Biochem, Block 4, Lectures 1-3 (Blake/enzymes)

Front 1

What kinds of bonds do enzymes work through?

Back 1

Enzymes use WEAK BONDS to attach to their substrates and use the energy from them to convert the product into a position more favorable to reacting.

Front 2

What do enzymes do?

Back 2

They reduce the activation energy required (Delta G) for a reaction to take place and reach the TRANSITION STATE.

Front 3

What is the transition state? What is its use?

Back 3

A fleeting molecular moment during a reaction where the products or the substrate are equally likely to be formed.

Drugs are designed to mimic transition state - they then can bind to enzymes more easily than their natural substrates/products. Good in HIV drugs.

Front 4

What are the 6 different kinds of enzyme reactions?

Back 4

1. Oxidoreductases (note - gain of hydrogens = reduction, gain of double bonds = oxidation)

2. Transferase: Transfer of a functional group from on molecule to another

3. Hydrolayse: 1 molecule, + H20 goes to 2 molecules

4. Lyases: 1 molecule + H20 goes to 1 molecule.

5. Isomerases: intramolecular rearrangements (isomers)

6. Ligases (have ATP as a reactant, 2 molecules joined, ATP is not incorporated but is converted to ADP)

Front 5

What is Vo? How does it change when enzyme is added?

Back 5

Vo, aka Vi, is the initial velocity of the reaction before the [S] decreased.

Vo increases linearly with the addition of enzyme.

Front 6

How does Vo change when the concentration of substrate is changed?

Back 6

Vo increases non-linearly when [S] goes up - it goes up for awhile, then plateaus (determined by the kind of enzyme used in that reaction).

Front 7

What is Vmax?

Back 7

Velocity if given an infinite [S]

Front 8

What is Km?

Back 8

It is the SUBSTRATE concentration at which an enzyme has 1/2 maximal activity (AKA Vmax). So, on a graph of [S] on X axis and V on Y axis, find half of the Vmax and trace it over to the line. Where it intersects the X axis is the Km.

Note - the LOWER Km, the GREATER the affinity the enzyme has for the substrate.

Front 9

What equation can we use to solve for V or Vo?

Back 9

V = Vo = Vmax X [S] / Km + [S]

Front 10

What happens when [S] is set precisely at Km?

Back 10

Then the Vo = Vmax/2

Front 11

If on the enzyme portion of the test you come across a weird graph with reciprocals in the x/y axis, what's up?

Back 11

It'll be 1/[S] for X and 1/[V] for Y.

X-intercept = -1/Km
Y-intercept = 1/Vmax
Slope = Km/Vmax

Front 12

In the world of enzyme regulation, what can you do to already made enzyme?

Back 12

You can adjust the activity of already-existing enzyme. Can be Non-covalent and Covalent.

Non-covalent is fast. Allosteric effects and reversable inhibitors are part of this.

Covalent is slower and is often phosphorylation. Can also be proteolytic processing (irreversable) and irreversable inhibitors (drug category)

Front 13

How else can enzyme activity be regulated?

Back 13

You can make more/less of an enzyme, but this can take hours.

Also can sequester - either in organelles or in membranes.

Front 14

Give me more detail about reversable inhibition:

Back 14

3 kinds.

1. Competitive Inhibition: Bind at active site and can be reversed by adding more [S].

2. Mixed inhibition: Bind distant to the active site, but bind both the E and ES complex.

3. Non-competitive inhibition: Bind only to the ES complex and in a place distant to the active site.

Front 15

Competitive Inhibitors: What should we know about them?

Back 15

They bind at the ACTIVE SITE and they generally resemble, structurally, the normal substrate.

Front 16

Competitive vs. Uncompetitive Inhibition: What are the effects on Vmax and Km?

Back 16

Competitive: no effect on Vmax (because infinite [S] will overcome this and Vmax is a function of infinite [S]. The apparent Km does change.

Uncompetitive: effects on both Vmax and apparent Km. (Parallel Lines)

Front 17

Allosteric inhibition: what's up?

Back 17

Allosteric inhibited enzymes are, by definition, multi-subunit. Allosteric effects happen when one region's confirmational change affects another region.

Products in metabolic pathways often feed back allosterically on the enzymes of earlier steps.

Front 18

What's the most common covalent modification of enzymes?

Back 18

phosphorylation is most common. reversed by phosphotases.

Front 19

Irreversible Inhibitors: what happens?

Back 19

Often binds COVALENTLY to the active site of an enzyme.

Note - suicide inhibitors are inactive inhibitors floating around that become active only when its target enzyme binds to it and makes it active -essentially, the enzyme kills itself.

Front 20

What are the six types of enzymes?

Back 20

1. Oxidoreductases

2. Transferases

3. Hydrolayses

4. Lyases

5. Isomerases

6. Ligases

Front 21

How can you tell if something is an oxidoreductase? transferase? hydrolayse?

Back 21

oxidoreducatse will clearly show a hydrogen being added/removed.

tranferase should move an entire functional group on/off a molecule

hydrolayses will clearly show H20 as a product

Front 22

What about lyases? Isomerases? Ligases?

Back 22

lyases should show something being added/removed across a double bond

isomerases are clearly a molecule changing shape

ligases show two molecules coming together, using ATP!!!

Front 23

What type of regulation are key steps in metabolic processes susceptible to?

Back 23

allosteric regulation!

Front 24

Digestive Enzymes and Blood Coagulation - what kind of processing do these experience?

Back 24

Zymogen activation - cleavage, etc. Proteolytic processing.