Friday, 18 December 2009

Biochemistry Exams - 2007/2008 3rd year Undenominated Science Semester I - Question 4

Hello Students,

I am sorry I have stopped posting on the Exam Questions, but I am back :)

Today Question 4 from the 3rd Year Undenominated Science Paper (to see which one click here Biochemistry Exams - 2007/2008 3rd year Undenominated Science Semester I.)

Question 4 Describe how proteins recognise DNA using bZip and zinc finger motifs as examples.

Proteins can interact with DNA by charge interaction (DNA negative, proteins positive), hydrogen bonding (between protein and nucleotides in the major or minor groove) or by wrapping/enclosing DNA, etc.

Zing finger motif is a part of the protein where neigbouring cysteines and histidines fold into a zinc-binding pocket (see here zing-finger motif binding to zinc or below).

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Presence of the zinc atoms are essential for proper protein function and conformation. On the next two picture you can easily see how binding of the zinc atoms allow protein to accommodate shape fitting into DNA double helix:

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Accesion number 1TF6

bZIP motif is a basic region of the leucin zipper, a part of the leucine zipper DNA binding domain. See picture below. Remember that leucine zippers are helical and always (similarly like the zinc fingers) act together. Two zipper proteins dimerise and interact with DNA.

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One face of each helix is hydrophobic (leucine rich region) and the other one is hydrophilic (charged aminoacids). The basic part of the dimer is interacting with DNA.

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Access number 1JUN

Examples: zinc finger domain TFIIIA and leucine zippers C/EBP.

I hop you enjoy it:)


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