Monthly Archives: April 2013

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Nuclei Acids :)

DNA and RNA are nucleic acids. They form polynucleotide chains with a sugar – phosphate backbone, these are nucleotides that act as monomers and are joined together each nucleotide consists of a phosphate, pentose sugar and an organic nitrogenous base. The phosphate condenses with the pentose sugar by a phospdodiester bond, building up the chain. The bases stick out along the side, and since there are different types of nucleotides the bases can be in any order along the chain. 

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The nucleotides join together to form a polynucleotide chain 

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The structure of DNA 

We have just learnt about nucleotides and well DNA is made up of four types that have different bases: 

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In DNA there are two strands of polynucleotide chains that are linked by Hydrogen bonds this occurs between the bases. Adenine pairs with Thymine forming two hydrogen bonds, and Cytosine pairs with Guanine forming three hydrogen bonds. 

Adenine and Guanine are know as Purines which are double ring structures 

Cytosine and Thymine are know as Pyrimidines which are single ring structures

The two strand are now twisted into a double helix, it is the arrangement of the bases and the bonds that form between them that makes DNA so stable. It is very important ar DNA’s function is to store genetic information. Because they are in a double helix with the bases attached to each other they are protected from most damage. In addition a purine must pair with a pyrimidine due to their sizes, so a small base will need to pair with a large bases to keep the same distance apart in the DNA strand. 

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Structure of RNA 

Just like in DNA, RNA is made up of four nucleotide bases, adenine and guanine ( purines) and uracil and cytosine (pyrimidine), as you can see it is very similar to DNA the only difference it that uracil replaces thymine. 

They produce single polynucleotide chains

There are three types of RNA: messenger RNA, transfer RNA, and ribosomal RNA. 

Messenger RNA ( mRNA) this is formed in the nucleus, and its a single chain twisted into a helix , its length and sequence varys. It is involved in protein synthesis

Transfer RNA (tRNA) this single chain is folded into a clover leaf shape. Involved in protein synthesis 

Ribosomal RNA (rRNA) it is produced in the nucleolus and forms over half the mass of ribosomes. 

 

 

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Lipids!!!!

We have all been introduced to this topic atleast once before, even if it was not school related we all knew that when someone said lipids they were talking about something fat related. Some common structures of lipids would be :

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Fats and oils. (triglycerides)

Fats are solids at room temperature, but oils are liquids

Fats contain SATURATED hydrocarbon  chains

Oils contain UNSATURATED hydrocarbon chains, this just means that they contain atleast 1 C-C double bond.

Waxes

They are lipids and their molecules have single hydrocarbon chains that are linked to an alcohol

Really important in fruits for two reasons:

1. Protective layer in fruits, vegetables

2. Added in some cases for appearance and protection

Functions and Properties 

  • source of energy 
  • energy reserve, bascially if there is any excess energy from carbohydrates , proteins and lipids they are stored as TAG in adipose tissues
  • Provide insulation for the body
  • Protects vital organs
  • helps in the formation of cell membranes
  • steroid hormones
  • flavor and taste

Saturated Fats

All carbons are bonded to H

there is no C-C double bond

they form long straight chains

solid at room temperature

Mostly animal fats

Unsaturated fats

They contain C-C double bonds

Found in plant and fish fats

They are liquids at room temperature

Because of the presence of the double bonds they form kinks in the hydrocarbon chains, and this prevents the molecules from packing tightly together.

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Effect of the double bond on Fatty acids

As the length of the fatty acid chain increases, the melting point of the fatty acid would increase but the solubility will decrease.

Stearic aicid and Linoleic acid both have the same number of carbon atoms but because of the presence of double bonds in Linoleic acid their melting points would vary.

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Essential Fatty acids

They are the fatty acids that the body cannot produceor synthesize on its own, two examples are Omega – 3 alpha – linolenic acid and Omega – 6 Linoleic acid.

Omega 3 Fatty acid 

It is a cis isomer

Found in  flaxseed, soybean oil, walnuts, some leafy green vegetables.

Omega 6 Fatty acids

It is a cis isomer

Found in seed nuts, common vegetable oils , sunflower seed, cottonseed.

Nonessential fatty acids – can be made in the body so it is not required in the diet. 

References : Biochem Jm youtube channel , video on Lipids part one.