biol+3+summary+notes-membranes

Your notes on biomolecules was excellent. Now it is time to summarise the plasma membrane and movement of substances in the same clarity.

The sodium/potassium pump is a good example of active transport being continually used by cells. The cell continues to get rid of sodium ions (into extraceullar space) while intaking potassium ions from extracellular space into the cell. Sodium is more concentrated outside the cell and potassium is more concentrated in the cell. Thus in order to achieve the cell's aims, the cell must move the substances against their concentration gradient - this requiring active transport. Sodium ions within the cell bind to three specific slots in the protein channel. An ATP molecule then breaks one of it's phosphate bonds (via hydrolysis) attaching to the membrane and releasing the energy required for active transport. This changes the shape of the protein channel, which enables the sodium ions to move against their concentration gradient (from an area of low sodium conc. to an area of high sodium conc.) out of the cell. Potassium ions outside the cell are attracted to the new shape of the protein channel. Two potassium ions bond to the protein channel, changing its shape - which results in a relase of the bound phosphate molecule ( which can rejoin ADP creating ATP). The protein channel reutrns back to its old shape and the potassium ions are pumped into the cell against their conc gradient (from low potassium conc to high potassium conc). This process clearly displaying active transport visibly differs from other membrane transport types because:
 * The Sodium/Potassium Pump**

1. It requires the expenditure of energy by the cell (diffusion/facilitated diffusion/osmosis) 2. Can transport substances against conc. gradient (diff/fac-diff/osmo) 3. Moves substances through protein channels in membrane (diff/osmo) 4. Not involving water molecules within movement (osmo)

- the sodium/potassium pump occurs in action potential where electrical impulses are sent around body through neurons. In this case the cell becomes briefly positive as Na + rush in and then briefly negative as K + rush out.

QUESTION: I remember hearing in class there are two different types of protein channels (have different names). Is this true? I think the one that was different to just a nromal protein channel changed shape. // Answer: yes your are right. There are protein channels which are really just like a tunnel that allows lets say cars to travel through a mountain. Then there are protein carriers which involves the protein changing its shape to allow the substance through. eg a draw bridge (if you know what that it is). Hmmm... I think I have just come up with a perfect analogy. woohoo! VM //
 * RYAN**

Transport of biomolecules Transport of bio molecules where? you ask. Bio molecules are constantly being transported into and out of cells. For example, proteins are transported out of a cell through the organelle called ribosomes. The synthesis of proteins occurs in the ribosome. When the cell no longer needs the protein, the ribosome attaches itself to the cell membrane, where it joins and the protein passes through the plasma membrane and out of the cell. Protein can take another transportation route which is through the endoplasmic reticulum which then travels to the golgi apparatus for packaging and exportation. **Davina** =  Plasmas membrane and cholesterol =  Plasma membrane is made up of phospholipid (if you don’t remember they lipids with a phosphate attached to a glycerol, replacing a fatty acid chain), and their tails (hydrophobic) are attracted to each other, which produces the double bi-layer. The purpose of the phospholipid is in order for polar molecules (water) to be able to pass through the semi permeable layer from their external environment to internal environment of the cell. Scattered across the membrane are proteins needed for active transport or as carrier proteins. Imbedded in them are cholesterol molecules which are very important for cells because they allow communication between cells and without cholesterol, cell membranes would be too fluid, not firm enough, and too permeable to some molecules (rigid). Cholesterol is mostly **hydrophobic**, but it has one polar group, hydroxyl.   question: are fatty acid tails attracted to each other or just 'hate' water? wow first question, and a good one.... fatty acid tails DO 'hate' water, because they are non polar (hydrophobic) therefore dislike water, whether they are actually attracted to each other, hmm... tough question, im not sure, it may just be their arrangement in order for the hydrophilic heads to surround the outer layer. Hope that helps :)

Passive and Active Transport via plasma membranes: The plasma membrane is 'selectively permeable', meaning that it allows some substances to pass through it but not others. Substances pass through the plasma membrance via different processes, depending on the structure and the make up of the specific molecule(s). These processes include: diffusion (passive), osmosis (passive), facilitated diffusion (passive) and active transport (active) -- 'passive' meaning no input of energy is required for the process; and 'active' meaning an input of energy is required. Substances that can pass through easily by dissolving into the phospholipid bi-layer of the membrane - such as alcohol and chloroform(a liquid that causes unconsciousness) - are called 'lipid-soluble' substances, and can pass through via the process of diffusion. Molecules that are small and uncharged - such as O2, CO2, H2O and urea - can diffuse into the cell via diffusion, (or via osmosis for water molecules only), also through the phospholipid bi-layer. Amino acids (proteins), some ions and monosaccharides (simple sugars) are examples of 'water-soluble' substances, meaning that they pass through the protein channels of the plasma membrane, via the processes of either facilitated diffusion (passive) or active transport (active), depending on the substances passing through, and whether they are being transported against the concentration gradient or not. LA

Diffusion Diffusion is the passive movement of small molecules from an area of high concentration to an area of low concentration along a concentration gradient. The process of diffusion can be affected by a variety of factors such as concentration and temperature. Differences in concentration between two areas will affect the rate of diffusion. The greater the difference, the greater the rate of diffusion. If the concentration is equal in both of the two areas, there will be no net diffusion. Temperature can have a large impact on the rate of diffusion. An increased temperature will result in an increased rate of diffusion and alternatively, a decrease in temperature will result in a decrease in the rate of diffusion. AK.

Specific Structures of the plasma membrane There are many specific structures of the plasma membrane including phospholipids, protein channels, cholesterol, glycoproteins and glyco lipids. Protien channels are (as you can guess) made of proteins and are there to facilitate the diffusion of larger molecules and molecules that can't diffuse through the lipid bilayer, for example amino acids. As for the phospholipid bilayer, the head of the phospholipid is made of phospate and is hydrophilic (attracted to a water environment). The phospholipid tails made of fatty acids are hydrophobic and face eachother rather than water. The phosphate head (to be continued)

=
**The phospholipid make up** The plasma membrane is made up of a phospholipid Bilayer. Within that phospholipid Bilayer there are other molecular ingredients, but the bilayer is the basis of the membrane. The phospholipid have attached to a glycerol, a phosphate molecule, replacing a fatty acid chain, therefore differentiating from a triglyceride. (to be continued)

Two types of movements across a membrane are osmosis and active transport. Osmosis is a special type of diffusion that involves the movement of water molecules. It moves from a high concentration of free water molecules to an area of low concentration of free water molecules. Active transport is the only movement across a cell membrane that uses an input of energy. The process works in the opposite direction to osmosis. It moves from an area of low concentration of a substance to an area of high concentration of a particular substance. Osmosis moves through the phospholipid bi-layer and active transport can go through either the bi-layer or a protein channel depending on what need to be moved. GR.
 * Movement of Substances**
 * //(Osmosis and Active Transport)//**

The plasma membrane is comprised of many molecules and structures, the main 3 being phospholipids, cholesterol (provides support) and protein channels. They each play an important role in the survival of the cell, protecting it from the potentially harmful substances in the extracellular fluid and helping molecules to pass through the membrane that are needed in the cell. As phospholipids are a type of lipids, it means that lipid soluble substances such as alcohol are to easily able pass through the phospholipid bi – layer via diffusion. Diffusion also allows small uncharged molecules, including carbon dioxide and oxygen, to pass through. A special case of diffusion, named osmosis is the passing of water through the membrane, occurring when there is a call for for water inside the cell. Water soluble substances (unable to mix with lipids) such as monosaccharides, amino acids and some ions move through the phospholipid layer using the protein channels embedded in the membrane via active transport or facilitated diffusion, depending on the substance.
 * In or out?**

Water travels through cells via the process of osmosis. This process is a passive process of which water travels from high free water concentration to a low free water concentration. Extra cellular environments can have an effect on the way water travels in and out of the cell. An Isotonic extra cellular environment means that the concentration of water inside and outside the cell is equal. A hypertonic environment means that there are less free water molecules __outside__ the cell, and so the water will leave the cell in order to balance out the concentration. A Hypotonic environment is the opposite, meaning there is less free water molecules __inside__ the cell and therefore water will enter the cell. If too much water enters a cell it can cause the cell to burst (lyse), however in plant cells creating a hypotonic situation is utilised as guard cells need to be filled with water in order to become turgid and open the pores of the plant's leaves so to get some oxygen and CO2. MW
 * Extra cellular environments **

**Active Transport** Active transport is the use of carrier and channel proteins to move substances that are too large or water soluble to move through the phospholipid bilayer in or out of the cell. However, what makes this type of movement different is that it usually moves substances against the concentration gradient (that is, from area of low concentration to area of high concentration). One example of this is the movement of sodium and potassium ions in and out of the cell into areas of respectively high concentration. Unlike diffusion which moves with the concentration gradient and is a passive process, active transport moves against it and therefore requires energy, and ATP is used by the proteins to facilitate the transport. SB

Exocytosis is the process of molecules leaving the cell. It is the complete opposite of Endocytosis. Starting from the nucleus, it then heads through to the Endoplasmic Reticulum, through the Golgi Body and out of the cell. It is like a transport route for the molecules, and it helps them make their way to the membrane.
 * Exocytosis**

LR

Movement of substrates and concentration

There are four ways in which a substrate can move through the plasma membrane: - Osmosis  free water molecules (no solute attached to molecule) move passively through the phospholipid bi-layer from high to low concentration. - Diffusion  passive movement of a solute from high to low concentration through the phospholipid bi-layer. - Facilitated diffusion  same as diffusion but through proteins - Active transport  movement of a solute through a protein channel with the use of ATP (energy) from high to low concentration. Animal cells and plant cells are very simular, but both have very different membranes. Animal cells have permeable membranes that expand can be damaged by pressure and the membranes of plant cells are not permeable giving them a certain capacity limit that cannot be exceeded.
 * MG**