Barbosa's Key Terms Flashcards
What enzyme in glycolysis does fluoride inhibit?
Enolase; Water fluoridation reduces lactate production by mouth bacteria, decreasing dental caries
What happens in exercising muscle when NADH production exceeds the oxidative capacity of the respiratory chain?
Pyruvate is reduced to lactate via lactate dehydrogenase
Where is the reduction of pyruvate to lactate likely to happen?
Lens and cornea of eye, kidney medulla, testes, leukocytes and RBCs
What causes cramps during intense exercise?
Lactate build-up in muscle lowers intracellular pH
What is lactic acidosis?
Elevated [lactate] in plasma (a type of metabolic acidosis) where there is a collapse of circulatory system, such as MI, PE, and uncontrolled hemorrhage
What is glycolysis?
The hub of carbohydrate metabolism
- ALL sugars can be converted to glucose
- End product = Pyruvate
The glycolytic pathway is employed by ___ _____ for oxidation of glucose to provide _____ and ______ for other metabolic pathways.
all tissues; energy (ATP); intermediates
What is the first step of glycolysis?
Phosphorylation of glucose
- Glucose -> G6-P
- Irreversible; traps sugar in cytosol
What is the second step of glycolysis?
G6-P -> F6-P
-Enzyme: Phosphoglucose isomerase
What is the most rate-limiting and committed step of glycolysis?
Step 3: F6P -> F 1,6-Bisphosphate
-enzyme: Phosphofructokinase-1 (PFK-1)
What activates the phosphorylation of F6-P (step 3 of glycolysis)?
Fructose 2,6-Bisphosphate
AMP
Insulin
What inhibits the phosphorylation of F6-P (step 3 of glycolysis)?
ATP
Citrate
Glucagon
In step 4 of glycolysis, F 1,6-BisP is cleaved by ______ to _______ and ________.
Aldolase B; Glyceraldehyde 3-P; Dihydroxyacetone Phosphate (DHAP)
- Glyceraldehyde 3-Pi and DHAP can be converted to one another by Triose Phosphate Isomerase
- Aldolase B also cleaves dietary fructose
What is the first oxidation-reduction reaction of glycolysis?
Step 5: Glyceraldehyde 3-P -> 1,3-BPG
-makes NADH
What catalyzes step 6 of glycolysis (1,3-BPG -> 3-Phosphoglycerate)?
Phosphoglycerate kinase
-makes 1st ATP
What steps of glycolysis use substrate level phosphorylation to make ATP?
Step 6 (1,3-BPG -> 3-Phosphoglycerate) Step 9 (Phosphoenolpyruvate -> Pyruvate)
What is substrate-level phosphorylation?
Energy for production of high-energy P comes from substrate rather than ETC
What is enolase responsible for?
In step 8 of glycolysis, dehydrates 2-Phosphoglycerate to Phosphoenolpyruvate (which is high-E)
What is pyruvate kinase responsible for?
Formation of pyruvate, producing ATP (last step of glycolysis)
What is the last step of glycolysis activated by?
Fructose 1,6-bisphosphate
Insulin
What is the last step of glycolysis inhibited by?
Glucagon
What is the net energy yield for anaerobic glycolysis?
2 ATPs for each glucose converted to 2 lactate
-No net production or consumption of NADH
What is the net energy yield for aerobic glycolysis?
2 ATP per glucose
2 NADH -> about 3 ATP for each NADH
What is a monosaccharide?
Simple sugars
What are monosaccharides classified by?
-Number of carbon atoms: 3 = trioses 4= tetroses 5 = pentoses 6 = hexoses 7 = heptoses 9 = nonoses -Type of carbonyl group: Aldehyde group = Aldose Ketone group = Ketose
What is a disaccharide?
2 monosaccharides
What is lactose?
Disaccharide; galactose + glucose
What is sucrose?
Disaccharide; glucose + fructose
What is maltose?
Disaccharide; glucose + glucose
What is an alpha-1,4 bond?
Glycosidic bond that can link monosaccharides; links C1 of first sugar to C4 of 2nd sugar (makes straight lines)
What is an alpha-1,6 bond?
Glycosidic bond that can make branches
What is glycogen?
Important polysaccharide
- branched
- animal source
What is starch?
Important polysaccharide
- branched
- plant source
What is a glycoprotein?
Sugar attached to a protein
-Sugar attached to noncarb via N- or O-glycosidic bond (-NH2 vs -OH group)
What kind of glycosidic bond does ATP have?
N-glycosidic
What kind of glycosidic bond does lactose have?
O-glycosidic
What kind of glycosidic bond does starch have?
O-glycosidic
What role does pancreatic alpha-amylase play?
Salivary alpha-amylase starts digestion in the mouth and breaks alpha(1->4) bonds, digestion stops in the stomach because high acidity inactivates salivary alpha-amylase; pancreatic alpha-amylase continues process in small intestine
What are dextrins?
Short, branched oligosaccharides produced by salivary alpha-amylase breaking down alpha(1-4) bonds in starch and glycogen
What does disaccharidase deficiency cause?
Passage of undigested carbs into large intestine -> osmotically active -> water drawn in -> osmotic diarrhea
- large volumes of CO2 and H2 gas cause abdominal cramps, diarrhea, and flatulence
- causes: genetic, intestinal diseases, malnutrition, and drugs that injure mucosa of small intestine
What is lactose intolerance and what population does it affect?
Lactase deficiency in small intestine -> lactose cannot be broken down into glucose and galactose -> lactose goes to large intestine and causes osmotic diarrhea
-more than 70% of world’s adults, 90% african/asian descent
Where does gluconeogenesis occur? When does it occur?
90% in liver, 10% in kidneys; during times of fasting
What are the major precursors of gluconeogenesis?
Lactate, glycerol, amino acids (especially alanine)
Gluconeogenesis is the reversal of glycolysis besides which 3 key steps?
1) Pyruvate to phosphoenolpyruvate
2) F 1,6 BisP to F6-P
3) Glucose 6-P to Glucose
How is lactate produced?
Anaerobic glycolysis in exercising muscle and RBCs
What role does lactate dehydrogenase (LDH) play in gluconeogenesis?
Reversible enzyme; converts lactate to pyruvate (regenerating NADH)
What role does alanine aminotransferase (ALT) play in gluconeogenesis?
Converts alanine (from muscle stores) to pyruvate -We measure ALT in liver function panel because it will be elevated in liver disease
What role does pyruvate carboxylase play in gluconeogenesis?
Carboxylates pyruvate to form oxaloacetate
- requires coenzyme biotin
- requires ATP
What role does phosphoenolpyruvate carboxykinase (PEPCK) play in gluconeogenesis?
Releases the CO2 from oxaloacetate (decarboxylation) to form phosphoenolpyruvate (PEP)
- GTP provides the energy
- There is mitochondrial and cytosolic PEPCK (50/50)