Carbohydrate Metabolism Flashcards
Glucagon
Fasting state
No glucose coming in
Liver breaks down glycogen to free glucose which enters the blood
Pull oxaloacetate out of CCA to make glucose-6-P which is converted to glucose
Breakdown of triglycerides which are transported to tissues, oxidized to acetyl-CoA and enter CCA to produce endrgy
Insulin
Fed state.
Glucose enters the cell, is phosphorylation and activated to glucose-6-P. 6C glucose is oxidized to 2 3C pyruvates which are converted to acetyl-CoA which enters the Krebs cycle, get a lot of high envy electrons from this. Inside the mitochondria, energy from electrons used to make ATP. Excess glucose used to make glycogen in the muscle and liver
Glycolysis
Energy producing pathway common to all cells
Cytosol
Oxidation of glucose, immediate energy source and source of reducing equivalents, NADH
Glucose to 2 pyruvates
Cn either enter Krebs cycle (aerobic) or convert to lactate (anaerobic)
2 ATP, 2 NADH
Citric Acid (Krebs) Cycle
Mitochondria
3C pyruvate to CO2 and H2O
Pyruvate dehydrogenase – converts pyruvate to acetyl-CoA and produces 1 NADH
CAC produces 3 NADH, 1 FADH2, 1 GTP
Oxidative phosphorylation
Electron transport chain
Occurs inside the mitochondria and requires oxygen
Aerobic
ATP production from energetic electrons
NADH produces three ATP
FADH2 produces two ATP
protein and fat requires mitochondria and oxygen for energy production
Carbs can generate energy in the absence because glycolysis generates a little ATP
Pentose Phosphate Pathway (Hexose Monophosphate Shunt)
Occurs in the cytosol of all cells and branches off from glycolysis
Produces NADPH and ribulose-P
NADPH for biosynthesis reactions: fatty acid and cholesterol synthesis and reduced glutathione (protects rbcs)
Ribose-P for nucleotide biosynthesis
Unneeded ribose-P reenters glycolysis to make ATP and pyruvate
Gluconeogenesis
Making new glucose
Liver makes new glucose to maintain blood glucose levels during fasting and excise
Adequate blood glucose is critical for rbcs and brain
Lactate and amino acids can be converted to glucose
Anabolic process: requires 6 ATP and NADH
Glycolysis backwards
Glycogen synthesis and breakdown
Glycogenesis - synthesis
Glycogenolysis - breakdown
Glycogen is a storage form of glucose
Important in the liver and muscle
Liver and kidney: formed in the fed state, broken down during fasting and exercise to maintain blood glucose levels
Muscle: formed in the fed state, utilized by muscle during exercise– stays inside muscle so no effect on blood glucose
Erythrocytes (RBC)
Bags of hemoglobin that carry oxygen to tissue
No mitochondria, use anaerobic glycolysis to make ATP
depends on glucose for energy
Cannot metabolize any fats or proteins
No glycogen stores, constant supply ofmglucose
Pyruvate is converted to lactate by lactate dehydrogenase. Lactate transported out of the cell and converted back to glucose—Cori Cycle
PPP maintains reduced glutathione which protects rbcnmembranes
Brain
Critical organ with high energy demands
Lots of mitochondria
Need to get a lot of glucose and it makes and uses lots of energy (aerobic)
No glycogen stores
Cannot use fat – blood brain barrier
Requires a constant glucose supply
Can slowly adapt to ketone bodies as energy sources
Adipose (fat tissue)
Synthesis and storage site for triglycerides (fat)
Insulin sensitive glucose uptake with lots of GLUT4, lots of FA syntheis
Glycolysis and PPP is active
Some acetyl-CoA is used for energy production
Excess acetyl-CoA is converted to fat
PPP generates NADPH for fatty acid biosynthesis
Not dependent on glucose for energ, can use its own fat
During fasting - FA from TG released into the blood a major energy source
Skeletal muscle (cardiac too)
Requires energy for muscle contraction
Insulin-sensitive glucose uptake, GLUT4
Glycolysis and CAC to make ATP
Can make, metabolize, and storage glycogen for own use
Resting: use carbs and fats to make ATP
Rapidly exercising: limited by rate of oxygen utilization, ability to use fat limited. Pyruvate converted to lactate for anaerobic glycolysis
Protein breakdown: provides aa’s for glucose synthesis during fasting
Liver (kidney too)
Central clearinghouse
Glycolysis/CAC/oxidative phosphorylation for energy production
PPP to make NADPH
Excess glucose made into glycogen and stored
Excess acetyl-CoA converted into fat and exported to other tissues as VLDL
Maintains blood glucose during fasting and exercise. Significant glycogen stores
Gluconeogenesis
Can use FA for energy
Pancreas
Secretes insulin or glucagon in response to a change in blood glucose concentration
Insulin: a time to build up
Glucagon: a time to break down
