Carbohydrate Metabolsim You will be able to Explain
Carbohydrate Metabolsim
You will be able to… • Explain how Carbs are digested & absorbed • Draw the steps involved in Glycolysis • Compare and contrast aerobic respiration to two different types of fermentation • Discuss the 3 possible fates of Pyruvate
Mass composition data for the human body Carbohydrates don’t make the man or woman
Carbs do run the man or woman: Carbohydrate recommendation is 45 to 65 percent of total calories. Sugars and starches supply energy to the body as glucose. Only energy source for red blood cells. Preferred energy source for brain & CNS
Energy sources Structural molecules
Salivary glands secrete saliva which contains mucus, water, ions, and amylase enzyme. Food is only briefly in the mouth, so carbohydrate digestion just begins. Starch polymers are broken down into smaller chains and into some disaccharides: maltose, sucrose, lactose.
Small intestine > 3 m long, 2 to 3 cm wide. Coils, folding, & villi give surface area of 500 -600 m long tube. Upper part (duodenum) most active in digestion: villi cells produce enzymes which complete digestion of carbohydrates.
Plasma membrane of microvilli use these enzymes to complete digestion: Disaccharidases: disaccharides converted into monosaccharide subunits. Maltase: hydrolyzes maltose into glucose. Sucrase: hydrolyzes sucrose into glucose & fructose. Lactase: hydrolyzes lactose into glucose & galactose.
Common Disaccharides: Maltose: (1 4) of two D-Glucose molecules Lactose (1 4) Milk sugar: galactose and glucose connected Sucrose: -Glucose and -Fructose , (1 2) glycosidic linkage
Small intestine’s second job: Absorption Uses increased S. A. with folds projecting into lumen (plicae circulares), villi and microvilli. Sugars into bloodstream: Fructose diffuses into villi, glucose & galactose absorbed by active transport.
Summary of carbohydrate digestion in the human body.
What to do with those sugars? Turn them into ATP = Cellular respiration – Aerobic respiration • Requires molecular oxygen • Includes series of redox reactions -Anaerobic respiration *Fermentation *Does not require oxygen All are exergonic (occur spontaneously) Use a lot of coupled reactions
Reaction Types in Cellular Respiration 1. Dehydrogenation - Hydrogens transferred to a coenzyme (an energy carrier molecule). 2. Decarboxylations - Carboxyl groups (COO-) removed from substrates as carbon dioxide (CO 2). 3. Preparation reactions - Molecules rearranged in preparation for dehydrogenation or decarboxylation. 4. Phosphorylation – phosphates added to provide energy or transform molecules.
Four stages of aerobic respiration Note location of each stage & amount of ATP formed Product of one stage becomes reactant of next stage
Glycolysis: Glyco = sugar Lysis = to split One 6 C glucose split into two 3 C pyruvates (eventually) Substrate (organic molecule) Phosphorylation of glucose occurs to make the reactions exergonic Also stops glucose from leaving the cell.
An overview of glycolysis. 6 C stages & 3 C stages Energy absorbing Energy producing
Glycolysis: energy investment Phase: Phosphorylation ATP kick start: Glucose turned into Fructose 1, 6 bisphosphate this turns eventually into 2 glyceraldehyde-3 phosphate molecules
Structural relationships among glycerol and acetone and the four C 3 intermediates in the process of glycolysis. This converts into That (isomers)
Glycolysis: E capture phase The two glyceraldehyde-3 phosphates eventually turn into two pyruvates (with what type of rxn? ) The end products of glycolysis include: • 2 molecules of pyruvate • 2 molecules of NADH • 2 ATP molecules net gain (4 made / 2 used)
Let’s go through the steps in detail: Glycolysis animation simplistic version Glycolysis animation more detailed steps Glycolysis animation details Enzymes involved in glycolysis
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