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DNA
The Secret of Life
Deoxyribonucleic Acid
• DNA is the molecule responsible for
controlling the activities of the cell
• It is the hereditary molecule
• DNA directs the production of protein
Structure of DNA
• In 1953, Watson and
Crick proposed that DNA
is made of two chains of
nucleotides held together
by nitrogenous bases.
• Watson and Crick also
proposed that DNA is
shaped like a long zipper
that is twisted into a coil
like a spring.
Structure of DNA
• Because DNA is
composed of two
strands twisted
together, its shape is
called double helix.
• A double helix
resembles a twisted
ladder.
Nucleotides
• DNA is made up of subunits called
nucleotides
• Nucleotides consist of the backbone,
which is made of sugar (deoxyribose) and
phosphate, as well as a nitrogenous
base
Nucleotide
Nitrogen base
Phosphate
Sugar
How Did DNA Get its Name?
• Based on what you just learned, how
do you think deoxyribonucleic acid
(DNA) got its name?
Nucleotides
• A nitrogenous base is a carbon ring structure
that contains one or more atoms of nitrogen.
• In DNA, there are four possible nitrogenous
bases: adenine (A), guanine (G), cytosine (C),
and thymine (T).
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
Nucleotide Sequence
• The four nucleotides are represented by the first
letter in their name
– A – Adenine
– G – Guanine
– T – Thymine
– C – Cytosine
Nucleotide Sequence
• In DNA, Adenine always pairs with Thymine
• Cytosine always pairs with Guanine
Nucleotides
• Nucleotides stack on top of one another forming
the double helix, or twisted ladder
DNA Building
• Click here to link to a DNA building activity
online!
Go Get It Moment!
• When you hear “Move it!” you will have
30 seconds to come get one piece of
paper with an A, G, T, or C on it.
• Then find someone else in the room
whose letter correctly matches with
your nucleotide letter and stand by that
person.
• What are the questions?
• “Move it!”
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Go Get It Moment!
• When you hear “Double Helix”, you
will have 1 minute to make a
classroom DNA strand by standing
next to another pair of nucleotides
• What questions are there?
• “Double Helix”
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DNA Replication
• In order for cells to divide, DNA must
be able to make exact copies of
itself
– This process is known as DNA
Replication
DNA Replication
• DNA Replication occurs before
mitosis and meiosis
• Replication results in two identical
DNA daughter strands from one
mother strand
Process of DNA Replication
• The DNA strand is unzipped at the
hydrogen bonds by an enzyme
named helicase.
• Nucleotides in the nucleus then
find their corresponding
nucleotides on each of the two
open DNA strands and produce
two new DNA double helixes.
Link to DNA Replication
Animation
• Click here to see how DNA
Replication works
Protein Synthesis
• The main job for DNA is to direct
the production of protein
• Protein makes tissues and organs
and carries out the organism’s
metabolism
• Proteins are polymers (chains) of
amino acids
Protein Synthesis
• The sequence of nucleotides in
each gene contains information for
assembling the string of amino
acids that make up a single protein
RNA
• RNA is a nucleic acid composed of
nucleotides that is crucial in making protein
• There are three differences between DNA and
RNA
– RNA is a single strand
– The sugar in RNA is called Ribose instead of
DNA’s Deoxyribose
– Like DNA, RNA has 4 nitrogenous bases, but
instead of Thymine, Uracil is the 4th base
RNA as a Single Strand
• You recall that
DNA looks like a
twisted ladder
and is referred to
as a double helix
• RNA looks like
half a ladder
– There is only one
side to RNA
RNA Contains Ribose
• Remember how DNA got it’s
name?
– It is a nucleic acid with deoxyribose
as the sugar on the backbone
– Hence the name Deoxyribonucleic
acid
• Ribonucleic acid (RNA) has the
sugar ribose on it’s backbone
RNA Has Uracil
• Remember the base pairs in DNA?
– Adenine pairs with Thymine
– Guanine pairs with Cytosine
RNA Has Uracil
• In RNA
– Adenine pairs with URACIL
– Guanine pairs with Cytosine
Making Protein
• Protein production starts with DNA
• DNA passes instruction to RNA
• RNA carries out the work of linking
together chains of amino acids
Three Types of RNA
• There are three types of RNA
involved in Protein Synthesis
– Messenger RNA (mRNA)
– Ribosomal RNA (rRNA)
– Transfer RNA (tRNA)
Messenger RNA
• Messenger RNA (mRNA), brings instructions
from DNA in the nucleus to the cell’s factory
floor, the cytoplasm
– On the factory floor, mRNA moves to the assembly
line, a ribosome
– Remember that a ribosome is either a free-floating
small dot in the cell or is attached to the endoplasmic
reticulum making it “rough” ER
Ribosomal RNA
• The ribosome, made of Ribosomal
RNA (rRNA) binds to the mRNA and
uses the instructions to assemble the
amino acids in the correct order
Transfer RNA
• Transfer RNA (tRNA) is the supplier
• Transfer RNA delivers the amino
acids to the ribosome to be
assembled into a protein
Genetic Engineering
• The manipulation of genes within a cell or
organism
• Gene Mapping – finding location of genes
on the chromosomes.
Gene Splicing
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Locate DNA Sequence
Enzymes are used to separate the DNA
of a particular location on the gene.
New DNA can be spliced in or
RECOMBINED with the remaining DNA.
– This is known as Recombinant DNA
Gene Splicing
•
•
The new DNA will have new
characteristics.
First use of this new technology was to
manufacture human insulin for diabetics.
Gene Splicing
•
One of the most interesting feats
accomplished by genetic engineering is
the splicing DNA from fire flies into a
tobacco plant
– The plant will glow in the dark.
Transcription
• The production of messenger RNA
(mRNA) is known as Transcription
• DNA acts as a template for the RNA
molecule
• To View a Link to Transcription Animation
Click Here.
Transcription
• The main difference between DNA
Replication and transcription is that
transcription results in one single strand of
RNA rather than an exact duplicate of a
double stranded DNA molecule
• Much of the information on the mRNA
strand codes for specific amino acids to
make protein
The Genetic Code
• A code is necessary to turn the language
of RNA into the language of amino acids
and proteins
• The four nitrogenous bases make up the
code
– The code letters are A, G, T, and C
• A set of three letters makes a “word”
called a Codon
– There are 64 possible codons
Codon
Amino Acids
• There are 20 different amino acids that
make up proteins
The Genetic Code
• As you could see on the chart of amino
acids, there are more than one codon that
code for certain amino acids
– This results in fewer errors in protein
synthesis
The Genetic Code
• All organisms use the same genetic code
• This provides evidence that all life on earth
may have evolved from the same origin
Ribosomes
• The newly produced strand of mRNA
travels from the nucleus to the cytoplasm
where it attaches to a ribosome
• The ribosome is the actual site for protein
synthesis
Translation: From mRNA to
Protein
• The process of “reading” the three letter
“words” , or codons, is known as
translation
• Translation takes place at the ribosomes
in the cytoplasm
– The amino acids are free-floating in the
cytoplasm and congregate at the ribosome
during protein synthesis
The Process of Protein Synthesis
• The first codon is usually A-U-G,
methionine, which starts the production of
a new protein
• Following the start codon, the remaining
codons call for amino acids in the order in
which they appear on the mRNA strand
Transfer RNA (tRNA)
Amino acid
• At the ribosome, Transfer RNA
(tRNA) identifies the code
through translation and finds
the appropriate amino acid
matching the codons
– Each tRNA molecule only
attaches to one specific
amino acid
– The Anticodon on the
bottom of the tRNA
molecule corresponds with
the codons on the mRNA
strand
Transfer RNA molecule
Chain of RNA
nucleotides
Anticondon
Protein Synthesis Animation
– Click Here to Link to An Animation