The Solar System

584 PART 5^ |^ LIFE

The traits you inherit from your parents,

the chemical processes that animate

you, and the structure of your body are

all encoded in your DNA. When people

say “you have your mother’s eyes,”

they are talking about DNA codes.

The DNA molecule looks like a spiral ladder

with rails made of phosphates and sugars.

The rungs of the ladder are made of four chemical

bases arranged in pairs. The bases always pair

the same way. That is, base A always

pairs with base T, and base G

always pairs with base C.

A

A

C

C

G

C

G

G

T

T

The key to understanding life is

information — the information that guides

all of the processes in an organism. In most

living things on Earth, that information is stored

on a long spiral molecule called DNA

(deoxyribonucleic acid).

Information is coded on the DNA

molecule by the order in which the

base pairs occur. To read that code,

molecular biologists have to “sequence

the DNA.” That is, they must determine

the order in which the base pairs occur

along the DNA ladder.

1

DNA automatically

combines raw materials to

form important chemical compounds.

The building blocks of these compounds

are relatively simple amino acids.Segments

of DNA act as templates that guide the amino

acids to join together in the correct order to build

specificproteins,chemical compounds important to the

structure and function of organisms. Some proteins called

enzymes regulate metabolic processes. In this way, DNA recipes

regulate the production of the compounds of life.

2

1a

1b

The Four Bases

Adenine

Cytosine

Guanine

Thymine

A

C

G

T

Jamie Backman