Review questions 1.Part of the cell that prevents most molecules from diffusing into and out of the cell. 2.Cell wall molecule that prevents cells from exploding when in hypotonic environments. 3.Staining technique that differentiates cell types based mostly on cell wall structure. 4.Complex molecule found in the cell walls of Gram negative bacteria (only). 5.Waxy molecule found in the cell walls of acid fast bacteria. 1

2 ampletour/medical/GramNegat iveEnvelope.gif ampletour/medical/GramPositi veEnvelope.gif Gram Negative Gram Positive

Gram negative cell wall 3 md.edu/courses/bio 141/lecguide/unit2/ bacpath/gncw/u1fi g10b.html

Features of the outer membrane Assymetric –The layer facing inward is phospholipids, but the outer layer of the lipid bilayer is lipopolysaccharide Proteins –Porins, 3 subunit proteins that transport substances through the membrane –Other proteins with other functions –Braun’s lipoprotein, attaches to peptidoglycan 4

Structure of LPS cell_envelope.htm Unique to different bacteria. Takes place of hydrophilic head group. 5

Why is the outer membrane important? To the bacterium: –Additional barrier to diffusion of unwanted substances such as antibiotics. –Barrier to enzymes that could harm the cell such as lysozyme. –Lipid A portion called endotoxin, harmful to host –Proteins help bacteria Attach to host cells to cause disease. Enter host cells to cause disease. To us –Triggers host defenses, immune recognition 6

Periplasmic Space theory.html Location of many useful proteins. 7

Glycocalyx: capsules and slime layers resources/visbulk.asp capsule cell “Sugar covering”: capsules are firmly attached, slime layers are loose. Multiple advantages to cells: prevent dehydration absorb nutrients protection from predators, WBCs protection from biocides (as part of biofilms) attachment to surfaces and site of attachment by others. In some bacteria, a covering outside the cell is made of proteins, e.g S-layers. 8

Fimbriae and pili oralenv/images/sex1.jpg Both are appendages made of protein Singular: fimbria, pilus Both used for attachment Fimbriae: to surfaces (incl. host cells) and other bacteria. Pili: to other bacteria for exchanging DNA (“sex”). 9

Fimbriae and pili

Flagella tk/ce/flagella-s.gif introduction/bacteria.html Flagella: protein appendages for swimming through liquid or across wet surfaces. Rotate like propellers. Different from eukaryotic flagella. Arrangements on cells: polar, Lophotrichous, amphitrichous, peritrichous. 11

Flagellar structures img.sparknotes.com/.../monera/ gifs/flagella.gif BIOL/Flagella.jpg Differences: Thickness and structure Membrane or not Whip or spin 12

Motility revisited Flagella: protein appendages for swimming through liquid or across wet surfaces. Axial filament: a bundle of internal flagella –Between cell membrane and outer membrane in spirochetes –Filament rotates, bacterium corkscrews through medium Gliding –No visible structures, requires solid surface –Slime usually involved. 13

Axial filaments imgrefurl= pF7UJ:&tbnh=90&tbnw=119&start=1&prev=/images%3Fq%3Daxial%2Bfilament%2Bbacteria%26hl%3Den%26lr%3D%26sa%3DG 14

15 Review of eukaryotic cells science/cell_biology.html

16 Eukaryotic cell reminders Eukaryotic cells have a variety of compartments –Membrane-bound organelles, carry out functions –DNA in nucleus. NO NUCLEUS in Prokaryotes! Mitochondrion is an enslaved bacterium –Inner and outer membrane like a Gram – bacterium –Mitochondrion has its own DNA and ribosomes –It is the same size as a bacterium. Lysozome is an organelle –Contains various digestive enzymes –Important part of WBC’s defenses against bacteria

17 How things get in (and out) of cells Eukaryotic cells –Have transport proteins in membrane –Have a cytoskeleton made of microtubules Allows for receptor mediated endocytosis, phagotcytosis, etc. Cell membrane pinches in, creates vesicle Prokaryotic cells –Can NOT carry out endocytosis Have a stiff cell wall Cytoskeleton newly discovered, not substantial –Entry of materials into cell by diffusion or transport processes ONLY.

18 Illustrations: entry into cells Both prokaryotes and eukaryotes. Only eukaryotes.

19 Type of molecule affects transport Small molecules can pass through a lipid bilayer –Water; otherwise, no osmosis –Gases such as O 2 and CO 2 Lipid molecules can –Dissolve in lipid bilayer, pass through membrane –Many antibiotics, drugs are lipid soluble Larger, hydrophilic molecules cannot –Ions, sugars, amino acids cannot pass through lipids –Transport proteins required

20 Transport through membranes Simple diffusion –Molecules travel down concentration gradient –Membrane is not a barrier to their passage Facilitated diffusion –Molecules travel down concentration gradient –Cannot pass through lipid bilayer; their passage is facilitated by protein transporters Active transport –Molecules travel against concentration gradient –Requires input of metabolic energy (ATP), transporter

21 How molecules get through the membrane

22 ATP is not always used directly in active transport An electrochemical gradient exists across the cell membrane (membrane potential) –Positive just outside the membrane, negative within –Gradient in the form of H+ ions Maintained by the hydrolysis of ATP or by the same metabolic reactions that make ATP Powers uniports, symports and antiports

23 Uniport Transport of a single substance Example: transport of K+ into the cell –Against its chemical gradient, but down its electrical gradient. –(red ball = K+) –Doesn’t require energy DIRECTLY, but making the electrical gradient DOES require energy. Antiport and Symport –Are other examples