Bacterial Anatomy/Genetics/Growth Flashcards
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.
Describe flagella
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.
