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Lecture 6

Learning Objectives -week 6

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BIOL 1500
Tanya Da Sylva

Learning Objectives Week 6 transcription and translation site from info below ** transcription vid ** translation vid ** protein synthesis (transcription and translation)  During translation, the following stages are taking place: (1) Messenger RNA strand passes through ribosome (2) Triplet CCC codes for the next amino acid to be brought into position in the ribosome (3) Transfer RNA brings in the appropriate amino acid (proline) (4) Amino acid added to polypeptide chain (5) Transfer RNA released to pick up amino acid to be recycled (6) "Used" messenger RNA strand may pass on to another ribosome (7) Process repeats with next triplet code until: (8) Triplet UAA causes translation to stop (9) If it is "long", the polypeptide chain folds into the shape of the final protein  Transcription o The 2 strands of the DNA molecule are temporarily split by enzymes which cause a short part to be copied into a similarly short section of RNA molecule. The copying is along the same lines as already explained, (A for T, G for C, C for G) except that a different base called U (uracil) replaces T (thymine). Also, RNA is only made of a single strand, and it contains a different sidechain subunit. o The two strands of DNA - shown here in black and grey - separate (under the influence of the enzyme RNA polymerase). Messenger RNA - here red - forms on one - black - strand of DNA. The other strand - grey - does not take part in the process. o The strand of messenger RNA (mRNA) formed then leaves the nucleus and passes into the cytoplasm. The opened-up section of DNA re-forms into a double helix, as before.  Describe the structure and function of ribosomes. o Structure  A ribosome is made of two pieces (subunits). These two subunits are named according to their ability to sediment on a special gel (the Svedberg unit, a measure of the rate of sedimentation in centrifugation). The bigger the number given to the subunit the bigger the molecule. o Function  A typical eukaryotic cell ribosome consists of two subunits named 60S (large subunit) and 40S (small). They make polypeptides.  A ribosome is a complex made up of one or more ribosomal RNAs and large and small proteins subunit. Ribosomes are made up of about 1/3 proteins and the rest are ribosomal RNAs.  The subunits of ribosomes are made in the nucleolus of eukaryotes and the transported to the cytoplasm. The large and small subunits only come together if they are attached to an mRNA molecule.  Ribosomes are located in the cytoplasm. They are responsible for bringing together tRNA and mRNA for translation to occur.  Ribosomes in prokaryotes and eukaryotes are very similar, but their differences are important. Inhibitors like streptomycin can inhibit bacteria ribosomes, while the eukaryotes ribosomes are unaffected. This difference is key to designing many antibiotics and medicines.  A ribosome has three sites, or docking stations, for tRNA: the P site, A site, and E site. The P site is where tRNAs add amino acids to the polypeptide chain. The A site holds the tRNA that is next in line to add an amino acid, and the E site is the site from which empty tRNA's exit the ribosome.  Describe the process by which amino acids are added to a growing polypeptide chain. o Transfer RNA (tRNA) brings in the appropriate amino acid o Amino acid is added to polypeptide chain. o Elongation adds an amino acid to the polypeptide chain until a stop codon terminates translation.  Diagram the overall process of transcription and translation. o  Describe the major types of mutations, causes of mutations, and potential consequences. (SEE WRITTEN NOTES) o Mutations  Mutations involve a physical change to genetic material that results in the abnormal encoding of protein sequences. o Point Mutation  Point Mutation occurs when there is a substitution of one nucleotide for another. This type of mutation usually only impacts one codon in a sequence. o Silent Mutation  A silent mutation is a type of point mutation that does not change the amino acid sequence of the protein. In silent mutation, a nucleotide mutates to another nucleotide. However, the new nucleotide also codes to the original amino acid. This type of mutation is likely to have little effect on the protein sequence. o Frame-shift Mutation  Frame-shift mutation involves the insertion or deletion of one or more nucleotides from the sequence.  This insertion or deletion results in a shifting of the nucleotides. This creates different amino acids in the protein sequence. Generally, the amino acid sequence after the insertion or deletion is devastated.  Types of mutations within a gene (same as above)  Substitution-the substitution of one nucleotide for anther.  Insertion-to insert or add a nucleotide.  Deletion mutations- to delete or remove a nucleotide.  Briefly describe and compare the regulatory mechanisms of the lac operon, and trp operon. o Lac operon  Protein synthesis is INDUCED (begins) when lactose is present. o Trp operon  Protein synthesis is REPRESSED (stops) when a high concentration of tryptophan is present. o Lac operon  Consists of a promotor, operator, and a cluster of 3 genes (lacZ, lacY, lacA).    Explain how selective gene expression yields a variety of cell types in multicellular eukaryotes. o Certain genes are activated through mechanisms such as feedback inhibition, positive feedback and negative feedback. Look up those terms for examples like the lac operon and the trp operon  Briefly explain how eukaryotic gene expression is controlled by explaining how mRNA breakdown, initiation of translation, protein activation, and protein breakdown regulate gene expression o mRNA Breakdown  Enzymes in the cytoplasm breakdown the molecules of mRNA and the timing of when this occurs is a very important factor in regulating the amounts of various proteins that are produced in the cell.  Long-lived mRNA’s can be translated into many more protein molecules than short-lived ones.  mRNA in eukaryotes have liftimes of hours or even weeks. o o Initiation of Translation  The process of translating an mRNA into a polypeptide also offers opportunities for regulation. Among the molecules involved in translation are a many proteins that control the start of polypeptide synthesis. Red bold cells for instance have an inhibitory protein that prevents translation of hemoglobin mRNA unless the cell has a supply of heme, the iron containing chemical group essential for hemoglobin function. By controlling the start of protein synthesis, cells can avoid wasting energy if the needed components are currently unavailable. o Protein Activation  After translation is complete, some polypeptides require alterations before they become functional. Post- translational control mechanisms in eukaryotes often involve cleavage (cutting) of a polypeptide to yield a smaller final product that is the active protein, able to carry our specific functions in the organism. In Figure 11.6, we see the example of the hormone insulin, which is a protein. Insulin is synthesized in the cells of the pancreas as one long polypeptide that has no hormonal activity. After translation is completed the polypeptide folds up, and covalent bonds form between the sulfur (S) atoms of sulfur-containing amino acids. Two H atoms are lost as each S-S bond forms, linking together parts of the polypeptide in a specific way. Finally, a large center portion is cut away, leaving two shorter chains held together by the sulfur linkages. The combination of two shorter polypeptides is the form of insulin that functions as a hormone. By controlling the timing of such protein modifications, the rate of insulin synthesis can be fine-tuned. o Protein Breakdown  The final control mechanism operating after translation is the selective breakdown of proteins. Some of the proteins that trigger metabolic changes in cells are broken down within a few minutes or hours. This regulation allows a cell to adjust the kinds and amounts of its proteins in response to changes in its environment. It also enables the cell to maintain its proteins in prime working order. When proteins are damaged they are usually broken down right away and replaced by new ones that function properly. Describe the basic tools used in biotechnology. Define recombinant DNA, PCR and transgenic organisms.  Describe the basic tools used in biotechnology. Define recombinant DNA, PCR and transgenic organisms. o Explain how plasmids are used in gene cloning including the purpose of restriction enzymes.  To manipulate genes in the laboratory, biologists often use bacterial plasmids, which are small, circular DNA molecules that replicate ( duplicate) separately from the much larger bacterial chromosome ( see Module 10.23). Because plasmids can carry virtually any gene and are passed from one generation of bacteria to the next, they are key tools for gene cloning, the production of multiple identical copies of a gene- carrying piece of DNA. Gene- cloning methods are central to the m mn production of useful products via genetic engineering.  1- a bacterial plasmid that will serve as the vector, or gene carrier, and  2- the DNA containing the gene of interest— in this case, gene V ( shown in red in the figure)— along with other, unwanted genes. Often, the plasmid comes from the bacterium E. coli. The DNA containing gene V could come from a variety of sources, such as a different bacterium, a plant, a nonhuman animal, or even human tissue cells growing in laboratory culture. The researcher treats both the plasmid and the gene V source DNA with an enzyme that cuts DNA.  3- An enzyme is chosen that cleaves the plasmid in only one place.  4- The other DNA, which is usually much longer in sequence, may be cut into many fragments, one of which carries gene V. The figure shows the processing of just one DNA fragment and one plasmid, but actually, millions
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