Transcript Chapter 12 DNA

DNA
Also known as deoxyribonucleic acid
History of DNA
• In the mid 1900’s scientists started
asking the question:
– “How do genes work?”
– Like many scientific stories, the
discovery of DNA was an accident
while a scientist was trying to find out
something else
Frederick Griffith
• Griffith was working on what was
causing the deadly disease
pneumonia
• Griffith isolated two separate strains:
– A disease causing strain
– A harmless strain
Figure 12–2 Griffith’s Experiment
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Control
Disease-causing Harmless bacteria Heat-killed, disease(no growth)
bacteria (smooth (rough colonies) causing bacteria
colonies)
(smooth colonies)
Dies of pneumonia
Lives
Lives
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Griffith’s Experiment
• He found that mice injected with the
disease-causing strain died of
pneumonia
• However, if he heated the diseasecausing strain and injected the mice
with it they did not die at all
• This suggested that the disease
wasn’t caused by a chemical toxin
released by the bacteria
Griffith’s Experiment
• When he injected
mice with the heat
killed diseasecausing bacteria
they did not die
– When he added
the harmless
bacteria to the
heat killed bacteria
they did develop
pneumonia and
die!
Griffith’s Experiment
• Somehow the heat killed bacteria
passed on their ability to cause
disease to the harmless strain!!
• Griffith called this process
transformation – one strain of
bacteria changing into another
Griffith’s Experiment
• Griffith hypothesized that some
“factor” was transferred from the
heat-killed bacteria to the live,
harmless bacteria
• He hypothesized that this factor was
a gene that the live bacteria
obtained from the heat-killed
bacteria
Oswald Avery’s Experiment
• In 1944 Avery repeated Griffith’s
experiment
– He changed it by creating an extraction
of the “combined” bacteria and treating
it with enzymes
– These enzymes destroyed all of the
proteins, fats, carbs, and RNA
– Leaving only the DNA!!
Oswald Avery’s Experiment
• After he destroyed most of the
organic components, transformation
still occurred!
• He performed it one more time:
– This time he destroyed the DNA in the
mixture
– As he had guessed, the mice lived
– He concluded that it was the DNA that
was responsible for the disease
Oswald Avery’s Experiment
• Avery’s Conclusion:
– DNA is the nucleic acid that stores and
transmits genetic information from one
generation of organism to the next
Hershey-Chase Experiment
• Alfred Hershey and Martha Chase
wanted to explain Avery’s findings
further
– They worked with bacteriophages
• “bacteria eater”
• They attach to the outside of a bacterium
and inject their DNA into the cell
• The DNA instructs the cell to make copies
of itself until the cell bursts with more
bacteriophages
Hershey-Chase Experiment
• They put radioactive markers on the
outside of the bacteriophage as well
as on the DNA inside
• These markers can be seen or
followed during an experiment to
determine which is left “inside” the
bacterium to “infect” it
Hershey-Chase Experiment
Bacteriophage
with phosphorus32 in DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage
with sulfur-35 in
protein coat
Phage infects
bacterium
No radioactivity inside
bacterium
Hershey-Chase Experiment
• Hershey and Chase concluded that
the genetic material of the
bacteriophage was DNA and not
protein
The Structure of DNA
• DNA is a long
molecule made up of
nucleotides
• Each nucleotide is
made up of three
parts:
– A 5-carbon sugar
called deoxyribose
– A phosphate group
– And a nitrogenous
base
The Nitrogenous Bases
• There are 4 kinds of Nitrogenous
Bases:
– The Pyrimidines:
• Cytosine
• Thymine
– The Purines:
• Adenine
• Guanine
*the sugar phosphate forms the
“backbone” of the molecule
The Nucleotides
Purines
Pyrimidines
Adenine Guanine
Cytosine Thymine
Phosphate group
Deoxyribose 5-Carbon
Sugar
Chargaff’s Rules
• According to Erwin Chargaff:
– Adenine always pairs with Thymine
– Cytosine always pairs with Guanine
The Double Helix
• James Watson and Francis Crick
– Using the X-ray taken by Rosalind
Franklin
– And compiling data and research over
many years
– Watson and Crick “unlocked” the secret
structure of DNA in 1953
• The building blocks of ALL life
The Double Helix
Nucleotide
Hydrogen
bonds
Sugarphosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine(C)
Guanine (G)
• base pairing- hydrogen bonds forming only
between certain “base pairs”
Chromosomes and DNA
Replication
• DNA is the genetic material for the
cell and the organism
• It is found in the nucleus of
Eukaryotic cells
– If Prokaryote cells don’t have a
nucleus, then where is the DNA
stored?
Chromosomes and DNA
Replication
• This E. coli bacterium has DNA but, it is
compacted into the cytoplasm of the cell
• Most bacteria have a single, circular DNA
molecule
– E. coli has 4,639,221 base pairs!!!
Chromosome
E. coli bacterium
Bases on the chromosome
Eukaryotic DNA
• Eukaryotic DNA has as many as
1000 times more base pairs as
Prokaryotic DNA
– It exists in the nucleus of the cell in
the form of chromosomes
– How many chromosomes make up a
diploid human cell?
Eukaryotic DNA
• How does the nucleus of a cell
contain more than 1 meter of
DNA?
• Eukaryotic chromosomes contain
DNA and protein in a substance
called chromatin
Eukaryotic DNA
• Chromatin – DNA tightly coiled around
proteins called histones
• Nucleosome – DNA and histones forming
a beadlike structure
Chromosome
Nucleosome
DNA
double
Supercoils
Coils
Histones
helix
DNA Replication
• The way that DNA is constructed
allows for exact duplication
• When DNA is separated one side
can be “copied” because of base
pairing
DNA Replication
• If you had a strand of DNA, but only
one half of the strand, how would
you create a complimentary strand?
– Suppose you had the base pairs:
• ATGCCCGTAATGTAACCGTTGAA
• What would be the complimentary
strand?
DNA Replication
• Replication – process by which DNA
duplicates or “copies” itself
– during replication the strand of DNA
separates into two strands
– While this is happening two new
strands are being formed
simultaneously
– This occurs at the replication fork
DNA Replication
• DNA is “unzipped” by a special enzyme
called DNA polymerase
– The polymerase adds new nucleotides to pair
with the “old” strand
– It also proofreads it before it finishes to make
sure there are no mistakes
DNA Replication
Original
strand
New strand
DNA polymerase
DNA polymerase
Replication
fork
Replication
fork Nitrogenous
bases
New strand
Original
strand
Chapter 12 – 3
RNA and Protein Synthesis
• At this point we all know that DNA
provides the genetic code for all life
on the planet
• So, “how does it work?”
• The key is it’s relationship with RNA
– Ribonucleic acid
RNA and Protein Synthesis
• DNA is like a “library” of information
in every cell of an organism
• RNA would be the “person” reading
the individual ‘books’ in the library
– The manufacture of proteins is
ESSENTIAL for the life of the
organism!
Structure of RNA
• RNA is much like DNA in that it is a
long chain of nucleotides
There are THREE main differences:
> the sugar in RNA is ribose
> RNA is single stranded
> RNA has Uracil in place of
Thymine
Three Types of RNA
RNA
can be
Messenger
RNA
also called
mRNA
which functions to
Carry
instructions
from
DNA
Ribosomal
RNA
also called
rRNA
to
Ribosome
which functions to
Combine
with
proteins
to make
up
Ribosomes
Transfer
RNA
also called which functions to
tRNA
Bring
amino acids
to
ribosome
Transcription
• Transcription is the process of
“making” RNA molecules by creating
a complimentary strand to a section
of DNA
• The enzyme responsible for
“reading” the DNA code is RNA
polymerase
Transcription
• During transcription, RNA
polymerase attaches to the DNA and
separates the strands
• The RNA polymerase then uses one
strand of DNA as a template to make
complimentary nucleotides into a
strand of mRNA
Transcription
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
RNA
DNA
Transcription
• Promoters – specific sites where the
RNA Polymerase binds to the strand
of DNA to begin transcription
RNA Editing
• The “finished” mRNA strand has
been edited before it goes to work
• The pieces that are kept are called
exons
• The pieces that are “cut” are called
introns
The Genetic Code
• Proteins are assembled in polypeptides
– These are long chains of amino acids
– There are 20 different types of amino
acids
– The properties of proteins are
determined by which order these amino
acids are joined
The Genetic Code
• mRNA is the key to the genetic code
and it provides for the manufacture
of all proteins in the body
• A strand of mRNA is read three base
pairs at a time
– UCGAAGCUUACA would be …..
– UCG-AAG-CUU-ACA
The Genetic Code
•Each of these amino acids that
mRNA “codes” for recognizes the
three base pair sequence
•A codon consists of three
consecutive nucleotides that specify
a single amino acid
The Genetic Code
•Along with the twenty amino acids
there are “special” base pair
sequences that “code for” start and
stop codons
•Stop codons are like the “period at
the end of a sentence”.
– They signify the end of a polypeptide
The Genetic Code
Translation
• The decoding of a strand of mRNA into
a protein is known as translation
• At this point we have taken a strand of
DNA and created a strand of mRNA by
the process of transcription
– DNA  mRNA  polypeptide chain
– Polypeptide chain  Protein
• The next step is to make proteins!!
Figure 12–18 Translation
Messenger RNA :
Messenger RNA is
transcribed in the nucleus.
Phenylalanine
Methionine
Nucleus
Lysine
tRNA
mRNA
Transfer RNA
Ribosome
mRNA
Start codon
Translation
• As a strand of DNA is read during
transcription a complimentary strand of
RNA is made
–TACAAGTTT (DNA)
–AUGUUCAAA (RNA)
Translation
• That strand of RNA is known as mRNA
and leaves the cell nucleus where it
attaches to a ribosome
• AUGUUCAAA (mRNA)
Ribosome
mRNA
Start codon
Translation
• Each strand of mRNA is separated
into three base pairs called codons
•AUG —- UUC --- AAA (mRNA)
•This is where transfer RNA comes
in (tRNA)
Translation
• tRNA is responsible for getting the right
anticodon with each of the mRNA codons
• An amino acid is attached to each
anticodon
Lysine
tRNA
Ribosome
mRNA
Figure 12–18 Translation
The Polypeptide “Assembly
Line” The ribosome joins the
two amino acids & breaks the
bond between the tRNA & it’s
amino acid
Lysine
Growing polypeptide
chain
Ribosome
tRNA
tRNA
mRNA
mRNA
Ribosome
Translation
direction
Completing the
Polypeptide
The process continues until the
ribosome reaches one of the three
stop codons. The result is a
growing polypeptide chain.
Translation
• The ribosome acts like an
assembly line worker and attaches
each amino acid to the next one.
• The ribosome also detaches the
amino acid from it’s tRNA
• This happens until a stop codon is
reached and there is a long chain
of amino acids (a polypeptide)
Mutations
• Mutations are changes
in the DNA sequence
that affect genetic
information
• Genetic mutations
result from changes in
a single gene
• Chromosomal
mutations involve
changes in whole
chromosomes
Mutations
• Mutations that only affect one
nucleotide are called point mutations
– Point mutations generally only affect one
amino acid in the sequence
THE DOG BIT THE CAT
THE DOG BIT THE CAR
Normal: AUG-AAG-GGC-UAA
Protein: Met - Lys - Gly - Stop
Normal: AUG-AAG-AGC-UAA
Protein: Met - Lys - Ser - Stop
Mutations
• Frameshift mutations are much more
dangerous to the genetic code!
• They occur when a nucleotide is added
(inserted) or deleted
• This “shifts” the reading frame of the
gene
THE DOG BIT THE CAT
** What happens if you remove the “G” in DOG
THE DOB ITT HEC AT
**The same would happen if you added a letter
Gene Mutations:
Substitution, Insertion, and
Deletion
Substitution
Insertion
Deletion
Mutations can be very dangerous
and VERY SCARY!!
Mutations
• Chromosomal mutations involves the
change in the number or structure of
chromosomes
• There are Four Types:
– Deletion – the loss of all or part of a
chromosome
– Duplication – when a segment of a
chromosome is repeated
– Inversion – When part of a chromosome
becomes oriented in the reverse direction
– Translocation – when part of a chromosome
breaks off and attaches to another
Chromosomal Mutations
Deletion
Duplication
Inversion
Translocation
THE END