Structure and Function of Proteins Flashcards
What are the 5 groups of amino acids?
Hydrophobic, aromatic, polar, negatively charged, positively charged
Do hydrophobic acids contain polar groups?
No
Where are hydrophobic amino acids found?
the hydrophobic core of proteins
Which amino acid group does glycine belong to?
Hydrophobic
What is the one letter code for glycine?
G
What is the three letter code for glycine?
Gly
Which amino acid group does alanine belong to?
Hydrophobic
What is the one letter code for alanine?
A
What is the three letter code for alanine?
Ala
Which amino acid group does valine belong to?
Hydrophobic
What is the one letter code for valine?
V
What is the three letter code for valine?
Val
Which amino acid group does leucine belong to?
Hydrophobic
What is the one letter code for leucine?
L
What is the three letter code for leucine?
Leu
Which amino acid group does isoleucine belong to?
Hydrophobic
What is the one letter code for isoleucine?
I
What is the three letter code for isoleucine?
Ile
Which amino acid group does methionine?
Hydrophobic
What is the one letter code for methionine?
M
What is the three letter code for methionine?
Met
Which amino acid group does proline belong to?
Hydrophobic
What is the one letter code for proline?
P
What is the three letter code for proline?
Pro
Name the 7 hydrophobic amino acids
Glycine, Alanine, Leucine, Isoleucine, Valine, Methionine, Proline
What do all aromatic amino acids contain?
A ring of delocalised electrons
Which amino acid group does phenylalanine belong to?
Aromatic
What is the one letter code for phenylalanine?
F
What is the three letter code for phenylalanine?
Phe
Which amino acid group does tyrosine belong to?
Aromatic
What is the one letter code for tyrosine?
Y
What is the three letter code for tyrosine?
Tyr
Which amino acid group does tryptophan belong to?
Aromatic
What is the one letter code for tryptophan?
W
What is the three letter code for tryptophan?
Trp
Are polar amino acids hydrophilic or hydrophobic?
Hydrophilic
Where are polar amino acids usually found?
On the surface of proteins
Which amino acid group does serine belong to?
Polar
What is the one letter code for serine?
S
What is the three letter code for serine?
Ser
Which amino acid group does threonine belong to?
Polar
What is the one letter code for threonine?
T
What is the three letter code for threonine?
Thr
Which amino acid group does cysteine belong to?
Polar
What is the one letter code for cysteine?
C
What is the three letter code for cysteine?
Cys
Which amino acid group does asparagine belong to?
Polar
What is the one letter code for asparagine?
N
What is the three letter code for asparagine?
Asn
Which amino acid group does gluamine belong to?
Polar
What is the one letter code for gluamine?
Q
What is the three letter code for gluamine?
Gln
Name the 3 aromatic amino acids
Phenylalanine, tyrosine, tryptophan
Name the 5 polar amino acids
Serine, threonine, cysteine, asparagine, gluamine
Which amino acid group does aspartate belong to?
Negatively charged
What is the one letter code for aspartate?
D
What is the three letter code for aspartate?
Asp
Which amino acid group does glutamate belong to?
Negatively charged
What is the one letter code for glutamate?
E
What is the three letter code for glutamate?
Glu
Name the 2 negatively charged amino acids
Aspartate, glutamate
Which amino acid group does lysine belong to?
Positively charged
What is the one letter code of lysine?
K
What is the three letter code of lysine?
Lys
Which amino acid group does arginine belong to?
Positively charged
What is the one letter code for arginine?
R
What is the three letter code for arginine?
Arg
Which amino acid group does histidine belong to?
Positively charged
What is the one letter code for histidine?
H
What is the three letter code for histidine?
His
Name the 3 positively charged amino acids
Lysine, arginine, histidine
Name the 7 uses of proteins
catalysis transport and storage motion mechanical support immune protection signal transduction growth and development control
Which amino acid is the most common replacement in mutation?
Alanine (she fit)
Why is hydrogen bonding limited in proline?
Lack of hydrogen on the nitrogen
What is the largest amino acid?
Tryptophan
Which amino acid contains an imidazole ring?
Histidine
Name the two processes by which protein structures can be determined
X-ray crystallography and Nuclear Magnetic Resonance (NMR)
What are the three types of protein structure?
Globular, Membrane, and Fibrous
Are globular proteins soluble in water?
Yes
What makes globular proteins soluble in water?
They have a hydrophobic core and a hydrophilic surface
What are possible protein structures limited by?
Properties of the peptide bond
What is the hierarchy of protein structure?
Primary: amino acid sequence
Secondary: secondary structure elements and motifs
Tertiary: whole protein/domain structure
Quaternary: whole protein structure
Can rotation occur around a peptide bond?
No
Which amino acid can form cis bonds?
Proline
Which bond is between C(alpha) and the amide group?
Phi
Which bond is between the carbonyl carbon and the C(alpha)
Psi
What does a Ramachandran plot show?
Which Phi and Psi bond combinations are possible
What types of bonding are in proteins?
- ionic interactions: between acidic and basic side chain groups of opposite charge
- hydrogen bond: between donor and acceptor groups
- disulphide bridges
- hydrophobic interactions: between aliphatic and aromatic side chain groups
- pi stacking between aromatic groups
What are domains built from?
Motifs
What can domains be stabilised by?
Disulphide bondes
What are two ways in which proteins can be post translationally modified?
Covalent and non-covalent
What are some examples of covalent modification?
Disulphide bridge formation, cleavage of peptide bonds, the N-terminus, the C-terminus, amino acid residues (side chains)
What are some examples of non-covalent modification?
Addition of metals, addition of cofactors
Why are proteins modified?
Stability, regulation of activity, localisation, ageing
Are alpha helices left-handed or right handed?
Right-handed
Do protein adopt the most thermodynamically stable or unstable structure?
Stable
Name the four methods of denaturation
Chemical denaturants, heat, acid/base, force/kinetic energy
What do protein disulphide isomerases (PDI) do?
Accelerate the formation of native disulphide bridging arrangements allowing disulphide shuffling and attacks incorrectly formed disulphide bonds
What do Peptidyl Prolyl Cis-Trans Isomerases (PPIs) do?
Catalyse the rotation around peptide bonds preceding proline
What do molecular chaperones do?
Prevent the improper folding and aggregation of proteins and prevent or reverse improper associations between proteins
What are the two types of molecular chaperones?
DnaK/DnaJ/GrpE (or Hsp70) family and chaperonin family (GroE chaperonin)
What do the DnaK/DnaJ/GrpE (or Hsp70) family do?
Prevent premature folding: bind to growing polypeptide chains while they are being synthesised on ribosomes
What do the chaperonin family do?
Bind to the solvent-exposed hydrophobic surfaces of an unfolded or aggregated protein and release them
Assist post-translational folding
What are proteopathies?
Diseases caused by misfolded proteins
What are the two classes if proteopathies?
Hereditary and acquired
Define hereditary proteopathies
Mutation causes loss of function or gain of function leading to disease
Define acquired proteopathies
Infectious prion disease caused by exposure to misfolded proteins from other organisms
Give two examples of a hereditary proteopathy
Cystic fibrosis and Alzheimer’s disease
Give two examples of an acquired proteopathy
Bovine spongiform encephalopathy (BSE) and vCJD
Why is Alzheimer’s disease associated with neuronal loss?
Due to deposition of amyloid plaques
What did Anfinsen’s experiment on Ribonuclease A demonstrate about protein folding?
- All of the information for folding to the correct structure is in the amino acid sequence
- Proteins will fold to the most thermodynamically stable conformation
Give 3 reasons why proteins might need to be purified
Protein characterisation, use in drugs & diagnostics, for commercial use esp. enzymes
Give 3 examples of when protein characterisation might be needed
Assay to investigate function, investigate post-translational modifications, to study structure-function relationships
What are the two sources of proteins?
Native (extracted from host organism) and heterologous protein expression systems
How do heterologous protein expression systems work?
- Gene cloned into a vector
- Inserted into an organism
- Produces the protein via constitutive expression or inducible expression (AraBAD promoter and arabinose)
Name the 6 characteristics used to separate proteins
Size Charge Specific binding Specific epitope Purification tag Hydrophobicity
How are proteins separated by size?
Size exclusion chromatography
How are proteins separated by charge?
Ion exchange chromatography
How are proteins separated by specific binding?
Affinity chromatography
How are proteins separated by specific epitope?
Affinity chromatography
How are proteins separated by purification tag?
Affinity chromatography
How are proteins separated by hydrophobicity?
Hydrophobic interaction chromatography
How can proteins be engineered for purification and detection?
- Add signal sequence that causes secretion into culture medium
- Add sequence of protein that helps the target protein fold and stay soluble
- Add a sequence that aids detection
- Add an affinity tag
How does hydrophobic interaction chromatography work?
- Add bacterial lysate to column matrix in high salt buffer (hydrophobic proteins will stick to column)
- Wash less hydrophobic proteins from column with low salt buffer (less hydrophobic proteins elute from column)
- Elute protein from column by adding salt-free buffer
What are the two techniques for analysing protein size?
Gel electrophoresis and mass spectrometry
What is the difference in the mass given by gel electrophoresis vs mass spectrometry?
Gel electrophoresis gives approximate mass; mass spectrometry gives accurate mass
What is the aim of polyacrylamide gel electrophoresis (PAGE)?
Separating mixtures of proteins by their relative rates of migration through a matrix in an electrical field
What type of PAGE should be used for denatured protein?
SDS-PAGE
relative migration rate based on mass of protein
What type of PAGE should be used for native proteins?
Native PAGE
relative migration rate based on both mass of protein and charge at the pH used
What is isoelectric focusing (IEF) used for?
To separate proteins according to their overall charge
What are the three basic components of a mass spectrometer?
Ioniser, mass analyser, detector
What is the proteome?
The primary sequence of all proteins
How can proteins be identified in complex mixtures?
Proteomics
- extract mixture of proteins from cells/tissue and 2D-PAGE
- extract proteins from gel and digest with trypsin
- identify by peptide mass fingerprinting