DNA Structure and
Function
DNA Structure and Function
KEY CONCEPTS
• Who helped discover
DNA?
• What does DNA do for
us?
• What is the structure of
DNA?
• What is DNA made of?
VOCABULARY
• DNA
• Adenine
• Guanine
• Cytosine
• Thymine
• Purines
• Pyrimidines
• Nucleotide
DNA
• DNA stands for deoxyribonucleic acid
• Large molecule that contains all genetic
information
• Functions of DNA:
– Directs the activities of cells
– Contains the instructions cells use to make
proteins
• What kinds of things do living organisms use
proteins for?
History
• Rosalind Franklin
took the first x-ray
pictures of DNA
molecules
• The x-ray pictures
helped scientists to
determine the
shape of DNA.
• What is the shape
of a DNA molecule?
History
• James Watson and
Francis Crick built
the first DNA model
• They are given
credit for first
determining the
double helix shape
Structure
•
A strand of DNA is
made of monomers
called nucleotides
• Each nucleotide has
three parts:
1. Sugar (deoxyribose)
2. Phosphate
3. Nitrogen base
• The nitrogen base
always binds to the
sugar of a nucleotide
Structure
There are four different DNA nitrogen bases:
1.
2.
3.
4.
•
•
Adenine
Guanine
Cytosine
Thymine
Adenine and guanine are single-ringed
purines
Cytosine and thymine are double-ringed
pyrimidines
Structure
• Label the following parts of the DNA nucleotides below:
adenine, thymine, guanine, cytosine, purines, pyrimidines,
phosphate, and sugar
Structure
• Nucleotides bond together to form a double
stranded DNA molecule
• DNA’s structure looks like a twisted ladder
– This structure is called the double helix
• The deoxyribose and phosphate form the
“sidepieces,” of the ladder.
• Nitrogen bases bond together to form the
“rungs,” of the ladder.
Structure
Structure
• Label the following parts of the DNA molecule below:
nucleotide, hydrogen bonds, sugar-phosphate backbone
Nucleotide
Sugarphosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Chargaff’s Base Pairing Rules
• Adenine always bonds
to thymine
• Cytosine always bonds
to guanine
• The nitrogen bases are
bonded with weak
hydrogen bonds
• Why do only certain
nitrogen bases bind to
each other?
Chargaff’s Base Pairing Rules
• Complete the other half of the DNA
molecule below using Chargaff’s base
pairing rules:
ATGAACGTCACCGTACATCGT
DNA and Chromosomes
• In eukaryotic cells, DNA molecules are
tightly wound into chromosomes
• Where are chromosomes located in
eukaryotic cells?
• Chromosomes contain all the DNA needed
to carry out cellular functions
DNA and Chromosomes
• Label the following parts of the diagram below:
double helix, chromosome, supercoils, coils,
histones, proteins
Histones