How does a change in the nucleotide sequence of a gene result in a change in the structure of the protein?

The difference in the sequence will result in a different codon which will be present in the mRNA after transcription. During translation a different tRNA with a different anticodon will assemble on the different mRNA codon. The different tRNA will carry a different aminoacid which will result in a different polypeptide. A different polypeptide has a different structure.

Pretty different.

Since its a long process...
But in short, you can still understand it easily....

Lets Start with an Example...
AUG which codes for Methonine...
Is tranlated form the Dna sequence- TAC...
if mutation takes place in the Dna and A is replaced by C then the mRna formed will be GUG(which codes for valine)
Hence during the Translation the tRna of Valine will attach the Val in The Polypeptide chain in place of methonine..
Therefore A new protein is formed...
which may be harmful.....

(I know that AUG is the starting codon...and without it no protein can be formed... :-)... )

DNA TRANSCRIBES THE NUCLEOTIDE SEQUENCE TO M-RNA IN THE FORM OF CODONS (ANY 3 NUCLEOTIDES) EACH OF THESE 3 NUCLEOTIDE SEQUENCES CODE FOR AMINO ACIDS

M-RNA LEAVES THE NUCLEUS WITH THE GENETIC INFORMATION TO CREATE A POLYPEPTIDE (A LONG CHAIN OF AMINO ACIDS).

M-RNA GOES TO THE RIBOSOMES WHERE IT IS 'READ'

T-RNA BRINGS AMINO ACIDS TO THE RIBOSOME

THE T-RNA HAS A 3 NUCLEOTIDE  SEQUENCE WHICH MATCHES UP WITH THE CODON ON M-RNA.

AS EACH CODON IS READ THE RIBOSOME MOVES ALONG ADDING AMINO ACIDS. THIS CHAIN OF AMINO ACIDS IS CONSIDERED A POLYPEPTIDE (A STRING OF AMINO ACIDS JOINED BY A PEPTIDE LINKAGE

Easy!

This is exactly how I would answer it.

The nucleotide sequence of a gene is TRANSCRIBED into mRNA, which is then TRANSLATED into protein to form POLYPEPTIDES.  mRNA is translated into protein with the help of tRNA.  Sets of 3 consecutive nucleotides in the mRNA sequence are called CODONS, which have specific binding sites on tRNA called ANTI-CODONS. Each CODON "codes" for a specific amino acid, so when the genetic sequence is altered, so is the sequence of nucleotides that code for the CODONS -- leading to a change in the amino acid sequence of the proteins/POLYPEPTIDES that are formed.