Proteins Flashcards
What are the 4 functions of proteins?
Structural- collagen, keratin
Signalling- hormones
Catalysts- enzymes that speed up reactions
Transport- haemoglobin transports oxygen
What is the specific name for protein monomers?
Amino acids
What is the specific name for protein diamers?
Dipeptides
What is the specific name for protein polymers?
Polypeptides (peptide is a short polypeptide)
Draw and label the structure of an amino acid:
How many different amino acids are there?
20 which all have the same general structure only the variable group changes
Draw and label the formation of a dipeptide:
How are amino acids joined together to form a dipeptide?
-Condensation reaction
-Water is removed
-Peptide bond forms between OH of carboxyl and H or amine group
What are the 4 levels of protein structure?
- Primary structure
- Secondary structure
- Tertiary structure
- Quaternary structure
What is the sequence of amino acids determined by?
Your genes
What can the secondary structure of protein formation be described as?
The initial folding of a polypeptide into an alpha helix or beta pleated sheet due to hydrogen bonding.
Where do hydrogen bonds form during protein formation?
between the C=O groups of the carboxyl group of one amino acid and the H in the amine group of another amino acid
What can the tertiary structure of protein formation be described as?
-The further folding of the secondary structure
-To form a unique 3D shape.
- Held in place by ionic, hydrogen and disulphide bonds.
Where do the ionic and disulphide bonds form during protein formation?
-The ionic and disulphide bonds form between the R groups of different amino acids.
-Disulphide bonds only sometimes occur, as there must be a sulfur in the R groups for this bond to occur
What can the quaternary structure of protein formation be described as?
A protein made up of more than one polypeptide chain e.g haemoglobin formed from 4 polypeptide chains
Why is the primary structure of a protein so important?
If even one amino acid in the sequence is different then it will cause the ionic/hydrogen/disulphide bonds to form in a different location and make a diff 3d shape.
What is the impact of even one amino acid changing in the sequence?
-Enzymes will have a different shaped active site (will be non-functioning)
-Carrier proteins will have a different shaped binding site
What are enzymes?
Biological catalysts that increase the rate of reaction by lowering the activation energy
What is the activation energy?
The energy required to cause molecules to collide hard enough to react (to break and form new bonds)
What is the active site of an enzyme?
the region where a complementary substrate can bind to form an enzyme-substrate complex
What is a metabolic pathway?
a series of enzyme catalysed reactions where the product of a reaction is the reactant in the next reaction eg. respiration
What is the lock and key model for enzymes?
- The shape of the active site is fixed and does not change shape
- Active site is complementary to substrate before during and after forming an enzyme-substrate complex
What is the induced model of enzyme action?
- Before the reaction, the active site is NOT complementary to substrate
- Shape of active site changes as enzyme-substrate complex forms
- This stresses bonds or brings substrates closer together
- Lowers the activation energy
What type of structure do enzymes have?
A complex tertiary structure
What do enzymes control?
All intracellular and extracellular reactions in organisms
Why would a molecule not get broken down by a specific enzyme?
The specific structure of the active site is complementary to the shape of one substrate, forming an enzyme-substrate complex
What are the two types of non-functional proteins?
- Mutations
- Denatured
How do you know if a protein has mutated?
- Changes to the base sequence of DNA
- Change to the base sequence of mRNA
- Change to the primary structure of protein which leads to change to tertiary structure
How do you know if a protein has denatured?
- Increase in kinetic energy
- breaks the hydrogen + ionic bonds between variable groups
- change to the tertiary structure of the protein
What is the result of a protein mutating or denaturing?
- changes the shape of the active site
- substrate is no longer complementary
- no enzyme-substrate complex forms
What are the 5 factors that affect the rate of enzyme-catalysed reactions?
- Temperature
- PH
- Enzyme concentration
- Substrate concentration
- Inhibitors
Describe and explain the graph for enzyme rate of reaction against temperature:
- At 0 degrees enzymes are frozen and catalyse no reactions
- The peak of the curve shows the optimum temperature for enzyme activity is 37 degrees
- When the graph hits the x axis again it shows that enzymes have denatured
Explain the effect of temperature on enzyme catalysed reactions:
- As temperature increases, the rate of reaction increases due to molecules gaining more kinetic energy.
- Most enzyme-substrate complexes form at optimum temperature
- As temp increases past 37 degrees, the rate of reaction decreases due to enzymes denaturing until it stops
Describe what the graph for time against volume of product for the effect of temp on an enzyme catalysed reaction looks like:
What is hydrogen peroxide?
toxic cellular waste product that must be broken down
What is the equation for the breakdown of hydrogen peroxide?
Hydrogen peroxide ———> water + oxygen
catalase enzyme breaks down
What does the first part of the graph for the progress of an enzyme reaction graph mean?
-initially lots of substrate and empty active sites
-many E-S complexes can form
-reaction starts off fast
What does the graph for the progress of an enzyme reaction look like?
What does the second part of the enzyme progress reaction graph mean?
-less substrate, more product
-more difficult for E-S complex to form
-reaction slows
What does the third part of the enzyme progress reaction graph mean?
-no more substrate
-no E-S complexes
-reaction stopped
How do you calculate the mean rate of reaction?
amount of product formed/ time taken to form product
Describe the graph for enzyme rate of reaction against PH:
- Enzyme activity increases until it reaches optimum PH
- Enzyme activity begins to decrease as enzyme is being denatured due to acidic conditions
Explain the effect of PH on enzyme catalysed reactions:
- Enzymes have an optimum PH
- Increasing or decreasing PH away from optimum causes enzyme activity to decrease
- The H+ or OH- will interact with hydrogen or ionic bonds
- Changes tertiary structure and active site shape so less e-s complexes form
What happens at PH 2 during an enzyme catalysed reaction and what does this graph look like?
-increased H+ attracted to amino acids of enzymes
-hydrogen/ ionic bonds of 3 degrees disrupted
-active site denatures
-fewer e-s complexes form
Describe the graph for enzyme rate of reaction against enzyme concentration:
Explain the effect of enzyme concentration on enzyme catalysed reactions:
- Rate increases with enzyme conc in positive correlation
-because there are more e-s complexes forming (more successful collisions)
-if substrate runs out, adding more enzymes will make no diff to rate of reaction
Describe the graph for enzyme rate of reaction against substrate concentration:
- Rate increases with substrate conc in positive correlation
-because there are more e-s complexes forming (more successful collisions) until all active sites are occupied
-enzyme conc is now the limiting factor and adding more substrate will not change rate
What do enzyme inhibitors do?
Slow down enzyme catalysed reactions
What are the two types of inhibitors that affect the rate of enzyme-catalysed reactions?
- Competitive
- Non-competitive
What does the graph for effect of competitive and non-competitive inhibitors on enzyme activity look like?
Explain the effect of competitive inhibitors on enzyme activity:
- Competitive inhibitors have a similar shape to substrate
-They can also bind to active site - This stops e-s complexes from forming
-The proportion of substate to competitive inhibitor will affect how much the rate of reaction changes
Explain the effect of non-competitive inhibitors on enzyme activity:
-Non-competitive inhibitors bind to the enzyme but not at the active site
-Changes the tertiary structure of the active site permanently
-No more e-s complexes form as no longer complementary
-Changing conc of substrate won’t make any difference
