Cell structure

• Describe the method for cell fractionation and ultracentrifugation

  • Cells are first broke open by homogenising the tissue in an ice-cold, isotonic buffer solution using a blender
  • Homogenate is then centrifuged at a low speed and the densest organelle i.e. nuclei forms a pellet at the bottom of tube
  • The supernatant (the liquid above the pellet) can be spun faster for a longer period of time to isolate the other organelles
• What are the requirements for optical microscope specimens?

  • Be thin - so light can pass through the specimen and a single layer of cells are visible
  • Be stained - so that the structures are visible
• What does a typical prokaryotic cell contain?

  • Cell wall
  • Cell surface membrane
  • Free circular DNA molecule in cytoplasm
  • Ribosomes
  • Cytoplasm
  • Capsule surrounding the cell wall
  • One or more plasmids
  • One or more flagella
• Describe the structure of viral particles

  Viruses are acellular and non-living

  • Genetic material (DNA/RNA)
  • Capsid (protein coat)
  • Attachment proteins
• Describe the structure and function of smooth endoplasmic reticulum

  Lacks proteins and is involved in the production and transport of lipids
• Why do we need to homogenise cells in ice cold, isotonic buffer solution during ultra centrifugation?

  • Isotonic = prevents osmotic movement of water into/out of the organelles which can cause them to burst/shrivel
  • Ice-cold = prevents the action of enzymes in the cell that may cause self-digestion (or autolysis) of organelles
  • Buffer solution = maintains ph so that enzymes do not denature
• compare prokaryotic and eukaryotic cells

  prokaryotic cells

  • no nucleus present
  • no membrane bound organelles
  • smaller 70s ribosomes
  • circular DNA
  • murein cell wall

  Eukaryotic cells

  • nucleus present
  • membrane bound organelles
  • larger ribosomes
  • linear DNA
  • cell wall does not contain murein
• Describe the structure and function of rough endoplasmic reticulum

  • Their surface has ribosomes that produce secretory proteins i.e. proteins released out of cell
  • These secretory proteins are sent to Golgi apparatus for modification and/or packaging
• Describe the several functions of the Golgi apparatus

  • Adds carbohydrates to proteins received from RER to form glycoproteins
  • Packages proteins/glycoproteins into Golgi vesicles (sacks) for secretion
  • Produces lysosomes - a Golgi vesicle that releases lysozymes (hydrolytic enzymes)
• Describe the structure and function of ribosomes

  • Made of proteins and ribosomal RNA
  • Used in protein synthesis to join together amino acids
• Describe the functions of the features present only in plant cells

  • Cell wall = provides support, strength and shape to the cell
  • Chloroplasts = contains chlorophyll which absorbs light energy for photosynthesis
  • Large vacuole = contains soluble sugars, salts and pigment
• Describe the functions of lysosomes

  • Digestion of material taken in by phagocytosis
  • Non-functioning organelles within the cell are engulfed and digested within lysosomes
  • Releases enzymes outside of the cell
• Describe the structure and function of the nucleus

  • Nucleus contains histones (protein), linear DNA and one or more RNA / nucleoli
  • Nucleus controls protein synthesis and thus the development and function of a cell
• Describe the arrangement of specialised cells

  • Tissues = group of similar specialised cells  that perform a specific function and have a common origin
  • Organs = structure that consists of different tissues which has a specific function e.g. stomach which has a role in the digestion of food
  • Organ system = consists of two or more organs e.g. stomach, liver and pancreas all form the digestive system
• Describe how SEM (Scanning electron microscope) works

  • Specimen is coated with a thin film of heavy metal e.g. gold
  • Electron beam is scanned to and across the specimen
  • Electrons that are reflected from the surface are collected and produce an image on a viewing screen
• What is the order in which cell organelles are isolated during this process?

  • Nuclei
  • Chloroplasts (if this is a plant cell)
  • Mitochondria
  • Endoplasmic reticulum
  • Ribosomes
• Describe how TEM (Transmission electron microscope) works

  • Beam of electrons are transmitted through the specimen
  • Specimen must be stained with electron dense substances such as heavy metal salts
  • These substances deflect the electrons in the beam and the pattern that the remaining electrons produce as they pass through specimen is converted into an image
• Describe the function and structure of the mitochondria

  Involved in aerobic respiration which produces ATP