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Unlock This CourseDNA (deoxyribonucleic acid) is like a twisted ladder that contains all the instructions needed to build and maintain living things. Think of it as nature's instruction manual - every cell in your body contains this amazing molecule that determines everything from your eye colour to your height.
The discovery of DNA's structure in 1953 by James Watson, Francis Crick, Rosalind Franklin and Maurice Wilkins revolutionised our understanding of how traits pass from parents to children. This breakthrough earned them the Nobel Prize and changed biology forever.
Key Definitions:
Imagine a ladder twisted into a spiral - that's exactly what DNA looks like! The sides of the ladder are made of sugar and phosphate molecules, whilst the rungs are made of pairs of bases. This twisted shape is called a double helix and it's incredibly stable, protecting our genetic information.
DNA contains four different bases, each with its own letter code. These bases are like a four-letter alphabet that spells out the instructions for life. The four bases are adenine (A), thymine (T), guanine (G) and cytosine (C).
The bases don't pair randomly - they follow strict rules, rather like pieces of a jigsaw puzzle that only fit together in certain ways. This is called complementary base pairing and it's crucial for DNA to work properly.
Adenine always pairs with thymine. They're held together by two hydrogen bonds, making them a perfect match.
Guanine always pairs with cytosine. They're connected by three hydrogen bonds, making this pairing even stronger.
These pairing rules ensure DNA can copy itself accurately during cell division, passing genetic information to new cells.
If you could unwind all the DNA in one human cell, it would stretch about 2 metres! Yet it's packed into a nucleus so small you need a microscope to see it. Your body contains about 37 trillion cells, so you have enough DNA to stretch from Earth to the Sun and back over 300 times!
The sequence of bases along the DNA molecule acts like a code. Just as different combinations of letters make different words, different sequences of A, T, G and C create different genetic instructions. A gene is a specific sequence of bases that codes for a particular characteristic, like eye colour or blood type.
Think of DNA like a recipe book. Each gene is like a different recipe and the bases are the ingredients and instructions. The order of the bases determines what the final product will be - whether it's a protein for brown eyes or one for blue eyes.
Each gene contains the instructions to make a specific protein. Proteins do most of the work in our cells - they might be enzymes that speed up chemical reactions, or structural proteins that give our hair its strength.
One of DNA's most important jobs is making copies of itself. This happens every time a cell divides, ensuring that each new cell gets a complete set of genetic instructions. The double helix structure makes this copying process possible and accurate.
During replication, the two strands of the double helix separate, like unzipping a zip. Each strand then serves as a template to build a new complementary strand. Because A always pairs with T and G always pairs with C, each new DNA molecule is identical to the original.
Special enzymes break the hydrogen bonds between base pairs, separating the two strands of the double helix.
New bases are added to each strand following the base pairing rules, creating two new complementary strands.
The result is two identical DNA molecules, each containing one original strand and one new strand.
Because everyone's DNA sequence is unique (except identical twins), scientists can use DNA to identify people. This technique, called DNA fingerprinting, is used in criminal investigations and paternity tests. It works by comparing specific regions of DNA that vary greatly between individuals, creating a unique 'fingerprint' for each person.
The double helix structure of DNA is perfectly designed for inheritance. When organisms reproduce, they pass copies of their DNA to their offspring. The complementary base pairing ensures that this genetic information is copied accurately from generation to generation.
In sexual reproduction, offspring receive half their DNA from each parent. This mixing of genetic material creates genetic variation, which is why children look similar to, but not identical to, their parents (unless they're identical twins).
The combination of DNA from two parents creates unique individuals. This variation is important for evolution and helps species adapt to changing environments.
Understanding DNA structure has led to incredible advances in medicine, agriculture and forensic science. Scientists can now read DNA sequences, modify genes to treat diseases and even bring back extinct species using preserved DNA.
Doctors are developing treatments that work by fixing faulty genes. For example, some forms of blindness caused by genetic defects can now be treated by inserting healthy copies of genes into patients' eyes.
Between 1990 and 2003, scientists worked together to read the complete DNA sequence of humans - all 3 billion base pairs! This massive project has helped us understand genetic diseases and develop new treatments. Today, reading someone's entire genome takes just a few hours and costs less than £1,000.
The DNA double helix is one of nature's most elegant solutions for storing and transmitting genetic information. Its twisted ladder structure, with complementary base pairing, ensures that genetic information can be copied accurately and passed from cell to cell and generation to generation. Understanding this structure has revolutionised biology and medicine, opening up new possibilities for treating diseases and understanding life itself.
Remember the key points: DNA is a double helix made of two complementary strands, A pairs with T, G pairs with C and this structure allows DNA to replicate accurately and store the genetic information that makes you unique.