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Biochem Ch.3
Amino Acids
| Question | Answer |
|---|---|
| ______ _____ are the building blocks of proteins | amino acids |
| proteins are built from a repertoire of _#_ amino acids | 20 amino acids |
| When four different groups are bonded to the alpha-carbon, the amino acids are ________, which means they exist as two mirror-image forms | chiral |
| these two mirror-image forms are called what? | L isomer and D isomer |
| Only the __ isomers are found in proteins | L isomers |
| ALL amino acids have at least _#_ charged groups. What are these groups? | 2, carboxyl and amino |
| importantly, the carboxyl group and the amino group are weak acids. What does this mean? | they will dissociate the H+s |
| Free amino acids in a solution at neutral pH exist predominantly as dipolar ions. Explain the two charged groups of an amino acid in the dipolar form | amino group is protonated (NH3+) and the carboxyl group is deprotonated (COO-) |
| The ionization of an amino acid varies with what? | pH (charge depends on the pH and respective pKa values) |
| Explain the two charged groups of an amino acid in an acid solution (pH 1) | the amino group is protonated and the carboxyl group is not dissociated (NH3+ and COOH) |
| As the pH rises, the carboxylic acid is the first group to give up a proton. Why? | because its pKa is near 2 (COO- and NH3+) |
| After pH passes 2 and the carboxylic acid gets dissociated, how long will the dipolar form persist? | until the pH reaches 9 (pKa of amino group) and the protonated amino group loses a proton (NH2 and COO-) |
| under physiological condition, amino acids exist in the _______ form | dipolar |
| The 20 amino acids found in proteins contain unique ____ _______ (groups that vary in size, shape, charge, hydrogen-bonding capacity, hydrophobic character, and chem reactivity) | side chains |
| We can sort these 20 amino acids into 4 groups, on thebasis of the general chemical characteristics of their R groups: | (1) Hydrophobic (2) Polar (3) Positively charged (4) Negatively charged |
| Hydrophobic amino acids have _______ R groups | nonpolar |
| Hydrophobic amino acids have mainly __________ side chains | hydrocarbon side chains |
| hydrophobic amino acids, particularly the larger aliphatic and aromatic ones, tend to cluster together inside the protein away from the aqueous environment of the cell. This tendency of hydrophobic groups to come together is called what? | the hydrophobic effect |
| the hydrophobic effect is the driving force for what? | the formation of the unique 3D architecture of water-soluble proteins. |
| What enables hydrophobic amino acids to pack together to form compact structure with little empty space? | the different sizes and shapes of the hydrocarbon side chains |
| Polar amino acids have what kind of R groups? | R groups that are neutral overall, yet are polar because the charge is not evenly distributed |
| Polar amino acids have side chains that contain what? | an electronegative atom that hoards electrons (O and S |
| Positively charged amino acids are __________ | hydrophilic |
| _________ can bind or release protons near physiological pH (found at active sites of enzymes) | histidine |
| Negatively charged amino acids are have ______ side chains | acidic (usually negatively charged) |
| In some proteins, these acidic side chains accept protons, which neutralize the negative charge. This ability is often ___________ important. | functionally |
| _#_ of the 20 amino acids have readily ionizable side chains. What are these side chains able to do? | 7; form ionic bonds as well as to donate or accept protons to facilitate reactions |
| the ability to donate or accept protons is called ____-_____ _________ and is an important chemical reaction for many enzymes | acid-base catalysis |
| Amino Acids: There are nine amino acids with hydrophobic side chains - | glycine, alanine, valine, leucine, isoleucine,m methionine, proline, and the aromatic amino acids phenylalanine and tryptophan |
| Amino Acids: There are six amino acids that are polar- | serine, threonine, tyrosine, cysteine, asparagine, and glutamine |
| Amino Acids: There are three amino acids that are positively charged- | lysine, arginine, and histidine |
| Amino Acids: There are two amino acids that are negatively charged- | aspartic acid and glutamic acid |
| What are essential amino acids? | amino acids that cannot be generated in the body and must be supplied by the diet (we do not have the genes that code for the enzymes that are required for their synthesis) |
| human being can make only _#_ of the 20 amino acids | 11 |
| What results if protein intake is inadequate? | pathological conditions |
| Ex: kwashiorkor | a severe form of malnutrition caused by deficiency in dietary protein |
| Ex: what are the defining symptoms of kwashiorkor? | edema, e.g. swelling of the feet and distended abdomen |
| Ex: kwashiorkor: due to lack of proteins, water cannot be drawn from the tissue back into the blood. What does this result in? | pooling of fluids, causing swelling and distension of the abdomen |
Created by:
cmccartney2