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Lecture 3
Amino Acids
Question | Answer |
---|---|
effect of hypotonic solution on RBC? | solution has lower solute concentration than in the cytosol causes H2O diffusion into the cell causing it to rupture |
effect of hypertonic solution on RBC? | solution has higher concentration than cytosol, H2O diffuses out of the cell causing it to shrink |
effect of isotonic solution on RBC? | solution has the same concentration as the cytosol, H2O diffusion in and out of the cell is balanced |
significance of proteins? | - 20% of human body is made up of proteins - play crucial role in almost all biological processes |
functions of proteins? | 1. enzymes- digest, pH reg, DNA copy 2. structure- collagen, keratin 3. movement/motor proteins- actin, myosin 4. fight infection-antibody 5. hormones- insulin, glucagon, GH 6. metabolism- lipoprotein, lipase, glycogen synthesis, phosphofructokinase |
what links amino acids into polypeptides? | peptide bonds |
what determines amino acid order or sequence? | genetic code |
proteins are __________ | polymers of amino acids |
polypeptides are _________ | repeating monomers of amino acids |
amino acid structure? | amino group and carboxyl group attached to an alpha carbon. As well as an R group which is unique for each amino acid |
what are zwitterions | dipolar and charged at physiological pH amino acids are that |
what are the two isometric forms of amino acids | L and D are the two forms, L forms are found in natural proteins (most common) |
peptide bonds | covalent bonds formed between α amino group of one amino acid and α carboxyl group of another |
what adds amino acids to polypeptides? | ribosomes during the process translation |
N terminal is the only amino acid that has _____________ and C terminal is the only one that has _________________ | free amino group, free carboxyl group |
direction of polypeptide? | to the α-carboxyl group of the last amino acid in peptide |
rotation in peptide bond? | limited |
configuration of peptide bonds? why? | trans(R's face diff directions), due to steric clashes between R groups when Cis |
why is an amino acid's sequence important? | because it determines a protein's shape, and shape determines function of proteins. Mutating a single amino acid can make protein dysfunctional and lead to diseases |
neutral nonpolar amino acids | glycine, alanine, valine, leucine, isoleucine, methionine, proline, tryptophan, phenylalanine |
neutral polar amino acids | serine, threonine, tyrosine, cysteine, asparagine, glutamine |
acidic amino acids | aspartate, glutamate |
basic amino acids | lysine, arginine, histidine |
branched chain amino acids | valine, leucine, isoleucine. used to build muscle |
aromatic amino acids | phenylalanine, tyrosine (not hydrophobic), tryptophan |
amino acids that absorb light | aromatic |
what amino acids are responsible for the absorbance of ultraviolet light by proteins | tryptophan and tyrosine |
amino acid that can form disulfide bonds | cysteine |
why is proline considered an "imino" acid | because its the only aa with a secondary amine |
where would a hydrophobic amino acid be found in a cytosolic protein? | in the core of the cytosolic protein contort to avoid water |
where would a hydrophobic amino acid be found a transmembrane protein? | would be found in the membrane-spanning regions of transmembrane protein because membrane is hydrophobic |
amino acids found mostly in active sites | positively charged/basic |
the negative charge on acidic amino acids is on the _________ and the positive charge on basic amino acids is on the____________ | carboxyl, amino |
amino acids that has sulfur | cysteine and methionine |
what does it mean to hydroxylate an amino acid | add OH to R group |
what aa's can be hydroxylated? | lysine and proline |
what aa's can be phosphorylated? | serine, threonine, and tyrosine |
what aas make turns and loops? | proline (for collagen) and glycine |
pKa value of amino acid refers to | point where protonated and non-protonated forms of the amino acid are found in equal concentrations. 50-50 |
If the pH is less than the value of the pKa of an aa, then the predominant form is the | protonated (acid, proton donor) |
If the pH is more than the value of the pKa of an aa, then the predominant form is the | non protonated (base/proton acceptor) |
what is an ampholyte | structure that can be acidic or basic depending on the solution they're in aa's are that |
Isolelectric point | pH at which there is 0 net charge |
what groups can ionize on aa | carboxy and amino groups for all aa's some aa's have ionizable R groups as well |
how to find PI | (pKa1+pKa2)/2 for normal aa's average lower pKa's for acidic aa average higher pKa's for basic aa |
what amino acids have ionizable side chains? | aspartic acid, glutamic acid, lysine, arginine, histidine, cysteine, tyrosine (acidic+basic+cysteine+tyrosine) |
what amino acid depends on the environmental pH and can bounce from neutral, to positively charged basic or negatively charged acidic | histidine |
why do we look for histidine when we find a protein that changes charge when pH changes? | because the pKa of histidine varies depending on pH of environment |
a polypeptide with a net positive charge at physiological pH (~7.4) most likely contains amino acids with R groups of what type? | Basic R groups |
in lysine, the pKa of the side chain is about 10.5. assuming that the pKa of the carboxyl and amino groups are 2 and 9, the pI of lysine is closest to | choose 2 higher 10.5+9 divide by 2 ~9.8 |