Who do two amino acids bond and what is formed?
Condensation reactions and a dipeptide
What is the structure of amino acids?
What are the bonds called between amino acids?
What are the two types of proteins?
Fibrous and globular proteins?
What are fibrous proteins?
These are parallel polypeptide chains held together by cross links (forming rope like fibres)
What are the properties of fibrous proteins and give some examples?
High strength, insoluble in water, high tensile
Collagen, keratin and silk
What are globular proteins?
Spherical, tightly folded polypeptide chains. Hydrophobic groups inside, hydrophilic groups outside
What are some examples of globular proteins and give some properties?
Soluble in water
Spherical due to tight folding of the polypeptide chains
Transport proteins, enzymes and hormones
What are proteins used for?
Structural, catalytic, signalling, immunological
Describe the primary structure of proteins
A simple sequence of amino acids in the polypeptide chain. Held together by peptide bonds
Describe the secondary structure of proteins
Hydrogen bonds form between the polypeptide chain. This makes the chain either coil (alpha helix) or fold (beta pleated sheet)
Describe the structure of tertiary structure of proteins
A polypeptide chain coiled or folded even more. This forms a 3D structure. The bonds that cause this are disulphide bonds (covalent)
Describe the structure of quaternary proteins
Made of more than one polypeptide chain held together by more bonds. This results in a final 3D shape. Examples include haemaglobin, insulin, collagen
What is collagen and what gives it, it’s properties?
Collagen is the main consonant of connective tissues in animals.
It has three polypeptide chains tightly coiled, which makes it strong. Good for support
What is keratin and what gives it, it’s properties?
Main component of hard structures in animals.
Examples are hair, nails and claws
What is silk?
What is the test for proteins and how is it done?
Test solution needs to be alkaline so add a few drops of sodium hydroxide solution
Then add some copper (2) sulfate solution
Colour change from blue to purple
What are enzymes?
Enzymes are biological catalysts. They speed up chemical reactions
Describe the structure of enzymes?
Tertiary structure, roughly spherical due to tight folding of polypeptide chains. Soluble as there hydrophilic groups are outside.
They have an active site which are specific to certain substrates
How do enzymes work?
They lower the activation energy of a reaction. When an enzyme substrate complex forms. This reduces the activation energy of a reaction
How does the enzyme substrate complex lower the activation energy where two substrates are joining?
The enzyme holds the substrate close together, reducing the repulsion between the molecules so they can bond more easily.
How does the enzyme substrate complex lower the activation energy where a substrate is breaking down?
Fitting the substrate into the enzyme puts strain on the bonds in the substrate, so it breaks up more easily
How are enzymes specific to substrates?
Only one substrate will fit into the active site of an enzyme. The active site shape is determined by the enzymes tertiary structure (which is determined by it’s specific primary structure)
What is the primary structure of a protein determined by?
A gene (determines the sequences if amino acids). If a mutation occurs in that gene, it could change the tertiary structure of the enzyme produced (so it cannot carry out it’s function as the active site shape has changed and is no longer complimentary of the substrate)
How do you measure the rate if an enzyme controlled reaction?
Measuring the amount of product produced (measuring the amount of product present at different times during the experiment, the reaction rate can be calculated)
Measuring the amount of substrate left (measure the substrate at different points of the experiments)
What is the effect of temperature on enzyme controlled reactions?
The rate of reaction increases as the temperature increases. The molecules vibrate more so the molecules move faster and are more likely to collide with the enzymes active sites.
It reaches the optimum temperature where the rate of the reaction is the largest.
If the temperature increases above this then the vibrating breaks more bonds in the enzyme and thus the active site of the enzyme changes shape, no longer complimentary of the substrate and the enzyme denatures.
How does pH affect the rate of an enzyme controlled reaction?
Enzymes are very specific to pH. If above or below this optimum pH, the H+ or OH- ions (in acids or alkalis) can disrupt the ionic or hydrogen bonds in enzymes, breaking their tertiary structure apart, denaturing the enzyme
How does the substrate concentration affect the rate of an enzyme controlled reaction?
The higher the substrate concentration, the higher the rate of reaction (more substrate molecules means more likely collision with substrate and enzyme so more active sites will be used)
This is true up to the saturation point where there are so many substrate molecules, there are not enough enzymes to catalyse substrate quicker (all active sites are full)
How does the enzyme concentration affect the rate of enzyme controlled reactions?
The more enzymes, the quicker the reactants are catalysed
Describe the lock and key model
Describes how enzymes and substrates bind
The enzymes are specific so there active site is rigid and are exactly complementary of the substrate and so binds to form an enzyme substrate complex. COMPLIMENTARY SHAPE
This was first thought, but then scientists realised this does not give a complete coverage of the formation of an enzyme substrate complex
Describe the induced fit model
Helps to explain why enzymes are so specific and so bond to only one substrate.
When binding to a substrate, the active site changes shape slightly so the substrate fits exactly forming an enzyme substrate complex.
This is widely accepted now
What are enzyme inhibitors?
They are molecules that bind to enzymes, inhibiting their actions (slowing down the rate of the reaction they catalyse)
How do competitive inhibitors work?
A molecule of the inhibitor has a similar structure to the substrate. This means they compete with the substate to bind with the enzyme. They bind with the enzyme but no reaction occurs, preventing the formation of enzyme substrate complexes, by blocking active sites. Slowing the rate of reaction.
How do non-competitive inhibitors work?
Non competitive inhibitors bind to the enzyme away from it’s active site (ask about it’s name). This causes the shape of the active site to change so that substrates can no longer bond to it, so less enzyme substrate complexes can form.
What does increasing the concentration of substrates have on an enzyme controlled reaction in the presence of non-competitive inhibitors?
No effect, enzyme activity is still inhibited