DNA and RNA. Genes are made of DNA Griffith’s “Transforming Factor” Is the Genetic Material...
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Transcript of DNA and RNA. Genes are made of DNA Griffith’s “Transforming Factor” Is the Genetic Material...
![Page 1: DNA and RNA. Genes are made of DNA Griffith’s “Transforming Factor” Is the Genetic Material Avery Shows DNA Is the Transforming Factor Virus Experiments.](https://reader034.fdocuments.in/reader034/viewer/2022042821/56649c855503460f9493bdf2/html5/thumbnails/1.jpg)
DNA and RNA
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Genes are made of DNA
• Griffith’s “Transforming Factor” Is the Genetic Material
• Avery Shows DNA Is the Transforming Factor
• Virus Experiments Provide More Evidence
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Frederick Griffith
• A 1928 army medical officer trying to find a vaccine against streptococcus pneumoniae bacteria
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Griffith’s Experiment• Injected several mice with a harmless strain of
bacteria and other mice with heat-treated deadly bacteria. All the mice survived.
• But when he injected mice with a mixture of the harmless bacteria and the heat-treated deadly bacteria, the mice died.
• The harmless bacteria had been “transformed” by something in the heat-treated deadly bacteria.
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Picture of Griffith’s Experiment
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Oswald Avery
• In 1944, Oswald Avery repeated Griffith’s experiment to see if the “transforming factor” was DNA or protein.
• When Avery treated the mixture of bacteria to destroy DNA, the transformation did not occur.
• He concluded that DNA was the “transforming factor.”
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Martha Chase and Alfred Hershey
• In 1952, Hershey and Chase used viruses to confirm Avery’s conclusions.
• Concluded that DNA was the portion of the phage that carried the genetic information.
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Picture of Hershey and Chase’s Experiment
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Nucleic acids store information in their sequences of chemical units
• The Building Blocks of DNA
• DNA’s Structure
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The Building Blocks of DNA
• Deoxyribonucleic Acid (DNA) is the molecule that stores genetic information.
• DNA is made up of units called nucleotides.
• Each nucleotide has three parts: a sugar, a phosphate group, and a nitrogenous base.
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DNA’s Structure
• A nitrogenous base is a single or double ring of carbon and nitrogen atoms with functional groups.
• Nitrogenous bases with single rings are called pyrimidines.
• Nitrogenous bases with double rings are called purines.
• Bonds connect the sugar of one nucleotide to the phosphate of the next nucleotide, forming a sugar-phosphate “backbone.”
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Rosalind Franklin and Maurice Wilkins
• In the 1950’s, first to obtain very good x-ray diffraction images of the DNA fibers.
• From these photos, Franklin determined that the DNA molecule must be long and thin.
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Franklin and Wilkins’s X-ray Picture of DNA
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James Watson and Francis Crick
• In 1953, Watson and Crick discovered the double helix structure of DNA using the information from Franklin and Wilkins.
• Built a model of a DNA molecule with a twisting shape called a double helix.
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Erwin Chargaff
• Biochemist who first figured out the equation for the different nitrogen bases.
• Here is what he concluded:
• The amount of (A)denine will always equal the amount of (T)hymine and the amount of (G)uanine will always equal the amount of (C)ytosine.
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DNA replication is the molecular mechanism of inheritance
• The Template Mechanism
• Replication of the Double Helix
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The Template Mechanism
• DNA is copied before a cell divides.
• DNA replication is the process of copying the DNA molecule.
• During DNA replication, the two strands of the double helix separate.
• The cell uses each strand as a template, or pattern, for making a complementary strand.
• Nucleotides are added to the new strand, according to the rules of base pairing.
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Replication of the Double Helix
• DNA replication begins at the origins of replication and proceeds in both directions, producing “bubbles.”
• Eventually, all the bubbles merge, resulting in two separate daughter DNA molecules.
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A gene provides the information for making a specific protein
• One Gene, One Polypeptide
• Information Flow: DNA to RNA to Protein
• The Triplet Code
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One Gene, One Polypeptide
• In the 1940s, George Beadle and Edward Tatum worked with bread mold Neurospora crassa to study the relationship between genes and proteins.
• Proposed the “one gene-one enzyme” hypothesis, stating that each gene controls the production of a specific enzyme.
• Scientists now know that most genes code for the production of a single polypeptide.
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Structure of RNA
• Ribonucleic Acid (RNA) is a nucleic acid whose sugar is ribose rather than deoxyribose of DNA.
• Another difference is that RNA contains a nitrogenous base called uracil (U) instead of thymine of DNA.
• And RNA typically forms a single, sometimes twisted strand, not a double helix like DNA.
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Information Flow: DNA to RNA to Protein
1. DNA sequence is converted to the form of a single-stranded Ribonucleic Acid (RNA) molecule in a process called transcription.
2. RNA moves from the nucleus to the cytoplasm.
3. Translation converts the nucleic acid sequence into a sequence of amino acids.
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What are the rules for translating the nucleotide sequence of RNA into an
amino acid sequence?• American biochemist Marshall
Nirenberg began cracking this code in the early 1960s.
• He built an RNA molecule that only had uracil nucleotides, called “poly U.” Because it contained only uracil nucleotides, it contained only one type of codon: UUU, repeated over and over.
• He concluded that the RNA codon UUU codes for the amino acid phenylalanine (Phe).
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The Triplet Code
• A codon, or three-base sequence, codes for one amino acid.
• The order of the codons in the RNA determines the order in which amino acids will be put together to form a polypeptide.
• There are 64 codons and 20 amino acids.
• Certain codons signal protein synthesis to start and stop.
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There are two main steps from gene to protein
• Transcription: DNA to RNA
• Editing the RNA Message
• Translation: RNA to Protein
• Review of Protein Synthesis
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Transcription: DNA to RNA
• Messenger RNA (mRNA) is transcribed from the DNA molecule.
• An enzyme called RNA polymerase joins the RNA nucleotides together during transcription.
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Editing the RNA Message
• The mRNA molecule contains sections, called introns, that do not code for amino acids.
• The process of RNA splicing removes the introns and joins the coding regions, which are called exons.
• After RNA splicing is complete, the mRNA molecule moves from the nucleus to the cytoplasm.
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Translation: RNA to Protein
• Transfer RNA (tRNA) is a molecule with an amino acid binding site at one end and a three-base anticodon at the other end.
• An anticodon is a sequence that is complementary to a codon in the mRNA.
• The tRNA anticodon binds to the mRNA codon, bringing and amino acid into position to be added to the polypeptide.
• This process takes place on a ribosome, which is made up of ribosomal RNA (rRNA).
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Review of Protein Synthesis
• What is the overall significance of transcription and translation?– The proteins that form
from the polypeptides determine the appearance and functioning of the cell and of the whole organism.
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Mutations can change the meaning of genes
• How Mutations Affect Genes
• What Causes Mutations?
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How Mutations Affect Genes
• A change in the nucleotide sequence of DNA is called a mutation.
• A mutation can be a change in a single nucleotide or a change in a large part of a chromosome. For example, sickle cell disease.
• Mutations include substitutions, in which one nucleotide is replaced by another. Other mutations are insertions or deletions, in which one or more nucleotides are added to or removed from a gene. Insertions and deletions usually have more serious effects than substitutions.
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What Causes Mutations?
• Mutations can be caused by errors in crossing over or DNA replication.
• A physical or chemical agent that causes a mutation is called a mutagen.
• Most mutations are harmful changes, but occasionally a mutation occurs that is beneficial.
• Mutations that are present in gametes, or sex cells, can be passed to an organism’s offspring.
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More Information
Websites:• The DNA Files• DNA Interactive• You Try It: DNA Workshop