Chapter 8 Viruses & Fungi PDF

NAMING VIRUSES The International Committee of Taxonomy of viruses names them based on three characteristics:...

NAMING VIRUSES The International Committee of Taxonomy of viruses names them based on three characteristics: - Type of nucleic acid (DNA or RNA) - Is the nucleic acid double or single stranded - Presence or absence of nuclear envelope VIRUSES & FUNGI VIRUSES: THE BOUNDARY OF LIFE PROKARYOTES VS EUKARYOTES VS VIRUSES - Infectious parasites of nucleic acids and proteins - Cannot live ( reproduce) outside a host - Viruses are at the boundary of life: between the macromolecules ( which are not alive) and the prokaryotic cells ( which are alive). - Viruses are found everywhere. - They consist of a core of nucleic acid ( either DNA or RNA), and a protective coat of protein molecules and sometimes lipids.  VIRUS STRUCTURE VIRUS STRUCTURES Viruses come in a variety of size and shapes. A typical virus is composed of either DNA or RNA surrounded by a protein coat or capsid. VIRION STRUCTURE TYPES AND SHAPES OF VIRUSES 1- Helical: Rod like with capsid proteins winding around the core in a spiral shape; The capsid consists of one arrangement of capsomeres. 2- Polyhedral: has many sides. 3- Complex: polyhedral capsid attached to helical tail ( Bacteriophages) A virion is an entire virus particle, consisting of an outer protein shell called a capsid and an inner core of nucleic acid (either ribonucleic or deoxyribonucleic acid—RNA or DNA). The core confers infectivity, and the capsid provides specificity to the virus.  BACTERIOPHAGES VIRAL REPRODUCTION The head consists of an icosahedron that has very tightly packed DNA. Steps of Lytic cycles: Nearly 20 proteins are found in the head. - Attachment An equally complex tail sheath forms a helical component. - Entry The head is connected to the tail sheath by a neck that is composed - Replication of four to five proteins. - Assembly An end plate with lysozyme activity and pins at the base of the - Lysis/ Release ( lyses the cell) sheath contain several different proteins. Tail fibers are used to recognize receptor proteins on the surface of the bacterial cell. VIRUSES AND LIVING CELLS HOW DO VIRUSES REPLICATE Viruses must infect a living cell in order to grow and reproduce. They also take advantage of the host’s respiration, nutrition and all the other functions that Two methods of replication: occur in living things. 1- Lytic cycle: the virus enters the cell, replicates itself hundreds of Therefore, Viruses are considered parasites. times, and then bursts out of the cell, destroying it. 2- Lysogenic cycle: The virus DNA integrates with the host DNA and the host’s cell helps create more virus DNA. An environmental change may cause the virus to enter the lytic cycle.  LYTIC CYCLE DIFFERENCES BETWEEN LYTIC AND LYSOGENIC CYCLES In the lytic cycle, the virus reproduces itself using the host cell’s chemical machinery. The red spiral lines in the drawing indicate the virus’s genetic material. The orange portion is the outer shell that protects it. LYSOGENIC CYCLE VIRUSES ENTER LIVING CELLS Viruses enter bacterial cells by punching a hole in the cells wall and injecting its In the lysogenic cycle, the virus reproduces by first injecting its genetic material, DNA. indicated by the red line, into the host cell’s genetic instructions. Viruses enter plant cells through tiny rips in the cell wall. Viruses enter animal cells by endocytosis. Lysogeny is characterized by integration of the bacteriophage nucleic acid into the host bacterium's genome. These viruses break, or lyse, the cell and spread to other cells to continue the cycle. Like the lytic cycle, in the lysogenic cycle the virus attaches to the host cell and injects its DNA. From there, the viral DNA gets incorporated into the host's DNA and the host's cells.  VIROIDS SLOW INFECTIONS CAUSED BY PRIONS Much smaller than viruses Just consists of small Single-stranded RNA molecule No protein coat Infect plants Viroids are infectious agents that consist only of naked RNA without any protective layer such as a protein coat. Viroids infect plants (but no other forms of life) and are replicated at the expense of the host cell. Viroid genomes are small single-stranded circles of RNA that are only 250–400 bases long. PRIONS FUNGI virus-like organisms made up of a prion protein. contain only protein, no nucleic acid Linked to number of fatal diseases in humans and animals Obligate intracellular parasite How does it replicate if no nucleic acid? Prion protein converts host protein to prion protein A prion is a type of protein that can trigger normal proteins in the brain to fold abnormally. Prion diseases can affect both humans and animals and are sometimes spread to humans by infected meat products. Cannot be killed by UV light or nucleases.  FUNGI ARE ADAPTED TO ABSORB THEIR FOOD KEY CONCEPTS: FROM THE ENVIRONMENT. Fungi are heterotrophs Plants Both Fungi Fungi are the decomposers Autotrophic (photosynthesize) Eukaryotic Heterotrophic (absorb and digest from the surface they Fungi use extracellular digestion – when enzymes are secreted live on for energy) outside of their body to digest food Most fungi are multicellular Roots Non-motile/ anchored in soil Decomposers or structure Fungal spores develop from hyphae 1 nucleus per cell Organelles Can have 1+ nuclei per cell Many fungi are symbionts with other organisms COMMON FUNGI EXAMPLES: Cell wall made of cellulose Cell Wall Cell wall made of chitin (carb)  Mushrooms, yeasts, molds, morels, bracket fungi, puff balls CHARACTERISTICS OF FUNGI 3 MAJOR FEATURES 1.Cell walls Multicellular  Made of Chitin  Plant looking  The same stuff that makes insects’ exoskeleton.  Mushrooms, molds Unicellular  Yeasts  Found in soil, on plants, in humans Yeast  Anatomy of Fungi Visible 2. HYPHAEThin filaments making up the fungus. Long, thread-like chains of cells. – hyphae Grow at the tips and branch… – mycelium – fruiting body Mycelium – mass of hyphae 3. CROSS-WALLS 5 PHYLA OF FUNGI septum - the wall that divides cells (internal cross- walls) 1. Chytridiomycota - Chytrids 2. Zygomycota – Common Molds 3. Ascomycota – Sac Fungi 4. Basidiomycota – Club Fungi 5. Deuteromycota – Imperfect Fungi  1. PHYLUM CHYTRIDIOMYCOTA 3. PHYLUM ASCOMYCOTA (SAC FUNGI) Mostly marine Most are multicellular (except for Mostly saprophytes (lives on dead yeast) or decaying organic matter) Most undergo asexual Have flagellated spores reproduction Largest phylum of Fungi ascoscarp Morels 2. PHYLUM ZYGOMYCOTA FUNGI REPRODUCTION Mostly terrestrial. 3 kinds of fungi reproduction: Budding Two types of hyphae: – Stolons – (horizontal) spread across the surface – Rhizoids – (vertical) digs into the surface Fragmentation Spore production All fungi form spores and zygotes.  SEXUAL REPRODUCTION GENERALIZED LIFE CYCLE OF A FUNGUS Sexual reproduction in the fungi consists of three sequential stages: plasmogamy, karyogamy, and meiosis. Plasmogamy, the fusion of two protoplasts (the contents of the two cells), brings together two compatible haploid nuclei. At this point, two nuclear types are present in the same cell, but the nuclei have not yet fused. Karyogamy results in the fusion of these haploid nuclei and the formation of a diploid nucleus. The diploid chromosomes are pulled apart into two daughter cells, each containing a single set of chromosomes (a haploid state). 3 4 THREE TYPES OF ASEXUAL REPRODUCTION SEXUAL REPRODUCTION Fragmentation – part of the Used when environmental mycelium becomes separated & conditions are poor (lack begins a life of its own of nutrients, space, moisture…) Budding – a small cell No male or female fungi forms & gets pinched off Some fungi show as it grows to full size dimorphism - Used by yeasts May grow as MYCELIA Asexual spores – production of or a YEAST –LIKE spores by a single mycelium state (Filament at 25oC & Round at 37oC) Dimorphic Fungi 36 FUNGI MAY BE DECOMPOSERS, PATHOGENS, OR MUTUALISTS. Fungi can act as mutualists. Fungi recycle nutrients in the environment. Fungi and bacteria are the main decomposers in any – lichens form between fungi and algae ecosystem. – mycorrhizae form between fungi and plants – decompose dead leaves, twigs, logs, and animals – return nutrients to the soil – can damage fruit trees and wooden structures The lichen fungus provides its partner(s) a benefit (protection) and gains nutrients in return LICHENS Fungi can act as pathogens. – human diseases include ringworm and athlete’s foot Bioindicators – help show when environmental – plant diseases include Dutch elm disease conditions are unsuitable. –Haustoria – hyphae that penetrate the host so that the Pioneer species – 1st to inhabit an environment. parasitic fungus can absorb nutrients Fungi (usually ascomycota) + algae (or foliose photosynthetic bacteria) crustose FUNGI ARE STUDIED FOR MANY PURPOSES. SOME PATHOGENIC AND TOXIC FUNGI Zygomycetes Ascomycetes Rhizopus - Food spoilage Ajeliomyces capsulatus- Fungi are useful in several ways. Histoplasmosis – as food Aspergillus – sinus, ear, lung – as antibiotics infection – as model systems for molecular biology Microsporium sp. Various ringworms. Bioremediation – help clean the environment. Verticillium sp Plant wilt Monilinia fructicola- Bioremediation is the use of microbial species to clean Brown Rot of Peaches up soil and groundwater that has been contaminated by discharged chemicals. FUNGI AND HUMANS Molds Yeasts Penicillium Saccharomyces cerevisiae  Penicillin  Bread, wine and beer  Camembert and Roquefort Candida albicans cheeses  Infections Aspergillus  Soy sauce  Soft drinks - citric acid