DNA & RNADNA & RNA

Section 1 Section 1 DNADNA

Discovery of DNA

Disease-causing bacteria

Harmless bacteria

Heat-killed, disease-causing bacteria

Control(no growth)

Heat-killed, disease-causing bacteria

Harmless bacteria

Dies of pneumonia Lives Lives

Live, disease-causingbacteria

Dies of pneumonia

Griffith’s Experiment - 1928

The harmless bacteria had been permanently changed or “transformed” into the disease-

causing bacteria

Griffith Experiment

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TransformationTransformation• Fred Griffith worked with 2

differnet strains of bacteria: virulent S (causes pneumonia) and nonvirulent R (does not cause pneumonia)

strain Pneumoccocus bacteria• He found that R-strain could

become virulent when it took in DNA from heat-killed S-strain

• Concluded that the transforming factor might be a gene.

• Oswald Avery – repeated Griffith’s experiment (1944)

• He concluded: DNA stores and transmits the genetic information from one generation to the next

Hershey-Chase Experiment - 1952

Alfred Hershey & Martha Chase experimented using Bacteriophages (a virus that infects and kills bacteria)

• Composed of a DNA or RNA core and a protein coat

• Attaches to a cell and injects its genetic information

Radioactive 32P was injected into bacteria!

Proved that DNA was the cell’s genetic material

Percentage of Bases in Four Organisms

Source of DNA A T G CSource of DNA A T G C

Streptococcus 29.8 31.6 20.5 18.0

Yeast 31.3 32.9 18.7 17.1

Herring 27.8 27.5 22.2 22.6

Human 30.9 29.4 19.9 19.8

Streptococcus 29.8 31.6 20.5 18.0

Yeast 31.3 32.9 18.7 17.1

Herring 27.8 27.5 22.2 22.6

Human 30.9 29.4 19.9 19.8

What do you notice about the amount of A compared to T and the amount of G compared to C?

Discovery of DNA Discovery of DNA StructureStructure

• Erwin Chargaff showed the amounts of the four bases on DNA ( A,T,C,G)

• % of A were roughly equal to the % of T and the % of G were roughly equal to the % of C

Chargaff’s RuleChargaff’s Rule

• AdenineAdenine must pair with ThymineThymine

• GuanineGuanine must pair with CytosineCytosine

• The bases form weak hydrogen bonds

G CT A

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DNA StructureDNA Structure•Rosalind Franklin (1952)

took diffraction x-ray photographs of DNA crystals

• Showed an X-shaped pattern with twisted strands

DNA StructureDNA StructureWatson and Crick – built cardboard models using Franklin’s x-rays; Given credit for determining the structure of DNA

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DNA DNA StructurStructur

ee

DNADNA•Stands for

Deoxyribonucleic acid•Made up of subunits

called nucleotidesnucleotides • NucleotideNucleotide made of: made of:

1. Phosphate groupPhosphate group2. 5-carbon sugar5-carbon sugar3. Nitrogenous baseNitrogenous base

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DNA NucleotideDNA Nucleotide

O=P-O O

PhosphatePhosphate GroupGroup

NNitrogenoNitrogenous baseus base (A, G, C, (A, G, C, or T)or T)

CH2

O

C1C4

C3 C2

5

SugarSugar(deoxyribose)(deoxyribose)

O

DNADNA•Two strands coiled called

a double helix•Sides made of a 5-

carbon sugar Deoxyribose bonded to phosphate (PO4) groups (the backbone)

•Center made of nitrogen bases bonded together by weak hydrogen bonds

DNA Double HelixDNA Double Helix

NitrogenousNitrogenousBase (A,T,G or C)Base (A,T,G or C)

““Rungs of ladder”Rungs of ladder”

““Legs of ladder”Legs of ladder”

Phosphate &Phosphate &Sugar BackboneSugar Backbone

Nitrogenous Nitrogenous BasesBases

• Double ring Double ring PURINESPURINESAdenine (A)Adenine (A)Guanine (G)Guanine (G)

• Single ring Single ring PYRIMIDINESPYRIMIDINES

Thymine (T)Thymine (T)Cytosine (C)Cytosine (C) T or C

A or G

Base-PairingsBase-Pairings•Purines only pair with

Pyrimidines•Three hydrogen bonds

required to bond G & C

CG

3 H-bonds

T A

•Two hydrogen bonds required to bond A & T

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DNADNA

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

DNASection 12-1

A & G Purines (2 rings)C & T Pyrimidines (3 rings)

A to T with double bondG to C with triple bond

DNA structure

Microscopic Image of DNA

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Section 2: Section 2: ChromosomChromosomes and DNA es and DNA ReplicationReplication

Where is DNA found in the cell?

• Prokaryotes – DNA is in the cytoplasm (because they do not have a nucleus!)

–One circular strand of DNA–One chromosome that contains all the genetic information

• Eukaryotes – DNA is in the nucleus as a number of chromosomes

–The number of chromosomes varies by species•Humans have 46 chromosomes•Fruit flies have 8 chromosomes•Dogs have 78 chromosomes

•DNA Length:

–DNA is long–It must be folded dramatically to fit in cells (it’s like trying to fit a thick rope that is 1000 feet long into a small backpack!)

• Eukaryotic chromosomes contain both DNA and protein tightly packed together to form chromatin

• Chromatin consists of DNA that is tightly coiled around proteins called histones

• DNA and histone molecules form a beadlike structure called a nucleosome

Chromosome Structure

Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

• The copying of DNA• Each strand of DNA can re-build

the other half due to base pairing (A-T and G-C)

• Strands are complementary• Replication begins at many

places on the DNA segment and continues in BOTH directions

• Replication Forks – sites where separation and replication occur

DNA ReplicationDNA Replication

 DNA Replication

Growth

Growth

Replication fork

DNA polymerase

New strand Original strand

DNA polymerase

Nitrogenous bases

Replication fork

Original strandNew strand

DNA ReplicationDNA Replication

• Begins atBegins at Origins of ReplicationOrigins of Replication• Two strands separateforming Two strands separateforming

Replication Forks (Y-shaped Replication Forks (Y-shaped region)region)

• 2 New strands grow at the forks2 New strands grow at the forks

ReplicationReplicationForkFork

Parental DNA MoleculeParental DNA Molecule

3’

5’

3’

5’

How Replication Occurs• Replication is carried out by a

series of enzymes• Main replication enzyme is DNA

polymerase

1.Enzymes “unzip” DNA by breaking the hydrogen bonds between bases

2.DNA polymerase joins individual nucleotides to produce a new DNA molecule

3.DNA polymerase also “proofreads” each new DNA strand

What would be the complementary strand of DNA for the following:

A T C T T G C G G A A T G G

T A G A A C G C C T T A C C

Example of Replication: If the original DNA molecule contained the following base pairs:

A C G T A A T G CT G C A T T A C G

The two strands would separate into:

A C G T A A T G Cand

T G C A T T A C G

The complementary bases would then pair with each of these strands to form two new strands of DNA

Replication of Replication of StrandsStrands

Replication Fork

Point of Origin

Section 3:Section 3:RNA and RNA and Protein Protein

SynthesisSynthesis

•Genes - coded DNA instructions that control the production of proteins

•To decode the instructions and make protein, DNA is copied into RNA

The Structure of RNA

• Long chain of nucleotides like DNA

• 3 main differences between DNA and RNA• RNA’s sugar is ribose• RNA is single stranded• In RNA, Uracil (U), replaces Thymine

(T)

• Main job of RNA is protein synthesis (assembly of amino acids into proteins)

Example of an RNA strand that is made from DNA

If this is your strand of DNA:A T G T A C G T A

What would be the complementary strand of RNA?

U A C A U G C A U

Remember Uracil (U) replaces Thymine (T) in RNA!!

1. mRNA – messenger RNA•Carry copies of instructions for assembling amino acids into proteins•“messengers” from DNA to the rest of the cell

2. rRNA – ribosomal RNA•Combine with protein to form ribosomes

3. tRNA – transfer RNA•Transfers each amino acid to the ribosome as it is specified by coded messages in mRNA

(pictures)

There are 3 main types of RNA

Transcription• Step 1 of protein synthesis

• Making mRNA from DNA

• Process in which part of the nucleotide sequence of DNA is copied into a complementary sequence of RNA

• Transcription requires the enzyme RNA polymerase

– This enzyme:•Binds to DNA•Separates the DNA strands•Uses one strand of DNA as a template to assemble a strand of RNA

How does RNA polymerase know where to start and stop making RNA from DNA?

• Enzyme will only bind to regions of DNA known as promoters, which have specific base sequences

• Tells the enzyme where to start and stop!

RNA editing

• RNA requires editing before it goes into action

• Introns – DNA sequences that are NOT used to make proteins

• Exons – DNA sequences that DO code for proteins

• Both introns and exons are copied, but the introns are removed before mRNA leaves the nucleus

The Genetic Code

• Proteins are made by joining amino acids into long chains called polypeptides

• There are 20 different amino acids

• The characteristics of proteins are determined by the order in which the amino acids are joined

• The genetic code is the “language” of mRNA instructions

• Remember RNA has 4 bases: adenine, uracil, cytosine, guanine

• The genetic code is read three letters (bases) at a time

• Each three-letter word is known as a codon, which stands for an amino acid

Codon Chart(read from the middle out)

EXAMPLE:

An RNA sequence – U C G C A C G G U

Codons – U C G – C A C – G G U

Amino Acids – Serine – Histidine - Glycine

• A codon cannot code for more than one amino acid

• The start codon is AUG, which signals to start

• The stop codons, UGA, UAA, and UAG signify the end of the polypeptide (like the period at the end of a sentence)

Translation

• STEP 2 of Protein Synthesis

• Translation – the decoding of an mRNA message into proteins– Takes place on ribosomes

Process of Translation1. mRNA is made from DNA and

released into the cytoplasm

2. mRNA attaches to a ribosome3. Ribosomes read the codons or

instructions4. tRNA brings the right amino

acid to the ribosometRNA is a single strand of

unpaired basesThese bases, called

anticodons, complement mRNAStarts at the codon AUG,

which is the anticodon UAC

• Example

mRNA (codon) :

U A U U G C G A C G C

tRNA(anticodon):

A U A A C G C U G C G

5. Ribosome forms peptide bonds between amino acids

6. The ribosome also breaks the bond that held the first tRNA molecule and then moves to the third codon

7. The polypeptide grows until a stop codon is reached

8. Ribosome releases the protein and the mRNA

Translation is complete!

Roles of DNA and RNA

Similar to information needed to construct a building:

• DNA – “master plan”• RNA – “blueprints”

Section 4:Section 4:MutationsMutations

• Mutations – changes in genetic material or “mistakes”– Sometimes cells make mistakes

when copying DNA

Types of Mutations:• Gene mutations – mistake is

made in a single gene• Chromosomal mutations –

mistake that affects the whole chromosome

Gene Mutations

• Point mutations – gene mutation involving changes in one or a few nucleotides– Occurs at a single point

• Substitutions – one base is changed into another– Affects only one amino acid

• Insertions – a base is inserted into DNA

• Deletion – a base is removed from DNA

- Can change every amino acid that follows because every codon will be changed!

•Frameshift mutations – shift the reading frame of the genetic message

-Can alter the protein so much that it can’t perform its function

Substitution Insertion Deletion

Examples of Mutations

Chromosomal Mutations

• Changes in the number or structure of chromosomes

-Many change the location of genes on chromosomes

-May change the number of copies of some genes

Four types of chromosomal mutations

• Deletion – loss of all or part of a chromosome

• Duplication – extra copies of a chromosome

• Inversion – reverse directions• Translocation – part of a

chromosome breaks off and attaches to another

Deletion

Duplication

Inversion

Translocation

Chromosomal Mutations

Significance of Mutations– Many are neutral – they have little

or no effect on gene expression or function

- Some cause harm – dramatic changes in protein structure or gene activity

•Cause genetic disorders•Associated with cancer

• Mutations are also the source of genetic variability in a species (Diversity)

– Helps species evolve (adapt) to changing environments

- If chromosomes fail to separate during meiosis – organism has extra set of chromosomes called polyploidy

- Polyploid plants are usually larger and stronger

- Used for bananas and citrus fruits

Section 5: Section 5: Gene Gene

RegulationRegulation

• Expressed gene – a gene that is transcribed into RNA– Some genes are expressed and

some are silent– Certain DNA sequences serve as

promoters – binding cites for RNA polymerase

– Others serve as start and stop signals for transcription

Gene Regulation

• Operon – a group of genes that operate together

• Two regulatory regions on a chromosome

1.Promoter (P) – where RNA polymerase binds and then begins transcription

2.Operator (O) – where a repressor protein (DNA binding protein) binds to turn the gene off

Eukaryotic Gene Regulation• Genes are controlled individually and

have regulatory sequences that are more complex than in prokaryotes

• Draw and label a typical eukaryotic gene

• “TATA” box – – Contains a sequence of TATATA or

TATAAA before the start of transcription

– Helps RNA polymerase position itself to begin transcription correctly

Development and Differentiation

• During development of an organism, cells undergo differentiation– This means they become

specialized in structure and function

• Hox genes – control the differentiation of cells and tissues in the embryo