Cell Ultrastructure

Unit 3 of the SNAB course

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  • Created by: G Redford
  • Created on: 14-09-13 13:55

Nucleus

Description:

  • Surrounded by a double membrane.
  • Pores in the nuclear envolope.
  • Dark staining area, nucleolus, within the nuclear envolope.
  • Contains most genetic material.
  • Largest organelle, aprox. 5 micrometers.

Function:

  • Contains DNA organised into chromosomes.
  • Pores allow ribosomes (synthesised by the nucleolus) to pass into the rest of the cell.
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Mitochondrion

Desciption:

  • Quantity depends on the activity of the cell.
  • Bound by a double membrane.
  • Inner membrane folded into finger like projections, called cristae.
  • Central area contains a jelly, called matrix.
  • Ribosomes and DNA (loop) float in the matrix.
  • 0.5 micrometres in length.

Function:

  • Cristae provide a large surface area for attaching enzymes.
  • Matrix contains enzymes involved in cellular respiration.
  • Inner membrane contains enzymes and proteins involved in respiration.

 

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Lysosome

Description:

  • Enclosed by a single membrane.
  • Containing digestive enzymes.
  • Spherical shape.
  • Up to 1 micrometer in diameter.

Function:

  • Enzymes used to recycle cell organic material or cell suicide.
  • Membrane allows enzymes to be seperated from rest of cell. 
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Centrioles

Description:

  • Two hollow cylinders.
  • Arranged at right angles to each other.
  • Forming a ring of microtubules.
  • Near the nucleus in animal cells.

Function:

  • Used to organise spindle fibres used in nuclear division (mitosis).
  • Only in animal cells.
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Rough Endoplasmic Reticulum

Desciption:

  • A series of single, flattened sacs enclosed by a membrane.
  • Ribosomes on surface.
  • The tubules forming ReR are up to 7.0x10-7m in diameter.
  • Polypetide chains from bound ribosomes are threaded through into the eR space.
  • Contains small membrane bound sacs called vesicles, containg the eR protein bud from the eR.

Function:

  • Bound ribosomes which are threaded into eR space have their polypeptide chains folded into proteins.
  • Glycoproteins may be formed by attatching carbohydrates to proteins.
  • Vesicles containing eR protein buds are transported to other parts of the cell.
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Smooth Endoplasmic Reticulum

Description:

  • No ribosomes.
  • Sacs surrounded by membranes.
  • Network of interconnected sacs in the cytoplasm.
  • Continous with the outer membrane of the nuclear envolope.

Function:

  • Synthesis of lipids.
  • Carbohydrate metabolism.
  • Detoxification of drugs and poisons.
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Golgi Body (Golgi Apparatus)

Desciption:

  • Stack of flattened sacs.

Function:

  • Productions from the eR are modifed and stored before being packed into vesicles for transport.
  • One side recieved vesicles from rest of cell.
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Ribosomes

Description:

  • Attatched to the ReR and produced in the nucleolus.
  • Can also be free floating in the cytoplasm.
  • Both prokaryotic cells and eukaryotic cells have ribosomes but prokaryotic cells are smaller.
  • Made of RNA and protein.

Function:

  • Site of protein synthesis.
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Cell Surface Membrane

Desciption:

  • Formed from 2 layers of phospholipid with proteins immersed inside.
  • Phospholipids have a hydrophilic head facing cytoplasm and a hydrophobic tail facing towards the centre of the biolayer.

Function:

  • Proteins in the membrane may be for structural support, enzymes, or in the assistance of molecule transportation across te membrane. 
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Vacuole

Description:

  • Fluid sac bound by a single membrane, called a tonoplast.
  • Containing a solution of sugars, amino acids, waste product and mineral salts.
  • Large vacuole in plant cells and a small non-permenant vacuole in animal cells.

Function:

  • Temporary store of waste but can also contain hydrolytic enzymes.
  • Supportive structure to keep cell rigid.
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Cell Wall

Description:

  • Rigid and made of celulose fibres running through a mixture of other polysaccharides (complex sugars) such as pectins and hemiculluloses.

Function:

  • Supportive structure.
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Chloroplasts

Description:

  • Large organelle only found in photosynthesising cells.
  • At high magnifications grana can be seen.
  • Have an envoloped membrane called a thylakid.
  • Stack arrangements called grana.
  • Surrounding the outer membrane is a stroma.

Function:

  • To photosynthesise.
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Middle Lamella

Description:

  • Pectin layer joining 2 cells.
  • Sticky to allow 2 cells to connect.

Function:

  • Cements walls of 2 adjoining cells.
  • Cell plate develops the middle lamella.
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Plasmadesmata

Description:

  • Microscopic channels in the plant cell wall and membrane.

Function:

  • Allows communication between cells and the transport of substances.
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Pit

Description:

  • Regions where the secondary cell wall is absent but primary wall is present.aka. Thinning of the cell wall.

Function:

  • A simple pit isn't bordered and may be round or a slit shape.
  • A circular bordered pit is round with a thickened margin.
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Amyloplasts

Description:

  • Non-pigmented organelle in a plant cell.
  • Are plastids (cells that carry out photosynthesis).

Function:

  • Synthesising and the production of starch granules using the polymerisation of glucose molecules.
  • Also able to convert starch back to glucose if needed by the cell.
  • Starch made is stored as it is insoluble.
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