chapter 7 carbohydrates. function: source of energy for life process. in plant : 1.simple sugars...
TRANSCRIPT
Function:
• Source of energy for life process.• In Plant :
1.Simple sugars (glucose,ribose) involved in energy transformation and tissue synthesis.
2.Starch as energy reserve.3.Insoluble fraction (cellulose, hemicellul
ose) provided structural support.
• Glycan: vary in shape and size, rangeing from linear chains (polysaccharides)to highly branched molecular
• Soluble components of the plant cell:starch, hemicellulose and beta-glucans, which are available to fermentation.
Cellulose: glucose(1-4)-β-glucoside linkage.
• Microflora of the rumen of ruminants and cecum and colon of nonruminants produce cellulase to hydrolyze cellulose.
• Other nonrumianats utilize cellulose by anaerobic fermentation in large intestine.
• Starch is soluble carbohydrate in plant• Two important molecular of glucose: Linked via a glucos
e-(!-4 )-α-glucoside linkage. • Amylose : glucose(1-4)-α-glucoside linkage linear polym
er of glucose, MW 15000 ~ 100000 D.Amylopectin: linear polymer with branches 10 - 100 milli
on D.• Maize contains 24% amylose and 76% amylopectin, Wa
xy maize contains 1%:99%• Rice and potatoes contain 20%:80%• The hydrolysis of starch in amylose and amylopectin to g
lucose is similar.
Carbohydrate Digestion
( 一 ) preparation for absorption
• Only monosaccharides can be adsorbed from GI tract, except in newborn animals.
• Poly-, tri-, disaccharides hydrolyzed (by enzymes from host or microbe) to monosaccharide
Plant cell wall digestion
• cellulose, hemicellulose, pectin, lignin 為植物細胞壁之主要成分 , 即 structure polysaccharides, insoluble polysaccharide 之生物可利用率 ( bioavailability ), 即影響其營養價值 ( nutritive value ).
• Anaerobic fermentation of carbohydrate results in the production of large quantities of volatile fatty acids (VFA, = acetic acid, propionic acid and butyric acid )and provides a large proportion of the total energy supply.
1.Absorption:
• proximal section of the small intestine (duodenum and jejunum) has greatest capacity to absorb monosaccharides.
• glucose and galactose are absorbed very efficiency. Mannose absorbed about 20% of the efficiency of glucose, arabinose at the lowest rate. (Table 7.3 )
Absorption and transport of monosaccharides
2.Mechanism• Sodium dependent active transport mech
anism transported against its concentration gradient which is maintained by membrane bound sodium-potassium ATPase (Na- K-ATPase)
• Facilitative glucose transporters transport glucose actively down a concentration gradient.
• These two families of glucose transporters are protein (500-600 amino-acids).
3. Factors that affect the absorption of glucose– Reduced by short-term (24 or 48h) fastin
g, increased by restricted feed intake.
– diabetic absorb more rapidly than normal
– adrenalectomy reduce in glucose absorption but no effect on xylose absorption.
– thyroidectomy and ovariectomy reduce glucose absorption.
4.Digestive enzyme deficiency and utilization of CHO
• Young mammals fed large amounts of sucrose develop diarrhea and death results from an insufficiency of sucrase.
• Ruminant species produce no sucrase.
• Some adults have lactase deficiency, like pig and human.
• Xylose feeding of young pigs results in depressed appetite and growth and causes eye cataracts.
The absorption of soluble CHO exceeds 90% Factors that affect the rate of starch digestion :
• particle size.• nature of starch (amylose, amylopectin co
ntent)• interaction of starch with protein, fat.• presence of antinutrient such as phytate, t
annin, saponins and enzyme inhibitors.
( 三 ) Metabolic conversions
• Homeostasis : maintaining the blood glucose concentration
glycogenesis insuline↑
blood glucose glycogen
glycogenolysis glucagon↑
Gluconeogenesis • glucose can be formed by body tissues fro
m noncarbohydrate metabolites, including lipids, amino acids.
• Glucogenic amino acids such as nonessential amino acids and several of essential (arginine, methionine, cystine, histidine, threonine, tryptophane, valine.)
• The amino acids used for gluconeogensis or for energy enter TCA cycle (Fig. 7.2).
• Glucose as an energy source • Glucose is metabolized to energy has two stage
s.
(1) glycolysis : occure under anaerobic condition and production of pyruvate. Referred to as the Embden-meyerhof pathway ( in the cytosol).
(2)oxidation of pyruvate: pyruvate produced by glycolysis is transported into the mitosol and is oxidized to CO2 and H2O with production of energy
• Energetics of glucose catabolism– 1 mole of glucose to 2 mole of pyruvate (pr
oduce 8 mole ATP(10-2))
– 2 mole of pyruvate to 2 mole of acetyl-CoA (produce 6 mole)
– 2 mole acetyl-CoA to CO2 and H2O (produce 24 mole)
Energetics of glucose catabolism 異化 1mole glucose 產生 38mole ATP
• One mole of ATP has a value of 8Kcal/mole• 1 mole glucose 氧化產生之能量為 8Kcal x 38 = 304Kcal (45% of efficiency).
• C6H12O6 → 6CO2 + 6H2O + 673 Kcal
• The conversion of the free energy of the oxidation of glucose has an efficiency of 40-65%.
glycolytic pathway 8 mole of ATP
pyruvate to acetyl CoA 6 mole of ATP
acetate to CO2 and H2O 24 mole of ATP
Totle 38 mole of ATP
Acetic acid as an energy source
• Acetic acid is the major product of carbohydrate digestion in the rumen and only present in the peripheral blood. It is used as a source of energy by various tissues
Propionic acid as an energy
• In ruminant propionate are produced from carbohydrate breakdown in the rumen. →
• Pass across the rumen wall to the liver→
• Change into glucose. : The first stage is conversion to succinyl-COA.(fig.9.7)
Butyric acid as an energy source
• Butyric acid is converted toβ-hydroybutyrate in its passage across the rumen walls and used as a source of energy by number of tissues
Abnormal carbohydrate metabolism
( 一 ) Ketosis:
• 因碳水化合物及脂肪代謝異常 , 使過量之酮體 (acetone, acetoacetate, B-hydroxybutyrate) 累積於體組織。
• 血中濃度增加稱 Ketonemia(acetomia), 出現在尿中則稱 Ketoneuria.
• 特別容易出現於反芻動物開始泌乳 ( 牛 ) 或懷孕期 ( 羊 ) ,對葡萄糖需要量大時, Vit B12 缺乏時。
hypoglycemia, depleted liver glycogen↓
elevated mobilization of adipose tissue lipids↓
increased production of ketones and Lipemia
↓Increase breakdown of tissue protein for energy
↓
• body weight loss (breakdown of tissue protein)
milk production decrease
abortion in pregnant animals
water consumption increase (loss body fluid )
loss of electrolytes (Na, K)• Treatment :
injection of intravenous glucose, adrenal corticoid hormones, or adenocorticotropic hormone(ACTH)
• hyperglycemia ( excessive blood glucose )
• three types :– insulin–dependent diabetes (type )Ⅰ– Non-insulin–dependent diabetes (type )Ⅱ– gestational diabetes
Diabetes mellitus
insulin
• promote glucose utilization
• increase protein synthesis
• decrease protein catabolism
• increase the entry of amino acids into the cell
• stimulates formation of triglycerides (TG)
• inhibit TG breakdown
Diabetes mellitus
• Type :Ⅰ– destruction of the beta cell of Islets of Langerh
ans in the pancrease ( 缺 insulin)– appear any age (genetic)– require insulin administration
Diabetes mellitus
• Type : Ⅱ– defect in utilization of insulin by liver and other
tissue (insulin 作用被破壞 ), defective cellular uptake of glucose and impaired release of glucose from liver, 造成高血壓。
Diabetes mellitus
• Type 3: – increased tissue resistance to the action of
insulin and increase the blood glucose.
• carbohydrate, lipid, amino acid metabolism abnormal
↓
» negative N balance
» glucose loss in urine
» polyuria
» electrolyte loss
Insulin deficiency
Insulin – like growth factors (IGF)
• IGF I and IGF are small polypeptides that Ⅱcontrol the growth of several types of cells, have a structure very similar to that of insulin.
• IGF and bone growth Ⅰ 有關 IGF and fetal growth Ⅱ 有關• IGF and IGF and their binding protⅠ Ⅱ
eins are major links between nutrient intake and anabolic response of cells.
Plant fiber as energy source
• Plant fiber :cellulose, hemicellulose, liglin, gum, and β-glucan are present as cellular membrane and storage form of energy in the plant.
• Tannin present in the seed coat of dark seed (sorghum), it is unpalatable to animal and birds.
• Van Soest partition plant tissues into two fractions.– Cell wall constituents
• Lignin, cellulose, hemicellulose
• Gum: pectin, glucan• - Cell contents
• Simple sugars, starches