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Functional Anatomy of Prokaryotic and Eukaryotic Cells

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Presentation on theme: "Functional Anatomy of Prokaryotic and Eukaryotic Cells"— Presentation transcript:

1 Functional Anatomy of Prokaryotic and Eukaryotic Cells
Lecture 2 Functional Anatomy of Prokaryotic and Eukaryotic Cells

2 Scale of Microbes

3 Comparing Prokaryotic and Eukaryotic Cells
Common features: DNA and chromosomes Cell membrane Cytosol and Ribosomes Distinctive features: ?

4 Eukaryotic Cell (protist, animal)

5 Eukaryotic Cell (plant) Eukaryo

6 Differences Between Cell Types
Prokaryotic Cell Eukaryotic Cell Single circular chromosome Multiple linear chromosomes Chromosome found in a cytoplasmic region called the nucleoid. Chromosomes found in a membrane-bound nucleus. No internal membranes Some infolded plasma membrane Extensive network of internal membranes Specialized areas called organelles

7 Prokaryotes One circular chromosome, not membrane bound No histones
No organelles Peptidoglycan cell walls Binary fission

8 Size and Shape of Prokaryotic Cells
Average size: µm  µm Three basic shapes Bacillus, Coccus, Spirals (Vibrio, Spirillum, Spirochete) Most monomorphic, some pleomorphic Variations in cell arrangements (esp. for cocci)

9 Rod-Shaped Bacteria

10 Spherical Bacteria

11 Spiral-Shaped Bacteria
Borrelia burgdorferi Spirochete:

12 Cell Arrangement Pairs: Diplococci, diplobacilli
Clusters: Staphylococci Chains: Streptococci, streptobacilli

13 Cytoplasm and Internal Structures
Location of most biochemical activities Nucleoid: nuclear region containing DNA (up to 3500 genes). Most bacterial chromosomes are circular Plasmids: small, nonessential, circular DNA (5-100 genes); replicate independently Ribosomes (70S vs. 80S) Inclusion bodies: granules containing nutrients, monomers, Fe compounds (magnetosomes)

14 Prokaryotic Cell

15 Closed Circular Chromosome
Also Plasmids, which are smaller, circular pieces of DNA. Plasmids usually encode expendable functions, e.g., antibiotic resistance.

16 Ribosomes: Sites of Translation
On order of 10,000 per cell!

17 Internal Structures: Cell Membrane
Analogous to eukaryotic cell membrane: Phospholipid bilayer with proteins (Fluid mosaic model) Permeability barrier (selectively permeable) Diffusion, osmosis and transport systems Different from eukaryotic cell membrane: Role in Energy transformation (electron transport chain for ATP production) Damage to the membrane by alcohols, quaternary ammonium (detergents), and polymyxin antibiotics causes leakage of cell contents.

18 Simple Diffusion -- Osmosis
solute molecules/ions Simple Diffusion -- Osmosis

19 Cytoplasmic Membrane

20 Protein-Mediated Transport

21 Active Transport

22 Cell Wall Rigid for shape & protection  prevents osmotic lysis
Consists of Peptidoglycan (murein)  polymer of two disaccharide subunits N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) Linked by polypeptides with tetrapeptide side chain attached to NAM Fully permeable to ions, aa, and sugars (Gram positive cell wall may regulate movement of cations)

23 Gram + Cell Wall Gram – Cell Wall Thin peptidoglycan No teichoic acids
Thick layer of peptidoglycan Negatively charged teichoic acid on surface Thin peptidoglycan No teichoic acids Outer membrane

24 Gram-positive Cell Wall
Fig 4.13

25 Gram-negative Cell Wall
Lipid A of LPS acts as endotoxin; O antigens for typing, e.g., E. coli O157:H7 Gram neg. bacteria are less sensitive to medications because outer membrane acts as additional barrier. LPS layer = outer layer of outer membrane (protein rich gel-like fluid)

26 Gram Stain Mechanism Crystal violet-iodine crystals form in cell.
Gram-positive Alcohol dehydrates peptidoglycan CV-I crystals do not leave Gram-negative Alcohol dissolves outer membrane and leaves holes in peptidoglycan. CV-I washes out

27 Atypical Bacteria: Mycoplasmas
Lack cell walls Instead, have cell membrane which incorporates cholesterol compounds (sterols), similar to eukaryotic cells Cannot be detected by typical light microscopy Mycoplasmas cannot be detected by the naked eye or even by typical light microscopy. The morphology of mycoplasma colonies is often likened to a "fried-egg" because they form a dense central core, which penetrates downward into the agar, surrounded by a circular spreading area that is lighter in color. When Mycoplasma species were first cultured, they were thought to have been viruses because of their size. Mycoplasma pneumoniae is a very small bacterium, in the class Mollicutes. This class of organisms lack a peptidoglycan cell wall present on all other firmicute bacteria. Instead, it has a cell membrane which incorporates cholesterol compounds, similar to eukaryotic cells. Lacking a cell wall, these organisms are resistant to the effects of penicillins and other beta-lactam antibiotics, which act by disrupting the bacterial cell wall. M. pneumoniae has one of the smallest genomes known, with 816 kilobase pairs (kbs). Its genome and proteome has been fully characterized. It uses some unique genetic code, making its code more similar to mitochondria than to other bacteria. It lacks the cellular machinery for making many essential compounds. Because of this, it is an obligate parasite. No mycoplasma is found free-living. In this respect, mycoplasma is more similar to viruses than to bacteria. M. pneumoniae is spread through respiratory droplet transmission. Once attached to the mucosa of a host organism, M. pneumonia extracts nutrients, grows and reproduces by binary fission. Attachment sites include the upper and lower respiratory tract, causing pharyngitis, bronchitis and pneumonia. The infection caused by this bacterium is called atypical pneumonia because of its protracted course and lack of sputum production and wealth of extra-pulmonary symptoms. Chronic mycoplasma infections have been implicated in the pathogenesis of rheumatoid arthritis and other rheumatological diseases. Second generation macrolide antibiotics and second generation quinolones are effective treatments. Disease from mycoplasma is usually mild to moderate in severity. Mycoplasma pneumoniae lacks a cell wall which leads to osmotic instability. The combination of these unique characteristics creates a different scenario for treatment of a mycoplasmal infection than other bacteria. The lack of a cell wall prevents the utilization of a B-lactam antibiotic, such as penicillin and cycloserine, because they act specifically to disrupt the cell wall. The use of cholesterol in M. pneumoniae, however, allows for a different avenue for antibiotic therapies usually ineffective on bacteria, such as the use of polyenes. The absence of a cell wall is likely to facilitate a bacterium to host interaction through which compounds can be exchanged. This transfer can include not only the nutrients and supplementary amino acids, etc. that is necessary for the support of bacterial growth, but also toxic metabolic compounds. It is thought that this bacterial surface parasitism causes severe damage to the host cell, however, not one toxin has been identified as the culprit. This EM shows some typically pleomorph mycoplasmas, in this case M. hyorhinis

28 Acid-fast Cell Walls Genus Mycobacterium and Nocardia
mycolic acid (waxy lipid) covers thin peptidoglycan layer Do not stain well with Gram stain  use acid-fast stain

29 Damage to Cell Wall Lysozyme digests disaccharide in peptidoglycan.
Penicillin inhibits peptide bridges in peptidoglycan. Protoplast is a wall-less cell. Spheroplast is a wall-less Gram-positive cell. L forms are wall-less cells that swell into irregular shapes. Protoplasts and spheroplasts are susceptible to osmotic lysis.

30 External Structures located outside of cell wall Flagella
Axial filaments Fimbriae Pili Glycocalyx

31 Glycocalyx Many bacteria secrete external surface layer composed of sticky polysaccharide (EPS), polypeptide, or both A capsule is neatly organized A slime layer is unorganized and loose Allows cells to attach  key to biofilms Prevents phagocytosis  virulence factor E.g.: B. anthracis, S. pneumoniae, S. mutans

32 Flagellum – Flagella Anchored to wall and membrane
Number and placement determines if atrichous, monotrichous, lophotrichous, amphitrichous, or peritrichous Allows for move toward or away from stimuli: Chemotaxis (phototaxis and magnetotaxis) Flagella proteins are H antigens (e.g., E. coli O157:H7)

33 Flagellar Arrangements
Polar Flagellum Flagellar Arrangements e.g., E. coli also “atrichous”

34 Fig 4.9 “Run and Tumble”

35 Axial Filaments Fimbriae and Pili Fimbriae allow attachment
Pili are used to transfer DNA from one cell to another Endoflagella In spirochetes Anchored at one end of a cell Rotation causes cell to move

36 Fimbriae

37 Endospores Dormant, tough, non-reproductive structure;  germination  vegetative cells Spore forming genera: __________ Resistance to UV and  radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants Relationship to disease Sporulation: Endospore formation Germination: Return to vegetative state

38 In response to starvation, B
In response to starvation, B. subtilis differentiates into a dormant stress-resistant cell-type known as a spore. Cells initiate spore formation with an asymmetric cell division that generates a large cell (the mother cell) and a small cell (the prospective spore or forespore). Initially these two cells lie side-by-side but later in development the mother cell engulfs the forespore in a phagocytic-like process to produce a cell-within-a-cell. The mother then nurtures the forespore as it prepares for dormancy. Once the spore is fully mature, the mother cell lyses. We use this elegant morphological process to address basic questions in bacterial differentiation.

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