Transport across membranes

JGlanvile
Mind Map by JGlanvile, updated more than 1 year ago
JGlanvile
Created by JGlanvile about 5 years ago
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mind map of transport across the plasma membrane

Resource summary

Transport across membranes
1 Lipid diffusuion
1.1 A few substances can diffuse directly through the lipid bilayer part of the membrane.
1.1.1 The only substances that can do this are lipid-soluble molecules such as steroids, or very small molecules, such as H2O, O2 and CO2. It’s a passive process.
2 Osmosis
2.1 Osmosis is the diffusion of water across a membrane
2.1.1 . Water molecules can diffuse freely across a membrane, but always down their concentration gradient, so water therefore diffuses from a dilute to a concentrated solution.
3 active Transport
3.1 The protein binds a molecule of the substance to be transported on one side of the membrane, changes shape, and releases it on the other side. The proteins are highly specific, so there is a different protein pump for each molecule to be transported.
4 Passive transport
4.1 Passive transport is the transport of substances across a membrane by a trans-membrane protein molecule.
4.1.1 . There are two kinds of transport protein:
4.1.1.1 Channel proteins
4.1.1.1.1 form a water-filled pore or channel in the membrane. This allows charged substances (usually ions) to diffuse across membranes. Most channels can be gated (opened or closed), allowing the cell to control the entry and exit of ions
4.1.1.2 Carrier proteins
4.1.1.2.1 Carrier Proteins have a binding site for a specific solute and constantly flip between two states so that the site is alternately open to opposite sides of the membrane. The substance will bind on the side where it at a high concentration and be released where it is at a low concentration.
5 Vesicles
5.1 Exocytosis: is the transport of materials into a cell. Materials are enclosed by a fold of the cell membrane, which then pinches shut to form a closed vesicle. Strictly speaking the material has not yet crossed the membrane, so it is usually digested and the small product molecules are absorbed by the methods above. When the materials and the vesicles are small (such as a protein molecule) the process is known as pinocytosis (cell drinking), and if the materials are large (such as a white blood cell ingesting a bacterial cell) the process is known as phagocytosis (cell eating).
5.2 Endocytosis: is the transport of materials out of a cell. It is the exact reverse of endocytosis. Materials to be exported must first be enclosed in a membrane vesicle, usually from the RER and Golgi Body. Hormones and digestive enzymes are secreted by exocytosis from the secretory cells of the intestine and endocrine glands.
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