LIPIDS – The finale!


Lipids are large, diverse molecules linked by the property of being insoluble in water. Along with proteins, carbohydrates and nucleic acids, lipids are one of the four main types of organic macromolecules necessary for life’s functioning. Lipids are involved in how the body stores energy, regulates biological processes, and maintains structural integrity at the cellular level.

Lipids (fat) at is also known as a triglyceride. It is made up of a molecule known as glycerol that is connected to one, two, or three fatty acids. Glycerol is the backbone of all fats and is made up of a three-carbon chain that connects the fatty acids together. A fatty acid is just a long chain of carbon atoms connected to each other.


Saturated and Unsaturated

There are two kinds of fats, saturated andunsaturated. Unsaturated fats have at least one double bond in one of the fatty acids. A double bond happens when four electrons are shared or exchanged in a bond. They are much stronger than single bonds with only two electrons. Saturated fats have no double bonds.



  • Energy store
  • Insulation
  • Major component of the phospholipid bilayer in cell membranes
  • Transmission of information in cells
  • Metabolism in cells


Essential fatty acids are:

–> as they sound, fats that are essential or important for the human body. Some essential fatty acids are necessary for your a healthy lifestyle. In their absense, serious health problems and issues can occur. Two essential fatty acids are:

  • Omega-3 Essential Fatty Acids
  • Omega-6 Essential Fatty Acids






In the The Citric Acid Cycle, we begin with only one molecule of Acetyl Co-A. During this cycle this molecule undergoes many reactions. In these reactions, Acetyl Co-A where it produces not one but two molecules of Carbon Dioxide. Another molecule used is FAD which is reduced to FADH2. A total of three molecules NAD were used which were all reduced to three molecules of NADH. One molecule, GTP was also produced. GTP is just as same as ATP. ATP is produced from ADP.


Enzymes which catalyse the reactions of the TCA cycle!

  • Reaction 1: Citrate Synthase 
  • Reaction 2: Acontinase
  • Reaction 3: Isocitrate Dehydrogenase
  • Reaction 4: Alpha-ketoglutarate deydrogenase
  • Reaction 5: Succinyl-CoA Synthetase
  • Reaction 6: Succinate Dehydrogenase
  • Reaction 7: Fumarase
  • Reaction 8: Malate Dehydrogenase



Enzymes are Biological catalysts (proteins) that speed up a chemical reaction by lowering its activity. Enzymes are not consumed during a reaction. One such example is catalase which is an enzyme that is found in all living cells. This enzyme breaks down hydrogen peroxide (H2O2).

Chemical reaction:

2H2O2   à 2H2O + O2.

The enzyme catalase breaks down H2O2 into water and oxygen.

Ebzymes contains active site, where substrate fits into. This substrate will be catalysed. The substrate in this example above was H2O2.

Substrates bind to the active site of the enzyme by two theories;

  1. Lock and key – this is where the substrate is identically shaped to the active site and fits perfectly into the active site
  2. Induced fit – this is where the substrate is not identical to the active site but still binds to the enzyme for a reaction to occur.

Enzymes are turned on (activated) and turned off (deactivated or inhibited)

Enzymes are turned off/ inhibited;

This is done by inhibition. It can either be competitive or non competitive inhibition. Competitive inhibition is when the inhibitor competes with the substrate for the active site of an enzyme and non competitive is where the inhibitor binds to another part (allosteric site)of the enzyme and causes a conformational change of the enzyme.

Enzymes are activated by;

  1. They are only produced when needed – this is a regulating method for reactions. These enzymes are activated when needed.
  2. Enzymes are activated using either cofactors (inorganic) or coenzymes (organic). These are small that are added to enzymes to activate the enzymes.
  3. Example of cofactor – Heme contained in hemoglobin
  4. Example of coenzyme – Thiamine (Vitamin B1)

Enzyme reactions are affected by;

  1. Substrate concentration
  2. Enzyme concentration
  3. Temperature
  4. pH
  5. Competitive inhibitors
  6. Non competitive/ allosteric inhibitors

Example of enzyme reaction vs temperature

As temperature increases, enzyme reaction increases until optimum temperature. Optimum temperature is the temperature or range of temperatures that the enzymes functions at its best. After this optimum temperature is passed enzymes becomes denatured and rate of reaction decreases as enzymes cannot bind to substrates due to conformational changes and breaking of chemical bonds within the active site and entire enzyme.




In this video, Khan aims to explain fully the Glycolysis process. He firstly explained that glycolysis is one of the major processes that take place during cellular respiration. He stated that glycolysis is simply the splitting of glucose. Glycolysis can occur either with oxygen or without oxygen. If oxygen is not present, we go to the fermentation process; if oxygen is present, we proceed to the Kreb’s Cycle.
Glycolysis consists of 2 phases: the investment phase and the payoff phase. In the investment phase, 2 ATP molecules are used which produces 2 ADP. At the end of this phase, we end up with 2 phosphoglyceraldehyde molecules. The molecules then lead us into the payoff phase. Unlike the investment phase, the payoff phase uses 4 ADP molecules and 2 NAD+ molecules which produce 4 ATP and 2 NADH molecules respectively.
Khan stated that:
Glucose + 2 NAD+ + 2 ATP + 4 ADP + 4Pi undergoes the process of Glycolysis and produces
2 Pyruvate + 2 NADH + 2 ADP + 4 ATP.


Khan then proceeds to explain each step of the glycolysis process. Firstly, Glucose forms Glucose-6-phosphate with the enzyme HEXOKINASE. In this reaction, ATP is used and produces ADP. Glucose-6-phosphate then reacts with the enzyme PHOSPHOGLUCOSE ISOMERASE to produce Fructose-6-phosphate which then forms Fructose-1,6-bisphosphate when reacted with the enzyme PHOSPHOFRUCTOKINASE-1. In this reaction, another ATP molecule is used which is converted to ADP. This Fructose-1,6-bisphosphate molecule then reacts with the enzyme FRUCTOSE BISPHOSPHATE ALDOSE and forms Glyceraldehyde-3-phosphate and Dihydroacetone phosphate. However, for the reactions in the payoff phase to occur, we need to convert the Dihydroacetone phosphate into Glyceraldehyde-3-phosphate. To do this, we need the help of another enzyme, TRIOSEPHOSPHATE ISOMERASE.

In the payoff phase however, because we begin with 2 molecules of Glyceraldehyde-3-phosphate, for every reaction, product, or reactant used it needs to be timed by 2 as everything is done twice, once per Glyceraldehyde-3-phosphate. The first step of the payoff phase is where the Glyceraldehyde-3-phosphate is converted to 1,3-bisphosphate by the enzyme GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE. In this reaction, NAD+ is used to produce NADH+H+. The 1,3-bisphosphate molecule then reacts with the enzyme PHOSPHOGLYCERATE KINASE which produces 3-phosphoglycerate. In this reaction, not 1 but 2 ADP molecules are used and produce 2 ATP molecules. Then, 2-phosphoglycerate is formed from 3-phosphoglycerate with the enzyme PHOSPHOGLYCERATE MUTASE. No ADP or NADH molecules are used in this reaction. This molecule of 2-phosphoglycerate then converts to Phosphoenol pyruvate. The enzyme ENOLASE is used to catalyse this reaction. This next reaction then produces the 2 final molecules of Pyruvate. These pyruvate molecules are formed from the Phosphoenol pyruvate molecules and this reaction is catalysed by the enzyme PYRUVATE KINASE. Here, 2 ADP molecules are used and produce 2 ATP molecules.
Pyruvate is a 3C structure. This is the end product of glycolysis as the glucose molecule was split. The carbons from the glucose molecule was oxidised hence the number of carbon is reduced, forming pyruvate.
The NADH molecules produced would be used in the ETC to produce ATP molecules per NADH molecule.





I used the shape of a key to do my word cloud as it depicts the lock and key hypothesis of enzymes. The lock and key hypothesis is where the substrate has a precise or specific shape to fit the active site of the enzyme. We say that the shape of the substrate is complementary to the shape of the active site on the enzyme molecule. 🙂


Enzyme Activity Factors



Enzyme activity is affected by many factors such as the presence of inhibitors, temperature as well as changes in pH. These factors tend to denature the enzyme by reducing the enzyme activity henceforth altering the enzyme’s its shape and orientation. When it changes shape, a substrate can no longer fit perfectly into the active site. When binding does not occur, the reaction discontinues therefore reducing the amount products being formed. These enzyme molecules can function up till a certain temperature and pH known as optimum temperature and optimum pH. This is because after these rates, enzymes begin to denature.


After experiencing heat above optimum temperature, the enzyme becomes denature therefore it changes shape and orientation where it can no longer bind to the substrate. 


naribiochemwiz007 🙂 ♥