the cell membrane also known as a “plasma membrane”
TRANSCRIPT
The Cell Membrane
Also known as a
“plasma membrane”
Plasma Membrane
• Controls materials entering and leaving the cell
• Helps regulate homeostasis
• Plasma membrane has selective permeability
similar to a window screen
Made of phospholipids with embedded proteins.
Phospholipid
Types of proteins in cell membrane
1. Cell-surface marker: identifies cell type and identifies cells as “self”.
2. Receptor Protein: recognizes and binds to substances outside the cell
3. Enzyme: Assists chemical reactions inside the cell
Example: sucrase and
maltase are embedded
into cells of the
small intestine,
where they digest
disaccharides
4. Transport protein: Helps substances move across cell membrane.
Cellular Transport
Sections 3-4 and 3-5
I. Passive Transport• Materials move across membranes
because of a concentration gradient.
• Does not require energy.
Diffusion is a type of passive transport.
• Molecules move from an area of high concentration to an area of low concentration.
A. Diffusion
• Continues until equilibrium is reached
B. Osmosis
• How is osmosis different from diffusion?
• It only deals with movement of water
• Isotonic: same concentration of dissolved particles inside and outside of cell; cell stays the same size
Three Types of Solutions
• Hypotonic: less dissolved particles outside cell than in
cell; cell gains water and swells
• Hypertonic: more dissolved particles outside cell than in cell; cell loses water and shrinks
• Osmosis in Plant cells
• Practice Problem:
• Sea water has a higher concentration of salt than human body cells have.
• Why might drinking large amounts of sea water be dangerous for humans?
• Facilitated diffusion is passive transport of materials across the plasma membrane with the aid of transport proteins .
• Molecules such as sugars or amino acids enter the cell through facilitated diffusion
• Channel protein shown at right – provides a tubelike opening for small molecules
C. Facilitated Diffusion
• Carrier proteins change shape to let larger molecules into the cell
Cells use energy to transport materials against the concentration gradient
II. Active Transport
• Active transport is powered by chemical energy (ATP).
Active Transport
• Active transport occurs through transport proteins
A cell can import large materials in vessicles during the process of endocytosis.
• Cells use energy to transport material in vessicles.
Endocytosis
Exocytosis
•Exocytosis is the process of expelling material from the cell.