Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Cytoplasmic streaming wikipedia , lookup
Cellular differentiation wikipedia , lookup
Cell culture wikipedia , lookup
Cell encapsulation wikipedia , lookup
Cytokinesis wikipedia , lookup
Organ-on-a-chip wikipedia , lookup
Endomembrane system wikipedia , lookup
Cell growth wikipedia , lookup
Cell nucleus wikipedia , lookup
Two Main Types of Organisms Sex and the Simpleton: Evolution of Sex and the Rise of the Eukaryotes Prokaryotes (include Archaea and Bacteria), distinguished by lack of a true nucleus -term derived from Greek pros meaning before and karyon meaning nut (referring to the nucleus). And Eukaryotes (Eukarya only), Distinguished by possession of a true nucleus -term derived from the Greek eus or true and karyon, meaning nut (again referring to the nucleus) Prokaryotes Very simple cells enclosed by cell wall containing an inner part of amino acids and sugars and an outer part of lipids. Prokaryotes have a single “chromosome”, contained within a “nucleoid region” rather than a distinct membrane-bound nucleus Prokaryotes: Reproduction Prokaryotes reproduce by the simple process of binary fission The cell makes an identical copy of its genetic material, and each of the two copies ends up in each daughter cell The daughter cells are clones of their parent Critical Question: What are the advantages and disadvantages of this approach ? 1 Eukaryotes: Reproduction Eukaryotes In eukaryotes, genetic material is contained within chromosomes, which are housed in the nucleus (humans have 23 pairs) Eukaryotes are complex cells with a membrane-bound nucleus, and other structures such as mitochondria (in animal and plant cells) and plastids (in plant cells). Cells of eukaryotes are also much larger than those of prokaryotes Eukaryotes have two instruction books on reproduction. We will call these “Mitosis” and “Meiosis” Note: “n” denotes number of chromosomes Mitosis involves replication of genetic material and splitting to form clones Meiosis involves splitting of genetic material that can later be recombined (via sexual reproduction) to restore full genetic code Functions of Mitosis and Meiosis in Eukaryotes Mitosis: the main process involved in maintaining tissue growth, and to some extent reproduction (e.g. splitting of amoebas or asexual budding to make colonies of clones- e.g. in corals). Meiosis: the fundamental process involved in reproduction among eukaryotes (meeting of cells [sperm and egg in animals] from two parents produce offspring) 2 Sources of Variation: Asexual vs. Sexual Reproduction Asexual Sexual Mutation Mutation Errors in code transcription Errors in code transcription Crossing over and trading of genetic material between chromosome pairs Splitting and recombination of genetic material Natural Selection acts on these sources of variation to weed out the bad and retain the good. Sexual reproduction in eukaryotes ensures lots of variation and lots of change. But not all eukaryotes are alike Why do we have plants and animals ? Answer probably lies in the types of organelles eukaryotes possess Origin of Nucleus ? Making a nucleus was probably not too difficult for the first eukaryote. It has been speculated that the nucleus was produced by the infolding of the cell membrane, and engulfing of genetic material within the cell. More complex models exist, but this is the basic idea. Genetic material in chromosome-like clump Infolded membrane surrounds genetic material Endosymbiosis Theory (Are Eukaryotes Composite Prokaryotes ?) Animals and plants have mitochondria -the “power plants” of cells -provide the energy a cell needs to move, divide, and produce secretory products -food (sugar) is combined with oxygen to produce ATP (adenosine triphosphate) - the primary energy source for the cell. -similar to some bacteria in form and function (quite similar to the bacterium Rickettsia- responsible for typhus) Plants have plastids -the “food factories” of plant cells -it is here that photosynthesis occurs (energy from sunlight is harnessed to produce sugar) -similar to cyanobacteria in form and function It has been suggested that mitochondria and plastids are actually bacteria that decided to reside in large host prokaryotes- additional evidence for this ? 3 Note that it is possible for a eukaryote to live without a mitochondrion (Giardia doesn’t have one) Serial Endosymbiosis Hypothesis (Lynn Margulis) cyanobacteria S S plant cell animal cell purple bacteria Giardia: Single Celled Eukaryote (Protist) with no mitochondrion -Likes anaerobic environment -eats anaerobic bacteria Evidence for Origin of Mitochondia and Chloroplasts As “Slave Bacteria” The basic thoughts on the origin of organelles -purple bacterium becomes mitochondrion -cyanobacterium becomes plastid Perhaps something like this might have become a protoeukaryotic cell upon formation of a nucleus and acquisition of symbiotic bacteria Mitochondria and Chloroplasts are of similar size as bacteria. Mitochondria and Chloroplasts have complex double membrane systems, similar to bacteria. Mitochondria and Chloroplasts are somewhat self-contained, as if they derived from functional cells. Mitochondria and Chloroplasts divide by binary fission, similar to bacteria. Largest known bacterium: 0.2 mm dia Thiomargarita namibiensis 4 Back to Reality…Oldest Evidence of Eukaryotes Note: “Ga” means billions of years before present (“giga annum”) Oldest Known Eukaryote Fossils: Grypania spiralis carbonized algal structures 2 mm wide and 10 cm long Found in rocks 2.1 Ga in Michigan and abundantly in rocks 1.4 Ga in China, Montana and Michigan Oldest known Acritarchs (algal cysts) up to 150 microns (0.15 mm) in diameter 1.6 to 1.4 Ga Up to about 575 million years eukaryotes remained relatively simple in form (cysts, blobs, and strands) Then something remarkable happened… END OF LECTURE 5