IP Week 6: Biological Membranes

Click the sound button for audio!

Course Competencies: 9. Describe the structure and functions of biological membranes. (IV) 10. Describe the importance of membrane structure to cellular permeability and transport processes. (IV)

• Become familiar with biological membrane structure
• Understand membrane permeability and transport mechanisms
• Understand the interaction of water and membranes, especially concerning tonicity (hypertonic, hypotonic, isotonic) and osmosis

Lecture Goals:

Biological Membranes

Biological Membranes

Presentation Links

Membrane Transport

Overview Video

Membrane Properties

Membrane Overview

Biological membranes are composed of...

• Lipids
• Proteins
• Sometimes carbohydrates

Functions:

• Gatekeeper of the cell
• Identifies and protects against invaders (like bacteria and viruses)
• Transports food, waste, hormones, etc.

Biological Membranes

Membrane Overview

One of the main components of the biological membrane are phospholipids.

• Phospholipids are amphipathic molecules
• Amphipathic - contain both nonpolar and polar regions

• Phospholipids are made from:
• Two hydrophobic (nonpolar) lipid "tails" attached to a...
• Hydrophilic (polar) "head"

Biological Membranes

Membrane Overview

Phospholipid Membranes

Test your Knowledge

• What are the three types of organic macromolecules found in a cell membrane?
• What are the two components of a phospholipid?
• Why are phospholipids amphipathic?

02:00

Check your notes

Video Transcript: https://www.biointeractive.org/how-does-stuff-get-your-cells-cell-membranes-crash-course-biology-24

How Does Stuff Get Into Your Cells? (BioInteractive - Crash Course Biology Video)

Membrane Properties

Vesicle

3D model of the phospholipid bilayer

General Properties

• Flexible and self-sealing

• Can fuse with other membranes
• Can spontaneously form rings called vesicles

Membrane Properties

Tranport Using Vesicles

• Endocytosis - type of transport that moves molecules into the cell
• Cell membrane pinches off to create a vesicle

• Exocytosis - type of transport that moves molecules out of the cell

• Vesicle fuses to the cell membrane and releases molecules out of the cell
• Endocytosis and exocytosis are used to transport larger molecules

Membrane Properties

• Are membranes rigid or flexible structures?
• What is exocytosis?
• What is endocytosis?

02:00

Check your notes

Hover your mouse over the blue water on each side of the membrane

Click the arrow to see the movement of water!

Passive Transport

Passive transport requires no energy to occur.

• Diffusion
• Chemicals move from high concentration to low concentration through the membrane
• 2 types: simple and facilitated diffusion

• Osmosis (special case of diffusion)
• Movement of water through a semi-permeable membrane
• Water moves from the hypotonic side to the hypertonic side
• Net movement is zero if sides are isotonic

Membrane Transport

Protein transport channel

What Moves By Diffusion?

Molecules that can move through the membrane easily via simple diffusion:

• Small, nonpolar or non-charged molecules

Molecules that can move through the membrane via facilitated diffusion:

• Polar or charged molecules
• Still typically small in size (endocytosis transports larger molecules)
• Requires a protein transport channel (type of membrane protein)

Membrane Transport

Active Transport

Active transport requires energy to occur.

• Chemicals move from low concentration to high concentration through a membrane
• Requires energy in the form of ATP and membrane proteins

• Energy is used to change the shape of membrane proteins:
• Opens protein channels
• Allows for temporary binding of molecules for transport

Membrane Transport

#3

Osmosis (diffusion of water) is not pictured here!

#4

#2

#1

Summary

Membrane Transport

• What is the difference between passive transport versus active transport?
• What are the types of passive transport?

02:00

Check your notes

On a sticky note, write down...

• A concept you still don't understand OR

• One question

End-of-Lecture Questions

02:00

Khan Academy article about membrane potentials in nerve cells

Negatively-charged

Positively-charged

Crash Course Video: Action Potentials

Membrane Potential

Membrane potential is the difference of ions between two sides of the membrane.

• Maintained through active transport
• Used for chemical signaling/cell communication
• Example: Nerve cells

Membrane Transport

Osmosis and Plants

• Plant cells are hypertonic to their surroundings causes excess water to enter and fill their cells

• Cell walls prevent the cell from bursting
• Turgor pressure - pressure exerted by fluids (mainly water) inside the cell against its cell wall
• Plants can manipulate turgor pressure through osmosis and the central vacuole
• Results in a range of plant behavior (movement and growth)

Membrane Transport

• If a plant cell is hypotonic to its environment, will water move into or out of the plant cell?
• If a plant cell is hypertonic to its environment, will water move into or out of the plant cell?

02:00

Check your notes

Membrane Transport

Membrane Transport

Membrane Transport

On a sticky note, write down...

• A concept you still don't understand OR

• One question

End-of-Lecture Questions

02:00

Not required, but highly recommended (Especially if there's something you still need review on)!

OpenStax Biology 2e: Chapter 5

Recommended Textbook Reading