Cofactors and enzyme kinetics (3 lectures worth of notes)
2 views 0 purchase
Course
BIOL201 (BIOL201)
Institution
Lancaster University (LU)
Learning Objectives
• To be able to define what cofactors and co-enzymes are
• To be able to identify the co-enzymes derived from water-soluble vitamins
• To be able to discuss the key chemical properties of the three co-enzymes discussed in this lecture: NAD/NADP, FAD, coenzyme A (Nucl...
Lecture 13 – Enzymology, enzyme regulation and pathway control
Position and direction of equilibrium are not affected by any catalyst
- Enzyme vastly increase the
rate of catalysis
- Enhance reaction rates so
biological reactions can occur
- Product at lower energy state,
its an exergonic reaction,
thermodynamically favourable
- Can’t tell rate of reaction most
biological molecules are stable
to without enzymes reactions
more slow
Enzymes enhance the rate of
reaction by lowering the
activation energy
- Bind to their substrates and lower the free energy of activation so the reaction reaches it
transition state
Historical perspective: enzymology is an old discipline
- Ancient application of biological catalysis: fermentation
- 1700 – early 1800s:
Early biological studies of catalysis
1700s digestion of meat by stomach secretions
, 1800s starch-to-sugar by saliva and plant extracts
- Victorian era: (1) origins of the term enzyme meaning “leavened” to modify or transform. (2)
specificity – “lock and key” hypothesis
- 1920s: Crystallisation of urease identifies protein as a source of enzyme activity
- 1960s: advent of x-ray crystallography facilitates structure-based studies of enzyme activity and
regulation
- 1980s: catalytic RNA molecules discovered
Key principle in enzymology
- In 1930 J.B.S. Haldane wrote the article
Enzymes. In this text he suggested that
multiple weak bonding interactions between
an enzyme and its substrate(s) might be used
to catalyse reactions
- Induced fit model (Daniel Koshland, 1959)
Some enzymes require no chemical groups other than
their amino acid residues, others do
- Some enzymes require a NON-PROTEIN component for their activity. Such components
are known as cofactors
- Organic cofactors are most generally known as co-enzymes
- Cofactors can be tightly or loosely associated with their enzymes. Tightly associated
cofactors are sometimes known as
prosthetic groups (e.g. Flavin group in
succinate dehydrogenase/mitochondrial respiratory
chain complex II)
- Co-enzymes that are loosely associated with their
enzymes (e.g. NAD/NADP) are often referred to
as co-substrates
- Co-enzymes can diffuse in and out of the
enzyme
- Another common group of cofactors are
metal cations (Na+, Mg2+). The multiple
oxidation states of some metal atoms (e.g.
Fe, Cu) is often important for their
cofactor function
- Metal cations cofactors help enzyme fold
correctly in polypeptide chain, or binding or catalytic pathway
- Multiple oxidation states of metal cations are important because they are excellent
acceptors for electrons
Co-enzymes participate in group transfer reactions
- i.e. they are transient carriers of function information
, - c.f. lecture 1 and use of the term ‘activated carrier’ by SKR
For enzymes with a tightly associated co-enzyme or cofactor (prosthetic group)
- in the absence of cofactor the protein is referred to as an apoprotein or apoenzyme
- in the presence of bound cofactor the protein is known as the holoprotein or
holoenzyme
- Transfer of a
chemical group,
transient carriers,
activated carriers
(coenzyme)
- Tightly associated
prosthetic group
absence apoprotein
- Presence
holoprotein
Many co-enzymes are derived from vitamins
, NAD+ and NADP function in 2e- transfer reactions
- Nicotinamide ring derived from niacin; these co-enzymes are sometimes referred to as
“pyridine nucleotides”
- NAD+ and NADP both undergo reversible reduction of their nicotinamide ring. Thus, for
a substrate undergoing enzyme-catalysed oxidation (dehydrogenation) the oxidised
form of co-enzyme accepts a hydride ion (:H. equivalent of 1 proton 2e-)
- Nature of R
group is the
only
difference,
NAD is
hydrogens
and NADP is
phosphate
group
- Purple is
nitrogenous
base, this is
the
nicotinamide
group
nucleotide,
attached to
another nucleotide – dinucleotide
- Involved in the transfer of 2 electrons derived from vitB3
- Reaction site where electrons removed or added
NAD+ functions primarily in the reversible oxidation of aldehydes and alcohols
- Oxidation of aldehydes or alcohols
- Accumulation of acetaldehyde by enzyme alcohol dehydrogenase, dependent of NAD+
reduced to NADH alcohol oxidised
- Acealdehyde more toxic than alcohol
- Aldehyde dehydrogenase breaks down acetaldehyde giving acetic acid
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller laurynwills. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.69. You're not tied to anything after your purchase.
