There are many different classes of lipids , such as fatty acids , triacyglycerols , phospholipids , steroids and glycolipids. Fats are solid at room temperature and oils are liquids at room temperature , this is because fats contain saturated hydrocarbon chains whereas oils contain unsaturated hydrocarbon chains , meaning that there is at least one carbon to carbon double bond In the chain. Fats are very important and have many different functions and properties , they are a source of energy , giving nine kilocalories per gram , they are an energy reserve meaning that any extra energy derived from food is stored as fat , they can provide insulation and protection to internal organs.
Saturated fats are fats which contain no double bonds , therefore all the carbons atoms are bonded to bonded to hydrogen atoms. Saturated fats contain long straight chains , they are solid at room temperature and are mostly animal fats.
Unsaturated Fats have carbon to carbon double bonds . they are found in plants and fish , and vegetable based oils , they are liquid at room temperatures and their structures contain kinks caused by the double bonds.
Naturally occurring fatty acids are found to have even numbers of carbons, and the double bonds are in the cis form. It must also be noted that the presence and number of carbon doubles decreases the melting point. This is why if u take a tub of butter that claims to contain no saturated fats , meaning it only contains unsaturated fats , and leave it at room temperature you would find it turns into an oily , greasy pool inside in the tub, hence this why manufacturers of butters and margarines made of unsaturated fats put a disclaimer on the tub saying , keep refrigerated.
Non essential fatty acids are fatty acids which our body can synthesize and are therefore not required to come from our diet , alternatively essential fatty acids are fatty acids which cannot be synthesized in the body and must come from our diet. Some examples of essential fatty acids are omega-6 linoleic acid and omega-3 alpha-lenoleic acid.
The iodine index is used as the degree of unsaturation and can be found by measuring the amount of iodine that reacts with the unsaturated fat or oil.
Pictures taken from
1) The BIOCHEMJM Youtube channel
The TCA cycle or Tricarboxylic acid cycle , also known as the Krebs cycle is a compilation of chemical reactions occurring under aerobic conditions to generate energy. The cycle is made up of 8 steps and is catalysed by a number of enzymes. The TCA cycle occurs in the matrix of the mitochondria of eukaryotic cells and in the cytosol of Bacteria which lack mitochondria. The link between glucose and the citric acid cycle is this , when glucose enters glycolysis it is converted to two molecules of pyruvate , these pyruvate molecules are then converted to Acetyl CoA via the link reaction which enters the Kreb’s and cycle continues . The TCA or Kreb’s cycle can be seen below;
Picture taken from
The Medical Biochemistry Page Online
We now enter the wonderful topic of Glcolysis , which is my favourite topic , glycolysis consists of 10 enzyme catalysed reactions. The first five reactions of glycolysis are what is referred to as the energy investment phase , since ATP is invested into the reactions , the last five reactions are known as the energy payoff phase since it is here that the ATP used is regenerated with two extra ATP molecules , giving glycolysis a net gain of two ATP per molecule of glucose used. It must be said however that the real stars of glycolysis are the enzyme since they allow the reactions to be fast and energy efficient.
This is the first Priming reaction of glycolysis and the first reaction of the energy investment phase as well. The reaction is irreversible. In this reaction Glucose is converted to Glucose-6-phosphate. The reaction uses an ATP molecule and converts it to ADP , the enzyme which catalyses the reaction is Hexokinase.
This reaction converts Glucose -6-phophate to Fructose-6-phosphate via the enzyme Phosphohexose isomerise.
This reaction is the second of two irreversible reactions which occur in the energy investment phase. This reaction is the second priming reaction and consumes an ATP molecule whoch is converted to ADP , in this reaction Fructose-6-phosphate is converted to Fructose-1.6-Bisphosphate via the enzyme Phospho-fructokinase-1 (PFK-1). It must also be noted that this is the most regulated step of glycolysis.
This is the splitting reaction , in this reaction the six carbon molecule Fructose-1.6-bisphosphate is converted to two three carbon molecules , one is called Glyceraldehyde -3-phosphate and the other is called Dihydroxyacetone phosphate. The enzyme which catalyses this reaction is Aldolase.
This is the final reaction of the energy investment phase , in this reaction the Dihydroxyacetone phosphate is converted to another molecule of glyceraldehyde-3-phosphate via the enzyme Triose phosphate isomerise. Hence when the energy payoff phase begins , there will be two molecules to glyceraldehydes-3-phosphates to be used.
ENERGY PAYOFF PHASE
In this , the first of the energy payoff reactions , an inorganic phosphate is used , as well as an NAD+ molecule which is converted to NADH and a proton. In this reaction the two molecules of glyceraldehyde-3-phosphate are converted to two molecules of 1,3-Bisphosphoglycerate via the enzyme Glyceraldehyde-3-phophate dehydrogenase.
In this reaction two ATP molecules are generated from two ADP molecules , the reaction converts two molecules of 1,3-bisphosphoglycerate to two molecules of 3-phosphoglycerate , via the enzyme Phophsglycerate kinase.
In this reaction the two molecules of 3-phosphoglycerate are converted to two molecules of 2-phophogycerate via the enzyme Phophoglycerate mutase.
In this reaction two molecules of water are removed , the two molecules of 2-phosphoglycerate are converted to two molecules of Phosphophenolpyruvate via the enzyme Enolase.
This is the final reaction in glycolysis , it generates two molecules of ATP from two molecules of ADP. In this reaction two molecules of Phosphophenolpyruvate are converted to two molecules of pyruvate via the enzyme Pyruvate kinase. It should be noted that this is the only irreversible reaction in the energy payoff phase of glycolysis.
It can be seen therefore that since two ATP molecules are used in the energy investment phase and Four ATP molecules are produced in the energy payoff phase , that there is a net gain of two ATP molecules from one glucose molecules from glycolysis.
So what happens to pyruvate after it’s produced? What’s the Fate of pyruvate?
Pyruvate has three main fates;
1) pyruvate under anaerobic conditions to produce ethanol and carbon dioxide , whereby , , pyruvate is converted to acetaldehyde via the enzyme pyruvate decarboxylase using cofactors TPP and Mg2+ ions , this reaction produces carbon dioxide as a by product . The acetaldehyde is then converted to ethanol via the enzyme alcohol dehydrogenase , this reaction also converts NADH to NAD+.
2) pyruvate under anaerobic conditions to produce lactate ,this reaction occurs via the enzyme lactate dehydrogenase and in this reaction NADH is converted to NAD+. Lactate is produced in vigorously contracting muscles because in such circumstances there is an oxygen debt present and hence anaerobic conditions would be prevalent , and in erythrocytes because they lack mitochondria to produce energy otherwise.
3) pyruvate under aerobic conditions to produce carbon dioxide and water. The first stage of this reaction is converting pyruvate to Acetyl-CoA , this reaction occurs via an enzyme complex referred to as the pyruvate dehydrogenase complex , which consists of three enzymes , this reaction produces carbon dioxide and uses CoA-SH as a cofactor , in the reaction NAD+ is converted to NADH. The second stage of the conversion occurs via the citric acid cycle where the Acetyl-CoA is converted to carbon dioxide and water.
It must also be noted that Fermentation ie. Fates 1 and 2 are used to regenerate NAD+ to be used in glycolysis.
Pictures taken from
1) The BIOCHEMJM Youtube channel
2) Windsor Education Online
This video was taken from the crash course Youtube channel and it is about cells , animal cells to be precise. The video contains 10 main points as seen in the recap at 11:23 in the video. The first point in the video deals with Robert Hooke , the scientist who did the first research on cells , this is a good strategy , it employs history as a tool in the learning process , and gives a background to the topic at hand. The second point deals with cilia and flagella and discusses how in certain cells , they are used for movement. The video gives examples of human cells which have cilia , ie lung cells and human cells which have flagella ie sperm cells , this gives the video a more relatable tone. The third point discusses the cell membrane and it is at this point that the video starts describing the cells as a type of city , run by a dictatorship , this helps the viewer develop a better idea of the topic. Describing cells as a city or country seems to be a very popular tool in teaching this topic as I have seen many videos employing this very technique. Points five to nine goes into the various organelles that can be found within a cell , endoplasmic reticulum both smooth and rough which take part in steroid synthesis and protein synthesis , ribosomes which can attach to mRNA, golgi apparatus which transports proteins and enzymes , lysosomes molecules which break down molecules within the cell and the nucleus which contains the genetic layout of the cell. In the last point the host describes what he states as his favourite organelle , the mitochondria , the video discusses briefly the role of mitochondria which is to provide energy to the cell . During the last point the video also discusses the endosymbiotic theory , which states that organelles such as mitochondria were once free living organisms and were engulfed by other organisms , the video also goes into the evidence of this, being that mitochondria have their own DNA , and also discusses how this information can be used to trace back family trees since the mitochondrial DNA within a child is identical the mitochondrial DNA in the mother.
Overall I enjoyed this video , however I do have some critiques about it , one such critique is that the video is not nearly as informative as a proper science video should be , I found it lacking in information. Another problem I had with the video was that it seemed to have very subjective tone used , meaning that a lot of opinions were used , another problem is that the video makes a lot of references to past videos , giving links every which way , this is confusing for a first time viewer of the channel and also means that someone will not be able to watch just that one video and have a decent understanding of cells. There were also things that I did quite like , for one the style of the video is very visual , there are a lot of pictures and video clips of animals and even animations showing how certain parts of the cells work , this keeps the attention of the viewer and would make them more likely to watch the entire thing . Also the fact that the video is short , encourages people to watch the video.
In conclusion , although the video was very entertaining with its animations and clips , it must be said that it lacked heavily in substance and does not fully explain how the cells works or even the proper functions of the organelles, therefore I would not recommend this video to a biochemistry student as they would find it non informative. I think the target audience for this video would be to a form 1 class of students who are just starting to learn about science , as it gives a simplistic and elementary view of the cell.