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medicalchanel

Amino Acids Help Appreciated!

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Hey guys! I was just wondering if anyone had any good websites/notes/info they would recommend in terms of amino acids for the new mcat. I find I don't quite understand a lot of questions related to them (i.e: "what charge would lysine have in ph 7?"). 

 

I would appreciate any kind of info you have to offer, including anything about the characteristics of each amino acid (i.e: which can H bond?)

 

Thank you!!!

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the wikipedia page on amino acids and hydrogen bonding would answer both of your question (and it a a primary resource for me in the biochem sections).

 

 

 "what charge would lysine have in ph 7?"

 

refers to the fact that most amino acids are Zwitterions (thus behaving like an acid or base depending on the pH),  From https://en.wikipedia.org/wiki/Amino_acid :
"Below pH 2.2, the predominant form will have a neutral carboxylic acid group and a positive α-ammonium ion (net charge +1), and above pH 9.4, a negative carboxylate and neutral α-amino group (net charge −1). But at pH between 2.2 and 9.4, an amino acid usually contains both a negative carboxylate and a positive α-ammonium group, as shown in structure (2) on the right, so has net zero charge"
At neutral pH, the backbone of an amino acid confers it no charge so it's all dependent on the charge of the side chain.  Lysine is a positively charged molecule due to its side chain having a positive charge.
 

 

I would appreciate any kind of info you have to offer, including anything about the characteristics of each amino acid (i.e: which can H bond?)

From https://en.wikipedia.org/wiki/Hydrogen_bond :
"A hydrogen bond is the electrostatic attraction between polar molecules that occurs when a hydrogen (H) atom bound to a highly electronegative atom such as nitrogen (N), oxygen (O) or fluorine (F) experiences attraction to some other nearby highly electronegative atom."

Which means any amino acid whose side chain contain -OH or -NH can hydrogen bond (and amino acids without -OH or -NH in their side chains cannot hydrogen bond). 

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Berkeley review did a solid a job covering AA in the biology or the orgo chem sections I believe. If you wish to remember the neutral/ positive/ negative charges at pH 7 then I suggest method of loci technique. Not trolling but for my biochem exam I used body parts. I pictured an item on my head that rhymed/ resembled an amino acid and associated it with a feeling of positive negative or neutral. Repeat a few times and it worked well. For example I picture lysine as happy lice on my knees while Aspartic acid as angry (negative) asparagus on my thigh. Each time I need a reference I just picture my body part and think what image I associated it with.

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