Unit 2: Cells

1. Unit 2: Cells Part II: Prokaryotes vs. Eukaryotes

2. Prokaryotes vs. Eukaryotes • The differences between these organisms go well beyond the presence or lack of a nucleus • This is the first major division of living things on earth – a very fundamental difference indeed • We can no longer think of prokaryotes as primitive and eukaryotes advanced

3. No nucleus “Naked” DNA in a DNA loop and plasmids Small ribosomes (70s; 50s/30s subunits) Cell walls made of peptidoglycans Flagella not made of microtubules No EMS (endo-membrane system) Double membrane bound nucleus DNA organized into chromosomes Large ribosomes (80s; 60s/40s subunits) Cell walls made of cellulose (plants) or chitin (fungi or protist) Flagella made of microtubules EMS present Prokaryotes vs. Eukaryotes

4. Prokaryotes: Diversity • The first forms of life were likely very similar to modern bacteria • Rapidly evolving, but surprisingly nearly unchanged over billions of years • Prokaryotes can be found in literally every environment and in every available niche on the planet • Prokaryotes split into to major groups: • Archaebacteria - extremophiles • Eubacteria – “true” bacteria

5. Prokaryotes: Structure • DNA Loop: a long single fiber in the cytoplasm which contains almost all of the genetic material (the rest is in plasmids); genes are usually kept small and devoid of introns (extra non-coding bits of DNA) – highly efficient • Ribosomes: freely floating in cytoplasm (unbound); site for protein synthesis • Antibiotics like tetracycline bind to the prokaryotic ribosome and interfere with the bacteria’s ability to produce proteins

6. Prokaryotes: Structure • Cell Wall: provide the cell with shape and structure, and some minimal protection against a hostile environment; most prokaryotes have them • Capsule: jelly-like coating that surrounds the cell wall; only some prokaryotes have them; 4 functions of a capsule: • Prevents cell from drying out • Helps cells stick together or on other surfaces (tissues of other organisms) • Helps prokaryotes slide on surfaces • Keeps some bacteria from being destroyed by the host organism

7. Prokaryotes: Structure • Flagella: solid crystal proteins that stick through the holes in the cell membrane and spin like propellers for locomotion (very different structure from eukaryotic flagella) • Pilli: short bristle-like appendages which have 2 functions: • Attach bacteria to surfaces • Assist in the transfer of DNA from one bacterium to another

8. Prokaryotes: Shape • Eubacteria typically come in one of 4 shapes: • Coccus (pl. cocci): spere shaped • Advantage: less distortion in a dried out organism • Bacillus (pl. bacilli): rod shaped • Advantage: high surface area • Spirillum (pl. spirilla): spiral/helical shaped • Advantage: highly motile (corkscrew motion) • Spirochete(s): spiral shaped cells with flagella inside the cell membrane

10. Prokaryotes: Movement • Chemotaxis: movement of an organism toward or away from a chemical • Positive chemotaxis: chemicals that attract organisms toward them are called attractants • Negative chemotaxis: chemicals that repel organisms are called repellants • Runs and twiddles

11. Prokaryotes: Survival • When environmental conditions are unfavorable, bacteria become inactive. • Some species form endospores (thick wall surrounding genetic material • Endospores go dormant until conditions are favorable • Endospores can survive very harsh environmental conditions • Boil water 2x

12. Prokaryotes: Reproduction • Asexual Reproduction • Binary Fission: single loop of DNA is copied, both attach to cell membrane; the cell divides by pinching off between the two loops. • Sexual Reproduction • Conjugation: a bridge is formed between cell pili; F plasmid (F=fertility, ~ 25 genes) injected with F pilus; new plasmid is recombined into bacterial DNA

13. Conjugation

14. Prokaryotes: Reproduction • Transformation: a living bacterium absorbs the genetic material of a dead cell or “naked” genetic material in the environment • Transduction: transfer of DNA from a host to another cell by means of a virus

15. Prokaryotes: Metabolics • Heterotrophs: must eat to acquire food • Photoheterotrophs: can use light to produce ATP, but must get organic carbon from another source • Chemoheterotrophs • Saprobes: decomposers that absorb nutrients from dead organic material • Parasites: absorb nutrients from the body fluids of living hosts • Phagotrophs: ingest food and digest it enzymatically within cells or multiple cellular bodies

16. Prokaryotes: Metabolics • Autotrophs: can produce their own food • Photosynthetic autotrophs (phototrophs): organisms that harness light energy to drive the synthesis of organic compounds from CO2 • Chemosynthetic autotrophs (chemotrophs): organisms that use energy from specific inorganic substances to produce organic molecules from CO2 and provide life processes • Chemoautotrophs: organisms that need only CO2 as the carbon source; they obtain energy by oxidizing inorganic substances like hydrogen sulfide, ammonia, ferrous or other ions

17. Prokaryotes: Oxygen • Prokaryotic oxygen requirements can be used to classify prokaryotes: • Obligate aerobes: use oxygen for cellular respiration and cannot survive without it • Facultative anaerobes: will use oxygen if present, but can grow by fermentation in an environment void of oxygen • Obligate anaerobes: cannot use oxygen and are killed by it

18. Prokaryotes: Archebacteria • Archebacteria lack peptidoglycan in their cell walls • Archebacteria have a unique lipid composition in their cell membranes • Archebacteria have a different rRNA structure than eubacteria and eukaryotes • Most Archebacteria live in extreme environments

19. Prokaryotes: Archebacteria • Examples (subgroups): • Methanogens: use elemental hydrogen (H2) to reduce CO2 into methane (obligate anaerobes) • Extreme Halophiles: live in high salinity environments • Thermoacidophiles: require environments that are hot and acidic

20. Eukaryotes: Diversity • Protists: single celled, mostly heterotrophic eukaryotic organisms • ie – amoeba, euglena, diatoms, etc… • Fungi: mostly multicellular, heterotrophic, sessile eukaryotic organisms • ie – mushrooms, molds, rusts (the living kind)

21. Eukaryotes: Diversity • Plants: multicellular, autotrophic (photosynthetic), sessile eukaryotic organisms • ie – trees, grasses, bushes, shrubberies • Animals: multicellular, heterotrophic, mostly motile eukaryotic organisms • ie – sponges, mollusks, fish, insects, reptiles, amphibians, birds, mammals

22. Eukaryotes: Structure • Nucleus • Contains primary DNA in the form of chromatin which can be packaged into chromosomes for cellular reproduction • Bound by a double membrane (nuclear envelope) with nuclear pores for the exchange of RNA

23. Eukaryotes: Structure • Nucleolus • Dense, irregularly shaped body in the nucleus • Makes and stores RNA • Forms new ribosomes

24. Eukaryotes: Structure • Mitochondrion (pl. mitochondria) • Generate ATP (adenosine triphosphate – a high energy molecule for cellular energy) • Double membrane; inner membrane = cristae, where much of cellular respiration takes place • The area inside the cristae is called the matrix • Contain their own DNA • Why?

25. Eukaryotes: Structure • Plastids • Leucoplasts – found in roots and tubers • Chromoplasts – contain accessory pigments • Chloroplasts – contain chlorophyll pigments, found in leaves and stems and are the primary photosynthetic organelle

26. Eukaryotes: Structure • Ribosomes • Non membrane-bound • Site for protein synthesis (very numerous) • Translate mRNA code into proteins • Made of RNA and proteins • 3 Types • 70s - found in prokaryotes • 70s (o) – associated w/ eukaryotes’ ER • 80s – found in cytoplasm of eukaryotes

28. Eukaryotes: Structure • Endoplasmic Reticulum • Provides internal framework, support • Provides transportation and temporary storage for organic compounds • Provides surface area for the synthesis of organic compounds • Rough – contains ribosomes, site of protein and glycoprotein synthesis (usually for secretion) • Smooth – no ribosomes, synthesize, secrete, and/or store carbohydrates, steroids, hormones, lipids, or other non-protein products

30. Eukaryotes: Structure • Golgi (complex, apparatus, bodies) • Flattened membranous sacs stacked together • Sacs are called cisterna • Interiors are called the lumen • Cis face = forming face (input) • Trans face = maturing face (output) • Functions: breaks down glycoproteins, concentrates materials into vesicles, forms the cell wall, and produces lysosomes

32. Eukaryotes: Structure • Lysosomes • Vesicle w/ highly reactive enzymes which can break down proteins, nucleic acids, and lipids • Contain 2 or more hydrolases (enzymes) • Proteases • Nucleases • Lipases • Acidic environment (pH 5) where enzymes work best • “Suicide Bags” = programmed cell death

33. Eukaryotes: Structure • Peroxisomes • Contain oxidative enzymes which transfer H from various substances to oxygen • Purines, fats, alcohol, poisons, hydrogen peroxide can all be broken down by peroxisomes

34. Eukaryotes: Structure • Vacuole • Membrane bound body with little or no internal structure • Vacuoles hold substances (varies from one cell to another) • Water, food, waste, pigments, enzymes • Formed by the pinching of the cell membrane • Very large in plant cells (central vacuole), smaller in animal cells

35. Eukaryotes: Structure • Cytoskeleton • Used to hold and change shape • Used for internal organization • Used for movement of molecules and/or movement of the cell • Made of smaller organelles • Microtubules • Actin Fibrils • Intermediate Fibrils

37. Eukaryotes: Structure • Cell Wall • Maintains cell shape, protection, prevents excessive uptake of water • Made of polysaccharide cellulose embedded in a matrix of other polysaccharides and protein • Walls of different cells glued together by middle lamella • Strengthens with age: secondary walls

38. Eukaryotes: Structure • Cell Membrane (or Plasma Membrane) • Semi-permeable membrane surrounding all cells • Made of phospholipids, proteins, cholesterol, carbohydrates, glycoproteins, and glycolipids

39. Eukaryotes: Structure • Cell Membrane • Fluid-Mosaic Model • Must be fluid to work properly • Cholesterol controls fluidity based on temperature • A mosaic of proteins is embedded and dispersed in the lipid bilayer • Integral proteins – inserted into the membrane • Peripheral proteins – not embedded, attached to membrane surface

41. Eukaryotes: Function • Movement of substances across the cell membrane • Bulk Flow • Diffusion • Osmosis • Facilitated Diffusion • Active Transport • Vesicle Mediated Transport • Cell-Cell Junction

42. Eukaryotes: Function • Bulk Flow • molecules move all together in the same direction due to force from hydrostatic pressure • Diffusion (no energy) • The movement of molecules from high concentration to low concentration with no energy requirement (small molecules only)

43. Eukaryotes: Function • Osmosis (no energy) • Special case of diffusion: movement of water across the membrane from high water potential to low water potential • Facilitated Diffusion (no energy) • Polar molecules cannot get through by diffusion, so cells use integral membrane proteins to transport them in/out • Transport proteins are highly selective • Uniport, symport, and antiport proteins

45. Eukaryotes: Function • Active Transport (energy) • When a substance is moved across the membrane against it’s concentration gradient • Requires energy and membrane proteins

47. Eukaryotes: Function • Vesicle-Mediated Transport • Vesicles/vacuoles can fuse with the cell membrane • Exocytosis: expulsion of contents outside the cell • Endocytosis: bringing in outside molecules • Phagocytosis (cell eating) • Pinocytosis (cell drinking) • Receptor-mediated endocytosis

49. Eukaryotes: Function • Cell-Cell Junction • Cells organized into tissues must communicate with each other • Chemical signals (exocytosis from one, endocytosis into the next) • Other junctions • Desmosome • Tight junction • Gap junction • plasmodesma