Download DNA, RNA and Protein Synthesis

DNA, RNA and Protein Synthesis
By the end of this lesson, I can
 Relate how Griffith’s bacterial experiments showed that a hereditary factor was involved in
transformation.
 Summarize how Avery’s experiments led his group to conclude that DNA is responsible for
transformation in bacteria.
 Describe how Hershey and Chase’s experiment lead to the conclusion that DNA, not proteins, is
the hereditary molecule in viruses.
 Evaluate the contributions of Franklin and Wilkins in helping Watson and Crick discover DNA’s
double helix structure.
 Describe the three parts of a nucleotide
 Summarize the role of the covalent and hydrogen bonds in the structure of DNA.
 Relate the role of the base-pairing to the structure of DNA.
 Summarize the process of DNA replication.
 Identify the role of enzymes in the replication of DNA
 Describe how complimentary base pairing guides DNA replication.
 Compare the number of replication forms in prokaryotic and eukaryotic cells during DNA
replication.
 Describe how errors are corrected during DNA replication.
 Outline the flow of genetic information in cells from DNA to protein.
 Compare the structure of RNA with that of DNA.
 Describe the importance of the genetic code.
 Compare the role of mRNA, rRNA, and tRNA in translation.
 Identify the importance of learning the human genome.
Vocabulary
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Virulent
Transformation
Bacteriophage
Nucleotide
Deoxyribose
Nitrogenous base
Purine
Pyrimidine
Base-pairing rules
Complementary base pair
Base sequence
DNA replication
Helicase
Replication fork
DNA polymerase
Semi-conservative replication
Mutation
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Ribonucleic acid (RNA)
Transcription
Translation
Protein synthesis
Ribose
Messanger RNA (mRNA)
Ribosomal RNA (rRNA)
Transfer RNA (tRNA)
RNA polymerase
Promoter
Termination signal
Genetic code
Codon
Anticodon
genome
1. Discovery of DNA
a. Griffith’s Experiments
 Fredrick Griffith was studying Streptococcus pnuemoniae (S. pnuemoniae)
 Some types or strains of this bacterium cause the lung disease pneumonia in
mammals.
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DNA, RNA and Protein Synthesis
 Griffith was trying to develop a vaccine against a disease causing or virulent
strain of the bacterium
 Bacteria are surrounded by a polysaccharide that protects it from an organism’s
defense mechanisms
 The virulent bacteria grow as smooth edged colonies. This bacterium does
cause pneumonia.
 The second strain of S. pneumonia does not cause pneumonia and lacks a
capsule. It is called R strain because it grows in rough edged colonies.
 Transformation is the transfer of genetic material from one cell to another cell
or from one organism to another organism.
1. This is the basis of Griffith’s experiment below
b. Avery’s Experiments
 Oswald Avery set out to test whether the transforming agent in Griffith’s
experiment was protein, RNA, or DNA.
1. Scientists used enzymes to separately destroy each of the 3 molecules
in heat killed S cells.
2. Used a protease enzyme to destroy protein in heat-killed cells in the
first experiment.
3. An enzyme called RNase to destroy the RNA in the second experiment
4. And an enzyme called DNase to destroy the DNA in the third
experiment.
5. They then separately mixed the three experimental batches of heatkilled S cells with live R cells and injected mice with the mixtures.
 Avery found that the cells missing protein and RNA were able to transform R
cells into S cells and kill the mice.
 But cells missing DNA did not transform R cells into S cells and the mouse
survived.
 Avery concluded that DNA is responsible for transformation in bacteria.
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DNA, RNA and Protein Synthesis
c. Hershey-Chase Experiment
 Martha Chase and Alfred Hershey set out to test whether DNA or proteins was
the hereditary material viruses transfer when viruses enter a bacterium
 These viruses are called bacteriophages or just plain phages.
1. Hershey and Chase used radioactive sulfur (35S) to label the protein and
radioactive phosphor (32P) to label DNA in the phage.
2. They then allowed protein labeled and DNA labeled phage to separately
infect Escherichia coli (E. coli) bacteria.
3. They then removed the phage coats from the cells in a blender
4. They then used a centrifuge they were able to separate the phage from
the E. coli.
a. Found that all of the viral DNA and little of the protein had
entered the E. coli cells.
b. Concluded that DNA is the hereditary molecule in viruses.
2. DNA Structure
a. DNA Double Helix
 In 1950s a James Watson teamed up with Francis Crick to try and determine the
structure of DNA.
 By 1953 they had put together a model for the structure of DNA.
 They proposed that DNA is made up of 2 chains that wrap around each other in
the shape of a double helix, similar to that of a winding spiral staircase.
1. Their final model was correct and was remarkable because it explained
how DNA could replicate.
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DNA, RNA and Protein Synthesis
 They relied on other scientists’ work to develop their DNA model.
1. Part of that work was X-ray diffraction photographs of DNA crystals
2. These photographs and crystals were produced by Rosalind Franklin and
Maurice Wilkins.
3. In 1962 Watson, Crick and Wilkins received the Nobel Prize in Medicine
for their work on DNA. Franklin died in 1958 and could not be named
on the award.
b. DNA Nucleotides
 DNA is a nucleic acid made of 2 long chains or strands of repeating subunits
called nucleotides.
 Each nucleotide consists of 3 parts
1. A 5 carbon sugar, a phosphate group, and a nitrogenous base.
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DNA, RNA and Protein Synthesis
a. 5 carbon ring is called deoxyribose
b. The Phosphate group consists of a phosphorus atom bonded to
4 oxygen atoms.
c. Nitrogenous base contains nitrogen atoms and carbon atoms
and is a base (accepted hydrogen ions)
 Bonds hold DNA together
1. The nitrogenous bases on one strand of DNA face and form bonds called
hydrogen bonds with the bases on the other strand.
2. Nitrogen bases are bonded together by 2 or 3 hydrogen bonds.
a. They for the steps of the staircase.
3. The base pairs are uniform in width because in each pair one base has a
2 ring structure and the other has a single ring structure.
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DNA, RNA and Protein Synthesis
 Nitrogenous Bases
1. Purines
a. Ademine
i. Nitrogenous bases that have a double ring of carbon
and nitrogen atoms
1. Adenine and Guanine
b. Pyrimidines
i. Nitrogenous bases that have a single ring of carbon and
nitrogen atoms
1. Cytosine and Thymine
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DNA, RNA and Protein Synthesis
c. Complementary Bases
 In 1949, Erwin Chargaff observed that the percentage of adenine equals the
percentage of thymine and the percentage of cytosine and guanine are also
equal to each other in the DNA of a variety of organisms.
1. This observation was key to understanding the structure of DNA
because it meant that bases pair by base-pairing rules.
a. In DNA cytosine on one strand pairs with guanine on the
opposite strand.
b. Thymine and Adenine pair up together.
c. These are known as complementary base pairs.
i. Each complementary base pair consists of one double
ringed purine and a single ringed pyrimidine.
2. Due to base pairing rules, the order of nitrogenous base pairs on one
strand is complementary to the order of bases on the other strand.
a. For example: ATTC on one strand would have a complementary
sequence of TAAG
i. This is known as base sequence.
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DNA, RNA and Protein Synthesis
3. DNA Replication
a. How DNA Replication Occurs
 DNA Replication is the process by which DNA is copied in a cell before a cell
divides by mitosis, meiosis, or binary fission.
 During replication the nucleotides strands of the original double helix separate
along the strands.
 Strands are complementary and each strand serves as a template to make a
new complementary strand.
 After replication the 2 identical stranded DNA molecule separates and move to
the new cells forming during cell division.
1. Steps of DNA Replication.
a. Step 1
i. Enzymes called helicases separate the DNA Strand.
1. Helicase moves along the DNA strand and
breaks the hydrogen bonds between
complimentary bases.
2. This action allows the 2 DNA strands of the
double helix to separate from each other.
3. The Y-shaped region that results when the two
strands separates is called a replication fork.
b. Step 2
i. DNA polymerases add complementary nucleotides
1. DNA polymerases adds complementary
nucleotides that are floating freely inside the
nucleus.
2. As the nucleotides on the newly forming
strands are added, covalent bonds form
between the adjacent nucleotides.
3. Covalent bonds form between the deoxyrobose
sugar on the nucleotide and the phosphate
group of the next nucleotide.
4. Hydrogen bonds form between the
complementary bases on the original and the
new strand.
c. Step 3
i. DNA polymerase finishes
1. DNA polymerase finishes replication of the DNA
and fall off.
2. Results in 2 separate and identical DNA strand
that are ready to move to new cells during cell
division.
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DNA, RNA and Protein Synthesis
3. Each strand contains 1 old DNA strand and 1
new DNA strand.
a. This is known as semi-conservative
replication because each new DNA has
CONSERVED one of the 2 original DNA
strands.
2. Action at the Replication Fork
i. DNA synthesis occurs in different directions on each
strand.
ii. As the replication fork moves along the original DNA,
synthesis of the one strand follows the movement of
the replication fork.
iii. Synthesis on the other strand moves in the opposite
direction, away from the replication fork, leaving gaps in
the newly synthesized DNA strand.
iv. These gaps are joined together by an enzyme called
DNA ligase.
3. Prokaryotic and Eukarytoic replication
a. Prokaryotic cells
i. These have circular chromosome.
ii. Replication begins at one pace along the chromosome.
iii. 2 replication forks are formed and proceed in opposite
directions (like 2 zippers opening in opposite directions.
Replication continues until they meet and the entire
DNA is copied.
b. Eukaryotic cells
i. Chromosomes long but not circular.
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DNA, RNA and Protein Synthesis
ii. DNA polymerase adds 50 nucleotides per second. At
this rate it would take 53 days to replicate the largest
human chromosome.
1. Replication begins in many points or origins
along the DNA.
2. 2 replication forks move in opposite directions.
3. Only simultaneous replication along
chromosomes could allow for rapid replication
of DNA.
b. Replication Errors
 DNA replication usually occurs with great accuracy.
 Only about one error occurs for every billion paired nucleotides added.
 DNA polymerase has repair functions that “proofread” DNA
 When a mistake occurs in replication the base sequence of the newly formed
DNA differs from the base sequence of the original DNA.
 A change in nucleotide sequence is called a mutation.
1. Mutations can have serious effects on the function of important genes
and can disrupt cell function.
4. PROTEIN SYNTHESIS
a. FLOW OF GENETIC INFORMATION
 A gene is a segment of DNA that is located on an autosome (chromosome) and
it codes for a hereditary character.
1. Gene determines hair color
a. Gene directs the making of the protein called melanin (a
pigment) in hair follicle cells through an intermediate – the
nucleic acid called ribonucleic acid or RNA
b. Below summarizes the flow of genetic information in a
eukaryotic cell.
i. During transcription DNA acts as a template for the
synthesis of RNA.
ii. RNA directs the assembly of proteins
iii. Forming protein based on information in DNA and
carried out by RNA is protein synthesis or gene
expression.
iv. This central concept is symbolized as:
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DNA => RNA => Protein
v. Proteins do important work in cells:
1. Protect the body against infections
2. Carry oxygen in red blood cells
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DNA, RNA and Protein Synthesis
b. RNA STRUCTURE AND FUNCTION
 Like DNA, RNA is a nucleic acid made of nucleotides
 However as shown below RNA differs from DNA in four basic ways
a. RNA contains the sugar ribose, not deoxyribose found in DNA.
b. RNA contains the nitrogenous base URACIL instead of Thymine
found in DNA.
c. RNA is usually single stranded rather that a double helix
i. However, within in a single stranded RNA molecule
some regions fold to form short double stranded
sections.
ii. In the double stranded regions guanine forms base pairs
with cytosine and URACIL forms base pair with adenine
d. RNA is usually much shorter than DNA
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DNA, RNA and Protein Synthesis
 Types of RNA
1. mRNA
a. messenger RNA
i. a single stranded RNA molecule that carries the
instructions from a gene to make a protein.
ii. In eukaryotic cells, mRNA carries the genetic “message”
from DNA in the nucleus to the ribosomes in the
cytosol.
2. rRNA
a. ribosomal RNA
i. is part of the structure of ribosomes.
ii. Ribosomes are organelles that carry out protein
synthesis.
iii. Ribosomes are mad of mRNA and other proteins.
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DNA, RNA and Protein Synthesis
3. tRNA
a. transfer RNA
i. transfers amino acids to the ribosome to make a protein
c. TRANSCRIPTION
 The process by which the genetic instructions in a specific gene are transcribed
or “rewritten” into an RNA molecule.
 Takes place in the nucleus of eukayriotic cells and in the DNA containing region
in the cytoplasm of prokaryotic cells.
1. Step 1
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DNA, RNA and Protein Synthesis
a. RNA polymerase, an enzyme that catalyzes the formation of
RNA on a DNA template, binds to a promoter.
i. A promoter is a specific nucleotide sequence of DNA
where RNA polymerase binds and initiates transcription.
ii. After RNA polymerase binds to the promoter, the DNA
strands unwind and separate.
2. Step 2
a. RNA polymerase adds free RNA nucleotides that are
complementary to the nucleotides on one of the DNA strands.
b. As in replication complementary base pairing determines the
nucleotide sequence in the newly formed RNA.
i. If the bases on the DNA strand was ATCGAC, the bases
on the RNA strand would be UAGCUG
ii. Unlike DNA replication transcription uses only a specific
region (a gene) on one of the two DNA strands to serve
as the template.
c. As RNA polymerase moves past the separated DNA strand
rewinds.
3. Step 3
a. During this step RNA polymerase reaches a terminal signal
i. Terminal signals are a specific sequence of nucleotides
that marks the end of a gene.
b. Upon reaching this stop signal, RNA polymerase releases both
the DNA and the newly formed RNA.
c. The RNA made during this transcription can be one of many
types including mRNA, tRNA, or rRNA.
d. This newly formed RNA can now do its job within the cell and
the RNA polymerase can begin transcribing another gene.
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DNA, RNA and Protein Synthesis
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DNA, RNA and Protein Synthesis
d. THE GENETIC CODE
 During the next process of gene expression , amino acids are assembled based
on instructions encoded in the sequence of nucleotides in the mRNA
1. The genetic code is the term for the rules that relate how a sequence of
nitrogenous bases in nucleotides corresponds to a particular amino acid.
2. In the code 3 adjacent nucleotides (“letters”) in mRNA specify an amino
acid (“word”) in a polypeptide.
a. Each 3-nucleotide sequence in mRNA that encodes an amino
acid or signals a start or stop signal is called a codon.
b. The figure below lists 64 mRNA codons and the corresponding
amino acid they encode for in most organisms.
i. For example the codon GCU specifies the amino acid
alanine in the genetic code.
ii. This ode is nearly universal to all life forms on Earth and
supports the notion that all organisms share an ancient
common ancestor.
c. Some amino acids are encoded by 2, 3, or more different
codons. These codon often differ from one another by just one
nucleotide.
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DNA, RNA and Protein Synthesis
e. TRANSLATION
 Although the instructions for creating a protein are copied from DNA to mRNA,
all three major types of RNA are involved in translation
 Translation is the making of proteins
1. Protein structure
a. Every protein is composed of one or more polypeptides.
b. Polypeptides are chains of amino acids linked together by
peptide bonds.
c. 20 different amino acids found in the peptides of living things.
d. Each polypeptide chain may consist of hundreds or thousands
of the 20 different amino acids.
i. They are arranged in a sequence specific to each
protein.
ii. The amino acid sequence determines how the
polypeptides will twist and fold into 3D structure of the
protein
iii. The shape of the protein is critical to the function of the
protein.
2. Steps of translation
a. Step 1
i. 2 ribosomal RNA subunits, tRNA and mRNA join
together
1. Enzymes first attach a specific amino acid to the
end of each tRNA according to the genetic code.
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DNA, RNA and Protein Synthesis
2. The other end of each tRNA contains the
anticodon, 3 nuleotides on the RNA that are
complementary to the sequence of a codon I
mRNA.
3. A tRNA carring the amino acid methionine at
one end and the anticdon UAC at other end
pairs with the start codon AUG on the mRNA.
4. The first amino acid in nearly all polypeptides is
methionine, but this amino acid maybe a
removed later
b. Step 2
i. The polypeptide chain is put together
ii. tRNA carrying the appropriate amino acid pairs its
anticodon with the second codon in the mRNA
iii. the ribosome then detaches methionine from the first
tRNA, and a peptide bond forms between methionine
and the second amino acid.
iv. The first tRNA then exits the ribosome. The ribosome
then moves a distance of one codon along the nRNA
c. Step 3
i. The polypeptide chain continues to grow as the mRNA
moves along the ribosome
ii. A new tRNA moves in, carrying an amino acid for the
mRNA codon
iii. The growing polypeptide chain moves from one tRNA to
the amino acid attached to the next tRNA.
iv. Chain grows one step a time
d. Step 4
i. The ribosome reaches the stop codon
e. Step 5
i. The components of translation come apart.
ii. The tRNA leaves the ribosome and the ribosome moves
away from the nRNA.
iii. The process starts all over again made
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DNA, RNA and Protein Synthesis
f.
Comparing and Contrasting Translation and Trancrption.
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