Till Before Gluconeogenesis Flashcards
What are the main dietary sources of carbohydrates?
- Monosaccharides: Glucose, Fructose
- Disaccharides: Maltose, Lactose, Sucrose
- Polysaccharides: Starch, Cellulose
Monosaccharides are simple sugars, while disaccharides consist of two monosaccharides, and polysaccharides are long chains of monosaccharides.
What is the primary function of cellulose in the human digestive system?
Increases the bulk of intestinal contents, stimulates intestinal contractions, and prevents constipation.
Cellulose is not digestible by humans due to its beta-glucose bonds.
What monosaccharides are primarily absorbed during carbohydrate digestion?
Glucose, Galactose, Fructose
These monosaccharides are absorbed via different mechanisms including simple diffusion.
What is the fate of absorbed galactose and fructose in the liver?
Converted to glucose.
This conversion is crucial for maintaining blood glucose levels.
What are GLUT transporters?
GLUT transporters are proteins that facilitate glucose transport across cell membranes.
Different GLUT transporters have varying roles in different tissues.
True or False: GLUT-4 transporters require insulin for glucose uptake.
True
GLUT-4 is found in heart, skeletal muscle, and adipose tissues, and insulin promotes its translocation to the cell membrane.
What are the major pathways for the oxidation of glucose?
- Krebs’ cycle
- Glycolysis
These pathways are essential for energy production.
Fill in the blank: The maximum capacity of the kidney to reabsorb blood glucose is known as the _______.
Renal threshold.
When blood glucose exceeds this threshold, glucose appears in urine.
What is the net gain of ATP during glycolysis under aerobic conditions?
7 ATP
This is calculated from ATP produced minus ATP used during the process.
What happens to pyruvate under anaerobic conditions?
Converted to lactate.
This process occurs when oxygen is not available for aerobic respiration.
What are the two shuttle mechanisms that transport NADH from the cytosol to the mitochondria?
- Glycerophosphate shuttle
- Malate shuttle
These shuttles are necessary because NADH cannot cross the mitochondrial membrane directly.
What is the role of 2,3-Bisphosphoglycerate (2,3-BPG) in red blood cells?
Binds to hemoglobin and facilitates oxygen release in tissues.
2,3-BPG is produced during glycolysis in red blood cells.
What inhibits the enzyme enolase during glycolysis?
Fluoride.
Fluoride binds irreversibly to magnesium at the active site of the enzyme, preventing glycolysis.
What are the key enzymes that regulate glycolysis?
- Hexokinase
- Glucokinase
- Phosphofructokinase-1 (PFK-1)
- Pyruvate kinase(pk)
## Footnote
These enzymes catalyze the three irreversible reactions of glycolysis.
What is the difference between hexokinase and glucokinase in terms of affinity for glucose?
Hexokinase has a high affinity, while glucokinase has a low affinity.
This reflects their roles in different tissues and conditions.
What is the function of glucokinase (GK) in glucose metabolism?
Catalyzes the conversion of glucose to glucose-6-phosphate
GK is found in liver and pancreatic B cells and is important for glucose uptake.
What is the substrate specificity of glucokinase compared to other hexokinases?
More specific for glucose and less specific for other hexoses
Other hexokinases have broader substrate specificity.
What is the affinity (Km) of glucokinase?
Low affinity (high Km) for glucose
This means it requires higher concentrations of glucose for activity.
What effect does glucose-6-phosphate have on glucokinase activity?
No effect
Unlike other hexokinases, GK is not inhibited by its product.
What regulates phosphofructokinase-1 (PFK-1) in glycolysis?
Allosteric regulation by various metabolites
PFK-1 is a key regulatory enzyme in glycolysis.
What hormones are involved in carbohydrate metabolism during fasting?
Glucagon and adrenaline
These hormones promote gluconeogenesis and inhibit glycolysis.
What is the role of insulin in carbohydrate metabolism?
Promotes glucose uptake and storage
Insulin secretion increases in response to high blood glucose levels.
What happens to glycolysis during fasting and low carbohydrate intake?
Glycolysis is reversed for gluconeogenesis
This allows for synthesis of glucose from non-carbohydrate sources.
What is the conversion of pyruvate to acetyl-CoA catalyzed by?
Pyruvate dehydrogenase complex (PDH)
This reaction is crucial for linking glycolysis to the citric acid cycle.
