Summary
Summary of Amino Acids
- Course
- Biochemistry (MCB2021F)
- Institution
- University Of Cape Town (UCT)
Notes are the summary for the Amino Acids lecture series for MCB2021F
[Show more]
Seller
Follow
Content preview
Amino AcidsAlanine – Ala (A) non-polar, has an alkyl side chain.
Valine – Val, (V) non-polar, has an alkyl side chain.
Leucine – Leu, (L) non-polar, has an alkyl side chain.
Isoleucine – Ile, (I) non-polar, has an alkyl side chain.
Methionine – Met, (M) non-polar, has s Sulphur containing side chain.
Proline – Pro, (P) non-polar, aromatic side chain with one cyclic structure.
Proline has the ability to undergo C-hydroxylation which turns it into 4-hydroxproline by the
use of prolyl hydroxylase. This is found in collagen in the body.
Tryptophan – Trp, (W) non-polar, aromatic side with two cyclic structures.
Glycine – Gly, (G) polar and uncharged, has no side chain.
Cysteine – Cys (C) polar and uncharged, sulfhydryl side chain. Contains disulfide bonds once
undergone a sulfhydryl reaction. These covalent links between Sulphur containing side
chains of cysteine are very strong and play an important role in 3D structure as they keep
polypeptide firmly attached.
Serine – Ser (S) polar and uncharged, has a hydroxyl side chain and participates in O-linked
glycosylation
Threonine – Thr, (T) polar and uncharged, has a hydroxyl side chain and participates in N-
linked glycosylation
Asparagine – Asp (N) polar and uncharged, has an amide side chain
Glutamine – Gln (G) polar and uncharged, has an amide side chain
Tyrosine – Tyr (Y) polar and uncharged, has an aromatic side chain
Aspartic acid – Asp (D) – polar, charged and acidic, has a carboxyl side chain
pI à 2.77
Glutamic acid – Glu (E) – polar, charged and acidic, has a carboxyl side change
pI à 3.22
deprotonation à E+; E0; E-; E2-
Lysine – Lys (K) polar, charged and basic, has an amine side chain
pI à 9.74
deprotonation à K2+; K+; K0; K-
Lysine has the ability to undergo C-hydroxylation by the use of lysyl hydroxylase which turns
it into 5-hydroxylysine and is found in collagen in the body.
Arginine – Arg, (R) polar, charged and basic, has a guanidinium side chain
pI à 10.76
Histidine – His (H) polar, charged and basic, has an imidazole side chain
pI à 7.59
uncommon amino acids à selenocysteine (SeCys, U) and selenomethionine (SeMet, SeM).
Phosphorylation of serine, threonine and tyrosine convert polar, uncharged side chain into a
polar, charged side chain that contains a negative charge. Phosphorylation is post
translational regulatory process that is very important process in cells.
Serine à phosphoserine
Threonine à phosphothreonine
,Tyrosine à phosphotyrosine
They contain a hydroxyl group where the phosphate is located and thus becomes negatively
charged.
Acetylation of lysine converts side chain from being positively charged into being
uncharged.
Lysine à acetyllysine
Acetylation attaches a amine group onto the lysine where the amino group is located.
Henderson-Hasselbalch equation:
pH = pKa + Log10[A-]/[HA]
Properties of Amino Acids:
In the absence of an ionizable side chain, amino acids exist at a neutral pH (7) as a dipolar
ion/ zwitterion. Zwitterions have the ability to either act as a proton donor or a proton
acceptor (acid or base). Amino acids which have dual acid-base properties are called
amphoteric/ ampholytes.
Amino acids are weak polyprotic acids, thus, they can donate more than one proton per acid
molecule an example is glycine which is diprotic.
Glycine has two pKa values – one is for the alpha amino group (higher on graph) and one is
for the alpha carboxyl group (lower on graph).
Isoelectric point (pI) is the pH at which a molecule has no net charge.
pI = (pKa 1 + pKa 2)/ 2
e.g. for glycine
pKa 1 = 2.3 and is the value when 50% of the carboxyl group is dissociated and is when there
is an addition of 0.5M of substance have been added.
pKa = 9.6 and is when 1.5M have been add, this is when 50% of the amino group is
dissociated.
Therefore, at 1M glycine is fully dissociated.
Deprotonation of glycine à G-; G0; G+1
, Triprotic acids have three pKa values e.g. glutamic acid
Here the pI is 3.25, this means that at a pH of 3.25 glutamic acid carries a net charge of 0.
Lysine is also triprotic and has a pI value of 9.75, this means that at a pH of 9.75 lysine
carries a net charge of 0.
Stereochemistry of Amino Acids:
There are four different chemical groups attached to a-carbon atom, the a-carbon is said to
be asymmetrical/ chiral center or stereocenter. Therefore, two different stereoisomers exist
(enantiomers) that are mirror images of each other.
Optical activity:
Enantiomers possess optical activity – they rotate the plane of polarized light, therefore,
clockwise rotation – dextrorotary (+) or D and anticlockwise rotation = levorotatory (-) or L.
D/L nomenclature:
Denotes the configuration with reference to D and L forms of glyceraldehyde, L-amino acids
dominate in nature.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through EFT, credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying this summary from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller calrosewitz. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy this summary for R200,00. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
68175 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy summaries for 15 years now