Lecture 1 Amino Acids Flashcards
What are amino acids and what are they made of?
- Amino acids are the building blocks of proteins FIVE elements are used in amino acids: - Hydrogen - Carbon - Oxygen - Nitrogen - Sulfur
What are the fundamental elements of life?
The elements used to make amino acids: - Hydrogen - Carbon - Oxygen - Nitrogen - Sulphur plus Phosphorus
An α-amino acid consists of:
Consists of: Cα => The Central carbon atom NH2 => Amino group COOH => Carboxyl (acid) group H => Hydrogen atom R => R-group, a side chain that differs between the 20 amino acids
What is a zwitterion?
Usually amino acids exist as a dipolar ion -Known as a Zwitterion
A zwitterion is a compound with no overall electrical charge, but which contains separate parts which are positively and negatively charged.
How does the pH affect the ionisation states?
Different ionisation states are found at different pHs:
- pH = 1 ==> Positively charged amino group
- pH = 7 ==> Dipolar ion (neutral) (+) amino group & (-) carboxyl group
- pH = 11 ==> Negatively charged carboxyl group
What atoms are attached to the α-carbon?
There are FOUR different atoms attached to the α-carbon - Amino acids exist as optically active pairs (each amino acid exists as an isomer=2 atoms) - L-Isomer - D-Isomer
Which amino acids are incorporated into proteins?
Only the natural/proteinogenic amino acids are found in proteins (22 in total) -20 encoded by universal genetic code -2 incorporated by specific mechanism
How many side chains exist and what are their features?
-Twenty different amino acids are found in proteins = Twenty different side chains Key features of the different side chains: - size - shape - charge - Hydrophobic Character - Hydrogen Bonding Capacity - Chemical Reactivity
What are the three nomenclature forms for amino acids?
There are three ways of referring to amino acids: - Full Name - Three Letter Abbreviation =The first three letters (with EXCEPTIONS) -One Letter Abbreviation =The first letter (again, with EXCEPTIONS) Important to know all three nomenclature forms for an amino acid
What are aliphatic amino acids and what are their properties?
(from left to right) Increasing Size, more Hydrophobic (Water hating)
- Inside proteins in the CORE (so core aa)
- Methionine contains Sulphur (one of few aa that contain sulphur)
What kind of side chain does the aa proline have?
Proline => Unique with a cyclic side chain - AA Often found at bends in protein structures
What are aromatic amino acids?
- All contain a phenyl ring (side chain)
- All are hydrophobic
- Tyrosine is less hydrophobic since it has an OH group
How does the change in size of the amino acid side chains affect electron transfer?
The side chains become increasingly bulky in size - Tryptophan = Trp = W = Widest amino acid - The π electron clouds allow for interaction with other π systems = This enables electron transfer to take place
what is cysteine?
Cysteine also contains Sulphur -This amino acid is polar - This is because of the SH group (R chain)
How do Serine and Threonine behave?
Serine and Threonine - Similar to Alanine and Valine respectively - Serine also similar to Cysteine - However, the OH group makes them more Hydrophilic - Hydrophilic => attracted to water/bonds to water - Usually found on the protein surface
Which are the basic amino acids?
There are three amino acids that have basic side chains at neutral pH. These are lysine (Lys), arginine (Arg), and histidine (His). Their side chains contain nitrogen and resemble ammonia, which is a base. Their pKa’s are high enough that they tend to bind protons, gaining a positive charge in the process.
What makes histidine special?
Histidine: - The charge on the side chain of histidine varies with the local pH - Very Important for enzyme catalysed reactions
Which amino acids are uncharged derivatives?
Uncharged derivatives: Asparagine and Glutamine - NH2 replaces a side chain Oxygen in the Carboxylate group
