Enzymes And The Digestive System (UNIT 1) Flashcards
What are amino acids?
The basic monomer units which combine to make up a polymer called a polypeptide. Polypeptides can be combined to make proteins.
What different groups is an amino acid made out of?
AROUND CENTRAL C ATOM- AMINO GROUP (-NH2) CARBOXYL GROUP (-COOH)- acidic HYDROGEN ATOM (-H) R GROUP- s variety of different chemical groups. Each amino acid has a different R group.
How is a peptide bond formed?
Amino acid monomers combine to make a dipeptide. CONDENSATION REACTION. Combine -OH from carboxyl group of one amino acid and -H from amino group of another. LINKED BY A PEPTIDE BOND BETWEEN CARBON OF ONE AND NITROGEN OF OTHER. BROKEN BY HYDROLYSIS
Describe the primary structure of proteins.
Through series of condensation reactions, may amino acid monomers can be joined together by POLYMERISATION. Resulting chain is called a POLYPEPTIDE. Sequence of amino acids in a polypeptide chain forms PRIMARY STRUCTURE of a protein.
What does the primary structure determine?
Final shape and function of amino acid. 1 change in primary sequence can change structure and stop it from carrying out function.
Describe the secondary structure of proteins.
Linked amino acids have both -NH and -C=O groups on either side of every peptide bond. HYDROGEN of -NH group has +ve charge while O of -C=O has -ve charge . Two groups readily form weak hydrogen bonds. THIS CAUSES LONG POLYPEPTIDE CHAIN TO BE TWISTED INTO 3D shape (alpha helix).
Describe tertiary structure of proteins.
Alpha helices of secondary structure can be twisted and folded more to give a complex, often unique, 3D structure. 3D shape determines how protein functions and allows it to recognise and be recognised by other molecules.
What bonds maintain the tertiary structure of proteins?
DISULFIDE BONDS- fairly strong IONIC BONDS- formed between any carboxyl and amino groups not involved in forming peptide bonds. Weaker than disulfide bonds, easily broken by change in pH. HYDROGEN BONDS- easily broken but lots of them.
Describe the quarternary structure of proteins.
Large proteins often form complex molecules containing a number of individual polypeptide chains that are linked in various ways. Also non-protein groups associated with the molecules.
What is the test for proteins?
BIURET TEST
Sample in test tube add equal volume of sodium hydroxide
Add a few drops of very dilute copper sulfate solution and mix gently.
PURPLE indicates peptide bond and hence a protein.
If NO PROTEIN, REMAINS BLUE
What are enzymes?
Enzymes are globular proteins which act as biological catalysts, they increase the rate of reaction with out changing or being used up.
What is activation energy?
The minimum amount of energy needed to start a reaction. Enzymes lower activation energy.
Describe the structure of an enzyme.
Specific 3D shape, result of sequence of amino acids (primary structure). Large but only small section functional- active site.
What is a substrate?
The molecule on which an enzyme acts upon. Fits into active site (COMPLEMENTARY SHAPE). Forms ENZYME-SUBSTRATE COMPLEX.
How is a substrate held to an active site?
By bonds that temporarily form between certain amino acids of the active site and groups on substrate molecule.
Describe the lock and key model. Limitations.
Substrate will only fit the active site of one particular enzyme. Enzymes are specific to the reaction the catalyse. LIMITATION: Enzyme considered a rigid structure but active site can be changed by other molecules binding to the enzyme.
Describe the induced fit model.
Enzyme changes shape slightly to fit profile of substrate. FLEXIBLE. As enzyme changes shape to fit the substrate, the enzyme puts strain on substrate molecule. This distorts a particular bond and consequently lowers the activation energy needed to break the bond.
Describe the effect of temperature on enzyme action.
Increases KINETIC ENERGY of molecules. Molecules move more rapidly and collide with each other more often. Enzyme and substrate come together more often. RATE OF REACTION INCREASES. Rise in temperature also cause hydrogen bonds and other bonds in the enzyme molecule to break - changes shape. At first substrate fits less easily into changed active site. AT SOME POINT, USUALLY AROUND 60 degrees, ENZYME BECOMES SO DISRUPTED THAT IT NO LONGER WORKS. DENATURED. (PERMANENT)
Describe the effect of pH on enzyme action.
Each enzyme has an optimum pH (WORKS FASTEST). Change in pH reduces effectiveness of enzyme and may cause it to denature. - Alters charges on amino acids of active site. Substrate can no longer become attached. DENATURED. -Can cause bonds that maintain enzymes tertiary structure to break. Changes shape of active site, substrate can’t fit. DENATURED.
Effect of substrate concentration on enzyme action.
If amount of enzyme is fixed at constant level and substrate slowly added, rate of reaction increases in proportion to the amount of substrate that is added. MORE COLLISIONS. Active site gradually become filled, until the point where all of them are working as fast as they can. RATE OF REACTION AT MAXIMUM. LEVELS OFF.
What are enzyme inhibitors?
Substances which directly or indirectly interfere with the functioning of the active site of an enzyme and so reduce its activity. Some permanent most temporary.
Describe competitive inhibitors.
SIMILAR SHAPE TO SUBSTRATE. Occupy active site of enzyme. Compete with substrate for available active sites.
Describe non-competitive inhibitors.
ATTACH ENZYME AT A SITE OTHER THAN ACTIVE SITE. When attaches to enzyme, the inhibitor alters the shape of the active site in such a way that substrate molecules no longer fit. ENZYME CANNOT FUNCTION. Not competing for same site so increase in substrate concentration does not decrease the effect of the inhibitor.
