DNAHow do genes work? What are they made of, and how do they determine the characteristics of organisms?

In the middle 1900’s questions like these were on the minds of biologists everywhere.

Gregor Mendel “Father of Genetics” (1864)

Genetics – the scientific study of heredity.

The Alphabet of Life• What are words? What really are letters?

• What is a code?

• Read this:

26224 2 47 843 2665378 489 66 32784.

The Components and Structure of DNA

• When scientists found out that the molecule DNA was responsible for our genetics they still were not satisfied.

• How could DNA or any molecule for that matter have the ability to carry, translate, copy, and be responsible for our heredity?

DNA(Dexoyribose Nucleic Acid)• DNA is a long molecule made up of units called

nucleotides.• Nucleotide is made up of three basic structures:

- A 5-carbon sugar called deoxyribose

- A phosphate group

- And a combination of four nitrogenous bases.

The Backbone of DNA• The “backbone” of

DNA is made of up of sugar and phosphate.

• This backbone allows for the nitrogeneous bases (adenine, cytosine, guanine, and thymine) to combine and construct our genetic code.

Nitrogenous Bases• DNA’s nitrogenous bases are the letters of

the words which make up our genetic code.

• Adenine always connects with Thymine.

• Cytosine always connects with Guanine.

Together these bases make up the steps of a ladder.

Nitrogenous Bases- Two nitrogenous bases belong to a group called the

purines. (outies)(Adenine and Gyanine) A and G

- The other two nitrogenous bases belong to a group called the pyrimidines. (innies)

(Cytosine and Thymine) C and T

Adenine and Thymine

Straights with Straights

Guanine and Cytosine

Curves with Curves

DNA• Each DNA molecule is made up of a series of

monomers called nucleotides. Each nucleotide has three parts:

• A deoxyribose sugar

• A phosphate group

• A nitrogenous base.

DNA’s History• Know that you know what DNA is and what it

is constructed, how do you think it was found?

Chargaff’s Rule• One of the puzzling facts about DNA was a

curious relationship between its nucleotides.

• Erwin Chargaff (an American biochemist) had discovered that the percentages of guanine and cytosine bases are almost always equal in any sample of DNA.

X-Ray Evidence• In the early 1950’s a British scientist named

Rosalind Franklin began to study DNA.

• Just like anyone else that is curious Rosalind wanted to see what she was studying, so she literally to a picture of DNA with an X-ray.

The Double Helix• At the same time that Franklin was continuing

her research, Francis Crick and James Watson were trying to build a three-dimensional model of the molecule.

• Watson and Crick used Rosalind’s picture to figure out DNA’s puzzle and the solved what is known as the double helix.

• DNA is a double helix in which two strands are wound around each other. Each strand is made up of a chain of nucleotides. The two strands are held together by hydrogen bonds between adenine and thymine and between guanine and cytosine.