Proteins and Enzymes Flashcards
Describe the structure of a protein
Amino acid polymers joined together by peptide bonds
Amino acid structure: central carbon atom attached an amine group, hydrogen atom, carboxyl group and R group
Explain the formation of a peptide bond
Condensation reaction - water is removed
water is formed by hydrogen atom on amine group and OH group from carboxylic acid
O=C - NH
Define primary structure
Sequence of amino acids in a polypeptide chain
Define secondary structure
Hydrogen bonds form between amino acids
Form alpha helix or beta pleated sheats
Define tertiary structure
Bonds form between the R group
3D structure created
Hydrogen bonds
Disulfide bridges
Ionic bonds
Hydrophilic - hydrophobic interactions
Define quaternary structure
Interaction of 2 or more polypeptide chains held together by bonds
Describe the structure of haemoglobin
4 polypeptide chains
2 alpha helix, 2 beta pleated sheets
4 haem groups = prosthetic group
Haem group is Fe
Structure and function of globular proteins
Spherical
Hydrophilic on the outside and hydrophobic on the inside
Soluble - Transported easily
Functions: enzymes, hormones or proteins
Globular protein with prosthetic groups are conjugated proteins
Structure and function of fibrous proteins
Long and thin
Strong and insoluble
Structural roles
e.g collagen, keratin, elastin
Describe the structure and function of collagen
3 polypeptide chains wrapped tightly around each other
chains held together by hydrogen bonds
found in connective tissue
what are enzymes?
Biological catalyst that speed up chemical reactions in our body by reducing activation energy
Explain the lock and key model
Substrate fits in active site perfectly
Active site is complementary
Substrate binds to active site and forms enzyme-substrate complex
Enzyme coverts substrate to product to form enzyme substrate complex
Product released
Explain the induced fit model
Active site is not completely complementary to the substrate
Substrate enters active site and forms enzyme substrate-complex
Enzyme undergoes conformational change which converts substrate to product, forming enzyme product complex
Product released
How does enzyme concentration affect rate of reaction?
Enzyme concentration increases
More active sites available for substrate molecules
More frequent collisions so more enzyme-substrate complexes
Rate increases
However, rate plateaus as something else becomes limiting factor
How does substarte concentration affect rate of reaction?
Substrate concentration increases
More substrate molecules to bind to enzyme active site
More frequent collisions so more enzyme substrate complexes
Rate increases
However, saturation is reached and every active site is occupied
How does temperature affect rate of reaction?
At low temperatures, rate is slow
enzyme and substrates have low kinetic energy
less frequent collisions so less ES complexes
At high temperature, rate increases
enzyme and substrates have more kinetic energy
more frequent collisions so more ES complexes
If temperature too high then enzyme denatures so substrate cant bind to enzymes active site as it is no longer complementary
How does pH affect rate of reaction?
Different enzymes have different optimum pH
If pH deviates, charge of the enzyme could change, which breaks ionic bonding and hydrogen bonding in tertiary structure
Enzyme denatures and is no longer complementary to substrate
What is temperature coefficient?
Rate at higher temp
Q10 = —————————-
Rate at lower temp
If Q10 = 2, the rate doubles for every 10oC
What is a cofactor?
non-protein molecules that need to be bound to an enzyme to function
They are not chemically changed
what are coenzymes?
organic molecules that are chemically changed during a reaction
Explain a competitive inhibitor
Bind to the active site of an enzyme
Blocks the active site for the substrate
Effect can be reduced by increasing substarte concentration
Explain a non competitive inhibitor
Bind to the allosteric site of the enzyme
Changes structure of active site so substrate can bind
Effect cannot be reduced
Reversible vs irreversible inhibitors
Reversible inhibitors form weak bonds and can be removed easily
Irreversible inhibitors form strong covalent bonds so cant be remove easily
What is end product inhibition?
the final product of a metabolic pathway inhibits an enzyme that acts earlier in the pathway
