DNA: Deoxyribonucleic Acid

Q2 WK6 D1 11/18/13

Scientists of DNA• 1953, James Watson & Francis Crick

were accredited for discovering the structure of DNA• Awarded the Nobel Prize for

Physiology and Medicine in 1962; Watson, Crick and Maurice WilkinsShould someone else

have received credit???

Scientists of DNARosalind Franklin:Rosalind refined the technique of X-ray

crystallography, to study DNA and produced “Photo 51”

From photo 51, Rosalind determined that DNA is the shape of double helix

Watson & Crick used photo 51 and published their results before Franklin

Rosalind Franklin died in 1985

Location of DNA• DNA is coiled in chromosomes; chromosomes

are located in the nucleus.• DNA is the shape of double helix

• Double stranded• Twisted• Similar to a spiral staircase

Draw me

Double Helix looks like…• If a DNA strand was

straightened, what would it look like???

A LADDER!

Make up of DNA• DNA is made up of Nucleotides strung together in a certain order.• Each nucleotide contains…

• Deoxyribose (Sugar)• Phosphate• Nitrogen base

• Adenine (A)• Thymine (T)• Guanine (G)• Cytosine (C)

How is DNA organized?• Sugar alternates with phosphate at the sides• The rungs (steps) of the DNA molecule are paired nitrogen bases• The nitrogen bases pair in the following way…

• Adenine ALWAYS pairs with Thymine (A-T)• Cytosine ALWAYS pairs with Guanine (C-G)

The rungs are connected at the sugars

Nitrogen bases

deoxyribose

phosphate

Nitrogen Base: PRACTICE1. Adenine -2. Cytosine -3. Thymine -4. Adenine -5. Guanine -6. Guanine -7. Cytosine -8. Thymine -

Add to notebook check

Write the appropriate pair with the listed nitrogen base…

Nitrogen Base: answers• Thymine• Guanine• Adenine• Thymine• Cytosine• Cytosine• Guanine• Adenine

1. Adenine2. Cytosine3. Thymine4. Adenine5. Guanine6. Guanine7. Cytosine8. Thymine

DNA structure: REVIEW• DNA shape = double helix• Rails = Phosphate & deoxyribose (sugar) alternate• Rungs= Nitrogen base pairs• Base Pairing Rule: Adenine – Thymine

Guanine – CytosinePurines: Adenine & Guanine; made of 2 carbon rings and nitrogen atoms.Pyrimidines: Thymine & Cytosine; made of a single ring of carbon and

nitrogen atoms

Q2 WK7 D1

DNA Replication

Purines & Pyrimidines

DNA Replication

• During the cell cycle DNA replication occurs the “S” (synthesis) phase• DNA Replication: The process of making a copy of DNA• DNA replication results in 2 identical DNA strands• DNA is copied BEFORE the cell divides

Steps of DNA Replication• Step 1: Before DNA can replicate, the double helix unwinds.

• An enzyme called “ DNA Helicase” breaks the bonds between the nitrogen bases.• Once the strands separate, proteins prevent the strands from making their

double helix shape.• Areas where the double helix separates are called “Replication forks”.

DNA unwindsDNA Helicase- Enzyme that opens the double helixReplication fork- areas where the DNA opens

Step 1

Tuesday 12/1/2015Agenda: DNA Notes: DNA Replication (Steps 2 and 3)

Activity: DNA Replication Worksheet

Homework:

DNA Replication Worksheet due Wednesday/Thursday 12/2-12/3/2015 for 15 Points

GRADEBOOK CLOSES FRIDAY 12/11/2015!!!

DNA Structure and Replication Quiz Friday 12/4/2015!!

Steps of DNA Replication• Step 1: Before DNA can replicate, the double helix unwinds.

• An enzyme called “ DNA Helicase” breaks the bonds between the nitrogen bases.• Once the strands separate, proteins prevent the strands from making their

double helix shape.• Areas where the double helix separates are called “Replication forks”.

DNA unwindsDNA Helicase- Enzyme that opens the double helixReplication fork- areas where the DNA opens

Step 1

Steps of DNA Replication• Step 2: At the replication fork, an enzyme known as “DNA

polymerase” moves along each of the DNA strands. • DNA polymerase starts adding nucleotides to the exposed

nitrogen bases; using the base pairing rules. • End result: 2 new double helices are formed.

DNA polymerase: An enzyme adding nucleotides to the EXPOSED bases; forming 2 identical copies of DNA

Step 2Step 1

Steps of DNA Replication• Step 3: Once DNA polymerase adds nucleotides to the exposed bases, it

continues until the polymerase is signaled to detach. • The 2 new double helices are made up of an old and NEW

strand

• DNA sequence is identical to each other and to the original DNA molecule

• End result: 2 identical DNA molecules

• Each made up of an OLD and NEW strand

Step 3