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DNA and enzymes


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Enzymes are large molecules that speed up the chemical reactions inside cells. Each type of enzyme does on specific job. Enzymes are a type of protein, and like all proteins, they are made from long chains of different amino acids.

DNA is a long molecule made up of twisted strands of the bases A, T, C and G.

Genes are sections of the DNA. Each gene has the code for creating a specific protein. The sequence of bases in the gene controls which amino acids are created and joined to make a specific new protein (or enzyme) molecule.

DNA, Enzymes and Energy

Aerobic respiration

Most of our energy comes from the process of aerobic respiration, which takes place inside the mitochondria of cells. Mitochondria are oval structures with a folded inner membrane. They occur in large numbers inside muscle cells and liver cells, where large amounts of energy are needed. The mitochondria hold a large number of different enzymes which are responsible for different stages of respiration.

Enzyme structure

Enzymes are soluble protein molecules that can speed up chemical reactions in cells. Like all proteins they consist of a string of different amino acid sub units.

The amino acids must occur in the correct sequence for the enzyme to work. This sequence is controlled by the genetic code for the protein. These genetic codes are held in DNA molecules.

How a protein is produced using the genetic code

Amino acids

Genes contain bases in groups of three


DNA molecules are very long and packed into compact structures called chromosomeschromosome: One of the rod shaped bodies found in the nucleus of cells that contain genetic information (DNA).. Each DNA molecule consists of two twisted strands of bases that form a shape called a double helix.

The two strands are held together by bonds between pairs of bases.

When a cell grows and divides into two, it first has to make a duplicate copy of each DNA molecule. This is done by the bonds breaking between the two strands, the strands unwinding, and then new bases joining each old strand to make new strands.

Genetic code - higher tier

DNA shown as a double twisted string with interlinking parts

Base pairs on a DNA molecule

If A occurs in one strand of a DNA molecule it will form a bond with T in the other strand. C and G will also only bond with each other. In this way it's possible to predict the order of bases on the other strand if the bases on one strand are known.

The sequence of bases in one section (gene) of a DNA molecule controls the sequence of amino acids in one protein molecule. Each amino acid has its own code of three bases. Every time the same sequence of three bases occurs in the DNA molecule, the same amino acid is added to make up the protein.

When a protein is being made, the two strands of the double helix unzip, so that the base sequence can be read. The amino acids used to make up new proteins are absorbed from food in the digestive system. It's possible for the liver to make more of a particular amino acid if needed in a process called transamination.

There are four different bases in DNA (A, T, C and G).


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