High energy molecules

What are high energy molecules???

The high-energy molecules include all the nucleoside triphosphoric and diphosphoric acids, the pyrophosphoric and poly-phosphoric acids, phosphocreatine, phosphopyruvic acid, diphosphoglyceric acid, acetyl coenzyme A, succinyl coenzyme A and the aminoacyl derivatives of adenylic and ribonucleic acids.

Introduction:

How Cells Obtain Energy from Food:

As we have just seen that cells require a constant supply of energy to generate, regulate and maintain the biological order that keeps them alive. This energy is derived from the chemical bond energy from food and nutrient molecules, which thereby serve as fuel for cells.

Sugars are particularly important fuel molecules, and they are oxidized in small steps to carbon dioxide (CO2) and water. In this section we trace the major steps in the breakdown, or catabolism, of sugars and show how they produce ATP, NADH, and other activated carrier molecules in animal cells. We concentrate on glucose breakdown as it dominates energy production in most animal and bacterial cells. A very similar pathway also operates in plants, fungi, and many bacteria. Other molecules, such as fatty acids and proteins, can also serve as energy sources when they are funnelled through appropriate enzymatic pathways.

ATP inter-dependent proteases differ substantially in their ability to unfold globular proteins.

ATP-dependent proteases control the concentrations of hundreds of regulatory proteins in the body and cells to remove damaged or misfolded proteins from cells. They select their substrates primarily by recognizing sequence motives or covalent modifications. Once a substrate is bound to the protease it develops the ability to be unfolded and folded, translocated into the proteolytic chamber to be degraded or to become unfunctional. Some proteases appear to be promising and degrading substrates with poorly defined targeting signals due to which it suggests that the selectivity may be controlled at additional levels. We  have to compare the abilities of representatives from all classes of ATP dependent and independent proteases to unfold a model substrate protein and find that the unfolding abilities range over more than 2 orders of magnitude but not direction. We understand that these differences in unfolding and unfolding abilities contribute to the fate of substrate proteins and may act as a further layer of selectivity during protein destruction or denaturation.

Food Molecules need to be broken down compulsorily into Broken Three Stages to Produce ATP

The proteins, lipids, and polysaccharides which make up most of the food which we consume must be broken down into smaller molecules before our cells can use them either as a source of energy and strength or as building blocks for other molecules. The breakdown processes must act on food taken in from outside, but not on the macromolecules inside our own cells.

Stage 1 In the enzymatic breakdown of food molecules is the process of digestion which occurs either in our intestine or outside the cells, or in a specialized organelle within cells, the lysosome. (A membrane that surrounds the lysosome keeps its digestive enzymes separated from the cytosol, as described. In either of the case the large molecules in food are broken down during digestion into their monomeric subunits i.e. proteins into amino acids, polysaccharides into sugars and fats into fatty acids- glycerol through enzymatic action. After digestion the small organic molecules obtained from food enter the cytosol of the cell, where their gradual oxidation and reduction begins. As illustrated in, oxidation occurs in two further stages of cellular catabolism: stage 2 starts in the cytosol and ends in the major energy-converting organelle, the mitochondrion; stage 3 is entirely confined to the mitochondrion, the three stages of cellular metabolism that lead from food to waste products in animal cells. This series of reactions produces ATP, which is then used to drive biosynthetic reactions and other energy-requiring processes in the cell. Stage 1 occurs outside cells.

Stage 2 occurs mainly in the cytosol except for the final step of conversion of pyruvate to acetyl groups on acetyl CoA that occurs in mitochondria matrix. Stage 3 occurs in mitochondria.

In stage 2 a chain of reactions called glycolysis glucose gets converted into two smaller molecules of pyruvate. Sugars other than glucose are converted to pyruvate after their conversion to one of the sugar molecules which are intermediates in the glycolysis process. During pyruvate formation, two types of activated carrier molecules are produced—ATP and NADH. The pyruvate then passes from the cytosol into mitochondria. There, each pyruvate molecule is converted into CO2 plus a two-carbon acetyl group—which becomes attached to coenzyme A (CoA), forming acetyl CoA, another activated carrier molecule. Large amounts of acetyl CoA are also produced by the stepwise breakdown and oxidation of fatty acids derived from fats, which are carried in the bloodstream, imported into cells as fatty acids, and then moved into mitochondria for acetyl CoA production.

Stage 3 is the oxidative breakdown of food molecules which  takes place entirely in the  mitochondrial matrix. The acetyl group in acetyl Coenzyme A is linked to coenzyme A through a glycosidic linkage, and it is therefore easily transferable to other molecules. After its transfer to the four-carbon molecule oxaloacetate, the acetyl group enters a series of reactions called the citric acid cycle. As we discuss shortly, the acetyl group is oxidized to CO2 in these reactions, and large amounts of the electron carrier NADH are generated. Finally, the high-energy electrons from NADH are passed along an electron-transport chain within the mitochondrial inner membrane, where the energy released by their transfer is used to drive a process that produces ATP and consumes molecular oxygen (O2). It is in these final steps that most of the energy released by oxidation is harnessed to produce most of the cell’s ATP.

Because the energy to drive ATP synthesis in mitochondria ultimately derives from the oxidative breakdown of food molecules, the phosphorylation of ADP to form ATP that is driven by electron transport in the mitochondrion is known as oxidative phosphorylation. The fascinating events that occur within the mitochondrial inner membrane during oxidative phosphorylation are the major focus.

Through the production of ATP, the energy derived from the breakdown of sugars and fats is redistributed as packets of chemical energy in a form convenient for use elsewhere in the cell. Roughly about 109 molecules of ATP are in the solution in a typical cell at any instant and in many cells, all this ATP is turned over (that is, used up and replaced) every 1–2 minutes.

In all nearly half of the energy that could in theory be derived from the oxidative reduction of glucose or fatty acids to water and CO2 is captured and used to drive the energetically unfavourable reaction Pi + ADP → ATP. (By contrast, a typical combustion engine, such as a car engine, can convert no more than 20% of the available energy in its fuel into useful work.) The rest of the energy is released by the cell as heat, making our bodies warm.

ATP SYNTHASE

Racker and his associates discovered that “knobs” or “little mushroom” are visible in negatively stained mitochondrial fragments or fragment of bacterial membranes which possess ATP hydrolysing (ATPase) activity. The knob protein has been recognized as one of the several coupling factors required for reconstitution of oxidative phosphorylation. The sub mitochondrial particles. The knob protein is known as coupling factor F1. Similar knobs present on the outside of the thylakoid became CF1 and which were inside the thermophilic bacteria is TF1. The ATPase activity of F1 was a clue that the knob were really ATP synthase. The ATP synthase is firmly embedded in the membranes. This part became to be known as Fo. Both the names F1Fo ATP synthase and F1Fo ATPase are applied to the complex. The ATPase activity is usually not coupled to the proton pumping but is a readily measurable property of the F1 portion. In a well-coupled sub-mitochondrial particle, the ATPase activity will be coupled to the proton transport and will represent a reversal of the ATP synthase activity.

Important High Energy Molecules:

ATP: ATP (Adenosine Triphosphate) consists of high energy bonds located between each of the phosphate groups. These bonds are known as phosphoric anhydride bonds.

ADP: ADP (Adenosine Diphosphate) also contains high energy bonds located between each phosphate group. It has the similar structure as ATP but with one less phosphate group. The same three reasons that ATP bonds are high energy applies to ADP  bonds.

NAD+: NAD+ (Nicotinamide adenine dinucleotide (oxidized form)) is the major electron acceptor for catabolic reactions. It is strong enough to oxidize alcohol groups to carbonyl groups, while other electron acceptors (like [FAD]) are only able to oxidize saturated carbon chains from alkanes to alkenes. It is a very important molecule in many metabolic processes like beta-oxidation, glycolysis, and TCA cycle. With out NAD+ the processes would be unable to occur

NADH: NADH (reduced form) is an NAD+ that has accepted electrons in the form of hydride ions. NADH is one of the molecules responsible for donating electrons to the ETC (electron transport chain) to drive oxidative phosphorylation and pyruvate during fermentation processes.

NADP+: NADP+ (Nicotinamide adenine dinucleotide phosphate (oxidized form)) is the major electron donator for anabolic reactions.

NADPH: Nicotinamide adenine dinucleotide phosphate (reduced form)

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