Chapter 4 Flashcards
What are enzymes?
biological catalysts that increase rate of chemical reactions
- proteins
How do enzymes work?
lowers activation energy required for a reaction to proceed
What is the structure of an enzyme?
3D shapes with pockets (active sites) where substrates fit
What is the mechanism of enzymes?
- substrate fits in active sites
- enzyme-substrate complex forms
- reaction occurs
- products dissociate
- enzyme is unaltered
What do phosphatases do?
remove phosphates
What do kinases do?
adds phosphate groups
What are cofactors?
metal ions necessary for normal activity of enzymes
- Ca++, Mg++, Mn++, Cu++
What are coenzymes?
derived from vitamins to transport small molecules needed by enzymes
- taxi cabs
How do cofactors work?
when it binds, it changes conformation of active site
- aids in temporary bonding between enzyme and substrates
What is the relationship between product formation and substrate concentration?
directly related
- As product formation increases, substrate concentration increases
UNTIL reaction rate reaches a plateau
Why does substrate concentration plateau?
enzyme is saturated
What is the law of mass action?
reaction flows from higher concentration to lower concentration
What are metabolic pathways?
sequences of enzymatic reactions that begin with initial substrate and progress through intermediates and end with a final product
What is end-product inhibition?
when 1 product inhibits activity of the branch-point enzyme
- prevents final product accumulation
- causes reaction to favor alternate pathway
How does end-product inhibition occur?
by allosteric inhibition
- product binds to enzyme causing it to change to an inactive shape
When enzymes are produced, are they inactive or active?
inactive
How are enzymes activated/inactivated?
activated: phosphorylation or ligands (2nd messengers)
inactivated: dephosphorylated
How are receptors and enzymes related?
receptors = ligands (binding site)
enzymes = substrates (active site)
- both need to be regulated/controlled to manage reactions and procedures
What are the 4 types of protein regulation?
- covalent modification
- allosteric modulators
- end-product inhibition
- competitive inhibition
What is covalent modification? What response does it provide?
- phosphorylation of receptors or enzymes
- active/inactive response
What are allosteric modulators? What is the response?
- cofactors bind to site other than active site
- can enable or inhibit reaction
What is end-product inhibition?
special case of allosteric inhibition
- product binds to allosteric site of enzyme in earlier part
What is competitive inhibition? What is the response?
binds to active site on enzyme or binding site of receptor
- inhibits activity
What is bioenergetics?
flow of energy in living systems
What is the first law of thermodynamics?
energy can be transformed but not created or destroyed
What is the second law of thermodynamics?
energy transformations increase entropy
- disorganization/chaos of a system
- all living organisms require continued input of energy
What is needed for work?
free energy
- systems go from higher free energy to lower free energy
What are endergonic reactions?
requires input of energy to proceed
- products have more free energy than reactants
What are exergonic reactions?
release energy as they proceed
- products contain less free energy than reactants
What are coupled reactions?
endergonic + exergonic reactions together
- exergonic breaks down ATP
What is a reducing agent? What is the action called?
donates electrons
- oxidizes
What is an oxidizing agent? What is the agent called?
accepts electrons
- reduced
NAD+ + 2H -> NADH + H+
In the equation above, what is the reduced form?
NADH is reduced
- more negative
(NAD+ = +1, NADH = 0)
What is another example of a coupled reaction? What does it involve?
reduction + oxidation
- transfer of H’s instead of electrons
- coenzymes (NAD+ and FAD)
