What are the 4 processes of life?
Growth, Reproduction, Responsiveness and Metabolism
What are the characteristics of prokaryotic cells?
DNA is not enclosed within a membrane and is one circular chromosome. DNA is not associated with histones. Lack membrane-enclosed organelles. Cell wall contains the complex polysaccharide peptidoglycan. Divides by binary fission.
What are the characteristics of eukaryotic cells?
DNA is found within the nucleus. DNA is associated with chromosomal proteins called histones. They have a number of membrane-enclosed organelles. Cell walls are chemically simple. Divide by mitosis.
What are the three common morphologies of bacteria?
Cocci are round but sometimes oval. Cocci that divide but stay attached are diplococci. Cocci that divides and remains in a chainlike pattern is streptococci.
Baccili are rod like in appearance. Diplobacilli appear in pairs after division. Streptobacilli occur in chains.
Spiral bacteria have one or more twists and are never straight.
What are the 5 structures external to the cell wall?
Glycocalyx, Flagella, Axial Filament, Fimbria, Pili
Describe the glycocalyx.
A sugar coat that surrounds the cell. It is viscous (sticky). If the substance is organized and firmly attached to the cell wall it is called a capsule. If it is unorganized and loosely attached, it is called a slime layer.
Flagella are long filamentous appendages that propel bacteria. They can be monotrichous (single flagellum). Amphitrichous (single flagellum at each end). Lophotrichous (two or more flagella at one pole). Peritrichous (Flagella distrubuted over the entire cell). The three parts of the flagella is the filament, hook and rod.
What are axial filaments?
Axial filaments are bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell. Spirochetes are a group of bacteria that have axial filaments.
What are fimbriae?
Fimbriae occur at the poles of bacterial cells or can be evenly distributed over the entire surface of the cell. The fimbriae allows the cell to adhere to surfaces including the surfaces of other cells.
What are pili?
Pili are usually longer than fimbriae and number only one to ten per cell. Pili join in preparation for the transfer of DNA from one cell to another. Can be referred to as sex pili.
What are the major functions of the cell wall?
- Prevents cells from rupturing when the water pressure inside the cell is great than the outside the cell. 2. Helps maintain the shape of the bacterium. 3. Serves as a point of anchorage for flagella.
Describe the composition and characteristics of the cell wall.
The cell wall is composed of a macromolecular network called peptidoglycans.
What are the characteristics of gram positive cells?
Gram positive cells contain a thick later of peptidoglycan. They contain teichoic acids. These acids are covalently linked to lipids forming lipoteichoic acids that anchor the peiptidoglycan to the cell wall.
Describe gram negative cells.
Gram negative cells have a thin layer of peptidoglycan. The inner layer of the outer membrane is composed of phospholipids and proteins. The outer leaflet of the outer layer is composed of lipopolysaccharides. These cells do not contain teichoic acids. The outer layer has a strong negative charge which helps evade phagocytes. It also provides a barrier against certain antibiotics.
What is an endospore?
An endospore is a special resistant, dormant structure formed within a cell that protects a bacterium from adverse environmental conditions. The Schaeffer-Fulton endospore stain is the most common stain used to identify endospores.
Give examples of atypical cell walls.
Mycoplasma has no cell walls or very little wall material. They are the smallest known bacteria that can grow and reproduce outside the living host cells.
Archaea are cells containing a variety of specialized polysaccharides and proteins but no peptidoglycan. However, they contain pseudomurein which replaces the peptidoglycan.
How can cell walls become damaged?
A cell wall can be damaged by exposure to the digestive enzyme lysozyme.
If a cell does not lyse and the cellular content remains surrounded by the plasma membrane, it may remain intact. This is called a protoplast.
For lysozyme to exert its effect on gram negative cells, the cells are first treated with EDTA.
Describe the plasma membrane.
The plasma membrane is a thing structure lying inside the cell wall and encloses the cytoplasm of the cell. Prokaryotic cells are incapable of endocytosis and exocytosis.
The plasma membrane is a double-layered structure. The phospholipids are arranged in two parallel rows called a phospholipid bilayer.
The phosphate heads of each phospholipid is hydrophilic which means they are attracted to water. The tails are composed of fatty acids that are hydrophobic and are insoluble in water.
Extrinsic proteins lie at the inner or outer surface of the plasma membrane. Intrinsic proteins are located between the phospholipid bilayer.
Describe the functions of the plasma membrane.
The most important function of the plasma membrane is as a selective battier which material enter and exit the cell. Plasma membranes are said to be selectively permeable.
How does material move across the plasma membrane?
In passive transport, substances cross the membrane from high concentration to low concentration.
In active transport, the cell must use ATP to move substances from low concentration to high concentration.
Describe simple diffusion.
Simple diffusion is the net movement of molecules or ions from an area of high concentration to low concentration until a state of equilibrium has been established.
Describe facilitated diffusion.
Similar to simple diffusion but the substance being transported combines with a plasma membrane protein called a transporter.
Some molecules are too big and need to be broken down by enzymes before transport. These enzymes are called extracellular enzymes.
What is osmosis?
Osmosis is the movement of water across a selectively permeable membrane from an area of greater concentration to an area of lesser concentration .
What is an isotonic solution?
A medium which the overall concentration of solutes is equal within the cell and the solution.
What is an hypotonic solution?
A solution where the concentration of solutes is lower than inside the cell. Cells with weak cell wall may burst as a result of excessive water intake.
What is an hypertonic solution?
A solution where the concentration of solutes is higher than inside the cell. Can cause the cell the shrink because water leaves the cell by osmosis.
What is group translocation?
Occurs exclusively in prokaryotes. The substance being transported is chemically altered during transport across the membrane. Once is is inside the cell, the plasma membrane is impermeable to it, so it remains in the cell.
Describe the cytoplasm.
The substance of the cell inside the plasma membrane. It is 80% water and contains proteins, carbohydrates, lipids, inorganic ions and other compounds.
What are the major structures of the cytoplasm?
- nuclear area. 2. Ribosomes. 3. Inclusions.
Describe the nuclear area of the cytoplasm.
Contains the single long, continuous arranged thread of double-stranded DNA called the bacterial chromosome.
Also contains small circular, double stranded DNA molecules called plasmids. They are not connected to the main bacterial chromosome and replicate independently of chromosomal DNA.
Describe ribosomes of the cytoplasm.
Functions as the site of protein synthesis. Composed of two subunits which consists of protein and ribosomal RNA (rRNA).
Prokaryotic ribosomes are called 70S and eukaryotic ribosomes are called 80S. S is for Svedberg unit which indicated the relative rate of sedimentation during high speed centrifugation.
What are inclusions?
Reserve deposits within a cell that are used when a certain nutrient becomes deficient.
What is a metachromatic granule?
Large inclusions that stain red with blue dyes such as methylene blue. They are a reserve of inorganic phosphate that can be used to synthesize ATP.
What are polysaccharide granules?
Typically consists of glycogen and starch. Presence can be demonstrated when iodine is applied to the cell. Glycogen appears reddish brown and starch granules appear blue.
What are sulfur granules?
A type of bacteria referred to as “sulfur bacteria” that derive their energy by oxidizing sulfur. and sulfur-containing compounds. The granules serve as an energy source.
What are carboxysomes?
Inclusions that contain the enzyme ribulose 1.5-diphosphate carboxylase. Bacteria the use carbon dioxide as their sole source of carbon require this enzyme for carbon dioxide fixation during photosynthesis.
What are gas vacuoles?
Hollow cavities found within aquatic prokaryotes that helps to maintain buoyancy so that cells can remain at the appropriate depth to receive sufficient amounts of oxygen, light and nutrients.
What are magnetosomes?
Inclusions of iron oxide that act like little magnets. Used to move downward until they reach a suitable attachment site. Can decompose hydrogen peroxide inside the cell.
What are endospores?
Highly durable dehydrated cells with thick walls. Can survive in extreme heat, lack of water and exposure to toxic chemicals and radiation.
What is sporulation or sporogenesis?
The process of endospore formation within a vegetative cell. Takes several hours. Returns to its vegetative state by germination.
What are the 3 parts of genetics?
The genetic information of a cell is called the genome. Chromosomes are structures containing the DNA that physically carries hereditary information. Genes are segments of DNA that code for function.
Define simple mutations.
a simple mutation may account for some variability but it is rare for a single point of mutation to change an organism in a helpful manner.
What is a missense mutation?
A genetic change involving the substitution of one base in the DNA for another.
Genes are transferred fro one bacterium to another as “naked” DNA. The recipient must be competent in order to accept the “naked” DNA.
A virus infects bacteria,, called a bacteriophage and carries a piece of bacterial DNA from one bacterium to another.
Describe the two types of bacteriophages.
Virulent phages infect the bacteria and reproduce inside the bacteria leading to lysis.
Temperate phages do not immediately lyse the bacteria they infect. It incorporates itself into the bacterial chromosome and awaits activation. Bacteria with this prophage are called lysogenic.
What is lysogenic immunity?
An immunity that blocks subsequent infection by a similar phage.
What is generalized transduction?
The process by which a virulent phage infects a cell.
What is specialized transduction?
The process by which temperate phage infects a cell.
What is the significance of transduction?
Transfers genetic material from one cell to another and alters the genetic characteristics of the recipient cell. The incorporation of a phage demonstrates a close evolutionary relationship. Suggest a possible mechanism of cancer.
What is chromosome mapping?
The study of different phage transduction. The findings of these studies may allow identification of the sequence of genes in a chromosome.
Direct cell-by-cell contact that results in an efficient exchange of genetic information. Can occur between unrelated bacteria. Is a major mechanism for transfer of antibiotic resistance.
How does conjugation happen?
One bacterium must have a self-transmissible plasmid, also called an F (fertility) plasmid. Plasmids are transmitted via a sex pilus.
What is the significance of plasmids?
Certain plasmids encode enzymes that degrade antibiotics.
What are transposons?
Segments of DNA that transpose themselves from one location in a DNA molecule to another location in the same or different molecule. The result of transposon is transposition.
What is the clinical significance of transposons?
Transposon genes that confers a particular drug resistance can move to the plasmids of different bacteria, resulting in the rapid spread of resistant strains.
What are the physical requirements for microbial growth?
Temperature, pH Level and osmotic pressure.
What are the three primary groups for temperature?
psychophiles (cold-loving microbes), mesophiles (moderate-temperature loving microbes), thermophiles (heat-loving microbes)
What is a psychrotroph?
A organism group that grows at a higher optimum temperature than psychophiles. They are more common and ususally encountered in low-temperature food spoilage because they grow well in refrigerator temperatures.
The most common type of microbe. Has an optimum growth temperature of 25 to 40 degrees celsius.
What is the optimum temperature for many pathogens?
37 degrees celsius.
What range of pH do most bacteria grow?
Between pH 6.5 and 7.5
What are acidophiles?
Bacteria that can grow in acidic environments.
What are the different types of halophiles?
Extreme/obligate halophiles (require salt for growth), Facultative halophiles (Do not require high salt concentrations but are able to grow at sale concentrations up to 2%)
What chemical requirements are there for microbial growth?
Carbon, Nitrogen, Sulfur, Phosphorus, Trace elements.
What is nitrogen fixation?
When some important bacteria use gaseous nitrogen directly from the atmosphere.
What are the two types of aerobes?
Obligate aerobes (requires oxygen to live), facultative anaerobes (bacteria that can grow in the absence of oxygen)
How can organisms be harmed by oxygen?
Singlet oxygen and superoxide free radicals (O2-) are toxic. Superoxide radicals must be neutralized by the enzyme superoxide dismutase. Peroxide anion is toxic and broken down by catalase and peroxidase.
What are aerotolerant anaerobes?
Bacteria that cannot use oxygen for growth but tolerate it fairly well.
What are microaerophiles?
Bacteria that is aerobic but does not require oxygen.
How do we preserve microbial cultures for long periods of time?
Deep freezing and lyophilization (freeze-drying)
Deep freeze places microbes in -50 to -96 celsius.
Lyophilization places them in -54 to -72 Celsius.
What are the steps of binary fission?
Cell replicates its chromosomes. The cell elongates and growth between attachment sites pushes the chromosomes apart. The cell forms a new cytoplasmic membrane and wall across the midline. When the septum is completed, the daughter cells may remain attached or they may separate completely.