Amino Acids + Protein Stucture + Folding Flashcards
(25 cards)
What bond is between amino acids?
Peptide bonds
Features of peptide bonds
- Planar
- Rigid
- Trans conformation
- Bonds on either side of peptide bond are free to rotate
Describe the molecular structure of an amino acid
Carboxyl- group
Amine group
R group - classified by R group
Polar vs non-polar classification of amino acids
- Polar: uneven distribution of electrons
- Non-polar: even distribution of electrons
What is the isoelectric point? pl
The pH at which there is no overall net charge
Describe the structure + formation of disulphide bonds
- R group of cysteine is -SH (sulfhydryl group)
- two -SH groups are oxidised > cystine which contains a disulphide bond
Cysteine vs cystine
Cysteine is an amino acid
Cystine is a dimer of cysteine
What is the range of physiological pH?
7.35-7.45
Outline the behaviours of acidic amino acids?
What 2 amino acids have acidic side chains?
- proton donors
- at physiological pH, the side chains have negative charg > negative carboxyl group (—COO-)
- Aspartate
- Glutamate
Outline the behaviours of basic amino acids?
What 3 amino acids have basic side chains?
- proton acceptors
- strong: at physiological pH, side chains are fully ionised + positively charged
- weak: at physiological pH, side chains are uncharged
- arginine - strong
- lysine - strong
- histidine - weak
What is determined by the amino acid sequence of a protein?
- folding
- physical characteristics
How can amino acids be classified based on their chemical properties?
- hydrophobic vs hydrophilic
- polar vs non polar
- acidic vs basic vs neutral
How can amino acids be classified based on their physical properties?
Aromatic
Aliphatic
Compare PKA values between acidic and basic amino acids
-
Basic: - positively charged R groups
- higher pKa -
Acidic: - negatively charged R groups
- lower pKa
Relationship between pK and pH values of amino acids
- R group is protonated: solution pH > amino acid pK
- R group is deprotonated: solution pH < amino acid pK
Relationship between pI and pH of proteins
- Protonated: pH < pI
- Deprotonated: pH > pI
What are conjugated proteins?
Proteins covalently bonded to other chemical components
e.g. haemoglobin
How are B sheets stabilised?
Hydrogen bonds
List the types of intermolecular forces present in the types of protein structure levels
- Primary: peptide bonds
- Secondary - hydrogen bonds
- Tertiary + Quaternary - non covalent forces
What are the N and C terminals of proteins
N - free amino acid terminal
C - free carboxyl terminal
5 biochemical roles of proteins and examples
- catalysts e.g. enzymes
- transporters e.g. haemoglobin
- structural support e.g.collagen
- immune protection e.g. immunoglobins
- receptors e.g. for hormones, neurotransmitters…
What interactions stabilise tertiary structure?
Disulphide bonds
Hydrophobic interactions
Hydrogen bonds
Ionic interactions
Describe the role + structure of fibrous proteins
Examples
- Role: support, shape + protection
- Structure: single repeating secondary structure > forms long strands or sheets
e.g. collagen, keratin
Describe the role + structure of globular proteins
Examples
- Role: catalysts, regulation + transport
- Structure: several types of secondary structure
e.g. myoglobin, haemoglobin
