revision for all chapters

• Light microscope

  • Source of radiation: Light
  • Wavelength of radiation: 400-700nm
  • Max resolution: 200nm
  • Lens: Glass
  • Specimen: Alive
  • Stains: Coloured dyes
  • Image: Coloured photomicrograph
  • View: Eye piece
• Electron microscope

  • Source of radiation: Electrons
  • Wavelength of radiation: ±0.005nm
  • Max resolution: 0.1-0.5nm
  • Lens: Electromagnet
  • Specimen: Dead
  • Stains: Heavy metal
  • Image: Black and white electron micrograph
  • View: Fluorescent screen
• Vacuum present in EM to prevent electrons from colliding with air particles to gain a sharp image.

  Water boils in RT in a vacuum, so specimen should be dead.
• Magnification


  Number of times larger an image is compared to the real size of the object

  Calculating magnification, use I = AM in a triangle

  Thus Actual image = Image size/magnification
• 1mm= 1000 μm
• 1μm= 1000 nm
• Calculation example


  1. 0.1mm of SM = 40 div of EG

  2. 1 div of EG= 0.1/40

  3. 0.0025mm*1000= 2.5μm

  4. 2.5μm*4 egu of chloroplast width= 10μm
• Resolution


  Ability to distinguish between two separate points. The amount of detail that can be seen- higher resolution, higher detail.

  Electrons have extremely short wavelength.

  They're negatively charged, thus easily focused using electromagnets.
• In an Electron micrograph

  -Very small particles can be observed as the electrons are easily absorbed.

  -The parts of the specimen that appear darker in the final image are denser and absorb more electrons.

  -Due to higher resolution, the electron micrographs of plant and animal cells show most organelles
• Organelles in a generalised animal cell (20μm)

  • Cell surface membrane
  • Nucleus
  • Rough endoplasmic reticulum
  • Smooth Endoplasmic reticulum
  • Golgi body/complex/apparatus
  • Mitochondria
  • Ribosomes
  • Lysosomes
  • Microtubules
  • Centrosome
  • Centriole
• Cell surface membrane

  A selectively permeable membrane in plant and animal cells that allows for the exchange of certain biological molecules and ions

  
• Cell surface membrane

  • Extremely thin with trilaminar appearance
  • Comprised of phospholipid bilayers which are assembled with the hydrophilic phosphate heads facing the aqueous environment (inside and outside the cell) and the hydrophobic tails facing each other
  • A selectively permeable membrane about 7 nm
• Functions of cell surface membrane

  • Barrier between cytoplasm and external environment
  • Cell signalling
  • Cell recognition (surface antigens)
  • Cell-to-cell adhesion
  • Site for enzyme catalysed reactions
  • Anchoring the cytoskeleton
  • Selection of substances that enter/leave the cell
  • Formation of Hydrogen bonds with water for stability
• Nucleus

  -The largest organelle surrounded by the double membraned nuclear envelope and is continuous with rough endoplasmic reticulum.

  -About 10 micrometer

  -Nuclear pore: gaps in the nuclear envelope that allow exchange between the nucleus and cytoplasm.
• Substances exchanged through nuclear pores

  • Substances leaving: mRNA and ribosomes for protein synthesis
  • Substances entering: protein to help make ribosome, nucleotide, ATP, & some hormones
• Chromosome

  Contains the hereditary material DNA that is organised into genes which controls the activities of the cell and inheritance
• Nucleolus

  One or more found (nucleoli) containing DNA and RNA, functioning to make ribosomes.

  0.2-0.5 micrometer
• Rough endoplasmic reticulum

  80S ribosomes of the rough endoplasmic reticulum are sites for protein synthesis and produce the rough appearance. The R.E.R provides a pathway for transport of materials through cell
• Rough endoplasmic reticulum

  • Made of two-dimensional flattened sacs, which are membrane-enclosed structures
  • Proteins made by ribosomes on RER enter sacs and move through them. Transport vesicles bud off from the RER and join forming the Golgi body
• Smooth Endoplasmic reticulum

  -Site for lipid synthesis and steroids eg cholesterol and reproductive hormones

  -Meshwork of tubular membrane vesicles with fluid filled sacs that have no ribosome on its surface..
• Golgi body/complex/apparatus


  Stack of flattened sacs formed by transport vesicles which bud off of the RER, and broken down to form Golgi vesicles
• Functions of Golgi body


  • Collects, processes, modifies and sorts molecules that are ready for transport in Golgi vesicles to other parts of the cell or out of the cell by secretion/exocytosis
  • Makes lysosomes, glycoproteins and functioning proteins
• Mitochondria


  Surrounded by mitochondrial envelope; provides energy for aerobic respiration, synthesizes lipids and is more in areas that require maximal energy.

  About 1 micrometer
• Mitochondria


  • Has a matrix that contains 70S ribosomes and circular DNA which is used to make some of the mitochondrion's own proteins
  • Cristae: folding of inner membrane that projects into interior solution, matrix
  • Intermembrane space: space between the two membranes
  • Porin: transport protein in outer membrane, forms wide aqueous channel allowing water-soluble molecules from cytoplasm to intermembrane space
  • Inner membrane: selective barrier controlling entrance of ions and molecules into the matrix
• Adenosine triphosphate (ATP)


  Made up of 3 phosphate groups, a nitrogenous base and a ribose sugar. The energy carrying molecule produced in mitochondria that spreads to parts where needed. Energy is released by breaking ATP to ADP, a reversible hydrolysis reaction

  
• Endosymbiont theory: mitochondrion and chloroplast were bacteria that now live inside larger cells of animals and plants, which is why chloroplast and mitochondrion have circular DNA
• Ribosomes


  The site at which mRNA (transcribed from the nucleus) is translated into polypeptides with the help of tRNA, therefore help with protein synthesis
• Types of ribosomes

  • 80S ribosomes: in the cytoplasm and R.E.R
  • 70S ribosomes: in chloroplast and mitochondria and prokaryotes.
• Lysosomes

  A single membrane with no internal structure in animal cells. They contain digestive (hydrolytic) enzymes that's kept separate from rest of cell to prevent damage.

  About 0.1-0.5 micrometer

  Responsible for breakdown of unwanted structures e.g old organelles or whole cells, in WBC to digest bacteria.
• Microtubules


  Long hollow tubes that make up the cytoskeleton which helps determine cell shape
• Microtubules

  • Made up of alpha and beta tubulin that combine to form dimers
  • Dimers join end to end to form protofilaments (polymerisation)
  • 13 protofilaments line up alongside each other in a ring to form a cylinder with a hollow center ie microtubule
  • Forms an intracellular transport system by moving along secretary vesicles, organelles and cell components on its outer surface
• Centrosome


  Pair of centrioles at right angles that's involved in nuclear division and act as MTOCs
• Centriole


  Formed by 9 triplets of microtubules. Microtubules extend from centriole and attach themselves to kinetochore of chromosomes, forming spindle fibres. Centrioles duplicate, and a pair of centrioles then move to opposite poles of the cell (2 centrosome regions), thus separating sister chromatids during nuclear division
• Centrioles at bases of cilia and flagella (basal bodies) act as MTOCs. Microtubules extending from basal bodies into cilia and flagella help with their beating movements
• Organelles in a generalised plant cell (40 μm)

  • Cell surface membrane
  • Nucleus
  • Rough endoplasmic reticulum
  • Smooth Endoplasmic reticulum
  • Golgi body/complex/apparatus
  • Mitochondria
  • Ribosomes
  • Lysosomes
  • Microtubules
  • Centrosome
  • Centriole
  • Chloroplasts
  • Cell wall
  • Plasmodesmata
  • Large vacuole and tonoplast

  
• Chloroplasts


  This cell structure is only found in plant cells in the palisade mesophyll, spongy mesophyll and surface of stem and carries out photosynthesis

  
• Chloroplasts


  • Has a double membrane and contains flattened sacs known as thylakoids
  • Chlorophyll is embedded in thylakoid membranes
  • Thylakoids stacked on top of each other to form grana
  • Grana are linked by lamella. These structures are present in a matrix called the stroma
  • Contains starch grains, circular DNA and 70S ribosomes

  
• Cell wall


  Rigid as it contains fibres of cellulose (polysaccharide)
• Functions of cell wall

  • Gives the cell its definite shape and prevents it from bursting (by osmosis), allowing turgidity
  • May be reinforced by lignin for extra strength
  • Freely permeable
• Plasmodesmata


  Pore-like structures found in cell walls that allow a link between neighbouring cells by fine threads of cytoplasm