ANSC315 carbs

role of carbs in plants

• energy transformations; tissue synthesis

• energy reserve

• structural support

neutral detergent fiber

made from cellulose and lignin

carbohydrates

• large amount in plant tissue: starch and cellulose

• small amounts in animal tissue: glycogen and glucose

heteropolysaccharide

2 or more different sugars make it

lactose

• made of glucose + galactose

• beta 1,4

• milk sugar

• broken down by lactase

sucrose

• made of glucose + fructose

• most abundant in nature

maltose

• made of glucose + glucose

• alpha 1-4

• partial hydrolysis of starch

• small intestine

simplest carb

monosaccharide

glycosidic linkage

joins sugars

starch

• most important polysaccharide

• homopolysaccharide

• made of glucose

pentose

ribose, deoxyribose (important for making RNA and DNA)

hexose

glucose, fructose galactose

animal enzymes

stereospecific and only recognizes d-form glucose

glucose

• commercially produced by hydrolysis of corn starch

• major end-product of carb digestion

galactose

• combines with glucose to from lactose

• component of galactolipids found in plants

fructose

• sweetest of all sugars (fruits, honey)

• component of sucrose

functions of ribose

• ribitol is a component of riboflavin

• riboflavin component of FAD, FMN

• transformation of pyridoxine and folic acid into their active forms

• conversion of tryptophan into niacin

alpha 1,4 and alpha 1,6

digested by mammalian enzymes

beta 1,4 and beta 1,6

cant be digested by mammalian enzymes only microbial can

polysaccharides

• many monosaccharide units joined by glycosidic bonds

• homo or hetero

types of starch granules

• amylose

• amylopectin

amylose

• long unbranched chains of glucose connected by a alpha 1,4 linkage

• soluble in water

• 20-30% of starch in cereal grains

• slowly digested

amylopectin

• branched polymer with alpha 1,4 and 1,6 linkages

• comprises 70-80% of starch

• de-branching enzyme of alpha 1,6 glucosidase for digestion

• digested fast

glycogen

• similar to amylopectin

• highly branched

• alpha 1,4 & 1,6

• storage form of glucose

cellulose

• long, linear polymer of repeating glucose units of beta 1,4 linkage

• insoluble in water

• indigestible in mammalian enzymes

hemicellulose

• heterogeneous group of polysaccharide substances

• sugars in backbone, side chains

• beta1,4

lignin

• highly branched poly-phenolic polymer composed of phenol units with strong bonding

• indigestible by mammalian enzymes; resistant to microbial enzymes

• plant content increases as plant matures

structure of NDF

• lignin (wove everything together)

• hemicellulose (supports and join frame)

• cellulose (frame)

pectin

• polysaccharide compounds

• backbone= alpha 1,4 galacturonic acid

• microbial fermentation

• produces energy but not present in high amounts in diets

beta-glucans

• homo-polymers of glucopyranose units with beta 1,4 and 1,3

• water-soluble, highly fermentable

• used commercially as functional fibre

soluble xylans

• beta-linked xylose backbone, arabinose side chains

• rye and wheat major sources

dietary fiber

natural fiber contained in food

functional fiber

isolated desirable components extracted from food or made in a lab, used as a supplement

effects of fiber

• solubility in water

• water-holding capacity and viscosity

• adsorption or biding ability

• degradability/fermentability

• disease prevention and management

carbohydrases

enzymes responsible for carb digestion

carb digestion in mouth

• salivary glands release alpha-amylase that hydrolyzes alpha 1,4 in amylose

• salivary glands release salivary alpha amylase that hydrolyze alpha 1,4 in amylopectin forming dextrins

carb digestion in stomach

• acidic gastric juices destroy salivary amylase

• dextrin pass unchanged into small intestine

carb digestion in small intestine step 1

• pancreas releases alpha amylase into small intestine to hydrolyze alpha amylase

• dextrins broken down into maltose and limit dextrins

carb digestion in small intestine step 2

• maltose is hydrolyzed by maltase (brush border enzyme) forming free glucose

• limit dextrins hydrolyzed by alpha dextrinase forming glucose

sucrase

brush border enzyme will take sucrose and break down to glucose + fructose

absorption of monosaccharides

• happens in duodenum and jejunum

• little ileal absorption

• very little stomach and large intestinal absorption

• active and facilitated transport

transport of monosaccharides

• portal circulation for transport to the liver

• galactose, fructose converted to glucose derivatives via phosphorylation

• glucose metabolized by liver

• glucose transporters important

GLUT2

low infinity transporter; glucose from enterocyte to blood

Glut 4

insulin-sensitive, in muscle and adipose tissue

glucagon

• antagonistic to insulin

• secreted when glucose is low

glycogenesis

• stores excess glucose

• when insulin is high

• helps control sugar levels

fatty acid synthesis

• use extra glucose

• glucose is store as triglycerides

oxicidation

• aerobic

• 1 glucose = 38ATP

pre-gastric carb fermentation

• microbial enzymes can breakdown beta-linkages

• volatile fatty acids are by-products

• energy used for microbial growth

VFA: acetate and butyrate

• results in the release of H+

• if they accumulate in rumen, fermentation will slow down

• combines with carbon to create methane + are released

VFA: propionate

excess production results in reduction of methane production