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DNA
The Code of Life
Mrs. Goodwin
Deoxyribonucleic acid
The Molecule
Shape was discovered by James Watson
and Francis Crick- Nobel Prize 1962
Found in all of the 80 trillion cells in the
adult human body
About 6 billion base pairs stretching out to be
about 6 meters long, in every single cell.
Found in every living thing in the world;
plants, animals and bacteria!
Why is DNA Important?
Different amounts of DNA are found in
different organisms.
6 billion in human cells
6 million in bacteria
The more base pairs in an organism, the
more complex the organism!
DNA is comprised of genes which are the
basic unit of inheritance.
What Is a Gene?
A section of DNA which codes for
polypeptide chains (proteins) on a
one-to-one basis
For every gene there is one unique
protein produced.
Cell to Gene
GENES
A section of DNA
Part of Chromosomes
Found in cell nucleus
Basic unit of inheritance!
Code for specific proteins!
(Polypeptides)
Comprised of nucleotides
What are Proteins?
A diverse and abundant class of
biomolecules which make up about 50% of
the dry weight of a cell
VIP- Play a central role in all aspects of
cell structure and function
Remember ribosome and Endoplasmic Reticulum
Each is uniquely tailored to play a
particular role in the cell - a specific protein
for specific function
Proteins
Long chains of
Amino Acid
molecules
Made from
combinations of 20
different Amino
Acids
The building blocks
of a cell
Proteins/ Polypeptides: Chains of
Amino Acids
Protein Again
The properties of a protein depends on:

every single amino-acid molecule in the chain
AND the order of the amino-acid molecules
With 20 amino-acids, you can make an
INFINITE NUMBER OF DIFFERENT aminoacid molecules !!!
These molecules can then be arranged in an
infinite number of sequences all producing
different proteins
The pattern for proteins unique tailoring is
found encoded in the specific sequences
of the nucleotides in DNA.
Proteins = Polypeptides
They have an amino-terminal
or N-terminal end
and a carboxyl-terminal or
C-terminal end. (read from N
to C)
Proteins are important
because they interact with other molecules as:
1.
2.
3.
4.
regulators of gene activity
enzymes
transporters
Central role in structural
elements
Controlling Protein Production
This is VIP! Because they play a huge role in
maintaining life !

proteins in the form of enzymes are responsible
for each step of all biochemical series reactions.
Each step of a biochemical reaction requires a unique
enzyme in order to proceed.
These biochemical reactions are how all of the
processes of life take place.

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Proteins act as transporters between cells
allowing for communication.
Proteins make up a large portion of the structure
of tissues.
How Does DNA Control Life?
DNA (genes) control life processes
because they control protein production!
One Gene -One Enzyme: Each enzyme is
the product of one gene. If the gene is
there, the enzyme can be produced, and
that step of a biochemical series can
proceed; if the gene is not there (or has
mutated), the enzyme may not be
produced, and that step may not proceed!
DNA
CODES FOR PROTEINS
THROUGH SEQUENCED
NUCLEOTIDES
What are Nucleotides ?
Remember* genes are Comprised of nucleotides
Nucleotides consist of:
One five-carbon
sugar,
One phosphate
group
One organic
nitrogenous base.
Nucleotides In DNA
In DNA, the pentose(5
carbon) sugar is always
deoxyribose
The phosphate group:
always one phosphate
molecule bonding with
four oxygen molecules.
VARY in the
nitrogenous base
(this one in adenine)
4 Nitrogenous Bases in DNA
Nitrogenous Bases in DNA
PLEASE NOTE THESE ARE NOT AMINO ACIDS!
Fall into two categories.

The pyrimidines, the smaller of the two,
have a ring of six carbon molecules.

cytosine (C) and thymine (T)
The purines, the larger group
each has the six carbon structure AND a five
carbon ring fused onto it.
Adenine (A) and guanine (G)
Base Pairing in DNA
adenine (A) can only form a
hydrogen bond with thymine (T) to
make a base pair,
guanine (G) can only bond with
cytosine (C)
This A-T / G-C pairing is very
important in the function of DNA
Differences in Base Pairing in DNA
Adenine and
Thymine are
connected by
two hydrogen
bonds
Guanine and
Cytosine are
connected by
three
hydrogen
bonds
The DNA Chain
The pairing of the
nucleotides with the
nitrogenous bases
are held together by a
backbone of the
pentose sugars and
the phosphate
groups, called the
DNA chain.
The Double Helix
DNA twists around an imaginary axis
and becomes a shape called the
double helix, (like a spiral staircase)
This helix consists of two separate
strands running in opposite directions
This helix helps the extremely long
DNA fit into a tiny space.
DNA Packaging
DNA is packed into separate
chromosomes
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which are long strands of DNA
coiled with some additional protein
molecules condensed into discreet
units.
All species have a characteristic
number of chromosomes, humans
have 46 chromosomes.
They appear as "X's" because the
DNA has replicated, making two
identical strands connected at a
central structure called the
centromere.
DNA to Chromosome Structure
DNA and proteins are packaged into
structures called chromosomes.
How does DNA Make Proteins?
The order of the amino acids in protein
is determined by DNA through the
genetic code
A sequence of 3 nucleotides in the
genetic code specify each amino acid
as well as start and stop
protein synthesis
The Steps of Protein Synthesis
Occur in the cell
Step 1: Zip open the DNA double helix that
contains the part of the GENE used to make the
needed protein
Step 2: Copy the GENE (a part of the DNA)
producing messenger RNA (mRNA)
Step 3: Transport the mRNA to a Ribosome organelle which constructs proteins.
Step 4: The mRNA is "shifted" through the
Ribosome; while transfer RNA (tRNA) transfers
amino-acid molecules to the Ribosome to be
"strung together" - ONLY the RIGHT amino-acid
can be strung into the NEXT spot in the chain:
Transcription and
Translation
Transcription: where DNA is
copied making mRNA

mRNA is similar to DNA –it has 4
nucleotide bases but does not
have thymine(T), the base
uracil(U) replaces T
Translation: where ribosomes
read the mRNA and translates
it into the amino acid
sequence of the protein


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AUG is the start signal- 3
nucleotides are read at a timecalled a codon
Each codon specifies a particular
amino acid
UAA,UAG and UGA are stop
signals, they indicate the protein
is complete
Transcription
the information stored in a gene’s DNA is
transferred to a similar molecule called RNA
(ribonucleic acid) in the cell nucleus.
The type of RNA that contains the information
for making a protein is called messenger RNA
(mRNA) because it carries the information, or
message, from the DNA out of the nucleus into
the cytoplasm
RNA polymerase (an enzyme) transcribes DNA
to make messenger RNA (mRNA).
Translation
the second step in getting from a gene to a
protein, takes place in the cytoplasm
The mRNA interacts with a specialized
organelle in the rough ER called a ribosome,
which “reads” the sequence of mRNA bases
Each sequence of three bases, called a
codon, codes for one particular amino acid
(the building blocks of proteins).
tRNA assembles the protein, one amino acid
at a time. Protein assembly continues until
the ribosome encounters a “stop” codon.
Translation
Molecular Look At Transcription and
Translation
Protein Synthesis
Gene expression
The journey from gene to protein
is complex and tightly controlled
within each cell.
Together, transcription and
translation are known as gene
expression.
How does DNA code for proteins?
Genes code for proteins via the
molecular trilogy:
DNA -> RNA, -> amino acids
Proteins are made of 20 different amino
acids (polypeptide)
Primary Protein Structure
Protein then folds into a three
dimensional shape
Sometimes Combines With Other
Proteins
Deciphering the Genetic Code
What is code?
Representation of information
Allows transferring and storing information
Examples of Codes
Morse code

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A
B
C
D
E
F
.-...
-.-.
-..
.
..-.
Braille
Codes
Letters to Stories
Letter codes can
make words
Words make
sentences
Sentences make
paragraphs
Paragraphs make
stories or reports etc
DNA to Life Stories
Dna codons make
amino acids
Amino acids make
proteins
Proteins make
structures and are
enzymes
These make all life
systems and stories