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Name the monomer for proteins
Amino acids
What elements do amino acids contain
Nitrogen, carbon, hydrogen, oxygen
What groups does an amino acid contain
Amine (NH2), carboxyl (COOH) and residual (R)
How many residual groups are there in nature
20
What can proteins form in cells
Enzymes, cell membrane proteins, transport proteins, hormones
What does the sequence, type and number of amino acids determine
Shape and function of proteins
How many amino acids are there in nature
20
Name the properties that change with the residual group
Molecule size, hydrophobic, hydrophilic and charge
Describe formation of a peptide bond
Removal of an OH from the carboxylic group and a hydrogen removed from the amine group of the other amino acid
What reaction forms a peptide bond
Condensation reaction
Define a dipeptide
The condensation of two amino acids
Define a polypeptide
The condensation of 3 or more amino acids
What are the two main structures of a protein
Globular and fibrous
Name a protein with a globular structure
Enzymes
Name a protein with a fibrous structures
Keratin
Describe globular proteins
Compact, roughly spherical and soluble proteins
Describe fibrous proteins
Long strands of polypeptide chains, cross-linked with hydrogen bonds
Define the primary structure of proteins
The sequence of amino acids bonded by peptide bonds, determined by nucleic acids in DNA
How many substructures do proteins have
4
Define the secondary substructure of proteins
Localised folding of polypeptides due to hydrogen bonds between the amino acids
Define localised in terms of amino acids
Between 30 amino acids
Name two types of localised polypeptide folding
Alpha helix and beta pleated sheet
Define the tertiary substructure of proteins
3D folding of the whole polypeptide
Name the 3 additional bonds in the tertiary structure
Hydrogen between R groups, disulphide between cysteine amino acids, ionic between R groups
Name the types of bonds which occur in tertiary substructure
Hydrogen, ionic and disulphide
Define the quaternary substructure of proteins
More than one polypeptide chain bonds to form a protein
Describe the strength of each bond in tertiary substructures
Disulphides are the strongest, ionic are stronger than hydrogen, and hydrogen are weakest
Describe where disulphide bonds occur
Between two cysteine R groups (containing a sulfur atom)
Describe where ionic bonding occurs
Between NH3 and COO
What is the name of the biochemical test for proteins
Biuret’s Reagent
Describe the Biuret’s test
Add copper sulphate solution, a colour change from blue to lilac/purple is positive
What does the Biuret’s test test for
Peptide bonds between protein molecules
Define denaturing
Breaking of hydrogen and ionic bonds causing a change to the polypeptide’s tertiary structure
Name causes for denaturing
pH, temperature and salt concentration
What form of secondary structure is this
Alpha helix
What form of secondary structure is this
Beta pleated sheet
Why do some proteins not have a quaternary structure
Some proteins only contain one peptide chain
How can keratin forms differ in structure
Depending on the amount of hydrogen bonds
Give a suitable control for an enzyme investigation to maintain viability
Boiled enzyme
Suggest control variables for investigation temperature and the rate of breakdown of a protein by protease
Concentrations of enzyme, pH, initial substrate concentration
How should data be presented on a graph
No extrapolation, linear scales and connected data points
Describe how amino acids would bond to form the primary protein structure
Peptide bond between amine and carboxyl groups with a condensation reaction
Describe how R groups can interact to determine tertiary structure of a protein
Some R groups attract, forming disulphide bonds between cysteine monomers, hydrogen bonds and ionic bonds between oppositely charged R groups
