Biochem lecture 23- Citric Acid Cycle Part 1

When is insulin secreted?

In response to INCREASED BLOOD glucose levels

What does the uptake of insulin by the cells lead too?

It triggers the protein kinase cascade that leads to glycogen synthesis or stimulates the reaction of GLUT4

What I what does the insulin signaling pathway do?

It regulates glycogen synthase

What is the first step of the insulin signaling pathway?

insulin binds to its insulin receptor on the cell membrane, triggering protein kinase cascade

What is the second step in the insulin signaling pathway?

The pathway promotes the insertion of GLUT4 (a glucose transporter) into the plasma membrane and allows glucose to enter the cell from the bloodstream. Glucose is also phosphorylated to G6P in this step

What is the third step in the insulin signaling pathway?

Insulin signaling inactivates GSK3 via phosphorylation. When GSK3 is inactivated it allows glycogen synthase to remain active

What is the fourth step in the insulin signaling pathway?

Phosphatase-1 (PP1) plays a role in activating glycogen synthase by dephosphorylating it promoting glycogen synthase

What is the fifth step in the insulin signaling pathway?

Allosteric activation through glucose-6-phosphate enhances synthesis, allowing the cell to store excess glucose

In its active form what does glycogen synthase promote?

Glycogen synthesis, allowing the cell to store excess glucose

What are the products of the Pentose phosphate pathway?

NADPH and ribose-5-phosphate

What is the Pentose phosphate pathway?

A pathway in sugar metabolism that gives rise to five-carbon sugars and NADPH (reducing agent)

what are some characteristics of NADPH?

-electron donor

-reductive biosynthesis of fatty acids and steroids

-repairs oxidative damage

What are some characteristics of ribose-5-phosphate?

-biosynthetic precursor of nucleotides

-used in DNA and RNA synthesis

-synthesis of select coenzymes

How dos the pentose phosphate pathway begin?

A series of oxidation reactions to produce NADPH and five-carbon sugars and is followed by non oxidative reshuffling of the carbon skeletons of the sugars involved

What is the first reaction of the two different reactions involved in the non oxidative reactions?

Catalyzed by phosphopentose isomerase and results in the production of an aldose ribulose-5-phosphate to ribose-5-phosphate

What is the second reaction of the two different reactions involved in the non oxidative reactions?

Catalyzed by phosphopentose-3-epimerase and involves the inversion of configuration around carbon atoms 3, producing xylulose-5-phosphate (ketose)

Group transfer reactions

Link the pentose phosphate pathway with glycolysis and requires 2 five-carbon sugars produced by the isomerization of ribulose-5-phosphate

Transketolase

Transfers a two-carbon unit

transaldolase

Transfers a three-carbon unit

What is the product of the group-transfer reactions?

The production of fructose-6-phosphate and glyceraldehyde-3-phosphate

What is the pentose phosphate pathway catalyzed by?

Transketolase and transaldolase (reversible) which allows the pentose phosphate pathway to respond to the needs of an organism

Summary: pentose phosphate pathway

A process by which cells can generate pentose phosphates and NADPH. The pentose phosphates can be regenerated into glucose-6-phopshate, which requires no ATP

What is the central role of the Citric Acid Cycle?

Processes that play key role in aerobic metabolism (more efficient)

Conversion of pyruvate to acetylene-CoA

Pyruvate is oxidized to an acetyl group, which becomes linked to CoA

Citric Acid Cycle

Central metabolic pathway

Electron transport

Series of oxidation-reduction reactions by which the electrons derived from oxidation of nutrients are passed to oxygen

Oxidative phosphorylation

Process for generating ATP, depends on the creation of a pH gradient within the mitochondrion as a result of electron transport

Catabolism

Oxidative breakdown of nutrients

Anabolism

Reductive synthesis of biomolecules

Amphibolic

Able to be part of both catabolism and anabolism

Where does the citric acid cycle take place?

The mitochondria (most enzymes in mitochondrial matrix)

Outer membrane of mitochondria

Defines the organelle

Inter-membrane space of the mitochondria

Between outer and inner membranes

Inner membrane of mitochondria

Encloses the mitochondrial matrix

Cristae in the mitochondria

Folds in the inner membrane that increase its surface area

Matrix in the mitochondria

Where the citric acid cycle is primarily located

What is special about NADH and FADH2 in the citric acid cycle?

They are generated by the citric acid cycle and pass their electrons to oxygen

What vital link does TCA cycle provide?

Between the chemical energy of nutrients and the chemical energy of ATP

Does O2 directly participate in TCA cycle?

NO!

What is the main reaction of TCA cycle?

Pyruvate is produced by glycolysis and then is oxidized further to one CO2 molecule and to one acetyl group, which becomes linked to an intermediate CoA

What are the immediate electron acceptors of TCA cycle?

NAD is reduced to NADH and FAD is oxidized to FADH2