DNAAn ExperimentMore ExperimentStructure of DNAMore DNA StructureDNA ReplicationGene ExpressionRNATranscriptionMore TranscriptionRNA processingGenetic CodeTransfer RNATranslationMore TranslationTranslation, part 3Translation, part 4Translation, endSummary of translationPost-translationMutationMutation Causes and RateGene ControlLac OperonLac Operon BasicsLac RegulationPositive ControlX Chromosome InactivationMore X InactivationHormone SignalingPlant Response to LightGenetic EngineeringMolecular CloningPlasmid VectorsRestriction EnzymesDNA LigaseThe Cloning ProcessUsing Cloned DNAGene TherapyGene Therapy ProblemsGenetically Modified PlantsMore Plant Genetic EngineeringNuclear CloningMore Nuclear CloningDNA•DNA is the molecule that carries all of the inherited information in the cell.•DNA was discovered as “nucleic acid”—an acidic material in the nucleus in the later 1800’s.•Its importance was discovered until later. For a long time, DNA was considered too simple to carry genetic information.An Experiment•How it was learned that DNA was the hereditary material: experiments by Griffith and then by Avery, Macleod, and McCarthy in the 1920’s through 1940’s.•They used bacteria called Streptococcus pneumoniae, one cause of pneumonia. They had 2 strains: R (formed “rough” colonies) and S (formed “smooth” colonies due to a polysaccharide coat). •When injected into mice, S bacteria caused pneumonia and killed them. R bacteria didn’t hurt the mice.•When he killed the S bacteria by heating them, they no longer caused pneumonia. Same for R bacteria.•Here’s the important result: if he injected live R along with the heat-killed S bacteria, the mice developed pneumonia and died. And, they contained live S bacteria.•What happened: the hereditary material from the S bacteria survived the death of the bacteria themselves, and it “transformed” the live R bacteria into S bacteria.. Demonstrated that the hereditary material is separate from the property of being alive.More Experiment•Later work showed that the “hereditary material’ was DNA.•Crude extracts were made from the S cells: breaking them apart. The extracts transformed live R cells into S cells and killed the mice, just like heat-killed S cells.•The extracts were treated with various enzymes known to digest different cellular components: protein, RNA, DNA, etc. •DNAase, the enzyme that digested DNA, stopped the transformation effect, but none of the other enzymes did. This demonstrated that DNA was the active material in transformation, the hereditary material.•Numerous other experiments, using different organisms and procedures, continued to show that DNA, and not protein or some other type of molecule, was responsible for inheritance.Structure of DNA•DNA is a macromolecule, a large molecule composed of many subunits. The subunits of DNA are nucleotides.•Each nucleotide is composed of 3 parts: a nitrogenous base, a sugar (called deoxyribose), and a phosphate group (which is a phosphorus atom bonded to 4 oxygen atoms).•There are 4 kinds of nitrogenous bases in DNA: adenine (A), guanine (G), cytosine (C), and thymine (T).More DNA Structure•The nucleotides are joined into long chains that connect the phosphate of one nucleotide to the sugar of the next nucleotide.•The nitrogenous bases of 2 different chains pair with each other, giving a DNA molecule that has 2 sugar-phosphate chains on the outside, with bases paired in the center.•Base pairing occurs by hydrogen bonds: partial positive and negative charges attract each other. Hydrogen bonds are weak, but there are lots of them in a DNA molecule.•The 2 chains are “anti-parallel”—they run in opposite directions. They are twisted together into a corkscrew shape: a double helix.•Base pairing is very specific: A pairs with T, and G pairs with C.DNA Replication•How DNA makes copies of itself. •Occurs during the S phase of the cell cycle, when each chromosome starts with 1 chromatid and ends with 2 identical chromatids. Each chromatid is 1 molecule of DNA.•Involves an enzyme: DNA polymerase.•The DNA double helix unwinds into 2 separate strands, and a new strand is build on each old one. Thus, each new DNA molecule consists of 1 old strand plus 1 new strand. This is called “semi-conservative” replication.•DNA polymerase makes the new strands, using the old strands as a template, with normal base pairing: A with T, and G with C. •The energy for this comes from the nucleotide precursors. They all have 3 phosphates on them, like ATP, and 2 of the phosphates are removed to make the DNA.Gene Expression•Each gene is a short section of a chromosome’s DNA that codes for a polypeptide. •Recall that polypeptides are linear chains of amino acids, and that proteins are composed of one or more polypeptides, sometimes with additional small molecules attached. The proteins then act as enzymes or structures to do the work of the cell.•All cells have the same genes. What makes one type of cell different from another is which genes are expressed or not expressed in the cell. For example, the genes for hemoglobin are on in red blood cells, but off in muscle and nerve cells. “Expressed” = making the protein product.•Genes are expressed by first making an RNA copy of the gene (transcription) and then using the information on the the RNA copy to make a protein (translation).•This process: DNA transcribed into RNA, then RNA translated into protein, is called the “Central Dogma of Molecular Biology”.RNA•RNA is a nucleic acid, like DNA, with a few small differences:• RNA is single stranded, not double stranded like DNA• RNA is short, only 1 gene long, where DNA is very long and contains many genes• RNA uses the sugar ribose instead of deoxyribose in DNA• RNA uses the base uracil (U) instead of thymine (T) in DNA.•There are 3 main types of RNA in the cell:• 1. messenger RNA: copies of the individual genes• 2. ribosomal RNA: part of the ribosome, the machine that translates messenger RNA into protein.• 3. transfer RNA, which is an adapter between the messenger RNA and the amino acids it codes for.Transcription•Transcription is the process of making an RNA copy of a single DNA gene.•The copying is done by an enzyme: RNA polymerase. Recall that in replication, a DNA copy of DNA is made by the enzyme DNA polymerase.•The bases of RNA pair