The Ultrastructure of Cells (1.2) IB Diploma Biology 1.2.4 Electron microscopes have a much higher resolution than light microscopes. • Resolution: making separate parts of an object distinguishable by the eye • Beams of electrons have shorter wavelengths than visible light; so much higher resolution Eye Light micro. Electron micro. mm 0.1 Resolution µm nm 100 100,000 0.0002 0.2 200 0.000001 0.001 1 1.2.1 Prokaryotes have a simple cell structure without compartments Prokaryotes “Before nucleus:” evolutionary precursors to eukaryotes. Escherichia coli (E. coli) http://en.wikipedia.org/wiki/Escherichia_coli 1.2.1 Prokaryotes have a simple cell structure without compartments Prokaryotic Cell Parts cell wall: protective protein-based coating (Gram + / Gram ) plasma membrane: selectively permeable, controls entry & exit of materials to and from the cell. pili: attach to other bacteria for DNA transfer cytoplasm: contains enzymes for metabolic reactions nucleoid: closed-loop of bacterial DNA in a condensed area ribosomes: protein synthesis (transcription & translation) flagella: whiplash-like motion causes movement Cell structures animation: http://www.wiley.com/legacy/college/boyer/0470003790/animations/cell_structure/cell_structure.swf Past-paper question: E. coli TEM image Identify these structures: I. II. III. IV. Calculate the magnification of the image. Image from IB Biology QuestionBank CDRom – get a copy here: https://store.ibo.org/biology Past-paper question: E. coli TEM image Identify these structures: I. Plasma membrane II. Cell wall / pili III. Nucleoid IV. Cytoplasm / ribosomes Calculate the magnification of the image. 1. Measure the scale bar in mm. 2. Multiply x 1000 to convert to μm. That is the magnification. How long is the bacterium? Image from IB Biology QuestionBank CDRom – get a copy here: https://store.ibo.org/biology 1.2.3 Prokaryotes divide by binary fission. PROKARYOTES E P R O D U C E through binary fission two-parts splitting PROKARYOTES binary fission E through P R O The closed-loop DNA of the bacterium makes copies through D semi-conservative DNA replication. U New plasmids are pulled to opposing poles by fibers. C E The bacterium divides in two. http://www.youtube.com/watch?v=gEwzDydciWc 1.2.7 Draw the ultrastructure of prokaryotic cells based on electron micrographs. So after absorbing all of that information, all you have to do is put it in the diagram! Annotate: to add brief notes to a diagram or graph. 1.2.2 Eukaryotes have a compartmentalized cell structure. 1.2.8 Draw the ultrastructure of eukaryotic cells based on electron micrographs. The Cell membrane is the boundary of the cell. • It acts as a “gatekeeper”, preventing the entry or exit of some molecules and facilitating the movement of others. • It is a phospholipid bilayer • It is permeable to oxygen and carbon dioxide • It is impermeable to water and charged particles, they must enter through special proteins embedded in the membrane More in 2.4 http://commons.wikimedia.org/wiki/File:Cell_membrane_detailed_diagram_en.svg The Nucleus contains the chromosomes which comprise most of the DNA in a cell - It is the largest organelle - It has a double layer membrane - mRNA, transcribed from DNA in nucleus, exits through pores - Some cells have multiple nuclei Rough Endoplasmic Reticulum Spot the difference? Smooth Endoplasmic Reticulum http://images.wellcome.ac.uk/ The ‘spots’ are the difference! The Rough Endoplasmic Reticulum is peppered with ribosomes that give it the rough appearance Proteins synthesized here are secreted Smooth ER is site of lipid production I shall name it……… The internal reticular apparatus!! Pretty catchy… no?* Camillo Golgi *Everybody thought that was a terrible name, so they called it the Golgi apparatus instead http://commons.wikimedia.org/wiki/File:C_Golgi.jpg http://commons.wikimedia.org/wiki/File:Golgi_in_the_cytoplasm_of_a_macrophage_in_the_alveolus_(lung)_- The Golgi Apparatus is a flattened stack of membranes responsible for the packaging and delivery of proteins Lysosomes are simple, membrane-bound organelles full of enzymes that digest engulfed bacteria and viruses and large molecules for recycling. The Mitochondrion (pl. Mitochondria) • The ‘power house’ of the cell • Has a smooth outer membrane and a folded inner membrane • Where aerobic respiration occurs Mitochondria in mammalian lung cells Free Ribosomes: • 80s sized in eukaryotes (v. 70s size in prokaryotes) • Proteins synthesized for use within the cell (i.e. enzymes used in the cytoplasm) Chloroplasts • Site of Photosynthesis in Plant Cells • Stacks of Thylakoids Vacuoles & Vesicles: • • • • Animal cells sometimes have small vacuoles for digestion Unicellular organisms have contractile vacuoles for expelling water Plant cells have large vacuoles that hold water and food Vesicles are small lipid sacs used for transport Centrioles & Microtubules: • Centrioles are bundles of microtubules found in Animal Cells • Microtubules separate chromosomes in cell division and make-up cilia and flagella 1.2.8 Draw the ultrastructure of eukaryotic cells based on electron micrographs. State: Give a specific name, value or other brief answer without explanation or calculation. Animals Plants Have a cell wall Don’t have a cell wall Have chloroplasts in photosynthetic cells Don’t have chloroplasts anywhere Carbohydrate stored as starch and plant oils V. Carbohydrate stored as glycogen and animal fat Rigid Shape (due to cell wall) Flexible shape Have a large permanent storage vacuole May have small, temporary vacuoles Compare: Give an account of similarities and differences between two (or more) items, referring to both (all) of them throughout Prokaryotic Eukaryotic Small cells Relatively larger cells Always unicellular Some multicellular, some unicellular No nucleus: DNA a ‘naked’ loop in the nucleoid region DNA in chromosomes in a membrane-bound nucleus Ribosomes smaller (70s) Ribosomes larger (80s) No mitochondria, respiration in cell membrane and mesosomes Mitochondria, where aerobic respiration occurs Cell division by binary fission Cell division by Meiosis or Mitosis Reproduction asexual (some gene exchange can occur via conjugation) Reproduction Sexual or asexual 1.2.5 The structure and function of organelles within the exocrine gland cells of the pancreas. Exocrine gland cells of the Pancreas secrete digestive enzymes into small intestine • Enzymes are proteins, so these cells must produce proteins in large quantities • Organelles involved: • • • • Rough ER Vesicles Golgi Apparatus Plasma membrane 1.2.6 The structure and function of organelles within palisade mesophyll cells of the leaf. Palisade mesophyll cells carry out most of the photosynthesis in plant cells • Organelles involved: • Chloroplasts • Mitochondria • Large Vacuole 1.2.9 Interpret electron micrographs to identify organelles and deduce the function of specialized cells. Identify the labeled structures in this liver cell TEM image. Source: http://www.udel.edu/biology/Wags/histopage/empage/empage.htm What can you see?