Glucose Metabolism and Transport Quiz

Study Notes

Glucose is the primary carbohydrate in blood and the main fuel source for human cells.
Brain function relies heavily on glucose as an energy source.
Cells without mitochondria, like red blood cells, depend on glucose for energy.
During exercise, glucose is a crucial fuel for muscles, particularly through anaerobic glycolysis.

Na+-independent facilitated diffusion transport (GLUT):
- Transports glucose according to the concentration gradient.
- Does not require energy (ATP).
- Utilizes a family of at least 14 glucose transporters (GLUT-1 to 14).
Na+-monosaccharide cotransporter system (SGLUT):
- Transports glucose against the concentration gradient.
- Requires energy.
- Coupled to the movement of sodium ions (Na+) into the cell - both move together.
- Occurs primarily in the epithelial cells of the intestines and renal tubules.

Carbohydrate in Diet:
- Provides glucose after meals.
- Excess glucose is stored as glycogen in the liver and skeletal muscles.
Glycogen Degradation (Glycogenolysis):
- Liver glycogen breakdown provides glucose during fasting.
- Muscle glycogen breakdown provides glucose for muscles during exercise.
Gluconeogenesis (Glucose Synthesis):
- Synthesis of glucose from non-carbohydrate sources (like certain amino acids).
- Occurs during prolonged fasting.

Free Monosaccharides:
- Primarily glucose and fructose.
- Fructose is converted to glucose in the liver.
Disaccharides:
- Sucrose (glucose + fructose).
- Lactose (glucose + galactose).
- Maltose (glucose + glucose).
- Digested into monosaccharides by disaccharidases (sucrase, lactase, and maltase) in the intestines.
Polysaccharides:
- Starch (plant-based, e.g., rice, potato, flour).
- Glycogen (animal-based).
- Digested by amylase into maltose and then further by maltase into glucose in the gastrointestinal tract.

Catabolic pathways:
- For energy (ATP):
  - Glycolysis and Krebs cycle.
  - Anaerobic glycolysis: produces lactate.
  - Aerobic glycolysis: produces pyruvate.
- For synthetic products:
  - Hexose monophosphate pathway: Produces NADPH and Ribose 5-phosphate.
Synthetic pathways:
- Glycogen synthesis.
- Lipogenesis.
- Protein synthesis.
- Other carbohydrate synthesis.

Hexose monophosphate pathway: Produces NADPH and Ribose 5-phosphate.
Glycogen synthesis: Stores glucose as glycogen.
Glycolysis: Breaks down glucose and produces ATP.
- Anaerobic glycolysis: Produces lactate.
- Aerobic glycolysis: Produces pyruvate.
Citric acid cycle: Further breaks down pyruvate and generates ATP.
Electron transport chain: Uses energy carriers (NADH and FADH2) to produce ATP through oxidative phosphorylation.