DNA Structure DNA Structure Powerpoint #1 Chapter 12

DNA is a type of nucleic acid. The building blocks of nucleic acids are nucleotides. One Nucleotide

Labeled drawing of a nucleotide: Nitrogen Base

DNA=Deoxyribonucleic Acid Nitrogen Base

DNA is found in the nucleus of the cell

DNA’s function is to store and transmit genetic information.

How did scientists determine the structure of DNA?

A little background in what was discovered so far… Oswald Avery and others determined that DNA stores and transmits genetic information

1950 - Erwin Chargaff Noticed a pattern: CHARGAFF’S RULE # A = # T Comparing ANY sample of DNA he discovered that the percentages of the nitrogen bases guanine(G) and cytosine(C) are equal. The same is true for the percentages of adenine(A) and thymine(T). CHARGAFF’S RULE # A = # T # G = # C

It was a RACE - lots of competition 1951 The Structure (shape) of DNA It was a RACE - lots of competition London, England Rosalind Franklin and Maurice Wilkins were photographing the DNA molecule. England Cambridge University, James Watson and Francis Crick build models USA Linus Pauling (Nobel prize -chemical bonds)

X-ray crystallography 1952 - Rosalind Franklin X-ray crystallography Shine X-rays on crystalized DNA, bounce off see an image. Clues Order/pattern Equal width Born:1920 Died:1958 (Age 37)

X-Ray crystallography

DNA DOUBLE HELIX 1953 Watson and Crick With Franklin's and many other scientists data, Watson and Crick were soon able to determine the structure of DNA. On March 18, 1953, Watson and Crick published the first accurate model of the DNA molecule. DNA DOUBLE HELIX

Watson & Crick accepting Nobel Prize 1960 Watson, Crick, and Wilkins received the Nobel prize for their work.                                                                                                    Watson & Crick accepting Nobel Prize Franklin had died of cancer in 1958, at age 37. Would you award her a Nobel Prize?

A DNA molecule is made of 2 strands which wind around each other in the shape of a double helix. The nitrogen bases point toward the center of the molecule.

The four different nitrogen bases in DNA (for different types of DNA nucleotides) are: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T)

The bases that pair with each other are called complimentary A always pairs with T G always pairs with C The bases that pair with each other are called complimentary

How can a seemingly simple code with only 4 letters produce millions of different genes? The code is read 3 bases at a time (4x4x4=64) and can be thousands or millions of base pairs long. (64 x 64 x 64 x 64…….)

A single DNA molecule may contain thousands of nucleotides (bases). The order of the nucleotides (bases) in a DNA is a code that provides instructions for making proteins.

What are genes? A segment of DNA that codes for a specific protein is called a gene. Genes code for traits such as: Hair color Eye Color How many fingers you have Skin color Enzymes to break down the food that you eat

In your cells, DNA wraps up tightly around proteins called histones to produce a substance called chromatin which condenses during cell division (mitosis) to form structures called chromosomes

Base Types Bases are either: Purines (A & G) – a nine-member, 4 nitrogen molecule Pyrimidines (T & C) – a six-member, 2 nitrogen molecule

Base Types The bases hydrogen bond to each other at the locations to the right. Look for these donors and acceptors to determine where bonds are located

Base Types G & C bond in three locations A & T bond in two locations

Drawing of DNA Backbone made of sugar and phosphate 1 Nucleotide Base Pairs: Adenine, Guanine, Cytosine, Thymine Backbone made of sugar and phosphate