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ASC273 > L9: Carbohydrates > Flashcards

L9: Carbohydrates Flashcards

1
Q

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

Give brief overview of CHO’s?

A
  • 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
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2
Q

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

A
  • Sugars are more simple, more digestible
  • Monosaccherides
  • Oligosaccherides
  • Tri, Hex, Pent-oses, di, tri-saccherides
  • Ribo, gluc, galact, lact, malt, suc, fruct -ose
  • Non-sugars are more complex
  • Polysaccherides
  • Heteroglycans
  • Glyco lipids & proteins
  • starch, cellulose, hemicelluloses, glycogen
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3
Q

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

A
  • 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
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4
Q

What is an enantiomer?

A
  • optical isomer
  • same chemical structure
  • same molecular order
  • But rotate plane-polarised light in opposite direction
  • MIRROR IMAGES
  • often means different chemical reactions
  • L and D isomers
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5
Q

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

A
  • T
  • Beta fo
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6
Q

Describe starch and its composition

A
  • 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
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7
Q

Describe glycogen

A
  • 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
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8
Q

Describe cellulose

A
  • 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
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9
Q

Describe the structure of the following monosaccheride derivatives:
Amino sugars

Deoxy sugars

Glycosides

How are they different to glucose?

A
  • 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
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10
Q

Describe heteroglycans

A
  • 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
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11
Q

Describe hemicelluloses

A
  • alkali soluble cell wall polysaccherides
  • composed of mainky hexoses and pentoses
  • joined by B glycosidic linkages
  • [] increases w/ plant age
  • Low digestibility
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12
Q

Describe lignin

A
  • NOT A CHO
  • Plant tensile strength
  • masking effect, major impact on nutritive value
  • decreases digestibility by encrusting plant fibres rendering them inaccessible to digestion
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13
Q

*Describe the process of carbohydrate digestion in monogastrics

Overview?

A
  • 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
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14
Q

*Describe the process of carbohydrate digestion in monogastrics

Describe the process

A
    1. Dietary polysac. converted to disacc. by salivary and pancreatic amylases
    1. Disacch. converted to monosacc. by brush border enzymes
    1. Depending on chemical composition, some monosacc. absorbed across apical membrane by by actively attaching to a specific carrier (aldoses)
    1. Others absorbed by facilitated diffusion (ketoses; fructose)
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15
Q

_*Describe the process of carbohydrate digestion in monogastrics_

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

A
  • Possible by microbial digestion in large intestine
  • caecum/colon
  • 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
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16
Q

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

Ruminant digestion of non-fibrous CHO?

A
  • 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
17
Q

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

Ruminant fibre digestion?

A
  • 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)
18
Q

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

Describe VFA synthesis

A
  • 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
19
Q

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

Describe the proportions of VFA’s

A
  • 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
20
Q

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

Describe the importance of VFA’s?

A
  • 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

ASC273 (30 decks)

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