Download - Carb Overview
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Overview of
Carbohydrate Digestionand Metabolism
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FST/AN/HN 761
FST 761 Dr. Jeff FirkinsCarbohydrates
Dr. Josh BomserLipids
TA- Amy Long, MS Reading / Writing Assignments
Text - Biochemical and Physiological Aspects of
Human Nutrition- Martha H. Stipanuk.TodayOverview of carbohydrates (Jan 7)
http://class.fst.ohio-state.edu/fst761/761home.htmlhttp://class.fst.ohio-state.edu/fst761/761home.html -
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Carbohydrates
Carbohydrates are called carbohydrates because theyare essentially hydrates of carbon (i.e. they are
composed of carbon and water and have a
composition of (CH2O)n.
The major nutritional role of carbohydrates is to
provide energy and digestible carbohydrates provide
4 kilocalories per gram. No single carbohydrate is
essential, but carbohydrates do participate in many
required functions in the body.
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Photosynthesis: Suns energy becomes part of glucose molecule
energyCarbon dioxide
Water
Chlorophyll
GLUCOSE
6 CO2 + 6 H20 + energy (sun) C6H12O6 + 6 O2
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120 grams of glucose / day = 480 calories
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Simple Sugars -
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Disaccharides
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Complex carbohydrates
Oligosaccharides
Polysaccharides
Starch Glycogen
Dietary fiber (Dr. Firkins)
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Starch
Major storage carbohydratein higher plants
Amyloselong straightglucose chains (a1-4)
Amylopectin
branchedevery 24-30 glc residues (a 1-6)
Provides 80% of dietary
calories in humans worldwide
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Glycogen
G GG
G
G
GG
G1-4 link
G
G
G
GG a 1-6 link
G
GG
GGG
Major storagecarbohydrate in animals
Long straight glucosechains (a1-4)
Branched every 4-8 glcresidues (a 1-6)
More branched than
starch Less osmotic pressure
Easily mobilized
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Digestion
Pre-stomach
Salivary amylase : a 1-4 endoglycosidase
GG
GG
G
GG
G1-4 linkG
G
G
G a 1-6 link
G
GGGG
G G G G
G
G
G
G G
G
maltose
G
G
G
isomaltose
amylase
maltotriose
G
G
G
G
a Limit dextrins
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Stomach
Not much carbohydrate digestion
Acid and pepsin to unfold proteins
Ruminants have forestomachs with extensivemicrobial populations to breakdown and
anaerobically ferment feed
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Small Intestine
Pancreatic enzymes
a-amylase
G G GG G
G
G G G
G G GG
GG G
amylose
amylopectin
G G G G G
a amylase
+
G
G G
G G
maltotriose maltose
a Limit dextrins
G
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Oligosaccharide digestion..cont
G
G G
G G
G
G
GG GG
G
Glucoamylase (maltase)
ora-dextrinase
G G
G
G
G
a-dextrinaseG GG
G
G G
Gmaltase
sucrase
a Limit dextrins G
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Small intestine
Portal for transport of virtuallyall nutrients
Water and electrolyte balance
Enzymes associated with
intestinal surface membranes
i. Sucraseii. a dextrinaseiii.Glucoamylase (maltase)
iv. Lactase
v. peptidases
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Carbohydrate absorption
Hexose transporter
apical basolateral
http://arbl.cvmbs.colostate.edu/hbooks/molecules/hexose_xport.htmlhttp://arbl.cvmbs.colostate.edu/hbooks/molecules/hexose_xport.html -
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Glucose and galactose absorption
Read Chapter 5 and answer the questions on
page 102 of Stipanuk. Be prepared to discuss
them on Friday
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Carbohydrate malabsorption
Lactose intolerance (hypolactasia),page 100.
Decline lactase with age
Lactose fermented in LI
Gas and volatile FA
Water retentiondiarrhea/bloating
Not all populations
Northern Europeanlow incidence
Asian/African Americans
Highb 1-4 linkage
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Metabolismthe chemical changesthat take place in a cell that produce
energy and basic materials needed for
important life processes
-millions of cells
-Multiple organs (liver, adipose, heart, brain)
-Thousands of enzymes-Various conditions (fed, fasted, exercise, stress)
C b h d
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Glucose
Glucose-6-P
Pyruvate
Hexokinase
PentosePhosphateShunt
glycolysis
Carbohydrates Serve as primary source of energy in the cell
Central to all metabolic processes
Glc-1- phosphate
glycogen
Cytosol - anaerobic
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Pyruvatecytosol
Aceytl CoAmitochondria
(aerobic)
Krebscycle
Reducing
equivalents
OxidativePhosphorylation(ATP)
AMINOACIDS
FATTY ACIDS
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No mitochondria GlucoseGlucoseGlucose
The Full
Monty
Glucose
GlycogenLactate
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Fasted State
Glucose
Glucose-6-P
Pyruvate
Hexokinase
PentosePhosphateShunt
glycolysis
Glc-1- phosphate
glycogen
Need 13.8 kJ/mol
ATP = -30 kJ/mol
-16.7 kJ/mol
GNG
G-6-Pase
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Controlling Metabolic Flux
1. Control enzyme levels
2. Control of enzyme activity (activation or inhibition)
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Control of enzyme activity
Rate limiting step
ins lin
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Glycogen synthase
(active)
OHPGlycogen synthase
(inactive)
Glycogen formation
Glycogen synthase kinase(active)
OH
IRinsulin
P
PProtein Kinase B
(active)Protein Kinase B
(inactive)OH
P Glycogen synthase kinase(inactive)
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Controlling Metabolic Flux
1. Control enzyme levels
2. Control of enzyme activity (activation or inhibition)
3. Compartamentalization
Fatty acid oxidation occurs in mitochondrial matrix
Fatty acid synthesis occurs in endoplasmic reticulum membrane exposed
to the cytoplasm of the cell.
4. Hormonal control
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Glucose utilization
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Stage 1postparandial
All tissues utilize glucose
Stage 2postabsorptive
KEY
Maintain blood glucoseGlycogenolysis
Glucogneogenesis
LactatePyruvateGlycerol
AAPropionateSpare glucose by metabolizing fat
Stage 3- Early starvation
Gluconeogenesis
Stave 4Intermediate starvation
gluconeogenesis
Ketone bodies
Stage 5Starvation
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Carbohydrate Metabolism/
Utilization- Tissue Specificity Muscle
cardiac and skeletal Oxidize glucose/produce and store glycogen (fed) Breakdown glycogen (fasted state) Shift to other fuels in fasting state (fatty acids)
Adipose and liver
Glucose acetyl CoA Glucose to glycerol for triglyceride synthesis Liver releases glucose for other tissues
Nervous system Always use glucose except during extreme fasts
Reproductive tract/mammary Glucose required by fetus Lactose major milk carbohydrate
Red blood cells No mitochondria Oxidize glucose to lactate Lactate returned to liver for Gluconeogenesis