DNA

Structure Replication

Something to think about… When a species reproduces, there is

genetic continuity that is maintained from one generation to the next. WHAT is responsible for this continuity? HOW does this continuity happen?

What is DNA? Genetic material present in ALL

organisms Usually found within the nucleus Different for each individual within a

species DNA = DeoxyriboNucleic Acid Polymer made of repeating

NUCLEOTIDE monomers

What is a NUCLEOTIDE? A molecule made of the following 3 parts:

1. a 5-Carbon sugar group (deoxyribose) 2. a phosphate group 3. a nitrogen base – 4 different possibilities!

(5 Carbon sugar)

4 Different Nitrogen Bases Adenine (A) Guanine (G)

Purines (2 carbon rings) Cytosine (C) Thymine (T)

Pyrimidines (1 carbon ring)

It is the arrangement of these 4 different nucleotides that allows DNA to be so unique!

4 Different Nucleotides Adenine ALWAYS

pairs with Thymine (double bond)

Cytosine ALWAYS pairs with Guanine

(triple bond)

To Help you Remember: AT C-G

The Double Helix 2 Scientists credited

with discovering the structure of DNA in 1953: James Watson &

Francis Crick (Watson & Crick)

Watson & Crick Model of structure = DOUBLE HELIX

They received the Nobel Prize (Medicine) in 1962

The Double Helix The key to Watson and

Crick’s discovery was an X-ray diffraction image (known as Photo 51) of DNA recorded by Rosalind Franklin Both the image and Franklin’s

interpretation of the image were shown to Watson without her permission

Watson, Crick, and Wilkins (the man who gave Watson the image) received the Nobel Prize▪ Franklin had died 4 years earlier

The Double Helix Characteristics:

1. DOUBLE stranded molecule

2. phosphate & sugar portion of nucleotides form the “backbone” of each strand

3. Nitrogen base of one strand forms a HYDROGEN BOND with the nitrogen base of a second strand

4. In 3-Dimensional space, it forms a “twisted ladder” (spiral staircase)

The Double Helix

DNA Replication

DNA must be able to make a copy of itself in order for genetic material to be passed on to the next generation and to preserve genetic continuity.

DNA Replication

This replication process occurs in 4 basic steps.

DNA Replication

Step 1 – HELICASE (an enzyme) cause the hydrogen bonds between the nitrogen bases to break (“Unzips the ladder”)

Step 2 – DNA POLYMERASE (another enzyme!) is responsible for reading the DNA template and matching up the complimentary nucleotide from the free floating nucleotides present in the nucleus

DNA Replication Step 3 – Base pairs form hydrogen

bonds and the phosphate group of one nucleotide bonds with the sugar of another to form the “backbone”

Step 4 – Bonding continues along the strands until 2 new strands are formed

RESULT = 2 new EXACT copies of the original DNA molecule!

DNA Replication

Pink = parent strand

Blue = daughter strands

DNA Replication

DNA Replication Simulation