AN SC 260 ch.4
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What are carbohydrates? Simple and complex?
- • Carbon combined with O and H
- – O and H ~ same ratio as water
- • CnH2nOn – simple carbohydrates
- • CnH2n-2On-1 – complex carbohydrates – Loss of 1 or more molecule of water
How much does CHO compose of DM in forages? in cereal grains? of the animal?
- – Up to 70% of the DM of forages
- – Up to 85% of the DM of cereal grains
- – Less than 1% of the weight of animals
- • Glycogen, glucose
General functions of carbohydrates?
– Major components of plant tissue
- • Photosynthesis – 6H20+6CO2 ==>C6H12O6 +6O2
- • Simple CHO (esp. glucose and ribose) – Energy transformations
- – Tissue synthesis
- • Complex CHO – Soluble (eg. starch) – energy reserves
- » Roots, tubers, seeds
- – Insoluble (eg cellulose, hemicellulose) -- structure
- – Main energy source for most livestock • Mainly glucose for monogastrics
- – Free CHO central to metabolism
- • Especially glucose
- • Little storage in the body – Glycogen <1% of body weight
CHO are needed essentially for?
- – Not essential for growth if protein and triglycerides present
- – Late gestation (rat pups)
- – Lactation
- – Fibre
Classification of CHO?
- – Pentoses – 5C sugars
- – Hexoses – 6C sugars
- – Monosaccharides – one
- – Disaccharides – two
- – Trisaccharides – three
- – Etc.
- – Oligosaccharides – 4-10 sugar molecules – Polysaccharides – >10 sugar molecules
Glucose (monosaccharide). Description and function?
- • Monosaccharide (1 sugar molecule)
- • Hexose (6 carbon atoms) – Also referred to as dextrose (actually d-glucose)
- • Ultimate source of energy for most animal cells
- – Ingestion of glucose or precursors – Conversion from other metabolites
- -central to metabolism
What are the isomers of glucose?
- • Isomers of glucose – D-glucose nutritionally relevant
- – L-glucose not used by organisms
How is glucose absorped?
- • Can be absorbed as glucose
- – No degradation needed for absorption
- – Competitive inhibition
- • Shared transport pathway across intestinal cell with other monosaccharides
What is fructose?
- • 6 carbon keto-sugar – Fruits, green leaves, honey
- • Sweetes tnatural sugar
What is a disaccharide?
2 monosaccharides joined together
What is sucrose? plus what does it break down into?
- – Common table sugar
- – Most common disaccharide found in plants
- • As much as 20% in sugar cane and beets
- – Sucrase hydrolyzes sucrose
- • Glucose and fructose released – Fructose converted to glucose for metabolism
- » After absorption – Ruminants do not produce sucrase – Young animals have low levels
What is lactose?
- -Disaccharide. Made up of galactose and glucose. Joined by a B glcosidic bond
- – Milk sugar
- • Less sweet than sucrose
- – Lactase
- • High at birth
- • Declines with age
What is maltose?
- – Uncommon in nature
- • Product of starch digestion
- – Present in germinating grain
- - Is a dissacharide with 2 glucose molecules and joined by a alpha glyocsidic bond.
What are polysacharides? Examples...
chains of sugar molecules joined together. Simple starch (alpha glycosicidic bond), cellulose (B glycosicidic bond), See figure page 3.
Which glyocosidic bonds can animals breakdown?
tricky question: enzymes in the animals body can break down alpha glycosidic bonds and microbes are able to break down the beta glycosidic bonds and produce VFA's
What is starch? Amylose? Amylopectin?
- • Glucose linked together with α-1,4 bonds (amylose)
- - • Glucose linked together with α-1,4 bonds plus å-1-6 branch points (amylopectin) is also plant storage of glucose.
Which products does the ratio of amylose to amylopectin vary? How does the ratio effect?
- -waxy corn
- -rice and potatoes
Affects the milling quality - high amylopectin = thickening agent
Can animals break down amylose and amylopectin? How is it broken down?
yes, but amylose is less digestable. It is broken down by amylase. Amylase is found in the saliva and pancreas. Starch is broken down by dextrins which are broken down by maltose which is broken down by glucose.
Starch characteristics? When heated?
- • Insoluble in cold water
- • When heated
- – Water in starch will gelatinize
- • Potato starch – burst open
- • Cereal grains – swell
- – Increases accessibility by enzymes
- • Amylose can re-crystalize (decreased availability)
- • Amylopectin tends to gel (increased availability)
What does it mean that starch is able to retrograde? What item is also able to do this?
It means that starch is able to go back to its normal form. Play doh has a retrograde inhibitor amylose so that it doesnt revert back
- • Glucose linked together with α-1,4 bonds – Highly branched (α-1,6 bonds)
- – Found in liver, muscle
- – Short-term maintenance of blood sugar
- • Glycogenesis
- • Glycogenolysis
formation of glycogen
breakdown of glycogen
- • Most abundant plant constituent
- – Glucose chain with β-1,4 bonds
- – Rarely found in nature by itself • Cotton
- – Present with lignin, hemicellulose, cutins and minerals
Many celluloses together?
- • Repeating units of cellobiose – Up to 15,000 residues per chain
- • Bonding within and between chains give strength
- • Degradability dependent on lignification
- • Polymers of hexoses and pentoses
- – Glucose, galactose, mannose, xylose, arabinose
- – More digestible than cellulose
Digestion of hemicellulose?
- • Digestion is complex
- – Digestion in lower digestive tract
- • Acid releases arabinose side chains
- • Not a CHO
- – Closely associated with cellulose and hemicellulose
- • Repeating phenylpropane units
- – Strength to plant structures
- -minimizes moisture loss
- • Soluble non-starch polysaccharides – “NSP”
- • β-linked sugar molecules
- – Indigestible by animals
- – Soluble in water
- Viscous digesta, these nutrients not being absorbed leads to pathogenic bateria. Which form a thick glue in the digestive tract making it hard for enzymes to function.
- -often thought as anti nutrional factors
- – Xylose chain with arabinose side chains
- – High in wheat, triticale
- • Wheat composed lots of Monogastric diets will find Exogenous arabinoxylanase
- – β -linked polymers of glucose (β -1,4 and 1,3 linked)
- – Exogenous β -glucanase
- – Cellulose is an insoluble β -glucan (β -1,4 linked)
What happens with the use of exogenous enzymes?
- – Reduce digesta viscosity
- – Monsaccharides available for absorption
- Found in plant cell walls
- – Associated with polysaccharides (Linear chains of α-linked D-galacturonic acids)
- – Gelling properties (Jam making)
See figure page 7 PLANT CARBOHYDRATES
Describe the breakdown of starch
It is broken down by amylase. Which is secreted from the saliva and pancreas.
Starch is broken down into dextrins then into maltose and finally glucose.
What are dextrins?
A mixture of branched and unbranched oligosccharides. dextrins are limited by how many are broken down by isomaltose
Disaccharide digestion? Is it important?
- – Two monosaccharides joined together
- • Must be hydrolyzed to be absorbed
Where is glucose absorped?
– Most in proximal small intestine (duodenum and jejunum)
How is glucose transported from intestinal lumen to inside cell?
– 2 molecules of Na required to transport 1 molecule of glucose into cell. See figure page 8
How is glucose transported from inside the cell to the intestinal lumen?
- • Facilitative transport out of intestinal cell
- – Down a concentration gradient
How is the absorption of other monosaccharides?
They are absorped way less effeciently and there is no active transport mechanisms
Transport of monosaccharides?
- Some monosaccharides
- • Converted to glucose in intestinal cell – No problem
- • Common transport pathway out of intestinal cell – leads to Competitive inhibition
Glycogen storage? Where does glycogen come from?
There is very little CHO storage if there is it is stored as glycogen. Glycogen is present in liver and muscle.
What happens when glucose and ATP are in high amounts?
insulin stimulates glycogenesis
• Formation of glycogen from glucose – 1 ATP required for each glucose incorporated
- • Release of glucose from glycogen
- – No hydrolysis of ATP required
what stimulates glycogenolysis?
- » Glucagon (pancreas)
- » Epinephrine (adrenals)
– Synthesis of glucose from non-glucose precursors
What are some of the precursors of gluconeogenesis?
- • Amino acids (gluconeogenic)
- • Lactic acid
- • Fat (glycerol via DHAP
- – precursor to pyruvate) – No net synthesis of glucose from fatty acids
- – Acetyl CoA produced must enter TCA cycle
What is completely dependent on glucose for energy and how long are the glycogen reserves?
- - RBC depend completely on glucose
- - have glycogen reserves for half day fasting
- breakdown of glucose for energy
- • Glucose => fructose 1,6 bisphosphate => pyruvate
- – 2 ATP used
- – 4 ATP produced
- – 2NADH=>6ATP
- – Net 8 ATP generated
• 2 Pyruvate => 2 Acetyl CoA – 2NADH=>6ATP
- • 2 Acetate => 2CO2 + 2H20 – 2GTP=>2ATP – 6NADH=>18ATP – 2FADH2 =>4ATP
- – Net 24 ATP generated
What is the total ATP generated from glycolysis? Is glycolysis worth it?
8+6+24=38 moles ATP. yes but lots of energy is lost in heat
What happens to excess glucose?
- • Excess glucose converted to fat
- – Limited ability to store glycogen
What is the process of glucose being turned into fat?
- – Glucose => pyruvate => acetyl CoA
- – Acetyl CoA is the precursor for fat synthesis
What happens to excess amino acids?
Excess amino acids to fat. Because the body doesn't store them
What is the process of amino acids being turned into fat?
- – Some amino acids converted to pyruvate
- • Then to acetyl CoA
- – Some amino acids converted to acetyl CoA – Acetyl CoA is the precursor for fat synthesis
What is ketosis?
- – Accumulation of ketones
- • Acetone
- • Acetoacetate
- • β-hydroxybutyrate
- – Ketonemia (high ketones in blood)
- – Ketonuria (ketones in urine)
How does ketosis happen?
There isnt enough glucose in the blood so fat is metabolized for energy. Thus ketones are being produced faster than they can be metabolized from the buildup of acetly CoA. It will smell like nail polish.
When does ketosis happen in cattle? in sheep?
- – Cattle – peak lactation
- – Sheep – late pregnancy
When do you see ketosis in monogastrics?
- • Diabetes
- • Excessive morning sickness
- • Beginning of lactation
- • Starvation
- • Atkins diet (all you eat is protein) wont have enough energy
What does insulin do?
- • Insulin enhances cellular uptake of glucose
- – Influences cell permeability to glucose
- – There is Protein, glycogen, fat synthesis
What is diabetes mellitus?
- – Common in humans, less common in animals
- – Impaired glucose tolerance, take a longer time to clear excess glucose from the blood
What is insulin dependent diabetes mellitus?
• IDDM (Type I; juvenile onset diabetes) leads to the Destruction of Islets of Langerhans in pancreas
- Can be caused virally and genetically
What is non-insulin dependent diabetes?
- • NIDDM (Type II; adult onset diabetes)
- – Deficiency of cell-surface binding sites for normal glucose uptake
- – Occurs in adults
- – Genetics
- – Aggravated by obesity
Gestational diabetes mellitus
- • Increased tissue resistance to insulin
- • Most important form of diabetes in domestic animals
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