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Lecture 3a- 22 September 2014

Most of this lecture derived from Chapter 4 of Gropper,

Chapter 4,7 of Rolfes et al(Understanding Normal and Clinical Nutrition(Nutrition 2104/2108 text)

Insel et al.(Nutrition)

and page 96 of Smolin and Grosvenor (Nutrition-Science and Applications)

TODAY’S LECTURE

Carbohydrate metabolism and regulation

Outline of lectures 3a and 3b

Carbohydrates                -forms                        -monosaccharides                        -disaccharides                        -oligosaccharides                        -polysaccharides                        -fibre-next week

Outline of lectures 3a and 3b

Carbohydrates               -foods where each is found                        -monosaccharides                        -disaccharides                        -oligosaccharides                        -polysaccharides

Outline of lectures 3a and 3b

-definitions                        -monosaccharides                        -disaccharides                        -oligosaccharides                        -polysaccharides

Outline of lecture 3a and 3b

-digestion                        -monosaccharides                        -disaccharides                        -oligosaccharides                        -polysaccharides

Outline of lectures 3a and 3b

-absorption, transport and distribution                                                -monosaccharides                        -disaccharides                        -oligosaccharides                        -polysaccharides                        -glucose transporters

Outline of lectures 3a and 3b-metabolism                        -glycogenesis                        -glycogenolysis                        -glycolysis                        -nicotinamide adenine dinucleotide                        -hexose monophosphate shunt                        -Krebs cycle                        -gluconeogenesis                        -regulation                                -allosteric                                -hormonal                                -changes in equilibrium

-rate limiting enzymes

More detailed comments-lecture 3a Carbohydrates    -forms        -simple carbohydrates  -monosaccharides

-glucose, fructose, galactose              -disaccharides

-maltose(glucose and glucose), -sucrose(glucose and fructose), -lactose(glucose and galactose)

Carbohydrates -forms

-complex carbohydrates                  -oligosaccharides-three to ten saccharide

units(some texts define as 2-10 units)-eg breakdown of starch  digestion

                  -polysaccharides-more than 10 saccharides units-eg starch, glycogen

Examples of foods where each is found     -monosaccharides-           -glucose-rare in foods as monosaccharide

(except mother's milk and sports drinks)  but is found in foods as disaccharides and starch

            -fructose-fruits and honey

           -galactose-seldom occurs free in nature             

Examples of foods where each is found     -disaccharides           -maltose- part of starch                         - minor component of few foods

           -sucrose-fruits, vegetables and grain                         -sugar cane- gives rise to table sugar                         -sugar beets-give rise to table sugar

           -lactose-dairy products (eg milk)

Examples of foods where each is found

      -oligosaccharides- eg raffinose and stachyoseare found in beans and other legumes

      -polysaccharides-glycogen-(storage carbohydrate

in animal muscle and liver)

-most of this is lost when meat is slaughtered

                  -starch-(storage carbohydrate in plants)-potatoes

Definitions

      carbohydrate

A compound or molecule that is composed of carbon, oxygen and hydrogen in the ratio of 1C:2H:1O

carbo = carbon

hydrate = H20

Definitions

       -monosaccharides-single carbohydrate units;        -contain 3-7 carbons(trioses, tetraoses,

pentoses, hexoses, heptoses)

       -disaccharides-two saccharide units

      -oligosaccharides-3-10 saccharide units

      -polysaccharides-more that 10 saccharide units

Digestion-monosaccharides-pass untouched into small

intestinal capillaries

-disaccharides-maltose- untouched until maltase in small

intestine -maltase produces two glucoses

         -sucrose-untouched until sucrase in small intestine

                       -sucrase produces glucose and fructose

        

Digestion

-disaccharides -lactose-untouched until lactase in small

intestine

           -lactase produces glucose and galactose

-oligosaccharides-undigested in stomach or small intestine-must be digested by colon bacteria which produce abdominal discomfort and flatulence andshort chain fatty acids (acetic, proprionic and butyric acids)

Digestion

-polysaccharides-starch digestion mildly in mouth-salivary

amylase (alpha-amylase), minimally in stomach via hydrochloric acid and mostly by pancreatic amylase in small intestine

         -maltose units ultimately produced followed by maltase digestion                                                   

Digestion

-polysaccharides

-resistant starch-common in legumes, raw potatoes and unripe bananas

                           -resistant to starch digestion as above due individual inefficiency in digesting starches (class discussion) and physical properties of food

                                                                                                                               

Digestion

-polysaccharides -resistant starch

          bacteria in colon ferment resistant starches and produce water gas and short chain fatty acids (acetic, proprionic and butyric acids)

                                                   

Absorption, transport and distribution     -monosaccharides-pass untouched into small

intestinal capillaries                   -glucose and galactose enter by

active transport and both go to liver

                                   -fructose enters by facilitated diffusion and goes to

liver

                                   -glucose goes to liver(some glycogen produced and other

metabolic pathways)                                                  

Absorption, transport and distribution

     -monosaccharides-   -fructose and galactose converted to

glucose in liver

                    -glucose also goes to directly to other tissues eg voluntary muscle(some glycogen produced and other metabolic pathways are followed)

                                                  

Absorption, transport and distribution

    oligosaccharides-undigested in stomach or small intestine-must be digested by colon bacteria which produce short chain fatty acids, abdominal discomfort and flatulence                                                     

Absorption, transport and distribution

    -polysaccharides-starch digestion mildy in mouth-salivary amylase (alpha-

amylase), minimally in stomach via hydrochloric acid and mostly by pancreatic amylase in small intestine

                               -maltose units ultimately producing glucose which is handled as above

                                                                         

                                                  

Absorption, transport and distribution

        -glucose transporters-proteins required to get

glucose into cells

-table 4.2 Gropper

                                                  

-metabolism         -glycogenesis                  -conversion of glucose to

glycogen(storage form of carbohydrate in humans)

                  -occurs in liver and muscle (cytoplast)                  -glucose converted to glycogen

precursors                  -most of glycogen arises from

gluconeogenic precursors rather than glucose directly

                   

-figure 4.11 Gropper

 

-metabolism        -glycogenolysis               -conversion of glycogen to glucose

(usable form of carbohydrate in humans for energy and anabolism)

Note:The end of the molecule containing a free carbon number one on glucose is called a reducing end. The other ends are all called non-reducing ends.                 -occurs in cytoplast

                -figure 4.12 Gropper

               -regulation-figure 4.13 Gropper 

 

-metabolism        

-metabolism       -glycolysis               -catabolism of glucose to yield energy and

products for anabolism(e.g. gluconeogenesis-see below)

               -anaerobic

               -occurs in cytoplast

               -figure 4.14 Gropper