Chapter 12.1DNA

Genes carry information from one generation to the next

Genes determine the heritable characteristics of organisms

Genes can be replicated or copied exactly

DNA’s Responsibilities

DNA is a nucleic acid◦ It has monomers called nucleotides

Each nucleotide is composed of three basic parts: 5 carbon sugar – deoxyriboseA phosphate groupA nitrogenous base

DNA’s Components

There are four nitrogenous bases categorized into two groupsPurines: (two rings)

Adenine (A) Guanine (G)

Pyrimidines: (one ring) Cytosine (C) Thymine (T)

Nitrogenous Bases

DNA can be considered to be like a ladder

The sugar and phosphate groups make up the backbone of the molecule, or the sides of the ladder◦ They alternate along the sides

The nitrogenous bases stick out of the sides of the sugar◦ They make up the rungs of the ladder

DNA’s Structure

Erwin ChargaffRealized the number of

A’s equals the number of T’s and that the number of G’s equals the number of C’s

Base pairing ruleA = T G = C Purines Pyrimidines

Rosalind FranklinUsed x-ray

diffraction to gather information about DNA structure

◦ Revealed that DNA is in helix form (coil or twisted ladder)

Made 1st 3-D model of a DNA molecule◦ Used the work of Chargaff and Franklin to create

this model

DNA structure is called a double helix, in which two strands are wound around each otherThe two strands are connected by hydrogen bonds

Watson and Crick

DNA and ChromosomesChromosomes are

tightly wound up DNA strands

Increased organization allows for the tremendous length of DNA to fit into the nucleus of the cell

DNA is tightly wound around proteins called histones8 histones + DNA = nucleosome◦ These form chromatin

Chromatin tightly wound up makes a chromosome

http://www.youtube.com/watch?v=yqESR7E4b_8&feature=related

Chromosome Structure

Prokaryotic Chromosomes Prokaryotic chromosomes are located

floating in the cytoplasm of the cell (not in the nucleus)They are circular in shape (not “X shape” like

in eukaryotes)