DNA, RNA and Protein Synthesis€¦ · DNA, RNA and Protein Synthesis 8 3. DNA Replication a. How DNA Replication Occurs DNA Replication is the process by which DNA is copied in a

DNA, RNA and Protein Synthesis

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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

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

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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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 heat-

killed 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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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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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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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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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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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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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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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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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:

1. 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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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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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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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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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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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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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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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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f. Comparing and Contrasting Translation and Trancrption.

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DNA, RNA and Protein Synthesis€¦ · DNA, RNA and Protein Synthesis 8 3. DNA Replication a. How DNA Replication Occurs DNA Replication is the process by which DNA is copied in a