IP Week 6: Biological Membranes

Biological Membranes

Click the sound button for audio!

Lecture Goals:

• 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

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)

Presentation Links

Membrane Transport

Membrane Properties

Overview Video

Biological Membranes

Biological Membranes

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"

Phospholipid Membranes

Membrane Overview

Test your Knowledge

Check your notes

• 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

Membrane Properties

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

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

Membrane Properties

General Properties

• Flexible and self-sealing

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

3D model of the phospholipid bilayer

Vesicle

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

Check your notes

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

02:00

Membrane Transport

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

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

Click the arrow to see the movement of water!

Membrane Transport

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)

Protein transport channel

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

Summary

#4

#1

#2

#3

Osmosis (diffusion of water) is not pictured here!

Check your notes

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

02:00

End-of-Lecture Questions

On a sticky note, write down...

• A concept you still don't understand OR

• One question

02:00

Membrane Transport

Membrane Potential

Positively-charged

Negatively-charged

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

Crash Course Video: Action Potentials

Khan Academy article about membrane potentials in 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)

Check your notes

• 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

Membrane Transport

Membrane Transport

Membrane Transport

End-of-Lecture Questions

On a sticky note, write down...

• A concept you still don't understand OR

• One question

02:00

Recommended Textbook Reading

OpenStax Biology 2e: Chapter 5

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