B: Proteins

Breakdown reactions

Synthesis reactions

Where molecules are broken down by the reaction of dilute acid/ alkali in high temps (reflux) • enzyme reactions 37C • Proteins –> amino acids • Starch –> simple sugars

Anabolism monomers combine together to form polymers and water is eliminated

• Enzymes - biological catalysts • Transport proteins - haemoglobin • Immunoproteins - antibodies • Hormones - chemical messengers • structural proteins - collagen • Energy source - when fats and carbohydrates become scarce

• COOH carboxy • can be considered as weak acids as they are partially dissociated aqueous solution • NH2 Amine • behaves as base because they accept protons

• Amino acids exist as zwitterions in solid or aqueous solution • Isoelectric point - pH wehre Amino acid becomes zwitterion

2-Aminoacids will combine together in a condensation reaction to form a dipeptide –> anabolic reaction, energy required compounds will have an amide/ peptide link

Alumina Al2O3 + Silica SiO2 Retardation factor x/y –> used to identitfy the components as long as external conditions remain the same

Buffer solution - zwitter ion used to control the degree of ionization • Polyacylamide gel (PAGE) • locating agent: Ninhydrin

Amino Acids will separate according to • their Mr • The overall charge on the molecule • potential difference applied

• Sequence of Amino Acids in the polypeptide chain • bond responsible: peptide bond/ amide link

The folding of the polypeptide chain as a result of hydrogen bonding

Polymers composed of amino acids (monomers)

alpha-helix H bond between the C=O of 1 peptide bond and the NH of the peptide bond 4 amino acids down

ß-pleated sheet consists of 2 or more stretches of amino acids in which the polypeptide chain is almost fully extended H bonds form between a C=O on one strand and an NH on an adjacent strand

The twisting and folding of the Secondary structure to form a specific 3D shape Bonds involved • LDF - between nonpolar side chains • Hydrogen - between polar side chains • Ionic - between polar side chains • Disulfide bridges (covalent) - between the side chains of cysteine which contain CH2-SH

• Interactions between polypeptide chains (sub-units) • sub-units held together by various intermolecular forces • Dimers - 2 sub-units • Trimers - 3 sub-units • Tetramers - 4 sub-units • (sub units may be identical or different)

• increases rate of reaction by lowering the activation energy of the forward and backward reactions equally • remains unchanged in mass and composition

E + S <—> ES —> E + P • Enzyme binds to substrate @ active side • hydrophobic pocket, nonpolar • Active complex • E –> unchanged in mass and composition ; P –> products

• Molecules must have Ea and a certain orientation to react successfully • As conc. of substrate increases, rate of reaction increases proportionally • because of sufficient active sites to bind to • As the reaction progresses, the active sites are becoming occupied –> fewer are available and rate of reaction decreases • Eventually, a maximum value is reached, after which the rate no longer increases

• collisions with E > Ea, orientation allows for the ES activated complex to form, frequency of collisions is high • optimum temperature at which the rate is a maximum • due to increased vibration of the molecule, the active site’s shape changes and hence fewer substrate molecules can bind –> denature