Proteins and Enzymes Flashcards
What is a protein?
A polymer built up of one or more amino acids
What is a proteins shape essential to?
Their function
What is an amino acid?
A protein monomer
What groups does an amino acid contain?
- An amine group- A carboxylic acid group- A r group- A hydrogen
What is significant about an amino acids R group?
The R group is different in all amino acids
What reaction forms a dipeptide?
A condensation reaction
What is the bond called that forms between amino acids?
A peptide bond
How is a peptide bond formed between amino acids?
The OH group of the carboxylic acid is removed and a h from the amino group is removed to form water and the bond forms between the carbon of one amino acid and the nitrogen of another
What is a dipeptide?
Two amino acids joined by a peptide bond
What are the four functions of proteins?
- Enzymes- Antibodies- Transport - Structure
What is the primary structure of a protein?
The sequence of amino acids
What bonds join amino acids in the primary structure?
Peptide bonds
How does the sequence of amino acids effect how the protein folds?
The different R groups on the amino acids have slight charges (delta)
What is the secondary structure of a protein?
The long chains of amino acids fold into regions with repeating patterns
Give examples of a proteins secondary structure
- Alpha helix’s- Beta pleated sheets
What bonds are present in a proteins secondary structure?
Peptide bonds between amino acids and hydrogen bonds holding the regions together
What is a proteins tertiary structure?
Its final 3D shape
What bonds are present in a proteins tertiary structure?
Peptide bonds(primary), hydrogen bonds(secondary) and ionic bonds and disulphide bridges
What is the role of ionic bonds and disulphide bridges in a proteins tertiary structure
They hold the protein together
What is a proteins quaternary structure?
A protein made from multiple polypeptide chains
Give an example of a protein with a quaternary structure
Haemoglobin
What is the test for proteins called?
The biuret test
How do you carry out the test for proteins?
Add the biuret reagent
What is the biuret reagent made up of?
Copper sulphate and sodium hydroxide
What is a positive result for the biuret test?
Colour change from blue to purple
What is a negative result for the biuret test?
No colour change (remain blue)
How do you answer a protein shape question?
The tertiary structure of the active/binding site is complimentary to the shape of the substrate and can form an enzyme-substrate complex/an antibody-antigen complex
How do you answer a non-functional protein question? (mutation)
A change in the proteins primary structure causes changes in the proteins tertiary structure which changes the shape of the active site therefore the substate is no longer complimentary and cannot form an enzyme-substrate complex
How do you answer a non-functional protein question? (Denature)
A change to the ionic bonds in a proteins tertiary structure which changes the shape of the active site therefore the substate is no longer complimentary and cannot form an enzyme-substrate complex
What happens to enzymes at 0 degrees?
They cannot catalyse because they are frozen but are not denatured
What happens to the rate of reaction of enzyme reactions as temperature increases?
It increases up to the optimum temperature
Why does the rate of enzyme catalysed reactions increase up to the optimum temperature?
As temperature increases molecules vibrate more therefore more collisions will take place with a higher percentage being successful and colliding with the activation energy therefore more enzyme - substrate complexes are formed
What happens to the rate of enzyme catalysed reactions after the optimum temperature?
After optimum temperature molecule energy continues to increase up to a point where vibrations cause internal bonds to break which changes the tertiary structure leading to a change in the active site (denature)
Does optimum pH change with enzymes?
Yes, both the optimum point and the denature point change depending on the function of the enzyme and where it is located
What happens to enzymes as the pH increases/decreases away from the optimum?
enzyme rate of reaction decreases as the increase/decrease in OH- or H+ ions interact with the hydrogen and ionic bonds causing the tertiary structure to change and the active site will no longer be complimentary to the substrate and an enzyme-substrate complex won’t be able to form
What happens to rate of reaction as enzyme concentration is increased?
it increases
Why does rate of reaction increase as enzyme concentration increases?
more successful enzyme-substrate collisions will take place at a quicker rate therefore more enzyme-substrate complexes will form
What happens to the rate of reaction of a reaction where enzyme concentration is increased if left to continue?
The rate will continue to increase up to the point where all substrate is used up therefore adding more enzyme will have no effect on the rate (substrate concentration becomes the limiting factor)
What happens to rate of reaction as substrate concentration is increased?
rate of reaction increases
Why does rate of reaction increase as substrate concentration increases?
more successful enzyme-substrate collisions will take place at a quicker rate therefore more enzyme-substrate complexes will form
What happens to the rate of reaction of a reaction where substrate concentration is increased if left to continue?
The rate will continue to increase up to the point where all enzyme active sites are occupied at any one time therefore adding more substrate will have no effect on the rate (enzyme concentration becomes the limiting factor). If no more substrate is added rate will decrease as substrate is used up.
How do competitive inhibitors work?
They have a similar shape to the substrate and can bind to the active site, preventing enzyme-substrate complexes from forming
How do competitive inhibitors affect rate of reaction?
The proportion of substrate to competitive inhibitor will affect how much effect it has on the rate of reaction
How do non-competitive inhibitors work?
They bind to the enzyme at an alternative location to the active site which changes the shape of the active site so that enzyme-substrate complexes can no longer form
How do competitive inhibitors affect rate of reaction?
Increasing substrate concentration will have no effect, rate will increase up to the point where no enzymes have a complimentary active site
What type of bond joins together two amino acids?
Peptide
Describe an enzyme
A biological catalyst
Which colour indicates a positive result in the biuret test?
Purple
What molecules do proteins consist of?
Amino acids
How does competitive enzyme inhibition work?
The inhibitor binds to the enzymes active site as they have a similar shape to a substrate molecule
Which organelle produces enzymes?
Ribosomes
What makes an enzyme highly specific?
Its tertiary protein structure
What is the test for proteins known as?
Biuret test
What is the name given to the intermediate molecule formed when a substrate has joined to the active site of an enzyme?
Enzyme-substrate complex
What is it known as when the active site of an enzyme changes shape and is no longer complementary to the substrate?
Denaturation
Where does the enzyme bind to the substrate?
Active site
What is the part of an amino acid that doesn’t stay the same called?
Variable (R) group
Where on an enzyme do non-competitive inhibitors bind?
A site on the enzyme which isn’t the active site
Within protein structure, which bonds are the weakest?
Hydrogen
Which protein structure can show an alpha helix structure?
Secondary
What term is used to describe the pH at which an enzyme works best?
Optimum pH
When an enzyme starts to denature, which type of bond breaks first?
Hydrogen bonds
Which protein structure is the sequence of amino acids in a polypeptide chain related to?
Primary
When starch and amylase are mixed in the presence of iodine solution, the blue-black colour rapidly disappears. This is due to the formation of which molecule?
Maltose
Enzymes differ from inorganic catalysts in that they are highly specific. Which property of an enzyme is responsible for this specificity?
The tertiary structure of the active site
Succinic acid dehydrogenase is the enzyme which catalyses the oxidation of succinic acid during cell respiration. If malonic acid is added to the system, the rate of reaction is reduced. An increase in the substrate concentration, succinic acid, increases the rate of reaction again. Using this information what might be deduced about the action of malonic acid?
It has a similar molecular configuration to succinct acid
A sample of a starch suspension was tested with iodine solution and the result was a blue-black colour. A second sample of the starch suspension was tested with Benedict’s reagent and the result was a blue colour. A third sample of the starch suspension was mixed with amylase and incubated at 30 oC for 10 minutes and then tested with Biuret reagent. What was the resulting colour of the third sample?
Purple
When an enzyme is subjected to temperatures above the optimum, it denatures. Which bonds are the first to be disrupted by high temperatures?
Hydrogen bonds
