Prokaryotic Cells

Prokaryotes PLASMA MEMBRANE CELL WALL GLYCOCALYX FLAGELLUM SEX PILUS CAPSULE SLIME LAYER FLAGELLUM SEX PILUS FIMBRAE

PLASMA MEMBRANE All cells (Prokaryote and Eukaryote) have a plasma membrane. It holds the organelles inside of the cell. Any substance that can rupture the plasma membrane will kill the whole organism Alcohol, soaps, and other detergents easily rupture the plasma membrane.

PLASMA MEMBRANE The plasma membrane is semipermiable Allows some substances to come and go (oxygen and water molecules), but does not allow other things to get inside or leave. It regulates the flow of nutrients in the cell. It allows low molecular weight (small sized) substances (such as water) to get in and out depending on their concentration within the cell and outside of it. This is called diffusion, and does not require the cell to expend any energy.

Plasma Membrane Phospholipid bilayer Peripheral proteins Integral proteins Transport proteins Figure 4.14b

Movement Across Membranes Figure 4.17

PLASMA MEMBRANE Hypertonic solution: salty water The concentration of salt outside of the cell is higher than the inside of the cell, so the water will follow salt out, and the cell will shrink. Hypotonic solution: pure water More salt inside of the cell; water will diffuse into the cell, causing the cell to explode (osmotic shock). The cell wall of bacteria is rigid and protects the organism from osmotic shock. Isotonic solution: same amount of salt on the inside and outside of the cell Normally, there is equilibrium inside and outside of the cell.

Figure 4.18c-e

Movement Across Membranes Osmosis Movement of water across a selectively permeable membrane from an area of high water concentration to an area of lower water. Osmotic pressure The pressure needed to stop the movement of water across the membrane. Figure 4.18a

PLASMA MEMBRANE Phospholipid bilayer. Two layers of a compound consisting of phosphates and lipids (fats). The outer and inner sides of the membrane are water soluble, and the area between is not water soluble. This gives the membrane semipermiablity, which allows it to take in certain substances and keep out other substances.

PLASMA MEMBRANE Lipoproteins (LP): made of lipid (fat) and proteins. These special proteins can transport larger molecules (like sugars) directly into the cell. This is called active transport. It requires the cell to spend some energy in the form of ATP.

Movement Across Membranes: Active Transport Figure 4.17

PLASMA MEMBRANE Gram negative bacteria have an inner and an outer plasma membrane, separated by a cell wall. Gram positive bacteria only have one plasma membrane, inside of its cell wall.

GRAM NEGATIVE GRAM POSITIVE Plasma membrane Cell Wall Outer plasma membrane

Bacterial Cell Walls 15 Figure 3.13a

Bacterial Cell Walls 16 Figure 3.13b

PLASMA MEMBRANE In Gram negative organisms, the outer plasma membrane contains lipopolysachharides (LPS), which means it is made of lipids (fats) and many sugars (polysaccharides). The LPS embedded in the plasma membrane of Gram negative bacteria contains a string called an O antigen. Also within the LPS is an endotoxin called Lipid A.

GRAM NEGATIVE O Antigen LPS Inner plasma membrane Cell Wall Lipid A (endotoxin) Outer plasma membrane LPS

CELL WALL More complex in Prokaryotes (bacteria) than in Eukaryotes (plants, etc). Its rigidity keeps the organism from exploding from osmotic shock. Composed of peptidoglycan, which is a combination of peptide (protein) and glycan (sugar). Peptidoglycan is only found in bacteria. Mycobacterium and Mycoplasma are the only bacteria without a normal cell wall.

Mycobacterium This causes TB or leprosy, depending on the species. The cell wall of Mycobacterium is 60% waxy. It is neither Gram-positive nor Gram-negative. It is called “Acid-fast” because it takes an acidic stain to color it.

Mycoplasma Mycoplasma has no cell wall. This makes Mycoplasma strains resistant to many kinds of common antibiotics like penicillin, that act on bacteria cell walls. One species causes pneumonia.

Peptidoglycan NAM NAG NAM NAG NAM Consists of a chain of two types of sugars (NAM and NAG) linked by proteins. The sugars are arranged in this order: NAG-NAM-NAG. NAG NAM NAM NAG NAM

Bacteria Cell Wall Semi rigid, ouside of membrane Chemical makeup peptidoglycan (aka murein layer) made up of polymer of: N-acetylglucosamine (NAG) N-acetylmuramic acid (NAM) NAM is connected to NAG via a beta 1,4 linkage Lysozyme enzymes break the beta 1,4 linkage 23

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Penicillin and cell walls Kills bacteria by preventing cell wall synthesis Prevents and destroys amino acid linkage (peptide bond formation) In Gram positive (G+) results in protoplast (cell wall dissolves away) In Gram negative (G-) partially lose cell wall resulting in spheroplast (round cell) Both sensitive to osmotic pressure so cell bursts

CELL WALL Not only do Gram negative bacteria have less peptidoglycan than Gram positives, they also have an inner and outer plasma membrane. The outer plasma membrane is external to the cell wall, and the inner plasma membrane is internal to the cell wall.

Outer membrane Peptidoglycan GRAM NEGATIVE GRAM POSITIVE

CELL WALL Gram positive organisms have much more peptidoglycan than Gram negatives. The dyes in a Gram stain enter the cytoplasm of both Gram positive and negative cells. The iodine forms large crystals with the dye that are too large to escape through the cell wall. Alcohol dissolves the outer membrane of the gram-negative cells and leaves small holes in the thin peptidoglycan layer through which the Crystal Violet-iodine complex leaks out. Although gram-positive and gram-negative cells both absorb safranin, the pink color of safranin is masked by the darker purple dye previously absorbed by gram-positive cells.

GRAM POSITIVE GRAM NEGATIVE Crystal Violet added Plasma membrane Cell Wall Outer plasma membrane

GRAM POSITIVE GRAM NEGATIVE Iodine Added

GRAM POSITIVE GRAM NEGATIVE Alcohol Added

GRAM POSITIVE GRAM NEGATIVE Safranin added

GRAM POSITIVE GRAM NEGATIVE Final Result

CELL WALL GRAM POSITIVE CELL WALL GRAM NEGATIVE CELL WALL No outer plasma membrane Inner and outer plasma membrane Thick peptidoglycan Thin peptidoglycan

Glycocalyx Outside cell wall Usually sticky Extracellular polysaccharide allows cell to attach Figure 4.6a, b

GLYCOCALYX CAPSULE SLIME LAYER

CAPSULE Non-slimy protein (made of polypeptides) or sugars (polysaccharides) covering the bacterium. It is neatly organized. Not every bacterium has a capsule. Purpose is to store nutrients and inhibit phagocytosis The capsule itself is an antigen, called the K antigen. It stimulates an immune response. Example is Mycobacterium tuberculosis.

Capsule TB nodules

SLIME LAYER Slimy protein covering the entire bacterium. Not neatly organized. Not every bacterium has a slime layer. Function is to attach to some structure in the host. Example is the bacteria in the mouth.

FLAGELLUM Whip-like tail used for motility. Can observe motility in live cells, but can’t see the flagella. Requires a special stain, and that kills the bacterium. Made of a protein called flagellin. Structure: Filament Hook Turning disks within a basil body.

FLAGELLUM ATP is needed to turn the disk, which turns the flagella. Chemotaxis: sensing chemicals in the environment and moving towards or away from them. Bacteria flagella contain a protein called an H antigen (Flagellar antigen).

FLAGELLAR ANTIGEN There is a particular strain of E. coli called O157.H7 The letter “O” followed by a number indicates the type of cell wall lipopolysaccharide (LPS) and the H7 indicates the type of flagellar antigen.

Flagella arrangements: Peritricous: Many flagella all around the perimeter of the cell. Lophotrichous: A group of flagella gathered at one end of the cell. Amphitrichous: One flagellum coming out of each end of the cell. Monotrichous: Only one flagellum, comes out of one end of the cell

Flagella Arrangement Figure 4.7

Flagella motility: Run: move in a straight line from point A to point B. Tumble: roll around themselves like a rock tumbling down a slope. Run and Tumble: Doing both movements alternately.

Motile Cells Figure 4.9

AXIAL FILAMENTS Special flagella found only in spirochetes Allows the spirochete to move in a motion like a corkscrew. This allows it to penetrate tissue. Example of a spirochete is the bacterium that causes syphilis.

Axial Filaments Endoflagella In spirochetes Anchored at one end of a cell Rotation causes cell to move Figure 4.10a

SEX PILUS Longer than flagella Helps cells connect cells to each other during conjugation Pili are used to transfer DNA from one cell to another

FIMBRAE Hair-like structures made of protein. In Eukaryotes, they are called cilia. In bacteria, fimbrae allow them to attach to the host. Example is Neisseria gonorrhoeae (causes gonorrhea).

Bacterial Antigens O Antigen: LPS of gram-negative H Antigen: Flagella K Antigen: Capsule

INTERNAL COMPOSITION OF PROKARYOTE CELLS 1. CYTOPLASM NUCLEOID PLASMIDS RIBOSOMES INCLUSIONS 2. ENDOSPORES

CYTOPLASM The watery substance inside of the plasma membrane. It is made up of 80% water and contains proteins (enzymes), carbohydrates, and lipids.

NUCLEOID A nuclear area (prokaryotes have no nucleus). There is only one chromosome, and the DNA is circular instead of linear. Prokaryotes have no histones, which are structures eukaryotes use to organize their DNA by wrapping around it.

PLASMIDS Small pieces of DNA fragments which are separate from the chromosome. They may carry genes for antibiotic resistance, production of toxins, etc. Plasmids can be transferred from one bacterium to another. Plasmid DNA is used for gene manipulation and biotechnology.

RIBOSOMES “Protein factories” The cytoplasm can contain 10,000 ribosomes Gives the cytoplasm a granular appearance Several antibiotics work by inhibiting the protein synthesis of ribosomes: Streptomycin Gentamicin Erythromycin Chloramphenicol.

Ribosomes Figure 4.6a

Ribosomes They are made of two subunits: Together, they are called a 70S ribosome unit (the numbers are NOT added to get this figure). Some antibiotics attack the 30S unit (streptomycin and gentamycin), some attack the 50S unit (erythromycin and chloramphenicol).

Ribosomes Figure 4.19

INCLUSIONS Reserve deposits of nutrients within the cytoplasm. These nutrients can be in the form of phosphate, glycogen, starch, and lipids.

ENDOSPORES Specialized resting cells formed by gram-positive rod shaped bacteria (Bacillus) when essential nutrients are depleted An example is Clostridium, which causes diseases such as gangrene, tetanus, botulism, and food poisoning. Another example is Bacillus, some species of which cause anthrax and food poisoning.

Figure 4.21a

ENDOSPORES Only bacteria make endospores. They are highly durable, dehydrated cells with thick walls. They are formed inside the cell membrane When released into the environment, they can survive extreme heat, lack of water, and exposure to toxic chemicals and radiation. Endospores require a special stain to be visualized. Only one cell comes from one endospore, therefore sporulation is not reproduction.

SPORULATION The vegetative (parent) cell forms one endospore because a key nutrient becomes unavailable. The cytoplasm of the vegetative cell dries up, the cell wall ruptures, and the endospore is released into the environment.

GERMINATION The endospore returns to its vegetative state. This is triggered by a change in the environment. Water enters into the endospore, and metabolism resumes. They are resistant to heating, freezing, desiccation (drying), use of chemicals, and radiation. Endospores can survive in boiling water for several hours or more.

TYPES OF ENDOSPORES Terminal endospore Sub-terminal endospore Central endospore

Prokaryotic Cell Drawing