DNA STRUCTURE Why Do We Study DNA DNA

DNA STRUCTURE

Why Do We Study DNA? DNA We study DNA for many reasons: • It’s central importance to all life on Earth • Medical benefits such as cures for diseases • Better food crops 2

Chromosomes and DNA • Our genes are on our chromosomes. • Chromosomes are made up of a chemical called DNA. 3

Watson & Crick • Built their work off of x-ray crystallography performed by Rosalind Franklin • Created an accurate model of DNA structure • Awarded Nobel prize in 1967

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 5

DNA Structure • DNA is often called the blueprint of life. • In simple terms, DNA contains the instructions for making proteins within the cell. • A molecule of DNA is made up of millions of tiny subunits called Nucleotides • Each nucleotide consists of: 1. Phosphate group 2. Pentose sugar 3. Nitrogenous base

Nucleotide Structure Phosphate Nitrogenous Base Pentose Sugar

�The phosphate and sugar form the backbone of the DNA molecule, whereas the bases form the “rungs” �There are four types of nitrogenous bases.

Four Nitrogenous Bases DNA has four different bases: C • Thymine T • Adenine A • Guanine G • Cytosine 9

Thymine and Cytosine are PYRIMIDINES • Thymine and cytosine each have one ring of carbon and nitrogen atoms. N O O C C C N N C C thymine O C C N C cytosine 10

Adenine and Guanine are PURINES • Adenine and guanine each have two rings of carbon and nitrogen atoms. N N C Adenine N C C N O N N C C C C N Guanine C N N C 11

Hydrogen Bonds N C N N C C N C O N C C C C 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 to the right with dotted lines N O 12

Hydrogen Bonds cont. N • When making hydrogen bonds, cytosine always pairs up with guanine • Adenine always pairs up with thymine (as shown to the right) N C C C O C N N C 13

Nitrogenous Bases cont. �Each base will only bond with one other specific base. �Adenine (A) �Thymine (T) Form a base pair �Cytosine (C) �Guanine (G) Form a base pair

One Strand of DNA nucleotide • One strand of DNA is a polymer of nucleotides • One strand of DNA has many millions of nucleotides 15

One Strand of DNA cont. • The backbone of the molecule is alternating phosphates and deoxyribose sugar • The teeth are nitrogenous bases phosphate deoxyribose bases 16

Two Stranded DNA • Remember, DNA has two strands that fit together something like a zipper • Complimentary base paring between the nitrogenous bases hold the strands together 17

Chargraff’s Rule: Adenine and Thymine always join together A T Cytosine and Guanine always join together C G 18

Chargraff cont. • Erwin Chargraff • Determined that the number of Thymine in a molecule of DNA has to equal the number of Adenine due to strict base pairing rules • Number of Cytosine is equal to the number of Guanine

Base Pairing �To crack the genetic code found in DNA we need to look at the sequence of bases. �The bases are arranged in triplets called codons AGG-CTC-AAG-TCC-TAG TCC-GAG-TTC-AGG-ATC

Central Dogma DNA RNA Protein �A gene is a section of DNA that codes for a protein �Each unique gene has a unique sequence of bases �This unique sequence of bases will code for the production of a unique protein �It is these proteins and combination of proteins that give us a unique phenotype (an organism’s physical appearance)

Central Dogma cont. • DNA is stored inside the nucleus of eukaryotic cells • Because it cannot leave the nucleus a messenger molecule, RNA, has to be made in order to send the genetic blueprint to the ribosomes in the cytoplasm that do the building • Proteins do the work of the genetic blueprints

DNA Gene Protein Trait

Central Dogma cont. • Transcription = the process of using DNA to make complementary RNA – RNA uses the nitrogen base Uracil in place of Thymine to pair with Adenine • Translation = the process of using the RNA to make proteins

Your Task �Draw a flow chart to show to get from: