Lecture 12: Enzymes III- Regulation

Question 1

Substrate-level control

Answer 1

Acts as a SINGLE reaction

Question 2

Feedback control

Answer 2

Targets a different step in the pathway

Question 3

What is the effect on product formation?

Answer 3

• Activators PROMOTE more products

- Inhibitors PREVENT more products

Question 4

Enzyme Regulation

Answer 4

1. Regulate the amount or availability (on/off)

2. Regulate the activity of the enzyme (volume control)

Question 5

Regulate the amount or availability (enzyme reg)

Answer 5

• Temporal control of gene expression
• Protein Degradation
• Enzyme Compartmentalization
• Substrate Availability

Question 6

Regulate the activity of the enzyme (enzyme reg)

Answer 6

• Isozymes and isoforms
• Covalent modifications
• Allostery

Question 7

Enzyme Compartmentalization

Answer 7

• Act in a specific location

- -> Can control how much E + S (reg how available)

Question 8

Substrate Availability

Answer 8

How is substrate coming and getting into cell

-Signaling cascade

Question 9

Isozymes and Isoforms

Answer 9

*Catalyze the SAME reaction but with DIFFERENT efficiences
-Not a clear destination
-“Mix and Match” subunits:
Paralogs, alt splicing, heterozygous alleles, monomer vs dimer/trimer, +/- covalent modifications and conformations

Question 10

Compartmentalized isozymes

Answer 10

Results in tissue specificity

Question 11

Temporal expression of isozymes

Answer 11

Common in development

Question 12

Lactate Dehydrogenase (LDH)

Answer 12

Participates in the lactic acid fermentation pathway

-LDH=tetramer : isoforms say where expressed (heart or sk muscle)

Question 13

LDH1=H4

Answer 13

Had a MI

Question 14

LDH5=M4

Answer 14

Liver is damaged

Question 15

Covalent modifications

Answer 15

Phosphorylation, acetylation, myristoylation, ADP ribosylation, farnesylation, gamma-carbox. sulfation, ubiquit

Question 16

Reversible Covalent Modifications

Answer 16

Lipids (myristic acid= fatty acid)
Farnesyl (intermediate in cholesterol synthesis)
Nucleic acids (ADP-ribose)
Proteins (Ubiquitin)
Small molecules- gamma carboxylation, sulfation, acetylation and methylation, phosphorylation (off of hydroxyl)

Question 17

Reversible covalent modifications - Carboyhydrates

Answer 17

The greatest source of diversity to the proteome!

• O vs N-linkages
• Composition of sugars
• Branched vs unbranched
• Length of oligosaccharide

Question 18

What is phosphorylation activating?

Answer 18

1. Thermodynamics - ATP hydrolysis can drive unfavorable reactions (delta G=50 kJ/mol)
2. Kinetics- Phys processes dictate reaction rate (msec-hrs/rxn)
3. Cell processes - APT amounts dictacted by metabolism (energy charge) and signal transduction amplification (catalytic turnover)
4. Shape and Charge Complementarity- each phosphate adds (-2) charge and (+3) H-bonds

Question 19

Kinases

Answer 19

ADD phosphate

[Name of kinase indicates on which AA the phosphate will be add]

Question 20

Phosphates

Answer 20

REMOVE phosphates

Question 21

Covalent Modifications: Irreversible

Answer 21

Proteolytic activation (Cleaves to activate)

Question 22

Proteases

Answer 22

[Many enzymes begin life as ZYGOMENS- need to be cleaved to be activated] –Digest enzymes, Collagenous (Development), Caspases (Apoptosis)

• Collagen
• Blood clotting factors
• Insulin/H’s

Question 23

Allosery

Answer 23

1. Heteroallostery - Effector binds at the allosteric site (Enzyme to other)
2. Homoallostery - Cooperativity (Enzyme to itself)

Question 24

Binding of CTP

Answer 24

Prefers the T/inactive state

“Tense state”

Question 25

Binding of ATP

Answer 25

Prefers the R/active state

“Relaxed state”