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.
