Transport Across the Cell Membrane L4

Structure of the Cell Membrane

• Composed of a phospholipid bilayer featuring hydrophilic heads and hydrophobic tails.
• Hydrophilic heads orient toward the aqueous environment, while hydrophobic tails face inward, creating a barrier that restricts water and water-soluble ions' passage.
• Integral proteins span the membrane, contributing to structural integrity and facilitating transport.

Membrane Protein Functions

• Channel Proteins: Provide pathways for the diffusion of water-soluble substances, such as glucose and electrolytes.
• Carrier Proteins: Assist in the transport of specific molecules across the membrane.
• Receptor Proteins: Serve as binding sites for hormones and neurotransmitters, facilitating cellular communication.
• Enzymatic Proteins: Catalyze chemical reactions that occur at the membrane surface.

Membrane Transport Definitions

• Cell-membrane transport: Mechanisms regulating the passage of solutes and molecules across the membrane.
• Permeability: Indicates how easily substances pass through the membrane; characterized as impermeable, freely permeable, or selectively permeable.

Types of Membrane Channels

• Leak Channels (Pores): Continuously open, allowing substances to pass freely.
• Voltage-gated Channels: Open in response to changes in membrane potential.
• Ligand-gated Channels: Activated by binding to specific molecules, such as neurotransmitters.

Mechanisms of Transport

• Directly through Lipid Bilayer: Fat-soluble substances (e.g., O2, CO2) diffuse through the bilayer directly.
• Through Protein Channels: Water-soluble substances (e.g., glucose, iron) utilize protein channels for transport.

Types of Membrane Transport

• Passive Transport:

  • Simple Diffusion: Movement along the concentration gradient without energy expenditure.
  • Facilitated Diffusion: Involves carrier proteins to assist diffusion.
  • Osmosis: Diffusion of water across a selectively permeable membrane.

• Active Transport:

  • Primary Active Transport: Directly uses ATP to move substances against their concentration gradient.
  • Secondary Active Transport: Relies on the energy from primary transport to move additional substances.
  • Vesicular Transport: Includes exocytosis and endocytosis for transporting large volumes or particles.

Factors Influencing Simple Diffusion

• Concentration Gradient: Greater differences in concentration between two sides of the membrane increase the diffusion rate.
• Molecular Size: Smaller molecules diffuse more easily than larger ones.
• Number of Open Channels: More available channels enhance the diffusion rate, such as sodium channels activated by acetylcholine at neuromuscular junctions.

Structure of the Cell Membrane

• Composed of a phospholipid bilayer featuring hydrophilic heads and hydrophobic tails.
• Hydrophilic heads orient toward the aqueous environment, while hydrophobic tails face inward, creating a barrier that restricts water and water-soluble ions' passage.
• Integral proteins span the membrane, contributing to structural integrity and facilitating transport.

Membrane Protein Functions

• Channel Proteins: Provide pathways for the diffusion of water-soluble substances, such as glucose and electrolytes.
• Carrier Proteins: Assist in the transport of specific molecules across the membrane.
• Receptor Proteins: Serve as binding sites for hormones and neurotransmitters, facilitating cellular communication.
• Enzymatic Proteins: Catalyze chemical reactions that occur at the membrane surface.

Membrane Transport Definitions

• Cell-membrane transport: Mechanisms regulating the passage of solutes and molecules across the membrane.
• Permeability: Indicates how easily substances pass through the membrane; characterized as impermeable, freely permeable, or selectively permeable.

Types of Membrane Channels

• Leak Channels (Pores): Continuously open, allowing substances to pass freely.
• Voltage-gated Channels: Open in response to changes in membrane potential.
• Ligand-gated Channels: Activated by binding to specific molecules, such as neurotransmitters.

Mechanisms of Transport

• Directly through Lipid Bilayer: Fat-soluble substances (e.g., O2, CO2) diffuse through the bilayer directly.
• Through Protein Channels: Water-soluble substances (e.g., glucose, iron) utilize protein channels for transport.

Types of Membrane Transport

• Passive Transport:

  • Simple Diffusion: Movement along the concentration gradient without energy expenditure.
  • Facilitated Diffusion: Involves carrier proteins to assist diffusion.
  • Osmosis: Diffusion of water across a selectively permeable membrane.

• Active Transport:

  • Primary Active Transport: Directly uses ATP to move substances against their concentration gradient.
  • Secondary Active Transport: Relies on the energy from primary transport to move additional substances.
  • Vesicular Transport: Includes exocytosis and endocytosis for transporting large volumes or particles.

Factors Influencing Simple Diffusion

• Concentration Gradient: Greater differences in concentration between two sides of the membrane increase the diffusion rate.
• Molecular Size: Smaller molecules diffuse more easily than larger ones.
• Number of Open Channels: More available channels enhance the diffusion rate, such as sodium channels activated by acetylcholine at neuromuscular junctions.