Notes From Reading
CHAPTER 5: A N INTRODUCTION TO CARBOHYDRATES PGS .85-98)
- Sugars and other carbohydrates are highly variable in structure
- Monosaccharides are monomers that polymerize to form polymers called polysaccharides, via
different types of glycosidic linkages.
- Carbohydrates perform a wide variety of functions in cells, ranging from energy storage to
formation of tough structural fibers.
5.1 Sugars as Monomers
Monosaccharides Vary in Structure
(1) Location of the carbonyl group.
o Aldose: The carbonyl is at the end of the monosaccharide.
o Ketose: The carbonyl is in the middle of the sugar’s carbon chain.
(2) Number of carbon atoms present.
o Triose: three
o Pentose: five
o Hexose: six
(3) Spatial arrangement of their atoms.
o Different arrangement of the hydroxyl groups.
5.2 The Structure of Polysaccharides
- Polysaccharides are polymers that form from monosaccharides through a condensation
reaction between two hydroxyl groups to create a glycosidic linkage.
(1) The monomers joined by glycosidic linkages can be identical or different.
(2) The glycosidic linkages can form between any two hydroxyl groups; so the location and
geometry of these bonds vary widely.
5.3 What Do Carbohydrates Do?
- Carbohydrates are important building blocks in the synthesis of other molecules.
- They indicate cell identity.
- They store chemical energy.
- They provide cells with fibrous structural materials.
Glycoproteins: Cell Identity
- Although polysaccharides are unable to store information, they do display information on the
outer surface of cells in the form of glycoproteins—proteins joined to carbohydrates by
- Glycoproteins are key molecules in cell-cell recognition and cell-cell signaling.
Starch and Glycogen: Storage Polysaccharides Notes From Reading
CHAPTER 5: A N INTRODUCTION TO CARBOHYDRATES (PGS.85-98)
- Plants store sugars as starch, which is made of many α-glucose monomers joined by α-1,4-
glycosidic linkages. This causes the monomer chain to form a helix. Animals store sugars as
- Starch can be branched (amylose) or unbranched (amylopectin). Glycogen is highly branched.
- Branching occurs when glycosidic linkages form between carbon 1 of a glucose monomer on one
strand and carbon 6 of a glucose monomer on another strand.
Carbohydrates and Free Energy
- In chemical evolution, the kinetic energy of sunlight and heat were converted into chemical
energy stored in the bonds of H CO 2nd HCN.
- Today, most sugars are produced via photosynthesis [CO + H O +