Chapter 3 Microbial Cell Structure According to the

Chapter 3 Microbial Cell Structure

According to the cell theory of life, a single cell is the smallest unit of life and is capable of carrying out all of the basic processes of a living organism. 5 important characteristics of all living organisms - ability to reproduce - ability to take in food, produce energy and grow - ability to excrete wastes - ability to respond to the environment - susceptible to mutation

Prokaryotic vs. Eukaryotic Cells Algae 80 S ribosomes Cell Wall simple – cellulose Cell Membrane phospholipids and sterols embedded proteins DNA several linear chromosomes billion base pairs m. RNA spliced before translation Endoplasmic Reticulum Nuclear Membrane Organelles Mitochondria and Chloroplasts Complex Flagella sheathed, several microtubules whipping motion

How big are typical microorganisms like protozoa, bacteria and viruses? Viruses 25 – 400 nm (. 025 -. 400 mm) Bacteria 0. 2 – 10 mm Protozoa 1 – 150 mm There is a lot of variation in the sizes of different types of microorganisms but as a general rule protozoa are bigger than bacteria and bacteria are bigger than viruses. There are of course exceptionally large bacteria and exceptionally small protozoa so one can find cases of a given bacterium that is bigger than a given protozoa.

The Prokaryotic Cell

Envelope Cell Membrane – diffusion barrier, always present Cell Wall – usually present, maintains cell shape, protects from osmotic lysis by preventing excessive swelling Glycocalyx – external layer of slime, protects bacterium from host immune system, freezing and dessication helps bacteria to stick together

Functions of the cytoplasmic membrane (cell membrane) The cytoplasmic membrane is an absolutely essential structure. All living cells are bounded by a cytoplasmic membrane. The cell membrane is a semipermiable barrier. It allows some substances to diffuse into and out of the cell but it prevents other substances from entering or leaving the cell. The cytoplasmic membrane is the structure that defines the border between the living matter within the cell and nonliving matter that is outside. In bacteria the enzymes and electron carriers of the respiratory chain are embedded in the cytoplasmic membrane. (In eukaryotic cells the respiratory enzymes are found in the inner mitochondrial membranes. Bacterial cells don't have mitochondria. )

Cytoplasmic Membrane Composition The bacterial cytoplasmic membrane is composed of a lipid bilayer that has protein molecules embedded within it. By mass a typical bacterial cytoplasmic membrane is about 50% protein and 50% lipid. The lipids found in bacterial cell membranes are phospholipids. See pages 70 – 74 of your textbook for more information about cell membranes.

The Bacterial Cell Wall - Functions A cell wall gives a cell its' shape and protects it from osmotic lysis. The cell wall is not rigid like a brick wall but rather it is a net-like bag that surrounds the cell and protects it from swelling up. There is a tendency for water to diffuse into a cell, except is when the bacteria are in a very salty solution. In low salt solutions, water diffuses into the cell and can cause it to swell up like a balloon. The cell wall prevents lysis due to osmotic pressure.

The Bacterial Cell Wall - Composition The bacterial cell wall is made of a chemically complex substance called peptidoglycan, which is made of long chains of modified sugars that are cross-linked by chains of amino acids. (peptides) The sugars are N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). (See figure 3. 11 of your textbook. ) (Chitin, found in fungal cell walls, insect shells and cartilage, is made of NAG. ) NAM is rarely found in nature, except in the bacterial cell wall, so the discovery of NAM in a sample is an indication of bacterial contamination. The cross-linking peptide chains are made of amino acids linked by amide bonds like those found in proteins. However, peptidoglycan contains several unusual amino acids that are never seen in proteins, including: D-alanine, ornithine and diaminopimelic acid. Presence of D-alanine or diaminopimelic acid in a sample is another indication of the presence of bacteria.

Gram Positive Cell Wall vs. Gram Negative Cell Wall Membrane

Lipopolysaccharide (LPS) LPS is found in the Gram negative outer membrane. The lipid A portion is embedded in the membrane, the O-antigen is a sugar polymer that sticks out on the outer surface and R-core joins Lipid A to O-antigen. LPS is also known as bacterial endotoxin. LPS is a potent pyrogen, a nonspecific activator of the immune response that causes the host to have fever. LPS is released from dead cells that are decomposing (lysing) and some is released from dividing cells. Teichoic acids are components of the thick cell walls of Gram positive bacteria. Teichoic acids are polymers of sugar acids. TA helps bind together the layers of peptidoglycan in the thick wall. Lipoteichoic acids help anchor the cell wall to the cell membrane.

The Bacterial Capsule or Glycocalyx The bacterial capsule is a layer of organic polymers that coats the outside surface of a bacterial cell like a layer of gravy on a meatball. (Your textbook uses the term "glycocalyx". If the glycocalyx is firm it is called a capsule but if it is loose and drippy it is called a slime layer. ) The functions of a capsule are: 1) protect the cell from drying out or freezing 2) help the bacterium to stick to surfaces and other bacteria (there are protein fibers called fimbrae that also help in this respect) 3) protect the cell from recognition by the host's immune system and phagocytosis 4) storage of sugars or other nutrients that may be abundant when the bacterium is making the capsule but may be broken down and used for food at a later time.

There are many different types of bacterial capsules. Different species of bacteria make different types of capsule. The most common capsular materials are polysaccharides. (long chains of sugar residues) Some bacterial capsules are composed of: hyaluronic acid, protein, or glycoproteins, others are made of high molecular weight hydrocarbons that resemble Vaseline. CLINICAL SIGNIFICANCE: Strains of Streptococcus pneumoniae that make a capsule are more virulent (able to cause disease) than strains that do not make a capsule.

Examples of Capsule Forming Bacteria Streptococcus pneumonia: A polysaccharide capsule that is poorly antigenic protects the bacterium from the host immune system and makes it more virulent. Streptococcus mutans: A dextran capsule (polysaccharide) helps the bacterium to stick to the surface of a tooth, calcium leeched from the enamel mineralizes the capsular matrix. Xanthomonas campestris: A soil bacterium that causes soft rot of vegetables is protected from freezing and desiccation (drying) by a polysaccharide capsule. Streptococcus cells negatively stained to show capsules

Bacterial Appendages Structures that are found on the outside of the cell Bacterial appendages are simple protein tubules. - Flagella: rotating helical fibers that act as propellers Monotrichous (one hair) Lophotrichous (a tuft or clump of hair) Amphitrichous (on both sides) Peritrichous (all around) Axial Filaments (inside the periplasmic space) - Fimbrae (or Pili): fibers that help bacteria stick to surfaces and to each other - Sex Pilus: a special fimbri that is used during conjugation

Bacterial Flagella A bacterial flagellum consists of a single protein fiber that is external to the cell membrane, it is a helical tube of protein that rotates like a propeller or corkscrew.

Bacterial Flagellar Arrangements

Axial Filaments are specialized flagella seen within the periplasmic space (endoflagella) of Spirochetes. (The Spirochetes includes such human pathogens as Treponema palidium, the causative agent of syphilis & Borrelia burgdorferi, causative agent of Lyme disease. ) Image from: classes. midlandstech. edu

Bacterial Appendages - Continued Pili or Fimbrae - Pili are hollow tubes of protein that stick out on the outer surface of bacteria. - Pili are about the same diameter as flagella but are shorter and straight. - Pili help bacteria to stick to surfaces and to each other. - Some pili are virulence factors that allow pathogenic bacteria to stick to host cells. - Other pili are important for the formation of biofilms. - In some strains of E. coli there is a special pilus made called the F-pilus. This pilus causes two cells to stick together so DNA can be transferred from one to the other by conjugation. (F is "fertility". )

Bacterial Cell With Fimbrae help some E. coli strains to stick to cells that line the urethra. This is an important factor in urinary tract infections. diagram from Urology 7 th ed. by Campbell

Bacterial Cell Physiology The Envelope: cytoplasmic membrane always present cell wall usually present (peptidoglycan) capsule sometimes present appendages sometimes present flagella, pili, fimbrae The Cytoplasm: nucleoid always present ribosomes always present plasmids often present endospore sometimes present chromatophore sometimes present inclusion bodies sometimes present starch granules, polyphosphate granules iron granules, sulfur granules, storage proteins 9/25/17

Structures of the Bacterial Cytoplasm Nucleoid: a region of cytoplasm where the DNA is located, it is not surrounded by a membrane

Ribosomes Enzyme complexes that read m. RNA and, with the t. RNAs, make proteins.

Cytoplasmic Structures: Bacterial Endospore The endospore is a tough resting state that allows bacteria to survive a period of harsh conditions such as when the soil dries out or they run out of food. The endospore is not a reproductive structure because sporulation begins with a single vegetative cell and ends with a single spore. Endospores are the toughest form of life known on Earth. Spores are very resistant to: heat, radiation, dessication, lack of nutrients, antimicrobial chemicals and physical abrasion. Spores can survive in an inert state for many years, even centuries. Endospore Structure The endospore coat is a highly modified cell wall that contains special coat proteins and dipicolinic acid in addition to peptidoglycan. Dipicolinic acid chelates calcium ions, so the spore coat is somewhat mineralized. The core of the spore contains everything found in the cytoplasm of a vegetative cell except it is very nearly metabolically inert and it contains much less water than normal cytoplasm.

Most spore forming bacteria belong to one of only two genera: Bacillus and Clostridium. Both are Gram + rods. Bacillus grows aerobically, while Clostridium is anaerobic. Anthrax is caused by inhalation of spores from Bacillus anthracis. Tetanus and gas gangrene are caused by contamination of a wound site by Clostridium spores. Botulism is caused by eating food that is contaminated by a toxin that is made by Clostridium botulinum. You can find more about endospores in your textbook on pages 316 – 319 including figures 11. 8 and 11. 9.

Cytoplasmic structures: The Chromatophore The chromatophore is a membrane structure found only in photosynthetic bacteria that contains light harvesting pigments. The pigments allow the cell to absorb sunlight and produce energy. Chromatophore means "colored body", from the color of the light harvesting pigments (green, purple, yellow-green).

Photosynthetic bacteria produce light harvesting pigments called bacteriochlorophyll and carotenoids. Bacteriochlorophylls are similar to plant chlorophyll except they often absorb different wavelengths of light. This means that photosynthetic bacteria are different colors. Many photosynthetic bacteria are purple or yellowish green rather than the more bluish-green of land plants. Also unlike plants, bacterial photosynthesis does not always involve the production of oxygen.

Inclusion bodies are insoluble particles that accumulate in some bacterial cells under certain conditions including: media recipe, availability of specific nutrients or oxygen and culture age. Some inclusion bodies can be visualized using special stains. Inclusion bodies are usually some form of stored material. Some inclusion bodies are metabolic waste products while others are stored nutrients. Some bacteria accumulate starch granules, others accumulate granules of sulfur, polyphosphates or polyhydroxybutyrate.

Common Types of Inclusion Bodies (Granules) That Are Found in Bacterial Cells 1. Starch (a glucose polymer) 2. Protein (storage) 3. Lipoid granules (globs of fat) 4. polyhydroxybutyrate 5. sulfur 6. iron

Differences Between the Archaea and the Bacteria 9/25/17

Differences Between the Archaea and the Bacteria 1. Cell Membrane Lipids – Fatty acids in bacterial lipids have straight chains, fatty acids in Archaea have branching chains. 2. Cell Wall Composition – Bacterial cell wall is made of peptidoglycan, Archaeal cell wall is made of other compounds. (pseudopeptidoglycan – lacks n-acetyl muramic acid) 3. RNA polymerase in Archaea is more like eukaryotic cells. DNA polymerase in Archaea is more like eukaryotic cells 4. Currently, there are no Archaea that are known to cause human disease, but there are more than 300 species of bacteria that are known to cause disease in humans

Eukaryotic Cells 9/25/17

Structures Seen in Eukaryotic Cells But Not in Prokaryotes - Endoplasmic Reticulum - Mitochondria - Chloroplasts - Nuclear Membrane - Cytoskeleton - Phagolysosomes - sn. RNPs The Endoplasmic Reticulum Endo- : inside -plasmic: the stuff, matter Reticulum: net The E. R. is a complex network of internal cell membranes that is attached to both the cytoplasmic membrane and the nuclear membrane. Ribosomes are often attached to the endoplasmic reticulum.

Mitochondria are membrane bound "energy producing factories" that are not seen in bacteria. Most mitochondria are rod shaped and they are the size of small to average bacterial cells. Mitochondria are essential for survival of most types of eukaryotic organism (there a few strange protozoa that lack them). Mitochondria have a double membrane. The enzymes of the electron transport chain are found in the inner mitochondrial membrane. Mitochondria consume oxygen.

Endosymbiotic Hypothesis of the Origin of Mitochondria have their own DNA and RNA and ribosomes and synthesize some of their own proteins. They are thought to have evolved from endosymbiotic Gram negative bacteria and are considered to be "autonomous” organelles. (No one has ever been able to culture mitochondria free from their host cell. )

Chloroplasts are membrane bound photosynthetic organelles that are not seen in photosynthetic bacteria. Chloroplasts have their own DNA and RNA and ribosomes and are capable of synthesizing some of their own proteins. They are thought to have evolved from endosymbiotic photosynthetic cyanobacteria and are considered to be "autonomous organelles”. (But no one has ever been able to culture chloroplasts free from the host cell). Chloroplasts contain the chlorophyll that is found in plant cells and thus are responsible for the green color of leaves.

Other Components Found in Eukaryotic Cells - Cytoskeleton The cytoskeleton is a network of microfibers and microtubules that helps a eukaryotic cell to maintain its shape. - Phagolysosomes are membrane bound compartments that can enclose food particles or bacteria that can be digested by enzymes and oxidative chemicals that are pumped into this compartment. - Nuclear Membrane The nuclear membrane of a Eukaryotic cell keeps the transcription machinery separated from the translation machinery. THat is: m. RNA synthesis occurs in the nucleus but protein synthesis occurs in the cytoplasm that is outside of the nucleus. - sn. RNPs Small Nuclear Ribonucleic Acid-Protein particles are involved in the processing of m. RNA molecules in Eukaryotic cells

Phagolysosome 9/14/14 www. study blue. com

Some Terminology Word Parts Phago- : swallow cyto- : cell lyso- : break down, lyse, digest -osis : a condition of soma- : body Words Phagocyte - a cell that can swallow Phagocytosis - the process of a cell swallowing Phagolysosome – a membrane bound organelle or compartment in a eukaryotic cell in which a particle that has been engulfed by phagocytosis is digested 9/14/14

A eukaryotic flagellum is a long whip-like structure. Bacterial flagella are smaller and less complex than eukaryotic flagella. The diameter of a bacterial flagellum is about 20 nm whereas the diameter of a eukaryotic flagellum is about 200 nm. A bacterial flagellum consists of a single protein fiber that is not membrane bound. A eukaryotic flagellum usually has 11 protein fibers in a membrane bound structure. The whipping motion of a eukaryotic flagellum is mechanically much more sophisticated than the rotation of a bacterial flagellum.