OCR b5 growth and development part 3

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  • Created by: Edd
  • Created on: 10-06-12 14:21

Genes are sections of DNA. Each gene is a set of coded instructions for making a particular protein. Different genes can switch off in different cells.


DNA is a very large molecule shaped like a twisted ladder. The shape is a double helix.

Long strands of DNA make up chromosomes. These are found in the nucleus of a cell.

The genetic code.

DNA is a chemical code, or set of instructions. Our bodies need proteins for growth and development, and the DNA controls which proteins are made. The code consists of four different chemicals, or bases, that always pair up in the same way.

DNA shown as a double twisted string with interlinking parts  (http://www.bbc.co.uk/schools/gcsebitesize/science/images/bidnabases.jpg)

Base pairs on a DNA molecule

T always pairs with A.

G always pairs with C.

The order of these pairs of bases along the DNA molecule codes for all the different proteins. A section of DNA that codes for one particular protein is called a gene. Each chromosome contains thousands of different genes.

The genetic code of the DNA always remains safe inside the nucleus. But the proteins are made outside the nucleus in the cytoplasm of the cell. For this to happen, a copy of the genetic code of a gene is made. This copy then passes out of the nucleus into the cytoplasm where the protein is made.

The genetic code - Higher tier.

Each gene acts as a code, or set of instructions, for making a particular protein. Some of these proteins control the cell's internal chemistry. They tell the cell what to do, give the organism its characteristics, and determine the way its body works.

To enable genes to code for proteins, the bases A, T, G and C get together not in pairs but in triplets. This is how it works:

  • Each protein is made up…


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