Proteins Flashcards
Polypeptide
Amino acids are the monomers that Join together to form polymers
Structure of amino acids
Each amino acid has a central carbon atom
Amino group on its lift - NH2
Carboxylate group on its right COOH ( double bonded oxygen)
H below
And R above
R group
Determines how the amino acid interacts and bonds with other amino acids in the polypeptide
Essential amino acids
20 different types of amino acids that are common in all organisms but only 10 of these are essential
Peptide bond
When two amino acids react together, a bond forms between the carboxyl group of one amino acid and the amine group of a second amino acid
Transport proteins
Channel proteins transport molecules across the cell membrane that are too large to diffuse freely or molecules that carry a charge
Enzymes
Biological catalysts which increase the rate of a reaction without being used up in the reaction
Antibodies
Made up of polypeptide chains and are used in the immune response
They are diverse proteins as every antibody has a different sequence of amino acids
Structural proteins
Long, strong polypeptide chains which are connected by cross-links that hold the chains parallel to each other
The biuret test
Add sample to distilled water and biuret solution and shake then leave upright for 5 mins
The biuret test changes colour from blue to violet when proteins are present
Primary structure
Sequence of amino acids which is determined by the gene encoding the protein
A change in the nucleotide sequence of the gene’s coding region may lead to a different amino acid being added to the growing polypeptide chain
Secondary structure
Primary polypeptide chain folds to form a secondary structure where amino acids can form hydrogen bonds which causes he protein to fold e.g alpha helix or a beta pleated sheet
The 2º structure is stable since although individual hydrogen bonds are weak, there are many bonds throughout the molecule
Tertiary structure
Secondary polypeptide folds further to form a tertiary, three dimensional polypeptide chain
Interactions between r groups creates the complex 3D tertiary structure of a protein
There are many weak and strong interactions that hold the final 3D shape of the protein - ionic, hydrogen and disulphides bridges
Quaternary structure
Multiple 3D polypeptides can come together to form a complex e.g collagen, insulin ( globular shape) , haemoglobin ( 4 polypeptide )
Biological catalyst
substance that speeds up a chemical reaction without being used up itself
Activation energy
specific amount of energy needed for a reaction to start , enzymes lower the activation energy by binding to reactant molecules and allowing chemical bond-breaking and bond-forming processes to happen more easily
The lock and key model
Originally used to explain enzyme action
Which proposes that the enzyme and substrate fit together perfectly
The induced fit model
Suggests that there is a more dynamic interaction between enzyme and substrate
As an enzyme and substrate come together, their interaction causes a small shift in the enzyme’s structure which means that the enzyme and substrate can bind to form an enzyme-substrate complex and catalyse a reaction
PH and enzymes
Changing the pH changes the number of hydroxide ions and hydrogen ions surrounding the enzyme which interact with the charges on the enzymes amino acids affecting hydrogen bonding and ionic bonding so resulting in changes to the tertiary structure
Temperature and enzymes
Increasing the temperature will increase the kinetic energy of the molecules which increases the chance of a collision between the enzyme and substrate and so more collisions are likely in a set period of time
Increasing the temperature by 10ºc will approx double the rate of reaction
Enzyme concentration
Increasing the concentration of enzyme in a solution means there are more enzyme molecules available to catalyse the substrate in a given amount of time
Substrate concentration
Increasing the conc. of the substrate increases the numbers of substrate molecules that can form ES complexes at any one time which increases the initial rate of reaction but when all the enzyme molecules are engaged in ES complexes the rate cannot increase any further
Competitive inhibitors
Competitive inhibitors are similar in shape to the usual substrate and affect the active site directly, blocking access for the formation of ES complexes, increasing the substrate concentration can compensate for the effects of a competitive inhibitor as there is no permanent damage to the shape of the active site
Non-competitive inhibitors
Affect another part of the enzyme molecule causing a change to the shape of the active site which is no longer complementary to the substrate molecules
