FInal_Review - MCB 250 FINAL EXAM NOTES -Note: These notes...

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MCB 250 FINAL EXAM NOTES -Note: These notes are incomplete- There's a section missing and I don't honestly know where. Why do cells need to regulate gene expression? -Making proteins is expensive- it takes a lot of energy, materials and time. Therefore, if a protein is not needed it is in the cell's best interest not to make it in the first place. -Regulation of gene expression also allows cells to express different genes at different times in response to changes in their environment. One example of this is the E. coli bacteria, which has two major habitats- the human intestines and fresh water. The human intestines, is a very high osmotic pressure environment, while fresh water is a very low-pressure one. If the E. coli are to survive the change in pressure, they must adapt by changing their structure and physiology. This requires making different sets of proteins. -Regulation allows for cell differentiation. This is especially easy to see in multicellular eukaryotes, although prokaryotes can differentiate too. (For example, some bacteria differentiate between a vegetative state and a sporulated state). All eukaryotes start as a single-celled zygote which must eventually give rise to all the distinct cell types, tissues, and organs found in their bodies. This is achieved by the expression of different genes at different times in different places. -Regulation also allows for tissue-specific function. Once the tissues are differentiated, they must perform different jobs. Different tissues express different proteins critical to their specific function. Liver cells produce very different proteins from brain cells. Gene Expression in Prokaryotes Recall that prokaryotes express proteins from genes through the following steps -RNA polymerase is recruited to a promoter and transcribes a mRNA with a RBS. -a ribosome binds to the RBS and translates the mRNA into a polypeptide -the polypeptide is folded into a protein -enzymes modify certain proteins by adding functional groups to them In addition, recall that proteins are eventually degraded. Gene expression can be regulated at any point in this process. Unlike eukaryotes however, prokaryotes do not splice mRNA nor export it through a nuclear membrane, so these levels of regulation cannot exist in prokaryotes. However, because prokaryotes lack a nucleus, the transcription and translation of proteins are coupled. This fact plays a major role in the regulation of expression in prokaryotes. Types of Gene Regulation Transcriptional response to a stimuli is one way of categorizing gene regulation -Repressible systems are systems that are shut off in response to a stimuli -most biosynthetic pathways, like the pathway for tryptophan synthesis, are repressible systems. -Inducible systems are systems that are turned on in response to a stimuli
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FInal_Review - MCB 250 FINAL EXAM NOTES -Note: These notes...

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