Cellular Transport Module 5 PDF

The cell is dynamic system that has its own organized ways of controlling the passage and transport of materials. The cell membrane is like a busy highway with lots of molecules being transported within and outside the cell. The traffic of the transport of molecules is well coordinated such that mol...

The cell is dynamic system that has its own organized ways of controlling the passage and transport of materials. The cell membrane is like a busy highway with lots of molecules being transported within and outside the cell. The traffic of the transport of molecules is well coordinated such that molecules know where to pass through, when and how to be transported. This module describes the cellular mechanism that ensures the efficient transport system of different important molecules into and out of the cell. **Intended Learning Outcomes** In this module, you will be able to: 1. Describe Passive and Active Processes 2. Differentiate the types of Passive and Active Process 3. Explain how molecules are transported across the plasma membrane 4. Describe osmosis and its effects to the cell 5. Compare phagocytosis, pinocytosis, and receptor-mediated endocytosis **Biological Membranes** Biology: Structure and function of plasma membrane Flashcards \| Quizlet ***Figure 5.1 Structure of Plasma Membrane*** (https://quizlet.com/123452318/biology-structure-and-function-of-plasma-membrane-flash-cards/) **The Membrane Structure** The fluid mosaic model characterizes the plasma membrane and other cell membranes as consisting of a double layer, or bilayer, of lipid molecules. A number of proteins are embedded in the lipid bilayer in a way that resembles a mosaic pattern. The membrane structure is fluid rather than motionless, and the lipids (and protein molecules, to a lesser extent) move laterally (sideways) within the membrane. One of the important lipid components of membranes is phospholipid, composed of a glycerol molecule to which are attached two fatty acids and a molecule containing a phosphate group. The phosphate end of the phospholipid molecule is polar---that is, slightly charged---whereas the fatty acid chains are nonpolar. The polar "head" is hydrophilic (from the Greek hydro, "water," and phil, "love"); that is, it has an affinity for water. The nonpolar "tail" is hydrophobic (from the Greek hydro, "water," and phobos, "fear"); that is, it has an aversion to water. Because the cell and its surroundings are composed largely of water, phospholipids and other lipid components of membranes spontaneously arrange themselves in a double layer. The hydrophilic heads are positioned on the outer edges of each side of the layer---toward the watery surroundings inside and outside the cell or organelle. The hydrophobic tails form the inside of the double layer (away from the water). No chemical reactions occur to hold the membrane molecules together, nor do covalent bonds connect adjacent molecules. The forces of hydrophilic portions that are attracted to water and of hydrophobic regions that are repelled by water are strong enough to form and maintain the membrane's structure. **Cell Physiology** Each of the cell's internal parts is designated to perform a specific function for the cell. Most cells have the ability to metabolize (use nutrients to build new cell material, break down substances, and make ATP), digest food, dispose waste, reproduce, grow, move and respond to a stimulus (irritability). **Membrane Transport** The fluid environment on both sides of the plasma membrane is an example of a *solution*. **Solution** is a homogenous mixture of two or more components (ex. Air we breathe, sea water, rubbing alcohol). The substance present in the largest amount in a solution is called **solvent** (or dissolving medium), water is the body's chief solvent. Components or substances present in smaller amount are called **solute**s. - **Intracellular fluid** (collectively, nucleoplasm and the cytosol) is a solution containing small amounts of gases (oxygen and carbon dioxide), nutrients, and salt, dissolved in water. - **Extracellular fluid**, the fluid that continuously bathes the exterior of our cells. It composes of nutrients, regulatory substances such as hormones and neurotransmitters, salt, and waste products, to remain healthy, each cell must extract from this fluid the exact amount of the substances it needs at a specific times and reject the rest. The plasma membrane is a **selectively permeable barrier**. This means that it allows some substance to pass through it and excluding others. Thus, it allows nutrients to enter the cell but keeps many undesirable or unnecessary substances out. At the same time, valuable cell proteins and other substances are kept within the cell, and wastes are allowed to pass out of it. Substances move through the plasma membrane in basically two ways -- passively or actively. In passive processes, substances are transported across the membrane without any energy input from the cell. In active process, the cell provides the metabolic energy (ATP) that drives the transport process. **Passive Processes: Filtration and Diffusion** 1. **Filtration** is a process by which water and solutes are forced through a membrane (or capillary wall) by ***fluid, or hydrostatic, pressure***. In the body, **hydrostatic pressure** is usually exerted by the blood. Like diffusion, filtration is a passive transport, and a gradient is involved. The **gradient** is a pressure gradient that actually pushes solute-containing fluid (filtrate) from the higher concentration area through the filter to the lower-pressure area. In Kidneys, water and small solutes filters out of the capillaries into the kidney tubules because the blood pressure in the capillaries is greater than the fluid pressure in the tubules. Part of the filtrate formed in this way eventually becomes urine. Filtration is not very selective. For most part, only blood cells and protein molecules too large to pass through the membrane pores are held back. 2. **Diffusion** is the process by which **molecules (and ions) moves from the area of high concentration to an area of low concentration**. The greater the difference in concentration between the two areas, the faster diffusion occurs. The rate of diffusion is affected by the size of the molecules (the smaller the faster) and temperature (the warmer the faster). The hydrophobic core of the plasma membrane is physical barrier to diffusion, However, molecules will diffuse through the plasma membrane if any of the following are true: - Molecules are small enough to pass through the membrane's pores (channels formed by membrane proteins). - The molecules are lipid soluble - The molecules are assisted by a membrane carrier. C:\\Users\\user\\Pictures\\Blausen\_0213\_CellularDiffusion.png ***Figure 5.3 Diffusion of different substance through a Plasma Membrane*** (https://en.wikipedia.org/wiki/Passive\_transport) **Types of Diffusion** 1. **Simple of Diffusion** -- unassisted diffusion of solutes through a plasma membrane. Solutes transported this way are lipid soluble (such as fats, fat-soluble vitamins, oxygen, carbon dioxide). 2. **Osmosis** -- diffusion water through a plasma membrane. Because water is highly polar, it is repelled by the (nonpolar) lipid core of the plasma membrane, but it can and does pass easily through special pores called **aquaporins** ***("water pores").*** 3. **Facilitated Diffusion** -- provides passage for certain needed substances (notably glucose) that are both lipid-insoluble and too large to pass through membrane pores, or charged, as in the case of chloride ions passing through a membrane channel. Although facilitated diffusion follows the concentration gradient (movement from high concentration area to low concentration area) a protein channel is used, or a membrane protein acts as a carrier is needed to move glucose and certain substances. **Tonicity** The tendency of a solution to hold water or "pull" water into its cell is called *osmotic pressure*. **Osmotic pressure** is directly related to the concentration of solutes in the solution. The higher solute concentration, the greater the osmotic pressure and the greater the tendency of water to move into the solution. Any changes in the concentration of on one side of the membrane to the other may cause the cell to lose or gain water. The ability of a solution to change the size and shape of cells by altering the amount of water they contain is called ***tonicity***. A cell's plasma membrane is relatively impermeable to sugars and salts, but water moves across the membrane freely in either direction. When a cell is placed in a solution with a solute concentration equal to that inside the cell, water molecules diffuse through the plasma membrane equally in both directions. Such solutions are said to be **isotonic** (from the Greek ***iso, "equal"***)---that is, they have a solute concentration equal to that in the cell. When a cell is placed in a solution with a solute concentration higher than that within the cell, the solution is said to be **hypertonic** (from the Greek ***hyper, "over")*** to the cell. In such a situation, water flows out of the cell and into the surrounding and the cytoplasm shrinks. When a cell is placed in a solution with a solute concentration lower than that within the cell, the solution is said to be **hypotonic** (from the Greek ***hypo, "under***") to the cell. In such a situation, water flows into the cell from the surrounding solution and the cell swell.  ***Figure 5.4. Osmosis in Blood Cells*** (http://encyclopedia.lubopitko-bg.com/OsmosisAffectsCells.html) **Active Processes** Whenever the cell uses ATP to move substances across the membrane, the process is active. Substances move actively are usually unable to pass in the desired direction by diffusion. They may be too large to pass through the membrane channels, the membrane lacks specific carrier proteins for their transport, they may not be able to dissolve in the fat core, or they may have to move "uphill" against their concentration gradients. The most important active processes are Active transport and Vesicular transport. 1. **Active transport** -- sometimes called ***solute pumping***, is similar to facilitated diffusion in that both processes require transport protein carriers that interact specifically and reversibly with the substances to be transported across the membrane. **Active transport uses energy (ATP) to energize protein carriers**, which are called solute pumps. Amino acids, some sugar, and most ions are transported by solute pumps, and most cases these substances move against the concentration gradients. - **Sodium Potassium (**[Na^**+**^]{.math.inline} **-**[**K**^**+**^]{.math.inline}**) pump** -- alternately carries sodium ions [(*Na*^+^)]{.math.inline} out of and potassium [(*K*^+^)]{.math.inline} into the cell. This process is absolutely necessary for normal transmission of nerve impulses. There are more sodium ions outside the cell than inside, so those inside tend to remain in the cell than inside unless the cell uses ATP to force, or "pump," them out. ATP is split into ADP and [*P*~*i*~]{.math.inline} (inorganic substance) and the phosphate is then attached to the sodium-potassium pump in a process called **phosphorylation**. Likewise, there are more potassium ions inside cells than in the extracellular fluid, and potassium ions leak out of cells must be actively pumped back inside. Because each of the pumps in the plasma membrane transport only specific substances, active transport provides a way for the cell to be very selective in cases where the substances cannot pass by diffusion. (NO pump -- no Transport). 2. **Vascular Transport -** involves help from ATP to fuse or separate membrane vesicles and the cell membrane, moves substances into or out of the cells "in *bulk*" without their actually crossing the plasma membrane directly. The two types of vesicular transport are **exocytosis** and **endocytosis**. - **Exocytosis --** is the mechanism that cells use to actively secretes hormones, mucus, and other cell products or to eject certain cellular wastes. The product to be released is first packaged in a secretory vesicle. These vesicle migrates to the plasma membrane, fuse with it, and then ruptures, spilling its contents out of the cell. Exocytosis involves a ***"docking"*** process in which docking proteins on the vesicles recognize plasma membrane docking proteins and bind with them. This binding causes the membranes to ***"cork screw"*** together and fuse.  ***Figure 5.6 Exocytosis in the Cell*** (https://www.thoughtco.com/what-is-exocytosis-4114427) - **Endocytosis** -- includes those ATP -- requiring processes that take up, or engulf, extracellular substances by enclosing them in a vesicle. Once a vesicle is formed, it detaches from the plasma membrane and moves into the cytoplasm, where it typically fuses with lysosome and its content are digested. However, in some cases, vesicle travels to the opposite side of the cell and release its content by exocytosis there. If the substances are relatively large particles, such as bacteria or dead body cells, and the cells separates them from the external environment by pseudopods, the endocytosis process is more specifically called ***PHAGOCYTOSIS*** ("cell eating"). Cell eat by phagocytosis and drink by a form of endocytosis called ***PINOCYTOSIS*** ("cell drinking"). **Activity 2.2** **Cellular Transport** I. **Completing the Table:** Complete the table by identifying the terms corresponding to the following descriptions. **Answer** **Description** ------------ -------------------------------------------------------------------------- 1\. Particle movement from an area of lower concentration to an area of higher concentration using a transport protein 2\. The diffusion of water through a cell membrane 3\. It is used during active transport but not passive transport 4\. Particles movement from an area of high concentration to lower concentration area 5\. When energy is required to move materials through a cell membrane 6\. Particle movement from an area of higher concentration to an area of lower concentration 7\. The internal pressure of water against the cell wall 8\. The ability of a solution to change the size and shape of cells by altering the amount of water 95% NaCl a. Water will \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 5% H~2~O b. The Cell will \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 5% NaCl c. Water will \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 95% H~2~O d. The Cell will \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 5% NaCl e. Water will\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 95% H~2~O f. The Cell will\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  III. Match the structure/process to the letter: 1. 2. 3. 4. 5. 6\. This cell would be in a\_\_\_\_\_\_\_\_\_\_\_\_\_ 7\. All of the processes in the image are examples of \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ transport. 8\. The cell membrane can be described as \_\_\_\_\_\_\_\_\_\_\_\_\_ 9\. There is more glucose \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ 10\. Over time, this cell will\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ **REFERENCES** Marieb, E. N. & Keller, S. M., (2018). *Essentials of Human Anatomy and Physiology: 12^th^ Edition*. North Buona Vista Drive, Singapore: Pearson Education Limited. MoranoL.N., Lopez C.S.,and Tan A. E..S., (2011) *Fundamental of Biology*. Quezon City, Manila: Lorimar Publishing, INC