Module 2-Bio membranes Flashcards
What is the fluid mosaic model?
-describes the structure of the plasma membrane as a mosaic of phospholipids, cholesterol, proteins and carbohydrates
-the phospholipid bilayer forms the fluid part
-the mosaic part is made of proteins, carbs, lipids that punctuate the membrane
Definition of the plasma membrane
-defines the border of cells
-is partially permeable as some materials can move freely whereas others can not.
Describe the structure of the phospholipid
-molecule consisting of glycerol, 2 fatty acid tails and a phosphate linked head group
-these molecules arrange themselves in a bilayer which range from 5-10 nm in thickness
-the hydrophilic head faces outwards and hydrophobic tails face inwards.
Structure of cholesterol
lipid that is found in the core of the membrane and makes it more rigid
Structure and function of membrane bound proteins
large molecules embedded in the bilayer that can form open pores that allow the diffusion of large molecules across the bilayer.
Function of transport proteins
bind to specific molecules and carry them across the membrane
Function of ATP synthase
membrane bound protein that catalyses the production of ATP
Functions of glycolipids and glycoproteins
-some are able to form hydrogen bonds with water molecules surrounding the cell which helps to stabilise the membrane
-other glycolipids and glycoproteins act as cell signalling receptors and have active binding sites for communication molecules e.g hormones
How does temperature affect the permeability of membranes?
High temperatures increase the fluidity of the membrane therefore increasing its permeability. Phospholipids in a cell membrane are constantly moving so whenm the temperature is increased the phospholipids will have more kinetic energy and will move more causing the membrane to lose its structure becoming more fluid. This makes it easier for particles to cross it.
How can you keep the temperature constant in an experiment?
by using a water bath
How do solvents affect the permeability of membranes?
solvents that are less polar than water dissolve membranes making it more fluid and permeable
Method for investigating cell membrane permeability
-beetroot is often used as a model as the release of the coloured pigment is easy to quantify using colorimetry
1)use a cork borer to collect samples of a uniform diameter
2)cut discs of uniform depth using a sharp knife on a white tile and rinse in cold water. this removes excess pigment that has leaked through physically broken cell membranes
3)prepare at least 5 concentrations of ethanol(e.g 0%, 20%, 40%, 60% 80%)
4)place the discs in the corresponding solution for 10 mins and mix frequently
5)remove the discs from the solutions and calibrate the colorimeter
6)measure absorbance of each concentrations and plot the data on a graph
How can solvent concentration be controlled?
by using the same solvent at the same concentration for each trial.
What is simple diffusion?
the net movement of particles from an area of high concentration to an area of low concentration
-passive movement of particles in fluids
-molecules move randomly but tend to move to any space available until its evenly distributed
-movement is down a concentration gradient
What is facilitated diffusion?
-molecules diffuse through carrier proteins or channel proteins across a membrane
-channel proteins allow polar compounds to avoid the non polar central layer of the plasma membrane
-when a substance binds to carrier proteins there is a change in the shape of carrier proteins which moves the substance from outside the cell to inside the cell.
-because these materials are too large to move through the membrane or they are polar molecules that are repelled by the hydrophobic part of the membrane
-describes the net movement of particles from an area of high to lower concentration.
-is passive so doesn’t require energy
What are aquaporins?
channel proteins that allow water to pass through the membrane
How does concentration gradient affect the rate of diffusion?
the bigger the difference in concentration between 2 areas, the greater the concentration gradient and the faster the rate of diffusion because the overall movement from the higher to the lower concentration will be larger
How does temperature affect the rate of diffusion?
the higher the temp the faster the rate of diffusion as the particles have more kinetic energy and therefore can move at higher speeds.
How does membrane surface area affect the rate of diffusion?
the larger the SA the faster the rate of diffusion as there is more space for particles to move through at one time.
How does the thickness of the exchange surface affect the rate of diffusion?
the thicker the exchange surface the slower the rate of diffusion.
How does the concentration of channel or carrier proteins affect the rate of diffusion?
the higher the concentration the faster the rate of facilitated diffusion until an equilibrium is reached and the rate will level off
What is active transport?
-uses energy from respiration
-dissolved molecules move from a less concentrated solution to a more concentrated solution
-in charge of moving ions and molecules across a partially permeable membrane against the concentration gradient
What are 2 examples of active transport?
1)active transport allows glucose to be absorbed into the blood from the gut even when the glucose concentration of the blood is higher
2)active transport in the root hairs of plants allows plants to absorb mineral ions even though the concentration is lower in the soil than the hair.
What factors affect the rate of active transport?
-SA or cell membranes
-number of carrier proteins in cell membranes
