Genetic Code DNA RNA anyone Genetic Code DNA
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Genetic Code DNA & RNA anyone? ?
Genetic Code
DNA & RNA being THE CODE OF LIFE Is something that we all Know today… But, how did they figure out That these molecules were SO extremely important? ? ?
Frederick Griffith • British microbiologist • Did an experiment with the disease-causing bacteria pneumococcus and laboratory mice • Griffith's experiment dealt with two strains of the bacteria pneumococcus. • One was a virulent (deadly) strain with a smooth polysaccharide coat necessary for infection • The other was a non-virulent (non-deadly) strain with a rough coat that could not cause infection
Frederick Griffith • Griffith injected one group of mice with the smooth virulent strain and these mice died after a few days. • He then injected another group with the rough non-virulent strain and these mice continued to be healthy • Griffith took a heat-killed strain of the virulent bacteria and injected it into mice and observed that they did not die. • Griffith's fourth experiment was to inject heat treated, killed, smooth virulent strain mixed with the non virulent rough strain. • He injected this mixture and found that after a few days the mice died
Transformation • When Griffith looked at the blood of the dead mice he found: – The virulent bacteria was present and very much alive – Griffith retested and found the same to be true • Some how, the dead VIRULENT strain transformed the non-virulent strain – But how is this possible… It was DEAD? !
Nucleic Acids • Once the same experiment was broken down into its most basic building blocks, it was found that the nucleic acids were what caused the transformation • They found that if they broke down the deoxyribonucleic acid that the transformation did not occur • Therefore, the “genetic code” must be found in this macromolecule
Bacteriophage
Alfred Hershey & Martha Chase • Radioactively labeled DNA or protein coat of bacteriophage (virus) • Found that bacteriophage injected DNA into cells in order to replicate • This meant that DNA is the genetic material, not proteins (which make up more than 50% of a chromosome)
Components of a Nucleotide • 3 components – Phosphate group – Sugar – Nitrogenous (Contains a nitrogen) Base
Sugar • A sugar is an organic compound with a carbonyl group – C=O This will actually help When finding the directionality Of DNA. The C=O is always pointing At the 5’ end!
The Roof of the Sugar Molecule • All sugar molecules have a distinct, house like, shape. • At the point of the roof is the C=O. • Remember! That always points at the five prime end!
Chargaff’s Theory • Found that the #of bases (Purines & Pyrimidines) are the same – The # of A’s = # of T’s – The # of C’s = # of G’s • Found that these bases must be relevant to its matching pair
Watson & Crick Model • Chemists found that DNA polymerized through the formation of phosphodiester linkages – This concluded a sugar-phosphate backbone • By analyzing the total number of purines and pyrimidines it was found that the number of A’s and T’s were equal to the number of C’s and G’s – This was called Chargaff’s rule after Erwin Chargaff • X-ray diffraction showed a repeating scatter pattern (. 34 nm, 2. 0 nm, 3. 4 nm) – This repeating pattern only makes sense if the molecule is shaped as a double helix
Scatter Pattern X-ray Diffraction • Watson & Crick began to analyze the size and geometry of deoxyribose, phosphate groups, and nitrogenous bases. • Using things like bond angles, and measurements, they were able to devise 2. 0 nm probably represented the width of the helix, and. 34 was likely the distance between bases stacked in the spiral • They arranged two strands of DNA running in opposite directions (5`-3` and 3`-5`)
DNA Size • Width of the helix = 2. 0 nm • Length of one full complete turn of helix = 3. 4 nm • Distance between bases =. 34 nm
Base Pairing • Using the x-ray diffraction patterns and measurements, it was found only to work if: • Adenine always bonded with Thymine • Guanine always bonded with Cytosine • This phenomena is called Complimentary Base Pairing
DNA REPLICATION • Occurs during S-phase of the cell cycle • DNA has a special “complimentary structure that acts as a template for reproduction – This means, it allows for simple DNA copying • The strand unzips, and the old strand acts for a model to create a new “compliment” • The strand copies in two directions: – The Leading strand starts at the 3’ end and moves towards the 5’ end – The Lagging strand pieces together new nucleotides starting at the replication fork and works toward the 5’
How Does a Cell Make Proteins? • The RNA molecule comes out of the nuclear envelope after it is transcribed from DNA (Its like a photocopy) – Transcription is the process of creating an RNA strand from a template of DNA nucleotides • The process of protein synthesis is called translation – Translation refers to the process of converting the “ 3 -nucleotide RNA codons” into amino acids and then into amino acid chains
RNA & Protein Synthesis • RNA has very specific blue prints that it uses to build the various amino acids (proteins) called Codons. • These codons allow for the difficult job of the synthesis of the many proteins to be grouped into simple readable prints (codons) including “stop and start” codons
RNA • Ribonucleic acid is very similar to Deoxyribonucleic acid, except that it contains an extra oxygen then DNA • It also contains the nitrogenous base “Uracil” instead of the “Thymine” base. • The final and often most obvious difference between the 2 nucleic acids is the fact that RNA is NOT normally a double stranded molecule
DNA & RNA • Where DNA is the “book” of your life, RNA is the photocopy • DNA = synthesized or replicated in the nucleus • RNA = Transcribed from DNA in the NUCLEUS and translated in the RIBOSOME – Transcription is a process by which a molecule of DNA is copied into a complementary strand of RNA • Because DNA does not leave the nucleus, the DNA information is brought to a ribosome through the use of a messenger RNA
How Does DNA Control a Cell? • DNA controls a cell by having the ability to be turned on or off. – Remember, DNA makes up our genes – Genes are regulated by being turned off or on • When a gene is turned on it is said that it is being “expressed” • If a gene is turned off it is said that it is “silenced” • The ability to control whether or not a gene is expressed or silenced is the GOAL of genetics
A Group of Genes = Operon • An Operon will have different segments that are used to control it. The Promoter: is where RNA polymerase binds when beginning transcription The Operator: is where the repressor binds in order to “silence” the genes The Initiator: The codon that signals the start of transcription The Terminator: The codon that signals the end of transcription (also called “stop codon”)
Lac Operon & Hox Gene • One of the more famous operons is the Lac Operon – Named because it controls the production of a protein called Lactase which breaks down the sugar Lactose found in milk • Another important gene mentioned is the Hox Gene – This gene controls differentiation of cells in animals and is common among many species
What is a Mutation? • A mutation is ANY change to genetic information (DNA) • Changing your hereditary information • It can happen as simply as an A changing to a T, or a G changing to a C when the DNA is synthesized • They can occur in ANY cell • It is why our bodies try to be incredibly precise when duplicating our genetic information, ESPECIALLY when transmitting it to the next generation
Types of Mutations • Mutations that affect your reproductive cells (often called ‘germ cells’) are called Germ Mutations – It is these mutations that are often studied in genetics (Tall, short, yellow, green) • Other mutations that affect the other cells are called Somatic mutations (occur in somatic cells – Because they do not affect the reproductive cells, somatic mutations are not inheritable – Often, somatic mutations are cancerous
2 Levels of Mutation • Both somatic & germ mutations can occur at 2 different levels: – The level of Chromosomes • Involve segments of the chromosome, whole chromosomes, and even sets of chromosomes – The level of Genes • Involve ONLY individual genes
Chromosomal Mutations • Whenever a chromosomal mutation occurs, there is a change in the number or structure of a chromosome • There are 4 types of Chromosomal mutations: – 1. Deletion – 2. Duplication – 3. Inversion – 4. Translocation
Nondisjunction • Chromosomal mutations that involve whole chromosomes or complete sets of chromosomes result from a process known as nondisjunction • Nondisjunction is the failure of homologous chromosomes to separate normally during meiosis • (Nondisjunction literally means ‘failed to separate’)
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