CH3 proteins Flashcards
what do proteins consist of
one or more polypeptides arranged as complex macromolecules
how many different amino acids are there
- 20 overall
- 9 are essential and are obtained from diet
- 6 are conditionally essential as are only needed by infants and growing children
- 5 are non-essential as can be made from different amino acids
how do amino acids join
- amine and carboxylic acids groups attached to central carbon atom react
- hydroxyl of the carboxylic acid group react with a hydrogen of the amine group
- peptide bond is formed and water is produced
what enzyme catalyses the formation of peptide bonds
peptidyl transferase
what is primary structure
- sequence in which the amino acids are joined
- directed by information carried within DNA
- bonds involved are peptide
what is secondary structure
- hydrogen, oxygen and nitrogen of the basic, repeating structure of amino acids interact
- hydrogen bonds form which can lead to either an alpha helix or a beta pleated sheet
what is tertiary structure
- folding of protein into its final shape
- coiling brings r groups close enough to interact
- formation of bonds such as, hydrophobic and hydrophilic, ionic, disulfide and hydrogen
what is quaternary structure
- association of two or more individual proteins called subunits
- same interactions as tertiary but between protein molecules rather than within one molecule
how do hydrophilic and hydrophobic interactions affect protein
- proteins are assembled in aqueous environment so way in which protein folds depends on whether R groups are hydrophobic or hydrophilic
- hydrophilic are on outside of protein whilst hydrophobic are on inside
how are peptides broken down
- protease breaks down peptides to amino acids
- water turns amino acid to carboxylic acid and amine group
how to test for proteins
add biuret reagent and if present, turns purple
what is a globular protein
compact, water soluble, usually spherical
how do globular proteins form
when proteins fold into tertiary structure in way that hydrophobic R groups are kept away from aqueous environment and hydrophilic are on outside
example of globular protein: insulin
hormone that regulates glucose concentration. transported in blood stream so needs to be soluble. have to fit into specific receptors so need precise shapes
what are conjugated proteins
globular proteins with a non-protein component called a prosthetic group
example of conjugated protein: haemoglobin
quaternary protein made of four polypeptides - two alpha and two beta subunits, each with a prosthetic haem group which are able to combine reversibly with oxygen
example of conjugated protein: catalase
enzyme. quaternary protein containing four haem prosthetic groups. interacts with hydrogen peroxide to speed up breakdown
what are fibrous proteins
limited range of amino acids, repetitive primary structure, organised, strong long insoluble molecules
how are fibrous proteins formed
have a high proportion of amino acids with hydrophobic r groups in primary structure
example of fibrous protein: keratin
large proportion of sulfur containing amino acid cytesine leading to many disulfide bonds which form strong, inflexible and insoluble materials
example of fibrous protein: elastin
made by linking many soluble tropelastin molecules to make a large stable cross linked structure. tropelastin molecules are able to stretch and recoil acting like springs. contain alternate lysine rich and hydrophobic areas
example of fibrous protein: collagen
- 3 polypeptide chains wound around eachother in a triple helix structure
- every 3rd amino acid is glycine which is small allowing three protein molecules to form a closely packed triple helix
- many hydrogen bonds form between polypeptide chains forming long quaternary proteins with staggered ends so proteins can join end to end
- high proportions of amino acids proline and hydroxyproline, the r groups repel eachother which adds to stability
