Proteins And Enzymes Flashcards
Structure of an amino acid
H2N-CHR-COOH
NH2 = amine group
R = variable side chain. Can be:
- positive
- negative
- hydrophobic
- hydrophilic
COOH = carboxylic acid group
Describe how a dipeptide is formed
Condensation reaction
Produces peptide bond
OH from carboxylic group combines with H from amine group in second amino acid
Water produced
Describe the structure of proteins
Polymer of amino acids
Joined by peptide bonds
Formed by condensation reaction
Primary structure is number and order of amino acids
- Secondary structure is folding of polypeptide chain into alpha helix and beta pleated sheets due to Hydrogen bonding
- tertiary structure is 3D shape due to hydrogen bonds and ionic bonds and disulfide bridges
- quaternary structure is 2 or more polypeptide chains joined together
Describe how an enzyme substrate complex increases the rate of reaction
- reduces activation energy
- due to bending bonds
When a pathogen causes an infection, plasma cells secrete antibodies that destroy this pathogen .
Explain why these antibodies are only effective against a specific pathogen
- Antigens have a specific tertiary structure
- Antibody is complementary to antigen
- antibody-antigen complex forms
Define activation energy
The minimum amount of energy required for a successful chemical reaction
How do enzymes increase the rate of the reaction
- lowers activation energy
- stressing/distorting bonds in substrate
- during formation of enzyme-substrate complex
Describe how a change in the base sewuence of a DNA coding for an enzyme may result in a non functional protein
- change in primary structure changes sequence of amino acids
- hydrogen/ionic bonds and disulphide bonds form in different positions
- alters the tertiary structure of the enzyme’s active site
- no enzyme-substrate complexes can be formed
What is a proteome of a cell?
Full range of proteins a cell is able to produce
Describe and explain how you can use the bieuret test to distinguish a solution of lactase enzyme from a solution if lactose
- add bieuret solution to both solutions.
- Lactase enzyme = purple
- because lactase is a protein
Sucrase doesnt hydrolyse lactose. Use your knowledge of the way in which enzymes work to explain why
- lactose has a different shape
- doesnt bind to the sucrase active site
- substrate and active site are not complementary
- No enzyme substrate complexes form
Describe the induced fit of enzyme action
- active site not complementary
- active site changes shape as substrate binds
- distorts/stresses bonds within substrate
-lowers activation energy - enzyme-substrate complex forms
Describe one way the lock and key model differs from the induced fit model
LAK: Active site doesnt change shape whereas IF: active site DOES change shape
- active site rigid vs flexible
- substrate is complementary to active site
An enzyme catalyses only one reaction. Explain why.
Enzymes active site has a specific tertisry structure
Only one substrate binds
Suggest why a protein can ve the substrate for two different enzymes
- different parts of protein have different amino acif sequences so have different shapes
- each enzyme active site is a specific shape and complementary to a different part of the protein
Diabetes mellitus is a disease that can lesd to an increase in blood glucose concentration. Some diabetics need insulin injections. Insulin is a protein so it cannot be taken orally. Suggest why insulin cab not ve taken orally.
- broken down by enzymes
- insulin no longer functional
What is the effect of substrate concentration on the rate of an enzyme controlled reaction
- increases then plateaus
- plateaus because no active sites are available/all AS are filled
- max number of enzyme-substrate complexes form per second
Explain how a competitive inhibitor works
- inhibitor similar shape to substrate
- inhibitor enters active site
- less substrate binds/ fewer ESC per second formed
Describe how a non-competitive inhibitor works
Attaches to enzyme at allosteric site (site other than AS)
- changes shape of active site
- so active site no longer complementary to substrate
- less/no substrate binds and fewer ESC form
Explain the results without inhibitor (curve A) shown in figure 6
- increases because more ESC form
- levels off because no free active sites
Figure 6 shows that max initial rate of reaction when a competitive inhibitor was present ( curve B) is different from when a non-competitive inhibitor was present (curve C)
Explain this difference.
- competitive inhibitor binds to active sites vs non competitive inhibitor binds to allosteric site
- competitive inhibitor binding doesnt change shape of AS vs non competitice inhinitors do
- with competitive inhibitor, high sub concentration = enzyme still available but non competigive at high sub conc = enzymes no longer available
- at high sub conc, ES collisions likelihood increases with comp inhibitor but not possible with noncomp inhibitor
describe how amino acids join to form a polypeptide so there is always a NH2 at one end and COOH at other.
- . One NH2 group joins to a COOH group to form a peptide
bond; - (So in chain) there is a free NH2 group
at one end and a free COOH group
at the other
