Biochemistry Essentials: Structure - Function Correlation for Exams

Glucose

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 → glucose has 6 carbon atoms.

Quick tips:

• Based on the no. of carbon atoms – glucose is a hexose
• Based on the functional group – glucose is an aldehyde

Fructose

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 the Ketone group – makes fructose ketose.

Quick Tips:

• Based on the no. of carbon atoms – 6 carbon atoms – fructose is a hexose
• Based on the functional group – one sugar unit makes it a ketose – ketone group.
• Glucose and fructose share same molecular formula – C H O 6 12 6.

Sucrose

How many carbon atoms in the ring?

• 4 carbon atoms - Fructose
• 5 carbon atoms - Glucose /Mannose /Galactose

How to know which out of the three it is?

• Check 2nd & 4th carbon atoms.
  • If in both 2nd & 4th carbon atoms, OH lies below the plane it is Glucose.
  • If in 2nd carbon atom, if OH lies above the plane of the ring it is Mannose.
  • If in 4th carbon atom, if OH lies above the plane of the ring it is Galactose.

Keratan Sulphate

Regularly arranged in the cornea such that it does not refract/ reflect/diffract light rays. Responsible for the transparency of the cornea. When a scar replaces the cornea, it doesn't have KS1 instead, it has collagen. Collagens refract/reflect/diffract light rays and is responsible for the cornea's opacity of the scar.

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Chondroitin Sulphate

Mucopolysaccharides with galactosamine are Chondroitin sulphate and Dermatan sulphate.

Anomerism

In the anomeric carbon atom or the functional carbon atom. If OH lies above the plane of the ring, it is called beta form. In the anomeric carbon atom or the functional carbon atom. If OH lies below the plane of the ring, it is called alpha form. Alpha  and beta forms are anomers. This is with respect to anomeric carbon atoms or functional carbon atoms. Anomerism is the property by which two or more molecules have same structural formula and same molecular formula but they differ in spatial orientation with respect to the anomeric carbon atom or the functional carbon atom.

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Epimerism

The molecule should differ in spatial orientation with respect to one of the one asymmetric carbon atoms other than the penultimate carbon atom. To call a molecule an epimer of glucose, they need to differ with respect to the 2, 3, and 4 carbon atoms. For example, D-Mannose, Galactose, etc.

Glucose and mannose are epimers at 2nd position. Glucose and galactose are epimers at 4th Position. In Ribose, the first and the last carbon atom are symmetric, and the fourth carbon atom is the penultimate carbon atom. Therefore, the 2nd and 3rd carbon atom differences can provide the epimers of ribose. They are Arabinose and Xylose. Ribose and arabinose are epimers at 2nd position. Ribose and xylose are epimers at 3rd position.

Diastereoisomerism

The molecule should differ in spatial orientation with respect to one or more asymmetric carbon atoms other than the penultimate carbon atom. D-Mannose and Galactose differ from each other with two carbon atoms; therefore it is diastereoisomerism.

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Enantiomerism

Enantio means mirror. Therefore, they are the exact image of the carbon atoms.

Other names for enantiomerism are Racemism. Racemase Enzymes are the ones that interconvert the D and L forms. However, the Racemic Mixtures are the which have an equal composition of D and L form; there will be an equal composition of d and l.

Lipids

Lipids are a group of heterogeneous substances.

• Non-polar in nature
• Soluble in non-polar solvents like chloroform and ether
• Insoluble in polar solvents like water.
• Ex: Triacylglycerol - Glycerol + 3 Fatty acids

Sphingosine

It is an amino alcohol. Functional groups: Amino and alcohol group.

Phosphatidate

• Glycerol has 3 OH groups.
• First 2 OH groups get attached to fatty acid.
• 3rd OH group gets attached to the phosphate group.
• This is called phosphatidate-Precursor of every glycerophospholipid.

Also Read: Amino Acid And Protein Metabolism: Important Questions In Biochemistry

Sphingophospholipids

Esters containing fatty acid, phosphate and sphingosine

Composition of myelin

• Sulphogalactosyl ceramide.
• Sphingomyelin.

Structure of Haemoglobin

• Contains molecules 4 heme, surrounded by globin chains.
• As it contains more than 1 polypeptide chain - forms a quaternary structure.
• Strong polypeptide chain interaction: Taut structure - favours deoxygenation.
• Weak polypeptide chain interaction: Relaxed structure - favours oxygenation.

Nucleoside

Structure of Nucleoside

The first hydroxyl group of ribose or deoxyribose sugar gets attached to N9 of purine or N1 of pyrimidine to get nucleosides. N-Glycosidic linkage - Formed with carbohydrate with the nitrogen atom. The link between base and sugar - beta-N-Glycosidic linkage.

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DNA Structure

DNA structure was given by Watson and Crick. Two strands are complementary (A-T, G-C) and anti-parallel (5'-3', 3'-5'). Strands are arranged in a ladder like fashion made of phosphodiester linkages with ribose or deoxyribose sugar. Steps are made of nitrogenous bases linked by hydrogen bonds. There are 2 hydrogen bonds between A and T and 3 hydrogen bonds between G and C.

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