ansc314 - carbohydrates pt 1

carbohydrates

hydrates of carbon formed from carbon dioxide & water (CH₂O)_n

• C:H:O = 1:2:1

• plants makes glucose & O₂ w/ water as by product

  • energy from sun transferred to chemical bond of glucose

• some carbohydrates contain P, N, & S

  • major component in omnivore diets

• simple carbs

• complex carbs

simple carbohydrates

found in foods like fruits, milk, & vegetables

complex carbohydrates

provide vitamins, minerals, & fiber

• in foods like breads, legmumes, rice, pasta, & starchy

blood glucose level

plants v animals

plants

• store carbohyd. (CHO) — sugars & starch

• cell walls: structural CHO — cellulose & hemicellulose

animals

• energy source & store (glycogen in liver/muscle)

• component of tissues & other compounds

• humans can make carbohydrates (from glucose) & store it for SHORT periods of time

  • instant energy

sugar

• monosaccharides

• disaccharides

monosaccharides

single CHO unit

• pentoses - (C₅H₁₀O₅) - Xylose, Xylulose, Ribose, Ribulose

• hexoses - (C₆H₁₂O₆) - Glucose, Galactose, Mannose, Fructose

disaccharides

2 CHO units

• sucrose

• lactose

• maltose

• cellobiose

  • alpha bonds can be broke down by human enzymes but not beta bonds

    • ruminants can b/c more extensive microbial gut biome

non-sugars

• polysaccharides

  • homoglycans

  • heteroglycans

• complex carbohydrates

  • glycolipids

  • glycoproteins

homoglycans

polysaccharide - 1 type of CHO

• Xylans

• Glucans…….starch, dextrins, glycogen, cellulose

• Fructans

• Galactans

• Mannans

• Glucosamines (chitin, shell of crustacea/insects)

heteroglycans

more than 2 types of CHO

• Pectic substances (oranges)

• Hemicelluloses (plant cell wall)

• Hyaluronic acid (libricant for connective tissue)

• Chondroitin (cartilage)

monosaccharide

one CHO unit

• hexose - C₆H₁₂O₆

  • aldoses (aldehyde)

    • glucose, galactose, mannose

  • ketose (ketone)

    • fructose

• reactive b/c functional groups

• ALL sugars are REDUCING in nature (reduce sugars)

sugars

• all monosaccharides are reducing sugars

  • open ring of glucose → reducing sugar

• reducing sugars react w/ amino acids in the Maillard reaction

• aldehyde → oxidized → carbox. acid (by donating e^-)

sugar forms

• D-form

• L-form

D-sugar

-OH group on RIGHT side of last chiral carbon

• only D sugars can be metabolized by animals

L-sugar

-OH group on LEFT side of last chiral carbon

• not occur naturally in higher living organisms

• cannot be used for energy

  • can’t be phosphorylated by hexokinase (1st enzyme in glycolysis pathway)

alpha carbon

first carbon which attaches to a functional group

• 2nd C is a beta carbon

different projections

glucose

aldo-sugar

• most important SUGAR in nutrition

• major end product of CHO digestion in non-ruminants

• primary form of sugar in blood for energy

• free (fruits, plants, honey) & polymerized (starched, dextrin) forms

• body can make glucose in liver (90%) & kidney (extreme cases)

galactose

aldo-sugar

• C-4 Epimer of glucose

• not found in nature

• component of lactose

• gums

• mucilages

epimer

one of a pair of steroisomers

fructose

keto-sugar

• only important ketose in nature

• free sugar in leaves, fruits, honey

• major sugar in corn syrup

• component of sucrose (table sugar)

• sweetest of CHO

mannose

aldo-sugar

• C-2 epimer of glucose

• not found in nature

• component of glycoproteins

• found in yeasts, molds, & bacteria

pentoses

C₅H₁₀O₅

• d-ribose

• d-xylose, d-arabinose

d-ribose

pentose

• part of nucleotides (ATP, GTP, etc.)

• vitamin B

• RNA → D-ribose (protein synth. template)

• DNA → D-deoxyribose (genetic coding)

  • modified sugar, locking 1 O atom

d-xylose

• only as intermediate in Pentose phosphate cycle

disaccharides

has 2 monosaccharides linked by glycosidic bond

• most nutritionally important sugar

  • sucrose

  • lactose

    • know which 2 monosacc are linked together

sucrose

disaccharide - table sugar

• α-D-GLUCOSE + β-D-FRUCTOS

• most abundant in plants (sugar cane, beets, maple syrup)

• broken down by sucrase in monogastric intestines, but not ruminants

lactose

disaccharide - milk sugar

• α-D-Galactose+ α/β-D-Glucose

• found in milk

  • promotes acidity in intestines (desirable bacteria)

• lactase in small intestine breaks bond

  • ↓ w/ age

• enhances absorption of Mg, Ca, & P

homopolysaccharides

• starch

  • amylose

  • amylopectin

• glycogen

• dextrin

• cellulose

starch

• α-D-glucose linked w/ α-1,4 linkages

• only in plants

• maltose is basic disaccharide unit

  • glucose + glucose = maltose unit

  • maltose + maltose = starch

• monogastric: digested by amylase (saliva & s. intestine)

• cereal sugar

• made up of

  • amylose

  • amylopectin

amylose

straight line of glucose

• α-1,4 glycosidic bonds, straight chains of D-glucose

• iodine stains blue

• 15-30% total starch in most plants

• α-amylase degrades amylose in s. intestine

• soluble in hot water

amylopectin

branching glucose along straight line

• α-1,4 bonds with α-1, 6 bonds at branch points every 25 residues

• has branches b/c

  • enzymes have more opportunities to bind

  • STORAGE (allows it to be more consolidated)

• iodine stains purple/red

• 70-85% total starch in plants

• broken down by amylase at α-1,4 bonds, needs de-branching enzyme for α-1,6 bonds

• less soluble in hot water

amylose vs amylopectin

• most plant starch is amylopectin

glycogen

• animal version of starch

• α-D-glycose linked & branched as amylopectin

  • small amts

    • liver (8-10%), muscle (2-3%)

    • liver DENSE in glycogen storage

    • muscle more important in ability to store glycogen

glycogen vs amylopectin

glycogen

• higher # of branch points

  • allows more glucose to be released at once

• smaller molecule

• very compact & soluble - lots of OH groups to form hydrogen bonds w/ water

glycogen vs starch

dextrin

intermediate product of STARCH + GLYCOGEN digestion

• low MW, small, highly branched intermediate

plant fiber

cellulose, hemicellulose, & pectin

• alpha vs beta (cellulose)

• undigestible for humans

  • only ruminants & hindgut fermenters

cellulose

β D-glucose w/ β-1,4 linkage straight chain

• disaccharide: cellobiose

• highly stable: no animal enzyme degrates it

• microbial cellulase breaks bond

  • cotton is one of purest forms

• most abundant CHO on planet (trees)

alpha vs beta

alpha (α)

• animal enzymes can break α-α linked D-sugars

  • starch & glycogen

beta (β)

• microbial enzymes can break β-β linked D-glucose bond

  • cellulose

heteropolysaccharides

• pectin

• hemicellulose

pectin

heteropolysaccharide

• linear chain of galacturonic acid interrupted by rhamnose w/ side chains of galactose, arabinose, & xylose

• abundant in soft tissue of citrus fruit peels

• soluble fiber

• exhibits gelling properties

hemicellulose

β-linages of D-glucose, D-galactose, D-mannose, D-xylose, & L-arabinose

• digested by rumen bacterial enzymes

  • easier to digest than cellulose

• grasses made of xylan chain in β-1, 4 linkages

• found in fruits, plant stems, & grain hulls

lignin

indigestible for several enzymes & just goes out (animals)

• can use as a marker (how much in/out?) in research

  • how digestible fiber & other components are