Essentials of Ecology

SUPPLEMENT 6 S43

Figure 10 Portion of the double helix of a

DNA molecule. The double helix is composed of

two spiral (helical) strands of nucleotides. Each

nucleotide contains a unit of phosphate (P), de-

oxyribose (S), and one of four nucleotide bases:

guanine (G), cytosine (C), adenine (A), and thy-

mine (T). The two strands are held together by

hydrogen bonds formed between various pairs

of the nucleotide bases. Guanine (G) bonds with

cytosine (C), and adenine (A) with thymine (T).

Fatty acid

(lipid)

HOO

C

H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H C H

H H

C

Fat molecule

(triglyceride)

Fatty tissue

(adipose cells)

Figure 11 Structural formula of fatty acid that is one form of lipid (left).

Fatty acids are converted into more complex fat molecules that are

stored in adipose cells (right).

0.1 nm 1 nm 10 nm 100 nm 1 μm 10 μm 100 μm 1 mm 1 cm 0.1 m 1 m 10 m 100 m
Redwoods

Proteins

Bacteriophages

Mitochondria,

chloroplasts

Most

bacteria

Most animal cells

and plant cells

Frog

eggs

Hummingbirds

Small

molecules

Humans

Lipids

1 centimeter

1 millimeter

1 micrometer

1 nanometer

1 meter = 10^2 cm = 10^3 mm = 10^6 μm = 10^9 nm

(cm)

(mm)

(μm)

(nm)

= 1/100 meter, or 0.4 inch

= 1/1,000 meter

= 1/1,000,000 meter

= 1/1,000,000,000 meter

Electron microscopes

Light microscopes

Human eye, no microscope

analyzing the 3.1 billion base sequences in hu-

man DNA.

Lipids, a fourth building block of life, are a

chemically diverse group of large organic com-

pounds that do not dissolve in water. Examples

are fats and oils for storing energy (Figure 11),

waxes for structure, and steroids for producing

hormones.

Figure 12 shows the relative sizes of simple

and complex molecules, cells, and multicelled

organisms.

T

T

A

OH

P

P

P

P P

PP

P P

T A

A

G

G

C

C

DNA consists
of two strands of
nucleotides linked
by hydrogen bonds
(shown as dotted
red lines)

DNA double helix

Nucleotide

Nucleotide base

(G, C, A, T)

5-carbon sugar

(deoxyribose)

Phospate

group

Hydrogen bond

S

S

S S

S S

S S

S

S

Figure 12 Relative size of simple molecules, complex molecules, cells, and multicellular organisms. This scale is
exponential, not linear. Each unit of measure is 10 times larger than the unit preceding it. (Used by permission from
Cecie Starr and Ralph Taggart, Biology, 11th ed, Belmont, Calif.: Thomson Brooks/Cole, © 2006)