2.6 - Structures of DNA and RNA

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Nucleic acids and nucleotides

There are two types of nucleic acid

DNA

RNA

A nucleic acid is very large molecules that are constructed/maybe by linking together nucleotides to form polymers.

They consist of three parts:

Sugar; 5 carbon atoms

Phospate group; acidic and -ve charged (Covalent bonds)

Base; nitrogen with one or two rings (Covalent bonds)

In order to link nucleotides into a chain, a covalent bond is formed b/n the phosphate and a pentose sugar.

Four d/f bases in DNA and RNA; four d/f nucleotides.

It can be linked together in any sequence; due to the same sugar and phosphate used to link the bonds.

Any base sequence is possible, which is the key to nucleic acids acting as a store of genetic information.

The base sequence is the store of info. and the sugar-phosphate backbone ensures that the store is stable and secure.

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Differences between DNA and RNA

The three important differences between DNA and RNA:

The sugar in DNA is deoxyribose and the sugar in RNA is ribose

Deoxyribose has one less oxygen atom than ribose.

Full names "Deoxyribonucleic acid" and "Ribonucleic acid"

Two polymers of nucleotides in DNA and only one in RNA

Polymers of nucleotides also known as "strands"

Four are in DNA: Adenine, Cytosine, Guanine, and Thymine. Four bases in RNA: Adenine, Cytosine, Guanine, and Uracil.

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Structure of DNA

A double helix made of two antiparallel strands of nucleotides linked by hydrogen bonds b/n complementary base pairs.

Each strand has a chain of nucleotides linked by covalent bonds

The 2 strands run in the opposite directions; one in 5' to 3' direction and the other in 3' to 5' direction.

Two strands wound together forming a double helix

strands held together by hydrogen bonds among complementary nitrogenous base pairs.

A-T

G-C

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