Lipid Metabolism, Fat Transport in the Body 
Lipid Metabolism, Fat Transport in the Body
by OSU
Video Lecture 7 of 25
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Date Added: February 15, 2015

Lecture Description

1. The chemiosmotic hypothesis, originally proposed by Peter Mitchell, explains how mitochondria make ATP in oxidative phosphorylation. Important aspects of it include:

a. Intact inner mitochondrial membrane
b. Electron transport creates a proton gradient
c. ATP is made by movement of protons back into the mitochondria

2. Coupling of electron transport and oxidative phosphorylation at a practical level means that the mitochondrial inner membrane remains impermeable to protons, except for those that enter via the ATP synthase and result in ATP production.

3. The ATP synthase consists of a turbine-like structure containing 3 sites called Loose (L), Tight (T), and Open (O). Functions of these forms include

L - Holds ADP and Pi in preparation for ATP formation
O - Releases ATP formed in T and binds ADP + Pi
T - Causes ADP and Pi to join and form ATP

4. Movement of protons through the ATP synthase cases rotation/conformational changes in the complex that result in formation of ATP from ADP and Pi. Conversions in the process occur as follows:

O goes to L
L goes to T
T goes to O

5. Mitochondria which are "tightly coupled" have intact membranes AND the only way protons get back into the matrix is by passing through Complex V. If you poke a hole in the membrane (using DNP or an uncoupling protein, such as found in brown fat), protons can leak back in without making ATP. This has the effect of generating heat AND burning up energy sources (like glucose and fat). As noted, DNP is a dangerous compound that killed people who tried to use it to lose weight.

6. When mitochondria are tightly coupled, metabolic (respiratory) control exists. This means that electron transport will stop if oxidative phosphorylation stops, since the protons don't come back int and the proton gradient gets very high, stopping the pumping of protons. When electron transport stops, NADH accumulates and the citric acid stops. Conversely, if one stops electron transport with cyanide, oxidative phosphorylation will stop very shortly because the proton gradient is lost when no protons are being pumped.

7. When mitochondria are uncoupled (by poking a hole in them to let protons leak back into the matrix without passing through Complex V), electron transport is no longer limited by oxidative phosphorylation and runs amok. That is why heat is generated. Protons are pumped, but they fall back in throught the hole in the mitochondrial inner membrane. No ATP is made. NADH is rapidly converted to NAD+, so the citric acid cycle and other pathways run rapidly.

8. Things that affect these processes are ADP (necessary for the Complex V to function), oxygen (necessary for electron transport to function), NADH (source of electrons for electron transport), and NAD+ (needed for citric acid cycle).

9. NADH cannot cross the inner membrane of the mitochondrion, as there is no protein to move it. Electrons make it into the mitochondria by means of shuttles. Insect muscles a glycerol-3phosphate/DHAP shuttle that transfers electrons from NADH ultimately to FADH2. Mammalian systems, by contrast, use a malate/aspartate system that converts oxaloacetate to malate (carrier of electrons) that then gets transported by a transport protein. Once inside the matrix, malate transfers electrons to NAD+, creating NADH and oxaloacetate.

Glycerolipid, Sphingolipid, and Cholesterol Metabolism

1. Glycerophospholipids typically contain a saturated fatty acid at position #1 and an unsaturated fatty acid at position #2 on the glycerol backbone.

2. Glycerophosphlipid biosynthesis occurs most commonly through the synthesis of phosphatidic acid. This can be made from glycerol-3-phosphate by esterifying fatty acids to positions 1 and 2 of glycerol-3-phosphate, yielding phosphatidic acid. Phosphatidic acid is a branch point between the synthesis of fats and glycerophospholipids.

3. For the synthesis of glycerophospholipids, phosphatidic acid is an immediate precursor of CDP-Diacylglycerol, which is a precursor of the various glycerophospholipids (see Figure 19.2). CTP combines with phosphatidic acid to yield a pyrophosphate and CDP-Diacylglycerol. Activation by CDP yields a high energy intermediate that can be readily converted to phosphatidyl glycerophospholipids.

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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