DNA: The Other MacroMolecule

Basic Structure

• DNA is a long chain polymers of small compound called nucleotides.

• Draw this picture in box in your notes

What is a Nucleotide?

Nucleotide contains:5-carbon sugar called

deoxyribosePhosphate groupOne Nitrogenous

base (there are 4 types)

How are the molecules positioned?

• Sugar and phosphate make up backbone (sides of ladder)

• Nitrogenous bases make up steps of ladder

• Bases are always paired (Chargaff’s rule)

• Draw a nucleotide in the box and label its parts.

There are two types of Nitrogen Bases:

• Make up the “steps” or rungs of the DNA ladder– One Step= Purine + Pyrimidine

• Purines– Double ring structure– Adenine– Guanine

• Pyrimidines– Single-ring structure– Cytosine– Thymine (in DNA only)

Watch the following videos to help you get a better

understanding of DNA and nucleotides

• http://www.youtube.com/watch?v=qy8dk5iS1f0

• http://www.youtube.com/watch?v=rromYAt1Lfw

How do they pair up to for the rungs of the ladder?

• Adenine (Purine) binds with Thymine (pyrimidine) or vice versa

• A-T or T-A.

• Cytosine (Purine) binds with Guanine (pyrimidine) or vise versa

• C-G or G-C.

• Held together by weak hydrogen bonds.

• Base pairs join together in complement.

• Draw that pairing

How does it all fit into your cells?

• Chromatin wrapped around proteins called histones.

• Chromatin condenses to form chromosomes during replication

DNA Replication

• The enzyme helixase “unzips”the helix by breaking the hydrogen bonds.

• DNA polymerase moves along the “exposed” strands, adding nuleotides. A new helix is made. You now have two.

• Polymerase proofreads, backtracks, and fixs errors in base pairs.

• Errors not corrected are called mutations

DNA Replication, now that’s easy!

• http://www.youtube.com/watch?v=zdDkiRw1PdU

• http://www.youtube.com/watch?v=cDlKrLJjRlY&feature=related cartoon

• http://www.youtube.com/watch?v=gI-TGzZNzVE remix of cartoon

Draw this in box for replication.Be sure to label old and new strands.

• Where might you draw in helixase?

• Polymerase?

How different are We?

• The difference between 2 people, 2-10 million nucleotides.

• That’s only 1% of our total DNA!• DNA replication only takes about 6

hours to happen.

Who discovered DNA and its structure?

• Rosalind Franklin and Maurice Wilkins• Rosalind Franklin, 1950s, Brit scientist who

studied DNA• Used X-ray diffraction technique to learn

about structure of DNA • She noticed an X-shaped pattern• This indicated that DNA had a helical

structure• She did not get a chance to publish her

research…and her idea was basically stolen

You’ve been ripped off, once again it’s a Man world!

• http://www.youtube.com/watch?v=7SN7aAkdt-0

Who got the credit? Crick and Watson

• 23-year old American Biologist James Watson went to work with English Physicist Francis Crick

• Used information from Rosalind Franklin and Maurice Wilkins (1950’s)– These two scientists used Rosalind

Franklin’s x-ray crystallography images to begin to piece together the DNA structure

– Showed that there were 2 strands twisted around each other

These guys got all the credit for discovering the structure of DNA

• http://www.youtube.com/watch?v=OiiFVSvLfGE

Watch the video on Secrets of the Sequence

• Do the accompanying worksheet called the Human Genome Project

• http://www.youtube.com/watch?v=sf0YXnAFBs8