DNA – the blueprint of life

The Real Deal DNA stands for DEOXYRIBONUCLEIC ACID DNA is the genetic material found in the nucleus DNA can be found as chromatin or condensed into chromosomes

The Real Deal A gene is the part of a chromosome that determines traits. (Generally a small piece of DNA with a certain number of base pairs) The order of letters (bases) is called a DNA sequence.

The Real Deal DNA is a code that cells use to make proteins. This code determines the traits of living things.

DNA is a Nucleic Acid Nucleic acids are one of the four macromolecules! DNA is the polymer Nucleotides are the monomers Many monomers coming together to form the polymer

The Nucleotides Nucleotides are composed of:  Phosphate group  5-carbon sugar  Nitrogenous base (contains nitrogen)

Nucleotides: the 5-carbon sugar Since there are 5 carbons, this is a pentose sugar. This sugar is deoxyribose (DNA = deoxyribonucleic acid) Carbons are numbers clockwise 1 through 5

Nucleotides: the nitrogenous bases Nitrogenous = contains nitrogen DNA has four different bases:  CytosineC  ThymineT  AdenineA  GuanineG

Nucleotides: the nitrogenous bases There are two kinds of bases: Pyrimidines Thymine (T) & Cytosine (C) Single ring base Purines Adenine (A) & Guanine (G) Double ring base

Nucleotides: the nitrogenous bases Another look! Single ring Double ring

So how do we get from monomer to polymer? Nucleotide (monomer) DNA (polymer)

How do we even know about DNA structure? DNA is a double helix (2 stranded spiral)

How do we even know about DNA structure? Rosalind Franklin took diffraction x-ray photographs of DNA crystals Watson & Crick built the first model of DNA using Franklin’s x-rays

The Double Stranded Helix DNA can be compared to a twisted ladder Rungs of the ladder = Bases (A, T, C, G) Legs of the ladder = Phosphate & Sugar Backbone

The rungs of the ladder Bases pair up to form the “rungs of the ladder” Chargaff’s Rule: Adenine (A) must pair with Thymine (T) Guanine (G) must pair with Cytosine (C)

Base pairing: How do the bases stay together? Weak hydrogen bonds! (represented by the dotted lines)

Base pairing: How do the bases stay together? Purines only pair with Pyrimidines Three hydrogen bonds required to bond G – C Two hydrogen bonds required to bond A – T

Hydrogen Bonds An attractive force between a hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Hydrogen bonds are weak, but there are millions of them in a single DNA molecules that keeps the strands together.

Why is there a different number of bonds?

The legs of the ladder The backbone of DNA is made up of alternating phosphates and deoxyribose sugar

A closer look at the backbone of DNA