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From Gene to Protein The Central Dogma GENES determine traits by building individual proteins for that trait An error in the gene = an error in the protein The Central Dogma DNA RNA Amino Acid Chain (Protein) Figure 14.3 DNA holds the instructions, while RNA carries out the instructions. RNA is a lot like DNA, except: 1. Ribose 2. Uracil 3. Single Strand 4. RNA can leave the nucleus, thus carries the "message" Figure 14.5 The instructions on mRNA (messenger RNA) are read by the ribosome as a series of 3 bases called a CODON Each CODON specifies one AMINO ACID. Some amino acids are repeated (third base wobble) to minimize mutations Figure 14.6 TRANSCRIPTION: The process where mRNA is made from DNA Follows base-pair rule has uracil instead of thymine RNA polymerase is used to build the strand of mRNA Where have you heard the term “polymerase” before? Transcription Animations Transcription: Stolaf.edu Transcription: University of Nebraska Transcription: Concord.org Translation: process by which protein is built from the mRNA Occurs at the ribosome (rRNA) tRNA brings amino acids to the developing protein chain Each 3 bases on mRNA (called a codon) codes for a single amino acid by matching the anti-codon on tRNA 3 bases on mRNA = a codon Matching 3 bases on tRNA = anticodon Before translation begins, a tRNA must be “charged.” This ACTIVE process occurs when an enzyme attaches the appropriate amino acid. Translation occurs on the ribosome in a series of steps. 1- initiation: the small subunit of the ribosome bonds to the start codon (AUG) of the mRNA. The charged tRNA (anticodon UAC) links to the start codon. The large subunit of the ribosome attaches and the process begins. (If AUG is always the start codon, what is always the starting amino acid?) Translation occurs on the ribosome in a series of steps. 2- elongation: the ribosome complex moves along the mRNA reading each codon. New, appropriately charged tRNA molecules enter at the A site, release their amino acid to the growing polypeptide chain at the P site, and leave (uncharged) at the E site. Note: The un-charged tRNA can be recharged and used in later translations. Translation occurs on the ribosome in a series of steps. 3- termination: When the ribosome reaches one of three stop codons, the complex releases and the created polypeptide chain begins protein folding. Note: Several ribosomes can translate the same piece of mRNA simultaneously to boost protein production. amino acids A U G TRANSLATION (protein synthesis) * All genes start with AUG, also called the START CODON It attaches to anticodon UAC and the amino acid methionine. This is the big picture. Can you explain it in your own words? Animations of Translation Translation: Stolaf.edu Translation: University of Nebraska Translation: Concord.org Regulation of Gene Expression Consider that.... Every cell of the body contains ALL the DNA for the organism. Not all genes are necessary all the time Cells must have the ability to turn a gene on and off ENTER: THE OPERON MODEL OF GENE EXPRESSION See other slides 55-57 & 61-69 Operons and Gene Control Experiments with E. Coli showed that it is capable of regulating the expression of its genes. Discovered prokaryote operons A prokaryote operon consists of the following elements 1. Promoter - gene sequence where RNA polymerase attaches, signalling the start of the gene 2. Operator - where a repressor binds, stopping the transcription of that gene 3. Structural Genes - genes coding for the enzyme, they are transcribed as a unit The trp Operon It controls the production of tryptophan. If tryptophan is already present, it binds to and activates the repressor to prevent more tryptophan from being made The lac Operon In this case, the prokaryote only needs lactase when lactose is present. This gene works in reverse of trp. The presence of lactose deactivates the repressor and turns on the gene. REMEMBER! Operons are only found in prokaryotes, but gene control in eukaryotes is similar. A little more complicated, but similar. Repressors versus Inducers The trp operon is a repressible operon, it is normally on but can be turned off when tryptophan is present. A repressor turns off a gene. The lac operon is an inducible operon because it is normally off but can be turned on when lactose is present. An inducer turns on a gene. Grammar Time A woman is pregnant and the baby is later. The doctor says they will "INDUCE" labor tomorrow. What does he mean? In eukaryotes, a variety of mechanisms regulate gene expression 1. chromatin structure 2. transcriptional control 3. post transcriptional control 4. translational control 5. post translational control Chromatin Structure Eukaryote DNA is wound around protein molecules called histones. More tightly wound regions cannot be reached for transcription. Less tightly wound are more easily accessed. The others are pretty self-explanatory once you practice your vocabulary! BARR BODIES In females, chromatin of one of the X chromosomes winds so tightly that it inactivates, this inactive chromosome is called a BARR BODY. This method of control can also be used in codominant pairs. Barr Body in Cats Genotype: XB XO The black patches are XB and the orange patches are XO, the cat is multicolored because not all X's are activated Gene Mutations Point Mutations - single base changes, causing a change in the amino acid structure (protein) Frameshift mutation 1-2 bases are added or deleted, shifting all codons downstream GAT CAT AAA GAT A CA TAA A What happens when you have a nonfunctional protein? Hemophilia PKU Cystic Fibrosis Etc. Cancer and Genetics Growth of cancer often begins with the loss of the TUMOR SUPPRESSOR GENE (p53) ONCOGENES activate, cell division occurs uncontrollably Breast Cancer Gene BRCA1 (brak-uh)