Component 1: Nucleic acids
Deoxyribonucleic acid (DNA)
There are two types of nucleic acid: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA). Both are built up of units called nucleotides. Individual nucleotides are made up of three parts that combine by condensation reactions. These are:
1. Phosphoric acid (phosphate H3PO4). This has the same structure in all nucleotides.
2. Pentose sugar, of which there are two types: in RNA the sugar is ribose; in DNA the sugar is deoxyribose
3. Organic base which contains nitrogen (which can also be called a nitrogenous base).
There are five different nitrogenous bases which are divided into two groups:
Deoxyribonucleic acid (DNA)
There are two types of nucleic acid: Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA). Both are built up of units called nucleotides. Individual nucleotides are made up of three parts that combine by condensation reactions. These are:
1. Phosphoric acid (phosphate H3PO4). This has the same structure in all nucleotides.
2. Pentose sugar, of which there are two types: in RNA the sugar is ribose; in DNA the sugar is deoxyribose
3. Organic base which contains nitrogen (which can also be called a nitrogenous base).
There are five different nitrogenous bases which are divided into two groups:
- Pyrimidine bases (single ring structures) are thymine, cytosine and uracil
- Purine bases (double ring structures) are adenine and guanine
In DNA there are four possible types of nitrogenous base. Adenine (A) and Guanine (G) both have a double ring structure and are called purines. Thymine (T) and Cytosine (C) both have a single ring structure and are called pyrimidines (*remember the word pyrimidine has the letter Y in it as do the words thymine and cytosine). DNA never has the nitrogenous base Uracil (U), rather this is found in RNA instead of the Thymine (T) nitrogenous base. You DO NOT need to be able to draw these molecular structures, they are here for reference only.
BY1: Nucleic acids
Deoxyribonucleic acid (DNA)
The structure of DNA:
- DNA is a double stranded polymer of nucleotides (each strand is called a polynucleotide chain)
- Each polynucleotide chain may contain many millions of nucleotide units.
- It is in the form of a double helix, the shape of which is maintained by hydrogen bonding between organic bases
- DNA can contain four types of nitrogenous base: adenine, guanine, cytosine, and thymine.
- Each strand is linked to the other strand by complementary pairs of organic bases.
- Cytosine always pairs with guanine, and adenine always pairs with thymine
- The complementary base pairs are held together by weak hydrogen bonds.
- DNA is like a coiled ladder with the "uprights of the ladder" being made up of alternating sugars and phosphate groups (called the sugar-phosphate backbone) and the "rungs of the ladder" are made up of the complementary base pairs.
- Between cytosine and guanine bases there are three hydrogen bonds
- Between adenine and thymine bases there are only two hydrogen bonds
- The pentose sugar is always deoxyribose
1. Replication in dividing cells
2. Carrying information in the form of a genetic code for protein synthesis
A double stranded DNA "double helix". Each polynucleotide strand is made from many nucleotide subunits with nitrogenous bases pointing to the inside of the double helix. Here complementary nitrogenous bases hydrogen bond with one another forming the "rungs" of the ladder. In DNA, the nitrogenous base Adenine (A) forms a complementary pair with Thymine (T) on the other strand and Guanine (G) forms a complementary pair with Cytosine (C). Each polynucelotide strand has a sugar-phosphate backbone formed by phosphodiester bonds.
Draw a part of a DNA chain showing a polynucleotide consisting of three base pairs.