Transport Across the Cell Membrane L4

Study Notes

Composed of a phospholipid bilayer which consists of hydrophilic heads and hydrophobic tails.
Restricts passage of water and water-soluble ions, making the membrane selectively permeable.

Integral Proteins: Provide structural integrity to the cell membrane and form channels for diffusion.
Channel Proteins: Allow water-soluble substances (like glucose) and electrolytes to cross the membrane.
Carrier Proteins: Facilitate the transport of specific substances across the membrane.
Receptor Proteins: Serve as sites for hormone and neurotransmitter binding.
Enzymatic Proteins: Control biochemical reactions occurring at the membrane.

Cell-Membrane Transport: Mechanisms that regulate the passage of solutes and molecules through the membrane.
Permeability: Degree to which substances can pass through the membrane. Characterized as impermeable, freely permeable, or selectively permeable.

Leak Channels: Continuously open pores that allow substances to pass freely.
Voltage-Gated Channels: Open in response to changes in electric potential across the membrane.
Ligand-Gated Channels: Open when neurotransmitters or hormones bind to receptor sites outside the cell.

Passive Transport: Does not require energy. Includes:
- Simple Diffusion: Movement from high to low concentration or according to an electrochemical gradient.
- Facilitated Diffusion: Uses protein channels to transport substances.
- Osmosis: Movement of water through a selectively permeable membrane.
Active Transport: Requires energy (ATP). Includes:
- Primary Active Transport: Directly uses ATP to transport substances against their gradient.
- Secondary Active Transport: Utilizes the energy from primary transport processes.
- Vesicular Transport: Involves exocytosis (exporting substances) and endocytosis (importing substances).

Involves the passive transport of molecules and ions based on concentration gradients without energy usage.
Lipid-soluble and non-polar molecules, such as oxygen and carbon dioxide, diffuse easily through the lipid bilayer.

Concentration Difference: Greater differences between the two sides of the membrane result in faster diffusion.
Molecular Size: Smaller molecules diffuse more easily across the membrane than larger ones.
Open Channels: The presence of more open protein channels enhances the rate of diffusion for specific ions and molecules.

Understanding the components and functions of the cell membrane is crucial for grasping how substances are transported, which is vital for cellular homeostasis and communication.