DNA: The Molecule of Life

What is a DNA ??

Deoxyribonucleic Acid (DNA) genetic material of all cellular organisms and most viruses used to encode genetic information for all life on Earth.

DNA organized into chromosomes Eukaryotes store it inside the cell nucleuscell nucleus prokaryotes in the cytoplasm. cytoplasm

In normal human cells, DNA is arranged in 23 pairs of chromosomes 22 pairs autosomes the 23 rd pair are the sex chromosomes XX (female) or XY (male) not all chromosomes are equal Ex. #1 – 4220 genes #18 – genes

General Structure of Nucleic Acid DNA is a long chain of nucleotides. Each nucleotide is composed of a base, a sugar (deoxyribose), and a phosphate group. The phosphate joins the sugars in a DNA chain

Types of Nucleotides 4 types of nucleotides only nitrogenous base is different A – adenine G – guanine C - cytosine T - thymine. A bonds with T (two hydrogen bonds) G bonds with C (three hydrogen bonds).

Purines: Adenine & Guanine double ring structure Pyrmidines: Cytosine & Thymine single ring structure the number of thymine always equal number of adenine number of cytosine always equal to guanine.

Discovery of DNA Structure In 1950’s scientists knew that DNA:  existed  was made of nucleotides sticking together like string  would have to be over 1 m long in each cell, so must have been compressed somehow  several scientists were working/competing to discover the structure of DNA  Greatest Genetics Discoveries 1/3 - YouTube Greatest Genetics Discoveries 1/3 - YouTube

James D. Watson Francis Crick Rosalind Franklin Maurice Wilkins

Franklin used x-ray crystallography to determine DNA had a spiral shape the photos she took were taken by Wilkins (without her knowledge or permission) and shown to Watson & Crick Watson & Crick were able to discover the shape of DNA in Watson, Crick & Wilkins were awarded the Nobel Prize in As Franklin had died 4 years earlier, she was not included and her work was ignored for years.

The Double Helix ‘sides’ made of deoxyribose sugar & phosphate molecules ‘rungs’ are pair of nitrogen bases joined by hydrogen bonds 3.5 billion base pairs & 30,000 genes on 46 human chromosomes (in each cell in body) each series of 3 base pairs (codon) code for 1 amino acid genes are a series of codons that create a chains of amino acids amino acids make up proteins therefore, a gene is the code for a protein proteins code for all your genetic traits pg 195 “Reading The Code”

Packaging of DNA (deoxyribonucleic acid) In eukaryotic cells, DNA is found in the nucleus.  Most of the time, DNA exists as long, invisible, tangled fibres called chromatin  As a cell prepares to divide, chromatin thickens and shortens into chromosomes. Each chromosome is made of many small segments called genes. Humans have 23 pairs of chromosomes (46 total).  Each human cell has 2 m of chromosomes (if stretched out).  Each species has a different number of chromosomes. DNA in chromatin is tightly coiled around bead-shaped proteins called histones.

DNA (deoxyribonucleic acid) Like thread wrapped around a spool to keep it organized and protected, chromatin consists of DNA wrapped in coils around protein “beads” called histones.