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midterm notes

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University of Toronto St. George
John Coleman

Notes 01:46 BIO 130 Notes Chapter 1 template polymerization- way in which info is copied. two strands of DNA are pulled apart, and each serves as a template for synthesis of a new complementary strand. Transcription: DNA RNA Translation: mRNA proteins Code read out by tRNAs Anticodon on tRNA helps recognize codon on mRNA In all cells, the expression of individual genes is regulated independently of one another. Therefore, the cell adjusts the rate of transcription and translation of different genes independently. Life requires free energy: energy in a physical system that can be converted to do work Universal feature of all cells: All cells require ATP for the synthesis of DNA and RNA. ATP is also the carrier of free energy and helps to drive other chemical reactions. Another universal feature: cells are enclosed by a plasma membrane. It is a selective barrier that enables the cell to concentrate all the nutrients it gathers from its environment. Helps to retain them and synthesize them. The molecules that form the plasma membrane are amphiphilic- one part is hydrophobic ( water-insoluble) and the other is hydrophilic (water-soluble). form bilayer. Hydrophobic tails are made of hydrocarbon polymers. General principle: cells produce molecules whose chemical properties cause them to self-assemble into structures a cell needs. Minimum number of genes for a viable cell in todays environment is 200-300. Summary The cell replicates its information by separating the paired DNA strands, and using each as a template for polymerization to make a new DNA strand with a complementary strand of nucleotides. The same strategy of templated polymerization is used to transcribe portions of information from the DNA into RNA. This in turn guides the production of proteins, which are principal catalysts in reactions in the cell, serve as selective transporters in he selective membrane. The function of a specific protein depends on the amino acid sequence, which is specified by the nucleotide sequence of a corresponding DNA Organisms that derive energy directly from the nonliving world fall into two categories: those that harvest the energy of sunlight (phototropic-feeding on sunlight), and those that capture their energy from energy-rich systems of inorganic chemicals in the environment (lithotropic-feeding on rock) Phototropic and lithotropic organisms are PRIMARY energy converters, and are the most plentiful form of life. Organotropic organism (feeding on organic chemicals in living things) depend on primary energy converters. Lithotropic organisms are microscopic, and humans do not usually see them because of where they are found, usually in Earths crust or deep in the ocean. Some use aerobic reactions and some anaerobic. Six elements required to make a cell: H, C, N, S, O, P Procrayotes are classified based on biochemistry and nutritional requirements. They have two groups: bacteria and archaea. Archaea are found in inhabiting environments such as ocean depths, and bogs. In appearance, they are NOT easily distinguished from bacteria. But at a molecular level, archaea resemble eucaryotes in the machinery used for handling gene info (replication..etc) but resemble bacteria more closely in the way of metabolism and energy conversion. New Genes Are Generated From Pre-Existing Genes Intragenic mutation- an existing gene is modified by changes Gene Duplication- an existing gene is duplicated Segment Shuffling- two or more existing genes are broken and rejoined to forma hybrid gene. Horizontal (intercellular) transfer- DNA is transferred from the genome of one cell to another, even to other species. This is opposite to vertical transfer, which is from parent to progeny (usually happens!). Orthologs- genes related by descent (common ancestor) Paralogs- related genes that have diverged Homolgs- genes related by descent (both above are homologs) Viruses (bacteriophages) vectors for gene transfer Horizontal gene transfer occurs more in prokaryotes (result: evolution of mitochondria) become resistant by this! Sex results in horizontal exchange of genetic info Summary Prokaryotes are most diverse obtain energy from inorganic (dead) chemical sources. All originated from a common ancestor. Eukaryote cells= bigger size, more elaborate, genomes are bigger too Differences from prokaryotes: have a nucleus, a nuclear envelope that separates DNA from cytoplasm, have larger cells, have a cytoskeleton to control shape and allow for movement. Free-living eukaryotic cells are called protozoa, which can change shape rapidly and engulf things by the process of phagocytosis. Eukaryotic cells MAY have originated as predators (flexible + large) Also contain mitochondria: take up O2 and harness energy to produce ATP. They have their own genome, RNAs and their own ribosomes like small bacteria. How Did Mitochondria Originate? When aerobic bacteria were engulfed by an ancestral anaerobic eukaryotic cell. The cell made no use of such oxygen. So, they evolved from symbiosis. The aerobic bacteria received shelter, while also performing as power generation for the host. Thus, they evolved as the modern eukaryotic cells. Many eukaryotic cells also contain chloroplasts. Like mitochondria, they have their own genome, and originated as symbiotic photosynthetic bacteria. Fungal cells, like animal cells, have a mitochondria but no chloroplasts, but in contrast to animal cells have an outer wall which prevents movement or swallow other cells. Turned from hunters to scavengers. The genetic info of eukaryotic cells has a hybrid zone- form the bacteria and from the ancestor anaerobic eukaryote. Evolution has favoured eukaryotes to have bigger genomes, and in turn bigger cells. Why? Predator is larger than prey! Eukaryotic species have lots of non-coding DNA which does have important function. It regulates the expression of adjacent genes. This is also known as regulatory DNA. This DNA controls when and where a gene is expressed. This is crucial for the formation of complex multicellular organisms. Example: puffer fish have removed all of its non-coding DNA (its a hard and time- consuming process).. yet they still behave and look and have the same fitness as other related species. A lot of genes in eukaryotic genome code for proteins that regulate the activity of other genes. These are called gene regulatory proteins. These proteins act by either binding directly or indirectly to regulatory DNA adjacent to the genes that must be controlled. Or by interfering with the ability of other proteins. Cells ACTIVELY exchange signals with their neighbors.
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