HUMAN BIOLOGY

Chemistry of Life 39

reVieW QUestions

1. Distinguish between an element, an atom, and a molecule.


2. Explain the difference between an ionic bond and a
   covalent bond.


3. Ionic and covalent bonds join atoms into molecules. What
   do hydrogen bonds do?


4. Name three vital properties of water in living cells.


5. Which small organic molecules make up carbohydrates,
   lipids, proteins, and nucleic acids?


6. Which of the following is the carbohydrate, the fatty acid,
   the amino acid, and the polypeptide?
   a. 1 NH 3 —CHR—COO^2 c. (glycine) 20
   b. C 6 H 12 O 6 d. CH 3 (CH 2 ) 16 COOH


7. Describe the four levels of protein structure. How do a
   protein’s side groups influence its interactions with other
   substances? What happens when a protein is denatured?


8. Distinguish among the following:
   a. monosaccharide, polysaccharide, disaccharide
   b. peptide bond, polypeptide
   c. glycerol, fatty acid
   d. nucleotide, nucleic acid

Table 2.5 Summary of the Main Organic Molecules in Living Things

Main Subcategories

Monosaccharides Simple sugars

Oligosaccharides Short-chain carbohydrates

Polysaccharides Complex carbohydrates

Glycerides Glycerol backbone with one, two,

or three fatty acid tails (e.g., triglycerides)

Phospholipids Glycerol backbone, phosphate group,

another polar group, and often two fatty acids

Sterols Four carbon rings; the number, position,

and type of functional groups differ among sterols

Mostly fibrous proteins Long strands or sheets of

polypeptide chains; often strong, water-insoluble

Mostly globular proteins One or more polypeptide

chains folded into globular shapes; many roles in cell

activities

Adenosine phosphates

nucleotide coenzymes

nucleic acids Chains of nucleotides

Some Examples and Their Functions

Glucose Energy source

Sucrose (a Most common form of sugar; the form

disaccharide) transported through plants

Starch, glycogen Energy storage

Cellulose Structural roles

Fats (e.g., butter), Energy storage

oils (e.g., corn oil)

Lecithin Key component of cell membranes

Cholesterol Component of animal cell membranes;

precursor of many steroids and vitamin D

Keratin Structural component of hair, nails

Collagen Structural component of bone

Myosin, actin Functional components of muscles

Enzymes Great increase in rates of reactions

Hemoglobin Oxygen transport

Insulin Control of glucose metabolism

Antibodies Immune defense

ATP Energy carrier

cAMP Messenger in hormone regulation

NAD^1 , NADP^1 , FAD Transfer of electrons, protons (H+)

from one reaction site to another

DNA, RNAs Storage, transmission, translation

of genetic information

Category

Carbohydrates

... contain an aldehyde or
a ketone group and one
or more hydroxyl groups.

Lipids

... are mainly hydrocarbons;
generally do not dissolve
in water but do dissolve in
nonpolar substances, such
as alcohols and other lipids.

Proteins

... are one or more
polypeptide chains, each
with as many as several
thousand covalently linked
amino acids.

nucleic acids

... are chains of units (or
individual units) that each
consist of a five-carbon
sugar, phosphate, and a
nitrogen-containing base.

sections 2.11, 2.12 Proteins are
built of amino acids that are linked to form
a polypeptide chain. A protein’s primary
structure is the linear sequence of these
amino acids. A protein gets its final shape
as the polypeptide chain bends, folds, and
coils. This shape determines the protein’s function. Many
proteins consist of more than one polypeptide chain. Some
have other organic compounds bonded to them; examples
are glycoproteins, which have oligo saccharides attached, and
lipoproteins, which have lipids attached. A protein becomes
denatured when some factor, like heat or acidity, changes its
usual three-dimensional shape.

section 2.13 Nucleic acids such as
DNA and RNA consist of nucleotides.
A nucleotide consists of a sugar (such as
deoxyribose, the sugar in DNA), one or
more phosphate groups, and a nitrogen-
containing base. The nucleotide ATP transfers energy for
chemical reactions.

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