By: Nina T

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Chloroplasts

• By Nina T

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Introduction

• Chloroplasts are found in mesophyll cells (in the
  leaves) of green plants.
• Guard cells also contain chloroplasts.
• They are not normally found in the cells of
  roots.
• Chloroplasts are organelles found in plant cells
  and other eukaryotic organisms that conduct
  photosynthesis.
• Their function is to produce glucose from carbon
  dioxide and water. To do this they need light
  energy.

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• Chloroplasts capture light energy to conserve
  free energy in the form of ATP and reduce NADP to
  NADPH through a complex set of processes called
  photosynthesis.
• There are two types of reactions that can occur
  the dark reaction and the light reaction.

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• In the light reaction, electrons in chlorophyll
  molecules are excited. In other words the energy
  photons is used to activate electrons.
• The energy in excited electrons is used to split
  water molecules this is photolysis. Oxygen is
  produced as a waste product and hydrogen is used
  to reduce NADP   to form NADPH.
• The process involves non-cyclic electron transfer
  producing both NADPH and ATP and cyclic electron
  transfer producing just ATP.
• The dark reaction requires energy from both NADPH
  and ATP.
• In this part of photosynthesis carbon dioxide is
  fixed. Energy from NADPH and ATP is used to
  convert glucose (a six carbon molecule) into
  ribulose diphosphate (a five carbon sugar
  molecule).
• Ribulose diphosphate can combine with carbon
  dioxide eventually forming glucose.

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Structure

• Chloroplasts are observable as flat discs usually
  2 to 10 micrometers in diameter and 1 micrometer
  thick.
• In land plants, they are, in general, 5 µm in
  diameter and 2.3 µm thick.
• The chloroplast is contained by an envelope that
  consists of an inner and an outer phospholipids
  membrane. Between these two layers is the inter
  membrane space.
• A typical parenchyma cell contains about 10 to
  100 chloroplasts.
• The material within the chloroplast is called the
  stroma, corresponding to the cytosol of the
  original bacterium, and contains one or more
  molecules of small circular DNA

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• It also contains ribosomes however most of its
  proteins are encoded by genes contained in the
  host cell nucleus, with the protein products
  transported to the chloroplast.
• Within the stroma are stacks of thylakoids, the
  sub-organelles, which are the site of
  photosynthesis.
• The thylakoids are arranged in stacks called
  grana (singular granum).
• A thylakoid has a flattened disk shape. Inside it
  is an empty area called the thylakoid space or
  lumen.
• Photosynthesis takes place on the thylakoid
  membrane.

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• Chloroplasts
• have a double membrane
• - the inner membrane
• - the outer membrane
• have their own DNA
• - this carries the information to make the
  enzymes
• have their own ribosomes
• - which are more like the ribosomes of
  prokaryotes than eukaryotes
• - these are used to synthesise proteins (the
  enzymes) from amino-acids
• make their own enzymes
• are required for photosynthesis
• require carbon dioxide and water
• produce glucose
• contain chlorophyll
• - this green chemical "traps" sunlight energy