Which of the following is a consequence of the fluid mosaic model of membrane dynamics?
Show In the Cell Membrane unit you will learn about cell size and the structure and function of cell membranes. Cell membranes protect and organize cells. All cells have an outer plasma membrane that regulates not only what enters the cell, but also how much of any given substance comes in. Like all other cellular membranes, the plasma membrane consists of both lipids and proteins. The fundamental structure of the membrane is the phospholipid bilayer, which forms a stable barrier between the compartments inside and outside of the cell. Proteins embedded within the phospholipid bilayer carry out the specific functions of the plasma membrane, including selective transport of molecules and cell-cell recognition. The unit is planned to take 2 school days Essential Ideas:
Nature of Science
Understandings 1.3.U.1 Phospholipids form bilayers in water due to the amphipathic properties of phospholipid molecules. (Oxford Biology Course Companion page 26). [Amphipathic phospholipids have hydrophilic and hydrophobic properties.]
Phospholipids are one of the principal components of cell membranes (in conjunction with membrane proteins) Phospholipids typically share a common basic structure that includes:
Hydrophilic and Hydrophobic Properties
Phospholipids may vary in the length and relative saturation of the fatty acid tails
image fromwww.boundless.com 1.3.U2 Membrane proteins are diverse in terms of structure, position in the membrane and function. (Oxford Biology Course Companion page 30).
Hormone binding sites (receptor proteins)
Immobilized Enzymes
Cell Adhesion
Cell-to-cell communication
Channels for passive transport
Pumps for active transport
The extracellular matrix typically provides structural and biochemical support to surrounding cells, including:
1.3.U.3 Cholesterol is a component of animal cell membranes. (Oxford Biology Course Companion page 32)
Cholesterol is able to stop the hydrocarbon from crystalizing and behaving as a solid, but the cholesterol also retricts molecular motion, which reduces the fluidity of the membrane. Also reduces the permiability to the hydrophilic particles like sodium ions and hydrogen ions It is absent in plant cells, as these plasma membranes are surrounded and supported by a rigid cell wall made of cellulose
Applications: 1.3.A.1 Cholesterol in mammalian membranes reduces membrane fluidity and permeability to some solutes. (Oxford Biology Course Companion page 33).
Cholesterol
embedded in the membrane will reduce the fluidity making the membrane more stable by the hydrophilic interactions with the phospholipid heads. 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.
Skills: 1.3.S.1 Drawing of the fluid mosaic model (Oxford Biology Course Companion page
31).
The diagram of the plasma membrane must show the
Integral proteins are embedded in the phospholipid of the membrane, whereas peripheral proteins are attached to its surface. Glycoproteins are carbohydrates attached to surface proteins. NOTE: 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
1.3.S.2 Analysis of evidence from electron microscopy that led to the proposal of the Davson-Danielli model. (Oxford Biology Course Companion page 28).
The fluid-mosaic model was not the first scientifically accepted paradigm to describe membrane structure. The first model that attempted to describe the position of proteins within the bilayer was proposed by Hugh Davson and James Danielli in 1935. Davson and Danielli proposed that the lipid bilayer was coated on either side with a layer of globular proteins. The hydrophobic tails of the lipids are orientated towards each other, while the hydrophilic heads are oriented to the outside. Although the membrane composition is correct, there are some problems with the proposed model: Membranes are not identical. The differ in thickness and the ratio of proteins:lipids.
The model was described as a 'lipo-protein sandwich’, as the lipid layer was sandwiched between two protein layers
When viewed under a transmission electron microscope, membranes exhibit a characteristic 'trilaminar’ appearance Trilaminar = 3 layers (two dark outer layers and a lighter inner region)
1.3.S.3 Analysis of the falsification of the Davson-Danielli model that led to the Singer-Nicolson model. (Oxford Biology Course Companion page 29).
There were a number of problems with the lipo-protein sandwich model proposed by Davson and Danielli:
Falsification Evidence:
New Model:
Key Terms:
PowerPoint Presentation Topic 1.3 by Chris Paine Correct use of terminology is a key skill in Biology. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary. TOK
Video Clips: Cell membranes are structures of contradictions. These oily films are hundreds of times thinner than a strand of spider silk, yet strong enough to protect the delicate contents of life: the cell’s watery cytoplasm, genetic material, organelles, and all the molecules it needs to survive.
The cell membrane, like a good jacket, protects the cell from everything outside of it. How is it simultaneously sturdy, flexible, and capable of allowing the right things to pass through? Ethan Perlstein rediscovers the scientists and their research that have changed the way we study the membrane and the cell as a whole.
Paul Andersen gives you a brief introduction to the cell membrane. He starts by describing amphipathic nature of a phospholipid and how it assembles into a membrane. He gives an overview of the fluid mosaic model inside cells. He also discusses the movement of material across a membrane and the role of proteins in movement and function.
Full version of inner life of the cell,
Hank describes how cells regulate their contents and communicate with one another via mechanisms within the cell membrane.
The Davson-Danielli model is an idea proposed on how cells regulate their environment. The proteins are on the outside of the bi-layer membrane. However, membranes need to allow for solute particles to pass back and forth. When proteins are on the outside, it blocks the solutes from passing through, preventing homeostasis. Therefore, we have to reject this model. In the Singer-Nicholson Fluid Mosaic Model, the integral proteins are embedded in the bi-layer. They have the ability to open up and let particles move back and forth.
What would be the impact of fluid mosaic model of cell membranes to you?The fluid mosaic model describes the cell membrane as a tapestry of several types of molecules (phospholipids, cholesterols, and proteins) that are constantly moving. This movement helps the cell membrane maintain its role as a barrier between the inside and outside of the cell environments.
What are the 3 components of the fluid mosaic model cell membrane?This model explains the structure of the plasma membrane of animal cells as a mosaic of components such as phospholipids, proteins, cholesterol, and carbohydrates.
Why fluid mosaic model is dynamic?The fluid mosaic model incorporates the dynamic nature of bilayer membrane organization that occurs due to the constant rotational and lateral motion of the integral lipid and protein molecules.
What are the main features of the fluid mosaic model?The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components —including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character. Plasma membranes range from 5 to 10 nm in thickness.
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