Proteins (3.1.4) Flashcards
Define a dipeptide
Forms from a condensation reaction between 2 amino acids
Define a polypeptide
Forms from the condensation of more than 2 amino acids
What are the monomers of proteins?
Amino acids
How many polypeptides form a protein?
1 or more
Describe the primary structure of a protein
-The sequence of amino acids in the structure
-sequence differs in each chain
Describe the secondary structure of a protein
-Sequence of amino acids causes parts of a protein molecule to bend into an alpha helix or fold into a beta pleated sheet
-Hydrogen bonds form between the carbon to oxygen double bond groups of the carboxyl group of 1 amino acid and the H in the amine group of another to hold the secondary structure together
Describe the tertiary structure of a protein
-Further folding of the structure forms a unique 3D shape held together by hydrogen, ionic and or disulphide bonds
-Ionic bonds or disulphide bridges form between the R groups, must be a sulphur present in the R group for a disulphide bridge to form
Describe the quaternary structure of a protein
-Protein made up of more than one polypeptide chain
-Only occurs in some proteins such as haemoglobin
What happens if one amino acid in the sequence of the primary structure is different?
Bonds holding structure together will form in a different location during the secondary structure resulting in a different 3D shape, causing the protein to change function or lose it
What happens to the structure when a protein is denatured?
The bonds holding the secondary and tertiary structure break, therefore losing its unique 3D shape
When will a protein denature?
-When the temperature is too high (too much KE)
-too high/low pH (too many H+ or OH- ions)
Explain the food test for proteins?
1) Add biuret solution (blue) to protein sample
2) If proteins are present = solution turns to purple
Many proteins are enzymes, what do enzymes do?
Catalyse (speed up) reactions by lowering activation energy
How do enzymes lower activation energy?
Lowered when the substrate binds the the active site of the enzyme
Describe the stages of the induced fit model
1) Substrate isn’t complimentary to the active site (cannot bind) as it does not have the correct tertiary structure
2) substrate can induce a conformational change in the tertiary structure of the active site allowing substrate to bind and form and enzyme - substrate complex
What is a conformational change?
A change in shape
What is a substrate?
The molecule that the enzyme reacts with
Explain enzyme specificity
-Tertiary structure of the active site is extremely specific
-Only complimentary substrates can bind to the active site to form an enzyme - substrate complex
What factors can effect enzyme activity?
-temperature
-pH
-enzyme concentration
-substrate concentration
-enzyme inhibition (competitive and non competitive)
How does temperature effect enzyme activity?
Temperature increases = Kinetic energy of the molecules increases = more likely the substrate and enzyme with bind to form an enzyme - substrate complex
Describe the optimum temperature for enzymes
-Temperature most enzyme - substrate complexes are formed is 40°C
-If the enzyme denatures H bonds are hydrolysed, changing the tertiary structure of the active site
How does pH effect enzyme activity?
-Activity will rise as pH increases and will peak
-If there is an imbalance of pH (H+ and OH- ions) this can disrupt the tertiary structure = substrate can no longer compliment active site
What effect does enzyme concentration have on enzyme activity?
-rapidly increases as more active sites are available for complementary substrates
-plateau’s as there’s not enough substrates, some active sites are left empty
What effect does substrate concentration have on enzyme activity?
-increases rapidly as there is more substrates for active sites
-plateau’s similar to enzyme conc as there are not enough active sites available for the substrates
