3 - Cell Structure

• List all of the components of an animal cell:

  • Cell Membrane
  • Vacuole
  • Rough Endoplasmic Reticulum
  • Golgi Apparatus
  • Cytoplasm
  • Lysosome
  • Ribosome
  • Centrosome
  • Smooth Endoplasmic Reticulum
  • Mitochondrion

  
• What 3 components are in plants cells, but NOT animal cells?

  • Permanent Vacuole
  • Cell Wall
  • Chloroplasts

  
• Cell Surface Membrane:~ Structure

  • Found in all cells
  • Phospholipid bilayer - molecules embed within and attached on the outside - fluid mosaic model (proteins, cholesterol, carbohydrates)
• Cell Surface Membrane:~ Function

  • Controls the entrance and exit of molecules
• Nucleus:~ Structure

  • Nuclear Envelope - double membrane with nuclear pores
  • Nucleoplasm - jelly like material
  • Chromatin - linear, protein-bound DNA
  • Nucleolus - smaller sphere inside which is the site of rRNA production and makes ribosomes
• Nucleus:~ Function

  • Site of DNA replication and transcription (making mRNA)
  • Contains the genetic code for each cell
• Mitochondria:~ Structure

  • Double membrane with an inner membrane (cristae)
  • Mitochondrial Matrix - Fluid centre
  • Loop of mitochondrial DNA
• Mitochondria:~ Function

  • Site of aerobic respiration
• Golgi Apparatus/Vesicles:~ Structure

  • Folded membranes making cisternae
• Golgi Apparatus/Vesicles:~ Function

  • Adds carbohydrates to proteins to form glycoproteins
  • Produces secretory enzymes
  • Secretes carbohydrates
  • Transport, modify & store lipids, and forms lysosomes
  • Molecules are 'labelled' with their destination
• Lysosomes:~ Structure

  • Bags of digestive enzymes (lysozymes)
• Lysosomes:~ Function

  • Hydrolyse phagocytic cells and completely breaks down dead cells (autolysis)
  • Exocytosis - release enzymes outside the cell to destroy the material
  • Digest worn-out organelles for reuse of materials
• Ribosomes:~ Structure

  • Made up of 2 sub-units of protein and rRNA
  • 80s found in eukaryotic cells
  • 70s found in prokaryotic cells, mitochondria & chloroplasts
• Ribosomes:~ Function

  • Site of protein synthesis
• RER & SER:~ Structure

  • Both have folded membranes (cisternae)
  • RER have ribosomes on the cisternae
• RER & SER:~ Function

  • RER - Protein synthesis
  • SER - Synthesis and store lipids/carbohydrates
• Cell Wall:~ Structure

  • In plants and fungi cells
  • Plants - made of microfibrils of cellulose
  • Fungi - made of chitin, a nitrogenous polysaccharide
• Cell Wall:~ Function

  • Provides structural strength to the cell
• Cell Vacuole:~ Structure

  • Filled with fluid surrounded by a single membrane (tonoplast)
• Cell Vacuole:~ Function

  • Makes cell turgid, providing support
  • Temporary store of sugars and amino acids
  • Pigment may attract pollinators
• What are the 5 key differences between prokaryotic and eukaryotic cells?

  Prokaryotic cells:

  1. are smaller
  2. have smaller ribosomes (70s)
  3. have no nucleus
  4. have no membrane-bound organelles
  5. have cell walls made of murein

  
• What are 3 additional organelles that some prokaryotic organisms have?

  • Plasmid
  • Capsule
  • Flagella

  
• Viruses:

  Viruses are non-living and acellular. They are even smaller than bacteria and only contain genetic material, a capsid, and an attachment protein.

  
  

  HIV is surrounded by a further lipid envelope that has attachment proteins on the outside. This is to enable the virus to identify the host cells to enter.
• What are the 3 key types of microscopes?

  1. Optical (light)
  2. Scanning electron
  3. Transmission electron
• What is magnification?

  How many times larger the image is compared to the object.

  
• What is resolution?

  • 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 of an electron microscope
• Why do light microscopes have a poor resolution?

  Light microscopes have a poor resolution due to the long wavelength of light.
• Why are small organelles in a cell are not visible using an optical microscope?

  They are too small to be visible due to the wavelength of light limiting the resolution and have a lower magnification too.
• What's the formula for magnification?

  Image size = Actual size x Magnification
• Optical Microscopes:~

  • What creates the image? - beam of light
  • Condenser - glass lens
  • Resolution - poor
  • Magnification - lower
  • Colour - colour
  • Types of samples - can view living samples

  
• Electron microscopes:~

  • What creates the image? - beam of electrons
  • Condenser - electromagnets
  • Resolution - high
  • Magnification - higher
  • Colour - black & white
  • Types of samples - samples must be viewed in a vacuum so cannot be living

  
• What are the stages of cell fractionation?

  1. Cells are broken down so that organelles are free to be separated
  2. This is done using a homogeniser, a blender
  3. Once the cell has been broken open, the solution must be filtered to remove larger pieces of debris
• The solution in cell fractionation must be:

  • isotonic
  • pH buffered
  • ice cold
• Why must the solution be isotonic in cell fractionation?

  to prevent any movement of water by osmosis resulting in organelles shrivelling (hypertonic) or bursting (hypotonic)
• Why must the solution be pH buffered in cell fractionation?

  to prevent pH changes, therefore not damaging the organelles/enzymes
• Why must the solution be ice cold in cell fractionation?

  to reduce enzyme activity to prevent the breakdown of cell components
• What is ultracentrifugation?

  Once filtered, the homogenate solution is ready to be centrifuged. The solution is placed into a centrifuge which spins at different speeds to separate organelles depending on their density due to the centrifugal force

  
• What are the stages of ultracentrifugation to separate the nuclei, mitochondria/chloroplasts, lysosomes and SER/RER and ribosomes?


  • Supernatant after the first spin at low speed- pellet contains the nuclei.
  • Supernatant after the second spin at medium speed- pellet contains mitochondria and chloroplasts (if a plant cell).
  • Supernatant after the third spin at high speed- pellet contains lysosomes and SER/RER.
  • Supernatant after the fourth spin at very high speed- pellet contains ribosomes

  
• During which stage of the cell cycle does DNA replicate?

  interphase/ S phase
• During which stage of the cell cycle does the cell divide to produce identical daughter cells?

  Mitosis