Pcog lec - 1st half of carbs

• Carbohydrates are structurally polyhydroxylated ketones or

  aldehydes
• Carbohydrates can exist as one distinct carbohydrate molecule

  (monosaccharide) or as repeating structures of the

  monosaccharide units (oligo- and polysaccharides)
• The biosynthesis of monosaccharides is derived from

  photosynthesis, consisting of the light-dependent and

  light-independent (aka carbon fixation or Calvin-Benson

  cycle) reactions.
• Formation of oligo- and polysaccharides usually involves

  formation of UDP-monosaccharide from uridine

  triphosphate + the monosaccharide, followed by reaction

  with a preexisting oligo- or polysaccharide in several (up to

  thousands of) times
• MONOSACCHARIDES - Smallest unit; cannot be further hydrolyzed
• MONOSACCHARIDES

  • Classified by functional group (aldose vs ketose) as well as

  by the number of carbons

  • D - or L -isomerism depends on the penultimate carbon

  • Crystalline, water -soluble and sweet

  • 3 to 9 carbon atoms (the most important ones are hexoses)
• 2 carbon = diose

  aldose name - Hydroxyacetaldehyde (never free in nature)

  no ketose name
• 3 carbon = triose

  aldose name - Glyceraldehyde

  ketose name - (DHA) Dihydroxyacetone
• 4 carbon= tetrose

  aldose name - Erythrose, Threose

  ketose name - Erythrulose
• 5 carbon = pentose

  aldose name - Ribose, Arabinose

  ketose name - Ribulose
• 6 carbon = hexose

  aldose name = Glucose, Galactose

  ketose name = Fructose
• 7 carbon = heptose

  no aldose name

  ketose name - Sedoheptulose
• 8 carbon = octose

  no aldose name

  ketose name = D-glycero-D-mannoctulose (found in avocado pulp and Sedum)
• LINEAR CONFIGURATION: FISCHER PROJECTION

  • L-glucose – less active

  • D-glucose – more active
• CYCLIC CONFIGURATION: HAWORTH PROJECTION

  • Pyranoses: 6-member ring (ex. glucopyranose)

  • Furanose: 5-member ring (ex. ribofuranose)

  o unstable but may be stabilised on glycoside formation
• Anomeric carbon

  o Spotted by finding a carbon with two oxygens

  o Alpha – anomeric OH down

  o Beta – anomeric OH up
• GLUCOSE

  Synonyms: Dextrose, blood sugar, grape sugar, physiologic sugar

  Chemical Nature: Aldohexose

  Source/s: Enzymatic hydrolysis of starch

  Uses: Sweetening agent
• GLUCOSE

  Derivatives:

  1. Liquid glucose - thick, syrupy liquid from incomplete hydrolysis of starch
  2. Calcium gluconate - electrolyte replenisher
  3. Calcium gluceptate and levulinate - calcium sources from 7C and 5C glucose derivatives
  4. Ferrous gluconate - hematinic, given for iron deficiency anemia
• FRUCTOSE

  Synonyms: Levulose, fruit sugar

  Natural source: Fruits and honey; hydrolysis of inulin (see polysaccharides)

  Chemical Nature: Ketohexose

  In nature, in furanose form; isolated in crystalline form as pyranose

  Source/s: From isomerization of glucose by Streptomyces through the

  enzyme glucose isomerase

  Uses: Food for diabetic patients, for infant feeding formula, for fructose injection

  • The sweetest monosaccharide
• GALACTOSE

  Chemical Nature: Aldohexose (C4 epimer of glucose)

  Source/s: Milk (as lactose) and neuronal fibers (as galactoceramides)

  • Convertible to glucose in the human body (enters glycolysis after 4 steps)
• XYOSE

  Synonym: Wood sugar

  Chemical Nature: Aldopentose

  Source/s: Boiled corn cobs, straw, heartwood of deciduous trees, and other materials soaked in dilute acids to hydrolyze its polymer form xylan

  uses: Diagnostic aid in conditions with intestinal malabsorption (ex. Crohn’s disease, celiac disease, etc.)
• Types of monosaccharides:

  • glucose
  • fructose
  • galactose
  • xylose
• Types of oligosaccharides:

  1. maltose
  2. sucrose
  3. trehalose
  4. lactose
  5. lactulose
• Other types of oligosaccharides:

  1. Maltotriose
  2. dextrins
  3. gentianose
  4. raffinose
  5. stachyose
• MALTOSE

  Chemical Nature: 2 units of glucose on a α(1→4) glycosidic bond

  Source/s: From diastatic fermentation of barley (Hordeum vulgare) and other grains

  Uses: Sweetener, tonicity adjuster, component of beers
• SUCROSE

  Synonyms: Table sugar, saccharum

  Chemical Nature: Glucose +fructose on a α-(1→2)-β glycosidic bond

  • Non-reducing sugar (negative on Benedict’s, Fehling’s, Barfoed’s, or Tollen’s tests)

  • Upon hydrolysis, yields a mix of glu and fru called invert sugar

  source/s:

  • Sugar beet (Beta vulgaris) through limp slivers called cossettes
  • Sugarcane (Saccharum officinarum)
  • Sugar maple (Acer saccharum)
• SUCROSE BIOSYNTHESIS

  • Recall: G6P can be converted to UDP-glucose

  • Then, UDP- glucose goes through 2 steps to become sucrose in plants
• SUCROSE

  Sugarcane/ sugar beet is boiled with lime (CaO) to invert the

  sugar and coagulate albumin, and is decolorized with sulfur

  dioxide;

  1. albumin floats as a layer and is removed
  2. sugar crystallizes and is removed from solution, and
  3. some sugar will not anymore crystallize, and the resulting thick mixture is known as molasses

  • Demulcent, coating agent, sweetening agent, syrups,

  preservative, anti-oxidant
• TREHALOSE

  Found in brown seaweed, widely distributed in fungi

  • Glucose + glucose via α-(1->1)-α glycosidic bond

  • Just like sucrose, is nonreducing
• LACTOSE

  Chemical Nature: Glucose + galactose on a β(1->4) glycosidic bond

  Source: Milk of cow (Bos taurus)

  From the crystallization of whey, a by-product of cheese production

  Use: Tablet diluent

  Lactose intolerance: Absence of enzyme lactase/ -galactosidase

  (diarrhea, GI disturbance)
• LACTOSE

  • Butter – fat globules united by churning

  • Buttermilk – liquid after globules unite

  • Skimmed milk – milk without cream/globules

  • Coagulum (coagulated casein) – skimmed milk treated with rennin/rennet

  • Further treated/fermented to become cheese

  • Whey – skimmed milk without coagulated proteins
• LACTOSE

  Variations of milk:

  • Condensed milk– partially evaporated, sweetened milk

  • It is very viscous due to addition of a lot of sugar

  • “Evaporated milk” is similar, but it is unsweetened

  • Malted milk– milk evaporated with malt extract

  • Kumyss– alcoholic beverage made from fermented mare's milk; made originally by nomads of central Asia
• LACTULOSE

  Chemical Nature: Product from the alkaline rearrangement

  (tautomerization) of lactose

  Source/s: Semi-synthetic

  Uses: Laxative

  Mechanism of action: Poorly absorbed; bacteria (colon) converts it to

  acetic acid & lactic acid

  1. both acids are GI irritants, ↑ peristalsis

  2) decreases blood ammonia concentration in portal-systemic

  encephalopathy (acidified stools trap ammonia as NH4+)
• OTHER OLIGOSACCHARIDE:

  1. Maltotriose
  2. Dextrins

  • Limit dextrins: products of partial hydrolysis of starch (amylase,

  glucosidase)

  • Browning of bread

  • α-glucosidase inhibitors – inhibits intestinal absorption of sugars; an oral hypoglycemic agent (specifically for postprandial sugar)

  3. Gentianose- glu + glu + fru (from Gentiana spp.)

  4. Raffinose – glu + gal + fru (from many seeds, such as cottonseed)

  5. Stachyose- glu + gal + gal + fru (from Stachys japonica)

  STARCH →(amylases)→ LIMITING →(α-glucosidases)→ GLUCOSE DEXTRINS
• sucrose - Non-reducing sugar (negative on Benedict’s, Fehling’s,

  Barfoed’s, or Tollen’s tests) Upon hydrolysis, yields a mix of glu and fru called invert sugar. Sugarcane/ sugar beet is boiled with lime (CaO) to invert the sugar and coagulate albumin, and is decolorized with

  sulfur dioxide;

  1. albumin floats as a layer and is removed
  2. sugar crystallizes and is removed from solution, and
  3. some sugar will not anymore crystallize, and the resulting thick mixture is known as molasses

  • Demulcent, coating agent, sweetening agent, syrups,

  preservative, anti-oxidant
• The main organelle involved in photosynthesis is the

  chloroplast and it consists of the thylakoid, the

  granum/grana, and the stroma
• It is in the surface membrane of the thylakoid where the light

  reactions take place
• Produces ATPs and NADPH that are used by the cell to

  convert carbon dioxide into an organic molecule in the

  process known as Calvin Cycle
• The Calvin Cycle initially produces a 3-carbon sugar which

  is known as 3-PGAL (3-Phosphoglyceraldehyde) which

  then produces the sugar CH2O that is stored in the

  cytoplasm
• Glucose is a cytosolic sugar