis stimulated by Ca2+ and AMP (low energy), epinephrine (SNS).
Give 4 reasons why glycogen is a good storage device for glucose
- ) Can be quickly mobilized when needed.
- ) Can be metabolized anaerobically (because it shares pathways with glycolysis.
- ) Can be used to maintain blood glucose homeostasis (liver).
- ) Does not create an osmotic problem for cell as would glucose monomers (hydroxyl groups on glucose attract water).
Describe the different muscle fibers (3) with regards to their energy needs
- ) Type 1 (red fibers): Slow twitch. Long-term activity (endurance, marathons). AEROBIC metabolism (thus, pyruvate –> CAC –> ETC). No lactic acid buildup. Have mitochondria.
- ) Type 2B (white fibers): Fast twitch. Short-term activity. Anaerobic, little mitochondria. Most GLYCOGEN STORES in these fibers. Less myoglobin for O2 delivery (reason for anaerobic metabolism). Glycolytic pathway favors pyruvate –> Lactate.
- ) Type 2A (intermediate): Between slow and fast twitch. Both aerobic and anaerobic. NORMAL MUSCLE.
Describe the initiation of glycogen synthesis.
Glucose 6-phosphate –> Glucose 1-phosphate –> UDP-glucose, this is the form in which more sugars are added. The first sugar that is added is GLYCOGENIN (a protein with a sugar attached via TYROSINE residue), and UDP is discarded. Each subsequent glucose molecule added bears a UDP which is discarded after attachment of the glucose molecule. The enzyme used to add glucose in the alpha-1,4 linear fashion is GLYCOGEN SYNTHASE. Glucose added 1,6 (branching) uses the enzyme 4,6 TRANSFERASE.
List the steps and enzymes associated with glycogen synthesis
- ) Glucose 6-P –> Glucose 1-P (mutase).
- ) Glucose 1-P + UTP –> UDP Glucose (activated glucose) + PPi.
- ) Glycogen synthase: UDPP glucose is used to add units of glucose to the non-reducing end of an existing glycogen polymer: alpha-1,4 linkages.
- ) Branching enzyme: alpha-1,6 linkages.
What end of glucose is considered the non-reducing end?
the carbon 4 position.
What is the benefit to branching in glycogen?
Increases the number of sites for synthesis and degradation.
Increases the number of non-reducing ends available for degradation when needed.
Increases solubility. Amylopectin has branching, amylose has straight chains. STRAIGHT CHAINS ARE LESS SOLUBLE
When is glycogen synthase activated or inhibited.
- ) Activated: When well fed.
2. ) Inhibited: During fasting.
How is glycogen synthase regulated?
Allosteric: positive regulation with Glucose 6-phosphate
Covalent: (-)dephosphorylate/(+)phosphorylate via hormonal regulation by glucagon/insulin.
Explain allosteric regulation of glycogen sythase
Activated under well-fed conditions by Glucose 6-phosphate, a product of glucokinase/hexokinase. It is activated in both the liver, and in muscle.
Explain covalent regulation of glycogen synthase via insulin (2 forms of the enzyme)
- ) Active (dephosphorylated): Glycogen synthase A or I (activated).
- ) Inactive (phosphorylated by glycogen synthase kinase (GSK3)): Glycogen synthase b or D (Dephosphorylated).
Describe how insulin activates glycogen synthase (8 steps).
- ) Insulin binds the receptor –> activation via autophosphorylation.
- ) Leads to activation of IRS (insulin receptor substrate) via phosphorylation of Tyr residues.
- ) Activated IRS leads to activation of PI-3 Kinase
- ) Leads to phosphorylation of PIP2 to PIP3
- ) Leads to activation of AKT (protein kinase B)
- ) AKT/PKB phosphorylates (inactivates) glycogen synthase kinase (GSK3)
- ) Inactivated GSK3 does not phosphorylate glycogen synthase (dephosphorylated glycogen synthase is ACTIVE).
- ) PP1 (phosphatase) dephosphorylates glycogen synthase, allowing it to produce GLYCOGEN.
Describe the 2 types of glycogen storage diseases (GSD)
- ) GSD type 0: Glycogen synthase deficiency. Fasting HYPOglycemia. Manage with frequent meals and eating uncooked cornstarch. Autosomal recessive.
- ) GSD type IV: Branching enzyme deficiency (Andersen Disease). Leads to the insolubility in glycogen, due to no branching and long strands. Glucose from glycogen cannot be released as quickly. Causes hepatosplenomegaly. Causes early death (by 5 years of age).
- ) Where do the enzymatic reactions of glycogenolysis occur?
- ) What is the main enzyme of glycogenolysis? Coenzyme?
- ) Where does it cleave?
- ) What is the product?
1.) Cytosol.
2.) Phosphorylase. Coenzyme is Pyridoxal phosphate (vitamin B6).
3.) It cleaves at alpha-1,4 linkages using Pi from non-reducing ends until it reaches 4 glucose units from a branch point (where a debrancher acts).
4.) The product is Glucose 1-P.
THEN TRANSFERRED IN TO ER LIKE IN GLUCONEOGENESIS!
Describe the debranching enzyme
Bifunctional protein with two actions.
- ) 4:4 TRANSFERASE: Transfers 3 glucose units of a 4-membered branch to another branch to make an alpha-1,4. It leaves one singular glucose behind (the 1-4 branch point).
- ) 1:6 GLUCOSIDASE: The second function cleaves the remaining single glucose to be released as free glucose.
What 2 steps in glycogenolysis happens after glycogen phosphorylase creates Glucose 1-P?
- ) Phosphomutase creates Glucose 6-P
2. ) Glucose 6-phosphatase creates free glucose.
Explain the glycogen storage diseases (degradation)
1.) Type 1a (Von-Gierke’s Disease): Deficiency of liver G-6Ptase. RESULTS IN: increase in liver glycogen stores, severe fasting hypoglycemia, hepatomegaly, hyperlipidemia (body releases fats b/c it cannot unlock glucose), lactic acidosis (forces glucose through glycolysis = lactate), hyperuricemia.
TREAT WITH: Frequent meals.
2.) Type 2 (Pompe Disease - Acid Maltase Deficiency): ONLY GLYCOGEN STORAGE DISEASE ASSOCIATED WITH LYSOSOME (accumulation of glycogen in the lysosomes). Autosomal recessive.
SYMPTOMS: CARDIOMEGALY (Pompe affects the PUMP). Normal blood glucose and glycogen. Muscle weakness.
AFFECTS: Liver, muscle, and heart.
TREAT WITH: Myozyme.
3.) Type 3 (Cori Disease - Debranching enzyme deficiency): Accumulation of abnormal structured glycogen having very short outer chains.
SYMPTOMS: Heptamegaly, fasting HYPOglycemia, myopathy. Type A has liver and muscle deficiency, type B has liver only.
TREATMENT: Frequent high carb meals, cornstarch. HIGH PROTEIN DIET because it drives gluconeogenesis (G 6-Ptase functioning well).
mnemonic -> ABCD: Anderson’s Branching, Cori Debranching
4.) Type 5 (McArdles Disease - Skeletal muscle phosphorylase deficiency, myophosphorylase): NORMAL LIVER enzyme, so no fasting HYPOglycemia b/c liver enzyme is ok.
SYMPTOMS: Skeletal muscle cramps, NO RISE in blood lactic acid after exercise because no glycolysis. MYOGLOGINemia or uria = Myoglobin in urine (red urine) or blood.
5.) Type 6 (Hers Disease - Liver phosphorylase deficiency): Extreme HEPATOMEGALY and mild hypoglycemia
Describe the allosteric regulating mechanisms of glycogen metabolism
- ) Glucose 6P, muscle and liver (well-fed state): Inhibition of phosphorylase (lysis). Activation of synthase (synthesis).
- ) Glucose (liver): Inhibition of liver phosphorylase (lysis)
- ) ATP, muscle and liver (high-energy): Inhibition of phosphorylase (lysis). DON’t NEED GLUCOSE IF ENERGY HIGH.
- ) AMP (low energy), muscle reacts: Activates phosphorylase.
- ) Calcium (muscle): Activation of muscle phosphorylase kinase –> (+) glycogenolysis.
Through what protein does phosphorylase kinase bind calcium?
Calmodulin
Which hormone activates glycogenolysis in 1.) liver and 2.) muscles
- ) Glucagon for liver
2. ) Epinephrine for muscles.
Name two ways glycogen phosphorylase can be activated WITHOUT being phosphorylated
- ) Calcium binds calmodulin and activates phosphorylase kinase, which then activates glycogen phosphorylase.
- ) AMP activates glycogen phosphorylase.
List the steps in the glycogenolysis cascade (5)
- ) G protein activated (glucagon in liver, epi in muscle)
- ) Adenylate cyclase
- ) cAMP –> PKA
- ) phosphorylation
- ) GLYCOGENOLYSIS
List the characteristics of glycogen stores when 1.) feeding and 2.) Fasting
- ) Feeding (5)
- High insulin, low glucagon
- activation of PKB
- inactivation of GSK3
- Phosphorylase not activated
- Glycogen synthesis increases - ) Fasting (5)
- Glucagon high, insulin low
- Activation of PKA
- Activation of phosphorylase
- Inactivation of GS
- Glycogenolysis (lasts 16-18 hours)
What is the composition of sucrose?
Glucose + fructose
What is considered the sweetest of the monosaccharides?
Fructose
How does the rate of fructose metabolism compare to glucose metabolism? Where is it metabolized? How?
Fructose is faster. Metabolized only in the liver. Fructokinase (low Km for fructose). It is faster because it BYPASSES PFK-1.
Why does fructose create less ATP that glucose? What enzyme is different in this pathway?
Because it produces F1-P, not F2-P.
The different enzyme is ALDOLASE B not A as in glucose
What is the consequence of lacking fructokinase?
Essential fructosuria: Benign. Fructose cannot be metabolized. Fructose in urine. DETECTED AS A REDUCING SUGAR (BENEDICT’s TEST).
What causes and what is the consequence of hereditary fructose intolerance (fructose poisoning)?
Caused by absence of ALDOLASE B, leads to intracellular trapping of fructose 1-P. Seen in babies after they start on formula. It DECREASES GLUCONEOGENESIS = HYPOglycemia.
It can cause hepatic failure and death. TREAT by removing fructose and sucrose from the diet.
What enzyme converts glucose to sorbitol? What is the change in functional groups? What is the cofactor?
Aldose reductase. Aldehyde –> Alcohol. The cofactor is NADPH.
Compare the sweetness of sorbitol to sucrose. What medical symptoms can it cause?
60% as sweet as sucrose. It can cause diarrhea, IBS, bloating, flatulence.
Describe sorbitol metabolism in male genitalia.
Called the “Polyol Pathway”. IN THE SEMINAL VESICLES: Aldose reductase converts glucose to sorbitol. In the TESTES: Sorbitol is converted to Fructose (a major energy source for spermatozoa) by sorbitol reductase.
Describe sorbitol metabolism in the lens, nerve, and kidneys.
Glucose converted to sorbitol by aldose reductase. Sorbitol DH converts sorbitol to fructose. Without/[low] sorbtiol DH = high [glucose] = high [sorbitol] = osmotic pressure = SWELLING. COMMON IN DIABETICS, this causes peripheral neuropathy, diabetic neuropathy, macular edema = poor vision.
Name two sugars that are non-insulin dependent
Fructose, galactose
Outline the steps of galactose metabolism
- ) Lactase (beta-galactosidase) in the intestinal mucosa converts lactose to galactose and glucose.
- ) Non-insulin dependent transport (make galactitol via aldose reductase)
- ) Galactose to Galactose 1-P via galactokinase using ATP
- ) Gal 1-P to UDP-Galactose via galactose transferase (GALT)
* UDP-galactose can be used to make glycoproteins, glycolipids, etc.* - ) UDP-galactose to Lactose via lactose synthase.
What are some enzyme deficiencies in galactose metabolism (2)?
- ) Galactose kinase deficiency: Galactoseuria (galactose in urine), galactitol accumulation.
- ) Galactosemia: Uridyltransferase deficiency. Seen in homozygotes. Gal 1-P increases in tissues and Gal seen in blood and urine. CONSEQUENCES: Mental retardation in infants. Liver, kidney damage and cataracts.
Describe the two types of lactose intolerance.
- ) Primary lactase deficiency
2. ) Secondary lactase deficiency: Due to intestinal injury or antibiotics.
Describe lactose synthesis
Produced by mammary gland under hormonal control (produced after progesterone levels drop after delivery). Requires two proteins: Protein A and B. Protein B is made after low progesterone, protein A is always present.
Describe the entry points for fructose, mannose, and galactose in the glycolytic pathway.
Already done. See notes.
Describe the main properties of the pentose phosphate pathway (PPP).
Different parts, energy use/consumption, products
- 2 parts*
1. ) Pt 1, Oxidative reaction (irreversible):
2. ) Pt 2, Nonoxidative (reversible) - No ATP used or made.
- Main products: NADPH. Ribulose 5-P for nucleotide synthesis (pt 1).
- Present IN ALL CELLS, MITOCHONDRIA NOT NEEDED.
Describe the oxidative reaction in the PPP.
Glucose 6-P to Ribulose 5-P + 2 NADPH via GLUCOSE 6-P DH (G6PD)
What is NADPH used for (5 things)?
- ) Biosynthesis of fatty acids, steroids, cholesterol.
- ) Reduction of H.Peroxide and glutathione. Removes reactive oxygen species.
- ) Removes toxins using cytochrome P450.
- ) Helps white cells phagocytize bacteria.
- ) Synthesis of Nitric Oxide (endogenous vasodilator): NO synthase.
Describe the non-oxidative part of PPP. What does it use/create?
Uses 3,4,5,6, and 7 carbon sugars. Interconverts between them using TRANSALDOLASE and TRANSKETOLASE, making glyceraldehyde (3C).
Main products: Ribose 5-P, via isomerase, for nucleotide synthesis. Fructose 6-P and glyceraldehyde 3-P for glycolysis, gluconeogenesis, etc.
What is the cofactor for TRANSKETOLASE? How is this clinically relevant?
Thiamine. Use transketolase to see if there is a deficiency in thiamine.
What are the consequences of a thiamine deficiency?
Wernicke encephalopathy. Can also present in alcoholism.
How is PPP regulated? 1.) primary regulatory step 2.) inhibition 3.) activation
- ) Glucose 6-P DH is Primary regulatory step.
- ) Product inhibition by high [NADPH] -> competitive inhibition. In most cases, this is slowed down because NADPH is higher
- ) It is activated when NADPH is needed (for lipid synthesis when WELL FED). INSULIN (activates PPP) leads to increased G6PD expression.
What is the consequence of G6PD deficiency? IMPORTANT
Hemolytic anemia, lysing of RBCs.
Explain the roles of G6-P
G6-P –> F6-P –> glycolysis –> energy
- -> Ribose 5-P --> PPP
- -> G1-P --> Glycogen
- -->
Give two main sources of NADPH
- ) 2NADPH from Glucose 6-PDH and 6-P Gluconate DH of the (PPP)
- ) Malic enzyme: L-malate –> pyruvate + NADPH + CO2
1-3.) Name and describe 3 ROS. 4.) Why are they bad?
- ) Superoxide anion (O2-): Electrons from Coenzyme Q to O2.
- ) H.Peroxide (H2O2): Produced by peroxysomal enzymes in peroxisomes.
- ) Hydroxyl radical (OH-): Produced from a metal ion-catalyzed reaction of superoxide and h.peroxide.
4.) Damage membranes, proteins, gradients, cells, DNA, MetHb and Hb (Heinz bodies).
How can ROS be formed? Are they ever good?
UV light can form ROS. They can be bacteriocidal, which is good.
Name and explain 3 enzymatic defense against ROS
1.) Superoxide dismutase (SOD): MnSOD = mitochondrial enzyme, CuZnSOD = mainly cytoplasmic, lysosomes, peroxisomes, nucleus.
O2- –> H2O2
- ) Gluathione peroxidase (GPx): cytosolic. Cysteine is important when in -SH form. H2O2 –> H2O.
- ) Catalase (CAT): Peroxisomes. H2O2 –> H2O + O2
Name enzyme associated with glutathione and cofactors and purpose
Glutathione reductase, with NADPH cofactor. Glutathione MUST BE IN ITS REDUCED FORM TO WORK. Thus, it needs NADPH. This prevents hemolysis and Heinz bodies. PPP IMPORTANT IN RBC in avoiding ROS.
NADPH and Cyto P450?
For steroid synthesis detoxifying drugs MEOS Bile acids Vit D hydroxylation.
Where and how is NADPH used to kill bacteria? What actually kills the bacteria?
Where: Phagocytic cell.
How: NADPH needed to make ROS (superoxide radical) via NADPH oxidase. This is called a RESPIRATORY BURST!
Actually kills: HOCL (myeloperoxidase)
What is Chronic Granulomatous Disease?
NADPH oxidase deficiency: Chronic bacterial infections.
How does NADPH contribute to smooth muscle dilation?
NADPH is needed, along with NO synthase, to form nitric oxide, which is for smooth muscle dilation. IT DECREASES SMOOTH MUSCLE CONTRACTION (viagra inhibits breakdown of cGMP so maintains erection=dilation)
Nitric oxide functions
Vasodilator, neurotransmitter, macrophage bactericidal, inhibitor of platelet aggregation.
Consequence of G6-PD deficiency. What is it? How does it present?
Not enough NADPH. Increase in ROS = hemolysis, hemolytic anemia, jaundice. Hepatosplenomegaly. Heinz bodies.
Inherited, x-linked.
It presents with hemolytic anemia, jaundice.
Name 3 drugs that can precipitate a G6PDH deficiency
AAA:
- ) Anti-malarial –> quinine
- ) Antibiotics
- ) Antipyretics (not acetaminophen).
* Mothballs, fava beans*
Tumors and associated cells upregulate which isoform of which transporter?
Lactate symporters (lactate with H+) –Monocarboxylate transporters (MCT). •Isoform –> MCT4
What allows for the high rate of glycolysis seen in cancer cells?
Reoxidation of NADH –> NAD+ in Lactate Synthesis
What increases (5) and decreases (2) are seen with Hypoxic Inducible Factor 1-alpha (HIF1-alpha)
Increases: • glycolytic gene enzyme expression • GLUT 1 • GLUT 3 • Lactate Dehydrogenase (LDH) • MCT4
Decreases:
• PDH
• Number of mitochondria
What increases (1) or decreases (2) with p53 tumor suppressor?
Increases:
• Expression of Glu transporter
Decreases:
• Proper formation of Complex IV (Cytochrome C Oxidase)
• Decrease in ETC
What types of upregulation do the following cause:
• PI3K/Akt1-PKB (2)
• cMyc (4)
PI3K/Akt1-PKB causes upregulation of:
• GLUT-1
• HK2 (hexokinase-2)
cMyc causes upregulation of: • GLUT-1 • HK2 (hexokinase-2) • PKM2 (pyruvate kinase isoform) • LDHA (L4-skeletal muscle)
What are five glycolytic targets for possible cancer therapy?
- GLUT-1
- HK2
- PKM2
- LDHA (converts pyruvate to lactate)
- H+ transporters
What are the five consequences of lactate export from cancer/tumor cells?
- ) Increased intracellular pH (more alkaline)
- ) Decreased extracellular pH (more acidic)
- ) Increased HIF-1 alpha = increased angiogenesis in tumor
- ) Immune suppression; T-cell proliferation, cytokine production, and cytotoxic activity of CD8+ cell (tumor infiltrating lymphocytes)
What are five things that are upregulated with lactic acidosis?
- ) GLUT-1
- ) HK2 (glycolysis regulatory enzyme)
- ) PKM2 (also regulatory enzyme)
- ) LDHA (converts pyruvate to lactate)
- ) MCT4 (transports lactate out of cells)
