proteins and enzymes Flashcards
What is the COOH group of an amino acid
carboxyl group
what is the R group of an amino acid
side group
what is the NH2 of an amino acid
amine group
how many amino acids are there in all organisms
there are 20 and they all differ in their side {R] group
what are polypeptide
formed by the condensation of many amino acids and a water molecule is released and a peptide bondis formed
what are dipeptides
formed by the condensation of 2 amino acids
describe a primary structure of a protein
sequence of amino acids in the polypeptide chain joined by peptide bonds
describe a secondary structure of a protein
sequence of amino acids have hydrogen bonds in the chain and holds it and makes it coil into an alpha helix or a beta pleated sheet
describe a tertiary structure of a protein
3D folding of polypeptide due to interaction between R groups hold by ionic, hydrogen bonds and disulfide bridges
describe a quaternary structure of protein
a protein held by more than one polypeptide chain that determines 3D shape e.g haemoglobin
- formed by interactions between polypeptides
test for proteins
biuret reagent
1. add sodium hydroxide
2. add copper sulfate solution
3. positive=colour change blue to purple
what are enzymes
biological catalysts that speed up a chemical reaction without being used upand they do this by loweing the activation energy
Explain the specificity of enzymes
● Specific tertiary structure determines shape of active site
○ Dependent on sequence of amino acids (primary structure)
● Active site is complementary to a specific substrate
● Only this substrate can bind to active site, inducing fit and forming an enzyme-substrate complex
Describe how models of enzyme action have changed over time
● Initially lock and key model (now outdated)
○ Active site a fixed shape, complementary to one substrate
● Now induced-fit model
what happens when a enzyme binds to the substrate
enzyme substrate complexes are formed
what is the acceptable model of enzyme action
induced fit model
describe the induced fit model
- Substrate binds to active site not completely complementary to
active site of enzyme - Causing active site to change shape slightly so it is complementary to substrate
- So enzyme-substrate complex forms
- Causing bonds in substrate to bend / distort, lowering activation energy
describe the lock and key theory
shape of enzyme active site is complementary to substrate exactly-lowers activation energy
enzyme substrate complex is formed
what are the factors that affect enzymes
temperature
PH
substrate concentration
enzyme concentration
competitive/non competitive inhibitors
how does temperature affect enzymes
● As temp. increases up to optimum, rate of reaction increases
○ More kinetic energy
○ So more Enzyme substrate complexes form
● As temp. increases above optimum, rate of reaction decreases
○ Enzymes denature - tertiary structure and active site change shape
○ As hydrogen / ionic bonds break
○ So active site no longer complementary
○ So fewer enzyme Substrate complexes f
how does PH affect enzymes
if PH is too high or low it will interfere with the charges of the amino acids
rate of reaction decreases
○ Enzymes denature - tertiary structure and active site change shape
○ As hydrogen / ionic bonds break
○ So active site no longer complementary
○ So fewer E-S complexes form
how does enzyme concentration affect enzymes
more enzymes mean more active sites so more enzyme substrate complexes form. rate of reaction increases until substrate concentration becomes the limiting factor[not enough substrates]
how does substrate concentration affect enzymes
more substrates mean more enzyme substrate complexes form which increase rate of reaction
when all substrates are complementary enzyme concentration becomes the limiting factor as all active sites are saturated
how does a competitive inhibitor affect enzymes
● As concentration of competitive inhibitor increases, rate of reaction decreases
○ Competes for / binds to / blocks active site
○ So substrates can’t bind
○ So fewer enzyme-substrate complexes form
● Increasing substrate concentration reduces effect of inhibitors
