Carbohydrates

ANSC 311 - Lecture 5

what elements make up carbohydrates?

carbon, hydrogen and oxygen

true or false: carbohydrates are the most abundant organic molecules in nature

true

what is the major component of plant tissue?

carbohydrates

what % of dry matter of forages does carbohydrates make up?

70%

what % of weight of animals does CHO make up?

less than 1%

how does CHO in plants arise?

from photosynthesis

how is CHO made in plants via photosynthesis?

radiant energy from the sun is captured by chlorophyl and changed to chemical energy

what is the function of CHO metabolically?

supports formation of glucose from CO2 and H20 (an endergonic rxn)

CHO includes:

• sugars

• starch

• cellulose

• gums

• related substances

CHO serves as a _________ component in plants

structural

list the soluble and insoluble CHO.

soluble:

• monosaccharide - 1 unit (sugar molecules)

• disaccharide - 2 units

• oligosaccharides - 3 to 10 units

• polysaccharides - greater than 10 units

insoluble:

• polysaccharides

how are monosaccharides classified?

by their number of Carbon atoms

what monosaccharides are nutritionally important?

pentose and hexose (5-C and 6-C)

what are examples of pentoses?

arabanose, xylose, ribose

what are examples of hexoses?

glucose, fructose, galactose, mannose

examples of disaccharides.

maltose = glucose+glucose

cellulobiose=glucose+glucose

sucrose= glucose+fructose

lactose= glucose+galactose

what are the 3 major polysaccharides that are important to nutrition?

starch, glycogen, cellulose

heteropolysaccharide

composed of 2 more types of monosaccharides

homopolysaccharide

composed of one type of monosaccharide

what is the primary digestible polysaccharide in plants?

starch

what is starch composed of?

repeating units of maltose, which is repeating units of glucose (so all glucose)

what are the 2 important forms of starch?

amylose and amylopectin

functions/characteristics of glycogen.

• animal starch

• small amounts in liver and muscle

• highly branched

• water soluble

characteristics of cellulose

• homopolysaccharide

• most important structural polysaccharide of plants

• basic unit: beta-D-glucose

• beta 1-4 linkage, straight chain

• highly stable

• cotton is purest form

why is cellulose such a stable compound?

no animal makes an enzyme that can digest beta bonds

in addition, the beta bond imparts a structural rigidity that makes the fibrous nature of cellulose so different from starch

what is the most abundant of naturally occurring organic compounds?

cellulose

cellulose is not digestible by mammals, so how are cattle able to eat roughages?

bacteria in the rumen produce enzymes able to break down cellulose

characteristics of hemicellulose.

• heteropolysaccharide

• complex mixture of glucose, mannose, arabinose, and galactose

• beta 1-4 linkage

• principal component of plant cell wall

• degraded only by microbial enzymes

characteristics of pectin

• heteropolysaccharides

• polymers of 1-4 linked glucose

• degraded only by microbial enzymes

• found primarily in the space between cell walls

• soluble in water

• plant glue

what are the components of feed carbohydrates?

soluble sugars and pectin, cellulose, hemicellulose and lignin

name a structural non-carbohydrate

lignin

lignification

reduces digestibility by acting as a barrier to the plant carbohydrate

list reasons why lignin is bad from a nutritional standpoint.

• decreases feed intake

• completely indigestible

• reduces digestibility of other feed components

lignin (increases/decreases) in content in plants, especially plant stems, as plants mature

increases

functions of carbohydrates

• source of energy

• source of heat

• building block for other nutrients

• stored in animal body by converting to triacylglgerols or glycogen

what are the main feeds we would use to feed to add energy to the diet in the form of carbohydrates?

• corn

• sorghum

• oats

• barley

• wheat

• other small grains (rice, millet)

• byproduct feeds from any of the above

what is the primary CHO for monogastrics?

starch

how is starch broken down in the small intestine of monogastrics?

starch is digested by pancreatic amylase

complex polysaccharides are completely digested to monosaccharides and readily absorbed into the bloodstream via small intestine

in what animal is the utilization efficiency of fibrous compounds the greatest in?

horses

in horses, what can an overconsumption of starch lead to?

can result in the overproduction of other acids such as lactic acid and/or gas, potentially resulting in colic

what type of animal is able to efficiently use both starch and fibrous compounds such as cellulose and hemicellulose?

ruminants

where is the primary site of CHO digestion in ruminants?

reticulo-rumen

what are the primary end-products of rumen fermentation of CHO?

volatile fatty acids (VFA) - produce energy-yielding compounds such as glucose

what are the primary VFA’s?

acetic acid, propionic acid and butyric acid

what are high starch diets characterized by? what are higher fiber diets characterized by?

high starch = higher propionic acid

high fiber = higher acetic acid

true or false: in mature ruminants, intestinal digestion of CHO is not limited.

false, it is limited