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Classification of Carbohydrates - NEET PG Pediatrics

May 19, 2023

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What are Carbohydrates?

Classification of Carbohydrates

Monosaccharide

Disaccharides

Lactose

Lactose Intolerance

Diagnosis:

Classification of Polysaccharides

Starch

Glycogen

Classification of Carbohydrates - NEET PG Pediatrics


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What are Carbohydrates?

Carbohydrates are the macronutrients which are mainly responsible for providing energy to our body. Since they are made up chemically of carbon, hydrogen, and oxygen, they are known as carbohydrates. Sugars, fibre, and starches are examples of the necessary nutrients known as carbohydrates. They can be found in milk and other dairy products, as well as in cereals, vegetables, and fruits..

When food containing carbohydrates is digested by the digestive system, glucose, or blood sugar, is produced. This sugar serves as a source of energy for the cells, organs, and tissues in our body. Our muscles and liver store the additional energy or sugar in case we need it later.

Read this blog further to get a quick overview of this important topic for PEDIATRICS and ace your NEET PG exam preparation.

Classification of Carbohydrates

Carbohydrates

Simple carbohydrates

Complex carbohydrates

  • They have carbohydrates units only
  • Carbohydrate attaches to protein or lipid and of 3 types
  • Glycoproteins
  • proteoglycans 
  • Glycolipids
    • Point to remember: Glycoproteins
      & proteoglycans are not at all the same things.

The classification of simple carbohydrates is based on the number of carbohydrate units– logically -into three types

  • Monosaccharides: Single carbohydrate unit in them
  • Oligosaccharides: 2 to 10 units of carbohydrates. E.g., disaccharides
  • Polysaccharides: These have more than 11 units of polysaccharides 

Monosaccharide

Two ways to classify the monosaccharides.

  • Number of carbon atoms
  • Functional group

Based on Number of carbon atoms

Based on functional group

  • Trioses: 3 carbon atoms.
  • Tetroses: 4 carbon atoms.
  • Pentoses: 5 carbon atoms.
  • Hexoses: 6 carbon atoms 
  • Aldoses: Aldehyde group
  • Ketoses: Ketone group

Only one functional group is present in glucose and that is monosaccharide. The functional group that presents in glucose is aldehyde. Therefore, glucose is an Aldose. Glucose is a hexose  that means glucose has 6 carbon atoms. In Fructose, only one functional group is present that is monosaccharide because it got only one sugar unit. The functional group that presents in fructose is Ketone group- makes fructose ketosis.

Based on a misnomer - Triose is a monosaccharide - 3 carbon atoms.Misnomer is maltotriose - not a triose - it’s a trisaccharide with 3 glucose residues → 3 * 6 = 18 atoms . If you see “Mal” in a compound’s name, it means made up of multiple glucose residues.

  •  Maltose: 2 glucose residues
  • Isomaltose: 2 glucose residues
  • Maltotriose: 3 glucose residues

Disaccharides

One of the types of oligosaccharides having - Two sugar units

Disaccharide

Sugars present

Linkage

Maltose

(Basic thumb rule)

2 glucose residues– glu+glu

⍺(1,4)

Isomaltose

(Six atoms)

2 glucose residues– glu+glu

⍺(1,6)

Trehalose

2 glucose residues– glu+glu

⍺(1,1)

Sucrose (non-reducing- although made up of reducing agents)

Also called table sugar

Glucose and fructose – glu +fru

⍺ (1,2)

Lactose

(Present in milk)

Galactose + glucose

β(1,4)

Lactose 

Linkage in lactose is β(1,4). One fact to note is humans cannot digest cellulose - a plant diet comes under a fiber diet– plants act as a source of fiber - plants have got cellulose. Undigested food will reach the colon - which will attract water. Most human digestive enzymes cannot attack β linkages – indirectly tells us linkage present in cellulose, which is made up of multiple glucose residues linked multiple β(1,4) linkage. The only human digestive enzyme which can attack β linkage is lactase– lactose.

Lactose Intolerance

Lactose intolerance is a digestion defect, while other disorders - fructose intolerance and galactosemia are metabolism defects. Lactose intolerance is called a digestion defect. Because caused by a defect of lactase in the intestinal villi–when lactase is absent in intestinal villi - any lactose present in the diet cannot be digested to give galactose and glucose. Not able to break disaccharides into monosaccharides - disaccharides cannot be absorbed; only monosaccharides will be absorbed. Disaccharides will stay back in the lumen - disaccharides are osmotically active, attracting water and causing osmotic diarrhea. Predominant clinical presentation of lactose intolerance is it always present with osmotic diarrhea - due to the absence of lactase in intentional villi - lactose cannot be digested, causing osmotic diarrhea. - undigested substances reach the colon. Colon has microorganisms that utilize lactose, converting lactose into hydrogen and methane. Both these are gasses that accumulate in the colon - other manifestations of lactose intolerance– it presents with flatulence, frothy stools, and bloating. Same hydrogen and methane generate the explanation for the methane breath test and hydrogen breath test. - done to detect lactose intolerant. IOC for lactose intolerance is methane breath test and hydrogen breath test.

Diagnosis:

The patient needs to fast overnight.  Early morning breath sample is taken. Amount of hydrogen or methane is measured based on laboratory preference. Measured qty of lactose is given to the patient - periodic interval breath samples are collected. Estimate the hydrogen or methane level in the sample. If these hydrogen or methane concentrations increase beyond the physiological - it is diagnostic of lactose intolerance. Additionally, colonic microorganisms act on this undigested lactose to form acids are responsible for acidic ph in stools. This pH acidic in stools is responsible for perianal excoriation – features of lactose intolerance.

Classification of Polysaccharides

Have Eleven or more numbers of units. 

Polysaccharides

Homopolysaccharides

Heteropolysaccharides

  • Individual units are the same. 
  • They are made up of repetitive units of one sugar moiety
  • Individual units are different.
  • Mucopolysaccharides /glycosaminoglycans GAG: Best Example

 Homopolysaccharides 

Homopolysaccharides

Structural homopolysaccharides

Storage homopolysaccharides

  • It acts as a structural component of the cell.
  • Storage forms of carbohydrates
  • Examples
    • Cellulose - is a component of plant cell wall - made up of multiple glucose residues - linked with ? (1,4) linkages.
    • Inulin - used to measuring glomerular filtration rate - present in plant tubes - made up of fructose. 
    • Chitin - exoskeleton scales of snake and cockroaches - made up of N-acetyl glucosamine (NAG)
  • Examples
  • Storage form of glucose in plants: Starch
  • Storage form of glucose in animals: Glycogen

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Starch 

 It is the Storage form of glucose in plants Porridge and starch have  resemblance

  • Porridge two components - solid and liquid components. Starch has 2 components-Highly branched amylopectin: it has multiple glucose residues which are linked by ⍺ (1,4) linkage along straight chain and ⍺(1,6) at branch points. Sequential linkages of ⍺(1,4) - Amylopectin. It is very stable and its melting temp. Is high — 50°  - solid part of starch - amylopectin. Unbranched Amylose - multiple glucose residues linked by ⍺(1,4) linkages along straight chains, Not that stable and has Less melting temperature that is at  room temp it is molten - liquid part of starch.

Also Read: Diaper Rash: Causes, Symptoms, Types, Diagnosis, Treatment, Prevention and Complications

Glycogen

It is the Storage form of glucose in animals. Two tissues store glycogen in the human body are Liver and Muscle.

Glycogen is the Highly branched carbohydrate structure. It is a Spherical molecule - center protein called as Glycogenin - every glucose residue is attached directly or indirectly. Straight chain - it is directly attached to glycogenin. Branch point is  indirectly attached to glycogenin Straight chain has 11-13 glucose residues - linked by ⍺(1,4) linkages and branch point ⍺(1,6) linkage alone. Entire structure is arranged in 12 concentric layers to enable compactness - glucose residues in a straight chain will form 1 concentric layer hence 12 layers.

This is everything that you need to know about disorder of carbohydrate metabolism for your PEDIATRICS PREPARATION. For more interesting and informative blog posts like this download the PrepLadder App and keep reading our blog!


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