Plant Organelles

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• Is surrounded by a nuclear envelope that is porous and has a double membrane. It contains: the chromosomes (genetic material of the cell/DNA) and one or more nucleoli (dark staining masses made up of protein and nucleic acids involved in rRNA synthesis).

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• A 3D network of continuous tubules and flattened sacs that course through the cytoplasm and connect to the nuclear envelope (distinct from the plasma membrane)

1. Rough ER

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   • Studded with ribosomes on its surface. Ribosomes make and package proteins.
2. Smooth ER

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   • Smooth, no ribosomes on surface. 
3. Principle Functions

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   • Synthesizing, processing, and sorting proteins targeting to membranes, vacuoles, or the secretory pathway. Synthesizing a diverse array of lipids. Plays a critical role in regulating cytosolic concentrations of Calcium, an ion which influences many other cellular activites.

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• Refers to saucer shaped stacks of membranes. The ends of the membranes appear to be swollen or ballooned and give rise to vesicles by pinching them off the pain structure. They are, essentially, another packaging system, though they are packaging something different than the ER. 

1. Principle functions

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   • Assembling complex carbohydrates for the cell wall and synthesizing carbohydrate side chains for glycoproteins in the membrane, cell wall, and vacuole. 

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• Organelles surrounded by a double unit membrane that are centres of respiration in the cell and are responsible for converting food (sugars) into energy rich compounds (ATP) to support all the metabolic activity i the cell)

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• A single organelle with one continuous membrane around it. The fluid filled compartment is surrounded by a membrane known as the tonoplast. Vacuoles are usually 30% of the cell volume, though they can go up to 90%. 

1. Storage

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   • In and out. Storage for water and various materials such as sugars, proteins, organic acids, and pigments - all of these primary metabolites can be retrieved from vaculoes and used in metabolic pathways to sustain growth).
2. Digestion

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   • Vaculoes contain digestion enzymes including proteases, nucleases, glycosideases, and lipases. Together, these can breakdown nearly all cellular components. 
3. pH and ionic homeostasis

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   • Vacuoles serve as reservoices of protons and metabolically important ions such as calcium. Vaculor pH is usually between 5 and 5.5, but can range from 2.5 to 7, depending on the fruit type. Because of this function, vaculoes can change the activities of enzymes in the cytoplasm and regulate cytosolic pH, activity of enzymes, the assmbly of the cytoskeletal structure, and membrane fusion events. 
4. Defence Mechanisms

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   • Accumulation of a variety of toxic compounds occurs in the vacuoles, including: -Phenolic compounds, alkaloids, cyanogenic glycosides, and protease inhibitors, all which discourage herbivore and insect predators.  -Cell wall degraded enzymes, such as chitinase and glucanase to destroy pahtogenic fungi and bacteria (recall that fungi and bacteria also have cell walls) -Latexes, wound clogging emulsions of hydrophobic polymers that possess insecticidal and fungicidal properties and also serve as anti-herbivory agents. These may contain discouraging toxic compounds, etc. 
   • These compounds are compounds that the cell actually makes on purpose and puts in the vacuole so they can have the desired defence mechanism effect. 
5. Sequestration

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   • Plants sequester toxic compounds such as heavy metals and toxic metabolies such as oxalate into the vaculoe. This is a one way deposit - most products in here build up naturally during metabolism, and are stored away from active cytoplasm. The accumulation of toxic chemicals in the leaf vacuole is why leaves are shed regularly. 
6. Pigmentation

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   • Vaculoes that contain anthocyanin pigments are found in many types of cells (in flowers and fruits they are used to attract pollinators and seed dispensers).  Some pigments sceen out UV and visible light, preventing photo-oxidative damage to the photosynthetic apparatus

1. Protoplastids

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   • Protoplastids are the precursors of all other plastids. Even though plastids can have many different functions down the road, they all start off the same. 
2. Amyloplasts

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   • Unpigmented plastids that contain starch granules. These are common in storage organs such as potato tubers. 
3. Leucoplasts

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   • Colourless plastids involved in the synthesis of monoterpenes, which are volatile compounds contained in essential oils. These are found in secretory glad cells associated with leaf and stem trichomes. Also found in citrus peel. 
4. Chromoplasts

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   • These synthesize and accumulate carotenoid and xanthophyll pigments, making they yellow, orange, or red in colour. These may be located in just the epidemis, or throughout all cells. 
5. Etioplasts

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   • Plastids where development from protoplastids to chloroplasts has been arrested by absense of light. This is NOT an intermediate stage in the normal development of plastids. These contain no chlorophyll, but have a colourless chlorophyll precursor (protochlorophyllide). Everything stops in these cells until light returns and triggers the development of these into chloropasts. 
   • Essentially, these are protoplastids that had and lost light partway through development. 
6. Chloroplasts

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   • Photosynthetic plastids responsible for energy capture that are green due to the presence of chlorophyll. These are bounded by a double membrane.
   1. Thylakoid network

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      • Chloroplasts have an inner membrane system called the thylakoid network that contains two distinct types of membrane domains. 
      • Chlorophull is contained in the thylakoid membranes. Plants grown in the shade, therefore, will generally have more granan and more thylakoids per granum. Thylakoid stacking is UBIQUITOUS in green plants and is believed to be involved in regulating the distribution of radiant energy between PSI and PSII during photosynthesis.
      • Leaves grown in the shade will see chloroplasts accumulate at the top of leaf cells where they will absorb as much sunlight as possible. In direct sunlight plants, chloroplasts move to the sides of the cells, likely to protect against excessive sunlight damage. 
      • The LIGHT reaction occurs in the thylakoid membranes, and the DARK reactions occur in the stroma. 
      1. Stacked grana
      2. Unstacked Stroma
   2. Light Reaction

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      • Capture of light energy and conversion to chemical bond energy, ATP and NADPH.
   3. Dark Reaction

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      • Enzymatic fixation of CO2 into carbohydrates utilizing the ATP and NADPH from the light rxn.