Cell biology

• Cell Theory


  • All living things are made up of cells
  • Cells are the smallest working units of all living things
  • All cells come from preexisting cells through cell division
• Cell


  The smallest unit that is capable of performing life functions
• Prokaryotic cell


  • Surrounded by cell wall and cell membrane
  • Do not have structures surrounded by membranes
  • Few internal structures
  • One-celled organisms, Bacteria
  • Contains circular DNA
• Eukaryotic cell


  • Contain organelles surrounded by membranes
  • Contain membrane bound nucleus
  • Most living organisms
  • Linear DNA which is wrapped around Histones
• Plant Cell


  • Cell wall
  • Plasma membrane
• Animal Cell


  • Plasma membrane
• Cell Membrane


  • Outer membrane of cell that controls movement in and out of the cell
  • Double layer
• Cell Wall


  • Most commonly found in plant cells & bacteria
  • Supports & protects cells
• Nucleus


  • Directs cell activities
  • Separated from cytoplasm by nuclear membrane
  • Contains genetic material – DNA (chromatin)
  • Site for DNA replication and RNA synthesis
  • Nucleolus is found inside nucleus, it contains RNA to build proteins
• Nuclear Membrane


  • Surrounds nucleus
  • Made of two layers
  • Openings allow material to enter and leave nucleus
• Mitochondria


  • Produces energy through chemical reactions – breaking down fats & carbohydrates
  • Controls level of water and other materials in cell
  • May be as few as 100 and can reach 1000 depending on the activity inside the cell
• Mitochondrial DNA is the DNA located in mitochondria
• Endoplasmic Reticulum


  • Interconnected network of tubules and cisternae and extending from the nucleus
  • Rough type: ribosomes embedded in surface - site of synthesis of many proteins
  • Smooth type: lacks ribosomes - site for synthesis of steroids and other lipids, Ca++ storage in muscles, detoxification of drugs, toxins, alcohol (especially in liver)
  • The highly convoluted surface provides a large surface area for enzymatic activity
  • Many enzymes are imbedded in the membranes
• Golgi Apparatus


  • A collection of membranes associated with the ER composed of flatten sacs
  • Concentrates and packages proteins synthesized on the ER
• Lysosome


  • Membrane-enclosed organelles that contain an array of enzymes capable of breaking down all types of biological polymers—proteins, nucleic acids, carbohydrates, and lipids
  • Function as the digestive system of the cell, serving both to degrade material taken up from outside the cell and to digest obsolete components of the cell itself
• Vacuoles


  • Membrane-bound sacs for storage, digestion, and waste removal
  • Contains water solution
  • Help plants maintain shape
• Chloroplasts


  • Sites of photosynthesis – in nearly all plants
  • Trap light energy and convert it into chemical energy
  • The light energy trapping molecules of photosynthesis are found in the membranes of the thylakoids
• Animal cell vs Plant cell

  • Both possess nucleus, rough and smooth endoplasmic reticulum, mitochondria, Golgi bodies and free ribosomes
  • Plant cells have a large central vacuole, unlike animal cells
• Crystals produced by plants are the final products of cellular metabolic processes, which usually are deposited in vacuoles and cytoplasm
• Types of crystals present in plant cell

  • Raphides
  • Druses
  • Prisms
  • Crystal sand
• Druse


  A group of crystals of calcium oxalate or calcium carbonates present in plants
• Functions of Calcium oxalate crystals


  • Act as a storage reservoir for calcium
  • Provide for the storage of toxic waste (detoxification)
  • Serve as protection against herbivory
• Vacuoles


  Membrane-bound sacs within the cytoplasm of a cell, important for structural support, storage, waste disposal, protection, and growth
• Many plant cells have a large, single central vacuole
• Vacuoles in animal cells tend to be much smaller, and are more commonly used to temporarily store materials
• Tonoplast


  The membrane that encloses the central vacuole in plant cells
• Functions of central vacuoles in plant cells

  • Contain cell sap, a concentrated solution of sugars, mineral salts, nutrients, proteins, pigments, helps in plant growth
  • Contain plant wastes that taste bitter to insects and animals for discouraging them from consuming the plant
• Osmosis


  The spontaneous passage or diffusion of water or other solvents from a solution of low concentration to a solution of high concentration through a semipermeable membrane
• Osmotic pressure


  The pressure required to stop water from diffusing through a membrane by osmosis, determined by the concentration of the solute
• Turgor pressure


  The difference between the osmotic pressure inside and outside of the cell, determines the rigidity of the plant cell
• Adequate water supply


  Central vacuoles swell, creating high turgor pressure, maintaining structural integrity of the plant
• Inadequate water supply


  Central vacuoles shrink, reducing turgor pressure, leading to wilting
• Osmosis function in cells

  • Allows transport of nutrients into the cell and waste materials out of the cell
• Osmosis function in maintaining cell structure


  • Maintains normal cell shape in isotonic conditions
  • Causes cell shrinkage in hypertonic conditions
  • Causes cell swelling in hypotonic conditions
• Osmoregulation is the physiological process by which animals regulate the concentration of solutes and the balance of water in their body fluids
• Clinical aspects of osmotic imbalance in animals

  • Dehydration
  • Edema
  • Renal disorders
• The cell membrane is composed of phospholipids, cholesterol, proteins, and carbohydrates.
• Phospholipids are amphiphilic molecules with hydrophobic tails and hydrophilic heads that form the bilayer structure of the cell membrane.
• Cholesterol helps maintain fluidity and stability of the membrane by interacting with phospholipid tails.
• Linear DNA


  Genetic material present in the nucleus of eukaryotic cells, organized into chromosomes and made up of DNA coiled around histone proteins. Contains instructions for development and function of the organism.