DNA Replication Transcription and Translation. Genes are Made of DNA Scientist discovered that DNA was a chemical inside the nucleus Frederick Griffith.

DNA Replication

Transcription and Translation

Genes are Made of DNA

• Scientist discovered that DNA was a chemical inside the nucleus

Frederick Griffith 1928

Oswald Avery 1944

Genes are Made of DNA• Further experiments by:

o Alfred Hersheyo Martha Chase

• Worked with viruses to support Avery’s work

Genes are Made of DNAVirus – a package of nucleic acid wrapped in protein• Not made of cells• They can only reproduce by infecting a living cell

Bacteriophage – a virus that infects bacteria

The Double Helix• At more or less the same time scientist:

o James Watsono Francis Crick

• Using Franklin’s X-ray crystalography to provide clues to their discovery

Double Helix – Model created by Watson and

Crick; in which two strands of

nucleotides wound about each

other• Sugar phosphate backbones on the outside;

Nitrogenous base on the inside.

Remember the monomer of DNA is a nucleotide

What is DNA and RNA??

• DNA and RNA are a class of macromolecules called Nucleic Acids

• DNA (Deoxyribonucleic Acid)o where genetic information is storedo Composed of

1. Deoxyribose sugar2. Phosphate group3. Nucleotide base

o Double stranded• RNA (Ribonucleic Acid)- involved in protein synthesis

o Composed of the sugar ribose, a phosphate group, and nitrogenous base

o Has the nitrogen base uracil in place of thiamine

DNA - Nucleotides• Each DNA and RNA monomer has three parts:

DNA - NucleotidesNitrogenous Base – 4 nucleotides found in DNA

differ only in their nitrogenous

bases

Pyrimidines: single ring structure• Thymine (T)• Cytosine (C)

Purines: double ring structure• Adenine (A)• Guanine (G)

DNA structure and bonding

• DNA is composed ofo the sugar-phosphate

“backbone” o The nitrogenous bases

“rungs”• The sugar-phosphate

molecules are joined by covalent bonds

• The nitrogen bases are joined by hydrogen bonds

Complementary Base Pairs

Base Pairing Rules

A with T

C with G• AT CG (Coral Gables)

Pyrimidines always pair with purines

Chargaff’s ruleIf….• Adenine (A) only pairs with Thiamine (T) • Guanine (G) only pairs with Cytosine (C)

Then for every DNA molecule,• the amount of A=T• The amount of C=G• C% + G% = 100%- (A% + T%)

Practice ProblemA molecule of DNA is composed of 20% Adenine. • What % is Thiamine?• What % is Guanine?• What percent is Cytosine?

• A= 20%

• A=T; T=20%

• A+T= 40%

• (C% + G%) = 100% - 40%= 60%

• C = G, thenoC = ½(60%)=30%oG = ½(60%)=30%

You Practice• Given the following problems, figure out

the % of the rest of the nucleotides

1. 10 % guanine

2. 15% thiamine

3. 30% cytosine

You Do: Draw a DNA Molecule

• Draw a molecule of DNA• Make sure to color code

o Phosphate Groupo Deoxyribose sugar o Nitrogenous Bases

• Adenine• Guanine• Thymine• Cytosine

• Show which bonds are hydrogen bonds and which are covalent bonds

DNA Replication

• When a cell divides; a complete set of genetic instructions are copied for each cell

• Genetic material uses the template principle to make more DNA

• Watson and Crick’s model for DNA allowed for the hypothesis of specific base pairingo A – To C - Go If you know one strand of DNA you can determine

the sequence on the other

What is the essential

vocabulary? Replication – the process of DNA duplication. Replication fork – Site where DNA strands

separate and replication occurs. Enzyme – a protein that

facilitates a specific chemicalreaction in the body.

Leading strand – DNA strandthat forms as a continuous strand during DNA replication.

Lagging strand – DNA strand that forms as a series of short segments, called Okazaki fragments, which are then connected together.

What is DNA replication? During DNA replication, the

DNA molecule produces two new complementary strands.

Each strand of DNA serves as a template for the new strand.

Described as semiconservative because each DNA molecule has one new strand and one original strand.

New nucleotides are always added in the 3’ to 5’ direction

How does DNA replication work?

A very complex process requiring the assistance of several enzymes and regulatory molecules. DNA helicases unwind parent strand.

Primase initiates replication by adding a short RNA fragment called a primer to the old strands

DNA polymerases join individual nucleotides to produce a new strand of DNA using the old strand as a template. They also carry out DNA proofreading and repair.

Ligase binds the DNA fragments together by addition of phosphates in the gaps that remain in the phosphate-ribose sugar backbone.

DNA Replication Overview

(a) Parent molecule

A

A

A

T

T

T

C

C

G

G

Each strand of the DNA double helix has all the information needed to reconstruct the other half by the mechanism of base pairing.

Because each strand can be used to make the other strand, they are said to be complementary.

DNA Replication Overview

(a) Parent molecule (b)Separation ofstrands

A

A

A

A

A

A

T

T

T

T

T

T

C

C

C

C

G

G

G

G

1. DNA helicase begins replication by separating the strands and exposing the nucleotide sequence.

2. Primase adds a primer to the DNA molecule to initiate replication

3. DNA polimerases move along the two strands, pairing complementary bases to the exposed nucleotides and proofreads the added segments

DNA Replication Overview

(a) Parent molecule (b)Separation ofstrands

(c)“Daughter” DNA molecules,each consisting of oneparental strand and onenew strand

A

A

A

A

A

A

A

A

A

A

A

A

T

T

T

T

T

T

T

T

T

T

T

T

C

C

C

C

C

C

C

C

G

G

G

G

G

G

G

G

4. DNA ligase seals up the fragments into one long continuous strand

5. Each original strand joins its complementary strand to form a DNA molecule, resulting in two identical DNA molecules.

DNA Replication Overview