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DNA, RNA, and Proteins

Chapter 13

Section 1: The Structure of DNA � Gene: A segment of DNA that is located

in a chromosome and that codes for a specific hereditary trait

� DNA: Deoxyribonucleic Acid; the material that contains the information that determines inherited characteristics

� Nucleotide: A subunit in a nucleic acid chain, that consists of a sugar, phosphate and nitrogenous base.

� Purine: A nitrogenous base that has a double-ring structure

� Pyrimidine: A nitrogenous base that has a single-ring structure

I. DNA: The Genetic Material A. Traits are passed from parents to offspring

B. Genes are instructions for inherited traits

I. DNA: The Genetic Material C. Genes are made

from DNA

D. DNA is a primary material that causes recognizable, inheritable characteristics in related groups of organisms

II. Searching for Genetic Material A.  Three major experiments led to the conclusion

that DNA is the genetic material in cells:

1.  Frederick Griffith’s Discovery of Transformation (1928)

A. Took 1st steps in figuring out whether genes are made of DNA or protein

B. Worked with Streptococcus pneumoniae

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2. 2 Strains a) S strain: looks smooth; cause pneumonia b) R strain: looks rough; doesn’t cause

pneumonia

3. Griffith’s Experiments a.  S bacteria caused pneumonia and death

when injected into mice. b.  R bacteria had no visible effect when

injected into mice

3. Griffith’s Experiments c.  S bacteria were killed by heating. Heat-killed S

bacteria did not harm mice. d.  Griffith grew live R bacteria after mixing with

heat-killed S bacteria. Mice injected with the mixture died of pneumonia

4. Griffith’s Conclusions a. Genetic material could be transferred

between cells b. No one knew this material was DNA

B. Oswald Avery’s Experiments with Nucleic Acid (1940s)

1. Wanted to determine if transforming material in Griffith’s experiments was protein, RNA or DNA

B. Oswald Avery’s Experiments with Nucleic Acid (1940s)

2.  Avery’s Experiment a. Used enzymes to destroy each of these

molecules in heat killed S bacteria b.  Found bacteria that were missing protein

and RNA were able to transform R cells into S cells

c.  Bacteria that were missing DNA did not transform R cells

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B. Oswald Avery’s Experiments with Nucleic Acid (1940s)

2.  Avery’s Experiment

B. Oswald Avery’s Experiments with Nucleic Acid (1940s)

3.  Avery’s Conclusions a. DNA is responsible for transformation in

bacteria

C. Hershey-Chase Experiment (1952) 1. DNA or Protein?

a.  Experimented using viruses called bacteriophages (phage)

b. Components of a phage 1. DNA 2. Protein

2. Hershey-Chase Experiment a.  Phages with radioactive (green) DNA

infected bacteria 1.  Bacteria became radioactive 2. DNA entered bacteria

b.  Phages with radioactive (green) protein infected bacteria

1.  Bacteria did not become radioactive 2.  Protein did not enter bacteria

2. Hershey-Chase Experiment 3. Hershey-Chase Conclusion a. Only the DNA of viruses is injected into

bacterial cells b.  Injected DNA cause bacteria to produce viral

DNA and proteins c.  DNA is hereditary material

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III. The Shape of DNA A.  A Winding Staircase

1.  DNA molecule is shaped like a spiral staircase and is composed of two parallel strands of linked subunits a.  Known as a double

helix b.  Each strand made up

of linked subunits called nucleotides

2.  Parts of the Nucleotide Subunits

a.  Nucleotide Components 1.  Phosphate Group 2.  5-carbon sugar

(deoxyribose) 3. Nitrogen containing base

b.  Backbone made up of phosphate group and sugar

c.  Bases pair to connect strands

IV. The Information in DNA A. The information in DNA is contained in the

order of the bases, while base-pairing structure allows the information to be copied

B. Nitrogenous Bases 1.  Each nucleotide has the same sugar and

phosphate backbone

2. Bases are what is different (1 of 4) a. Purine (large molecule)

1. Adenine (A) 2. Guanine (G)

b. Pyrimidine (small molecule) 1. Cytosine (C) 2. Thymine (T)

C. Base-Pairing Rules 1. Purine always pairs with Pyrimidine

2. Adenine always pairs with Thymine

3. Guanine always pairs with Cytosine

D. Complementary Sides 1. Base pairs are Complementary

2. Fit together like puzzle pieces

3. Information on one side is reverse of information on the other side.

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4. A T C G A T T A C T A G G A

5. T A G C T A A T G A T C C T

V. Discovering DNA’s Structure A. Watson and Crick used information from

experiments by Chargaff, Wilkins and Franklin to determine the 3D structure of DNA

B. Observing Patterns: Chargaff’s Observations (1949)

1. For each organism he studied a. amount of Adenine was equal to amount

of Thymine b. amount of Guanine was equal to amount

of Cytosine 2. Watson and Crick used this information to

determine how bases paired.

B. Observing Patterns: Chargaff’s Observations (1949)

C. Using Technology: Photographs of DNA (1952)

1. Rosalind Franklin and Maurice Wilkins developed high-quality X-ray diffraction images of strands of DNA

C. Using Technology: Photographs of DNA (1952)

2. X-rays showed DNA molecule resembled a tightly coiled helix and was composed of 2 chains of nucleotides

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D. Watson and Crick’s Model of DNA 1.  Built a 3D model 2.  Used information from Chargaff,

Wilkins, and Franklin

Section 2: Replication of DNA � DNA Replication: The process of making a

copy of DNA

� DNA Helicase: An enzyme that unwinds/unzips the DNA double helix during DNA replication

� DNA Polymerase: AN enzyme that catalyzes the formation of the DNA Molecule

I. DNA Replication A. DNA is made of 2 complementary base pairs

B. Adenine always pairs with Thymine

C. Guanine always pairs with Cytosine

D. If strands are separated each can serve as a pattern for new complementary strands

E. Allows 2 exact copies of DNA to be made from the original molecule

F. Process of making a copy of DNA is DNA replication

G. Steps of Replication 1. Unwinding and

separating DNA strands a. Double Helix unwinds b. (Helicase) enzymes

separate DNA strands, forming Y-shapes

c. Y-shape at each end of “unzipping” is called a replication fork

2. Adding Complementary Bases a. At each replication fork, new

nucleotides are added to each side of the DNA strand (DNA polymerase, Primase, Ligase)

b. The original 2 strands are unchanged. Each serves as a template for a new strand = 2 new strands

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3. Formation of two identical DNA molecules a. Each identical double-stranded DNA

molecule is made of one new strand and one original stand

II. Replication A. During replication of DNA, many

proteins/enzymes work together like an assembly line.

B. DNA Helicase 1. Protein/enzyme unwinds/unzips DNA

during replication

C.  DNA Polymerase

1.  Protein/enzyme that catalyzes the formation of the DNA molecule

2.  Also has a “proofreading” function a.  Helps to reduce errors

Amoeba Sisters DNA Replication (7:58)

Section 3: RNA and Gene Expression

�  RNA: Ribonucleic acid; a natural polymer that is present in all living cells and that plays a role in protein synthesis

� Gene Expression: The manifestation of the genetic material of an organism in the form of specific traits

�  Transcription: The process of forming a nucleic acid by using another molecule as a template

�  Translation: The portion of protein synthesis that takes place at ribosomes and that uses the codons in mRNA molecules to specify the sequence of amino acids in polypeptide chains

I.  DNA provides the original information from which proteins are made

A.  DNA does not actually make the protein B.  RNA is essential in taking the genetic

information from DNA and building proteins

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II. An Overview of Gene Expression A.  Gene expression produces proteins by

transcription and translation

B.  Transcription: DNA to RNA 1.  1st stage of gene expression 2.  Making RNA from information in DNA 3.  Transcription is similar to copying

(transcription) notes from the overhead (DNA) to your note packet (RNA)

C. Translation: RNA to Protein 1.  2nd Stage of Gene Expression

2.  Uses the information in RNA to make specific proteins

3.  Translation is similar to translating a sentence in one language (RNA, the nucleic acid language) to another language (protein, the amino acid language)

III. RNA: A Major Player A.  In cells, three types of RNA complement

DNA and translate the genetic code into proteins

B.  RNA Versus DNA

1. Similar a.  Both have nucleic acids b.  Both have 4 bases c.  Both carry information d.  Both have bases adenine, cytosine, and

guanine

2. Different a.  RNA is single stranded / DNA is double

stranded b.  RNA nucleotides have ribose sugar / DNA

nucleotides have deoxyribose sugar c.  RNA has a nitrogen base called uracil (U)

instead of DNA’s thymine

DNA v. RNA 3. DNA Base Pairs

a.  A=T

b.  C=G

4. RNA Base Pairs

a.  A=U

b.  C=G

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C. Types of RNA 1. 3 Types of RNA play a role in gene expression

a. Messenger RNA (mRNA) 1)  Produced when DNA is transcribed in

RNA 2)  Complementary to the DNA sequence of

a gene 3)  mRNA carries instructions for making a

protein from a gene and delivers them to the site of translation

mRNA

Types of RNA b.  Transfer RNA (tRNA)

1)  During translation, tRNA “reads” the mRNA sequence

2)  Translates the mRNA sequence into a specific sequence of protein subunits or amino acids

3)  tRNA has amino acids attached 4)  Act as decoders by matching mRNA

sequence and placing amino acids on protein chains

tRNA

Types of RNA c.  Ribosomal RNA (rRNA)

1)  RNA that is found in ribosomes to help make proteins

IV. Transcription: Reading the Gene A. During transcription, the information in a

specific region of DNA (a gene) is transcribed, or copied into mRNA

B. Transcription carried out by protein called RNA polymerase

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C. Steps of Transcription 1.  Step 1

a.  RNA polymerase binds to the specific DNA sequence in the gene called the promoter

b.  Promoter site is the start location 2.  Step 2

a.  RNA polymerase unwinds and separates 2 strands of double helix to expose DNA bases

3.  Step 3 a.  RNA polymerase reads the gene b.  RNA polymerase moves along the bases on

the DNA like a train moves along the track

Steps of Transcription, cont. 3.  Step 3

a.  RNA polymerase reads the gene b.  RNA polymerase moves along the bases on

the DNA like a train moves along the track c.  Transcription follows same base pairing rules

as DNA replication except uracil takes the place of thymine

d.  Forms single strand of RNA e.  DNA double helix closes up behind the moving

RNA polymerase f.  RNA polymerase eventually reaches a stop

location

D. Transcription vs. Replication 1.  Similar

a.  Both use DNA as a template

2.  Different a.  Transcription: RNA is made from DNA

Replication: DNA is made from DNA b.  Transcription: 1 strand of DNA is used to

make RNA strand Replication: both strands of DNA are used to make 2 DNA strands

V. The Genetic Code: Three letter “Words”

A.  A gene is compared to a sentence of words that is first transcribed and then translated into a protein.

B. Codons of DNA 1.  Each word is made up of 3 adjacent nucleotide bases

called a codon

2.  Codons match 1 of 20 amino acids or act as a start or stop signal

Codons of DNA, cont. 3.  Each codon specifies only one amino acid

4.  Several amino acids have more than one codon

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Codons of DNA, cont. 5.  System of matching codons and amino acids is called

the genetic code

6.  Genetic code is based on codons that each represent a specific amino acid.

Amino Acids to Proteins

VI. Translation: RNA to Proteins A.  Process of converting the language of RNA into the

language of proteins

B.  Translation occurs in a sequence of steps, involves three kinds of RNA, and results in a complete polypeptide

1. Step 1 a.  Amino acid is added to one end of each tRNA b.  Other end has anticodon b.  Anticodon is 3-nucleotide sequence that is

complementary to an mRNA codon c.  After leaving the nucleus, mRNA joins with

ribosome and tRNA d.  RNA start codon AUG signals the beginning of a

protein chain e.  tRNA molecule carrying methionine at one end

and the anticodon UAC, at the other, binds to the start codon

2. Step 2 a.  tRNA molecule that has the correct anticodon

and amino acid binds to the second codon on the mRNA

b.  Peptide bond forms between the two amino acids

c.  1st tRNA is released from the ribosome d.  tRNA leaves its amino acid behind

3. Step 3 a.  Ribosome moves one codon down the

mRNA b.  Amino acid chain continues to grow as

each new amino acid bonds to the chain

4. Step 4 a.  Process is repeated until a stop codon is

reached

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5. Step 5 a.  Newly made protein falls off the ribosome b.  Ribosome is free to begin translation again

with another mRNA

C. Repeating Translation 1.  Translation happens quickly and often

2.  Several ribosomes can translate one DNA strand at a time a.  This makes several copies of a protein very

quickly

Translation VII. Complexities of Gene Expression

A.  The relationship between genes and their effect is complex. Despite the neatness of the genetic code, every gene cannot be simply linked to a single outcome

B.  Some genes are expressed at certain times under certain conditions

C.  Some traits result from the expression of multiple genes

D.  Final outcome of gene expression is affected by: 1.  The environment of the cell 2.  Presence of other cell 3.  Timing of gene expression

https://www.youtube.com/watch?v=8nQH0GqFn6k&list=PLj8vIYYJwwPnf60rp2QQhVRzq-EFNOU3k&index=5