How to calculate molecular weight (kDa) from amino acids?

[xDriftAway]

There's a question in the AAMC Section Bank that says that IN (integrase) is a 288-residue protein, and it's asking what the molecular weight would be of an inactive tetramer of IN. The solution says that since the integrase monomer is composed of 288 amino acids, it will have a ~32 kDa, and thus the answer is 128 kDa for the size of a tetramer. How did they get the 32 kDa?? Is there a formula for this kind of question?

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[jhu2016]

[deleted]

 

[xDriftAway]

The average molecular weight of an aa is around 110 dalton. 288 x 110 dalton is around 32kDa

thanks so much! you're a life saver

 

[Perseverance7779311]

could someone please explain this? Thank you.

 

[theonlytycrane]

could someone please explain this? Thank you.

AAMC decided that we should know that an amino acid residue has an average weight of 110 Da which is equal to 110 g / mol for reference.

IN is a 288-residue protein so it weights about 288 * 110 Da = 31680 Da. They want the weight of a tetramer of IN, which is composed of 4 IN units. 31680 Da * 4 = 126,720 Da which is about 128 kDa.

 

[Perseverance7779311]

@theonlytycrane , thank you!! I would have never guessed that all that was expected!

 

[Ro300!]

Can some please explain how the phrase " IN is a 288-residue protein composed of three domains...." provided in the passage translates to a monomer? (I thought the 288-residue referred to the tetramer. Were we supposed to know that 288-residue refers the monomer?)

Having a little trouble understanding this. Thanks in advance!

 

[aldol16]

Can some please explain how the phrase " IN is a 288-residue protein composed of three domains...." provided in the passage translates to a monomer? (I thought the 288-residue referred to the tetramer. Were we supposed to know that 288-residue refers the monomer?)

Because "tetramer of integrase" means four integrases.