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76 Cards in this Set
- Front
- Back
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amino acids contain....
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amine group
carboxyl group hydrogen atom R-group all are attached to alpha carbon |
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the alpha carbon is chiral/achiral
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chiral
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all amino acids are optically active/inactive...except for....
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active (means they are chiral)
glycine = achiral |
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all naturally occurring amino acids are L/D enantiomers
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L-enantiomers
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as with the fischer projection, all being L-enantiomers, means that the amino acid appears on the left/right side
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left
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L-amino acids have R/S configurations...except for
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S
cysteine = R (sulfur affects direction/priority) |
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the amino group is ____ while the carboxyl is _____
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basic
acidic |
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amphoteric =
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can act as acid or base
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situation:
lots of protons in solution means the amino acid will pick up protons and act like a base/acid |
base
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situation:
if there few protons in solution means the amino acid will donate protons and act like a base/acid |
acid
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amino groups take on pos/neg charges when protonated
carboxyl groups take on pos/neg charges when deprotonated |
positive = amino
negative = carboxyl |
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zwitterion =
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has both + and - charges simultaneously on amino and carboxyl respectively\
= neutral |
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put neutral(zwiterrion) amino acid in an acidic solution, the amino/carboxyl will pick up protons
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carboxyl
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put neutral(zwiterrion) amino acid in a basic solution, the amino/carboxyl will donate protons
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amino
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at a low pH, the amino acid will carry a +/- charge and at a very high pH the amino acid will carry a +/- charge
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+ = acidic
- = basic |
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the intermediate pH, at which the amino acid becomes a zwitterion =
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pI = isoeletric point
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the pI lies between pK1 and pK2 (since the amino acid has two different locations that can be de/protonated
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know
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titration curve acts like it has 2-3 monoprotic acids
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3 distinct points; know
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which group (carboxyl, r-group or amino group) is first to become deprotonated when placed in basic soln NaOH?
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carboxyl
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when pH = Pka1...
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solution is in a buffer zone = flat horizontal line on titration curve
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when added equal amts of acid and base...pH =
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pI
represented by vertical region of graph |
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after pI reached and in NaOH solution, the carboxyl/amino group becomes deprotonated
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amino
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things to know about titrations and AA
1. when adding base, amino/carboxyl group lose protons first |
carboxyl
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after all the carboxyl groups have become deprotonated, the amino acids become deprotonated
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know
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2. moles of base must be added to deprotonate 1 mole of amino acids
-what does the first/second mole deprotonate??? |
the first mole deprotonates the carboxyl
the second deprotonates the amino |
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3. the buffering capacity of the amino acid is greatest at or near the pH of the two dissociation constants...
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pKa1 and pKa2
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at the pI (isoelectric point), the buffering capacity is...
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minimal; appears as a vertical line
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4. some amino acids contain acidic/basic R-groups...how can you determine the pI?
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average the two pKas for the acids or bases
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5. it is possible to perform titrations in reverse, from alkaline(basic)t to acidic pH with the addition or a base/acid
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acid; sequence of events is reversed...the amino would be protonated first!
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henderson-hasselbach EQ =
pH = pKa + log[conj. acid/conj. base] |
know
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an amino acid has __ buffering stages during a titration
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2; one at each pKa
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best buffering regions occur within 1 pH of the pKa or pKb
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know
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side chains give the amino acid its defining characteristics
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know
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4 categories for amino acids...
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nonpolar
polar acidic basic |
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nonpolar AA
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r-group = hydrocarbons
r-group = hydrophobic -decreased water solubility |
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polar AA
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uncharged r-groups
hydrophilic r-groups soluble in water |
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acidic AA
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r- group = carboxyl
negative charge @ physiological pH = 7.4 (exist as a salt) 3 distinct pKa's aspartic and glutamic acid isoelectric point (pI) shifted toward acidic pH = avg of 2 acids -require 3 moles of base to neutralize 2 carboxyls and 1 amino! |
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basic AA
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R-group = amino
carry positive charge at physiological pH = 7.4 3 pKas isoelectric point (pI) shifted toward basic pH = avg of 2 aminos -require 3 moles of acid to neutralize 2 amino and 1 carboxyl basic AA = lysine, arginine and histidine |
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peptides
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composed of amino acids subunits called residues
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when two AA combine, a ____ bond holds them together
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peptide
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peptide bond =
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amide bond
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peptides are small proteins
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know
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dipeptide = 2AA
tripeptide = 3AA polypeptide = 4+ AA |
know
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peptide bonds form between....
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carboxyl of one AA and amino of other AA
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formation of peptide bonds requires condensation to occur =
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loss of water molecule
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reverse rxn =
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hydrolysis (add water to break peptide bond)
-catalyzed by an acid or base |
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amino =
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N-terminal
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carboxyl =
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C-terminal
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N terminal is on the __ side and C terminal is on the __ side
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left
right |
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rotation around the C-N bond of an AA is restricted since capable of short-term d-bond between them = peptide bond region
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know
http://www.phschool.com/science/biology_place/biocoach/images/translation/peptbond.gif |
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bonds on either side of the peptide bond can rotate freely
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know
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proteins
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1000's or AA in length
act as enzymes, horomones, membrane pores, receptors, |
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4 levels of proteins
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primary
secondary tertiary quaternary |
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primary structure
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sequence of AA
N-->C terminal arrangement |
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secondary structure
2 types |
-local structure of neighboring AA
-result of Hydrogen bonding 2 types 1. alpha helix 2. beta pleated sheet |
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alpha helix
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rodlike structure
peptide chain coils clockwise Hydrogen bonds side chaind pt away from core |
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beta-pleated sheet
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peptide chains form rows
hydrogen bonds rippled appearance -side chains point above and below |
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tertiary structure
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3-D shape of protein
-hydrophilic/hydrophobic interactions -disulfide bonds |
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disulfide bond
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when 2 cysteine molecules become oxidized to for cystine
-create loops in protein chain |
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amino acids with hydrophilic(polar/charged) r groups tend to arrange themselves toward the outside/inside of the protein
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outside
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amino acids with hydrophobic(nonpolar/uncharged) r groups tend to arrange themselves toward the outside/inside of the protein
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inside
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proteins are split between 2 class on basis of tertiary structure...
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fibrous proteins
globular proteins |
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fibrous proteins
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collagen
found as sheets/long strands |
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globular proteins
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myoglobin
spherical |
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quaternary structure
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-contains more than one polypeptide subunit
-the way these subunits arrange themselves to yield a functional protein ex) hemoglobin = 4 different subunits |
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conjugated proteins
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have covalently bonded prosthetic groups
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prosthetic groups
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can be organic molecules
vitamins metal ions |
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lipoproteins
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proteins with lipid prosthetic groups
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glycoproteins
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proteins with carbohydrate prosthetic groups
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nucleoproteins
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proteins with nucleic acid prosthetic groups
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prosthetic groups can determine function of proteins
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know
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denaturation/melting
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process by which proteins lose their 3-D structure and revert to a random-coil state
-destroys tertiary structure(3-D) it renders the protein functionless |
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methods of protein denaturation
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1. detergent
2. change in pH 3. temperature change 4. solute concentration change |
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denaturation interferes with weak intermolecular forces tha keep the protein stable and functional
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know
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denaturation = permanent
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know
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proteins can renature though if the reagent is removed
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can be reversible
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