lecture 10 - carbohydrates

what are carbohydrates

a group of organic compounds made of oxygen, carbon, and hydrogen

formula of carbohydrates

[CH₂O]_n

purpose that carbohydrates serves

serves as energy sources, storage molecules, and structural components

where are carbohydrates found

they are found in sugars, starches, glycogen, cellulose, and nucleic acids

3 different classifications of carbohydrates

monosaccharides, disaccharides, polysaccharides

monosaccharides

• simplest form (single sugar units)

• examples - glucose, ribose, deoxyribose

  • ribose = aldopentose found in ATP and RNA

  • 2-deoxyribose = sugar found in DNA

disaccharides

• two monosaccharides linked by a glycosidic bond

• sucrose = gluclose + fructose

• cellobiose = two glucose with a beta-1,4 linkage (cannot be digested by humans)

polysaccharides

• long chains of monosaccharides

• glycogen = storage carbohydrate in humans

  • has an alpha-1,4 and alpha-1,6 glycosidic bonds

  • highly branches for quick glucose release

enantiomers

mirror images (D- and L- forms of the same carbohydrate)

• ex: D- and L-glucose

epimers

differ at one chiral center (ex: glucose and galactose)

anomers

alpha- and beta- forms created when glucose cyclizes

• interconvert through mutarotation

conformers

glucose can exist in chair and boat forms

aldohexose (glucose family)

• has 16 stereoisomers (8 D- and L- pairs)

• comes from 4 chiral centers (2⁴ possibilities)

aldotetroses

have 2 asymmetric centers and 4 stereoisomers

functions of carbohydrates

energy storage and release, structural roles, building blocks for biomolecules

carbohydrates - energy storage and release

• glucose = primary energy molecule

• glycogen = stored glucose for later use

structural roles of carbohydrates

• cellulose in plants, though indigestible in humans

• cellobiose is the repeating unit of cellulose, linked by beta-1,4 bonds

building blocks for biomolecules in carbohydrates

ribose and deoxyribose sugars are part of nucleic acids (ATP, DNA, RNA)

why are carbohydrates important

• provide energy for life (glucose metabolism, glycogen storage)

• serves as structural materials (plant cell walls, bacterial cell walls)

• involved in cell communication and recognition (sugar modifications on proteins/lipids)

• small structural differences can completely change biological activity

  • ex: glucose vs galactose differ at one carbon but are metabolized differently