DNA (AQA GCSE Chemistry): Revision Notes
DNA
DNA is one of the most important natural polymers found in all living things. Understanding DNA helps us learn how life works at the molecular level.
What is DNA?
DNA stands for deoxyribonucleic acid. It's a large molecule that is essential for life. Every living organism and virus contains DNA that stores vital information.
DNA has a special job - it encodes genetic instructions. This means it contains all the information needed for living organisms to develop and function properly.
Think of DNA as nature's instruction manual - it contains all the blueprints needed to build and maintain every living thing on Earth, from the smallest bacteria to the largest mammals.
DNA structure
DNA has a unique double helix structure. Think of it like a twisted ladder:
- The molecule consists of two strands twisted together
- These strands spiral around each other to form the famous double helix shape
- The structure is held together by chemical bonds between the strands
The double helix structure is crucial for DNA's function. This twisted shape allows DNA to be compact enough to fit inside cells while still being accessible for reading genetic information when needed.
DNA monomers - nucleotides
Like all polymers, DNA is made up of smaller units called monomers. For DNA, these monomers are called nucleotides.
There are four different types of nucleotides in DNA:
- A (Adenine)
- T (Thymine)
- C (Cytosine)
- G (Guanine)
These four nucleotides join together in long chains to form the DNA polymer. The specific order of these nucleotides creates the genetic code that makes each organism unique.
DNA Base Pairing Example:
In the double helix, nucleotides pair up in a specific way:
- A always pairs with T
- C always pairs with G
So if one strand has the sequence A-T-C-G, the opposite strand will have T-A-G-C. This complementary pairing is essential for DNA replication and function.
DNA as a natural polymer
DNA is one of four main naturally occurring polymers found in living things:
- Proteins - made from amino acid monomers
- DNA - made from nucleotide monomers
- Starch - made from sugar monomers
- Cellulose - made from sugar monomers
DNA is special because it stores and passes on genetic information from one generation to the next.
Key facts about DNA
Essential DNA Facts:
- DNA is found in the cells of all living organisms
- It contains the instructions for making proteins
- The double helix structure was discovered by scientists studying X-ray images
- DNA can make copies of itself during cell division
- Changes in DNA sequence can lead to genetic variation
Key Points to Remember:
- DNA is a natural polymer made from nucleotide monomers
- It has a double helix structure (like a twisted ladder)
- DNA stores genetic instructions essential for life
- The four DNA bases are A, T, C, and G
- DNA is found in all living organisms and viruses