DNA – The Code for Life
Question: Why don’t we all
look alike?
Characteristics of Living Things
All living things reproduce…
All living things have DNA…
We have been told that DNA is the blueprint for life,
BUT what does that mean?
DNA holds the instructions that tell a
cell how to construct amino acid chains.
SO WHAT?
That is important
because amino
acid chains build
proteins.
Proteins
AND build
cells
We do not look alike because we all have
different DNA or genes. We got half from
our mom and half from our dad. How did
this happen? This is what we are going to
answer.
 Gene: segment of DNA on your chromosomes
that determines your traits.
 Trait: characteristics about you. It can be a
body part or a behavior. You inherited your
traits from your parents.
DINO DNA!!!
DNA
DNA stands for – Deoxyribonucleic acid
Functions of DNA:
1. Carries the codes to make
proteins.
2. Carries the genetic material
that is passed on from the
parents to the offspring.
Discovery of DNA
Rosalind Franklin - Invented X-ray diffraction
photography. Photo used
to determine the shape of
DNA is spiral.
DISCOVERY OF DNA
James Watson and Francis
Crick used the information
from Franklin and other
scientists to build a 3-D
model of DNA.
Won the
Nobel Peace
Prize in
Chemistry in
1961.
Structure of DNA
Shape of DNA - Like a twisted rope ladder.
This shape is called Double
Helix.
A single spiral would be
called Helix.
STRUCTURE OF DNA
Side Pieces (The Rope Part)
Are alternating units of
a 5 carbon sugar and a
phosphate group.
These go down both
sides of the molecule
phosphate
Sugar (called deoxyribose)
STRUCTURE OF DNA
Nitrogen Bases (Steps of the ladder) 1.
2.
3.
4.
Adenine – A
Thymine – T
Cytocine – C
Guanine - G
The bases are
connected to the
sugar only !!!!!
STRUCTURE OF DNA
The nitrogen bases fit together in this way:
Adenine always goes
with Thymine
Cytosine always goes
with Guanine
The bases are held together by a weak hydrogen
bond. Two (2) bonds between A and T, three (3)
bonds between C and G.
STRUCTURE OF DNA
These three parts form the basic unit of DNA
called the NUCLEOTIDE.
phosphate
Sugar
(deoxyribose)
Nitrogen base
Can be A, T, C or G
STRUCTURE OF DNA
The nitrogen bases fit together in this way:
Adenine always goes
with Thymine
Cytosine always goes
with Guanine
The bases are held together by a weak hydrogen
bond. Two (2) bonds between A and T, three (3)
bonds between C and G.
STRUCTURE OF DNA
One complete
turn of the
double helix is
10 base pairs or
10 steps on the
ladder
phosphate
adenine
sugar
thymine
cytocine
guanine
How does DNA copy itself?
Purpose: DNA copies itself to ensure that each
new cell that is produced gets the correct number
of chromosomes and receives an EXACT copy
of the DNA molecule.
This is called DNA REPLICATION.
The DNA molecule serves
as its own pattern or
template so as an exact
copy can be made.
STEPS OF DNA REPLICATION
1. DNA untwists and unzips down the hydrogen
bonds. This is why the bonds had to be WEAK.
2. New nucleotides fill in the naked ends produced
by the unzipping process.
3. Nucleotides continue to fill in until the entire
strand is complete.
4. This results in 2 new identical DNA molecules.
DNA REPLICATION
What if there is a
mistake?
There is always a chance
that the wrong
nucleotide bonds to
another. HOWEVER,
DNA has a special
enzyme that is
responsible for “reading”
the bases and
recognizing and
replacing damaged or
wrong nucleotides. This
PROOFREADING
allows for only one (1)
error in ONE BILLION
nucleotides.
Replication #1
Replication #2