DNA The Code of Life

DNA DNA = Deoxyribose nucleic acid The master copy of an organism’s information code. GENES – units of genetic material that CODES FOR A SPECIFIC TRAIT Made up of NUCLEIC ACIDS DNA is made up of repeating molecules called NUCLEOTIDES

DNA Nucleotide O O=P-O N CH2 O C1 C4 C3 C2 Phosphate Group Nitrogenous base (A, G, C, or T) CH2 O C1 C4 C3 C2 5 Sugar (deoxyribose)

HISTORY OF THE STUDY OF DNA Rosalind Franklin – discovered that the DNA molecule was a strand of molecules in a spiral form. By using the an X-ray technique, Dr.Franklin showed that the spiral was so large that it was probably made up of two spirals

HISTORY OF THE STUDY OF DNA X-Ray Image of DNA Dr. Rosalind Franklin

HISTORY OF THE STUDY OF DNA James Watson and Francis Crick – proposed the structure of DNA to be in double helix

HISTORY OF THE STUDY OF DNA Watson and Crick and their model of DNA Double Helix Model of DNA

Watson and Crick Model According to their model, the sides of the DNA are made up of two twisted strands of sugar and phosphate molecules. The “stairs” that hold the two sugar-phosphate strands apart are made up of molecules called nitrogen bases.

DNA Double Helix “Rungs of ladder” Nitrogenous Base (A,T,G or C) “Legs of ladder” Phosphate & Sugar Backbone

DNA Double Helix P O 1 2 3 4 5 P O 1 2 3 4 5 G C T A

Nitrogenous Bases A or G T or C PURINES 1. Adenine (A) 2. Guanine (G) PYRIMIDINES 3. Thymine (T) 4. Cytosine (C) A or G T or C

Chargaff’s Rule Adenine must pair with Thymine Guanine must pair with Cytosine Their amounts in a given DNA molecule will be about the same. T A G C

BASE-PAIRINGS C G H-bonds T A

Genetic Diversity… Different arrangements of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms.

A T C G T A T G C G G… The Code of Life… The “code” of the chromosome is the SPECIFIC ORDER that bases occur. A T C G T A T G C G G…

DNA is wrapped tightly around histones and coiled tightly to form chromosomes

DNA Replication Step 1: And enzyme breaks the bonds between the nitrogenous bases. The two strands of DNA separates. ENZYME

DNA Replication Step 2: The bases attached to each strand then pair up with new bases from a supply found in the cytoplasm.

DNA Replication Step 3: Sugar and phosphate groups from the side of each new DNA strand. Each new DNA molecule now contains one strand of the original DNA and one new strand.

(1961) Watson & Crick proposed… …DNA controlled cell function by serving as a template for PROTEIN structure. 3 Nucleotides = a triplet or CODON (which code for a specific AMINO ACID) AMINO ACIDS are the building blocks of proteins.

DNA Transcription DNA can “unzip” itself and RNA nucleotides match up to the DNA strand. Both DNA & RNA are formed from NUCLEOTIDES and are called NUCLEIC ACIDS.

The cell uses information from “messenger” RNA to produce proteins DNA Translation The cell uses information from “messenger” RNA to produce proteins

DNA vs. RNA DNA RNA Name Deoxyribonucleic Acid Ribonucleic Acid Type of Sugar Deoxyribose Ribose Nitrogenous Bases A, T, G, C A, U, G,C Where found Nucleus Cytoplasm Strand Double Single

(a library of about 1,000 books) AMAZING DNA FACTS… DNA from a single human cell extends in a single thread for almost 2 meters long!!! It contains information equal to some 600,000 printed pages of 500 words each!!! (a library of about 1,000 books)