Cell Structure & Taxonomy

• Cell - fundamental living unit of any organism
• Metabolism - refers to all of the chemical reactions that occur within a cell.
• Mutation -accidental changes in the genetical material of cells.
• Cells Classification

  Prokaryotes and Eukaryotes
• Prokaryotes - do not have complex system of membranes and organelles; bacteria and archaea
• Eukaryotes - more complex cells, containing true nucleus.
• Cell Membrane - Enclosed and keep the cell intact; Composed of large molecules of proteins and phospholipids; Like a “skin”; Regulates passage of substances in and out; Selective permeability
• Cytoplasm - semi-fluid, gelatinous nutrient matrix; contains the “organelles”
• Nucleus Components

  Nucleoplasm, Nuclear Membrane, Chromosomes, Nucleolus
• Nucleus - command center or what controls the functions of the entire cell.
• Nucleoplasm – gelatinous matrix or base material of the nucleus
• Nuclear membrane – “skin” around the nucleus, contains holes
• Chromosomes – consist of linear DNA molecules where GENES are located
• Endoplasmic Reticulum - Highly convoluted system of membranes that are interconnected to form a transport network tubules and flattened sacs within the cytoplasm.
• Ribosomes - 18 to 22 nm in diameter; consists of rRNA; play important part in protein synthesis
• Golgi Apparatus - Packages newly synthesized proteins into small, membrane-enclosed vesicles for storage within the cellar export outside the cell (exocytosis).
• Lysosomes - –contain lysozyme and other digestive enzymes that break down foreign material taken in by the cell
• Peroxisomes - where hydrogen peroxide is both generated and broken down
• Mitochondria - Where most of the ATP (energy carrying molecules) are formed by cellular respiration
• Plastids - Contains various photosynthetic pigments
• Chloroplasts – one type of plastid, contain a green, photosynthetic pigment called chlorophyll
• Cytoskeleton - system of fibers present throughout the cytoplasm; Strengthen, support and stiffen the cell, giving its shape.
• Microtubules - slender, hallow tubules (tubulins)
• Microfilaments – Slender, thread-like contractile structures which facilitate cell contraction
• Cell Wall - External structures that provide rigidity, shape, and protection.
• Cellulose -polysaccharide, present in algae and plants
• Chitin - present in fungi and exoskeleton of arthropods
• Flagella – relatively long, thin structure, the organelle of locomotion.
• Cilia - tend to be more shorter (hair-like), thinner and more numerous
• Prokaryotic Cell Structure

  Chromosome (Bacterial Nucleoid) - Consists of a single, long, super coiled, circular DNA molecule; Serves as the control center of the bacterial cell.
• Prokaryotic Cell Structure

  Plasmid - Small, circular molecules of double-stranded DNA that are not part of the chromosome; Extrachromosomal DNA; May contain 10 to hundred genes; May or may not be present in bacterial cell.
• Cytoplasmic Particles - Many tiny particle in the bacterial cytoplasm; Most of these are clusters of ribosomes-polyribosomes or polysomes
• Bacterial Cell Wall (Prokaryotic) - Rigid exterior cell wall that defines the shape of bacteria.
• Bacterial Cell Wall

  Consist of a complex macromolecule known as Peptidoglycan (murein) – only found in bacteria
• Gram positive bacteria - thick layer
• Gram negative bacteria- thinner layer
• Gram Stain - The most widely used procedure for staining bacteria; Developed over a century ago by Dr. Hans Christian Gram
• Steps in Staining

  1. Crystal Violet
  2. Iodine (Mordant)
  3. Alcohol (Decolorizer)
  4. Safranin (Counterstain)
• Glycocalyx - Slimy, gelatinous material produced by the cell membrane and secreted outside the cell wall.
• SLIME LAYER- not highly organized and is not firmly attached to the cell wall. Enables certain bacteria to glide along solid surfaces