topic 2

• Optical light microscope


  • Uses visible light through a system of lenses
  • A stain is used to differentiate between cells and components
  • An eyepiece graticule and stage micrometre are used to measure the actual size of a sample
  • It has low resolution and low magnification
• Transmission electron microscope


  • It transmits a beans of fast travelling electrons through a sample
  • The sample must be dead as it will be put in an electron vacuum
  • As the electrons pass through the sample, they scatter by electrostatic potential
  • It produces a 2D black and white image
  • Darker areas are denser and lighter areas are thinner
  • It has high resolution and magnification
• Scanning electron microscope


  • It produces a 3D black and white image
  • It has a lower resolution and magnification than TEM
  • It uses an electron vacuum so all samples must be dead
• Cell fractionation


  1. Place the tissue in a cold, buffered solution with the same water potential as the cells

  2. Cells are broken up by a homogeniser, releasing organelles from the cell, producing homogenate

  3. Homogenate is filtered to remove complete cells and debris

  4. Ultracentrifugation is when fragments are separated in a centrifuge which spins the filtrate at a high speed
• Eukaryotic cell


  • Humans are made up of eukaryotic cells
  • All eukaryotic cells contain a nucleus and membrane bound organelles
• Nucleus


  • Contains the cells hereditary information and controls the cells growth and reproduction
  • It regulates gene expression and suppression
  • It contains chromatin in the nucleoplasm which can become chromosomes. It consists of DNA strings
• Mitochondria


  • The site of aerobic respiration in eukaryotic cells
  • It synthesises ATP
  • It contains ribosomes, granules, and mitochondrial DNA
• Cell wall


  • A rigid structure that is made of cellulose in plants
  • It surrounds the plasma membrane of plants cells and provides strength and protection against mechanical and osmotic stress
  • It maintains the shape of the cell and provides protection against pathogens
• Vacuole


  • A membranous sac which stores water, nutrients and waste material of the cell
  • They store waste products to prevent the cell from becoming contaminated
• Ribosome


  • They are made of a small and large unit
  • They contain enzymes that control metabolic reactions
  • They synthesise proteins from mRNA during translation
• Lysosome


  • A type of Golgi vesicle that contains lysozymes, which are hydrolytic enzymes
  • Lysozymes are responsible for digesting invasive cells
• Rough endoplasmic reticulum


  • A network of channel-like structures filled with fluid
  • It is attached to the nuclear membrane
  • It has ribosomes attached along its outer surface
  • It processes and produces 3D protein structures
• Smooth endoplasmic reticulum


  • It is responsible for storing, synthesising, and processing lipids, phospholipids and cholesterol
  • It stores calcium ions within skeletal muscle cells
  • It is where carbohydrates are made
• Chloroplast


  • It has a double membrane that surrounds the gel like stroma
  • Thylakoids are sacs whose membranes contain photosynthetic pigments
• Prokaryotic cell


  • Prokaryotic cells are simpler and smaller than eukaryotic cells
  • They don't have a nucleus and do not contain membrane bound organelles
  • They contain smaller ribosomes
  • Their cell wall is made of murein
  • They are surrounded by a slim capsule
  • Some have flagella
  • Bacterial cell walls are made of peptidoglycan
  • Not all bacteria have a flagellum, pili, or capsule
• Binary fission


  1. The nucleoid replicates once

  2. Plasmids replicate multiple times

  3. The cell size increases, and DNA moves to the opposite poles

  4. The cytoplasm and membrane divide

  5. A new cell wall forms and 2 daughter cells are produced

  6. Each daughter cell contains 1 nucleoid and multiple plasmids
• Stages of the cell cycle

  • Mitosis
  • Interphase
  • Cytokinesis
• Mitosis


  1. Prophase: The chromosomes condense and become visible. Spindle fibres appear from the centrosome. The nuclear envelope breaks down.

  2. Metaphase: the spindle fibres extend from the centrosomes and attach to the centromeres of chromosomes that are lined up on the equator.

  3. Anaphase: the spindle fibres contract, pulling the sister chromatids away from the centromere and to opposite poles.

  4. Telophase: the chromatids arrive at opposite poles and de-condense. The nuclear envelope reforms around each set of chromosomes and spindle fibres break down.
• Biological membranes


  • All cells and organelles are surrounded by a partially permeable membrane composed of a phospholipid bilayer embedded with proteins
  • The main function of the membrane is to control the movement of substances in and out of the cell or organelle
  • The membrane contains receptors for other molecules such as hormones and enables adjacent cells to stick together
• Phospholipid bilayer


  • Phospholipids are amphipathic molecules, with hydrophilic and hydrophobic parts
  • When phospholipids are exposed to water, they form a bilayer
  • This structure allows lipid soluble molecules to pass through, but not water-soluble molecules
  • Charged or polar ions cannot cross the membrane
• Membrane components


  • Integral proteins are found throughout the membrane
  • Intrinsic proteins span the entire membrane. These include carrier and channel proteins which allow substances to cross the membrane. They aid movement across the membrane and provide support.
  • Extrinsic proteins do not span the entire membrane.
  • Cholesterol increases membrane rigidity and reduces later movement of phospholipids. It also prevents water leakage as its hydrophobic.
  • Glycolipids act as cell surface receptors. They allow cells to adhere to another to form tissues.
  • Glycoproteins are carbohydrates attached to extrinsic proteins. They act as cell surface receptors and neurotransmitters.
• Diffusion


  The passive movement of small, non-polar, lipid soluble molecules from an area of high concentration to low concentration. These molecules move directly through the phospholipid bilayer. These molecules include carbon dioxide and oxygen.
• Facilitated diffusion


  Requires channel proteins in the cell membrane to transport polar and water-soluble molecules across the membrane.
• Osmosis


  The net movement of water molecules from an area of high-water potential to an area of low water potential.
• Active transport


  The movement of all molecules through carrier proteins from an area of low concentration to high concentration. This process requires ATP.
• Co-transport and absorption of glucose in the ileum


  The movement of ions to an area of high concentration. When the ions move back to the area of low concentration, it is through a co-transporter protein, bringing an amino acid of glucose molecule.
• Defence mechanisms


  • Organisms have physical and chemical defence mechanisms against pathogens
  • Physical barriers include the skin
  • Chemical barriers include hydrochloric acid in the stomach
• Phagocytosis


  • This can be a specific or non-specific immune response
  • It is the proc
• Simple diffusion


  Molecules move directly through the phospholipid bilayer, including carbon dioxide and oxygen
• Facilitated diffusion


  Requires channel proteins in the cell membrane to transport polar and water-soluble molecules across the membrane
• Osmosis


  The net movement of water molecules from an area of high-water potential to an area of low water potential
• Active transport


  The movement of all molecules through carrier proteins from an area of low concentration to high concentration, requiring ATP
• Co-transport and absorption of glucose in the ileum

  1. The movement of ions to an area of high concentration

  2. When the ions move back to the area of low concentration, it is through a co-transporter protein, bringing an amino acid or glucose molecule
• Defence mechanisms


  • Physical barriers (e.g. skin)
  • Chemical barriers (e.g. hydrochloric acid in the stomach)
• Phagocytosis


  A specific or non-specific immune response where phagocytes engulf pathogens via endocytosis
• Phagocytes


  • Free-living, single-celled organisms (e.g. amoeba)
  • Body cells (e.g. white blood cells)
• Neutrophils


  Phagocytes that engulf pathogens but do not present their antigens, the most common and motile type of phagocyte
• Phagocytosis process


  1. Pathogen produces chemicals that attract neutrophils by chemotaxis

  2. Antigens on pathogen bind to receptors on phagocyte

  3. Phagocyte engulfs pathogen into a phagosome

  4. Lysosomes fuse with phagosome, forming phagolysosome

  5. Hydrolytic enzymes in phagolysosome break down pathogen

  6. If phagocyte was a neutrophil, no antigens are presented

  7. If phagocyte was a macrophage, antigens are presented on its surface
• T helper cells


  Found in the lymphatic system, specifically in lymph nodes, with different CD4 receptors specific to different pathogen antigens
• Immune response


  1. Macrophage secretes interleukin 1, attracting T helper cells

  2. Clonal selection occurs when complimentary T helper cell is located

  3. T helper cell binds to macrophage