Membrane Transport 
Membrane Transport
by OSU
Video Lecture 4 of 25
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Date Added: February 15, 2015

Lecture Description

1. Diffusion is a process in solutions where molecules move from a high concentration to a low concentration.

2. We break transport across membranes into two main categories - 1) passive transport (diffusion driven, so materials move only from high concentration to lower concentration and don't require outside energy), and 2) active transport (an energy-requiring process that moves at least one molecule from a low concentration to a higher concentration - this is contrary to simple diffusion).

3. Active transport moves at least one molecule in the opposite direction of where diffusion would operate (that is, active transport moves at least one molecule from a low concentration to a higher concentration).

4. ATP is a primary energy source for active transport, but there are other sources, as well (see below). The term 'pump' is used to describe the protein component of an active transport system. Pumps that move two molecules in the same direction across a membrane are called symports (or synports), whereas pumps that move two molecules in opposite directions across a membrane are called antiports. Pumps are called electroneutral if their action does not result in a net change in charge and electrogenic if their action changes the charge across the membrane as a result of their action.

5. An example of a passive transport system is a glucose transporter in blood cells that simply lets glucose diffuse into cells. No energy is required for that particular transporter. Other glucose transporters in other cells are active in that they use energy to move glucose against a concentration gradient.

6. An example of a passive transport system is a glucose transporter in blood cells that simply lets glucose diffuse into cells. No energy is required for that particular transporter. Other glucose transporters in other cells are active in that they use energy to move glucose against a concentration gradient.

7. P-type ATP-using transport systems use phosphoaspartate as a covalent intermediate in their mechanism of action.

8. The mechanism of transport of the Ca/ATPase pump includes binding of ATP and the relevant ions (calcium, in this case), transfer of phosphate from the ATP to the protein (making phosphorylaspartate), conformational change in the protein causing movement of the ions across the membrane, hydrolysis of the phosphate from an asparatic acid side chain in the protein, a second conformational change to bring the protein back to its original state. The Ca/ATPase pump is called a symport because all of the molecules are being moved in the same direction across the membrane.

9. Another P type ATPase is the Na/K ATPase. The Na/K ATPase transports three sodiums out of the cell and two potassiums in for each cycle. This is an electrogenic transport mechanism and uses hydrolysis of ATP to drive the process. Movement of Na and K is essential for the cell being able to maintain osmotic balance. The Na/K ATPase is called an antiport because it moves molecules in opposite directions.

10. Another class of transporter proteins that use ATP to move molecules are the ABC transporters. An example is the Multidrug Resistance Protein that is involved in the resistance of cancer cells to chemotherapy agents. They act by binding the compound first. This causes a conformational change in the protein that allows ATP to bind. Binding of ATP causes the protein to 'evert' (move its opening from one side of the membrane to the other). This has the effect of moving the bound compound to the outside of the cell. After this happens, ATP is hydrolyzed to change the protein to evert again and change back to its original conformation (opening facing inwards).

Course Index

Course Description

This course in general biochemistry is intended to integrate information about metabolic pathways with respiration (respiratory control) and initiate the student into a microscopic world where blueprints are made of deoxyribonucleic acids, factories operate using enzymes, and the exchange rate is in ATPs rather than Yens or Euros. Beyond explaining terms, and iterating reactions and metabolic pathways, this course strives to establish that the same principles that govern the behavior of the world around us also govern the transactions inside this microscopic world of the living cell. And by studying and applying these principles, we begin to understand cellular and bodily processes that include sensory mechanisms.

Topics include:
1. Lipids, Membranes and Transport
2. Electron Transport, Oxidative Phosphorylation and Mitochondrial 3. Transport Systems
3. Lipid Metabolism
4. Nucleotide Metabolism
5. DNA Replication
6. Transcription
7. Translation

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