Amino Acids Flashcards
What components make up amino acids?
A carboxyl group (COOH-), an amine group (NH3+) and an R-group
How do amino acids differ one one another?
They have different R-groups
What are the functions of proteins?
Transport, as catalysts, structure, and motion
What type of bonds join amino acids and how do they form?
Peptide bonds
Formed by hydrolysis, the -OH from the carboxyl group and the -H from the amine group split ad join to form a water molecule and a peptide bond between amino acids
All amino acids are chiral except ______
glycine
What are the five groups for classification of amino acids?
Polar, non-polar, positive, negative, aromatic
Which amino acids are polar and what are their characteristics?
- serine, threonine, cysteine, asparagine, glutamine
- hydrophilic
Which amino acids are non-polar and what are their characteristics?
- glycine, alanine, valine, proline, methionine, leucine, isoleucine
- hydrophobic
Which amino acids are aromatic and what are their characteristics?
- phenylalanine, tyrosine, tryptophan
- relative non-polar, absorb UV light, can form H-bonds
Which amino acids are positive and what are their characteristics?
- histamine, lysine, arginine
- the most hydrophilic, acids
Which amino acids are negative and what are their characteristics?
- aspartate, glutamate
- basic
What are essential amino acids?
Amino acids humans cannot synthesis at all or synthesize enough of to satisfy the bodys needs, must be included in diet
Which amino acids are essential?
histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
What are conditionally essential amino acids?
Amino acids that aren’t synthesized enough at certain periods of life
Which amino acids are conditionally essential?
arginine, cysteine, glutamine, glycine, proline, tyrosine
How can amino acids be ionized?
Both the carboxyl group and amine group are ionizable as they have charges, they can both be protonated
The carboxyl group has a(n) _____ pKa and is protonated at ____ pH, the amine group has a(n) _____ pKa and is protonated at _____ pH
acidic/low/basic/high
At low pH the amino acid is a(n) ____ and at high pH it is a(n) _____ because …
cation/anion
because at low pH the negatively charged COOH is protonated and only the positive charge from the NH3 remains, the reverse is true for high pH
What is a zwitterion?
When the amino acids are between pKas and both charges are present, making it neutral
How does the side chain affect ionization?
If the side chain has a positive or negative charge it will affect whether the amino acid is a cation or anion at a given pH
Isoelectric point (pI) = ?
pI=[pK1][pK2]/2 (net=0) unless the side chain is ionizable)
Primary protein structure:
All peptide bonds linking amino acids into a polypeptide chain, not functional
Secondary structure:
Spatial arrangement of the polypeptide chain, stabilized by H-bonds, not functional
What are the types of secondary structure?
α helix: H-bonds between nearby amino acids, order affects stability
β pleated sheet: H-bonds between adjacent amino acids, not necessarily nearby, sheets are held together by H-bonds between them which are either parallel (diagonal) or antiparallel (horizontal)
random coil: irregular arrangement of polypeptide chain
Tertiary structure:
Overall spatial arrangement of the protein, stabilized by side chain interactions (hydrophobic, polar, or disulphide), functional
What are the types of tertiary structure?
Fibrous: insoluble PRO, usually structural or protective, mostly have the same secondary structure
Globular: soluble PRO with a globular shape
Quaternary structure:
Assembly of individual polypeptide chains into a cluster, functional, optional
What are the advantages of a quaternary structure?
Increased stability, reduced exposed surface, cavities form for activity, improves catalysis
What are the disadvantages of quaternary structure?
Not optimal for rapid diffusion, not optimal for radio degradation
