H Week 6: Biological Membranes

Biological Membranes

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)

Click the sound button for audio!

"Venus Flytrap" by USFWS/Southeast is marked with Public Domain Mark 1.0.

Membrane Properties

Overview Video

Membrane Transport

Presentation Links

Biological Membranes

"0303 Lipid Bilayer With Various Components" by OpenStax is licensed under CC BY 4.0.

Biological Membranes

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.

Membrane Overview

Nanoparticles Coated with Cell Membranes for Biomedical ApplicationsNanoparticles designed for diagnosing and treating different diseases have impacted the scientific research in biomedicine, and are expected to...MDPI

Biological Membranes

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

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

• Phospohlipids are made from...
• Two hydrophobic lipid "tails" attached to a polar hydrophilic "head"

Membrane Overview

"0302 Phospholipid Bilayer" by OpenStax is licensed under CC BY 4.0. "0301 Phospholipid Structure" by OpenStax is licensed under CC BY 4.0.

Phospholipid Membranes

Membrane Overview

"0303 Lipid Bilayer With Various Components" by OpenStax is licensed under CC BY 4.0.

Test your Knowledge

Check your notes

02:00

Check your notes, can you:

• Describe what is found in a cell membrane
• Define amphipathic
• Describe the two components of a phospholipid

Membrane Properties

• Flexible and self-sealing

• Can fuse with other membranes
• Spontaneously form rings called closed vesicles

General Properties

3D model of the phospholipid bilayer

"Cell membrane" by Lukas Ded is licensed under CC BY 4.0. https://www.thoughtco.com/what-is-exocytosis-4114427

Membrane Properties

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

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

Check your notes

02:00

Check your notes, can you define:

• Osmosis
• Exocytosis
• Endocytosis

(Make sure you watched the Crash Course overview video!)

Membrane Transport

Passive transport requires no energy to occur.Types of Passive Transport:

• Diffusion
• Chemicals move from high concentration to low concentration
• Osmosis (special case of diffusion)
• Movement of water across a semi-permeable membrane
• Water moves from the hypotonic side to the hypertonic side
• Net movement is zero if sides are isotonic

Passive Transport

Click the arrow to see the movement of water!

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

Hypotonic solution (more water and less solute)

Hypertonic solution (less water and more solute)

Membrane Transport

Molecules that can move through the membrane easily via diffusion:

• Small, non-polar or non-charged molecules

Molecules that can move through the membrane via facilitated diffusion:

• Polar or charged molecules
• Still typically small (endocytosis transports larger)
• Requires a protein transport channel - transmembrane protein

What Moves By Diffusion?

Protein transport channel

"File:0306 Facilitated Diffusion Channel Protein labeled.jpg" by OpenStax is licensed under CC BY 3.0.

Membrane Transport

Active transport requires energy to occur.

• Chemicals move from low concentration to high concentration
• Requires energy in the form of ATP

• Causes proteins to change shape:
• Opens channels
• Allows for the temporary binding of molecules for transport

Active Transport

Membrane Transport

Three Types of Transport

#1

#2

#3

"Passive vs Active Membrane Transport" by LSumi is licensed under CC BY-SA 4.0.

Membrane Transport

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 Potential

BioInteractive: Neuron Activity

Positively-charged

Negatively-charged

"Membrane potential ions en" by Gibbs-donnan-en.svg: Biezl derivative work: Looie496 (talk) is licensed under CC BY-SA 3.0.

Membrane Transport

• 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)

Osmosis and Plants

Check your notes

02:00

Check your notes, can you define:

• Passive transport
• Active transport
• Tonicity (hypertonic, hypotonic, and isotonic)
• Membrane potential

Recommended Textbook Reading

OpenStax Biology 2e: Chapter 5

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