Cell Membrane Biology PDF

Do you know?? - The cell membrane, also known as the plasma membrane, is a thin, flexible barrier that surrounds the cell, providing it with structural support and protecting its internal environment. It primarily comprises a double layer of phospholipids, with proteins, cholester...

Do you know?? - The cell membrane, also known as the plasma membrane, is a thin, flexible barrier that surrounds the cell, providing it with structural support and protecting its internal environment. It primarily comprises a double layer of phospholipids, with proteins, cholesterol, and carbohydrates embedded within this bilayer. **Fluid-mosaic model** a\. Fluid = [pliable/easily moved] b\. Mosaic = made of many different molecules (lipids, proteins, carbohydrates) - The principal components of the plasma membrane are lipids (phospholipids and cholesterol), proteins, and carbohydrates. - The plasma membrane protects intracellular components from the extracellular environment. (security) - The plasma membrane mediates cellular processes by regulating the materials that enter and exit the cell. (checkpoint) - The plasma membrane carries [markers] that allow cells to recognize one another and can transmit signals to other cells via receptors. (to avoid confusion) Selectively Permeable Predict the two reasons things can't directly go through the membrane: - Size (duh)-H2O, ethanol, benzene, CO2, O2(smaller in size) - Polarity (from last unit) Phospholipid Bi-Layer - polar heads are hydrophilic "water loving" - tails (fatty acids) are hydrophobic "water fearing" and face inward Bi-Layer - a type of lipid that is made up of a polar head group and a hydrophobic tail. Because of their amphipathic nature (being composed of both hydrophilic and hydrophobic portion), they are able to create bilayers when placed in water. - In this kind of environment, the hydrophilic heads of the phospholipid are what face the water at the surface whereas the hydrophobic tails are protected from the water inside. Cholesterol - Changes fluidity of cell membrane (not watery, rigid - enough and it will be not permeable to any ions and - molecules.) - Higher temps -- stiffens membrane - Lower temps -- prevents membrane from freezing - Its OH (hydroxyl) group is what connects to the phospholipid head while the rest just connects with the fatty acid. Proteins (types) **Recognition Proteins (name tags)** - Proteins that have carbohydrate chains attached - Carbohydrate chains aid in cell identification - Example: Red Blood Cells (A, B), Identify Viruses as foreign (destroy) **Receptor Proteins (fit)** - Proteins that receive chemical signals from other cells; - Such as nervous system cells **Channel Proteins (large)** - Proteins that involved in letting certain substances in and out of cells. - [Aquaporins-] let water in and out of cells **Integral** - Proteins that cross both layers of the phospholipid bilayer **Peripheral** - proteins that are only on the top half or bottom half of the phospholipid bilayer Carbohydrates (outer surface) - They are linked to lipids and proteins in these locations, producing glycolipids and glycoproteins respectively. - Most plasma membranes are highly permeable to [small uncharged particles and some non-polar molecules] like oxygen and carbon dioxide. They also allow uncharged polar molecules like water but not larger ones like sugars (i.e. glucose). - Also, do not allow the entry of charged molecules, regardless of their size. - Such semi-permeability is highly necessary for [overall] cell control, maintenance of cell composition, and constant internal environment. CELL TRANSPORT - It is the movement of substances across the cell membrane either into or out of the cell. **Passive Transport** - occurs when substances cross the plasma membrane without any energy input from the cell. - Water solutions are very important in biology. When water is mixed with other molecules this mixture is called a solution. Water is the solvent, and the dissolved substance is the solute. - A solution is characterized by the solute. **Concentration\ - [Both ions are moved from areas] of lower to higher concentration, so energy is needed for this \"**uphill\" process.** - The energy is provided by **ATP**. The sodium-potassium pump also requires carrier proteins. - The primary active transport moves ions across a membrane and creates a difference in charge across that membrane. - The secondary active transport describes the movement of material using the energy of the electrochemical gradient established by the primary active transport. **Vesicle/Bulk Transport** - requires energy, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. **Endocytosis**- engulfs the/ particle - **Phagocytosis**- large material - **Pinocytosis**- liquid/ very small particles - **Receptor**-mediated endocytosis- coded pit **Exocytosis-** Release the contents outside the cell. - The movement of macromolecules such as proteins or polysaccharides into or out of the cell is called bulk transport. - Substances that can move via bulk transport are like hormones, polysaccharides, etc. An example of this is the engulfing of pathogens by phagocytes (endocytosis), then the release of the hydrolyzed pieces of the pathogen outside the cell by exocytosis. **ENZYMES** - Enzymes are **proteins** - Enzymes are very **specific** One enzyme, One function! - The substance that an enzyme change is called a **substrate**. - Each **chemical reaction requires a specific enzyme** - An enzyme cannot cause a reaction, however\... - Enzymes can be used over and over again - Recycle!! Example: digestion of food - They are made of protein - They work because they have a specific shape...works like a lock and key! **Enzyme Reactions** - **Digestion- Br**eaking down molecules - **Synthesis-** Building up molecules - On the surface of the enzyme is a region called an **active site**. The substrate will bond to the "[active site]" of the enzyme, then break into smaller "**pieces"**. Works like a **"lock and key".** AN ENZYME REACTION:  - When the substrate binds to the enzyme...A.K.A. - **THE ENZYME-SUBSTRAT E COMPLEX** **Naming Enzymes** **Add -ase to the end of the substrate** **Example:** **Substrate = maltose** **Enzyme = maltase** **Factors Affecting Enzyme Action** **1) Amount and concentration of enzyme/substrate** **2) Extreme Temperature** **3) pH -- Too acidic or basic** **Denaturation- an enzyme shape is changed and can no longer do its job.** Oxidation−Reduction Reactions Rust forms when the oxygen in the air reacts with iron. In this process, electrons are transferred from one substance to another. - provides us with energy from food. - provides electrical energy in batteries. - occurs when iron rusts: In an oxidation--reduction reaction, [electrons are transferred from one substance to another]. **OIL RIG** **O**xidation **I**s **L**oss of electrons. **R**eduction **Is** **G**ain of electrons.  **Oxidation** - always involves a loss of electrons. - may also be seen as an addition to oxygen. - may also be seen as the loss of hydrogen atoms. **Reduction** - always involves a gain of electrons. - may also be seen as the loss of oxygen. - may also be seen as the gain of hydrogen.