WJEC Biology: 1.2- Cell Organisation and Structure

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  • Created by: Sam
  • Created on: 13-04-16 16:34

Nucleus

  • Bound by two membranes, the nuclear envelope, with pores allowing molecules, such as mRNA and ribosomes in and the outer membrane connects to the endoplasmic reticulum.
  • The granular material inside is called nucleoplasm. It contains chromatin, that condenses into chromosomes during cell division.
  • Within the nucleus is the nucleolus. It is the site of formation of rRNA.

                                   

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Mitochondria

  • Function: Production of ATP in aerobic respiration
  • Features: two membranes, separated by the inter-membrane space. The inner membrane is folded inwards to form cristae.
  • An organic matrix, which is a solution containing many compounds, including lipids and proteins.
  • Small (70S) ribosomes and a small circle of DNA which allow mitochondria to make some of their own proteins and self-replicate.
  • Found in: Metabolically active cells, such as muscle cells, needing a good supply of ATP.

                                               

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Endoplasmic Reticulum (ER)

  • Rough ER: Has ribosomes on the outer surface and transports the proteins made there, either to be secreted or for use in the cell membrane. Found in cells that make a lot of protein, such as cells making amylase in the salivary glands.
  • Smooth ER: Comprises membranes that lack ribosomes. It is associates with the synthesis and transport of lipids.
  • Cells that store large quantities of carbohydrates, proteins and fats, including liver and secretory cells, have extensive ER.

                                         (http://cronodon.com/files/Cell_ER_labeled.jpg)

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Golgi Body

  • A stack of membrane bound, fluid filled sacs, often found near the nucleus.
  • Functions: Producing secretory enzymes, packaged into secretory vesicles.
  • Secreting carbohydrates, e.g. for the formation of plant cell walls.
  • Producing glycoprotein.
  • Transporting and storing lipids.
  • Forming lysosomes, containing digestive enzymes.

                                                     (http://medicaltreasure.com/wp-content/uploads/2013/08/golgi-apparatus.png)

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Lysosomes

  • Small, temporary vacuoles surrounded by a single membrane, formed by being pinched off from the Golgi body.
  • Function: They contain digestive enzymes to break down foreign materials and recycle old organelles.
  • Lysosomes fuse with the vesicle made when a white blood cell engulfs bacteria by phagocytosis and their enzymes digest the bacteria.

                             (http://nptel.ac.in/courses/102103012/module3/lec3/images/1.png)

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Centrioles

  • Composed of two rings of microtubules, making hollow cylinders positioned at right angles to one another.
  • Together they are sometimes referred to as the centrosome.
  • Function: During cell division, centrioles organise the microtubules that make the spindle.
  • Found near the nucleus.

                                         (http://creationrev.wpengine.netdna-cdn.com/wp-content/uploads/2010/12/centriolesfigure1-300x245.jpg)

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Chloroplasts

  • Features: Each chloroplast is surrounded by two membranes, the chloroplast envelope.
  • The stroma is fluid-filled and contains some of the products of photosynthesis, including lipid droplets and starch grains.
  • They contain 70S ribosomes and circular DNA which enable them to make some of their own proteins and self-replicate.
  • Flattened sacs called thylakoids which contain chlorophyll. A stack of thylakoids is a granum. They produce a large surface area, efficient for trapping light energy.
  • Each granum is connected by an inter-granal lamella

                                          (http://www.sciencekids.co.nz/images/pictures/plants/chloroplastdiagram.jpg)

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Vacuole

  • Most plant cells contain a permanent vacuole: A fluid-filled sac bounded by a single membrane, the tonoplast.
  • Contains cell sap, a solution which stores chemicals and possibly vitamins and pigments.
  • Vacoules have a major role in supporting soft plant tissues.

                                        

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Ribosomes

  • Function: The site of translation in protein synthesis, where mRNA is used to assemble the polypeptide chain
  • In prokaryotic cells they are 70S in size; in eukaryotic cells they are 80S.
  • Composed of one large and one small subunit.
  • Assembled in the nucleolus from rRNA and protein.

                                         (http://cronodon.com/images/Ribosome.jpg)

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Cell Wall

  • Consist largely of cellulose and held together in microfibrils, which are aggregated into fibres, embedded in a polysaccahride matrix called pectin.
  • Functions: Allows transportation of molecules through the apoplast. The apoplast pathway is the main way that water crosses the plant root.
  • Provides mechanical strength for the cell when the vacuole is full of solution and pushes against the cell wall, the cell wall resists expansion and becomes turgid.
  • Allows communication between adjacent cells via the plasmodesmata.

                                                  

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