Protein Structure Flashcards
Which type of protein tends to feature a single type of secondary structure
Fibrous proteins
Which type of protein tends to feature more than one type of secondary structure
Globular proteins
What are the two prominent secondary structural arrangements
a helix and beta conformation
What is the primary sequence
Sequence of amino acid residues involving all covalent bonds (peptide and disulphide) in a polypeptide chain
What is the secondary structure
Stable arrangements of AA residues leading to recurring structural patterns
What is the tertiary structure
All aspects of 3 dimensional folding of a polypeptide
What is the quaternary structure
Spatial arrangement when a protein has more than one polypeptide subunits
What are AA residues
AAs joined by a peptide bond
What does the primary structure determine
3D structure and functions of the polypeptide/protein
Where do disulphide linkages occur in proteins
Cross links formed by adjacent cysteine residues involving the same PP chain or to link two PP chains
What two chains does a PP consist of
Main chain (backbone) of repetitive peptide bonds and alpha carbons and variable side chains
How is the PP backbone/main chain both rigid and flexible in the primary structure
Rigid as peptide bond is planar owing to partial double bond character as they partially share electron pairs (C=O and C=N) but flexible as limited rotation possible in either side of the alpha carbon
What bond forms the secondary structure of proteins and where are they
Hydrogen bonds between the peptide NH and CO groups
What is the importance of hydrogen bonding in the secondary structure
Causes polarity in the C=O, N-H and O-H groups are attraction between positive and negative charges
How many A residues are in each Tuen of the alpha helix
3.6 AA residues
What can affect alpha helix stability
Interactions between R groups
Describe the beta conformation
Backbone of PP is extended in zigzag structure with chains arranged side by side and linked by H bonds, adjacent segments can be from the same or different PP chains and can be parallel or anti parallel to eachother
What is a beta sheet
Arrangement of several segments side by side all in beta conformation
What is the difference in the tertiary structure to the primary and secondary
Tertiary is overall 3D structure and has lower range effects such as folds in chains that may cause interactions between AA residues far apart in the polypeptide
What are the 3 main classes of quaternary structures
Fibrous, globular and intrinsically disordered
Describe fibrous proteins
Extended PP chains with usually one type of secondary structure, Insoluble in water and relatively simple tertiary structures
Describe globular proteins
Folded PP chains often with several types of secondary structure and a complex tertiary structure
What is the function of fibrous proteins
Provide structural support to cells and tissues
Give two examples of important fibrous proteins
alpha keratin and collagen
Describe alpha keratins properties
Very strong coiled-coil protein, 2 alpha helices intertwined to form a coiled- coil super helix
Where is alpha keratin found
Mammal’s hair, wool, nails, hooves and outer layer of skin
What are the properties of collagen
3 helical chains each nearly 1000 residues with 3 AA residues per turn (unlike alpha helixes) , every third residue is glycine (smallest AA) so the interior is very crowded, three chains wind together to form triple stranded superhelical cable stabilised by H bonds
Where is collagen found
Skin, bone, tendon, cartilage and teeth
What type of protein is myoglobin
Globular
What are the functions of myoglobin
Oxygen binding protein in muscle cells, Stores O2 and facilities diffusion in muscle tissue
What are the properties of myoglobin
Relatively small, single PP chain, 153 AA residues , prosthetic group, contains heme, interior contains almost entirely nonpolar residues hidden from exposure to water, exterior is mostly charged and polar side groups of AAs that interact with water molecules
What is a dimer
A protein with 2 subunits
What is an oligomer
Protein with a few subunits
What are the properties of human haemoglobin
A tetramer with two identical subunits of one type ( 2 alpha subunits and two beta subunits)
