12.2 Proteins and enzymes Flashcards
Haemoglobin function
Allows oxygen to bind to be transported around the organism
Antibody function
binds to specific antigen, used in organisms immune response to pathogen
Enzymes fucntion
Reduces activation energy within a metabolic reaction
Actin and myosin function
Structural protein involved in muscle contraction
Keratin function
Structural protein found in nails, hair and hooves
Collagen function
Structural protein found in tendons
What are proteins made from?
Amino acids
How many types of amino acids are there?
20
What is the general structure of an amino acid?
NH2 - C(RH) - COOH
What two groups do amino acids have ?
Amino group - NH2
Carboxylic acid group - COOH
How do two amino acids join?
By condensation reaction to form a dipeptide joined by peptide bonds
What does a peptide chain always have?
An amine group at the N terminal and a carboxyl group at the C terminal
What is the protein structure?
Primary, secondary, tertiary, quaternary
What is primary structure?
The number and sequence of amino acids in a polypeptide chain
What is secondary structure?
Alpha helices or beta pleated sheets
Held together by weak hydrogen bonds
What is tertiary structure?
Contains 3 types of bonds -
Weak hydrogen bonds
Ionic bonds
Disulphide bridges
Gives them a specific active site shape
What is quaternary structure?
Two or more polypeptide chains joined together
What is denaturation?
A permanent change to the specific 3d tertiary structure of a protein
What is the structure of proteins?
A polymer of amino acids joined by peptide bonds formed by condensation reaction. Primary structure is order and sequence of amino acids. Secondary structure is folding of polypeptide chains due to weak hydrogen bonds, forming alpha helices and beta pleated sheets. Tertiary structure is the 3d folding due to hydrogen bonding and ionic/disulphide bonds. Quaternary structure is two or more polypeptide chains joined together.
How do you test for proteins?
Add equal volume of buret solution
Colour changes from blue to purple if protein is present
Activation energy definition
The m minimum energy required for a successful chemical reaction
What do enzymes act as?
Biological catalysts
They take part in the reaction but do not get used up
What do enzymes do?
Increase the rate off reaction by lowering the activation energy by stressing the bonds in the substrate during forming an enzyme substrate complex
Describe the lock and key theory
The active site is rigid and doesn’t change shape
The substrate binds to the enzymes active site
The substrate is complimentary to the active site
Products are formed and no longer fit the active site
The enzyme is free to take part in another reaction
Describe the induced fit model
Thye substrate enters the enzymes active site and binds to it forming an enzyme substrate complex
This induces a change in the shape of the active site
This distorts the bonds, lowering the activation energy
When the substrate leaves, the active site returns to its original shape
Contrast the way that the lock and key is different to the induced fit model
The active site of the lock and key model does not change shape whereas in the induced fit model the active site does change shape
One enzyme will catalyse one reaction, explain why
Enzyme has a specific active site shape
Only one substrate fits the active site
Suggest why a protein can be a substrate for 2 different enzymes
Different parts of the protein have different amino acid sequences so are a different shape
each enzyme active site is a specific shape and complementary to a different part of the protein
What factors affect enzyme action
Temperature
pH
Inhibitors
Substrate concentration
Optimum temperature definition
The maximum energy that can be supplied to the molecules before the hydrogen and ionic bonds start to break
What happens when you increase the temp of a reaction?
The atoms have more kinetic energy and vibrate more. This breaks the hydrogen and ionic bonds between the amino acids, causing a change in the tertiary structure and active site. Active site no longer complimentary so less ESC can be formed. Enzyme denatures
effect of pH on enzyme action
Changing the pH changes the charge on the R group and the ionic bonds are broken. The active site changes and then substrate can’t bind. Less ESC formed and enzyme is denatured
effect of substrate concentration
Low substrate concentration = less frequent successful collisions so fewer ESC. The substrate is a limiting factor.
High substrate concentration = more active sites filled, rate of reaction increases, more ESC formed, substrate is a limiting factor.
The rate of reaction doesn’t increase any further as all active sites are saturated. Enzyme concentration is now the limiting factor.
Inhibitors definition
Substances which decrease the rate of reaction
How do competitive inhibitors work?
Have similar structure to substrate
Inhibitor binds to active site
Less substrate binds so less ESC formed
Less product is produced
How do non-competitive inhibitors work?
Inhibitor is not similar shape to substrate
Inhibitor binds away from active site at allosteric site
Changes the shape of active site
Less substrate binds so less ESC formed
Less product formed
How do you overcome a competitive inhibitor?
Increase substrate concentration
