BIOL 118 Chapter 16: Chapter 16

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BIOL 118
Dennis Mc Gee, Steven Tammariello

How Genes Work - DNA is blueprint of the cell a. Cells are like construction sites b. Enzymes are like Construction workers - Biologists knew about DNA, heredity, chromosomes and genes - Didn't Understand gene expression a. The process of converting information in DNA into fn molecules within the cell. The Genetic Code Hypothesis - Francis Crick proposed that the sequence of bases in DNA acted as a code a. DNA is information storage molecules b. Different combinations of bases specify specify the 20 amino acid sequences - A particular stretch of DNA (A gene) specifies the amino acid sequence of one protein - The info in the sequence of DNA is not directly translated to the amino acid sequence of a protein. *** Must be an intermediate molecule (RNA) RNA as the Intermediary Between Genes and Proteins ● Messenger RNA (mRNA) was found to carry information from DNA to the site of protein synthesis ● The enzyme RNA polymerase synthesizes RNA ○ Use DNA strand as a template ○ Copies the code by matching complementary nucleotides FIG 16.3 - protein synthess in ctyoplasm *** GO OVER A LOT OF EXPERIMENTS ABOUT MRNA AS AN INTERMEDIATE Central Dogma of Molecular Biology ● Transcription is the process of using a DNA template to make a complementary RNA ○ Making a copy of information ● Translation is the process of using the info in Mrna to synthesize proteins ○ Interprets nucleotide “language” to amino acids DNA (info storage) →(Transcription) → mRNA (info carrier) → (Translation) → proteins activate cell machinery Linking Genotypes to Phenotypes Genotype: determined by the sequence of bases in its DNA Phenotype: product of the proteins it produces Allele: of same gene differ in their DNA sequence ** Fun fact** of the 11,000 genes for sickle cell anemia, all you need is one to obtain it ● Proteins produced by different alleles of the same gene frequently differ in their amino acid sequences. Figure 16.4 -- difference in genotype even by only 1 protein can cause difference in phenotype - white vs dark coats and where one is better than oter Exceptions to the Central Dogma ● Many genes code for RNAs that do not fn as mRNA and are not translated into proteins ○ These RNAs perform important ○ Gene flow is DNA → RNA ● Sometimes info flows from RNA back to DNA ○ Some viruses contain reverse transcriptase ○ Synthesize DNA from an RNA template ○ Gene flow is RNA → DNA Genetic Code ● The genetic Code specifies how a sequence of nucleotides codes for a sequence of amino acids ● Gamow predicted that each “word” contains 3 bases ○ A 3 base code is least that could specify the 20 amino acids ○ It could code for 4 x 4 x 4 = 64 diff amino acids ● Triplet code allows us enough variation to code for 20 dif amino acids for 644 different codes ● A 3 base code is known as a triplet codon
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