carb overview

7/27/2019 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

carb overview

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