What do you think this is a model of and why? Warm up What do you think this is a model of and why?

Learning Objectives Describe the basic structure (double helix, sugar/phosphate backbone, linked by complementary nucleotide pairs) of DNA Describe its function in genetic inheritance

DNA DNA is often called the blueprint of life. DNA contains the instructions for making proteins within the cell.

Role of DNA The main role of DNA in the cell is the long-term storage of information it contains the instructions to construct other components of the cell, such as proteins and RNA molecules. The major function of DNA is to provide the code for the making of proteins.

Why do we study DNA? We study DNA for many reasons all living organisms contain DNA. its central importance to all life on Earth, medical benefits such as cures for diseases, better food crops.

Chromosomes and DNA Our genes are on our chromosomes. Chromosomes are made up of DNA. DNA is located in the nucleus.

Who discovered DNA? Rosalind Franklin took diffraction x-ray photographs of DNA crystals She died from cancer before she could publish her findings

Watson and Crick In the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays Some say they took credit for work they stole from Franklin Their original model was a single strand.

Deoxyribonucleic Acid A DNA nucleotide is made up of three parts 5 C Sugar-Deoxyribose Phosphate group Nitrogenous base

The Shape of the Molecule DNA is a very long polymer. The basic shape is like a twisted ladder or zipper. This is called a double helix.

Each strand has: A backbone of alternating sugar and phosphate groups Covalent bonds between nucleotides The teeth are nitrogenous bases. deoxyribose bases

Double Stranded DNA DNA has two strands that fit together something like a zipper. Each strand is held together with hydrogen bonds between the nitrogen bases.

Four nitrogenous bases DNA has four different bases: A-Adenine T-Thymine G-Guanine C-Cytosine

Two Kinds of Bases in DNA Pyrimidines are single ring bases. Purines are double ring bases. N C O C C N C C N

Thymine and Cytosine are pyrimidines Thymine and cytosine each have one ring of carbon and nitrogen atoms.

Adenine and Guanine are purines Adenine and guanine each have two rings of carbon and nitrogen atoms. C N O Guanine C N Adenine

Complementary base pairs Hydrogen bonds G C Cytosine always pairs up with guanine Adenine always pairs up with thymine T A The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak bonds

DNA MOLECULE PYRIMIDINE ONE RING PURINE TWO RINGS Purines and pyrimidines alternate along the double helix Complementary base pairs adenine + thymine guanine + cytosine

The ratio of A to T and C to G equals 1:1 Chargaff’s Rule: The ratio of A to T and C to G equals 1:1

Complementary Base Pair Review Complementary Base Pairs A - T + C - G Apple in the Tree Car in the Garage Complimentary base pairs are lined up in the middle of the double helix. The hydrogen bonds that hold them together will break during replication and transcription.

Write out the strand that is complimentary to: A C G T T C G A G G C T A A C G T

Answer: A C G T T C G A G G C T A A C G T T G C A A G C T C C G A T T G C A

DNA by the Numbers Each cell has about 2 meters of DNA. The average human has 75 trillion cells. The average human has enough DNA to go from the earth to the sun more than 400 times. DNA has a diameter of only 0.000000002 m. The earth is 150 billion m or 93 million miles from the sun.

Wrap-up: What is the role/function of DNA? Where is DNA located? What are the three molecules the make up a nucleotide? What are the four bases?