Cells

• Animal cell structure

  • RER
  • Cell Membrane
  • Nucleus
  • Golgi apparatus
  • Mitochondria
  • SER
  • Cytoplasm
  • Lysosomes
  • Ribosomes
• Plant cell structure

  • RER
  • Cell membrane
  • nucleus
  • Golgi apparatus
  • Mitochondria
  • Cytoplasm
  • Lysosome
  • Ribosome
  • SER
  • Vacuole
  • Cell wall
  • Chloroplasts
  • nucleolus
• Nucleus

  • Structure - Nuclear envelope, Nuclear pores, Chromosomes, Nucleolus
  • Function - Site of DNA replication and transcription , Contains the genetic code for each cell
• Endoplasmic Reticulum

  • Structure - Both have folded membranes, RER has ribosomes
  • Function - RER - Protein synthesis SER - Synthesis and stores lipids and carbs
• Lysosomes

  • Structure - Bag of digestive enzymes
  • Function - Hydrolyses phagocytic cells, breaks down dead cells, Exocytosis, Digests worn out organelles for reuse of materials
• Golgi apparatus and vesicles

  • Structure - Folded membranes making cisternae, Secretary vesicles pinch of from the cisternae
  • Function - Adds carbs to protein to form glycoproteins, Produces secretory enzymes, Secretes carbs, Transport, modify and store lipids, Forms lysosomes, Fuse with membrane and contents is released
• Mitochondria

  • Structure - Double membrane, Inner membrane called cristae, Fluid centre called matrix, Loops of mitochondria DNA
  • Function - Site of aerobic respiration, Site of ATP production, DNA to code
• Vacuole

  • Structure - Filled with fluid surrounded by a single membrane called a tonoplast
  • Function - Makes cells turgid - Provides support, Temp store of sugar and amino acids
• Ribosomes

  • Structure - Made up of protein tRNA, 80s - Larger - Eukaryotic, 70s - Smaller - Prokaryotic - Mitochondria - Chloroplasts
  • Function - Site of protein synthesis
• Chloroplasts

  • Structure - Surrounded by a double membrane, Contains thylakoids, Found is plant cells, Contains enzymes for photosynthesis
  • Function - Site of photosynthesis
• Cell Wall

  • Structure - In plant and fungi cells, Plant - Made of microfibrils of the cellulose polymer, Fungi - Made of chitin a nitrogen containing polysaccharide
  • Function - Provides structural strength
• Plasma membranes

  • Structure - Found in all cells, Phospholipid bilayer - molecule embedded within and attached on the outside
  • Function - Controls the entrance and exit of molecules
• Eukaryotic cells enter the cell cycle and divide by either mitosis or meiosis
• Prokaryotic cells divide by binary fission
• Viruses do not undergo cell division as they are non living. They replicate in side host cells
• The cell cycle

  1. Interphase (G1,S,G2)
  2. Nuclear division
  3. Cytokinesis

  
• Interphase

  The longest stage and is when the organelles double. The cell grows and the DNA replicates
• Nuclear division

  Can be either mitosis, creating 2 identical diploid cells, or meiosis, creating 4 genetically different haploid cells
• Cytokinesis

  The final stage is where the division of the cytoplasm creates the new cells
• Mitotic index 


  $Number . of.cells/Total.number.of.cells.X.100$
• Stages of mitosis

  • Prophase
  • Metaphase
  • Anaphase
  • Telophase
• Prophase

  • Chromosomes condense and become visible
  • centromeres separate and move to opposite poles
  • nucleolus disappears
• Metaphase

  • Chromosomes line up along the equator of the cell
  • The spindle fibres released form the poles now attach to the centromere and chromatid
• Anaphase

  • The spindle fibres pull the centromere and chromatids to opposite poles this causes the centromere to split in two
  • The individual chromatids are puled to each pole. They are now known as chromosomes
• Telophase and cytokinesis

  • The chromosomes are now at each pole of the cell and become longer and thinner again
  • The spindle fibres disintegrate and the nucleus starts to reform again
  • The final stage in the cell cycle is when the cytoplasm splits in two to create the two new genetically identical cells
• Magnification

  Refers to how many times larger the image is compared to the object
• Resolution

  Is the minimum distance between two objects in which they can still be viewed as separate. The resolution in an optical microscope is determined by the wavelength of light, and the wavelength of the beam of electrons determines the resolution in electron microscope
• Eye piece graticule 


  This can be sued to measure the size of the object
• Calibration

  A stage micrometre is used to calibrate the eye piece graticule. This is a glass slide with a scale on it which you place on the stage
• Optical microscopes

  • A beam of light condensed to create the image
  • poorer resolution due to light having a longer wavelength
  • Lower magnification
  • Colour images
  • Can view living samples
• Electron microscopes

  • A beam of electrons is condensed to create the image. Electromagnets are used to condense the beam
  • Higher resolving power as electrons have a short wavelength
  • Higher magnification
  • Black and white images
  • Sample must be in a vacuum and therefore non-living
• Transmission electron microscope

  Extremely this specimens are stained and placed in a vacuum. An electron gun produces a beam of electrons that pass through the specimen. Some parts absorb the electrons and appear dark. The image produced is 2D and shows detailed images on the internal structure of cells
• Scanning electron microscope

  The specimens do not need to be thin, as the electrons are not transmitting through instead, the electrons are beamed onto the surface and the electrons are scattered in different ways depending on the contours this produces a 3D image
• Magnification equation

  $Image=$$Actual size X Magnification$
• Cell fractionation

  • Used to isolate different organelles so they can be studied
  • This enables individual organelle structures and functions to be studied
  • Cells are broken open to release the contents and the organelles are then separated
  • The cells must be prepared in a cold, isotonic and buffered solution
• Why must the cell be prepared in a cold solution for cell fractionation

  To reduce enzyme activity when the cell is broken open enzymes are released which could damage the organelles
• Why must the cell be prepared in a isotonic solution for cell fractionation

  The organelles must be the same water potential as the solution to prevent osmosis as this could cause the organelles to shrivel or burst
• Why must the cell be prepared in a buffered solution for cell fractionation

  The solution has a PH buffer to prevent damage to the organelles
• Step 1 cell fractionation - Homogenisation

  The cells must be broken open and this is done using a blender the cells are blended in the cold, isotonic and buffered solution then filtered
• Step 2 cell fractionation - Ultracentrifugation 


  The filtered solution is spun at a high seed in a centrifuge this separated the organelles according to their density