4- enzymes as biological catalysts

Question 1

what does enzyme do?

Answer 1

-speeds up rate at which reaction reaches equilibrium
-catalyse many chemical rfeactions which together make up process of metabolism

Question 2

do enzymes affect equilibrium position?

Answer 2

NO

Question 3

are all catalysts proteins?

Answer 3

mostly yes but some types of RNA are catalysts

Question 4

are enzymes catalysts?

Answer 4

yes

Question 5

what conditions are enzymes most efficient?

Answer 5

-at body temp
-in aqeous solutions
-near neutral pH

Question 6

what does it mean by enzymes are potent?

Answer 6

each enzyme molecule can convert many substrate molecules into product per second= we mean they’re very efficient catalysts

Question 7

what is the general concept of enzyme action to reactions?

Answer 7

-enzymes specifically bind and stabilise the transition state
-enzymes reduce activation energy by providing alternative reaction pathways

Question 8

what is transition state?

Answer 8

the reaction intermediate species which has the greatest free energy

Question 9

what does catalytic activity of many enzymes depend on?

Answer 9

presence of small molecules called cofactors and coenzymes (they help improve catalytic activity)

Question 10

what are cofactors?

Answer 10

metal ions that are inorganic (non-protein chemical compound or metallic ion that is required for an enzyme’s role as a catalyst)

Question 11

what are coenzymes?

Answer 11

organic molecules (an organic molecule that binds to the active sites of certain enzymes to assist in the catalysis of a reaction)

Question 12

what has happened when enzyme referred to as metalloprotein?

Answer 12

metal cofactors have formed metal co-ordination centre in enzyme

Question 13

what do you call tightly bound coenzymes?

Answer 13

prosthetic group e.g. haem in haemoglobin (non-protein unit necessary for function)

Question 14

are coenzymes permanent part of enzyme?

Answer 14

no, they mostly associate with enzyme only transiently (temporarily)

Question 15

what happens to coenzymes during a reaction?

Answer 15

they can change charge or structure during the course of reaction but are then regenerated

Question 16

what do you call an enzyme without a cofactor?

Answer 16

apoenzyme (doesn’t have co-factor but needs one)

Question 17

what do you call an enzyme with a cofactor?

Answer 17

haloenzyme (=apoenzyme + cofactor)

Question 18

what are examples of cofactors?

Answer 18

1. metal ions e.g. zinc, iron, copper
   -> they’re involved in redox reactions and stabilise transition states
2. coenzymes
   ->many are derived from vitamins ->many involved in redox reactions
   ->many involved in group transfer processes like ATP transfer phosphate groups and coenzyme A transfer acetyl group

Question 19

Are cofactors and coenzymes the same thing?

Answer 19

no, all coenzymes are cofactors, but not all cofactors are coenzymes

Question 20

what do most vitamins function as?

Answer 20

coenzymes which means symptoms of vitamin deficiencies reflect the loss of specific enzyme activity

Question 21

what is a common co-enzyme for redox reactions?

Answer 21

NAD+
-it acts as intermediate and may donate or recieve electrons during enzyme catalysis
-it’s easily regenerated and ahs to be recycled many times

Question 22

what is free energy change?

Answer 22

change in free energy when one substance or a set of substances in their standard states is converted to one or more other substances, also in their standard states.

Question 23

what is the activation energy?

Answer 23

the minimum energy required to cause a process (such as a chemical reaction) to occur.

Question 24

what is transition state?

Answer 24

state of highest potential energy

Question 25

what are the ways a substrate binds to an active site?

Answer 25

-by a cleft or crevice -enzyme contains amino acid that essential for catalytic activity and for highly specific interactions

Question 26

what are the 2 ways a substrate and enzyme are described as binding?

Answer 26

1. lock and key model (active site of unbound enzyme is complementary to shape of substrate) 2. induced fit model (binding of substrate induces a conformational change in enzyme that results in complementary fit)

Question 27

what are proteases?

Answer 27

enzyme with active site which breaks down proteins

Question 28

what are the characteristics of substrate binding active sites in chymotrypsin?

Answer 28

hydrophobic pocket bins aromatic amino acids (cleaves after as hydrophobic side chains fit very nicely) =example of induced fit (hydrophobic pocket in active site means side chains fit nicely and tghen it adjusts again = cosy fit)

Question 29

what are the characteristics of substrate binding active sites in trypsin?

Answer 29

negatively charged Asp interacts with positively charged Lys or Arg (since - charge it likes to cleave + charge)

Question 30

what are the characteristics of substrate binding active sites in elastase?

Answer 30

active site partially blocked, only amino acids with small or no side chains can bind

Question 31

what are 3 examples of pancreatic serine proteases?

Answer 31

chymotrypsin, trypsin and elastase = they all contain reactive serine residue and catalyse hydrolysis of peptides at specific sites

Question 32

what is relationship of enzyme activity and rate?

Answer 32

each enzyme will have optimum pH that will vary for each enzyme

Question 33

what is optimum temp for a) human enzymes b) bacteria enzymes?

Answer 33

a)optimum temp of 37.5 degrees b)optimum temp of about 70 degrees

Question 34

what happens to active site if temp/pH exceeded optimum?

Answer 34

denatures and enzyme changes conformation so no longer functional

Question 35

what are isozymes?

Answer 35

isoforms of enzymes, they catalyse the same reaction but have different properties and structure (and sequence)

Question 36

when are isozymes synthesised?

Answer 36

during different stages of foetal & embryonic development

Question 37

where are different isozymes present?

Answer 37

different enzymes are present in different tissues and in different cellular locations

Question 38

how are relative amounts of isozymes in blood useful for diagnostic purposes?

Answer 38

-because different isozymes are produced in different places in the tissue and they're not meant to leave that location so if you find for example brain form (BB) in blood then it suggests stroke or tumour

Question 39

what is creatine kinase?

Answer 39

a dimeric protein which bind to muscle sarcomere (helps regenrate ATP)

Question 40

what reaction can regulate enzyme activity?

Answer 40

phosphorylation, it's very fast & reversible and found in all cells - especially involved in energy generating processes (quick way to switch activity on/off)

Question 41

what is role of protein kinase?

Answer 41

catalyses transfer of phosphate from ATP to other protein (addition of phosphate to protein)

Question 42

what is role of protein phosphatase?

Answer 42

catalyses transfer from other protein to form ATP (removal of phosphate from protein)

Question 43

what are zymogens?

Answer 43

inactive precursors of an enzyme, they're irreversibly transformed into active enzymes by cleavage of a covalent bond (cleaved to form fully active enzyme)

Question 44

why don't you want zymogens to be always activated?

Answer 44

because they form specific functions like blood clotting enzymes - you only want to be released when major bleed not always otherwise that leads to health problems like heart attack etc

Question 45

what are examples of zymogens in pancreas?

Answer 45

trypsinogen and chymotrypsinogen, inactive precursors, are formed

Question 46

what are examples of zymogens in small intestine?

Answer 46

enteropeptidase cleaves trypsinogen to form active trypsin which cleaves chymotrypsinogen to form active chymotrypsin