The Cells Genetic Library Information to make a living organism is stored in chromosomes like information/facts are stored in a library. Chromosomes can be compared to the stacks of shelves in the library and each shelf has many books. The information in a book can be compared to the genetic information found in a gene. Chromosomes contain many genes like a library contains many books.

The Language of Books The information in books consists of marks on a paper: letters, punctuation, or other symbols. These marks are useless unless the reader knows the written language, right? How is genetic information stored in chromosomes? What code or language is a gene “written” in? How does the cell interpret this language?

The Language of Genes To answer these questions biologists first had to research which biological molecule in the cell contains genetic information. In other words scientists had to find the organic molecule of heredity! These scientists were Watson and Crick

DNA: The Language of Genes Genes are made of DNA The information that genes contain are coded or written in the DNA molecule. All the Information to Make and Operate a Living Organism is found in the molecules that make-up DNA How can a molecule carry information?

The Written Code The code is “written” in the molecules that make up the DNA just like the “marks/words” that make up the language of books. Let’s take a closer look at the structure of DNA!

DNA: The Double Helix Double: 2 strands Helix: twists To better understand DNA we “untwist” it and compare it to a Ladder

DNA is a Macromolecule called a Nucleic Acid Monomer: nucleotide Polymer: repeating nucleotide units

Nucleotide: 3 parts Phosphate 5 carbon sugar: deoxyribose Nitrogen base

What is this Molecule and the 3 Parts? 1: 2: 3:

Nucleotide of DNA 1: phosphate group 2:deoxyribose 3: nitrogen base (A, T, C, G)

The “Backbone” of DNA (sides of the ladder) NOT responsible for the genetic code. Holds and supports the nitrogen bases Made up the repeating units of: – A Phosphate group – Deoxyribose: 5 carbon sugar

The “Rungs of the Ladder” 4 Nitrogen Bases: base pair RULE Adenine (A) pairs with Thymine (T) Cytosine (C) pairs with Guanine (G) The order of the nitrogen bases is responsible for the GENETIC CODE!

Hydrogen Bonds Hold the 2 Strands Together

Putting it All Together to Form a Polymer: DNA Backbone Rungs Hydrogen bond

Let’s Review DNA’s Structure DNA is: The genetic code of instructions for LIFE. A macromolecule with repeating units (polymer). Made of repeating Nucleotide Units (monomer). Double stranded helix held together by H bonds. The backbone molecules (phosphate and Deoxyribose) hold the bases. The rungs are made from pairing of nitrogen bases (A and T; C and G). The order of nitrogen bases is the CODE or Language the Cell Understands!

Another Way: Library Analogy Library = Nucleus (in cell) 46 Shelves = 46 Chromosomes (in a human cell) 1 shelf = 1 chromosome 1 Book on the shelf = 1 gene So what is a gene exactly?

Genes A gene is a small section of a chromosome (DNA) that codes for a trait! A specific order of Nitrogen bases (A,T,C,G) Where do we find genes specifically?

DNA and Chromosomes Genetic information is contained in chromosomes located in the cell’s nucleus

The Human Nucleus Contains 46 “pieces” of DNA (about 6 feet long). These “pieces” are called either chromatin, chromosomes, or sister chromatids Chromatin: loosely packed DNA during interphase Chromosomes: densely packed DNA during mitosis Sister chromatids: duplicated chromosomes (some phases of mitosis).

Let’s take a Closer Look at Chromosomes Chromosomes are wrapped around proteins called histones. Each chromosome contains about 6 billion nucleotide pairs or about 3000 genes.

Chromosome Structure “Sister Chromatid”

So what does a Gene do? A Gene (specific order of nitrogen bases) Codes for a Specific Protein The Protein produced is responsible for the physical characteristic we call a trait. So what is a trait??

Trait: Physical Characteristic –Skin tone –Eye color –Height –Hair texture –Color blindness –Liver function Etc.…. More on this later

If the order of nitrogen bases is incorrect on a gene then the protein changes causing the trait to change. Remember Sickle Cell Disease? This results from 1change to the order of the nitrogen bases. Causing a faulty hemoglobin protein Further causing the red blood cells to not function properly

Sickle Cell Disease