Protein Structure Flashcards
Describe the structure of an amino acid
Amino group Carboxyl group Hydrogen atom R group N-C-C
How many amino acids are used in the body?
20
What are the 9 essential amino acids?
Isoleucine (if) Leucine (learnt) Threonine (this) Histidine (huge) Lysine (list) Methionine (may) Phenylalanine (prove) Valine (valuable) Tryptophan
What chemical properties are amino acids classified from?
Hydrophobic/hydrophilic
Polar/non-polar
Acidic/basic/neutral
What physical properties are amino acids classified from?
Aliphatic
Aromatic
What is an amino acid residue?
What remains of an amino acid after it has been joined by a peptide bond to form a protein
What does a lower pK indicate?
More likely to dissociate and stronger the acid
What causes the group on amino acid to be protonated?
If the pH of the solution < the pK value
What causes the group on an amino acid to be deprotonated?
If the pH of the solution > the pK value
Describe primary protein structure
Linear amino acid sequence of polypeptide chain
Covalent bonds hold it together
Angles determine conformation of peptide backbone and hence ‘fold’ of protein
Describe secondary protein structure
Local spatial arrangement of polypeptide backbone
Alpha helix/beta sheets
Describe tertiary protein structure
Overall 3D configuration of protein
Spatial arrangement of amino acids far apart in protein sequence
Describe quaternary protein structure
Association between different polypeptides to from a multi-subunit protein
What are the properties of peptide bonds?
Produce water when formed Planar Rigid Trans conformation Bonds on either side of peptide bond free to rotate
Why are amino acids important in proteins?
Amino acid sequence determines the way in which polypeptide chain folds and physical characteristics of protein
What is an isoelectric point?
The pH at which there is no overall net charge
What is the pI of basic proteins?
pI >7 as it contains many positively charged amino acids
What is the pI ion acidic proteins?
pI < 7 as they contain many negatively charged amino acids
How many amino acids in peptides or oligopeptides?
<100
How many amino acids in polypeptides or proteins?
> 100
What are conjugated proteins?
Proteins that contain covalently linked chemical components in addition to amino acids
E.g. prosthetic group - haem or iron
What are the bonds present at each level of protein structure?
Primary: covalent (peptide)
Secondary: H bonds
Tertiary: covalent (disulphide), ionic, H bonds, London forces, hydrophobic
Quaternary: covalent (disulphide), ionic, H bonds, London forces, hydrophobic
Describe fibrous proteins
Role is to support, shape and protect
Long strands or sheets
Single type of repeating secondary structure
E.g. collagen
Describe globular proteins
Role is catalysis and regulation Compact Several types of secondary structure Form enzymes and transporter proteins E.g. carbonic anhydrase
Describe the structure of collagen
Triple helical arrangement of collagen chains
Contain gly-x-y repeating sequence
Hydrogen bonds stabilise interactions between chains
Collagen fibrils formed from covalently cross-linked collagen molecules
What are motifs in globular proteins?
Folding patterns containing one or more elements of secondary structures
E.g. beta-alpha-beta loop
What are domains in globular proteins?
Part of a polypeptide chain that fold into a distinct shape, often has a specific functional role
What is protein denaturation?
Losing its negative state
Disruption of protein structure
Caused by breaking of forces that hold proteins together
E.g. by heat, pH, or detergents/organic solvents
