Page 148 - Science Course 3 (Book 1)
P. 148
Mo4-L3a: What is DNA?
Let’s Begin DNA is shaped like a
twisted ladder which
is referred to as a
double helix.
The Structure of DNA
Chromosomes are made of proteins and
deoxyribonucleic acid, or DNA—an organism’s
genetic material.
A gene is a segment of DNA on a chromosome.
A nucleotide is a molecule made of a nitrogen base,
a sugar, and a phosphate group.
Sugar-phosphate groups form the sides of the DNA
ladder.
Chromosome
DNA
The nitrogen bases, adenine (A), cytosine (C),
thymine (T), and guanine (G), bond and form the
rungs of the ladder.
Gene
Key Concept
What is DNA?
What is DNA?
A and T always bond together, and C and G always
bonds together.
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