DNA Structure and Function

Notes DNA: Structure and Function Chapter 12 Section 1 The First three-dimensional Life Instruction Life Deoxyribose Nucleic Acid The Blueprint of Heredity The Molecule of Manual xerox machine The Architect of Life DNA Why Study DNA? To truly understand genetics, biologists first had to discover the chemical structure of the gene This would then help them understand how genes control the inherited characteristics of living things Gene expression is what enables cells of the same organism to take on so many different sizes, shapes and functions (even though just about every cell in an individual contains the same DNA) Review 1. What organelle is known as the control center of the cell? nucleus 2. What structures are found in the nucleus? chromosomes 3. What are short segments of chromosomes? genes 4. What are genes/chromosomes composed of? DNA 5. How do genes/chromosomes control the activity of the cell? produce proteins that regulate cell functions and become cell structures Review History 1869 - Friedrich Miescher – “discovered” DNA in nucleus 1928 - Frederick Griffith – Identified DNA as source of genetic material using bacteria 1930’s - Oswald Avery, Colin MacLeod and Maclyn McCarty - Confirmed that genes made of DNA 1950 - Alfred Hershey and Martha Chase confirmed DNA is the biochemical of heredity using radioactive markers bacteriophages 1952- Maurice Wilkins and Rosalind Franklin X-rayed DNA to show repeatingX-ray of double helix nucleotide structure 1953- James Watson and Francis Crick combined data Oswald Avery MaclynFrederick Griffith McCarty to create a 3-D model of structure called the Rosalind Franklin Alfred Hershey double Martha Chase James Watson helix Francis Crick Watson-Crick Model DNA Structure • Is a polymer of 1000’s of nucleotide monomers • Is a double strand of covalently bonded nucleotides in twisted ladder shape •twisted ladder shape = double helix DNA Shape Double helix: 2 spirals wound around each other But joined in the middle DNA Structure • Is a polymer of 1000’s of nucleotide monomers Sugar • Is a double strand of Phosphate Backbone covalently bonded nucleotides in twisted ladder shape twisted ladder shape = double helix • ‘Rungs’ of ladder = nitrogen bases • ‘Sides’ of ladder = sugar & phosphate groups (also called the DNA backbone) Nucleotide •Nucleotide- Individual unit of DNA. •Made of three parts: •Deoxyribose (5-carbon sugar) •Phosphate group •A nitrogen-containing base adenine A base with a double-ring structure Bases sugar (deoxyribose) (T) base with a adenine A single-ring base with a structure double-ring structure •Four nitrogen-containing bases •Adenine •Guanine •Cytosine •Thymine sugar (deoxyribose) adenine A base with a double-ring structure thymine (T) base with a single-ring structure guanine adenine (G) A base with a base with double-ringa double-ring structure structure sugar (deoxyribose) guanine (G) base with a double-ring structure guanine thymine adenine cytosine (G) (T) A (C) base withwith a a basewith aa cytosine base base with double-ring (C) single-ring base double-ring single-ring structure with a single-ring structure structure structure structure Bases  Adenine double ringed = purines Guanine   Thymine single ringed = pyrimidines Cytosine  Nucleotide Deoxyribose (like ribose) P base is a sugar with 5 carbon atoms in a ring sugar Oxygen is one of the ring members In Deoxyribose, one of the OH groups is missing and replaced with hydrogen Thus deoxy = - 1 oxygen H OH Nucleotide P - the Phosphate group P Is important because it links the sugar on one sugar nucleotide with the phosphate of the next nucleotide to make a polynucleotide Nucleotides are connected to each other via a covalent bond base ‘Base Pairing Rule’ • Bases are paired together in specific manner  Because of chemical structure and shape •Adenine only pairs with Thymine •Guanine only pairs with Cytosine  Exactly enough room for only one purine and one pyrimidine base between the two strands of DNA ‘Base Pairing Rule’ •Bases held together in ‘rungs’ by weak hydrogen bonds •2 hydrogen bonds between A & T •3 hydrogen bonds between C & G DNA DNA Function • Scientists wondered how DNA worked. They knew genes do these critical things: • Carry information from one generation to another • Put information to work to determine an organism’s characteristics • Can be easily copied • Store and transmit genetic information needed for all cell functions • In order to do these things it had to be a special molecule! Understanding DNA • Our knowledge of DNA put to use: • Inheritance/ Genetic Counseling • Cell function/protein synthesis • Embryonic development/gene regulation • Evolution/ phylogenetic relationships • Medicine/genetic diseases • Genetic engineering/ recombinant DNA Structure of DNA Review Nucleotide Hydrogen bonds Sugar-phosphate backbone Key Adenine (A) Thymine (T) Cytosine (C) Guanine (G) Structure of DNA Review Purines Adenine Guanine Pyrimidines Cytosine Thymine Bases Phosphate group Deoxyribose DNA’s Size To get an idea of the size of the human genome present in each of our cells, consider the following analogy: If the DNA sequence of the human genome were compiled in books, the equivalent of 200 volumes the size of a Manhattan telephone book (at 1,000 pages each) would be needed to hold it all. It would take about 9.5 years to read out loud (without stopping) the 3 billion bases in one person's genome sequence, calculated on a reading rate of 10 bases per second, equaling 600 bases/minute, 36,000 bases/hour, 864,000 bases/day, 315,360,000 bases/year. Human Genome Project A DNA How Am I Packaged? • Nitrogen bases 1. Are like letters in the code 2. Put them in different order make a different gene A DNA Package CAT HAT DOG • Genes 1. Are like words made up of letters 2. A group of nitrogen bases that makes sense 3. Tells the cell to do something The cat sat. DNA Package • DNA strand One dog ate. The big hat. 1. Are like sentences made up of words 2. A long line of genes on each DNA strand DNA Package • Chromosomes 1. Are like books full of sentences 2. DNA strand twists around and around itself DNA Package • Nucleus 1. Is like a bookcase 2. Inside the cell, where all the chromosomes are stored DNA Package • So what would a library full of rows and rows of bookcases represent? many cells together which is a tissue