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Flashcards in L9: Carbohydrates Deck (21)

*Describe how carbohydrates are classified as sugars or non-sugars

Give brief overview of CHO's?

  • CHO = sugars + fibres
  • Major component of plant tissue
  • General formula (CH2O)n (n = 3 or more)
  • Major energy source for herbivores
  • Classified as sugars or non-sugars
  • Nutritionally classified as fibrous or non-fibrous
  • CHO consist of 70-80% of feed consumed by grazing animal


*Describe how carbohydrates are classified as sugars or non-sugars


  • Sugars are more simple, more digestible
    -Tri, Hex, Pent-oses, di, tri-saccherides
    -Ribo, gluc, galact, lact, malt, suc, fruct -ose
  • Non-sugars are more complex
    -Glyco lipids & proteins
    -starch, cellulose, hemicelluloses, glycogen


*Describe what is meant by soluble (non-fibrous) and insoluble (fibrous) carbohydrate


  • Fibrous
    -structural component of plant (cell walls)
    -Plant fibre increases w/ age and height
    -animal emzymes unable to digest
    * microbes able to do some fermentative digestion (rumen/hindgut)
  • Non-fibrous
    -easily digested energy source
    -e.g. lactose or starch


What is an enantiomer?

  • optical isomer
  • same chemical structure
  • same molecular order
  • But rotate plane-polarised light in opposite direction
    -often means different chemical reactions
  • L and D isomers


Starch and glycogen are polymers of the alpha form of glucose.
T or F?
Cellulose is a polymer of which form of glucose?

  • T
  • Beta fo


Describe starch and its composition

  • Reserve CHO in plants
  • Large amounts of lactic acid are produced when it is digested
  • Abundant in seeds and fruit
  • Mix of amylose and amylopectin


Describe glycogen

  • Main CHO storage in animals
  • often called animak starches
  • Found in liver and muscle
  • Used as immediate energy source
    -fight or flight
  • Mobilised by glucagon
    -converted by liver into glucose
  • -ve feedback
    < BG
    -glucagon released, glycogen released
    -enters blood, circulates to liver
    -converted to glucose, then to pyruvate
    -enters TCA cycle, returns to glucose


Describe cellulose

  • Most abundant CHO
  • plant stucture to cell walls, rigidity
  • comprised of B-D-glucose
  • Often found w/ lignin and hemicellulose
    -influences digestibility through enzyme access


Describe the structure of the following monosaccheride derivatives:
Amino sugars

Deoxy sugars


How are they different to glucose?

  • Amino sugars
    -hydroxyl group of C2 replaced w/ amino group NH2
  • Deoxy sugars
    -hydroxyl (OH) group replaced w/ hydrogen
  • Glycosides
    -H ion at C1 is replaced w/ an alcohol or phenol


Describe heteroglycans

  • Help give plant resistance
  • Pectic substances
    -found in primary cell walls (gelling properties)
  • Exudate gums (saps)
  • Hyaluronix acid
    -present in skin, umbilical cord (joint lubricant)
  • Chondroitin
    -cartilage, tendon, bone
  • Hemicelluloses


Describe hemicelluloses

  • alkali soluble cell wall polysaccherides
  • composed of mainky hexoses and pentoses
    -joined by B glycosidic linkages
  • [ ] increases w/ plant age
  • Low digestibility


Describe lignin

  • Plant tensile strength
  • masking effect, major impact on nutritive value
    -decreases digestibility by encrusting plant fibres rendering them inaccessible to digestion


*Describe the process of carbohydrate digestion in monogastrics


  • Animal enzymes digest CHO in SI
  • Enzymatic digestion
  • simple sugars formed and absorbed into BS
  • Specific enzymes for each type of polysaccheride
  • all polysaccherides are digested to monosacch. before absorption


*Describe the process of carbohydrate digestion in monogastrics

Describe the process


  • 1. Dietary polysac. converted to disacc. by salivary and pancreatic amylases
  • 2. Disacch. converted to monosacc. by brush border enzymes
  • 3. Depending on chemical composition, some monosacc. absorbed across apical membrane by by actively attaching to a specific carrier (aldoses)
  • 4. Others absorbed by facilitated diffusion (ketoses; fructose)


*Describe the process of carbohydrate digestion in monogastrics

How is fibre digestion in MNG possible and what limits this?

  • Possible by microbial digestion in large intestine
  • VFA production
    -energy but no protein digestion
  • Large caecum = reasonably efficient fibre digestion
  • small caecum = limited fibre digestion
  • Type of monogastric animal determines how much fibre digested


*Describe and understand the process of carbohydrate digestion in rumen/hindgut 

Ruminant digestion of non-fibrous CHO?

  • enzymes secreted by microbes access first
  • Fermentation = VFA
  • VFA's absorbed across rumen wall and used for energy by ruminant
  • Inefficient in high quality feed as microbes use 30% of the energy


*Describe and understand the process of carbohydrate digestion in rumen/hindgut 

Ruminant fibre digestion?

  • Fibrous CHO fermented in rumen
  • Digested to VFA
  • Highly efficient w/ low quality/high fibre feed
    -But if too low quality, need to feed N source as well
  • CHO attacked by hydrolytic microbial enzymes
  • Monosacch. and short chain polysacc. liberated in rumen
  • Rapidly absorbed by microbes and metabolised to provide energy
  • End products are VFA, CO2, CH4 (methane)


*Describe volatile fatty acid (VFA) synthesis and the importance of VFAs as an energy source 

Describe VFA synthesis

  • Cellulose and starch are converted to pyruvate via glycolysis, which is then converted to VFA
  • VFA produced depends on aa composition
  • Acetate and butyrate enter TCA cycle
  • Proprionate is the only one thatis able to be converted to glucose
  • Methane and CO2 also produced


*Describe volatile fatty acid (VFA) synthesis and the importance of VFAs as an energy source 

Describe the proportions of VFA's

  • Proportions of individual rumen VFA reflect nature of diet
  • High roughage = increased acetate
  • high grain = increased proprionate
    -High levels of H2O soluble CHO or concentrate
  • Increases in acetate:proprionate reduces both efficiency of ME use & microbial protein production
  • Methane production needed for acetate and butyrate production


*Describe volatile fatty acid (VFA) synthesis and the importance of VFAs as an energy source 

Describe the importance of VFA's?

  • VFAs are essentially end products of anaerobic material metabolism
  • still considerabke energy which can be derived from aerobic metabolism
  • accumulation of VFAs in rumen suppresses or alters femerntative process by > pH
  • Host animal must maintain conditions for fermentation by buffering and removing VFAs via absorption