2.4++Membranes

2 Cells - 2.1 Cell theory - 2.2 Prokaryotic cells - 2.3 Eukaryotic cells - 2.4 Membranes - 2.5 Cell division - Cell Labs

2.4 Membranes
Back to chemistry from previous years; distinguish between //solute, solvent// and //solution//.
 * Starter**

Crash Course Biology: In Da Club - Membranes & Transport media type="custom" key="24901766"

Challenge yourself to build and defend the membrane with this game media type="file" key="CellDefense.swf" width="640" height="480"

How well are your drawing skills progressing? Watch and draw your own example membrane media type="custom" key="24508108"


 * Assessment statements ** (IBO notes added to some point to clearly indicate what needs to be understood and what does not)
 * 2.4.1 || Draw and label a diagram to show the structure of membranes. The diagram should show the phospholipid bilayer, cholesterol, glycoproteins, and integral and peripheral proteins. Use the term plasma membrane, not cell surface membrane. ||
 * 2.4.2 || Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes. ||
 * 2.4.3 || List the functions of membrane proteins. Include the following: hormone binding sites, immobilized enzymes, cell adhesion, cell-to-cell communication, channels for passive transport, and pumps for active transport. ||
 * 2.4.4 || Define diffusion and osmosis. ||
 * 2.4.5 || Explain passive transport across membranes by simple diffusion and facilitated diffusion. ||
 * 2.4.6 || Explain the role of protein pumps and ATP in active transport across membranes. ||
 * 2.4.7 || Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane. ||
 * 2.4.8 || Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis. ||

__Diffusion__ is the passive movement of particles from a region of high concentration to a region of low concentration. __Osmosis__ is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration.
 * Key definitions**

Cell membranes are critical to cell formation. Understanding cell membranes is very important in understanding what makes a cell and how they function. You will be using knowledge from this topic repeatedly through the course. Respiration, Photosynthesis, Nerves and the nervous system being just a few examples.

Log in to the [|DCS Bridge] to obtain your workbooks and supporting resources
 * Workbooks and Worksheets**

[|McGraw-Hill online learning] has a good basic introduction membranes. It lacks the detail you need, but it does set a good context and gives a good overview.
 * Presentations and tutorials**

The John Kyrk tutorial on membranes contains a lot of key terms you don't need, but does give a good clear understanding of structure and function. This resource is recommended for HL students.

Steven Taylor ([|i-Biology]) has a great presentation to view and take notes from before starting your notebook media type="custom" key="23681298"

Jason De Nys also has a very good presentation to use for note development media type="custom" key="24508056"

[|This tutorial] shows the fluidity and structure of the plasma membrane This [|interactive tutorial] allows you to build your own plasma membrane - very helpful for learning the structure Here's an alternative [|tutorial] to learn and review plasma membrane structure

Biocoach has a couple of nice tutorials on [|Membrane Structure and Transport] and [|Membrane Dynamics & Communication] along with quizzes to test your learning

The University of Utah has great pages on [|vesicles] and the [|complexity and importance membranes]

The [|biostuff tutorials] can be used later after note taking to check and reinforce knowledge as it directly reflecting the assessment statements

Use teaching and visualization animations from St Olaf:
 * Diffusion
 * Osmosis
 * Facilitated diffusion
 * Examples of active transport, uniports, symports, antiports (e.g. resting potential in neurones)
 * Phagocytosis shows not just how endocytosis happens, but the following events leading to assimilation of nutrients
 * The fluidity of membranes


 * The approach**

__Learn by teaching (peer teaching)__ You will teaching others in the class and learning from them. Below are the rules of the game: > - membrane structure (2.4.1-2.4.2) > - functions of membrane structures (2.4.3) > - transport of small substances (2.4.4-2.4.6) > - transport of large substances (2.4.7-2.4.8) > - notes which they can consult, but not share with students when teaching > - a teaching aid which may consist of a maximum of 2 sheets of A4 and may contain a __maximum of 5 words__. > //During note completion and self-assessment you will be given the opportunity, if you feel it is necessary to attend mini-tutorials to further develop your understanding of membranes.//
 * 1) Decide in cooperation with the rest of the class what you will become an expert in choices are:
 * 1) You will be allocated time to review the resources above or your texts to become expert in your chosen area.
 * 2) You will work in small teams (3-4 people).
 * 3) Each person needs to develop a set of resources:
 * 1) You allotted time (approximately 8 minutes) to teach others.
 * 2) You will take turns to learn from other groups and develop notes.
 * 3) Teachers should give the learners time to ask questions when concepts are not clear.
 * 4) You will have two opportunities to teach and consequently two opportunities to learn from each of the other groups.

__Note development__ For this topic you will be building your own set of notes. Create a document and entitled //2.4 Membrane Notes//. Create section heading in the document to match the assessment statements. For each section complete the assigned tasks and add notes and learning gathered by the peer teaching activity. It is suggested that you leave extensions until all other work has been completed.

2.4.1 Draw and label a diagram to show the structure of membranes. The diagram should show the phospholipid bilayer, cholesterol, glycoproteins, and integral and peripheral proteins. Use the term plasma membrane, not cell surface membrane.
 * Draw and label a diagram as outlined above
 * Include a textbook diagram for reference

2.4.2 Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes.
 * Annotate a diagram of a single phospholipid molecule to include show how it's hydrophobic and hydrophilic properties
 * Explain how these properties relate to the formation of a bilayer
 * Include a simple diagram of a bilayer

2.4.3 List the functions of membrane proteins. Include the following: hormone binding sites, immobilized enzymes, cell adhesion, cell-to-cell communication, channels for passive transport, and pumps for active transport.
 * For each of the above named proteins briefly state their function
 * Extension: outline their location in the membrane (e.g. integral/peripheral) and, if relevant, structural adaptations that aid their function.

2.4.4 Define diffusion and osmosis.
 * Write out a definition of both terms
 * Add a footnote to outlining how diffusion happens, include the word //random// in your footnote

2.4.5 Explain passive transport across membranes by simple diffusion and facilitated diffusion.
 * Distinguish between simple diffusion and facilitated diffusion.
 * Detail facilitated diffusion and make sure to distinguish between carrier proteins and protein channels.
 * Extension: how is the variable hydrophobic/charged/polar nature of the protein related to it's function?

2.4.6 Explain the role of protein pumps and ATP in active transport across membranes.
 * Outline the conditions in which a cell needs to carry out active transport
 * Describe the structure and location of a protein pump in the plasma membrane
 * State what ATP is and why it is need in the process of active transport, what effect does ATP have upon the protein pump?
 * Use annotated diagrams to detail active transport

2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane.
 * Explain means to give a detailed account, do so
 * Be sure to include: protein synthesis by the ribosome, path taken by proteins, vesicle formation (x2), the role of the golgi apparatus and exocytosis.
 * Include an annotated diagram as part of your notes

2.4.8 Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis.
 * Describe and distinguish between endocytosis and exocytosis
 * Fluidity of the membrane can be explained by the directions membrane phospholipids can and can't move. Give a short account, you may find a diagram helpful.
 * State the effect that cholesterol has upon membrane fluidity
 * Outline what happens to the arrangement of phospholipid moelcules when membranes touch (reverse is true of when the lose contact)

__Self assessment__ Complete the following questions, without the help of texts. Add the questions and answers to your notes. You will be given an opportunity later to amend your answers:
 * 1) What are the general functions of the plasma membrane?
 * 2) Why is the term 'fluid mosaic model' used to explain what we know about the structure of the plasma membrane?
 * 3) Describe the term selectively permeable in the context of the plasma membrane.
 * 4) Distinguish between receptor proteins and adhesion proteins.
 * 5) How can the rate of diffusion across a membrane be increased? //Hint: there is more than a single answer.//
 * 6) In what conditions would a cell need to carry out active transport across the plasma membrane?
 * 7) If a substance is transport actively across a plasma membrane can it cross the membrane in any other ways?
 * 8) Given the various ways a substance can travel across a membrane why are the processes of endocytosis and exocytosis necessary?

Exploring Life's Origins has a nice page of micelle and vesicle formation and the importance of membranes to living cells - more than you need to know, but useful background information Explore learning has a nice [|simulation to show how diffusion works] North Harris College has lots of useful [|animations] on membranes The [|John Kyrk animation/tutorial] is very good, but has more information than you need on some membrane components Not just for fun this rap video made by students at Standford Uni has a lot of useful information in it too: media type="custom" key="23681328"
 * Useful Links**