DNA / RNA
DNA
• Deoxyribonucleic acid (DNA) is a nucleic acid
that contains the blueprint for making the
proteins the cell needs.
• DNA contains genes.
• Genes are specific messages instructing the
cell on how to construct a protein.
DNA
• DNA is the chemical used to pass genetic
information on to the next generation of
organisms.
• DNA controls the synthesis of proteins, which
helps determine the characteristics of the
organism and regulate the cell’s metabolism.
DNA
• DNA contains the genetic instructions used in
the development of all known living organisms
and some viruses.
• DNA molecules are used for long term storage
of information.
• DNA carries the instructions necessary to
create RNA and proteins; therefore, it is often
compared to a blueprint.
DNA Structure
• DNA is a nucleic acid.
• Nucleic acids are large polymers of
nucleotides.
DNA Structure
• DNA consists of two long polymers of simple
units known as nucleotides.
• These two strands run in opposite directions
to each other and are therefore known as antiparallel.
• The strands have backbones made of sugars
with phosphate groups attached.
DNA Structure
• Attached to each sugar is one of four types of
molecules called bases.
• Information is encoded in the sequence of
these four bases along the backbone.
• The information is read using the genetic code.
DNA Structure
• The genetic code specifies the sequence of
amino acids within proteins.
• The code is read by copying stretches of DNA
into RNA (A process known as transcription).
DNA Structure
• A nucleotide consists of a sugar molecule, a
phosphate group, and a nitrogenous base.
• There are four different nitrogenous bases in
DNA:
DNA Structure
• Adenine (A), guanine (G), cytosine (C), and
thymine (T).
• The DNA nucleotides can combine into a long
linear DNA molecule that can pair with another
linear DNA molecule.
DNA Structure
• The two paired strands of DNA form a double
helix with sugars and phosphates on the
outside and the nitrogenous bases on the
inside.
• The nucleotides form hydrogen bonds with
one another, which helps to stabilize the
helical structure.
DNA Structure
• Adenine pairs with Thymine (A-T).
• Guanine pairs with Cytosine (G-C).
Nitrogenous Bases
• The nucleotide bases are nitrogenous bases
that are involved in pairing in DNA and RNA.
This is known as base pairing.
• In genetics they are simply called bases.
• Adenine, Guanine, Cytosine, and Thymine are
DNA bases.
• Adenine, Guanine, Cytosine, and Uracil are
RNA bases.
Adenine
Guanine
Thymine
Cytosine
Uracil
Chromosomes
• Within cells, DNA is organized into structures
called chromosomes.
Chromosomes
• The chromosomes are duplicated before the
cell divides, a process known as DNA
replication.
• Within the chromosomes, chromatin proteins
such as histones compact and organize DNA.
The chromatins help determine which parts of
the DNA are transcribed.
Eukaryotes Vs.
Prokaryotes
• Eukaryotic organisms (animals, plants, fungi,
and protists) store their DNA inside the cell
nucleus.
• Prokaryotic organisms (bacteria and archae)
have no nucleus; therefore, the DNA is found
in the cytoplasm.
DNA Replication
• When a cell grows and divides, two new cells
result.
• DNA replication is the process by which a cell
makes another copy of its DNA.
• Base pairing rules and many enzymes make
replication possible.
DNA Replication
• DNA replication is the process of copying a
double-stranded DNA molecule to form two
double-stranded molecules.
DNA Replication
• Each DNA strand holds the same genetic
information; therefore, both strands can serve
as a template for the reproduction of the
complementary strand.
• The template strand is conserved in its entirety
and the new strand is assembled from
nucleotides. This is known as
semiconservative replication.
DNA Replication
• The resulting double-stranded DNA molecules
are identical.
• DNA replication must happen before cell
division can occur.
DNA Replication
• Helicases are enzymes that bind to the DNA
and separate the two strands of DNA.
• DNA polymerase incorporates DNA
nucleotides into the new DNA strand. The
nucleotides enter according to the base
pairing rules.
DNA Replication
• In prokaryotic cells, this replication process
starts at only one place along the DNA
molecule (origin of replication).
• In eukaryotic cells, the replication starts at the
same time along several different places of the
DNA molecule.
DNA Replication
• Two new identical, double-stranded DNA
molecules are formed.
• The new strands of DNA form on each side of
the old DNA strands.
DNA Replication
• The exposed nitrogenous bases of the original
DNA serve as the pattern on which the new
DNA is formed.
• Two double helices are formed with identical
nucleotide sequences.
• A portion of the DNA polymerase molecule
edits the newly created DNA molecule and
makes corrections if needed.
DNA Replication
Repair of Genetic
Information
• If an error or damage occurs to the DNA helix
on one strand, the pairing arrangement of
nitrogenous bases on the other undamaged
strand can be read.
• This information is used to repair the damaged
strand.
DNA Code
• DNA stores information.
• The order of the nitrogenous bases is the
genetic information that codes for proteins.
• The nucleotides are read in sets of three.
• Each sequence of three nucleotides is a
codeword for a single amino acid.
• The information to code one protein can be
thousands of nucleotides long.
RNA Structure And
Function
• Ribonucleic Acid (RNA) is important in protein
production.
• RNA’s nucleotides contain a ribose sugar
whereas DNA’s nucleotides contain a
deoxyribose sugar.
• Ribose has an –OH group and deoxyribose has
an –H group on the second carbon atom.
RNA Structure And
Function
• RNA contains the nitrogenous bases Uracil (U),
guanine (G), cytosine (C), and adenine (A).
• DNA is found in the cell’s nucleus, while RNA is
made in the nucleus and then moves out into
the cytoplasm of the cell.
RNA Structure And
Function
• DNA directs protein synthesis by using RNA.
• RNA is made by enzymes that read the protein
coding information in DNA.
• RNA nucleotides pair with DNA nucleotides.
• RNA contains Uracil instead of Thymine so
adenine in DNA pairs with Uracil in RNA.
Nucleic Acid Base Pairing
Rules
DNA pairs with DNA
DNA pairs with RNA
RNA pairs with RNA
A pairs with T
A pairs with U
A pairs with U
T pairs with A
T pairs with A
U pairs with A
G pairs with C
G pairs with C
G pairs with C
C pairs with G
C pairs with G
C pairs with G
Transcription
• Transcription is the process of using DNA as a
template to synthesize RNA.
• The RNA polymerase enzyme reads the
sequence of DNA nucleotides and follows the
base pairing rules between DNA and RNA to
build the new RNA molecule.
Transcription
• The two strands of the double stranded DNA
molecule are separated to expose the
nitrogenous bases.
• The DNA’s nitrogenous bases are read and
paired with the RNA nucleotides.
• Only one strand of the DNA molecule is read
(the coding strand). The other strand is
referred to as the non-coding strand.
Transcription
• Promoter sequences are specific sequences of
DNA nucleotides that RNA polymerase uses to
find a protein-coding region of DNA and to find
out which strand of DNA is the coding strand.
Transcription
• Termination sequences are DNA nucleotide
sequences that indicate when RNA
polymerase should finish making an RNA
molecule.
3 Types of RNA
• Messenger RNA (mRNA) – carries the
blueprint for making the necessary protein.
• Transfer RNA (tRNA) – reads mRNA and brings
in the necessary amino acids.
• Ribosomal RNA (rRNA) – reads the mRNA and
brings in the necessary amino acids.
Translation
• Translation is the process of using information
in RNA to direct protein synthesis.
• mRNA is read in sets of three nucleotides
called codons.
Translation
• A codon is a set of three nucleotides that
codes for a specific amino acid.
• The ribosome is made up of proteins and
ribosomal RNA (rRNA).
• The ribsome holds the mRNA in place and
reads it’s codons.
3 Phases of Translation
• Initiation
• Elongation
• Termination
Initiation
• The small ribosomal subunit binds to the
mRNA and moves along until it reaches an
AUG codon to signal the beginning of
translation.
• Transfer RNA (tRNA) carries amino acids to the
mRNA complex.
Initiation
• The anticodon portion of the tRNA interacts
with the mRNA to match the correct amino
acid to the codon in the mRNA nucleotide
sequence.
• The tRNA that binds to the AUG codon that
signals the beginning of translation carries the
amino acid methionine; therefore, every
protein begins with this amino acid.
Elongation
• The ribosome functions as an assembly line.
• New amino acids are carried by tRNA to the
corresponding mRNA segment.
• The anticodon on tRNA matches with the
codon on mRNA.
• The amino acid is then attached to the end of
the chain and the protein becomes elongated.
Termination
• The ribosome will continue to add new amino
acids until a stop signal is reached on the
mRNA molecule.
• The stop codon can be either UAA, UAG, or
UGA.
Termination
• When these codons are encountered, a release
factor enters the ribosome. The ribosomal
subunits release mRNA.
• The mRNA can then either be reused or
broken down to stop protein production.
Translation
Nearly Universal Genetic
Code
• The code for making protein from DNA is the
same for nearly all cells.
• Bacteria, protists, plants, fungi, and animals all
use DNA to store their genetic information.
• They all transcribe information in DNA to RNA.
• They all translate the RNA to synthesize
protein using a ribosome.
Nearly Universal Genetic
Code
• Almost all use the same three nucleotide
codons to code for the same amino acid.
• In eukaryotic cells, transcription always occurs
in the nucleu, and translation always occurs in
the cytoplasm.
Nearly Universal Genetic
Code
• These similarities make it possible to use
bacteria to synthesize human proteins (i.e.
insulin).
• Some viruses use RNA to store their genetic
information (retroviruses). HIV is an example
of this. Retroviruses use RNA to make DNA,
which is then used to make proteins.
Gene Expression
• Gene expression occurs when a cell transcribes
and translates a gene.
• Cells control which genes are used to make
proteins.
• The different cell types in the human body are
due to which proteins the cell is producing.
Controlling Protein
Quantity
• An enzymes activity can be regulated by
controlling how much of that enzyme is made.
• The cell controls how much mRNA is available
for translation, which in turn determines the
quantity of the protein produced.
Controlling Protein
Quantity
• Enhancer and silencer sequences affect the
ability of RNA polymerase to transcribe a
specific protein.
• Enhancer sequences increase protein synthesis
by increasing transcription.
• Silencer sequences decrease protein
production by decreasing transcription.
RNA Degradation
• Cells regulate gene expression by limiting the
length of time that mRNA is available for
translation.
• Enzymes in the cell break down mRNA.
Mutations
• A mutation is any change in the DNA sequence
of an organism.
• Errors during DNA replication can cause
mutation.
• External factors can cause mutation:
Mutations
• Radiation, carcinogens, drugs, viruses.
• Not all mutations cause a change in the
organism.
• If the mutation occurs away from the proteincoding sequence of the DNA, it is unlikely to be
harmful to the organism.
Silent Mutation
• A silent mutation is a change that does not
change the amino acids used to build a
protein.
Nonsense Mutation
• A nonsense mutation causes a ribosome to
stop protein synthesis by introducing a stop
codon too early.
• This prevents the formation of functional
proteins.
Missense Mutation
• A missense mutation causes the wrong amino
acid to be used in making a protein.
• This will change the shape of the protein and
affect its active sites.
• This can cause an abnormally functioning
protein.
Insertions And Deletions
• Some mutations involve larger spans of DNA
than a change in a single nucleotide.
• An insertion mutation adds one or more
nucleotides to the normals DNA sequence.
Insertions And Deletions
• This can add amino acids to the protein and
change its function.
• A deletion mutation removes one or more
nucleotides.
• This can delete amino acids from the protein
and change its function.