One gene - one protein - Genes - the units of inheritance (7/10)

Uploaded by OUlearn on 25.07.2008

The blood group gene makes a protein.
When this has to be manufactured,
a copy of the gene is taken in the nucleus,
and this messenger molecule,
carrying the code for the blood group protein,
travels out into the cell.
It's made of RNA, like DNA, but it uses U instead of T.
It turned out that the four letters are in words three letters long,
each word picks a special adapter carrying one of 20 protein sub-units,
the amino acids.
So, the point of the DNA code is to carry protein sequences.
Once the blood group protein chain has been put together, it folds up.
The 20 amino acids can be arranged in any order,
making all the proteins in the living world.
But tiny DNA spelling mistakes can have a huge impact.
The code for the A and B blood group proteins
is an identical 1,062 letters long.
But the B code has seven different letters.
These mutations change the meaning of the words,
so the B protein gets seven different amino acids.
The O code is identical to the A code except for a single spelling mistake,
but the effect is dramatic.
This is a deletion, a missing letter.
Because the code is read three letters at a time,
all the words downstream are now out of place,
making a very different protein.
The blood groups show that there is no such thing as the Human Genome.
Although some genes have to be exactly the same in all of us,
or their proteins won't work at all,
thousands of others are like the blood group gene
and can have three or four or more varieties.
Since we have 30,000 genes, that's an awful lot of variation,
and helps explain why each of us is unique.