IB Biology - Curriculum Notes
1.3 Membrane structure
∑ - Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules.
|Hydrophilic and Hydrophobic Properties|
∑ - Membrane proteins are diverse in terms of structure, position in the membrane and function.
Hormone binding sites (receptor proteins)
Proteins embedded in the membrane, which bind to specific hormones.
When the hormone binds, it causes the receptor protein to undergo a conformational change, which signals the cell to perform a function.
For example, insulin receptors.
Integral proteins that catalyze specific chemical reactions.
Many of these enzymes catalyze metabolic reactions or are a part of a metabolic pathway, such as ATP Synthase in aerobic respiration.
Proteins that form tight bonds between adjacent cells in tissues and organs.
For example, gap junctions.
Receptors for neurotransmitters at synapses between two nerve cells.
Glycoproteins on the surface can also be used for cell identification purposes.
Channels for passive transport
Integral proteins that span the membrane and provide a passageway for molecules to move from an area of high concentration to low concentration.
Specific proteins are also used for facilitated diffusion.
Pumps for Active Transport
Proteins use ATP to move substances from a low concentration to a high concentration across the membrane.
For example, Sodium/Potassium (Na+/K+) pumps and the proton (H+) pumps
∑ - Cholesterol is a component of animal cell membranes.
Most of the cell membrane contains phospholipids and proteins
Cholesterol is a lipid that belongs in the steroid group and is also a component of the cell membrane
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
Membrane Structure and Function - https://www.youtube.com/watch?v=qBCVVszQQNs
Applications and skills: ß
ß - Application: Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes.
ß - Skill: Drawing of the fluid mosaic model.
**Please note the when you draw a peripheral protein for the IB exam, the peripheral protein must not be embedded into the membrane in order to score the point*** Also, you should label the whole phospholipid bilayer not just the individual phospholipid on the majority of mark schemes
ß - Skill: Analysis of evidence from electron microscopy that led to the proposal of the Davson-Danielli model.
ß - Skill: Analysis of the falsification of the Davson-Danielli model that led to the Singer-Nicolson model.
Davson and Danielli proposed a theory that the lipid bilayer was coated on either side with a layer of globular proteins (as seen below)
Using your text, the web and the library analyze the evidence and the falsification of the Davson-Danielli model of the cell membrane by completing the analysis on pages 26-27 in your text.
Write your paragraph here.