IBDP CORE>TOPIC 1.3>MEMBRANE STRUCTURE
HELPFUL LINKS |
UNDERSTANDINGS
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INTRODUCTION-LAB ACTIVITY
WHAT WILL HAPPEN IF A CELL IS PLACED IN SOLUTIONS OF DIFFERENT CONCENTRATIONS?
AFTER THE LAB ACTIVITY COMPLETE THE DOCUMENT ON MANAGEBAC AND SUBMIT IT.
AFTER THE LAB ACTIVITY COMPLETE THE DOCUMENT ON MANAGEBAC AND SUBMIT IT.
U-1. Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
The main component of the biological membrane is a molecule- phospholipid. It consists of
1. The polar head (hydrophilic) made from glycerol and phosphate 2. The non-polar part which has two fatty acid tails (hydrophobic).
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- U-2. Membrane proteins are diverse in terms of structure, position in the membrane and function
The proteins in the plasma membrane help the interaction of the cell with its environment.
For example, transporting nutrients across the plasma membrane, receiving chemical signals from outside the cell, translating chemical signals into intracellular action, hormone binding sites and sometimes anchoring the cell or cell adhesion. |
Membrane proteins vary in their positions within the membrane and in their functions. Outline the positions and functions of proteins in membranes. 8M
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Explain how the hydrophilic and hydrophobic properties of phospholipids help to maintain the structure of cell membranes. 6M
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Integral proteins are embedded in the membrane/phospholipid bilayer;
peripheral proteins are on the surface of the membrane; some integral proteins (are transmembrane proteins that) extend from one side ofthe membrane to the other; hormone binding sites; e.g. insulin; enzymes; e.g. sucrase / succinate dehydrogenase; cell adhesion; cell-to-cell communication recognition / antigenic markers / glycoproteins / contact inhibition; Channels/pores for passive transport/facilitated diffusion; pumps/carriers for active transport; Receptors for neurotransmitters; such as acetylcholine;electron carriers; e.g. electron transport chain of cellular respiration;pigments (in rods/cones); (Award any of the above points if clearly drawn in an annotated diagram.) |
Membranes are surrounded by water;
hydrophilic molecules are attracted to water; hydrophobic molecules are attracted to one another/repel water; phospholipids are amphipathic/have a hydrophobic tail and a hydrophilic head; tails are positioned away from water / heads are positioned towards water; phospholipids have a hydrocarbon tail and a phosphate head; phospholipid bilayer/ membranes self-assemble in water; protein association with membrane is determined by hydrophobic interactions; phospholipid bilayer is hydrophilic on the outside and hydrophobic on the inside; |
- U-3. Cholesterol is a component of animal cell membranes.
Cholesterol is a component of the animal cell membrane.
It is a type of lipid, and is called steroids. Most of the cholesterol molecule is hydrophobic and therefore embeds within the tails of the bilayer. A small portion (hydroxyl –OH group) is hydrophilic and is attracted to the phospholipid head. These cholesterol molecules are positioned between the phospholipids in the membrane. |
APPLICATION: Cholesterol in mammalian membranes reduces membrane
fluidity and permeability to some solutes.
Cholesterol embedded in the membrane will reduce the fluidity making the membrane more stable by the hydrophilic interactions with the phospholipid heads
While cholesterol adds firmness and integrity to the plasma membrane and prevents it from becoming overly fluid, it also helps maintain its fluidity by disrupting the regular packing of the hydrocarbon tails.
At the high concentrations it is found in our cell's plasma membranes (close to 50 percent, molecule for molecule) cholesterol helps separate the phospholipids so that the fatty acid chains can't come together and crystallise.
The amount of cholesterol in the membrane varies depending on the function- in the membranes of the vesicles that hold neurotransmitters at synapses there are about 30% of cholesterol. Cholesterol can help membranes to curve into a concave shape, like forming vesicles.
Therefore, cholesterol helps prevent extremes-- whether too fluid, or too firm-- in the consistency of the cell membrane
While cholesterol adds firmness and integrity to the plasma membrane and prevents it from becoming overly fluid, it also helps maintain its fluidity by disrupting the regular packing of the hydrocarbon tails.
At the high concentrations it is found in our cell's plasma membranes (close to 50 percent, molecule for molecule) cholesterol helps separate the phospholipids so that the fatty acid chains can't come together and crystallise.
The amount of cholesterol in the membrane varies depending on the function- in the membranes of the vesicles that hold neurotransmitters at synapses there are about 30% of cholesterol. Cholesterol can help membranes to curve into a concave shape, like forming vesicles.
Therefore, cholesterol helps prevent extremes-- whether too fluid, or too firm-- in the consistency of the cell membrane
SKILL: Drawing the Fluid Mosaic Model.
Skill: Analysis of evidence from electron microscopy that led to the proposal
of the Davson-Danielli model.
• Skill: Analysis of the falsification of the Davson-Danielli model that led to the
Singer-Nicolson model
References-
Damon, Alan et al, Higher level Biology for the IB diploma. Pearson Baccalaureate
Clegg, CJ, Biology for the IB diploma. London: Hodder Murrray, 2007, 978-0340926529
Taylor, Stephan, Science Video resources Wordpress,
Burell, John. Click 4Biology(online)
http://ibworld.me/Cells.html
All picture have been downloaded from Google images for educational purpose only
Damon, Alan et al, Higher level Biology for the IB diploma. Pearson Baccalaureate
Clegg, CJ, Biology for the IB diploma. London: Hodder Murrray, 2007, 978-0340926529
Taylor, Stephan, Science Video resources Wordpress,
Burell, John. Click 4Biology(online)
http://ibworld.me/Cells.html
All picture have been downloaded from Google images for educational purpose only