Carbohydrate metabolism Flashcards
Carbohydrate metabolism occurs in
Occurs in cytoplasm
catabolic and anabolic processes
Sources of carbohydrates
Diet
Breakdown of glycogen or glycerol
Propionate stored in the liver (ruminants)
Primary carb found in blood
Glucose
Glucose is absorbed by all cells by
Facilitated diffusion
Active transport
Diabetes mellitus
caused by insufficient insulin levels or decreased insulin receptor proteins
Body cells are starved of energy because cannot absorb and use glucose
When blood glucose levels are low
liver converts stored glycogen to glucose
Can make new glucose from non-carbohydrate material
What does liver do to glucose
Liver removes glucose from blood after meal
Converted to glycogen or triglycerides for storage
What is the key organ involved in regulating blood glucose
Liver
Carbohydrate metabolism
Glucose enters cell
Glucose broken down to pyruvate through glycolysis
If adequate oxygen, aerobic respiration follows
If not adequate oxygen in muscle cells, pyruvate is converted to lactic acid
Causes stiff feeling in muscles
Glycolysis occurs in
Cytoplasm
Glycolysis process and net product
Occurs in cytoplasm
Glucose broken down to form two pyruvate (pyruvic acid)
Net production of energy is:
2 NADH
2 ATP
Regulation of glycolysis
Glycolysis pathway is constantly controlled
Regulated by three enzymes:
Hexokinase
Phosphofructokinase
Pyruvate Kinase
Hexokinase
Inhibited by glucose-6-phosphate
Feedback inhibition
Phosphofructokinase
Inhibited by ATP and citrate
Activated by ADP and AMP
Pyruvate Kinase
Inhibited by ATP
Aerobic respiration occurs in and has two stages
Occurs in the mitochondria
2 stages:
Krebs cycle
Electron transport chain
Enzymes and cofactors found in cristae
Each turn of the krebs cycel produces energy carrier molecules
1 ATP
1 FADH2
3 NADH
Krebs cycle
Pyruvate enters mitochondria through outer and inner membrane
Before enters Krebs cycle is transformed into an acetyl group
Acetyl group binds to coenzyme A → acetyl coA
Acetyl coA enters Krebs cycle and binds with oxaloacetateAfter several steps citric acid is converted back to
oxaloacetate
By product of the krebs cycle
CO2
How many times does the krebs cycle run
Since two pyruvate were produced from one glucose, the cycle runs two times for each glucose molecule
Regulation of krebs cycle
Rate of Krebs cycle is adjusted to meet cellular needs for ATP
Entry of acetyl-CoA into the cycle and rate at which the cycle operates are reduced by high ATP levels
When ATP supplies are low the cycle is stimulated
Electron transport system
Final stage of cellular respiration
Produces majority of ATP for cell
NADH and FADH2 donate high energy electrons to a chain of electron carrier molecules
Called cytochromes
At each step energy is used to pump protons from mitochondrial matrix into intermembrane space
Last electron acceptor is oxygen
Oxygen joins with two hydrogen atoms to form water
Pumping of protons across membrane establishes an electrochemical gradient
Potential energy
Protons flow back into matrix through ATP synthase complex
Energy is released
Used to combine ADP and inorganic phosphate to make ATP
Glycogen synthesis
Glycogen Synthesis
Glucose consumed in excess of immediate body needs is converted to glycogen
Glycogen stored in liver and muscle
Glycogenesis
Glycogen synthase forms bonds between glucose using ATP as energy source
Glycogen synthesis occurs in
Can occur in all cells but important function of liver and muscle
Glycogenesis is
Synthesis of glycogen from glucose
Glycogenolysis is
Breakdown of glycogen to glucose
When does glycogen breakdown occur
Occurs when muscles need energy and when liver is restoring low blood sugar level to normal
Where does glycogenolysis occur
Occurs in liver, kidney, and intestinal cells
Not in muscle because enzyme for last step is missing
What can muscle cells produce instead of free glucose during glycogenolysis
Muscle cells cannot form free glucose, but can produce glucose-6-phosphate which can be used in glycolysis pathway
Gluconeogenesis is
Synthesis of glucose from noncarbohydrate molecules
Synthesizes glucose from lactate, some amino acids, and glycerol
Primarily occurs in the liver (~90%)
What happens during the cori cycle
Under anaerobic conditions, lactate produced by muscles is reconverted to glucose by the liver through the Cori Cycle Pyruvate is converted to glucose by gluconeogenesis
Glucose enters the blood and returns to the muscles
During active exercise what does lactate do
lactate levels increase in muscle tissue
lactate diffuses into the blood
lactate is taken to liver and converted back to pyruvate
What main hormones control carb metablsism
Insulin
Glucagon
Epinephrine
Insulin does what to carbs
decreases blood glucose levels
increases absorption of glucose by cells
increases the synthesis of glycogen, fatty acids, and proteins
stimulates glycolysis
Glucagon does what to carb
increases blood glucose levels
activates glycogen breakdown in liver
Epinephrine does what in carb metabolism
increases blood glucose levels
stimulates glycogen breakdown in muscle
