3.6 (2.1.2) structure of proteins

define primary structure

The sequence/ order of amino acids in the polypeptide

describe secondary structure of proteins

The O, H, and N atoms of the amino acids interact in the formation of hydrogen bonds. This may twist the chain of amino acids into an alpha-helix. Or it may form beta-pleated sheets

why may secondary structure of proteins include beta-pleated sheets

parallel polypeptide’s hydrogen bonding

what is a peptide bond

a covalent bond which joins two amino acids by removing H2O from an amino group (–NH2) of one amino acid and a carboxyl group (–COOH) of the adjacent amino acid in a polypeptide chain

general structure of amino acid

includes a basic amino group (-NH2), an acidic carboxyl group (-COOH), and an organic variable group

define tertiary structure of protein

the folding of the protein into its final 3D shape

name 4 types of bonding in tertiary structure of protein

1) hydrophobic/ hydrophilic interactions 2) hydrogen bonding 3) ionic bonds 4) disulphide bridges

define disulphide bonds in protein

the strongest covalent of the forms which bonds one S atom with another S atom from a different amino acid

define quaternary structure of protein

more than one polypeptide

describe properties of globular proteins

compact. spherical. hydrophobic variable groups on amino acids. hydrophilic variable groups. soluble. important in reactions within aqueous medium

example of globular proteins

enzymes, insulin

define conjugated protein

globular proteins with a prosthetic group

describe haemoglobin as a conjugated protein

quaternary protein made of 4 polypeptide subunits. each subunit has a haem group. role is to transfer oxygen around the body

what does a haem group do

binds reversibly with oxygen

structure and function of catalase

contains 4 haem prosthetic groups. breaks down hydrogen peroxide in water + oxygen

describe properties of fibrous proteins

long. insoluble due to many hydrophobic variable groups within primary structure. limited type of amino acid. repetitive sequence of amino acids. not folded into 3D shapes

describe structure and properties of keratin

more cysteine= more disulphide bridges= stronger and inflexible

describe structure of elastin

made of tropoelastin. found in elastic fibres

describe structure and properties of collagen

there are 3 polypeptides wrapped around each other in rope-like structure. flexible but strong. in connective tissues in skin, ligaments, tendons

role of globular proteins

functional (catalysts, transport)

role of fibrous proteins

structural (strength and support)

solubility of globular proteins

soluble in water

solubility of fibrous proteins

insoluble in water

sequence of globular proteins

irregular amino acid sequence

sequence of fibrous proteins

repetitive amino acid sequence

stability of globular proteins

more sensitive to changes in temperature, pH

stability of fibrous proteins

less sensitive to changes in temperature, pH

examples of globular proteins

catalase, haemoglobin, insulin, immunoglobulin

examples of fibrous proteins

collagen, keratin, elastin, actin, myosin