Week One Medical Physiology: Plasma Membranes

Name the membrane transport processes

The basic principles of passive membrane transport processes are that: There is no expenditure of [blank_start]energy[blank_end] The substances move [blank_start]down[blank_end] their concentration gradient: moving from area of [blank_start]high[blank_end] concentration to [blank_start]low[blank_end] concentration Movement is by [blank_start]diffusion[blank_end]: the tendency for substances to distribute themselves evenly in the environment

The rate of diffusion, as outlined by [blank_start]Fick[blank_end]'s Law of Diffusion, is determined by 1. [blank_start]Molecular size[blank_end] of the Solute: big molecules move slower than small molecules. Small molecules have less collisions and travel further and quicker 2. [blank_start]Distance[blank_end]: the greater the distance traveled, the slower the rate of diffusion. More distance = more collisions = slower diffusion 3. [blank_start]Concentration gradient[blank_end]: a shallow concentration gradient = slower diffusion 4. Plasma membrane [blank_start]permeability[blank_end]: substances can only move across if the plasma membrane is permeable to them 5. [blank_start]Surface Area[blank_end]: The bigger the cell, the larger the surface area, the more opportunity for substances to move across, the higher the rate of diffusion

The two passive processes of membrane transport include

Simple Diffusion:

In simple diffusion, the following substances enter the cell in the following ways Through the lipid bilayer Substances with high lipid solubility [blank_start]O2[blank_end] [blank_start]CO2[blank_end] [blank_start]N2[blank_end] [blank_start]Alcohols[blank_end] [blank_start]Fatty Acids[blank_end] Through protein channels, which can highly selective and gated, or non-selective and open all the time [blank_start]Small water soluble molecules[blank_end] [blank_start]H+[blank_end] [blank_start]K+[blank_end] [blank_start]Na+[blank_end] [blank_start]Ca2+[blank_end]

The following is a description of which type of diffusion. The substances traverse the plasma membrane by binding to a [blank_start]carrier[blank_end] protein. The protein undergoes a [blank_start]conformational[blank_end] change. The substance is released on the other side of the membrane. It is employed by essential metabolic substrates such as [blank_start]glucose[blank_end], amino acids and soluble [blank_start]vitamins[blank_end]. This type of diffusion exhibits [blank_start]saturation[blank_end] kinetics. This is [blank_start]facilitated diffusion[blank_end]

In saturation kinetics, if the graph shows a plateau then it is facilitated diffusion; but if it keeps rising, then it is simple diffusion.

Passive processes: Substances which are [blank_start]lipid soluble[blank_end] diffuse across the plasma membrane by diffusing through the [blank_start]lipid bilayer[blank_end] [blank_start]Small water-soluble ions[blank_end] diffuse through [blank_start]protein channels[blank_end] which traverse the membrane [blank_start]Lipid insoluble substances[blank_end] and those [blank_start]too large[blank_end] to fit through channel proteins diffuse across the membrane by binding through a [blank_start]carrier protein[blank_end]

Active process involve the use of metabolic energy and are the mechanisms of substrates moving with their concentration gradient

The two types of active process include [blank_start]active transport[blank_end] and [blank_start]bulk transport[blank_end]. [blank_start]Bulk transport[blank_end] has two categories, [blank_start]exocytosis[blank_end] and [blank_start]endocytosis[blank_end]. [blank_start]Endocytosis[blank_end] also has three categories: [blank_start]phagocytosis[blank_end], [blank_start]pinocytosis[blank_end] and [blank_start]receptor mediated endocytosis[blank_end]

Active transport

A substance can be transported in only one way. Ie a H+ is only ever transported via H+ pump

Bulk transport is one of the active transport processes and

Endocytosis is where [blank_start]macromolecules[blank_end] are transported into a cell. There are three types. [blank_start]Pinocytosis[blank_end], [blank_start]phagocytosis[blank_end] (which involves formation of a [blank_start]phagosome[blank_end] which then fuses with a [blank_start]lysosome[blank_end]. Used predominantly by [blank_start]macrophages[blank_end] and [blank_start]white blood cells[blank_end]), and r[blank_start]eceptor mediated endocytosis[blank_end], whereby there is [blank_start]selective binding[blank_end] of macromolecules to a plasma membrane. It is a much more specific interaction.

The plasma membrane is highly permeable to water. This is because the O2 molecule is a small, fast moving molecule and has high kinetic energy. It can also enter the cell via protein channels. It moves down its concentration gradient and, unlike other substances, produces a change in volume of the cell

Water will move down its concentration gradient from an area of low (non-penetrating) solute concentration to an area of high (non-penetrating) solute concentration

Osmolarity is the quantitative value and direction of osmotic pressure. It can be determined by the concentration of a solution

The osmolarity is the quantitative value and direction of osmotic pressure. It can be calculated in the following way: Osmolarity = molarity of a solute x number of particles is dissociates into

[blank_start]Tonicity[blank_end] is the relative osmolarity of the bathing solution of a cell [blank_start]Hypertonic[blank_end]: the osmolarity of the bathing solution is [blank_start]greater than[blank_end] than of the intracellular space of the cell. Water will [blank_start]leave the cell[blank_end] [blank_start]Hypotonic[blank_end]: the osmolarity of the bathing solution is [blank_start]less than[blank_end] the intracellular space of the cell. Water will [blank_start]enter the cell[blank_end] [blank_start]Isotonic:[blank_end] the osmolarity of the bathing solution is [blank_start]the same as[blank_end] the intracellular space of the cell. There will be [blank_start]no net movement of water[blank_end]

If you were a well-paid scientist working for a big drug company and were given the task of improving the delivery of a new wonder drug INTO red blood cells, which of the following strategies might you adopt? 1. Increasing the size of the molecule 2. Increasing the lipid solubility of the molecule 3. Decreasing the size of the molecule

Which of the following molecules can move across the plasma membrane of cells by facilitated diffusion? 1. soluble vitamins 2. amino acids 3. enzymes

The mechanisms by which substances move across the plasma membrane without the expenditure of metabolic energy are collectively known as?

Which of the following substances is/are transported across the plasma membrane of cells by receptor-mediated endocytosis? 1. cholesterol. 2. sodium. 3. insulin.

The mechanism by which macrophages and some white blood cells are able to ingest cellular debris is known as?

The rate of diffusion of a molecule is inversely related to its molecular radius because?

If two substances had the same molecular weight but one was more soluble in lipids than the other, which would pass through the plasma membrane of a red blood cell the quickest?

Which of the following statements about simple diffusion is TRUE?

For any substance passing through a membrane by diffusion, the rate of diffusion of this substance will do which of the following?

Which of the following statements about facilitated diffusion is TRUE?