Chapter 8 From DNA to Proteins Introduction to Protein Synthesis
Griffith finds a ‘transforming principle.’ • Griffith experimented with the bacteria that cause pneumonia. • He used two forms: the S form (deadly) and the R form (not deadly). • A transforming material passed from dead S bacteria to live R bacteria, making them deadly. Experiment Video
Avery identified DNA as the transforming principle. • Avery isolated and purified Griffith’s transforming principle. • Avery performed three tests on the transforming principle. • Qualitative tests showed DNA was present. • Chemical tests showedthe chemical makeupmatched that of DNA. • Enzyme tests showedonly DNA-degradingenzymes stoppedtransformation.
Hershey and Chase confirm that DNA is the genetic material. • Hershey and Chase studied viruses that infect bacteria, or bacteriophages. • They tagged viral DNA with radioactive phosphorus. • They tagged viral proteins with radioactive sulfur. • Tagged DNA was found inside the bacteria; tagged proteins were not.
8.2 Structure of DNA http://ghr.nlm.nih.gov/handbook/basics/dna
The Genetic code • The program of the cell is the genetic code. • Genetic code- the way in which cells store the program that they seem to pass from one generation of an organism to the next generation
Genetic Code http://lifeofplant.blogspot.com/2011/04/genetic-code.html
DNA is the nucleic acid that stores and transmits information from one generation to the next. • DNA (Deoxyribonucleic Acid) http://www.forbes.com/fdc/welcome_mjx.shtml
The structure of DNA • DNA is formed from units called Nucleotides • Each Nucleotide is made of: • A 5-carbon sugar called deoxyribose • A phosphate group • A nitrogenous base/nitrogen containing base
Nitrogenous bases • DNA had 4 nitrogenous bases divided into two groups: • 1. Purines: • Adenine • Guanine • 2. Pyrimidines • Cytosine • Thymine • Bases come together to form a chain
Nitrogenous bases http://student.ccbcmd.edu/~gkaiser/biotutorials/dna/fg4.html
X-Ray Evidence • Rosalind Franklin used x-ray diffraction to visualize the DNA molecule • She discovered that they are twisted, and that it is spaced out in intervals http://jewishcurrents.org/april-16-rosalind-franklin-and-the-double-helix-1555
Chargaff discovered that there is the same amounts of adenine as Thymine and cytosine as Guanine in DNA http://pangzho.blogspot.com/2011/01/chargaffs-rule-of-dna-composition.html
The Double Helix • Watson and Crick saw Franklin’s work and came up with the Double Helix model • The nitrogenous bases of each of the strands of DNA are positioned opposite each other • Causes Hydrogen bonds to form
Adenine bonds with Thymine • Cytosine bonds with Guanine • They only bond With each other • Known as base pairing Holds two strands together http://www.mikeblaber.org/oldwine/bch5425/lect02/lect02.htm
The Replication of DNA • The strands of DNA are complimentary, meaning they are not exact copies but you know what the other side looks like • One strand can direct the sequence of the other by complimentary base pairing
Complimentary Base Pairing http://dedunn.edublogs.org/2011/06/08/complementary-base-pairing/
Each strand is a template for another http://science.howstuffworks.com/environmental/life/cellular-microscopic/dna3.htm
A cell must duplicate its DNA before it divides • The copying process is known as Replication (synthesis) • This is carried out by enzymes (proteins)
The enzymes unzip the two strands of DNA and insert the appropriate bases • They then insert the appropriate bases for the new strand • Some enzymes even proofread the strands to make sure the DNA is replicated
DNA Replication http://www.nature.com/scitable/content/dna-replication-of-the-leading-and-lagging-14668888
Replication starts when the molecule unzips (hydrogen bonds are broken) • Each strand is a template for complimentary bases • T-A-C-G-T-T What is the complimentary Strand? • DNA Replication Video!!!
8.4 Transcription http://www.biologycorner.com/bio1/DNA.html
RNA • Knowing the structure of DNA doesn’t explain how it holds information • The first step into decoding the DNA is by copying part of it in RNA (ribonucleic acid) • RNA-the nucleic acid that acts as a messenger between DNA and the ribosomes and carries out the process by which proteins are made from amino acids
The Structure of RNA • RNA is a long chain of nucleotides like DNA • Made up of a sugar, phosphate, and a nitrogenous base • This makes up the backbone just like DNA
The Structure of RNA http://allyncali16.tripod.com/id1.html
RNA follows base pairing: • Adenine – Uracil Cytosine – Guanine • RNA is used as a copy • There are three types we will talk about
Transcription: RNA Synthesis • Transcription-a molecule of DNA is copied into a complementary strand of RNA • Process of transferring info from DNA to RNA • Why do you think this is necessary?
Transcription: RNA Synthesis • DNA is in nucleus and ribosomes are in cytoplasm • Messenger RNA (mRNA)- a molecule that brings a copy of DNA from the nucleus to the cytoplasm • One of the three types of RNA
Transcription: RNA Synthesis • RNA polymerase (enzyme) separates the strands of the DNA double helix • It then creates a mRNA strand • mRNA is complementary to one of the strands • Base pairing makes it complimentary
Transcription: RNA synthesis • Special sequence of DNA serves as start signals • Special sequences of DNA serves as termination sites • RNA polymerase recognizes those spots
Transcription Video Video http://www.ck12.org/user:a2JyYWRidXJuQGxvdmV0dC5vcmc./concept/Matter-and-Organic-Compounds-%253A%253Aof%253A%253A-The-Chemistry-of-Life/
The info that DNA transfers to mRNA is in code depending on the arrangement of the bases • Two questions come up: • What kind of info is contained in DNA? • How is the info decoded?
The bases in DNA direct protein synthesis (creation) • Why proteins? • Responsible for: control biochemical pathways; direct the creation of lipids, carbohydrates and nucleotides; cell structure; and cell movement
DNA issues orders to the organelles of the cell to make proteins • DNA and RNA are the nucleic-acid executives who run the cell factory
The Nature of the Genetic Code • Proteins are made of long chains of amino acids which form chains called polypeptides • Each polypeptide is made of the 20 different amino acids • How can a particular order of nitrogenous bases in DNA and RNA be translated into a particular order of amino acids in a polypeptide?
Amino acid<polypeptide<protein http://lfsummer201110005.blogspot.com/
Genetic code • There is a four letter alphabet arranged by bases • The code words are copied from DNA to RNA in transcription • Each combination of three bases on a mRNA makes a codon or three letter code word