2b. Protein and enzymes Flashcards
what elements do proteins contain
C H O N
What is a protein
A polymer made of one or more chains of amino acid monomers - a polypeptide
Some proteins are conjugated - have other chemicals within their structures
What are amino acids made of
An amine
A carboxyl group
A side chain
what is the general structure of an amino acid
R
H2N- C - COOH
H
What is a polypeptide
Many amino acids linking together by a condensation reaction
How do amino acids form chains
By linking together.
2 Amino acids join to form a dipeptide
The bond between amino acids is a dipeptide bond
Condensation reaction
What is the primary structure of proteins
The sequence of amino acids in a polypeptide chain
What is the secondary structure of proteins
The folding of regions of the polypeptide chain due to the formation of many weak H-bonds.
Produces either an alpha helix or a beta-pleated sheet
What is the tertiary structure of a protein
The further folding of the whole chain into a specific shape.
Stabilised by ionic bonds, hydrogen bonds, and disulphide bonds.
It’s the specific shape of the tertiary structure that determines its function
What happens to a protein is subjected to high temperatures or extreme pH
It can become denatured.
H-Bonds break first as they are very weak
Disulphide bonds are stronger and can withstand higher temperatures.
When bonds break the tertiary stucture is lost and the protein loses its function
What is the quaternary structure of a protein
Found in proteins made out of more than one polypeptide chain
What are the different types of protein shape
Globular
Fibrous
What is a fibrous protein
Form long chains running parallel to each other with cross-bridges between the chains.
Produces very stable molecules like collagen.
Tend to have a structural role in organisms
What are globular proteins
Carry out metabolic functions
e.g enzymes and haemoglobin
How do you test for proteins
Biuret test
What is the biuret test
- Add biuret solution to a sample of the solution to be tested
-Pale blue -> Lilac
What is chromatography used for
Used to separate mixtures of monosaccharides or amino acids.
Molecules have a different molecular size and solubilities.
The smaller or more soluble the molecule, the further is will move
What is an Rf value used for and what is the calculation
To identify the spots that appear on the chromatogram and compare with different chromatographs with the same solvents.
Rf = Distance from origin to solute / Distance from origin to solvent front
What is activation energy
The minimum amount of energy required for a chemical reaction to take place
What are enzymes
biological catalysts which increase the rate of a reaction by lowering the activation energy
What happens to cells without enzymes
The temperature in living cells would be too low for chemical molecules to react fast enough to support life
What are the different types of enzymes
Intracellular (inside cells) and extracellular (outside cells)
How does ezymes structure relate to its function
Globular protein molecules so each enzyme and its active site has a specific tertiary structure and shape
How do enzymes bind
Enzymes usually only work on the substrate which molecular shape is complementary to the active site.
They combine reversibly to form an enzyme-substrate complex
What did the lock and key model suggest
The substrate combines with the enzymes active site precisley.
The active site is always the exact complementary shape at optimum temp so reactions are fastest in these conditions.
What proved the lock and key model false
The enzyme is considered a rigid structure however later proved to be flexible
What does the induced fit model suggest
The substrate and active site are not exactly complementary to begin.
But when the substrate binds to an enzyme, it induces a change in the enzymes structure and moulds to the substrate to form an E-S complex. It causes particular bonds in the substrate to undergo stress and distortion, thus reducing the activation energy needed to break the bond.
The active site changes shape to become complementary
Why is the induced fit model a better explanation of enzyme action
It explains how the binding of other molecules can affect enzymes shape and activity and also explains how the activation energy is lowered
What is the rate of reaction
The amount of product made per unit time
What are factors effecting enzyme action
Subtible temperature
Subtible pH
adequate supply of substrate and enzyme
Inhibitors
How does temperature effect enzyme action
As temperature increases, enzyme and substrate molecules gain more kinetic energy so move about more quickly.
They collide more frequently and so a greater number of enzyme-substrate complexes are formed so more product is made leading to an increased rate of reaction.
What happens to enzymes after optimum temperature
Enzymes are denatured.
H-Bonds break
Tertiary structure changes
Active site changes and substrate is no longer complementary
ES Substrates can no longer form
They higher the temperature the more enzyme molecules will denature
How does pH affect enzyme action
pH alters the charges on the amino acids of the active site
H-Bonds and ionic bonds in tertiary stucture may break and reform in different places
Alters shape of active site
substrate doesnt fit and no ES complexes form
Enzyme is denatured
How do you calculate pH
pH = -log10(H+)
How can pH of a solution be controlled
A buffer solution
How does substrate conc affect the rate of reaction
As conc of substrate increases, RoR increases.
There are more substrate molecules so more collisions and more ES complexes.
RoR reaches a max and remains constant at a certain conc of substrate. All the active sites are occupied/saturated – maximum number of ES complexes
The conc of enzyme is a limiting factor
What are the types of inhibitors
Competitive and non-competitive
What is a competitive inhibitor
Have a similar shape of active site.
Binds to active site which blocks any substrates from binding
Fewer ES Complexes
RoR is reduced
What is a non-competitive inhibitor
Bind to some other region of the enzyme, changes its tertiary sturcture and shape of active site
Fewer ES complexes form
RoR decreases
