DNADNA

DNA StructureDNA Structure• DNA stands for Deoxyribonucleic

acid

• DNA is composed of 3 things:• Sugar (Deoxyribose)• Phosphate• Nitrogen Base

• These 3 things put together make up what is called a nucleotide.

• There are 4 nitrogen bases that can be used in DNA.• Adenine (A)• Guanine (G)• Thymine (T)• Cytosine (C)

DNA StructureDNA Structure

• DNA is a double helix.

• The sides = sugar & phosphate.

• The steps = nitrogen base pairs

• When pairing bases:

• Adenine binds to Thymine (A-T)

• Guanine binds to Cytosine (G-C)

James Watson (left) was only twenty-five years old at the time of the discovery, 1953. He, Francis Crick (right) and Maurice Wilkins shared the Nobel Prize for it in 1962. Some considered it bad judgment that Rosalind Franklin, who had died very young in 1958, was not included in thePrize. Watson wrote about the discovery in The Double Helix in 1968. The book recounts what may be the most important discovery in biology in this century.

Who Discovered DNA?

ACTIVITY – Read aloud “The Birth of a Molecule”

How did Watson and Crick Discover DNA?

• Discovering DNA was like putting together a puzzle.

• http://www.dnalc.org/view/15492-Discovering-the-double-helix-structure-of%20DNA-James%20Watson-video-with-3D-animation-and-%20narration.html

James Watson at the NYC Genome Center on Jul 6, 2013 (85 yrs old)

DNA ReplicationDNA Replication• The structure of DNA makes it easy to copy. This is

called DNA replication.

Overall Process http://www.hhmi.org/biointeractive/dna/DNAi_replication_schematic.html

Lewport’s Biology Placehttp://www.lpscience.fatcow.com/jwanamaker/animations/DNA%20Replication%20-%20long%20.html

• Sometimes when copying, the DNA sequence can become changed or mutated.

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

Ribosome reads this order

Protein is made to run the cell

cycle

Cells divide normally

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

Healthy Gene Cancer Gene

There is an error in one base. Ribosome can’t read this properly.

Faulty protein is made or None at

all

Cells divide out of control!

Spelling mistakes or changes in the DNA are called mutations

How does DNA make us who we How does DNA make us who we are?are?• It’s simple! Use this analogy to understand:

• Think of the nitrogen bases (A,T,G,C) like letters of the alphabet.

• When you put these letters together they make words.

• These words are called our “genes”. Humans have ~ 30,000 genes.

• When a ribosome reads these genes it knows what proteins to make.

• The proteins give an organism its traits.

Activity – Decoding the DNA of a MouseGENE #1ATTGCC – Brown furATTGCG – Black furATTGGG – Grey fur GENE #2TCAGGG – Blue eyesTTAGGG – Red eyesTTAGGC – Black eyes GENE #3CGCGCC – No WhiskersCGGGAA – Short WhiskersCGCGAA – Long Whiskers

What will this mouse look like? Draw in the traits.

ATTGCC TTAGGG CGCGAA

THINK! – What if the DNA of Gene#1 was mutated to TTTGCC. Would a protein be made?

No, the ribosome will not be ableto read this sequence and willnot make a protein.

Can we Change an Organism’s DNA on purpose?

Activity – Look who’s coming to dinner!http://www.pbs.org/wgbh/harvest/coming/coming_lo.html

1.Look in your lab bucket. Read your example of a genetically modified organism (GM).2.When the timer sounds, pass your card back. 3.After you have read all 10, discuss the following:

- Which idea do you think is the best? Why?- Which idea do you have concerns about?

Why?