-Of the 92 elements that occur naturally on the earth, only six were selected in the course
of evolution to form complex, highly organized material of living organisms. These siz
are carbon, hydrogen, nitrogen, oexygen, phosphorus, and sulfur – make up 99 percent of
the weight of all living matter.
-Of the thousands of different organic molecules found in cells, just four different types
make up most of the dry weight of living organisms. They are
(consisting of sugars and chains of sugars),
(most of which contain fatty acids),
(composed of amino acids), and
(DNA and RNA, which are made
up of complex molecules known as nucleotides). All of these molecules consist mainly of
carbon and hydrogen and most of them contain oxygen as well.
Carbohydrates are the most abundant organic molecules in nature and are the primary
energy-storage molecule in most living organisms. The walls of young plants cells, for
example, are made up of the universally important carbohydrate cellulose embedded in a
matrix of other carbohydrates and proteins.
--the simplest carbohydrates are small molecules know as sugars; larger carbohydrates
are composed of sugars joined together. There are three principal kinds of carbohydrates,
classified according to the number of sugar subunits they contain.
(“single, or simple, sugars”), such ass ribose, and glucose, and
fructose, consist of only one sugare molecule.
Monosaccharides are the simplest carb.
The are proportioned by one carbon atom to two hydrogen atoms to one oxygen atom.
Summed up by the formula (CH2O)n, where n can be as small as 3, as in C3H6O3, or as
large as 7, as in C7H12O7. These proportions gave rise to the term carbohydrate,
meaning “carbon with water added”. Each monosaccharide chain as a carbon backbone.
Attached to each carbon, except one, is –OH. The last carbon is double bonded to an
oxygen atom(C=O). Both carbon bonds (-OH and C=O) are hydrophilic, thus
monosaccharides as well as many other carbs readily dissolve in water. Fig 2-2 shows
how carbs can be either chain form or ring form (when dissolved in water they are
normally found in ring form).
(“two sugars”) contain two sugar subunits linked covalently.
Familiar examples are sucrose (table sugar), and lactose (milk sugar). Although glucose
in the common transport for sugar for many animals, sugars are often transported in
plants and other organisms as a disaccharides.
, a disaccharide composed of
glucose and fructose, is the from in which sugar is transported in most plants from the
photosynthetic cells (primarily in the leaves), where it is produced, to other parts of the
plant body. In the synthesis of a disaccharide from two monosaccharide molecules, a
molecule of water is removed and j a new bond is formed between the two
monosacchardies. This type of chemical reaction, which occurs when sucrose is formed
from glucose and fructose, is know as