Cell Project!!

My cell project! Okay, so this is my cell project for Living Environment ES. More specifically, on the cell membrane, not the entire cell. There are links on this page to sections explaining the different parts of the membrane, their functions, etc. etc. So look around, enjoy, and don't get too confused.

Introduction What you see up there is a nice simple diagram of the cell membrane. It took me about a minute to find online, and about two hours or so (no, really) to get it to show up on the web page, but that's okay. As you can see there are a few different parts labeled, and they are, in no particular order: membrane protein, cholesterol, glycoprotein, phospholipid, and plasma membrane. What I'm going to try and do is have a separate little section devoted to each of these, to explain them and how they all fit together for that picture. Also, farther down on this page is some stuff on different types of transport through the membranes, but they don't get their own page. Below the transport sections, there's a picture to better explain them. Okay, here goes.
Links Here's where you'll find all the links to other sections of the project.
Membrane Proteins
Cholesterol
Glycoproteins
Phospholipids
Plasma Membrane

Ads
See the ads up at the top of the page? I did not put those there! The webpage processor I'm using puts them there for me, and apparently they use stuff related to the website topic because it all seems to be cell-membrane-related. (Who finds ads about cell membranes, though? "50% discount on glycoproteins!" Right.) Anyway, just ignore them. They have absolutely nothing to do with the project and I don't know where they came from. All right, moving on.

Passive Transport
Passive transport is how material gets across the membrane without the cell using up any energy. Lazy transport, if you will. The definition given by my textbook here is "the movement of a substance through a cell's membrane without the expenditure of cellular energy," but if you don't know what expenditure means, my definition works just as well. This mainly works by diffusion; substances move into the cell down their concentration gradient. Different proteins in the membrane (that's right, membrane proteins, which have their own section. It's all coming together!) let different substances through. Facilitated diffusion is a type of passive transport in which a protein has a certain shape that will fit only one sort of molecule. These are called selective pores, because they SELECT what kind of molecule can go through. When a molecule enters the open end of the protein, it will open on the other end, close on the end that was previously open, and let the molecule out on the other side. This works based on the concentration gradient of the molecule, because wherever the concentration is greatest, it's more likely that those molecules will end up in the protein. Ion channels are another form of passive transport. Ions (charged particles) can't get through using facilitated diffusion, because only molecules with no charge are able to pass through those proteins. Ion channels are specially charged to allow ions through. Water molecules, because they're so small, can also pass through a membrane using simple diffusion; when the moving phospholipids have a gap between them, the water can fit right through. Diffusion of water is called osmosis.

Active Transport If passive transport is moving molecules across the cell membrane without using up energy, then logic follows that active transport is moving molecules across the membrane with the use of energy. This is used when a molecule needs to be moved against its concentration gradient. I'll put in the textbook definition again, which is "using energy to transport a particle through a membrane against a concentration gradient." This involves the use of membrane proteins called proton pumps, which are active transport channels. Proton pumps bring protons into the cell against their concentration gradient to build up a higher concentration of protons in the cell. The energy from the protons is then used to make ATP (adenosine triphosphate), a form of cell energy. ATP is used to power other kinds of active transport channels, like the sodium-potassium pump. The sodium-potassium pump brings potassium ions into the cell while releasing sodium ions from the cell in a way that is similar to facilitated diffusion (opening & closing channels). It builds up the amount of sodium outside the cell, and that sodium is later brought back in along with food molecules (like glucose) through another protein (these proteins working together are called coupled channels).

This shows a bunch of different types of transport through the membrane: active, passive and diffusion.

Citations (Web Sites)

Source of the first diagram (top of the page)
Source of the transport diagram