Biology BY1- cell ultrastructure

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  • Created by: mickey243
  • Created on: 05-12-13 10:28



-spherical, between 10-20 micrometres in diameter

-bounded by a double membrane called the nuclear envolope/membrane.The nuclear envelope has got pores to allow the passage of larger molecules out of the nucleus

-it's outer membrane is continuous wih the rough endopolasmic reticulum

-the granular jelly-like material inside the nucleus is called the nucleoplasm and it contains chromatin, made up of coils of DNA

-within the nucleoplasm, there's a smaller spherical body called the nucleolus and it manufactures the rRNA

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-rod-shaped, between 1-10 micrometres in length

-bounded by a double membrane that's separated by a naroow fluid-filled intermembrane space,folded inwards to form cristae

- an organic matrix is surrounded by the inner membrane and cristae

-mitochondria are sites of aerobic respiration. The cristae provide larger surface area for the attachement of the enzymes so that energy in the form of ATP can be produced. The matrix contains chemicals that allow mitochondria to control the production of their own protein

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Endoplasmic reticulum

-consists of an elaborate system of double membranes forming flattened sacs. It is connectected to the nuclear membrane.The cavities are interconnected and this allows the transport of materials within the cell

-the membranes are separated by  fluid-filled spaces called the cisternae. 

- there are two types of ER

1.ROUGH ER is continuous with ribosomes and it allows the transport of proteins. Similarly it folds the polypeptide chain into a more compact, 3D shape

2.SMOOTH ER is not continuous with ribosomes, but it transports and synthesises lipids

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-ribosomes are manufactured in the nucleolus and are made of rRNA. 

-they consists of one large and one small sub-unit

-they may occur singly in the cytoplasm, but most of the time, they are associated with the rough endoplasmic  reticulum

-they are important in protein synthesis because they join amino acids together in order to make a polypeptide chain

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Golgi Body

-it is formed when small sacs pinch off the endoplasmic reticulum and fuse together

-it contains small vesicles on its outer surface

-it receives, modiefies and packiges lipid and proteins. For example, it modifies proteins by adding carbohydrates to the polypeptide chain. The modified chain then travels to the cell membrane in a vesicle

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- lysosomes are formed when portions of the Golgi body are pinched off 

-they isolate and contain any potentially harmful chemicals or digestive enzymes

- they also destroy worn out organelles

-they act as a digestive unit within the cell

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-they are two hollow cylinders positioned at right agnle to one another

-they are important in mitosis, because during the cell division, they split apart and travel to the opposite poles where they develop spindles

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functions of internal cell membranes

-to isolate any potential harmful enzymes

-to increase the surface area for the attachement of enzymes

-to provide a transport system with the cell

-it keeps the shape of the organelle which might be essential for some organelles

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- found in the cells of photosynthesising tissue and therefore they are not present in animal cells.

-each chloroplast is bounded by a double membrane

-the stroma is fluid-filled and it contains ribosomes and molecules such as lipids and starch (source of energy)

-within the stroma, there are many flattened sacs called the thylakoids. These are closed, parallel and flattened sacs and a stock of several thylakoids is called a granum. The photosynthetic pigments, including chlorophyll,are found in the thylakoids

-this arrangement increases the surface area needed for trapping light energy

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-vacuole is present in both animal and plant cells but unlike animal cells, plant cells have a large permanent, fluid-filled vacuole bounded by a single membrane called the tonoplast.

-vacuoles contain cell sap, where many biological molecules are stored. Secondly, it also helps to keep the cell to keep it's shape and is important in osmosis. The water enters the vacuole if the cell is placed in a hypotonic solution. This creates a pressure on the cell wall because the vacuole expands

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Cell Wall

-this organelle is absent from animal cells

-it consists of cellulose microfibrils embedden in a polysaccharide matrix

-the cell wall is fully permeable to water and substances in solution. For these reasons, it is also strong (due to the presence of cellulose) so it can withstand the pressure created by vacuole and other organelles

-the cell was provides a mechanical support 

-it also enables cells to connect with each other through narrow pores through which the strands of plasmodesmata can pass.

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