Metabolism, Fuels, Uptake Of Carbohydrate- Leture 9/14/21 Flashcards
Brain fuel
Glucose
Pathway
A series of enzyme assisted reactions that do chemistry proteins are capable of
Types of pathway (examples (3)
Linear (glycolysis)
Cycles (urea cycle)
Spirals (fatty acid synthesis)
Where does regulation occur in pathways
The steps furthest from equilibrium in the cell (the most negative delta G)
Regulation of enzyme (4)
- Inhibition or stimulation by small molecules
- Covalent modification
- Regulation of amount of enzyme
- Compartmental separation
Role of phosphorylation (rough rule)
Phosphorylation tends to promote breakdown
Insulin
Hormone of the well fed state, promotes oxidation of glucose
Epinephrine
Hormone of acute stress, tends to promote oxidation of glucose
Glucagon
Hormone of the starved state, tends to promote glucose synthesis
Cortisol
Hormone for long term stress response, tends to promote the synthesis of glucose
Examples of disaccharides (3)
Maltose, sucrose, lactose
Maltose
Glucose-glucose
Lactose
Galactose-glucose
Sucrose
Fructose (glucose
Polysaccharides example (2)
Amylose
Amylopectin
Starch
Polyglucose
Amylose
Linear polyglucose
Amylopectin
Branched poly glucose
Glycemic index
Area under the blood glucose curve, the higher the glycemic index, the more insulin response
Factors influencing glycemic index (8)
Sugar content Type of starch Physical barriers Viscosity of soluble fiber Fat and protein content Acid content Food processing Cooking
Carbohydrate digestion
Starts in mouth, continues in intestine and colon
Salivary alpha amylase
Cleaves 1->4 glucose, cannot cleave the 1->6 bonds
Limit dextrins
Smaller polyglucose with branches
Pancreas amylase
Continued digestion after passing through stomach
CCK
Cholecystokinin, food reaching the intestine stimulates I-cells to produce CCK that stimulates pancreas enzymes to release digestive enzymes
Sucrase-isomaltase
Breaks down sucrose and dextrins
Maltose-glucoamylase
Breaks down maltose and amylase to glucose compenents
Lactase
Breaks down lactose
Glut 5
Facilitated diffusion, moves fructose into cell from intestinal lumen
Glut 2
Moves glucose to the blood from the intestinal epithelium, liver from portal system
SGLT1
Moves glucose and galactose into intestinal epithelial against concentration gradient by coupling with sodium transport
SGLT locations
Intestinal mucosa, kidney brush border
Glut4
Moves glucose into skeletal muscle, fat, and white blood cells, INSULIN DEPENDENT
Fanconi-Bickel Syndrome
It is a glut2 deficiency, glucose can’t be filtered by the liver and leads to post-prandial hyperglycemia
Insulin mechanism of actio
Moves GLut4 from intracellular vesicles to cell surface, effectively increasing Vmax
Lactose intolerance
Lack of lactase, creates osmotic effect in lower GI tract to pull water out of cells and also bacterial actions create dissension cramps
Benefits of malabsorption
Undigested polysaccharides important in gastric emptying, stool bulk, lower cholesterol, may absorb carcinogens
Reasons carbs may not be absorbed
- Not digestible by our enzymes
- Insufficient enzyme levels
- Transporter insufficiency or defect
- Lack of sufficient intestinal surface (celiac)
