Getting In And Out Of Cells

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Getting In And Out Of Cells

• By Alice and Danielle

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Things We Will Cover

• Structure of the plasma membrane
• Diffusion
• Active transport
• Endocytosis and exocytosis

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Structure of the plasma membrane

• A membrane is a phospholipid bilayer which means
  it has two layers of molecules called
  phospholipids
• Phospholipid molecules have 2 parts
• Heads which are hydrophylic and which are always
  on the outside of the membrane
• Tails which are hydrophobic and which are always
  on the inside of the membrane
• Other molecules are in the membrane with the
  phospholipids like lipids, proteins and
  polysacharides

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Structure of the plasma membrane phospholipid
bilayer

• The yellow part of this structure is hydrophilic
  and can mix with water but not fat
• The green part is a protein
• The blue section is water, the heads (yellow)
  like water, but the tails are hydrophobic and do
  not like water

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Diffusion

• Diffusion is where molecules and ions move from
  an area of higher concentration to an area of
  lower concentration down a concentration gradient
• A concentration gradient occurs when there is
  more of an ion or molecule in once place then in
  another nearby place
• The larger the concentration gradient, the faster
  the movement of molecules and ions down it

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Rate of diffusion

• The rate of diffusion is affected by many things
  like concentration
• Two other factors also affect diffusion rate
• The surface area across which diffusion occurs
• The thickness of the surface

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Active transport

• Cells need to use energy to make substances cross
  their membranes against the concentration
  gradient
• Involves the use of carrier proteins in the
  phospholipid bilayer in the membrane
• The substance needing transporting binds to a
  carrier protein
• The protein changes shape and releases the
  substance on the other side of the membrane
• In active transport the carrier protein needs to
  be activated by an input of energy from the cell

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Active Transport Diagram
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Endocytosis exocytosis

• Endocytosis and exocytosis move substances across
  membranes in larger quantities then passive and
  active transport
• They use small sacks going to the membrane,
  called vesicles, to do this
• Vesicles are formed when they bud off another
  membrane

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Endocytosis

• Part of the plasma membrane sinks into the cell
• It then buds off and seals back onto itself
• Produces a vesicle that substances from outside
  the cell
• Two types of endocytosis
• Phagocytosis brings solid material into the cell
• Pinocytosis brings fluid into the cell

Substance being taken into cell
Plasma membrane
Vesicle containing substance
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Exocytosis

• A vesicle is formed in the cytoplasm (e.g. a
  vesicle could bud off in the golgi apparatus in
  the cytoplasm)
• Once formed the vesicle moves to the plasma
  membrane
• It fuses with the plasma membrane so that its
  contents are pushed outside the cell
• Hormones like insulin are secreted this way

Vesicle fuses with membrane
Product released
Secretory product, e.g. enzyme
Secretory vesicle