DNA:
An Introduction to structure and function
Hopefully a review
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Questions to be able to answer:
 What are the functions and types of DNA?
 What are chromosomes and how many do we
have?
 Draw a labeled sketch of DNA
 Draw the nucleotide structure
 Pyramidines or purines?
 Why is DNA like a zipper?
 How are bases held together?
 How do bases pair?
 Sketch DNA replication
 How does DNA hold information?
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The Human Genome Project — DNA Video
• http://www.nclack.k12.or.us/18242019171932910/blank/brow
se.asp?A=383&BMDRN=2000&BCOB=0&C=64959
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The Importance of DNA
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DNA by the numbers
• A human has 46
chromosomes, a plum tree
has 48, a chicken has 78 and
an ant has 2
• Each human cell has about
2m of DNA
• The average human has 75
trillion cells
• The average human has
enough DNA to go from the
earth to the sun more than
400 times
• DNA has a diameter of only
0.000000002 m
The earth is 150 billion m
or 93 million miles from
the sun.
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DNA
• DNA is often called the
blueprint of life - Why?
• In simple terms, DNA contains
the instructions for making
proteins within the cell.
• DNA stands for
Deoxyribonucleic acid.
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Functions of DNA
• Two primary functions
- transmit information from one
generation to the next
- provide blueprint for making proteins
the same way every time
Two Types of DNA
• nuclear or chromosomal DNA (inherited from
mother and father)
• mitochondrial DNA (inherited from mother
only)
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Why do we study DNA?
• Importance to all life on Earth
• Medical benefits such as cures
for diseases
• Genetic Engineering
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Chromosomes and DNA
• Chromosomes are
made up of a
chemical called
DNA
• Genes are coded
for in different
regions of
chromosomes
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Chromosomes
• Our body’s way of
organizing all the
information that our
genetic material
contains
• 23 pairs in humans
- Each pair contains one
from mother and one from
father
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The Shape of the Molecule
DNA is a very
long polymer
The basic
shape is like a
twisted ladder
double helix
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The Double Helix Molecule
• The DNA double helix
has two strands twisted
together — looks like a
twisted ladder.
• Need to look at the
structure of one strand
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Finding the Structure
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One Strand of DNA
• Backbone is
alternating
and
,a
sugar
• The teeth are
deoxyribose
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One Strand of DNA
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Nucleotides
One deoxyribose together with
its phosphate and base make a
nucleotide.
O
O -P O
O
Phosphate
Nitrogenous
base
O
C
C
C
O Deoxyribose
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The Structure of DNA
• One strand of DNA is a polymer of nucleotides
• One strand of DNA has many millions of nucleotides
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Four nitrogenous bases
DNA has four
different bases
•Cytosine C
• Thymine T
• Adenine
A
• Guanine G :
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Four Nitrogenous Bases
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Easy to Remember Shapes for Diagrams
Cytosine C
Curved Lines go Together
Thymine T
Straight Lines go Together
Adenine
A
Straight Lines go Together
Guanine
G
Curved Lines go Together
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Two Kinds of Bases in DNA
• Pyrimidines are single ring
bases
N C
O C
N
C
N C
• Purines are double ring
bases
N
N C
C
C
N
N C
N C
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Pyrimidines:
Thymine and Cytosine
• Thymine and cytosine each have one ring of carbon and
nitrogen atoms
N
O
N
O
N
C
C
C C
N
C
Thymine
O
C
C
C
N
C
Cytosine
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Purines:
Adenine and Guanine
• Adenine and guanine each have two rings of carbon and
nitrogen atoms
O
N
N
N
C
C
N
C
C
C
C
N
N
N
Adenine
N
C
N
C
Guanine
C
C
N
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Two Stranded DNA
• DNA has two strands that fit together something like a zipper
• The teeth are the nitrogenous bases but why do they stick
together?
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Hydrogen Bonds
• The bases attract
each other because
of hydrogen bonds
• Hydrogen bonds are
weak but there are
millions and millions
of them in a single
molecule of DNA
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Hydrogen Bonds, cont.
• When making
hydrogen bonds,
cytosine always
pairs up with
guanine — C-G
or G-C
• And adenine
always pairs up
with thymine —
A-T or T-A
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Important:
• Adenine and Thymine always
join together
A
T
• Cytosine and Guanine always
join together
C
G
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DNA Replication
• DNA is unwound
• An enzyme
called DNA
Polymerase adds
complementary
bases to “single
stranded”
- A with T
- C with G
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DNA Replication
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Transcription
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Practice
• Simple replication
Draw the replication for the sequence of
bases:
Include labels of the backbone
structure and the hydrogen bonds
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The Structure of DNA:
Can you do these things?
• Make a labeled sketch
• Label the structure of a nucleotide
• Know which bases pair up and how they are
held together
• Explain why the structure of the DNA
Molecule is often described as a zipper.
• Make a sketch of DNA replication
• Explain how DNA holds information
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