M2: Carbohydrates

Carbohydrates

  • organic compounds composed of carbon, hydrogen, and oxygen atoms.
  • Functional groups:
    • Hydroxyl and Carbonyl groups
    • polyhydroxy aldehydes or ketones, or compounds that can be hydrolyzed by them.
  • called sugars and starches
  • Functions:
    • Energy source, structural component
    • In the body, they are used for bursts of energy needed during exercise in the form of glucose.
  • Synthesized:
    • In green plants by photosynthesis (the energy from the sun is stored as chemical energy in carbohydrates

     

Main Branches:

Classification of Carbohydrates

  1. Monosaccharides
  2. Disaccharides
  3. Polysaccharides

1. Monosaccharides

  • Description:
    • Sweet tasting (relative sweetness varies greatly)
    • polar (hydroxyl groups; dipole-dipole) compounds with high melting points
    • presence of so many polar functional groups capable of hydrogen bonding makes the monosaccharides very water-soluble
  • Definition: Simplest form of carbohydrates
  • generally have 3-6 C atoms in a chain with an aldehyde or ketone ending and many -OH groups
  • Simplest forms (isomer: same molecular formula but different structural formula)
    • aldehyde monosaccharide: aldose
    • simplest: glyceraldehyde
    • ketone monosaccharide: ketose
    • simplest: dihydroxyacetone

 

  1. Classification: (by the number of C atoms in its chain
    • Trioses
      • 3 carbon atoms,
      • such as glyceraldehyde (aldotriose) and dihydroxyacetone (ketotriose).
    • Tetroses
      • 4 carbon atoms,
      • such as erythrose and erythrulose.
    • Pentoses
      • 5 carbon atoms,
      • such as ribose and deoxyribose (found in DNA).
    • Hexoses
      • 6 carbon atoms,
      • such as glucose (blood sugar), fructose (fruit sugar), and galactose (found in milk).
    • Heptoses
      • 7 carbon atoms,
      • such as sedoheptulose.
Common Monosaccharides
  1. Glucose (dextrose)
    • blood sugar and most abundant
    • normal blood glucose level 70-110 mg/dL ..100mL
    • excess is stored as polysaccharide glycogen or fat
    • Insulin regulates blood glucose level
  2. Galactose
    • sugar in milk
    • one of the components of disaccharide lactose (glucose + galactose)
    • Galactosemia- lack enzyme needed to metabolize galactose, which accumulates and causes cataracts and cirrhosis
  3. Fructose
    • sugar in fruits
    • one of the components of disaccharide sucrose (glucose + fructose)
    • a ketohexose in honey, twice as sweet as table sugar w/ the same # of calories per gram
Fischer Projection Formula (Open chain)
  • all carbohydrates have 1 or more chirality centers
  • optical isomers → enantiomers
    • one chirality center : two possible enantiomers
    • ~~D~~ → -OH on the right side
    • L → -OH on the left side
    • if many, the farthest from the carbonyl group is considered
    • D naturally occurring enantiomer
  • wedged and dashed lines can be withdrawn
Haworth Projection (Cyclic Form/Close Chain)
  • Hemiacetal - when an aldehyde reacts with an alcohol
  • the c atom that is part of the hemiacetal is the new chirality center, called anomer carbon
  • 2 cyclic structures
    • alpha anomer (-OH down)
    • beta anomer (-OH up)
  • Mutarotation of D-Glucose
    • powder form (open chain) but when dissolved in water (goes cyclic structure)
  • Ketohexoses
    • like fructose
    • form five-membered rings with two anomers
Reduction and Oxidation of Aldehyde Carbonyl Group
  • Reduction
    • decrease of carbon to oxygen
    • lose oxygen
    • gain of Hydrogen
    • reduce to alcohol
  • Oxidation
    • increase of carbon to oxygen
    • gain oxygen
    • lose of hydrogen
    • into acid
  • Aldoses can be oxidized
  • Ketones cannot be oxidized

2. Disaccharides

  • Two monosaccharides linked together
  • link together to form an acetal (chiral center with an OR group and water)
  • The bond that joins them is a glycosidic linkage
    • free anomeric carbon - anomeric carbon + 4th
    • Reducing
    • no free anomeric carbon - anomeric carbon +anomer carbon
    • alpha glycosidic bond - linkage is downwards
    • carbon #1 of mono 1 to carbon #4 of mono 2
    • 1→4 alpha glycosidic bond
    • beta glycosidic bond - linkage is upwards
    • first mono on top and 2nd mono is a little bit higher
  • Functions:
    • Energy storage, sweetening agents
  • Hydrolysis
    • water (H2O) is added
    • cleaves the C-O glycosidic linkage
    • 2 monosaccharides form
    • aided by enzymes during metabolism
    • ex. maltose
Common Disaccharides

1. Sucrose

  • Components:
    • Glucose + Fructose
    • not a reducing sugar because it lacks a free anomeric carbon
  • Functions:
    • Table sugar, energy source
  • very sweet but contains many calories, many artificial sweeteners are developed
    • Aspartame
    • sold as Equal
    • hydrolyzed into phenylalanine
    • cannot be processed by those with the condition phenylketonuria
    • Saccharine
    • sold as Sweet’n Low
    • used extensively during World War I
    • Sucralose
    • Sold as Splenda
    • similar structure to sucrose

2. Lactose

  • Components:
    • Glucose + Galactose
    • joined by 1→4 beta glycosidic bond
  • Functions:
    • Milk sugar, the energy source for infants
  • Lactose Intolerance:
    • no longer produce the enzyme lactose-- making it impossible to digest causing abdominal cramps and diarrhea

3. Maltose

  • Components:
    • Glucose + Glucose
  • Functions:
    • Produced during starch digestion

3. Polysaccharides

  • Definition: Long chains of monosaccharides
  • Examples: Starch, Glycogen, Cellulose
  • Functions: Energy storage, structural support
Common Polysaccharides

1. Starch

  • anomer: alpha
  • made up of repeating glucose units joined by alpha glycosidic linkages
  • present in:
    • corn, rice, wheat, and potatoes
  • Types: Amylose, Amylopectin
    • both can be digested by enzyme amylase
    • Amylose (20%)
    • unbranched polymer
    • 1→4 alpha glycosidic linkages
    • the first main type of starch
    • Amylopectin (80%)
    • branched polymer;
    • second main type of starch
    • 1→4 and 1→6 alpha glycosidic linkages
  • Functions:
    • Energy storage in plants

2. Glycogen

  • major form of polysaccharide storage
  • similar to amylopectin structure
    • many ends available for hydrolysis
  • Functions:
    • Energy storage in animals
  • when glucose is needed for energy:
    • glucose units are hydrolyzed from the ends of glycogen polymer
  • Location:
    • Stored in liver and muscle cells

3. Cellulose

  • anomer: beta
  • unbranched polymer made up of repeating glucose units joined by 1→4 beta glycosidic linkages
  • Found:
    • cell walls of all plants;
    • gives support and rigidity to woods, plant stems, and grass
  • Functions:
    • Structural component of plant cell walls
  • Digestion:
    • Indigestible by humans; we do not possess the enzyme to hydrolyze cellulose (beta-glycosidase)
    • dietary fiber
  • still important in our diets:
    • makes up the insoluble fiber; important in adding bulk to waste to help eliminate it more easily

Useful Carbohydrate Derivatives

  1. Glycosaminoglycan (GAGs)
    • group of unbranched carbohydrates derived from alternating amino sugar and glucuronate units
    • ex. hyaluronate
      • extracellular fluids that lubricate joints and in the vitreous humor of the eye
    • ex. chondroitin
      • component of cartilage and tendons
      • osteoporosis - supplements
  2. Chitin
    • joined from N-acetyl-G-glucosamine units joined together
  3. Blood Type
    • based on 3 or 4 monosaccharides attached to a membrane protein of red blood cells
    • each blood types have these:
    • Typa A has a fourth monosaccharide:
    • Type B contains additional D-galactose unit
    • Type AB has both Type A and Type B carbohydrates
    • The blood of one individual may contain antibodies to another type.
    • Those with type O blood are called universal donors, because people with any other blood type have no antibodies to type O.
    • Those with type AB blood are universal recipients because their blood contains no antibodies to A, B, or O.

Mind Map: Isomers

Central Idea: Isomers

  • Isomers are molecules that have the same molecular formula but different structural arrangements.

Main Branches:

  1. Structural Isomers
  2. Stereoisomers
1. Structural Isomers
  • Structural isomers have different connectivity of atoms.
Sub-branches:
  • Chain Isomers
    • Differ in the arrangement of the carbon chain.
  • Position Isomers
    • Differ in the position of functional groups or substituents.
  • Functional Group Isomers
    • Differ in the functional group present.
  • Ring Isomers
    • Differ in the arrangement of atoms to form different cyclic structures.
2. Stereoisomers
  • Stereoisomers have the same connectivity of atoms but differ in the spatial arrangement.
Sub-branches:
  • Geometric Isomers
    • Differ in the arrangement of substituents around a double bond or a ring.
  • Optical Isomers
    • Differ in the arrangement of substituents around a chiral center.
    • Enantiomers
      • No
      • n-superimposable mirror images.
    • Diastereomers
      • Stereoisomers that are not mirror images.

Conclusion:

  • Isomers are important in understanding the diversity and complexity of organic molecules. They can have different physical and chemical properties, which can impact their behavior and reactivity.