Lecture #3 Cell Biology PDF

Lecture #3 Cell Biology Textbook Chapter #4  Prokaryotes Pro means before and karyon means nucleus no nucleus DNA is not enclosed within a membrane Chromosome is single and circular Chromosome exists within a specific region of the cell called t...

Lecture #3 Cell Biology Textbook Chapter #4  Prokaryotes Pro means before and karyon means nucleus no nucleus DNA is not enclosed within a membrane Chromosome is single and circular Chromosome exists within a specific region of the cell called the nucleoid - They do not have membrane bound organelles such as mitochondria arche ↑ bacteria d Single-celled organisms only membrane bound Bacteria, archaea no organelles  Eukaryotes Eu means true and Karyon means nucleus - DNA is contained within a membrane bound nucleus DNA is arranged as multiple chromosomes Organelles are present and membrane bound Can be either single celled or multicellular Most eukaryotes are multicellular Includes: protists, fungi, plants, animals  Bacterial Morphology Morphology means shape Coccus (pleural: cocci) Bacillus (pleural: bacilli) Spirillum (pleural: Spirilla) Spherical Rods Spiral Ex: Streptococcus pyogenes Ex: Escherichia coli Ex: Treponema pallidum  External Structures Glycocalyx (sugar coat): Sugar coat Gelatinous, sticky polymer Can be composed of either polysaccharide, protein or both When it’s made only of sugar it’s called an extracellular polysaccharide Secreted from the prokaryote onto the outside of the cell wall Glycocalyx Capsule Slime Layer When the substance of the When the substance of the Glycocalyx is firmly attached Glycocalyx is disorganized and to the cell wall and organized only loosely attached to the cell wall  External Structures Capsules: Contribute to an organisms virulence (ability to cause disease) Does so by protecting the organism from phagocytosis Certain organisms such as Bacillus anthracis can only cause disease if they are encapsulated The capsule also allows the organism to adhere to and colonize host cells Also protects the bacterial cell against dehydration and holds nutrients inside of the cell  External Structures Capsules: Allow the bacterium to survive by attaching to different surfaces within the microbe’s environment This quality allows the bacterium to attach to other bacteria, medical devices such as implants and catheters, human teeth, plant roots and water pipes Example: Streptococcus mutans attaches to teeth and causes cavities Some organisms such as Streptococcus mutans may use their capsule as an energy source, breaking down the sugars when energy sources are low  External Structures Flagella: These are found on some prokaryotic cells They are long, filamentous and used for motility Composed of three primary parts: 1. Filament: composed of the circular flagellin protein forming a helix around a hollow core Is not covered by a sheath 2. Hook: made of different protein than the flagella 3. Basal body: anchors the flagellum to the plasma membrane and the cell wall  External Structures Flagellar Arrangements: 4 possible arrangements: 1. Peritrichous: flagella distributed over the entire cell surface 2. Monotrichous: single polar flagella 3. Lophotrichous: two or more flagella at one or both ends of the cell 4. Amphitrichous: a tuft of flagella at each cell end  Bacterial Motility Flagellar proteins are used to differentiate in between strains of different bacteria Example: E.coli 0157:H7 (the H7 is the type of flagellar protein) Flagella can rotate either clockwise or counterclockwise This flagellar movement depends on energy production  Bacterial Motility The bacterium is able to change direction and speed on its own Movement in one direction for a continuous period of time is called a run or a swim Abrupt or random changes in direction are called tumbles Results when the flagellum changes its direction of rotation Being motile allows the bacterium to move away from dangerous environments and toward favorable environments which is called taxis Movement toward a chemical stimulus is chemotaxis Movement toward a light stimulus is called phototaxis Bacteria move toward an attractant and away from a repellant  Pili and Fimbriae Found in many gram negative bacteria Hair like appendages that are shorter, thinner and straighter than flagella and are not used for motility Made of pilin protein Fimbriae: Bacterial cell can contain a few or hundreds Can be all over cell surface or only at the poles Enables the bacterial cell to adhere to surfaces and other bacterial cells Allow the bacterium to adhere and colonize, without fimbriae colonization cannot occur and thus disease does not occur Example: Neisseria gonorrhoeae  Pili and Fimbriae Pili (pilus-singular): Longer than fimbriae Only one or two per cell These filaments join two bacterial cells in order to transfer DNA in between them in a process called conjugation  Bacterial Cell Wall Semi-rigid, complex and semi- permeable Provides the cell with its characteristic shape Protects the cell from environmental changes Prevents cell rupture Important means of classifying bacteria Composed of the polysaccharide peptidoglycan  Peptidoglycan Polysaccharide composed of repeating disaccharides Polysaccharide chains are layered on top of one another Polysaccharide chains are linked together by short polypeptides This creates a lattice Creates a strong cell wall that is resistant to osmotic changes The disaccharide unit is composed of: N-acetyl glucosamine (NAG) N-acetyl muramic acid (NAM)  The Gram Positive Cell Wall Contains a thick layer of peptidoglycan outside of the plasma membrane Also contains teichoic acids which are only found in gram positive organisms 2 forms of Teichoic acids: 1. Wall teichoic acids: Extend out from the peptidoglycan 2. Lipoteichoic acids: Connect the plasma membrane to the peptidoglycan Gram positive bacteria have only one membrane: the plasma membrane  The Gram Negative Cell Wall Thin peptidoglycan layer Gram negative bacteria contain a plasma membrane and an outer membrane The outer membrane contains: Lipids (phospholipids) Proteins Lipopolysaccharides (LPS) Lipopolysaccharide Lipid Portion: Toxic Polysaccharide Portion: Referred to as Composed of O sugars endotoxin Used to distinguish gram negative organisms  The Gram Stain Gram positive cells contain thick peptidoglycan which holds the primary stain with crystal violet (appearing purple) Gram negative cells are not stained with crystal violet because the outer membrane is intact and is not penetrated by the dye The third step involves an alcohol wash which disrupts the outer membrane and washes away remaining crystal violet The last step adds safranin (counterstain) which is taken up by the peptidoglycan in gram negative cells which consequently appear pink  The Importance of Peptidoglycan Peptidoglycan is unique to bacteria Eukaryotes do not have a similar compound Peptidoglycan is a common target for both host defenses and chemotherapies Lysozyme is a host enzyme produced in saliva, tears and mucous which degrades peptidoglycan Many antibiotics are also active against peptidoglycan including Penicillin which targets peptidoglycan synthesis  The Plasma Membrane Composed of a classic phospholipid bilayer Provides a barrier in between the intracellular and extracellular environments Semi-permeable barrier: Selectively allows the inflow and outflow of materials Exists in a semi-fluid state: Fluid enough that membrane proteins are able to move and perform their function Solid enough to maintain cell shape **Alcohol disrupts the plasma membrane  Cytoplasm The material that is contained within the plasma membrane Composed of ~80% water Cytoplasm also contains many of the materials needed for life: Amino acids, carbohydrates, nucleotides Enzymes Inorganic ions (ex) iron Cytoplasm is aqueous but thick and semi-transparent Cytoplasm also contains the major cellular structures such as: The nucleoid: containing the cells genetic material Ribosomes inclusion bodies some bacteria may also have endospores within the cytoplasm  Nucleoid The nuclear area of the bacterium Contains the bacterial chromosome Contains all genetic information required for the cell’s structure and function Not surrounded by a nuclear membrane Bacteria may also have plasmids Small, usually circular double stranded DNA molecules These house non-essential genes which can help the bacterium to survive adverse conditions such as high antibiotic concentrations Ex) plasmids contain genes for antibiotic resistance  Ribosomes These are where protein synthesis occurs Made of protein and ribosomal RNA (rRNA) Consist of two subunits, a large subunit and a small subunit 50S subunit: large 30S subunit: small These two subunits come together to form a 70S ribosome  Ribosomes Ribosomes of prokaryotes are different than those of eukaryotes They both function in protein synthesis Eukaryotic ribosomes are larger and heavier (80S): the large subunit is 60S and the small subunit is 40S Several antibiotics target bacterial ribosomes because it is the perfect opportunity to execute selective toxicity relationship endosymbiotic Eukaryotic ribosomes are different and thus an antibiotic that targets ribosomes will not cause harm to host cells mitochondria was prokaryotic. Examples: Streptomycin, Erythromycin in we have prokaryotic bacteria - mitochondria inhibitors protein synthesis  Inclusion Bodies These are deposits of nutrient granules which are stored for later use Different bacterial species contain a variety of inclusion bodies which can therefore serve as a basis for identification Types of Inclusion Bodies include: Sulfur granules lates e Polysaccharide granulesJorganise Important energy sources Lipid inclusions Enzymes reactions  like a seed enclosed during Endospores dormant phase Only gram positive bacteria form endospores => purple These are special structures that allow the bacterium to resist heat, desication, chemicals and radiation The bacterium will remain dormant for long periods of time and will leave dormancy only when good growth conditions occur Spores are very resilient and some can even survive in boiling water for hours making them very difficult to get rid of Examples of spore forming bacteria include: Bacillus anthracis Clostridium botulinum - botox , paralytic  Sporulation 1) The bacterial cell replicates its DNA 2 copies of CHRS 2) A septum forms dividing the cell 3) The larger compartment engulfs the smaller one forming a forespore within the mother cell forms 2 membranes 4) Peptidoglycan and other protective material forms around the forespore (the spore coat) 5) The spore is freed from the mother vegetative articlea cell -  Eukaryotic Cells This group of cells includes both unicellular organisms and multicellular organisms These cells are larger and more complex than Prokaryotes Simple Eukaryotes Higher Eukaryotes Protozoa: Fungi: Unicellular Multicellular except yeasts Plants Animals Algae: Some are unicellular and some are multicellular  Eukaryotic Flagella and Cilia These are long and flexible They also contain protein and cytoplasm Prokaryotes have hollow flagella and cilia These move in a whip-like fashion Prokaryotes move in a cork screw motion Both cilia and flagella are used for motility  Eukaryotic Cell Wall Not present in animal cells Structurally simple compared to peptidoglycan of bacteria & Composed of a single polysaccharide Cellulose: algae and plants Chitin: fungi  Eukaryotic Plasma Membrane Same basic structure as prokaryotic cells Contains phospholipids, proteins and sterols Prokaryotes do not have sterols in their plasma membrane, as a result the Eukaryotic plasma membrane is more rigid than that of bacteria Eukaryotes are often capable of endocytosis Engulfs particles outside of the cell and brings them inside membrane. in plasma cholesterol  Eukaryotic Cytoplasm This is similar to that found in prokaryotes but there are a few key differences This is located within the boundary of the plasma membrane but outside of the nuclear membrane The cytoplasm has a complex internal structure called a cytoskeleton which: Provides support and shape to the cell Acts to transport substances through the cell Composed of protein filaments on the inside of the plasma membrane  Membrane Bound Organelles These structures are absent in bacteria They are structures with specialized functions Examples of membrane bound organelles include: Nucleus: contains the genetic material Mitochondria: powerhouse of the cell, site of ATP synthesis3 Chloroplasts: site of photosynthesis, found in plants and algae only