Cell Biology

• Eukaryotes


  Cells that have a nucleus and membrane-bound organelles
• Prokaryotes


  Cells that lack a nucleus and membrane-bound organelles
• Components of animal and plant cells

  • Cell membrane
  • Cytoplasm
  • Nucleus containing DNA
• Components of bacterial cells

  • Cell wall
  • Cell membrane
  • Cytoplasm
  • Single circular strand of DNA and plasmids
• Organelles


  Structures in a cell that have different functions
• Orders of magnitude


  Used to understand how much bigger or smaller one object is from another
• Prefixes


  • Centi (0.01)
  • Milli (0.001)
  • Micro (0.000,001)
  • Nano (0.000,000,001)
• Structures in animal and plant cells

  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional structures in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• Structures in bacterial cells

  • Cytoplasm
  • Cell membrane
  • Cell wall
  • Single circular strand of DNA
  • Plasmids
• Specialised cells


  • Undergo differentiation to gain new sub-cellular structures suited to their role
  • Most animal cells only differentiate once, but many plant cells retain the ability to differentiate throughout life
• Specialised animal cells


  • Sperm cells
  • Nerve cells
  • Muscle cells
• Specialised plant cells


  • Root hair cells
  • Xylem cells
  • Phloem cells
• Cell differentiation


  The process where stem cells gain new sub-cellular structures and functions by having certain genes switched on or off
• Cell division in animals

  • Most cells only divide to repair or replace damaged cells
  • Red blood cells cannot divide and are replaced by adult stem cells
• Cell division in plants


  • Many plant cells retain the ability to differentiate throughout life
  • They only differentiate when they reach their final position in the plant, but can re-differentiate when moved
• Light microscope


  • Has two lenses (objective and eyepiece) to magnify and direct the image into the eye
  • Maximum magnification of x2000 and resolving power of 200nm
• Electron microscope


  • Uses electrons instead of light to form an image
  • Scanning electron microscope creates 3D images, transmission electron microscope creates 2D images
  • Magnification up to x2,000,000 and resolving power of 10nm (SEM) and 0.2nm (TEM)
• Calculating magnification


  Magnification of eyepiece lens x magnification of objective lens
• Calculating size of object

  Size of image / magnification = size of object
• Standard form


  Used to represent very large or small numbers by multiplying a number between 1 and 10 by a power of 10
• Culture medium


  Contains carbohydrates, minerals, proteins and vitamins to grow microorganisms
• Growing microorganisms in nutrient broth solution

  Make a suspension of bacteria and mix with sterile nutrient broth, stopper with cotton wool to prevent contamination, shake regularly to provide oxygen
• Growing microorganisms on agar plates

  Spread bacteria suspension on agar plate, seal with parafilm, incubate at optimum temperature
• Standard form


  Multiplying a certain number by a power of 10 to make it bigger or smaller, with the 'number' being between 1 and 10
• Standard form examples


  • 1.5 x 10^-5 = 0.000015
  • 3.4 x 10^3 = 3400
• Culturing microorganisms


  • Microorganisms are very small, so scientists need to grow many of them in the lab using nutrients
• Components of culture medium

  • Carbohydrates for energy
  • Minerals
  • Proteins
  • Vitamins
• Growing microorganisms in the lab

  1. In nutrient broth solution

  2. On an agar gel plate
• Steps in making an agar gel plate
• Reasons for sterilisation


  To prevent contamination with other microorganisms that could compete for nutrients and space, or be harmful
• Reasons for other steps in culturing microorganisms
• Binary fission


  One bacterium splitting into two, which can happen as fast as every 20 minutes
• Calculating number of bacteria after a growth period

  Bacteria at beginning x 2^(number of divisions) = bacteria at end
• Antibiotics can be tested on bacteria to see their effectiveness
• Testing antibiotic effectiveness


  Soak paper discs in antibiotics, place on agar plate with bacteria, measure inhibition zone after incubation
• Calculating cross-sectional areas involves using the formula πr^2
• Chromosomes


  Contain coils of DNA, with each chromosome carrying many genes
• Humans have 23 pairs of chromosomes (46 total) in body cells, and 23 chromosomes in sex cells
• Cell cycle and mitosis

  1. Interphase: cell grows, organelles increase, DNA replicates

  2. Mitosis: chromosomes line up and are pulled to opposite sides

  3. Cytokinesis: cytoplasm and cell membrane divide to form two daughter cells