3- Active transport

What is active transport?

• Movement of molecules/ ions into or out of a cell, from a region of lower concentration to a region of higher concentration

• As its movement is against the concentration gradient, carrier proteins and ATP are used

• E.g. root hair cells accumulate more of an ion that they could via diffusion/ facilitated diffusion

Carrier proteins and active transport

• Specific regions or sites which bind reversibly to a complementary shaped molecule

• This then allows the hydrolysis of ATP to ADP which releases energy

• The energy released changes there conformation of the carrier protein

• In doing this, it moves the molecule form one side of the membrane to the other

Active transport process

• Molecule binds to carrier protein

• ATP binds to carrier protein on the opposite side of protein and hydrolysed to ADP

• Free phosphate binding to the protein causes it to change shape

• Molecule is released to the inside of the cell

• Phosphate molecules are released from carrier protein and reforms ATP

• Carrier protein returns to original shape

• Molecule has been moved from a low to high concentration

• Example: guard cells and potassium:

  • Guard cells use ATP provided by mitochondria

  • Actively transport potassium ions into the cells

  • Lowers water potential in the guard cell

  • Water moves in

  • Cell swells and stomata open

Bulk transport

• Large molecules such as enzymes or hormones

• Whole bacteria

• Moved into and out of the cells Lowers water by bulk transport

• Uses ATP for the movement of vesicles

• Cytoskeleton moves the vesicles

• Vesicle fuses with the CSM

Endocytosis

• Movement of materials into cells

• Phagocytosis- uptake of solids

• Pinocytosis- uptake if liquids

• Phagocytosis steps:

  • 1)Encounter/ detection

  • 2)Pseudopods form and move around substance/ cell

  • 3)Pseudopods mobile to enclose the substance being phagocytosed, ‘engulfing’

  • 4)Particulate is now internalised in a vesicle, cell surface membrane reforms

  • 5)Cytoslelton moves vesicle to a lysosome where they fuse together, the hydrolytic enzymes breakdown/ hydrolyse what was in the vesicle

  • 6)The broken down products of this are either absorbed by the cytoplasm or excreted by the cell if it is a waste product

Exocytosis

• Removal of substances from cells

• Vesicles formed by Golgi move towards CSM

• Vesicle fuses with CSM

• Contents of vesicle released to outside of cell

• Active process