BIOA01H3 Lecture Notes - Lecture 32: Protein Structure, Methionine, Nuclear Membrane

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Beadle and tatum grew nutritional mutants (auxotrophs) of neurospora on a minimal medium supplemented with a single amino acid such as arginine (arg). They hypothesized that each strain had a defect in a gene that codes for an enzyme needed to synthesize a particular amino acid (one gene one enzyme hypothesis). It was updated to the one gene one polypeptide hypothesis. They thought that one gene created one enzyme, but that was not the case. All the required nutrients is required (medium complete) or you can provide only the simplest most basic nutrients needed to growth (minimal medium). Example: neurospora crassa is a wildtype that grows on minimal medium. The arg mutants require arginine to be present in the medium for it to grow. They tested arg mutants for the ability to grow on mm when each of the following was added: ornithine, citrulline, argininosuccinate, arginine.

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PoB researcher Zhongshan has 10 yeast mutants that he isolated by mutangenizing yeast. None of them can grow on minimal media alone, or on minimal media (MM) supplemented with ornithine (Orn). He also finds that all of these mutants can grow on citrulline (Cit) or arginine (Arg). He wants to check if these mutants are "allelic", (i.e. the hypothesis that they affect the same gene), or if any are non-allelic (i.e. the hypothesis that they affect different genes). Which of the following would provide the best test of these alternative hypotheses?

Test if the mutants can grow when both Cit and Orn are added to MM.

Test if the mutants synthesize Arg or not when grown in the presence of Orn.

Do pairwise crosses of the mutants to see if their diploid progeny (i.e. daughter cells with a copy of every gene from one mutant parent plus a copy of every gene from the other mutant parent) can grow on MM supplemented with Cit or not.

Do pairwise crosses of the mutants to see if their diploid progeny can grow on MM supplemented with Orn or not.

None of the above experiments will be able to distinguish between allelism or non-allelism.

ultramarineclam721

Fungi Fungi are the great decomposers of the biosphere. Most plants form mycorrhizae with fungi to increase absorptive area without having to grow more roots, in this relationship fungi recieve carbohydrates from plants. Humans consume fungi, mushrooms, may use fungi as a source of drugs for blood pressure, antibiotics and immunosuppresive drugs. Fungi are used in biotechnology to produce fermetation products, and some have been very useful models to study gentics in eukaryotic cells that are unicellular such as yeasts. About one third of fungi may cause infections, mycoses, in plants, animals and humans. Fungi tolerate concentration of salt and sugar that plasmolyze bacteria in perserved foods exposed to air which contains fungal spores may germinate and may spoil food. Fungi have two body shapes, molds and yeasts. Mold are large and made of long filamentous hyphae. Hyphae form mats called mycelium ( plural is mycelia). Mycelia may extend for miles underground, making fungi the largest organism on earth. The visible portion of subterrean fungi are the fruitng bodies such as mushrooms. Yeasts are globular and unicellular. They may bud forming up 24 daughter cells from a single cell. When budding is incomplete it may produce a psuedohypa. Fungi that may exist in both body types are dimorphic fungi. In general, the yeast form of a dimorphic fungus is a pathogen, the filamentous form is not pathogenic. Examples are Histoplasmosis capsulatum (histoplasmosis) and Coccidiodes immitis (coccidioidomycosis). Fungi are saprobes, they absorb nutrients from the remains of dead plants or they lasso nematodes. Fungi may derive nutrients from a living plant utilizing haustoria which are modified hyphae that penetrate living plant tissue. Some fungi use melanin to absorb gamma rays which they convert to chemical energy. Some herbivores have fungi in thier gut microbiome to help digest plants. Zygomycota contains 1100 species and reproduces asexually through sporangiaspores, which form in a sac called a sporangium on a stalk called a sporangiaphore. An example is Nosema which is an obligate intracellular parasite in insects and honeybees. Ascomycota havd 32,000 species form haploid ascospores in sacs called ascus (asci plura) and reproduce asexually with condiospores which develop on the tips of hyphae on stalks called conidiophores. Examples are Claviceps purpurea, ergot, which grows on grain and causes abortions in cattle and hallucinations in humans. Penicillium the source of the first antibiotic discovered by Fleming in the 1940s. Saccharomyces, a facultative anaerobe, ferments sugar to produce alcohol and carbon dioxide gas and is used in baking and brewing. Neurospora was used as a model to study molecular biology, Beadle and Tatum established one gene one enzyme using this model organism.

14. Why are there more antibacterial drugs than antifungal drugs? Basidiomycota have fruiting bodies called basidiocarps. Basidiospores are dispersed by the wind and germinate in warm moist environments. An example is the pathogen Cryptococcus neoformans the leading cause of fungal meningitis

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BIOA01H3 Lecture Notes - Lecture 32: Protein Structure, Methionine, Nuclear Membrane

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