2b. Biological Molecules: Protein & Enzymes Flashcards
What elements do all Proteins consist of?
N, H, C, O
What are Proteins?
Proteins are POLYMERS, made up of one or more chains of Amino Acid monomers
What are Polypeptides?
One or more chain of Amino Acid monomers
All Amino Acids are made of:
- carboxyl group
- amine group
- variable group (side chain) e.g Glycene (H)
Why do Amino Acids have different chemical properties?
Different R groups (variable groups)
How many types of Amino Acids are there?
20
Amino Acids can form ____ by linking together
Chains
What do two Amino Acids join to form?
Dipeptide + Water
What type of reaction is the joining of Amino Acids?
Condensation
What is the bond linking the two Amino Acids?
And Where?
- Peptide bond (strong covalent bond)
- Peptide bond between the Carbon from the Carboxyl group of one monomer to the Nitrogen from the Amine group of another
___ Amino Acids can be linked together by ______ to produce a long chain polymer called ____
- Many
- Condensation
- Polypeptides
How many levels does the Protein Structure have?
4
What are the 4 structures?
Primary
Secondary
Tertiary
Quaternary
What is the Primary Structure?
The sequence of amino acids in the POLYPEPTIDE CHAIN
What is the sequence in the Primary Structure?
- what amino acids the polypeptide consists of
- what order are they ordered in
Each ____ has a different sequence
protein
What is the Secondary Structure?
(hint - 3 steps)
- Folding of polypeptide chains in localised regions
- The sequence of amino acids are processed, and due to the many weak hydrogen bonds, parts of the polypeptide chains are bent into (alpha helix shapes), or bent and folded into (beta-pleated sheets)
- These secondary structures are stabilised through hydrogen bonds
Where are the Hydrogen Bonds in Secondary Structures found?
- they occur between the Oxygen from the Carboxyl group of one amino acid, and the Hydrogen from the Amine group of another amino acid
What are the Secondary Structures?
Alpha Helix
Beta-Pleated Sheet
What is the Tertiary Structure?
(hint - 2 steps)
- The further folding of the WHOLE chain, (including the Secondary Structure), which folds into specific unique 3D shapes
- The Tertiary Structure is stabilised by Ionic, Hydrogen and Disulphide bonds
What are Disulphide bonds?
Covalent bonds between sulphur-containing amino acids
Why don’t Disulphide bonds always occur?
Only occur if Sulphur is present in its R group (variable group)
What are the location of bonds in Tertiary Structure?
- ionic and disulphide bonds occur between the different R groups of amino acids
- hydrogen bonds occur between the Oxygen from the Carboxyl group of one amino acid, and the Hydrogen from the Amine group of another amino acid
What does the specific Tertiary Structural shape determine?
- function of protein
What conditions cause Protein Denaturation?
- extremely high temperatures
- extreme pH (too high or too low)
How does Protein Denaturation occur?
- Due to the change in conditions, the intermolecular forces between bonded R-Chains break + Hydrogen bonds
- This causes a change of shape of protein
Which order of bonds will be broken down first if Protein Denaturation occurs?
- Hydrogen bonds break down first, as they are very weak
- Ionic bonds
- Disulphide bonds can last longer as they are stronger, withstanding high temperatures
Why do proteins lose their function, if there is protein denaturation?
There is a change in shape of the Tertiary Structure
Give an example of a protein losing its function
- enzyme losing its unique active site shape
What is the Quaternary Structure?
- protein made up of MORE THAN ONE polypeptide chains e.g haemoglobin
Protein’s can either have a _______ or _______ molecular shape
- Fibrous
2.Globular
Describe Fibrous Protein Structure:
Fibrous Proteins form long chains which run parallel to each other forming cross bridges between the chains.
Describe how the structure of Fibrous Proteins helps their function:
- Fibrous Proteins form long chains which run parallel to each other forming cross bridges between the chains.
- This produces very stable molecules, which means fibrous proteins tend to have a very structural role in organisms
What type of protein is collagen?
What role does collagen play?
- Fibrous
- Gives strength and structure in (blood vessels, skin, tendons)
Name 2 other types of Fibrous Proteins:
- Keratin (Hair & Nails)
- Elastin (skin, blood vessels, lungs)
What role do Globular Proteins have?
Give 2 examples of Globular Proteins:
- Carry out metabolic functions
- Enzymes & Haemoglobin
Describe Test for Proteins:
- Add Biuret Solution (Potassium Hydroxide + Copper Sulphate) to solution
- If protein present colour change from blue -> lilac
- If no protein pale blue colour present from Copper Sulphate
What is Activation Energy?
What type of energy is usually used?
1.The energy required for a chemical reaction to take place
2. Heat
Define Enzymes in terms of catalysts:
Biological Catalysts, which increase the rate of reaction by lowering the activation energy without being used up in the reaction.
Why are Enzymes required in the Human Body?
Temperature in living cells would be too low for chemical molecules to react quickly enough to support life
Do all metabolic reactions get catalysed by Enzymes?
Yes
Metabolism definition:
- all the reactions in the body
There can be both ___cellular and ____cellular
- intra
2.extra
Why can Enzymes be reused?
they do not undergo any permanent changes in structure as a result of the reaction they catalyse
Describe the Mechanisms of Enzyme Action:
- Enzymes are globular proteins
- Since they are proteins they contain a Tertiary Structure, which means that that the enzyme and the
active site has a unique specific shape + structure - As well as this USUALLY the enzyme only works on one type of substance (the substrate)
- In this reaction the molecular shape of the active site is said to be COMPLEMENTARY to the molecular shape of the substrate
- They both react reversibly to form Enzyme-Substrate Complexes
Describe the Lock & Key Model:
- The model suggest that the substrate combines with the enzyme at the active site in an EXACT, PRECISE way “like a lock & key”
- The Active Site is ALWAYS the exact COMPLEMENTARY shape to the molecular shape of the substrate (at the optimum temperature), so reactions will happen fastest in these conditions to form Enzyme-Substrate complexes
- These then form Enzyme-Product complexes after the reaction
- Then the product + enzyme would leave the active site since after the reaction the products do not fit the active site
What is the limitation of the Lock & Key model?
- the enzyme in this model is describes as a rigid structure, however some enzymes can act on more than one substrate
Explain the ‘Induced fit model’?
- model suggests that the enzyme’s active site isn’t exactly complementary to begin with
- However, when a substrate binds with an enzyme, it INDUCES change in the enzyme’s structure
- the amino acids that make up the enzyme are moulded into precise formations, to wrap around the substrate to form ENZYME-SUBSTRATE COMPLEXES
- So the active site changes shape to become complementary
How does the ‘Induced Fit’ explain the reduction of Activation Energy?
-‘stressed fit’ of the enzyme and substrate, causes bonds in the subsrate to undergo stress + distortion, reducing activation energy to break the bond, when Enzyme-Substrate complexes form
Why are rate of reaction’s fastest at the start of reactions, and are slower at the end of reactions?
-since there is more substrate at the start, there are more likely to be collisions, so more Enzyme-Substrate complexes
-substrate gets used up as reaction progresses
Why is the rate slow at low temperatures?
enzyme + substrates move around very slowly due to lower KE, so collisions are less frequent as are the formation of Enzyme-Substrate Complexes
As Temperature increases:
- enzyme + subsrate molecules gain more KE, so move around faster
- therefore more frequent collisions, so a greater number of enzyme-substrate complexes form
- increased rate
What happens to enzymes of which have temperature above 40 degrees Celcius?
Enzymes will denature:
- hydrogen bonds in enzymes break
- tertiary structure changes, as does the shape of active site, so the substrate no longer fits
- less/ no more enzyme-substrate complexes form
What is pH?
- concentration of H+ ions in a solutions
In what factors of H+ ions do PH go up in?
Factors of 10 as you go down in pH
How does pH affect enzymes?
- change in pH alters the charges of amino acids which make up the active site of the enzyme
- this causes some of the hydorgen and ionic bonds that maintain the enzymes teritary structure to break and reform in other areas
- these changes alter the shape of active site, which means the substrate may no longer fit
- less/no enzyme-substrate complexes can be formed
- enzyme is denatured
Why do Enzymes work best at the optimum pH?
- active site is exactly complementary to the substrate, so max number of Enzyme-substrate complexes
Describe + Explain effect of substrate concentration on rate of reaction:
- As the concentration increases the rate of reaction increases
- This is because the increased substrate molecules means, that more likely to be collisions between enzyme + substrate so more enzyme-substrate complexes can form per sec.
- rate of reaction will eventually reach a max, and will remain constant
- this is because all the active sites would be occupied, which means max number of enzyme-substrate complexes, so the active site number is limiting
What is the correlation between enzyme concentration and rate of reaction when the substrate concentration is excess?
- enzyme concentration has a proportionate increase in rate of reaction
What is the correlation between enzyme concentration and rate of reaction when the substrate concentration is limiting?
- as enzyme concentration increases so would substrate concentration, as more enzymes means more frequent collisions, which therefore means more enzyme-substrate complexes forming
- however, at a point there would be a constant rate of reaction and a maximum because at this point the substrate concentration is limiting
What is an inhibitor?
- a substance which decreases the rate of an enzyme-controlled reaction and may bring it to a halt
Explain how a competitive inhibitor works?
- the competitive inhibitor has a similar shape to the substrate
- this allows it to bind to the active site of the enzyme
- since the active sites are blocked by the competitive inhibitor, fewer enzyme-substrate complexes are formed
- reducing rate of reaction
Describe + Explain the effect of increasing substrate concentration on competitive inhibiton:
- rate is reduced with an inhibitor at LOW substrate concentrations
- however, as the concentration of substrate increases the effect of inhibition will eventually decrease
- high substrate concentration would end up in the same maximum rate of reaction as with no inhibition
- this is because there is a greater proportion of substrate then inhibitor, which gives it an increased chance of occupying the active site, in competition with inhibitor
Explain how non-competitive inhibitors work:
- these do not mind with the active site as their shape isn’t similar
- non-competitive inhibitors bind to another region of the enzyme (allosteric site)
- This binding will cause a change of tertiary structure, and therefore a change in shape of active site, so less enzyme-substrate complexes can form
What is the difference in graph for non/comp inhibtors?
- non-competitive inhibitors rate with inhibitor is always below without inhibitor
