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Chapter 10
DNA, RNA and Protein Synthesis
1) How did scientist discover that
genes are made of DNA
DNA
- Deoxyribonucleic Acid
- Molecule of heredity
- Contains the genetic
information in all living things
Genes
- genetic informational units
-A length of DNA codes for
proteins
Historical Look at DNa
Late 1800’s
• Scientist new of genes and that
heritable information was
contained in genes.
• Studies of cell division showed
that genes are located on
threadlike structures called
chromosomes
• Chromosomes are composed of
DNA and protein. Genes are
made of DNA and protein.
1920’s
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Frederick Griffith transformed bacteria in an
experiment to find a vaccine to prevent pneumonia
Griffith used two strains of streptococcus
pneumonia bacteria
The R-strain did not cause pneumonia
The S-strain was deadly
Injected mice with the weakened R-strain to
produce an immune response, mice did not die
Injected mice with he S-stain, killed mice
He then heat killed the S-strain, injected mice, mice
did not die
He then mixed the live R-strain and dead S-strain,
mice died
Autopsied mice and found living form of S-strain
S-strained transformed the living, but harmless Rstrain into a harmful one
Discovered genes are made of genes
1940’s
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Oswald Avery and colleagues, made and
extract of the S-strain 9heat killed) bacteria
They treated it with enzymes that would
destroy proteins, lipids and carbohydrates
but not DNA
Transformation still occurred, the enzyme
did not destroy DNA
They then used an enzyme that would
destroy DNA, transformation did not occur
They concluded that when the S-strain (heat
killed) bacteria and the R-strain were mixed,
fragments of the DNA from the S-strain
entered some R-strain making it a deadly
strain, concluding that the fragments
contained genes needed to cause disease.
1940’s
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Chargaff analyzed relative
amounts of nucleotides in
DNA and found equal
amounts of Adenine and
Thymine and equal amounts
of Cytosine and Guanine
1950’s
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Rosalind Franklin and
Maurice Wilkens used X-ray
diffraction to study the
structure of DNA
Took photo’s to determine
the shape
They knew it was helical
shaped
Knew it had a uniformed
diameter (2 nanometers)
1953
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James Watson and Francis Crick proposed a new
model for DNA
Used Franklins photo’s to determine the structure
Noted that DNA consisted of two separate strands of
linked nucleotides
Contains a phosphate group linked to a sugar that
are covalently bonded making up a sugar phosphate
backbone
The two DNA strands are held together by hydrogen
bonds
DNA strands are a ladder like structure that is twisted
The rungs of the ladder are made up of
complementary nitrogenous bases, bonded together
by hydrogen bonds
Twisted double helix
Structure and Review of Nucleic
Acids
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Composition of a nucleotide.
Nucleic acids are composed
of nucleotides.
Nucleotides can be broken
down even further to yield
three components
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Phosphate
Sugar
Base
Overview of DNA
A. The Scientist’s Who
Discovered DNA Were:
Watson and Crick
B. Structure of the Nucleic
Acid
•Phosphate
•Sugar
•Base
C. Overview of DNA
. Nucleotides are joined together
in DNA by bonds between
the phosphate component of
one nucleotide and the
sugar component of the next
nucleotide.
DNA
Detailed representations of DNA
D. DNA
. DNA has four Nitrogenous
Bases:
Purines (double rings)
1.
2.
3.
4.
Adenine
Cytosine
Guanine
Thymine
- adenine and guanine
Pyrimidines (singe rings)
- cytosine and thymine
E. Watson – Crick Model of Base
Pairing
A single ring always bonds with
a double ring
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Adenine bonds with Thymine
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Cytosine bonds with Guanine
The Four Nucleotides
of DNA
DNA Thymine
DNA Cytosine
DNA Adenine
DNA Guanine
Watson and Crick Model of Base
Pairing (view it as a ladder)
1.
2.
3.
4.
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Sugar phosphates form the sides of
the ladder
Nitrogen bases are held together by
weak hydrogen bonds and form the
rungs of the ladder
Base pairing is called
complimentary rather than identical
Double helix
(A – T, C –G) The amount of A=T,
the amount of C=G
The Watson-Crick
Model of DNA Structure
Hydrogen bonds form
between
complementary bases
DNA is a double helix Complementary base
of two nucleotide
pairs hold the two DNA
strands
strands together
DNA Replication
F. How Does DNA Replication Ensure
Genetic Constancy? DNA Replication
- Cells reproduce themselves in the process of cell
division
- One cell will divide to produce two daughter cells
exactly like the parent cell
- Cell division must ensure that each daughter cell
receives exact copies of genetic information from
parent
- In order for this to occur, DNA must replicate itself
– that is to make exact copies
Process is know as DNA Replication.
G. DNA Replication
Enzymes are involved
DNA Helicase
DNA Polymerase
Replication produces two DNA double helices
– each contain one new strand strand
and one original strand
Chromosomes contain one DNA double
helices
Replication results in two identical DNA
double helices passed within
chromosomes to each of the new
daughter cells
DNA Replication Steps
Steps of Replication:
1. DNA Helicase is an enzyme that breaks apart the
double helix. The bases are held together with
weak hydrogen bonds that are broken apart by
DNA helicase enzyme
2 . DNA Helicase uses energy of ATP to break apart
the hydrogen bonds between the
complimentary bases
3. The DNA starts to separate and unwind
4. DNA Polymerase is an enzyme that plays a critical
role in DNA synthesis
DNA Replication
5. DNA polymerase recognizes an unpaired
nucleotide base in the parental strand
and matches it up with free nucleotides
(Example – DNA polymerase matches up
a unpaired adenine with a free floating
thymine)
6. While helicase moves along the parental
DNA double helix separating the parental
strand, one DNA polymerase moves
along in the same direction, adding
nucleotides.
7. You end up with two daughter double helix
strands of DNA.
The Semiconservative
Replication Model
Both strands
of original
DNA serve
as templates
Sister
Chromatids
Duplicated
Chromosome
Chromosome
One DNA
double helix
Daughter
chromosomes
half old, half new
DNA Has Proof Reading Abilities
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The Enzyme DNA Polymerase Has
Proofreading Ability
Replication errors can result in
mutations – is a change in a
nucleotide sequence)
DNA polymerase has proofreading
ability
1 mistake per 10,000 base pairs
occurs
DNA polymerase can repair damage
If errors are not fixed you get
mutations
How Does DNA Replication Ensure
Genetic Consistency
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Cells reproduce themselves by cell
division
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One cell will divide to produce two
daughter cells exactly like the parent cell
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Cell division must ensure that each
daughter receives exact copies of
genetic information from the parent
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In order for this to occur, DNA must
replicate itself – that is to make exact
copies
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Process is known as DNA Replication
(draw DNA replication)
DNA’s Primary Function:
DNA’s Primary Function is to
Provide instructions to Make
proteins
H. Transcription
- How Does DNA Provide the Instructions to
Make Proteins? DNA uses a messenger in
the process called transcription
- DNA needs to use a messenger to carry the
instructions on how to make proteins to
the ribosomes.
- DNA is found in the nucleus and uses a
“messenger” to carry the instructions
from DNA out to the ribosomes.
- DNA uses messenger RNA
I. RNA and Transcription
What is RNA and how is it different
from DNA?
RNA = Ribonucleic Acid
Comparision of DNA and RNA
Nucleus
Nucleus and
Cytoplasm
Deoxyribose
Ribose
Adenine, Thymine,
Guanine, Cytocine
Adenine, Cytosine,
Guanine, Uracil
DNA
mRNA, tRNA, rRNA
J. Types of RNA:
- Messenger RNA (mRNA) – Carries
the instructions from DNA (gene) to
make a protein
- Ribosomal RNA (rRNA) – Part of
ribosomes where protein synthesis
takes place
- Transfer RNA (tRNA) – Transfers
amino acids to the ribosome to make
a protein
K. Transcription: Re-writing DNA into RNA
- Simply stated, one gene (DNA) is
re-written into MRNA in the
nucleus.
- A gene is a segment of DNA that
an be copied or transcribe into
MRNA.
K. Transcription
Transcription consists of the following
steps:
1.DNA separates into 2 strands (one strand is the
template). RNA Polymerase binds to a segment of DNA
and initiates transcription to start
2.RNA Polymerase (enzyme) adds free nucleotides to
the complimentary DNA strand
3.RNA Polymerase reaches a sequence of nucleotides
that marks the end of a gene
4. 3 base pairs of mRNA = triplet codons that will
correspond to an amino acid.
Draw diagram
Transcription
L. How is the sequence of Messenger RNA
translated Into a protein?
• mRNA acts a intermediate between the permanent storage
form of DNA and the process that uses the information –
Translation = Protein Synthesis
•The language of RNA is in the form of codons – which are
groups of three nucleotides, such as AUG, GCC or AAA.
•This is called the triplet code.
•The sequence of codons on the mRNA determines the
sequence of amino acids.
•Each codon codes for a specific amino acid.
•There are only 20 amino acids that code for all the
thousands of proteins made.
•Some codons are used for more than one amino acid and
some are used as stop codons.
Translation – Protein Synthesis
Translation – Protein Synthesis Steps
1.
A single strand of DNA serves as a template for mRNA
2.
mRNA carries the sequences of nucleotides to the
ribosomes
3.
AUG signals translation to begin
4.
tRNA picks up individual amino acids and takes them to
the ribosome
5.
The amino acids are bonded together in a chain by
peptide bonds and a protein is synthesized
6.
Translation ends when one of the stop codns (UAA,
UAG, and UGA) in the mRNA is reached
Diagram
Translation
The End.