BIO_SC 1010 1st Edition Lecture 7 Outline of Last Lecture I. What is DNA?II. Where is DNA found?III. DNA and GenesIV. What is a Chromosome?V. EpigeneticsVI. Humans have 23 pairs of chromosomes: this is their genomeVII. The structure of DNAVIII. DNA ReplicationIX. Chromosomes at cell division have unique propertiesX. What makes DNA a great molecule for hereditary information?Outline of Current Lecture I. Genes are not active all the timeII. How are genes turned on and off?III. X-chromosome inactivation is an extreme case of gene regulationIV. Building a protein moleculeCurrent LectureGenes are not active all the time• Expressed- transcribed into mRNA and translated into protein, i.e. the protein is actually produced • Gene expression is regulated by:1. Turning genes ‘on’ or ‘off’-when gene is on = transcription -when the gene is off = no transcription These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Varying the rate of transcription or translation • Whether or not a gene is expressed, and the rate at which it is expressed, varies among cells and over time • Genes may be turned on/off depending on:-developmental stage of the organism -type of tissue that the cell is part of-external environmental cues (food, sunlight, temperature, behavior)• Gene coding for:-enzyme used in glycolysis-crystallin -insulin-growth hormone• Expressed in:-nearly all cells-eye lens cells-pancreas cells-pituitary gland How are genes turned on and off?• Activator proteins- bind to genes, turning them on• A gene that codes for an activator protein is an example of a regulatory gene-regulatory genes control the expression of other genes by turning them on and off • One regulatory gene may control the expression of many other genes • Example: SRY gene o human Y chromosome-SRY codes for an activator protein that binds to other genes, turning them on-these other genes code for proteins needed for the development of testes• Regulatory genes are particularly important during early development • Sometimes there are mistakes in gene activationX-chromosome inactivation is an extreme case of gene regulation• In female mammals one X chromosome in each body cell is highly compacted and almost entirely inactive Building a protein molecule • Step 1: transcription-getting the information from the DNA to the ribosome, where proteins are made-during transcription, mRNA serves as the messenger who delivers the instructions to the ribosome-RNA is similar to DNA, except single stranded U instead of T (bases = CGAU)a) An enzyme unzips the double-stranded DNA of a geneb) One strand of the DNA serves as a template for making mRNA c) The strand of mRNA leaves the nucleus through a nuclear pore, and goes to a ribosome• Step 2: translation -turning the sequence of bases into a sequence of amino acids bound together a) The ribosome binds to the bases 3 at a time-each triplet of mRNA bases = a codon codes for 1 amino acid -e.g. AAG codes for lysine and AGU codes for serine b) Transfer RNA (tRNA) brings the correct amino acids to the ribosome -anti-codon= group of 3 bases on the RNA-each tRNA carries one type of amino acid, depending on its anti-codon -the tRNA whose anti-codon binds complimentarily to the codon brings its amino acid to the ribosome-complimentarily = according to the binding rules of bases• The genetic code- the correspondence between particular mRNA codons and amino acids-e.g. UCU = serine, CGU = arginine and GGG =