Carb Metabolism Flashcards
Define Catabolism (major functions)
- Breakdown
- Formation of smaller molecules from larger molecules
- Proteins to AA
- Starch to glucose
- Energy released in the form of ATP
Define Anabolism (major functions)
- Synthesis
- Synthesis of larger molecules
- Requires energy (energy is used)
- AA to proteins
- Glucose to starch
What are the major steps in carbohydrate metabolism?
- Glycogenesis
- Glycogenolysis
- Glycolysis
- Gluconeogenesis
Define Glycogenesis
- Formation of Glycogen from glucose-6-phosphate
- Enzyme= Glycogen synthase
- Excess glucose entering the blood is sequestered as glycogen
- Stored in liver and transported to the muscle
Glycogen Structure
- Highly branched so water can get inside
- Soluable
- Temporary storage molecule
- a-1,4 and a-1,6 glycosidic bonds
- Branching makes it more soluable than starch
- Allows for much faster synthesis/degradation
- Glycosidic bonds (hydrophillic)
Which enzyme in glycogenesis acts as a primer, by polymerizing the first few glucose molecules, after which other enzymes take over?
Glycogenin
In carnivorous animals who do not consume carbohydrates, what is the predominant process for getting glucose?
Gluconeogenesis
In the glycolysis pathway:
Glucose is converted to pyruvate
Which hormones are involved in regulation of carbohydrate metabolism and what do they control?
- Insulin & Glucagon
- Fed, fasting and starving states
Describe glycolysis.
Why is this an important process?
- Glucose → pyruvate
- Free energy released is used to form high energy compounds like ATP
- Glycolysis product = pyruvate → common entry and exit path in glucose synthesis
Briefly describe the process of gluconeogenesis.
- Making glucose from amino acids and non-hexose carbohydrates
- Make glucose-6-phosphate from pyruvate
- Important in carnivores bc their diet doesn’t have carbohydrates
- Lactate → Pyruvate via lactate dehydrogenase (from RBC’s and other tissues w/o mitochondria, and exercising muscle)
- Alanine → Pyruvate via alanine aminotransferase (degradation of muscle proteins)
- Pyruvate is the common entry and exit in glucose synthesis
What role does insulin and glucagon play in controlling the glucose levels in the fed state?
- Glucose is stored as glycogen
- Insulin levels go up→ removes glucose from blood → promotes glycogen formation
- Glucagon function decreased (releases glucose from glycogen)
- Insulin promotes the absorption of glucose from blood and inhibits the production of glucose by the liver
What role do insulin and glucagon play in controlling the
glucose levels in the fasting state?
- Low levels of blood glucose= liver begins breakdown of glycogen
- Glycogen converted to glucose
- Insulin levels decreased
- Glucagon levels increased
- Glycogen→ glucose → transport to Brain, RBC, other tissues
Glycogenolysis is mainly in this state, some gluconeogenesis
What role do insulin and glucagon play in controlling the
glucose levels in the starved state?
- Gluconeogenesis ONLY!!!
- No glycogenolysis b/c there aren’t any more glycogen reserves
- Decreased insulin levels
- Increased glucagon levels→ promote gluconeogenesis
- Gluconeogenesis peaks as glycogenolysis ends→ when reserves are exhausted
More extreme version of the previous fasting state
What transporters help in the active uptake of glucose by the cells?
- Cell membranes are impermeable to glucose
- Mediated by integral membrane glucose transporters (GLUTs)
- Transport of glucose to liver-linear
Define Glycolysis
- When glucose-6-phosphate is broken down into pyruvate
- Energy released
- Used to form high-energy compounds like ATP
Carbon substrates for gluconeogenesis
- RBC’s
- Other tissues w/o mitochodria
- Exercising muscle
- Degradation of muscle proteins
What is the common entry & exit molecule in glucose synthesis?
Pyruvate
Glycogenesis Diagram
