What Does DNA Stand For DNA Deoxyribonucleic Acid

What Does DNA Stand For? � DNA Deoxyribonucleic Acid � ‘Deoxyribo’ refers to the sugar found in DNA � DNA is a nucleic acid- which is one of the four major organic compounds we studied earlier in the year. � Nucleic acids are composed of smaller monomers put together called nucleotides.

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

Why do we study DNA? We study DNA for many reasons, e. g. , 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. Genes are instructions to build proteins. We all have the genes but each of our genes say different things. That’s what makes everyone unique!

Discovery of DNA � First isolated by Swiss scientists Friedrich Miescher (1869) from pus from used bandages. � The function of DNA was unknown but later experiments proved that DNA was the genetic material. � The next question to answer was to determine the structure of DNA.

DNA Structure Discovered James Watson and Francis Crick solved the mystery of DNA by combining information from Maurice Wilkins and X-ray diffraction from Rosalind Franklin. Watson, Crick and Wilkins earned the noble prize in 1962. Watson and Crick 1953

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

The Double Helix Molecule The DNA double helix has two strands twisted together. (In the rest of this unit we will look at the structure of one strand. )

One Strand of DNA The backbone of the molecule is alternating phosphate and deoxyribose, a sugar, parts. The teeth are nitrogenous bases. phosphate deoxyribose bases

O One deoxyribose together with its phosphate and base O make a nucleotide. O O -P O O Phosphate Nitrogenous base O C C O O O -P Nucleotides C O O -P O C C O Deoxyribose

One Strand of DNA One strand of DNA is a polymer of nucleotides. One strand of DNA has many millions of nucleotides. nucleotide

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

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

Thymine and Cytosine are pyrimidines �Thymine and cytosine each have one ring of carbon and nitrogen atoms. N O N C C N N O C thymine O C C C N C cytosine

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

Two Stranded DNA Remember, DNA has two strands that fit together something like a zipper. The teeth are the nitrogenous bases but why do they stick together?

Hydrogen Bonds C N C O C N N The bases attract each other because of hydrogen bonds. Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. (The bonds between cytosine and guanine are shown here. ) N N C C C N O

Hydrogen Bonds, cont. When making N hydrogen bonds, cytosine always O C pairs up with N guanine, N And adenine always C pairs up with N thymine. C N (Adenine and thymine are shown C C C here. ) N N O C C

Important: • • Adenine and Thymine always join together A T Cytosine and Guanine always join together C G

Chargaff’s Rule � The bases form the “rungs” on the DNA ladder by complementary pairing A == T C == G T == A G == C A == T T == A Sugarphosphate backbone

DNA by the numbers Each cell has about 2 m 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. The earth is 150 billion m DNA has a diameter of or 93 million miles from only 0. 00002 m. the sun.

How do we contain all that DNA in each cell? � In order for each cell to store all that DNA, it must be packed into structures called chromosomes. � DNA gets wrapped around protein like string on a spool. � Those spools of DNA will continue to condense to form chromosomes.