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Describe the tertiary structure of AAs

Folding of secondary requiring series of non-covalent interactions
Held by electrostatic, VDWs, disulphide, hydrophobic interactions


What are electrostatic bonds?

Strong interactions between ions/charged groups of opposite charge
In protein called a salt bridge


What are Van der Waals forces?

Weak, close range temporary dipole-dipole interactions


What are disulphide bonds?

Strong covalent S-S bonds between specific cysteine residues
Tend to lock molecule into configuration allowing it to withstand v high temperatures


What are hydrophobic interactions?

Interactions between polar and non-polar molecules causing the spontaneous folding of hydrophobic residues away from water


Describe the quaternary structure of proteins

Association of multiple tertiary polypeptides
Haemoglobin is association of 4 globin groups and 4 heme groups


What is a protein domain?

Part of a polypeptide that can fold independently of polypeptide into compact, stable tertiary structure
Usually identified by presence of prolIne
Can be cut, isolated and studied separately from main chain


What is protein folding?

Process by which higher structures are formed from primary (AA) sequence


What are transitions in shape of tertiary or quaternary structures called?

Conformational changes - proteins may shift between several similar structures in performing their function
(Tertiary and quaternary structures referred to as conformations)


What is the reversible nature of protein folding dependent on?

Primary structure being maintained


What are the three classes of proteins?



Describe globular proteins

Are soluble, nearly all enzymes are globular
Carbonic anhydrase and haemoglobin are examples


Describe carbonic anhydrase

Catalyses interconversion of CO2 + H2O to carbonic acid
Different classes have little sequential or structural similarities but share identical AS thus all perform same function and require a Zn atom
Contains large B sheet in centre


Describe haemoglobin

Assembly of 4 globular protein subunits each composed of protein chain (2 a chains, 2 B chains) tightly associated with prosthetic heme group


What is a prosthetic group?

Non-protein group tightly bound to protein that confers function
Heme has an Fe atom held in heterocyclic ring equally to all 4 N atoms
Fe is site of O2 binding


Describe fibrous proteins

Form rod/wire like shapes, usually structural or storage proteins
AA sequence often lacks repeating units
From unusual 2ndary structures (collagen triple helix) due to cross-links between chains e.g. S-S bonds between keratin
Usually used to construct CT, tendons, bone matrix, muscle fibre


What are keratins and what do they form?

Family of fibrous structural proteins, they are tough and insoluble
Form non-mineralised structures found in reptiles, birds, amphibians, mammals (hair)


Describe the structure of keratin

High proportion of glycine (smallest) and alanine (2nd smallest) AAs
High amounts of cysteine (sulphur containing) required for S-S bridges confer strength, rigidity by permanent, thermally stable cross-links


Describe the structure of keratin monomer and the assembly into intermediate filaments

3 domains: head, rod, tail
Monomers associate to dimers, associate to tetramers, finally to intermediate filaments forming part of cytoskeleton


What is collagen?

Family of fibrous proteins secreted by CTs with triple helix AA structure
28 different types
Unique sequence of glycine-proline/hydroxyproline-alternative AA


What are the 3 type of membrane-associated proteins?

Transmembrane (intrinsic) - cross membrane, usually a-helix
Lipid associated (extrinsic) - bound to outer surface
Proteins attached to transmembrane protein - increase ionic strength to detach i.e. add NaCl


What are the 2 domains of membrane proteins?

Interdomain - intracellular
Outer domain - extracellular


What are some of the functions of membrane proteins?

Transporters, linkers, receptors, enzymes


Define enzyme

Proteins that catalyse biochemical reactions (biological catalysts)


Define active site

Parts of enzyme that react with substrate (+ cofactors) in reaction


Define co-enzyme

Small, diffusible organic residue that participates in enzyme catalysed reaction, is stable to heat


Define prosthetic group

Coenzyme covalently bound to enzyme so that not removed by dialysis


Define zymogen

Inactive precursor of enzyme


Define holoenzyme

Protein (apoenzyme) with coenzyme/ions required for activity


Define apoenzyme

Protein with coenzyme required for activity, liable to heat