Class notes
Krebs cycle - Biochemistry
- Course
- Institution
Here are lecture notes for a biochemistry lecture on the Krebs cycle
[Show more]
Seller
Follow
lucygodbeer
Content preview
BIOCHEMISTRY – LECTURE 8 PART 1krebs cycle
At the end of glycolysis, we ended with 2 molecules of pyruvate. One of the fates
of pyruvate is to be imported into the mitochondria, be converted to a molecule
called acetyl CoA an enter the Krebs cycle. Acetyl CoA is also the starting point
for fatty acid synthesis. The reactions catalysed by PDH (pyruvate
dehydrogenase) is the link between pyruvate and its aerobic fate. CO 2 is
produced and a molecule of NADH, leaving a molecule of acetyl (linked to Co
enzyme A). This reaction is irreversible and marks a committed step to the
complete oxidation of glucose. Because of this commitment, activity of the PDH
complex is an important point of metabolic control.
As PDH catalyses a committed step to complete the oxidation of glucose, the
control over its activity is vital. When phosphorylated, PDH is inactive, this is
catalysed by PDH kinase. The removal of the phosphate group is catalysed by
PDH phosphatase. High energy signals activate PDH kinase, while low energy
signals inhibit it. The purpose of the Krebs cycle is to produce high energy
molecules, however molecules formed in the process are also used for synthesis
of other important biomolecules such as amino acids and porphyrins.
1. After the initial enzyme catalysed step, the unstable intermediate, citryl
CoA, is rapidly hydrolysed to release the CoA molecule. It is a
condensation reaction. This second, rapid reaction drives the whole
reaction in the forward direction. It is irreversible.
2. This is an isomerisation reaction to form isocitrate, a suitable substrate for
the next reaction. Aconitase catalyses the dehydration to form cis-aconite,
which remains bound to the enzyme prior to hydration. The overall effect
is to move the hydroxyl group from one carbon to another.
3. Oxidative decarboxylation of isocitrate where NAD+ is reduced to NADH.
The first part of the reaction is to convert the hydroxyl carbon into an
unstable carbonyl, which rapidly cause the intermediate molecule
(oxalosuccinate) to lose CO2. This reaction is irreversible and regulated.
4. Oxidative decarboxylation of a-ketoglutarate where NAD + is reduced to
NADH. The a-ketoglutarate dehydrogenase complex is not dissimilar to
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 lucygodbeer. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $7.09. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
72042 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now