BIOL 2020: Lecture 5 (movement against the gradient)

ATP

• adenosine triphosphate

• source of energy for use and storage at the cellular level

  • movement against the concentration gradient requires ATP

• structure:

  • nitrogenous base (adenine)

  • ribose sugar

  • 3 bonded phosphate groups

• ATP → ADP

  • releases energy

• ADP → ATP

  • requires energy

Indirect active transport

• involves the transport of a solute in the direction of its increasing electrochemical potential coipled to the facilitated diffusion of a second solute

  • ex. symporters and antiporters 

    

Direct active transport

• involves using ATP to directly pump a solute across a membrane against its electrochemical gradient 

transport ATPases

• ATP-driven pumps 

• hydrolyze ATP to ADP and single phosphate 

  • use the energy released to pump ions or other solutes across a membrane 

P-type pump

• p-ATPases (ATP-driven pump) which phosphorylates itself during the pumping cycle 

• 4 types: 

  • P1: tranport heavy metals

  • P2: maintain electrochemical gradients

    • Ca²⁺/H⁺ 

    • Na⁺/K⁺

    • H⁺/K⁺

  • P3: membrane potential for plants and fungi

  • P4: moves phospholipids (flippase)

Ca²⁺/H⁺  P2-ATPases

• occurs within eukaryote muscles 

  • sarcoplasmic reticulum, or plasma membrane 

• keeps [Ca²⁺] low in cytosol 

Na⁺/K⁺ P2-ATPases 

• occurs within animals

  • plasma membrane 

• maintains membrane potential (via electrochemical ion gradients in all cells)

  • -60mV

• continuously pumps Na+ ions out of the cell, and K+ ions into the cell

  • cycles between two conformations

  • E1: open inside

  • E2: open outside

H⁺/K⁺ P2-ATPases 

• occurs in animals

  • plasma membrane

• pumps H⁺ to acidify stomach

Vacuolar-ATPase

• two rotary motors

  • ATP driven motor turns an axle, which turns a second motor that pumps protons across the membrane

• the linkers hold the complex together

• pumps H⁺ ions to increase acidity in specific organelles

  • vacuoles

  • lysosomes

• not phosphorylated

• regulated by separating the ATP-powered motor form the proton pumping motor

F-type ATPases

• ATP synthases

  • moves ions with the concentration gradient to produce ATP 

• F stands for “factor” 

H⁺ F-type ATPases

• occurs in eukaryotes

  • inner mitochondrial membrane 

• uses H⁺ gradient to drive ATP synthesis 

• 2 motors connected together via stator 

  • F₀: electric motor powered by flow of H⁺

  • F₁: chemical motor powered by ATP

    • joins ADP and phosphate together by force to create ATP

ABC-type ATPases

• ATP-binding cassette transporters mediate ATP-powered translocation of big molecules

  • 2 conformational states 

  • importers and exporters

  • some need a binding protein 

• conserved protein domain 

  • all ABC-type ATPases have a shared amino acid sequence in the ABC domain