Review on Carbs !!

For my first you tube video review I chose to reflect on Carbohydrates part 1 by BiochemJM 

Some basic stuff on carbs 🙂

From our secondary school knowledge on biology we all know that carbohydrates are a group of organic compounds, there molecules are made up of atoms of Carbon, Hydrogen and Oxygen.

Carbohydrates provide our body with energy, while also taking part in alot of required functions in the body. There is not a single carbohydrate that is essential. Remember that essential means that the body cannot synthesis it on its own, it needs a tad bit of help from its diet.

The big question is : Where do we get all this energy from to begin with?


The answer is simple it comes from the big yellow thing in the sky called the SUN!!


So in case you cant remember how energy from the sun reaches us here is a little re-cap 🙂 . The sun will convert its light energy into chemical energy, which is enclosed in the bonds of glucose molecules, it does this by using reactants such as carbon dioxide and water, also chlorophyll as the pigment. This process is called photosynthesis and has the general equation : 6CO2 + 6H20 + energy ——> C6H1206 + 6O2.

So why do we really need carbs ?

There are a number of reasons and we would start with the most important one.


We break down carbohydrates to get CO2 and H2O during metabolism. Monosaccharides and dissaccharides would break down really quickly to provide energy, some examples would be the hexose sugar glucose and the dissaccharide sucrose. Polysaccharides however take a longer period for example starch and cellulose. What is special about cellulose is that humans, such as me and you, cannot break down this component, because we lack the specific enzyme required to breakdown the beta- (1,4) linkage present in the cellulose structure.


In carbohydrates we mainly use the polysaccharides starch and glycogen.

Something extremely important to note is that :


Usually when the body would have a high glucose concentration the pancreas would release INSULIN and this would convert the excess glucose into glycogen and would store it in the liver and muscles.


Now when there is a low glucose concentration, the hormone GLUCAGON will now convert the glycogen stored in the liver back into glucose. As we can see glucose is very important it is the main respiratory substrate when oxidized it releases large amounts of energy, this is done by a process called glycolysis.


When it comes to structure there are two important polysaccharides and they are cellulose and chitin.

Cellulose : This form about 20-50% the mass of cell walls of all plants. It is abundant and strong so humans have found alot of uses for it such as cotton and paper which is almost pure cellulose. Cows and other animals have the enzymes needed to break down cellulose, It is called cellulasesImage

Unfortunately humans don’t have this enzyme Image

Chitin : This is a common biological molecule, found in the exoskeleton of all arthropods. It is a light, stable , strong transparent and even permeable to water and gases. It is used in medicine for sutures , because it is so strong and flexible, but it does not last forever over time it decomposes.


Carbohydrates act as percursors for the synthesis of biomolecules. Ribose forms part of the nuclei aids RNA and DNA. It is the skeletons that serve as the raw material for synthesis of the other molecules such as amino acids and fatty acids.

Carbohydrates metabolism.

Since the video I am reviewing is for a level 1 biochemist we would focus mainly on Glycolysis even thought there are other pathways involved in metabolism.

So if carbs are an important energy supply to the body why do people who diet stay away from  it? 

Yes carbohydrates are good for you, but there are also some carbohydrates that are of no nutritional value and they are called empty calories! For example cakes, cookies, beer and so on Image

Getting down to business!

We know that carbohydrates are made up of either monosaccahrides, disaccharides, polysaccharides and oligosaccharides.

There are two types of monosaccharides Aldoses and Ketoses.

An aldose has an aldehyde group, and a ketose has a keto group.


From the picture above we can see that the aldehyde group from the aldose is on the first carbon, while the keto group is on the second carbon of the ketose.

The aldehyde group CHO is very similar to a carboxylic group COOH , they differ with respect to an oxygen.

The two most common aldoses and ketoses would be :


Both aldose and ketose have a carbonly group (C=O)

Something simple in the world of biochemistry.

Glyceraldehyde is an aldotriose. What does this mean? It means that it is an aldose whose structure has 3 carbons. Image

Dihydroxyacetone is a ketotriose. A ketose with 3 carbons. Image

These two molecules are very important when it comes to glycolysis.

Chiral Objects!!!

A chiral carbon is one in which it has 4 different groups attached to it. Another word for chiral is asymmetric.

Mirror image !!!

The 3D structure of a chiral compound has a mirror image.


D vs L designation

This is based upon the configuration about the single asymmetric carbon. When the OH is on the right hand side of chiral carbon it is said to be D, and when the OH is on the left hand side it is said to be L. An easy way to remember is that L stands for L.

Now what would happen if there were more than one chiral carbons in a compound?

In a case like this the D or the L would refer to the chiral carbon furthest away from the aldehyde or keto group.


D and L are mirror images of each other, they have the same name.

To calculate the number of stereoisomers the formula is 2 to the power of n where n is equal to the number of asymmetric centers.


Epimers are sugars that differ in configuration around ONE carbon atom. An example would be D- glucose and D- mannose they differ at C2 , whereas D-glucose and D- galactose differ at C4


Hemiacetal and Hemiketal formation.

Aldehdyes reacts with alcohol to form a hemiacetal

Ketones react with alcohol to form a hemiketal


The pentoses and hexoses can cyclize. Glucose can form an intra- molecular hemiacetal when the C1 reacts with C5 and form a 6- member pyranose ring.

This cyclization results in glucose having a new asymmetric center at C1. Because of the tetrahedral nature of carbon bonds, pyranose sugars can assume either a ‘chair’ or ‘boat’ configuration, this depends on the sugar.

Glucose can be represented in many ways some examples would be :


Sugar derivatives

Sugar alcohol : This lacks an aldehyde or a ketone group.

Sugar acids: Either when the aldehyde at C1 or the OH at C6 is oxidised to a carboxylic acid.

Amino sugar : An amino group substituted for a  hydroxyl group.

Carbohydrates such a wide field, lots of things to learn , I do hope that you found my review helpful in any way , with studying or even with a particular section. If you did find it helpful please click the like button 😀 For more information on this topic you can check out the video itself : 


2 thoughts on “Review on Carbs !!

  1. geeta2013 says:

    sounds really great!!! it basically covers everyting that we did on carbs 🙂

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