Chapter 2 Chapter 2 - The Cell - Structure and...

Chapter 2 - The Cell - Structure and Function
2.1 Biomolecules
Biomolecules
 Carbon has four electrons in its outer shell and forms covalent bonds by sharing these
electrons with other atoms, including other carbon atoms
o Other atoms common to biomolecules include oxygen, hydrogen, and nitrogen
o Ability of carbon to share four electrons and to form covalent bonds with other
carbon atoms enables carbon-containing molecules to be large and complex
 Four basic types of biomolecules are carbohydrates, lipids, proteins, and nucleotides
Carbohydrates
 Carbohydrates are composed of carbon, hydrogen, and oxygen in a ratio of 1:2:1, with
the general chemical formula (CH
2
O)
n
.
 The carbons actually bond to hydroxyl groups (-OH) and hydrogens (-H)
o Presence of several hydroxyl groups makes carbohydrates polar molecules so
they readily dissolve in water
Monosaccharides, Disaccharides, and Polysaccharides
 Carbohydrates can be classified further into 3 major groups: Monosaccharides,
Disaccharides, and Polysaccharides
 Monosaccharides are simple sugars composed of a single unit
o Most common is glucose, an important source of energy for our cells
o General formula is C
6
H
12
O
6
o Two other common: Fructose and galactose
 Share the same general formula as glucose
 Atoms are arranged differently, given each its own chemical properties
o Ribose and deoxyribose – important component of nucleotides
 Disaccharides are carbohydrates formed by the covalent bonding of two
monosaccharides
o Common examples:
 Sucrose: composed of a glucose subunit and a fructose subunit joined
together
 Table sugar
 Lactose: composed of a glucose subunit and a galactose subunit joined
together
 Carbohydrate found in milk
 Polysaccharides are carbohydrates formed by the covalent bonding of several
monosaccharides
 Glycogen is a polymer of glucose subunits
o Found in animal cells

o Several types of cells in the body can store glucose as glycogen and later break it
down when they need glucose for energy
o Glycogen is needed for that reason: if cells store energy in the form of
monosaccharides, they would exert an osmotic force that would draw water into
the cells, making them swell and possibly burst
 Starch is a polysaccharide found in plants
o Humans consume starch in various plant food products
 The digestion process makes the glucose subunits of starch available as
energy sources
 Cellulose is another polysaccharide found in plants and consumed by humans but we’re
unable to digest and absorb it
o Known as dietary fiber
 Passes through our GI tract
Synthesis and Breakdown of Saccharides
 To synthesize disaccharides and polysaccharides, monosaccharides must be linked
together by covalent bonds.