Lipids

LIPIDS

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Fats and oils are storage lipids which are derivatives of fatty acids.

Fat are molecules that are solid at room temperature whereas oils are in the liquid state at room temperature. This is because of their saturation that is presence of double bonds.
Two fatty acids containing compound are triacylglycerols and waxes.

A fatty acid structure contains a carboxylic group with hydrocarbon chains which may be branched or unbranched (which may consist of hydroxyl groups alkyl groups, saturated and unsaturated). Commonly occurring fatty acids tend to have even numbers of carbon atoms in an unbranched chain (which may have 12 to 24 carbon atoms). Common patterns that may exists within fatty acids molecules are double bonds in a monounsaturated fatty acid may be located on the 9th and 10th Carbon atom.

In naturally occurring fatty acids (unsaturated) the double bonds are in the cis configuration.

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Triacylglycerols are the simplest form of fatty acids which consists of three fatty acids bonded through an ester linkage with a single glycerol. The ester linkage is formed by the polar hydroxyl of the glycerol and the polar carboxylates of the fatty acids. If the three fatty acid units are the same this is termed a simple triacylglycerol and is consequently named after the fatty acids.

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However most naturally occurring triacylglycerol tend to be mixed that is they may contain different fatty acids. Based on the ester linkage, triacylglycerols are hydrophobic ( that is it is repelled by water), nonpolar and therefore insoluble in water.

Lipids have lower specific gravities than water this basically means that it is less dense than water hence the reason oil floats on water.
The main function of triacylglycerols is to provide stored energy and insulation. In specialized cells known as adipocytes or fat cells, large quantities of triacylglycerol are stored as fat droplets.

In seeds found in plants triacylglycerols are stored as oils, so that during germination it is used to provide energy and as biosynthetic precursors. Adipoctyes and the germinating seeds both contains an enzyme known as lipases.

The lipase enzyme catalyses the hydrolysis of the triacylglycerol, thus releasing fatty acids so that it can be moved to where it is needed as seen in the diagram below.

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There are two benefits to using triacylglycerol as a form of fuel; the fatty acids are more reduced that any carbohydrate and therefore its oxidation yields twice the amount of energy. Also, the fat molecules are hydrophobic and thus repel water. Organisms that rely on this form of energy do not have to have the added molecular weight of water as do organism that relies on carbohydrates. The triacylglycerols that is in the fat tissue under the skin forms insulation for the organs as well as protection from temperature changes.
Lipids are also found as a structural component in membranes. Membranes consist of a bilayer of lipids which prevents the passage of polar molecules or ions. The lipids that are present in the membrane have two distinct properties that it; one end of the molecule is hydrophobic and the other end is hydrophilic. The bilayer allows the hydrophobic regions to form the inner part of the membrane and the hydrophilic area is the outer layer of the membrane. Some of the membrane lipids are glycerophospholipids, galactolipids, sulfolipids, tetraether lipids, sphingolipids and sterols.

                                     Image 106

Lipids also serve as signals, cofactors and pigments. Some lipids such as hormones provide signals, enzyme cofactors or as pigment molecules with double bonds that are able to absorb light. For example the pigments that are found in bird feathers to give their characteristic colour is composed of conjugated lipids.

 References for images:

http://www.quickmeme.com/meme/3pphrp

http://courses.washington.edu/conj/membrane/fattyacids.htm

http://skinchakra.eu/blog/archives/85-Butters,-Fats,-Oils-and-Co.-part-III.html

http://chemistry.ewu.edu/jcorkill/biochem/soap2000.html

http://vusc-chem430-fall2010.wikispaces.com/Sphingolipids

enzymes

Carbohydrates

Enzymes

Enzymes

Have you ever wondered who discovered enzymes?
Well, enzymes were actually discovered accidently by a scientist known as Eduard Buchner in 1897 (that was just a little known fact that the video failed to mention).
Ok, now you may be thinking how was it discovered?
Like any other discovery it was by accident. Buchner was interested in how yeast could convert sugar to alcohol but more specifically he had the idea that yeast may contain proteins. Basically he proved that fermentation actually occurred by what is known to be enzymes.
This video explains with a suitable example the function of enzymes…
What are enzymes?
Enzymes are proteins but they can also be RNA molecules. A familiar function of enzymes are as catalyst which serves to speed up a reaction, without enzymes chemical reactions would be too slow which would not make life possible.
Enzymes as catalyst:
Enzymes are specific and only work for a specific reaction, for example proteinase which hydrolyzes peptide bonds. So, an enzyme-catalyzed reaction occurs when an the enzyme binds to the substrate to form a complex. The enzyme has an area known as the active site where the substrate binds. After this occurs the enzyme may undergo minute changes to accommodate the substrate this is described as the
induced fit. As this occurs it lowers the activation energy, i.e. the minimum energy required to allow the reaction to proceed.
The affects of temperature, pH on the enzyme…
In chemicals reactions as the temperature increases, the rate of the reaction also increases. However, this is not the case with enzymes, instead as the temperature increases the denaturation of the enzyme occurs. Therefore the optimal temperature for the enzymes to work in the human body is 37°C.
pH is the measure of the H+ concentration. The pH meter ranges from 1 to 14 that is acidic-neutral- alkaline. Enzymes work in the optimum pH of 6 to 8. However, pepsin is the exception, since it needs a pH of 2 which is in gastric juice. Changes in the pH affect the complex particularly when the substrate binds to the enzyme as well as the rate of the breakdown of the complex. Note that buffers in the system adjust the change in pH.

 

Tca cycle/ krebs cycle/ citric acid cycle……………..

What is it???

Where does is take place???

What is its significance???

 

Image 98

The pyruvate that was formed in glycolysis  goes through oxidation and result in carbon dioxide and water using oxygen. All of this happens in the matrix of the mitochondria and involves the Kreb’s cycle.

First there is a transition stage  . In the matrix each pyruvate molecule enters and there is the conversion into an acetyl group.  These are carried by coenzyme A as acetylcoenzyme A. There are two carbon atoms in the acetyl  groups so when the pyruvate  which contains 3 carbons  is converted to the  acetyl which has two carbons there is the loss of a carbon. This is lost as a result of carbon dioxide in a decarboxylation reaction.  There is also a dehydrogenation  as there is the reduction of NAD.

STEP 1.  There is the combination of   the acetic acid subunit of acetyl CoA which has two carbon  with a 4 carbon oxaloacetate to form  the six carbon  compound citrate. After this step  due to the process of hydrolysis the coenzyme is released  so that it can be able to combine with other acetic acid molecule to start over the Krebs cycle

STEP 2.  Isomerization of the citric acid molecule takes place.  There is the removal of both a hydroxyl group  and a hydrogen molecule and this happen in the form of water. A double bond is formed between the two carbons until there is the replacement of the water molecules. And this result in the formation of isocitrate.

STEP 3.  At this stage an NAD molecule oxidizes  the isocitrate molecule. The hydrogen atom and the hydroxyl group causes the NAD molecule  to become reduced. There is the binding of the NAD  molecule and a hydrogen atom. The NAD also  takes away the other hydrogen atom leaving behind a carbonyl group. The resulting structure is not stable so there is the release of a carbon dioxide molecule and the resulting structure is a 5 carbon compound known as alpha-ketoglutarate.

STEP 4.  Here is where there is the return of the coenzyme A . It comes back to oxidize the alpha-ketoglutarate. There is another reduction of NAD to NADH  leaving with another hydrogen.  There is instability once again and to restore this a carbonyl group is kicked out as carbon dioxide and there is the replacement of a thioester  bond  between the previous alpha-ketoglutarate and the coenzyme A creating succinyl coenzyme A complex.

STEP 5. Being generous the water molecules gives its hydrogen atoms to coenzyme A. A greedy free phosphate floating group then pushes out the coenzyme A and this leads to the formation of a bond with the succinyl complex.

STEP 6. Here a molecule of Flavin adenine dinucleotide  (FAD) oxidizes succinate. This FAD takes away both of the hydrogen from the succinate forcing a double bond to form between two carbon atoms formingggggg……. fumarate.

STEP 7. Hmmmm  To the fumurate an enzyme adds water and this creates malate. This malate is a result of adding to a carbon a hydrogen atom. And then to the carbon that is next to the terminal carbonyl group the addition of a hydroxyl group

STEP 8. Woosh finally the last step…. A NAD molecule oxidizes the malate molecule.  The carbon that was initially carrying the hydroxyl group is now turned into a carbonyl group. The final product is the four carbon compound oxaloacetate. This compound can start over the Krebs cycle by combining with acetyl coenzyme A.

 

 Image 99

THE LINK BETWEEN CHEMIOSMOSIS AND THE GENERATION OF ATP IN THE MITOCHONDRIA!!!!!!!

 

  To understand how ATP is generated in the mitochondria by chemiosmosis, we need to break things down first.   

    Firstly, what is Chemiomosis?????????????????

 

This is when ions move across a selectively permeable membrane, down an electrochemical gradient. It is paired with ATP generation by moving hydrogen ions across a membrane when cellular respiration is taking place.

CELLULAR RESPIRATION

  Cellular respiration involves the breaking down of food (more specifically glucose) to yield energy. This energy is in the form of chemical energy and in the body. The cells of our body recognise this energy in another form known as ATP, so they convert the energy from the food we into ATP which they can use.

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 There are a few terms that we should be familiar with at this stage, but if you’re not, here’s a quick reminder:

• Glucose- this is the main energy source of the body and it is a sugar that consists of 6 carbons.
• ATP- (Adenosine Triphosphate) – This is what we would call the main energy or “money source” of the cell. It has a large amount of energy in storage and it also transports that energy in the cell.
• NADH– An electron carrier with high amounts of energy. It is what transports the electrons made in Glycolysis and Kreb’s cycle to the Electron Transport Chain. In other words, “The Shuttle service.”
• FADH2– Also an electron carrier with a high amount of energy, this is also a “Shuttle Service.”

Cellular respiration takes place in three main steps:

1. GLYCOLYSIS

This is when the glucose molecule from food sources is divided into two molecules known as pyruvate. Two ATP molecules are made and also 2 NADH molecules. So for every 1 glucose molecule, we get pyruvate, 2 ATP and 2 NADH.

 

2. KREB’S CYCLE

Here the pyruvate molecule made in glcolysis is use to 2 ATP and some FADH2 and NADH are also made for the 3^rd step.

 

3. ELECTRON TRANSPORT CHAIN

The NADH and FADH2 made previously are used to form a proton gradient which eventually forms 32 molecules of ATP.

 

Now that we have recapped what cellular respiration entails, we can now make the link between chemiosmosis and the generation of ATP in the mitochondria.

 

In the mitochondria of cells, there is something we would call a proton gradient, which is the inner membrane of the mitochondria.

  Electrons are journeying through the electron transport chain, hydrogen ions are pushed or pumped out from the mitochondria into a space known as the inter-membrane space.

 When this happens, a concentration gradient is formed or a more in depth term would be “proton motive force.”

Proton motive force is simply the energy that causes the movement of protons or the “driving force” of protons. 

This causes the protons to move from an area of high concentration to one of lower concentration by diffusion, which in turn, causes the ion to be diffused back into the cell by a process called ATP synthase.

ATP synthase is a form of enzyme that produces ATP by chemiosmosis and it is what allows the protons to be able to go through the membrane.

So to recap: ATP is made in cells that respire by an electrochemical gradient that is found across the inner membrane of the mitochondria. It uses the NADH and FADH2 as the energy source.

Now that the protons have moved back into the membrane by ATP synthase, this same energy that does this, supplies a sufficient amount of energy for ADP to join together with inorganic phosphate to thus form ATP (oxidative phosphorylation).

 This is what it mainly looks like………………………………………………..

Image 101

References for Images:

 

 

http://blog.cholesterol-and-health.com/2012/01/we-really-can-make-glucose-from-fatty.html

http://guweb2.gonzaga.edu/faculty/cronk/CHEM440pub/L30-index.cfm

http://apps.cmsfq.edu.ec/biologyexploringlife/text/chapter7/concept7.4.html

http://en.wikipedia.org/wiki/Electron_transport_chain

 

 

Glycolysis Made Easy

YouTube Video 2- Glycolysis

This video on glycolysis is very concise and appealing to the eyes. The video makes use of a step by step diagram which is easy to follow. The notes are short and to the point. According to the video glucose is converted to glucose-6-phosphate by adding a phosphate group from ATP in the presence of hexokinase. Glucose-6-phosphate is converted to fructose-6-phosphate by phospoglucose isomerase which is then converted to fructose-1,6-bisphosphate by adding a phosphate group from ATP in the presence of phosphofructokinase. The fructose-1,6-bisphosphate is converted to 2 triose phosphate isomers, dihydroxyacetone Phosphate and glyceraldehyde-3-phosphate, by the enzyme aldose. The enzyme triose phosphate isomerase regulates these isomers by favouring one over the other depending on the concentration of ATP and ADP. When the body requires ATP glceraldehyde-3-phosphate is favoured and is converted to two 1,3-bisphosphoglycerate by the removal of H+ and addition of a phosphate group from NAD+P in the presence of glyceraldehyde phosphate dehydrogenase. 2 ATP is produced by removing a phosphate group in the presence of phosphoglycerate kinase to produce two 3-phosphoglycerate. These are converted to 2-phosphoglycerate by phosphoglyceromutase. Enolase is used to remove 2 water molecules to produce two phosphoenolpyruvate. Finally pyruvate kinase converts the phosphoenolpyruvate to 2 pyruvate by removing a phosphate group per compound to produce 2 ATP. Therefore in total 4 ATP is produced per glucose, 2 ATP is used per glucose, 2 pyruvates is produced per glucose, 2 NADH+H is produced per glucose and 2 water molecules is produced per glucose.

GLYCOLYSIS 1

Hellloooo and Welcome

Our topic for today isssssssssss…………………….

GLYCOLYSIS!!!!!!!!

 

 

 IMAGE 89

When you hear the word glycolysis ….what comes to mind????

Well lets split it up

Glyco… isn’t that like glucose

And

Lysis… doesn’t this mean splitting

So lets put it together …

The splitting of glucose

In this process we begin with the 6 carbon glucose and end with 2 molecules of 3 carbon pyruvate.

There are ten reactions which can be divided into two main stages.

ENERGY INVESTMENT STAGE & ENERGY GENERATION STAGE

In these reactions 10 enzymes are involved…

FIRST STAGE

ENERGY INVESTMENT STAGE

1. Here glucose is converted into glucose -6 phosphate. ATP is converted into ADP. The enzyme involved is hexokinase . This is a transferase enzyme that transfer a terminal phosphoryl  group from the ATP unto the glucose. This is significant as by the addition of the phosphate group to the glucose, it activates the glucose resulting in it being unstable and this promotes the reaction. This reaction is not reversible however.

 2. Then glucose-6-phosphate is converted into fructose -6-phosphate. The enzyme that catalyses this reaction is phosphohexose isomerase.  This is important as an aldose sugar is being converted to a ketose sugar. This reaction is reversible.

 3. After the fructose 6-phosphate is converted into fructose1,6-bisphosphate. The enzyme responsible for this reaction is phosphofructokinase-1. This enzyme is the most regulated in glycolysis .  In this reaction ATP is converted into ADP. This reaction is not reversible.

 4. Next the fructose 1,6- bisphosphate a 6 carbon compound  is converted into glyceraldehyde 3-phosphate and Dihydroxyacetone  phosphate  both of which are 3 carbon compounds. The enzyme here is aldolase. The reaction is reversible.

 5. Here  the enzyme, triose phosphate isomerase converts the Dihydroxyacetone phosphate into glyceraldehyde 3-phosphate.At the end of this stage there are two glyceraldehyde 3-phosphate molecules.

The Second Stage

ENERGY GENERATION  STAGE

 6. Then the two glyceraldehyde 3-phosphate is converted into two  1,3- bisphosphoglycerate .  Here oxidation and phosphorylation takes place.  Oxidation  is an energetically feasible reaction. NAD+  has gained  a hydrogen. Glyceraldehyde 3-phosphate has lost a hydrogen  and given it to the NAD + . The enzyme is glyceraldehyde 3-phosphate dehydrogenase. This reaction is the only oxidation reaction of glycolysis. This reaction is reversible.

 

7. The two 1,3- bisphosphoglycerate  is then converted into two  3-phosphoglycerate. The enzyme that catalyses this reaction is phosphoglycerate kinase. It is a reversible reaction. Here two molecules of ADP is converted to two molecules of ATP. This is the first reaction that produces ATP.

8.  Here the two molecules of 3- phosphoglycerate is converted to two molecules of 2- phosphoglycerate. The enzyme for this reaction is phosphoglycerate mutase. Firstly the 3- phosphoglycerate is converted into an intermediate called 2,3- bisphosphoglycerate and then the enzyme phosphoglycerate mutase removes the  phosphate group on carbon 3 to  end up with two molecules of 2- phosphoglycerate.This reaction is reversible

 9. The two molecules of  2-phosphoglycerate is converted to two molecules of phosphoenol pyruvate. The enzyme for this step is enolase. There is the loss of water in this step or a dehydration reaction. The phosphoenol pyruvate has alot of energy. This reaction is reversible.

 10. The two molecules of phophoenol pyruvate  is then converted to two molecules of pyruvate . The enzyme here is pyruvate kinase   .This reaction is the most energetically favourable in glycolysis and it is not reversible.

 

                          

Image 90

So folks we have went through each step and I am sure we have understood them.

Hope this has enlightened you on the topic glycolysis…….

See you again soooooooooooon……………….

 

Image 91

 Reference for Images:

http://quotespics.com/one-does-not-simply-learn-chinese-lord-of-the-rings/

http://www.lactate.com/triathlon/lactate_triathlon_anaerobic_energy.html

http://funny-pics.co/wp-content/uploads/funny-animal-bye-bye-445×299.jpg

Glycolysis part 2&3

Glycolysis:

·       Image 92

The fates of pyruvate

What is the fate of pyruvate in the cell? Well, that depends on whether the conditions are aerobic or anaerobic…

If oxygen is available, then the pyruvate moves to the mitochondria through active transport. In the mitochondria the pyruvate is changed to Acetyl CoA this is known as the link reaction. During this reaction CO₂ and H ⁺ is removed from the pyruvate which is a 3C compound. NAD which stands for nicotinamide adenine dinucleotide is a coenzyme which is needed for the reaction to follow through, NAD is reduced. . The enzyme responsible for this reaction is pyruvate dehydrogenase, the remaining 2C pyruvate combines with the coenzyme A to produce acetyl CoA. Most of the ATP is made through aerobic conditions. The link reaction produces 5 ATP molecules, this is of course theoretically!

Now, what if there was no oxygen present? Well, under anaerobic conditions the pyruvate is turned into lactate.  This conversion occur in mature red blood cells which depend on glycolysis for its energy. Why convert pyruvate to lactate? Well, there is limited NAD therefore if the NAD is used up then glycolysis stops… Therefore when the pyruvate is converted to lactate in the presence of lactate dehydrogenase the NAD⁺ is regenerated. Thus no ATP is generated! An example of this occurring in the body… during vigorous exercise the decreasing oxygen allows the lactate or lactic acid to accumulate which then causes muscular cramps.

Also, under anaerobic conditions there is another fate for the pyruvate that is; in yeast fermentation ethanol and carbon dioxide are produced. The enzymes; pyruvate decarboxylase and alcohol dehydrogenase are involved. The pyruvate is first changed to acetaldehyde by the enzyme pyruvate decarboxylase and carbon dioxide is removed or decarboxylation occurs. For this to occur it needs TPP(thiamine pyrophosphate), which is a cofactor for the enzyme. In the second step the acetaldehyde is converted to ethanol. Then H⁺ is removed by NAD and it is during this step that the NAD⁺ is regenerated.  

 Image 93

·       FEEDER PATHWAYS FOR GLYCOLYSIS:

 

So far we have spoken extensively about glucose and its metabolism. However, we have failed to recognize that glucose is not the only carbohydrate consumed in the daily human diet. Other carbohydrates such as fructose and galactose also contribute to the energy levels within the human body.

 

·       Metabolism of fructose:

The main source in which fructose is consumed is from sucrose. For fructose to be metabolized by the body it has two steps involved; phosphorylation of fructose and cleavage of fructose-1-phosphate.

In the phosphorylation of fructose, fructokinase is the enzyme that catalyses the reaction. A phosphate group is added to the fructose molecule (i.e.phosphorylation) to produce fructose-1-phospahte. This allows the energy level of the fructose compound to be higher thus allowing it to participated in the second step. The phosphate group is from the ATP molecule.  In the next step, another enzyme aldolase B disintegrate the fructose-1-phosphate to the products; dihydroxyacetone phosphate and glyeraldehyde. Note that aldolase B is found in the liver. The dihydroxyacetone phosphate can then enter glycolysis.

 

·       Image 94

Metabolism of galactose:

Image 95

 

The source of galactose in the diet is from milk products. The metabolism of galactose is similar to that of fructose. For instance the galactose is phosphorylated to galatose-1-phosphate which is catalysed by the enzyme galactokinase. Galactose-1-phosphate is then changed to UDP-galactose. In this reaction the UDP-glucose reacts with the galactose-1-phosphate which produces UDP-galactose and glucose-1-phosphate with the aid of the enzyme galactose-1-phosphate uridyltransferase. Then the UDP-galactose is converted to a C4 epimer which is UDP-glucose by the enzyme UDP-hexose 4-epimerase. The UDP-glucose can then enter the glycolytic pathway.

 Image 96

References:

Google Books. “Biochemistry.” 2014. http://books.google.tt/books?id=-Lhp0ppRYWoC&pg=PA137&dq=metabolism+of+fructose&hl=en&sa=X&ei=IicSU-WBOMafyQGy1YHoCw&ved=0CCUQ6AEwAA#v=onepage&q=metabolism%20of%20fructose&f=false (accessed 1 Mar 2014).

Unknown. Fructose metabolism – Acumen. Fructose metabolism – Acumen. 2014. http://www.breakspearmedical.com/files/documents/fructosemetabolism230910_AM_.pdf. (accessed 1 Mar 2014).