Module 1: Cells

Module 1: Cells

Microscopes
1. light microscope
  1. resolution of 200nm (low resolution means means structures closer together than 200nm will appear as one object)
  2. Maximum magnification of 1,500x
2. Electron micropscope
  1. Transmisson Electron Microscope: 2D image produced, max. magnification is 500,000x. Electron beam passes through a very thin prepared sample, electrons pass through denser parts less easily, giving contrast.
  2. Scanning Electron Microscope: Electron beam directed on the sample, electrons don't pass through specimen, hey are bounced off. Final image is 3D. Max. magnification is 100,000x
  3. Advantages: Higher resolution, means they can be used to produce more detailed images of structes of organelles. SEM produces 3D image revealing contours and cellular arrangement - not possible with a light microscope.
  4. Limitations: Electrons deflected by molecules in air, so needs to be in vacuum. V. expensive and need specialist training and equipment.
3. Staining
  1. Biological material not coloured. hard to distinguish features.
  2. Coloured stains are used to stain specimens, chemicals bind to other chemicals on the specimen allowing it to be seen.
4. Sectioning
  1. Specimens are embedded in wax. Thin sections cut without distorting the structure
  2. V. useful for soft tissue
5. Magnification: is the degree to which the size of an image is larger than the object itself.
  1. mag = image size / actual size
6. Resolution: is the degree to wihch it is possible to distinguish two objects that are very close together
Organelles
1. NUCLEUS
  1. Houses all the genetic information in the form of DNA, contains instructions for for making proteins.
  2. Largest organelle, when stained contains darker parts of chromatin.
2. NUCLEOLUS
  1. Makes ribosomes and RNA which pass through the nuclear pores into the cytoplasm and are used in protein synthesis.
3. NUCLEAR ENVELOPE
  1. Double membrane with nuclear pores to allow mRNA to go out to the ribosomes for use in protein synthesis.
4. ENDOPLASMIC RETICULUM
  1. Series of flattened membrane bound sacs called cisternae. Rough ER studded with ribosomes and smooth is not.
  2. Rough ER transports proteins that were made by attached ribosomes. Smooth ER is involved with making lipids.
5. GOLGI APPARATUS
  1. A stack of membrane-bound flattened sacs
  2. Receives proteins from the ER and modifies and packages them into vesicles that can be transported.
6. MITOCHONDRIA
  1. Inner membrane is highly folded to form the cristae, the central part of the mitochondrion is called the matrix.
  2. Site of respiration, where ATP is produced. Almost of activites in the cell are driven by the energy released from ATP.
7. CHLOROPLASTS
  1. Only found in plant cells. Have network of flattened membrane sacs called thylakoids, a stack of these are called a granum. Contain chlorophyll in thylakoids membranes.
  2. Site of photosynthesis in plant cells. Light energy is used to drive the reactions of photosynthesis are carbohydrates are made from water and carbon dioxide.
8. LYSOSOMES
  1. Contain lysins which are powerful digestive enzymes which break down organelles, pathogens and cells.
  2. Specialised lysosome is acrosome found the hea dof a sperm cell helps penetrate the egg by breaking down materials.
9. RIBOSOMES
  1. Ting organelles
  2. Site of protein synthesis in the cell, code mRNA from the nucleus and assemble proteins from amino acids.
10. CELL SURFACE MEMBRANE
  1. Controls the entry and exits of substance into and out of the cell
11. FLAGELLA (UNDULIPODIA)
  1. Found in eukaryotes. Hair like extensions that stick out the surface of the cells, Move by using ATP.
12. CYTOSKELETON
  1. Network of protein fibres the keep the cells shape porviding an internal framework.
  2. Also determine the cells shape. Moves organelles such as mitochondira, RNA, chromosomes. Move vesicles along the microtubule network, hold organelles in places
  3. MIRCOTUBULES
    1. Cyclinders 25nm in diameter, made of tubulin. They themsevles do no tmove, but they provide an anchor for protein to move along, move organelles along the fibres. eg. chhromosomes are moved during mitosis, how vesicles move from the ER to the golgi. They use atp to drive these movements.
Protein Synthesis
1. 1. The gene containing the instructions for the porduction of the hormone is copied onto a piece of mRNA.
2. 2. mRNA leaves the nucleus through the nuclear pore.
3. 3. mRNA attaches to a ribosome.
4. 4. Ribosome reads the instructions to assemble the protein.
5. 5. Molecules are pinched off in vesicles and travel towards the golgi appartus.
6. 6. Vesicle fuses with the Golgi apparatus.
7. 7. Golgi apparatus processes and packages the molecules ready for release.
8. 8. The molecules are pinched off in vesicles from the golgi and move towards the cell surface membrane.
9. 9. Vesicles fuses with the cell surface membrane.
10. 10. Cell surface membrane opens to release molecules outside this is exocytosis.
Propkaryotes and Eukaryotes
1. Prokaryotes do not have a nucleus, they are bacteria and are much smaller than Eukaryotes.
2. Prokaryotes have no mitochondria, instead they have mesosomes.
3. They have smaller ribosomes; prokaryotes have 70s and eurkaryotes have 80s.
4. Prokaryotes do not have a vacuole.
5. Prokaryotes' cell walls are made of peptidoglycan, whereas eurkaryotes cell walls are present in plant calls and are made of cellulose.

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	Criado por emmawaugh mais de 10 anos atrás