Metabolism Lectures 1 and 2 Flashcards
What is the common “product” and fuel of metabolism?
Acetyl Co A
- all metabolic components give rise to acetyl-coA
- to be used in CAC (Citric Acid cycle) for energy generation
- CAC is a combustion reaction and produces ATP, H20 and CO2
How are fatty acids stored?
What are they converted to after beta oxidation? Only cells with what?
- stored as triacylglycerol
2. Acetyl coA, only cells with mitochondria
Amino Acids:
- Storage
- Catabolism into what?
- what byproduct is made?
- Storage - Proteins
- Catabolism into what? –> Acetyl Co A
- what byproduct is made? Ammonia
What are the preference of energy for the following:
- Liver
- Adipose tissue
- Skeletal Muscle (rest & exertion)
- Heart
- Brain (fed, starved)
- Liver - fatty acids, glucose, AA’s
- Adipose tissue - fatty acids
- Skeletal Muscle
rest - fatty acids
exertion - glucose - Heart - fatty acids
- Brain (fed, starved)
fed: glucose
starved: ketone bodies/glucose
What is the driving force for the coordination of metabolism?
Provide glucose for the brain
Calculate the following:
500 kcal/day, of which 10 g of dry protein, what is the percent in total calories?
10g * 4 g (chart) = 40 kcal
40kcal/500 kcal/day * 100 = 8%
What is the source of the following carbs and state the enzyme that digests them:
- Amylose
- Sucrose
- Lactose
- Fructose
- Glucose
- Amylose
- potatoes, rice, corn, bread
Enzyme: Maltase - Sucrose
- table sugar, deserts
E: Sucrase - Lactose
- milk & products
E: Lactase - Fructose
- fruit, honey
E: - Glucose
- fruit, honey, grapes
What type of starch linkages does pancreatic amylase break down?
alpha 1,4 linkages
What is the main cause of lactose intolerance?
What expresses the LCT gene?
How is his different from milk allergy?
Deficiency in Lactase Enzyme production which breaks down lactose due to environmental factors, decline due to aging, damage to mucosa
Lactose is not sufficiently hydrolyzed/absorbed and remains in intestine
- causes the osmosis of water into the intestine
- intestinal bacteria (colonic) metabolize the lactose to lactic acid and mixtures of hydrogen, carbon dioxide, and methane gas
- result is bloating, flatulence, and diarrhea
2. LCT gene is expressed by intestinal epithelial cels and produces the lactase enzyme
3. Milk allergy is due to allergic reaction to alpha-S1 casein
(secondary lactose intolerance can be found in children with gastroenteritis = damage to intestinal lining)
What cells secrete insulin and glucagon? Under what conditions?
- insulin = beta cells of pancreas
- when glucose is high - Glucagon = alpha cells of pancreas
- when glucose is low
What is glycogenesis?
GLycolysis?
Gluconeogenesis?
Glycogenesis?
- Breakdown of glycogen to glucose 1 - phosphate and glucose in the liver and muscles by Glycogen phosphorylase
- Single glucose makes net 2 ATP, 2 NADH, and 2 H20
- generation of glucose from non-carb substrates (pyruvate or lactate)
- occurs in hypoglycemia (glucagon increases) - Formation of glycogen from glucose (hyperglycemia - insulin increases)
What is the level of glucose that causes hypoglycemia? What is the result
What about for HYPERGLYCEMIA?
Which leads to Type 2 Diabetes Mellitus?
- 60 mg/dL
- neurological issues, coma, death - 110 mg/dL
- lead to Type 2 Diabetes Mellitus
What carbohydrate metabolic pathway do RBC’s rely on?
Glycolysis since no mitochondria
What are the 2 types of glucose transportation?
- Facilitated Diffusion
- Secondary Active Transport via Na - Glu - Transport
- using energy gradient of Na
State the km, affinity, and max for the following:
- GLUT 1, 3, an 4
- GLUT 2
- GLUT 1, 3, an 4
- LOW km
- low max
- high affinity! - GLUT 2
- high km
- high max
- LOW AFFINITY
* * two sided**
State the following for GLUT 2 and GLUT 4
- Insulin dependent/independent
- Where are they found?
- bidirectional?
- High or low concentrations of glucose
GLUT 2:
- Insulin Independent
- low affinity for glucose - Liver, pancreatic beta cells, kidney, small intestine
- BIDIRECTIONAL
- sees HIGH concentrations of glucose
GLUT 4:
1. Insulin DEPENDENT
(affected in Type 2 Diabetes Mellitus)
2. Heart, Skeletal Muscle, Adipocytes!!!!
3. not bidirectional
4. HIGH affinity for glucose and sees LOW CONCENTRATIONS
What are the 3 important steps of glycolysis?
- Priming stage (ATP INVESTMENT)
- conversion of glucose to G-6-P (cannot reverse after this) - Splitting Stage
(aldolase A splits F-2,6,-BP to DHAP and Gly-A-3-P) - Oxidoreduction -phosphorylation stage (ATP EARNINGS)
- Where does glycolysis occur? Which cells?
- What is the end result
- When is glucose trapped in the cells ? (which step)
- What mediates the most highly regulated part of glycolysis?
- Cytoplasm, all cells
- 4 atp (2 Net ATP), 2 NADH, 2 H20
- when Glucose is converted to G-6-P (phosphorylated)
- Aldolase A (splitting step)
What enzyme deficiency causes hemolytic anemia?
- Pyruvate Kinase
- folded improperly
- cannot bind well to Pyruvate Enolase Phosphate (PEP)
- thus small amount of ATP is made from glucose
- the ATP cannot be used for Na-K ATPase pump
- Na accumulates in the cell
- cell is abnormally strutted and gets stuck in capillaries
- macrophages lyse these cells
- premature death
What are the 3 key enzymes in glycolysis?
- Hexokinase/Glucokinase
- PFK-1
- Pyruvate Kinase
When does substrate level phosphorylation occur?
When Gly-3- P is converted to 1,3, BPG
What are the 3 types of regulation of enzyme activity?
- Allosteric regulation
- Covalent Modification
(phosphorylation, de phosphorylation) - Induction/Repression of Enzyme synthesis (via Insulin and Glucagon)
Hexokinase:
- Present in which cells?
- What ALLOSTERICALLY inhibits it?
- Is it made at a constant amount?
- What is the km (low or high) for glucose? (saturated at low or high levels)
- Handles high or low levels of glucose?
- ALL cells
- allosterically inhibited by its product G- 6 - P
- CONSTANT, non-inducible, constitutive
- LOW km (saturated at low levels of glucose)
- handles low levels
Glucokinase:
- Present in which tissue cells? (WHERE in cell)
- what decreases its activity by translating it back to the nucleus?
What increases its activity?
- Is it made at a constant amount? (inducible or not? hormone?)
- What is the km (low or high) for glucose? (saturated at low or high levels)
- Handles high or low levels of glucose?
- Pancreas and liver
- in nucleus of cell - F - 6 - P
GLUCOSE allows it to leave the nucleus
- INDUCIBLE by insulin
- HIGH km for glucose
(not saturated at normal physiologic conditions)
- handles HIGH levels of glucose in the liver
What activates PFK- 1?
What is this enzyme formed from?
Which enzyme regulates its activity?
What hormones inhibit this enzyme?
- F- 2,6 - BiP
- formed only when glucose and insulin are high - F-6 - P
- PFK 2
- Glucagon and Epinephrine
(via PKA)
What inhibits PFK - 2?
How?
What enzyme does it regulate?
PKA from glucagon and epinephrine
by phosphorylation
- has a kinase and phosphatase domain
(kinase is inactivated when it is phosphorylated)
- therefore it inhibits F-2,6 BiP
In the liver, only ______ activity is inhibited by glucagon and epinephrine
PFK - 2
What allosterically regulates PFK - 1? (3)
Which are negative inhibitors an which are positive?
What enzyme SPECIFICALLY regulates PFK- 1??? (test)
- ATP (negative)
- Citrate (negative)
- AMP (positive)
** F - 2,6 - BiP
(Fructose 2,6, BiP) = (+) **
via PFK - 2!!
How do glucagon and epinephrine indirectly regulate PFK-1?
Glucagon and Epinephrine phosphorylate the kinase domain of PFK -2 (inactivating it) and thus reduce the phosphorylation and formation of Fructose - 2,6, BisPhosphate!
- thus PFK - 1 cannot be activated
How does epinephrine affect glycolysis in the heart?
Stimulates glycolysis
- no glucagon receptors in heart and skeletal muscles
How does epinephrine act in heart and skeletal muscle?
Specifically, which enzyme is activated by epinephrine in heart and skeletal muscle, that is usually INHIBITED by epinephrine (in liver)?
Activates PFK - 2 and glycolysis
- PFK - 2 different form in heart and skeletal muscle
- lacks a hydroxyl group on kinase domain, but has one on phosphatase
- thus phosphorylation causes the ACTIVATIOn of kinase domain and inhibits phosphatase activity
- which allows phosphorylation of F,6 P to form F - 2,6 - BiP
- What activates pyruvate kinase
- What 2 things inhibit it
- What can phosphorylate it via PKA and inactivate HEPATIC pyruvate kinase?
- What clinical disease can result in genetic deficiency of Pyruvate kinase?
- Fructuse -1,6 phosphate
- ATP and alanine
- Epinephrine Glucagon
- Hemolytic Anemia
Where are the only place glucagon receptors are found?
Liver only!
- actions are limited here
Where is epinephrine released from? Where are its receptors?
Are its actions limited?
- Adrenal Medulla
- Hepatocytes, skeletal, heart muscle, adipose tissue
- NOT limited to th liver
What are the 2 steps where glucagon regulates hepatic glycolysis via covalent modification?
- PFK - 1
(via phosphorylation and inhibition of PFK-2, less F - 2,6 BiP, and more F-6 - P
- F -2,6 - Bip in low amounts cannot activate PFK-1 - Pyruvate kinase
- phosphorylated by PKA
What enzyme is needed to convert pyruvate to lactate?
What is oxidized?
- Lactate Dehydrogenase
2. NADH is oxidized to NAD+
There are 2 LDH isozymes. Where is the following present, and does it prefer conversion of lactate to pyruvate or vice versa?
- M4
- H4
- M4
- skeletal muscle
- prefers to catalyze PYRUVATE TO LACTATE
- high bursts of energy
- reason that we get muscle cramps is due to lactate build up and thus lactic acidosis
- H4
- HEART muscle
- lactate to pyruvate for sustained production of energy
What catalyzes the formation of Pyruvate to Acetyl Co A?
Pyruvate Dehydrogenase (PDH)
How is epinephrine activity act n heart muscle PFK-2?
ACTIVATES IT!!!
- unlike hepatic epinephrine
- phosphorylates the phosphatase domain and inactivates phosphotase activity
- thus only kinase is active
- INCREASED PFK - 2
- and increased Fructose 2,6 - Bisphosphate
A deficiency in PDH mainly affects which tissues?
Brain and heart
- inable to make Acetyl CO A from pyruvate
What mimics a PDH deficiency?
Poisoning with Arsenic
- pyruvate and lactate accumulate in the blood and causes lactic acidosis
What inhibits PDH? (how specifically)
What doesn’t?
- NADH and Acetyl CoA inhibit it!!!
- allosteric inhibition
- covalent modification via kinase activity
2.NOT regulated by glucagon and epinephrine inhibit it through ALLOSTERIC REGULATION
What does Hexokinase/Glucokinase convert?
PFK-1?
Pyruvate kinase?
- Glucose to G-6-P
- F-6-P to F-1,6-Bi P
- PEP to Pyruvate
Glucagon and Epinephrine inhibit which type of glycolysis specifically?
Which 3 enzymes do they repress the synthesis of?
HEPATIC
(eppinephrine stimulates skeletal and heart muscle glycolysis)
- Glucokinase!!!
- PFK-1
- Pyruvate Kinase
What are the two ways that accumulation of the end-products of PDH mechanism inhibit it?
covalent Modification
Allosteric Inhibition
What does PDH require to be active?
Vitamin requirement!
- Thiamin (B1)
- Pantothenate (B5)
- Riboflavin, Niacin
Under anaerobic conditions how much ATP and NADH is produced?
2 ATP
NO NADH
What 2 enzymes are deficient in Galactosemia?
Which is most common and severe?
What accumulates?
What does it lead to?
What accumulates?
- Galactokinase AND
Galactose 1 - Phosphate Uritidyl transferase - Gal- 1-P- UTD
- Galactitol
- Cataracts, hepatic dysfunction , brain dysfunction
- Gal- 1 - P accumulates in Gal - 1 - P UTD deficiency
What is the cause of Hereditary Fructose Intolerance?
Genetic deficiency (recessive) of Aldolase B
What are the various fates of pyruvate?
- Alanine (transamination)
- Oxoloacetate (pyruvate carboxylase)
- Lactate (lactate dehydrogenase)
- TCA cycle (pyruvate dehydrogenase)
What builds up in Pyruvate Carboxylase deficiency?
What increases in PDH deficiency?
Pyruvate carboxylase genetic deficiency leads to increase blood
- Alanine
- Lactate
- Pyruvate levels.
Diagnosis: Developmental delay, recurrent seizures, and metabolic acidosis.
PDH:
1. Pyruvate and Lactate concentration increases
Diagnosis:
reduced head circumference (microcephaly), poor muscle coordination and mental retardation
** cannot go forward with the Citric Acid cycle***
What must be constantly regenerated to maintain glycolytic flux?
NAD+
What supplies a steady state of NAD+?
3
- Gly A- 3 - Phosphate DEHYDROGENASE reaction
- produces NAD+ - Anaerobic respiration replenished NAD+
- through reduction reaction leading to lactate or ethanol production
3.AEROBIC respiration replaces NAD+ through a metabolite shuttle system since NADH cannot cross the mitochondrial membrane
What are the 3 main generators of NAD+? (and state if it takes place in cytosol or mitochondria)
- Lactate Dehydrogenase (cytosolic)
- Malatate - Aspartate Shuttle (cytosol & mitchondria)
- Glycerol - Phosphate Shuttle
(cytosol & mitochondria)
This is because the mitochondrial inner membrane is impermeable to NADH.
What enzyme catalyzes the conversion of pyruvate and coenzyme A to acetyl coA?
What vitamin cofactors are required?
Pyruvate Dehydrogenase (PDH)
- Thiamine (TPP, B1)
- Riboflavin (FAD, B2)
- Niacin (NAD, B3)
- What vitamin & coenzyme is required to activate PDH?
- Dihydrolipoyl transacetylase - E2
- Dihydrolipoyl Dehydrogenase - E3?
- Thiamine –> Thamine (B1)
- Lipoate CoaA –> Pantothenate (B5)
- FAD - Riboflavin (B2)
NAD - Niacin (B3)
What occurs in Lactate Dehydrogenase A Deficiency (LDHA)?
- What is limiting?
- What cannot be made
- What rxn. is inhibited?
Level of NAD+ becomes limiting during exercise
- cannot make lactate from pyruvate
- cannot move through Gly-A-3- Dehydrogenase reaction!!
If there are low levels of NADH, what formation is decreased?
LACTATE
Galactosemia is caused by a deficiency in what?
What 2 substances accumulate?
UTD - Glc (and sometimes Galactokinase)
- Galactitol and Gal - 1- P accumulate
Hereditary Fructose intolerance causes an accumulation of fructose which leads to what? (3)
- High uric acid
- High Lactic acid
- Fructose Toxicity
