Biological Membranes

by Kevin Ahern, PhD

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    The lipid bilayer of a cell's membrane is both the defining boundary and barrier between the cell and the rest of the world around it. In this lecture, membranes will be the subject, and in this talk I will talk about structure of membranes and how they relate to the function. The fluidity of membranes and the importance of fluidity as it relates to temperature. And the transport functions carried out by membranes and why they're important with respect to cellular function. Now membranes are part and parcel of every living system. In prokaryotes, membranes are relatively simple because the prokaryotic cell does not have internal organelles, as can be seen in this figure. The prokaryotic cell has a lipid bilayer and it also has a capsular cell wall protecting the cell from the rest of the world. The eukaryotic cell does not have typically, at least in an animal cell, does not have a cell wall that protects it and has a fairly thin lipid bilayer. But in addition to that lipid bilayer forming the cell membrane, there are also internal membranes that cover and protect the individual organelles, such as the mitochondrion, the nucleus, and so forth. Now the lipid bilayer as I said, defines the boundary of cells and organelles. It is comprised of two layers of amphiphilic molecules. These layers of amphiphilic molecules provide a significant barrier to most substances. Now there are some exceptions to that barrier. Lipid bilayers are relatively permeable to water, molecular oxygen, carbon dioxide and carbon monoxide. Now this turns out to be pretty important, at least for the oxygen and carbon dioxide parts, because oxygen is needed for respiratory functions by non-aerobic cells and carbon dioxide is expelled or given away, given off as a result of oxidation and cells...

    About the Lecture

    The lecture Biological Membranes by Kevin Ahern, PhD is from the course Biochemistry: Basics. It contains the following chapters:

    • Structure of Membranes
    • Lipid Bilayer
    • Bilayer Composition
    • Membrane Fluidity
    • Diffusion
    • Active Transport - Sodium-Potassium ATPase
    • Active Transport - Sodium-Calcium Exchanger
    • Transporter Types and Types of Transport Proteins
    • Ion Channel
    • Ion Channel Blocker/Opener

    Included Quiz Questions

    1. ...are comprised of a lipid bilayer.
    2. ...are found only in the cell walls of eukaryotic cells.
    3. ...are impermeable to all substances.
    4. ...are notable for their rigidity.
    1. They have a polar head and a pair of polar tails.
    2. They contain fatty acids.
    3. They contain at least one phosphate.
    4. They contain glycerol.
    1. ...contains a fatty acid.
    2. ...contains glycerol.
    3. ...does not contain phosphate.
    4. ...is not found in membranes.
    1. ...mediate cellular signaling and transport of materials.
    2. ...are called integral if they have a fatty acid anchoring them.
    3. ...are called peripheral if they project through both layers of the lipid bilayer.
    4. ...have non-polar fatty acids preferentially in their interiors.
    1. ...involves more unsaturated fatty acids for cells in colder temperatures.
    2. ...does not include cholesterol.
    3. ...includes proteins, lipids, and phosphates, but not carbohydrates.
    4. ...does not involve charged substances.
    1. ...it always requires a protein.
    2. ...it is affected by concentration of materials on either side of the membrane.
    3. ...requires an energy source to move from lower to higher concentration.
    4. ...Regulation/control of it is essential for cells.
    1. ...requires only the energy of diffusion.
    2. ...uses ATP or GTP.
    3. ...does not require a protein.
    4. ...requires antiports.
    1. ...moves materials from low concentration to a higher concentration.
    2. ...requires ATP or GTP.
    3. ...does not require a protein.
    4. ...is only involved in moving molecules into cells.
    1. ...are used to create ATP as a result of the ion gradients they create.
    2. ...do not change the charge across a membrane as a result of their actions.
    3. ...are always uniports.
    4. ...always involve sodium.
    1. ...rely on diffusion.
    2. ...require ATP or GTP.
    3. ...allow a wide range of ions to pass through them.
    4. ...are found in the cytoplasm of cells.
    1. They are electroneutral.
    2. They are gated.
    3. Blockers of their action can have both medicinal and neurotoxic effects.
    4. Opening/closing changes the voltage across a membrane.
    1. ...help to build proton gradients.
    2. ...use triphosphate energy go move ions across membranes.
    3. ...promote movement of ions across membranes.
    4. ...are not produced by living cells.

    Author of lecture Biological Membranes

     Kevin Ahern, PhD

    Kevin Ahern, PhD

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