What is DNA? • DNA stands for Deoxyribonucleic acid • Discovered by 2 scientists Watson & Crick • DNA stores all of your genetic information • THINK! – How many DNA molecules does a human body cell have? 46
Structure of DNA • DNA is composed of 3 things: • Sugar (Deoxyribose) • Phosphate • Nitrogen Base • These 3 things put together make up what is called a nucleotide. • DNA is merely 2 chains of nucleotides linked together. • There are 4 nitrogen bases that can be used in DNA. • Adenine (A) • Guanine (G) • Thymine (T) • Cytosine (C)
Structure of DNA • The shape of DNA is referred to as a double helix. • A DNA molecule is not flat, but resembles a twisted ladder. • The sides of the ladder are made up of alternating sugar and phosphate groups. • The rungs of the ladder are made up of nitrogen base pairs • When pairing nitrogen bases together follow this rule: • Adenine always binds to Thymine (A-T) • Guanine always binds to Cytosine (G-C)
HEALTHY PERSON Diabetic C C A T A G C A C G T T C C A T A G C A T C T G OH NO! The order of the bases is not correct. Ribosome can’t make sense of the word! Ribosome reads this order and makes protein Protein is called INSULIN INSULIN is NOT made! Insulin controls blood sugar Person has diabetes!
How does DNA make us who we are? • It’s simple! Use this analogy to understand: • Think of the nitrogen bases (A,T,G,C) in DNA like letters of the alphabet. • When you string enough of these letters together they form words. • These words are called our “genes”. Humans have ~ 30,000 genes. • When a ribosome reads these words it knows what proteins to make. • It is the proteins that give you your traits. For example, the darkness of my hair is due to a protein giving it the color.
DNA Replication • DNA replication is the process by which DNA makes a copy of itself. • THINK! – At what point during the cell cycle does a cell copy its DNA? • THINK! – Where in the cell would a DNA molecule copy itself? Interphase Nucleus
Steps in DNA Replication • Step 1 – Unzipping The 2 DNA strands are first separated or “unzipped.” • Step 2 – Base pairing Once separated, the nitrogen bases floating in the nucleus pair up with the bases on each half of the DNA molecule. • THINK! – What is the rule when base pairing? • THINK! -But what if the cell makes a mistake when adding the bases? A binds with T; G binds with C The DNA is now changed. This is called a mutation. Some mutations can be good while others can be harmful.
DNA Replication Animations HHMI SITE WHERE ANIMATIONS ARE FROM- http://www.hhmi.org/biointeractive/dna/animations.htm • Overall Process - http://www.hhmi.org/biointeractive/dna/DNAi_replication_schematic.html • Paired DNA Strands – http://www.hhmi.org/biointeractive/dna/DNAi_paired_strands.html • Replication from DNA tube- http://www.dnatube.com/video/365/DNA-Replication • Lewport’s Biology Place – http://www.lpscience.fatcow.com/jwanamaker/animations/DNA%20Replication%20-%20long%20.html