Lecture 7B

Question 1

why do cells need enzymes?

Answer 1

to speed up the reactions

Question 2

what is an enzyme?

Answer 2

a catalyst or catalytic protein that speeds up the rate of a reaction without being consumed or altered by the reaction

Question 3

what is activation energy?

Answer 3

the amount of energy required to convert the reactants into products.

EA

Question 4

what is the unstable state of a chemical reaction?

Answer 4

the transition state

Question 5

what does thermal energy do to a reaction?

Answer 5

it increases the movement/speed of molecules causing them to collide more often thus breaking the bonds between them to which will allow new bonds to form.

energy is released when new bonds are formed

heat speeds up a reaction allowing the reactants to reach the transition state

Question 6

why is using thermal energy inappropriate for biological systems?

Answer 6

• high temperatures denatures proteins
• heat would speed up all cells and not just the necessary ones.

Question 7

how to enzymes catalyze a reaction?

Answer 7

they catalyze by lowering the activation energy barrier which will allow the reactants to absorb the sufficient amount of energy to reach the transition state even at moderate temperatures.

Question 8

what type of reaction is the hydrolysis of sucrose?

Answer 8

it is an exergonic reaction and a catabolic reaction

exergonic = spontaneous

• The reaction however is slow
• The change in free energy stays the same
• Lowered activation energy

Question 9

can enzymes turn an endergonic reaction into an exergonic reaction?

Answer 9

No enzymes cant, but they can speed up this process of conversion.

Question 10

what is an enzymes substrate?

Answer 10

the reactant an enzyme acts on

Question 11

what is the enzyme-substrate complex?

Answer 11

enzyme + substrate/reactant = enzyme + product

Question 12

can enzymes work both forward and reversed?

Answer 12

yes

Question 13

what is the active site?

Answer 13

region where the enzyme binds to the substrate

A pocket/groove on surface of protein formed by amino acids

Needs to be compatible fit between the shape of the active site and the shape of the substrate.

Question 14

what is the substrate held by?

Answer 14

hydrogen and ionic bonds

Question 15

what is the induced fit?

Answer 15

the interaction between the substrate and amino acids to cause a change in structure of the active site so that it can fit properly with the substrate

It brings chemical groups into positions that increase the rate

Question 16

How do enzymes lower the rate?

Answer 16

• be a template for substrate molecules to come together
• stress the substrate molecule bonds
• participates in the chemical reactions (at times)
• provides favorable microenvironments for the reaction

Question 17

how do enzymes stress the substrate?

Answer 17

they stress the substrate by stretching the substrate molecules towards the transition state.

Sometimes enzymes are involved in brief covalent bonding between an active site R-group and the substrate.

Question 18

what is a good example that presents an enzyme as a good microenvironment?

Answer 18

an active site composed of amino acids with acidic R groups creating a pocket of low pH in neutral cell.

Question 19

what are the five steps to an enzyme catalysis?

Answer 19

1) substrate binds to the active site of an enzyme
2) enzyme-substrate complex if formed
3) reaction proceeds and the products are formed
4) product leaves
5) enzyme returns to original shape.

Question 20

Name factors that influence the rate of a reaction?

Answer 20

• subtrate concentration (the greater the concentration of substrate molecules the more they will will reaction and interact with the enzymes active site
  -enzyme concentration ( can be saturated with subtrate )
• temperature
• pH
• the presence of other chemicals

Question 21

what does the rate of reaction give you?

Answer 21

provides you with the slope of the amount of products formed per unit of time.

this is dependent on the initial subtrate concentration

Question 22

what does it mean when the enzyme is saturated?

Answer 22

this is when all the active sites of the enzyme is taken up by substrates

This is the subtrate concentration

Question 23

What does high enzyme concentration mean for a reaction?

Answer 23

This means that there needs to be a high substrate concentration to saturate the enzymes and ensure a maximum reaction rate is higher.

A higher enzyme concentration will lead to a higher Vmax

Question 24

what is Km?

Answer 24

the measure of affinity of the enzyme for the substrate

1/2 Vmax
affinity = the tendency of the substrate binding to the enzyme

high Km= low affinity = needs a higher concentration of substrate to achieve Vmax

Question 25

How does a cell regulate its metabolic pathways?

Answer 25

Does this by controlling when and where enzymes are active.

Question 26

What are the two ways in which an enzyme can regulate metabolic pathways?

Answer 26

1) regulating activity of that enzyme (*enzyme activators* = molecule that promotes enzyme function, *enzyme inhibitors* = molecule that interferes or prevents an enzyme from functioning 2) Switching genes that code for the making of an enzyme on/off to increase/decrease the number of enzyme molecules present.

Question 27

what are cofactors (prosthetic groups)?

Answer 27

organic or inorganic molecules that allow the enzyme to function properly | Non-protein part of the enzyme ## Footnote Coenzymes= organic cofactors zinc, copper, iron = inorganic enzymes

Question 28

What is the protein part of an enzyme?

Answer 28

apoenzyme

Question 29

What is the holoenzyme?

Answer 29

the apoenzyme + the cofactor

Question 30

What makes a enzyme reaction irreversible?

Answer 30

when the inhibitor attaches to the enzyme by covalent bonds

Question 31

what makes an enzyme reaction reversible?

Answer 31

when the inhibitor attaches to the enzyme by weak interactions

Question 32

What do competitive inhibitors do?

Answer 32

- bind to the same site as the substrate on the enzyme - blocks substrates from entering active sites which reduces the productivity of an enzyme - be overcome by increasing the substrate concentration so that as active sites become available, more substrate molecules than inhibitor molecules are around to gain entry to the sites

Question 33

What do non-competitve inhibitors do?

Answer 33

- bind to a different site on the enzyme than the substrate - causes the enzyme molecule to change conformation so that the active site becomes less effective at catalyzing the conversion of substrate to product.

Question 34

How can you overcome a competitive inhibitor?

Answer 34

By adding more substrate | Vmax stays the same but Km increases ## Footnote A noncompetitve inhibitor cannot be overcome by adding substrate which means Vmax decreases but Km remains the same.

Question 35

what is an allosteric site of an enzyme?

Answer 35

a site other than the active site of an enzyme

Question 36

what happens when molecules bind to a allosteric site?

Answer 36

causes a conformational change in the enzyme which may result in an inhibition or stimulation of the enzymes activity. ## Footnote causes the entire enzyme complex to move between active and inactive

Question 37

what is a conformational change?

Answer 37

when one subunit is transmitted to the entire complex.

Question 38

# allosteric regulation what is cooperativity?

Answer 38

the binding of one substrate molecule to one active site which may affect the other active sites in the complex.

Question 39

Feedback inhibition is what type of common control?

Answer 39

metabolic control ## Footnote - pathway is shut off by its own end-product - the end-product of the pathway becomes the inhibitor to an enzyme that acts early in the pathway - prevents the cell from wasting resources by avoiding making more product than needed

Question 40

what is an example of feedback inhibition?

Answer 40

cellular respiration: - inhibited by ATP - stimulated by AMP

Question 41

what is gene regulation?

Answer 41

slower but long term method of regulating the speed a metabolic pathway occurs. ## Footnote Makes more enzymes, stops making enzymes example: enzymes in the liver = cytochrome P450

Question 42

what is a multi-enzyme complex?

Answer 42

facilitates the product from one enzyme into becoming the substrate for the next enzyme in line. ## Footnote often found in the plasma membrane as organelles like the mitochondria