Cell Organelles

The cell organelles topic: Cellular Ultrastructure, Cell Fractionation and Microscopes

All that you need to know for the first AQA Biology AS Module 1.

By Natalie Beard :)

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Eukaryotic: With Nucleus

  • Cytoplasm: Contains all substances required by cell
  • Nucleus: Double membrane, interior called nucleoplasm heart of which is nculeous, this is full of chromotin: Controls exit and entry of substances
  • Mitochondria: Two membranes, inner folded into cristae, space known as matrix contains circular DNA: site of ATP synthesis/aerobic respiration
  • Ribosomes: Made of protein and RNA, made in nucleous. Either found free or on RER: Protein synthesis
  • SER: Membrane channels: Lipid syntheis and transport
  • RER: Membrane channels studded with Ribosmes: Protein syntheis and transport
  • Golgi Appartus/Body: Flattened membrane vesicles: transport and modify proteins, produce enzymes, transport and store lipids.
  • Lysosomes: Membrane bound vesicles containing digestive enzymes: destroy worn out organelles/digest unwanted material.
  • Cell Membrane:Phospholipid bilayer thin and flexible: controls exit and entry and seperates cell from enviroment.
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Prokaryotic: Before Nucleus

  • Cytoplasm: Contains all substances needed by cell
  • Ribosomes: Smaller 70s type: Protein Syntheis
  • Nucleiod: Region of cytoplasm that contains DNA: No nuclear envelope
  • Plasmid: Circle of DNA: used to exchange DNA between bacterial cells
  • Cell Membrane: Phospholipid bilayer: controls exit and entry and seperates cell from outside
  • Mesosome: Tightly folded region: Contains all membrane bound proteins for respiration and photosynthesis
  • Cell Wall: Made of glycoprotein, network of fibres: Adds strength and rigidity to cell
  • Capsule: Thick polysacchardide layer outside of cell wall: Used for sticking cells together, food reserve and protection.
  • Flagellum: Rigid rotating tail: Propulsion
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Endosymbiosis and Comparison

Prokaryotic: smaller, unicellular, no nuleus/membrane bound organelles, DNA is circular, 70S ribosomes, flagellum, asexual reproduction and variety of metabolic pathways.

Eukaryotic: Larger, multicellular, nucleus and membrane bound organelles, linear DNA, 80S ribsomes, No flagellum, sexual or asexula reproduction, common metabolic pathways.

Evidence that mitochondria could be descended from prokaryotic cells:

  • Circular DNA like prokaryotic
  • 70s ribosomes like prokaryotic
  • Double membrane: As though engulfed and surronded by larger cell
  • They reproduce via binary fission, like prokaryotic
  • Very alike live prokaryotic bacteria today
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Cell Fractionation

Seperates cell organelles. After each stage filter the supernantant to recieve the pellet and to carry on centrifuging.

1. Cut tissue (break cell membranes) and place in cold isotonic buffer soultion. Cold to stop enzyme action. Isotonic to stop osmosis. Buffer to stablise PH.

2. Filter to remove insoluble tissue: cell walls, connective tissue etc.

3. Centrifuge at low speed: 1000g for 10 mins: Pellet: Nuclei

4. Centrifuge at medium speed: 10000g 1/2 hour: Pellet: Chloroplasts. Mitochondria

5. Centrifuge at high speed: 100000 hour: Pellet: ER, Golgi and other membrane bits

6. Centrifuge at very high speed: 300000 3 hours: Pellet: Ribsomes

7. Now organelle free cytoplasm

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Magnification and Resolution

Measurements: 1mm = 1000 micrometres 1 micrometre= 10000 nanometres 1mm= 1000000 nanometres

Magnification Equation: magnification= observed size/actual size. Formulae with observed size on top and actual bottom left and magnification bottom right.

Magnification= How much bigger a sample is under the microscope then its actual size: more lenses increase this.

Resolution= Shortest distance at which two seperate objects can be distinguished: limited by wavelength of radiation used: wavelength of light larger then electrons so resolution of light microscopes are a lot lower.

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Light and Electron Microscopes Comparison

Light Microscopes Electron Microscopes

  • Cheap to purchase and operate Expensive
  • Small and portable Large, requires room
  • Simple and easy sample prep Lengthy and complex prep
  • Material rarely distorted by prep Prep distorts material
  • Vacumn not required Vacumn required
  • Natural sample colour maintained Black and white images
  • Magnifies only 1500 times max Magnifies up to 500000
  • Specimens can be living or dead Specimens must be dead
  • Stains often needed to see Coated with gold= prevents damage
  • Resolves at 500nm: Poor Resolves at 0.5-1nm: Lots of detail
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Scanning Microscopes

Used to examine surface of specimen:

  • Coated with metallic gold or palladium
  • Fine beam of electrons scanned over specimen and bounced off
  • Reflected beams amplifiy to form image of specimen surface
  • Lower resoultion= 5nm : Transmission (Nomal Electron): 0.5-1nm: S Worse
  • Greater depth of field= 3D Image
  • Magnification= 200000x: Transmission: 500000: S Worse

Only advantage being the 3D effect, so best for surface only.

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Reaaly useful - clear and full of content! more would be even better.

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