Topic 2

• Primary Response

  1. B cells develop into plasma cells or memory cells

  2. Memory cells divide rapidly and produce larger numbers of memory and plasma cells when encountering the same antigen at a later date
• Humoral response

  1. A specific B cell with a complementary receptor binds to a specific antigen and is activated by chemicals released by TH cells

  2. The activated B cell divides rapidly to form plasma cells or memory cells

  3. Plasma cells secrete antibodies
• Phagocytosis

  1. Phagocytes recognise and bind to antigens on the pathogen

  2. Phagocytes engulf pathogens

  3. Pathogens are enclosed in a vacuole/vesicle

  4. Lysosomes containing lysozymes digest/destroy the pathogen by hydrolysis
• Facilitated diffusion


  Transport facilitated by intrinsic proteins (channel and carrier proteins) spanning the bilayer
• Cell-mediated response

  1. TH cells release chemicals to activate specific Cytotoxic T cells (Tc cells) and B cells

  2. Tc cells destroy infected body cells presenting the same antigen

  3. B cells divide rapidly to form plasma cells or memory cells
• Osmosis


  Passive transport of water across membranes
• Antigen


  A foreign/non-self protein (or glycoprotein) that stimulates an immune response / production of antibodies
• Secondary Response

  Memory cells divide rapidly and produce larger numbers of memory and plasma cells when encountering the same antigen at a later date
• Simple diffusion


  Transport of small, non-polar molecules across membranes
• Cotransport

  Transport of two substances simultaneously across membranes
• Active Transport


  Transport requiring energy to move molecules against their concentration gradient
• Prokaryotic cell division

  1. Replication of circular DNA, including plasmids

  2. Cell membrane grows between two main DNA loops, pinching inward to divide cytoplasm

  3. New cell wall forms between DNA loops, forming two daughter cells
• All cells arise from other cells
• Phospholipid bilayer


  • Barrier to large, polar molecules but permeable to small, non-polar ones
• Movement across cell membranes occurs by: Simple diffusion, facilitated diffusion, osmosis, active transport, or co-transport
• Viral replication

  Replicate by attaching to host cell, inject nucleic acid into host cell, produce viral components, assemble into new viruses
• Cell cycle

  1. Interphase: DNA replicates, protein synthesis occurs, increase in number of organelles, ATP production occurs

  2. Consists of G1, S, and G2 phases: G1 (Gap 1), S (DNA replication occurs), G2 (Gap 2)

  3. Mitosis: Prophase (Chromosomes condense/shorten, nuclear membrane breaks down), Metaphase (Chromosomes line up along equator of cell, attach to spindle fibre), Anaphase (Centromere divides, spindle fibres contract pulling apart chromatids), Telophase (Chromosomes uncoil, new nuclear membrane forms)

  4. Mitotic index = number of cells undergoing mitosis / Total number of cells
• Intrinsic proteins


  • Span the bilayer and used for transport
• Cancer results from mutations in genes that control cell division, causing rapid, uncontrolled growth and division of cells
• Extrinsic proteins

  • Attach to outer or inner part of bilayer, can function as enzymes, antigens (for cell recognition), or receptors (for cell signalling)
• Glycoproteins


  • Consist of carbohydrate bonded to a protein, act as antigens or receptors
• Glycolipids


  • Consist of carbohydrate bonded to a phospholipid, act as antigens and to attach cells together
• Movement of substances from higher concentration to lower concentration

  Occurs by simple diffusion, facilitated diffusion, osmosis, active transport, or co-transport
• Fluid-mosaic model of membrane structure

  Fluid because molecules can move around, Mosaic because there are different types of molecules embedded within the phospholipid bilayer
• Cholesterol


  • Restricts movement of other molecules in the membrane, reducing fluidity
• Diffusion of water across a partially permeable membrane

  Down a water potential gradient from higher to lower water potential
• Movement of two different substances at the same time using a carrier protein

  E.g. sodium ions and glucose enter epithelial cells in ileum by cotransport
• Cells may be adapted for rapid transport across their membranes by an increase in surface area or by an increase in the number of channel and carrier proteins
• Movement of substances against their concentration gradient

  Uses a carrier protein and ATP
• Transmission electron microscope

  • Electrons are transmitted through specimen or absorbed and blocked by stain
  • Provides 2D image and can see internal details with high resolution
• Magnification


  The number of times bigger the image appears compared to its actual size
• Methods of studying cells

  1. Microscopes

  2. Magnification

  3. Resolution

  4. Eyepiece

  5. Graticule

  6. Optical microscope

  7. Transmission electron microscope

  8. Scanning electron microscope
• Production of viral components

  Proteins are produced and assembled into new viruses
• Scanning electron microscope


  • Electrons are reflected and detected by scanners
  • Provides 3D image used to view surface
• Optical microscope


  • Uses light with long wavelength resulting in low resolution
  • Specimen should be thin to transmit light
  • Can view live specimens and get color image
  • Lower resolution compared to electron microscopes
• Resolution

  The minimum distance between 2 objects/points at which they can be seen as separate
• Cell fractionation

  1. Cells are broken open using a homogenizer to release organelles

  2. Cell debris and whole cells are filtered off

  3. Solution used should be ice cold, isotonic, and buffered

  4. Eyepiece graticule scale is used to measure objects under the microscope
• Prokaryotic cells have circular DNA, form new cells by binary fission, lack membrane-bound organelles, have a cell wall made of murein, and may have a capsule, flagella, and plasmids
• Ultracentrifugation

  1. Suspension is centrifuged to separate organelles based on density

  2. Nucleus separates out at the bottom, chloroplast and mitochondria are separated in subsequent spins

  3. Smaller organelles like ribosomes are separated in further spins
• Viruses have genetic material (DNA or RNA), a protein coat (capsid), attachment proteins to attach to host cells, and may have circular DNA not associated with protein and not in the nucleus