β-oxidation is a catabolic reaction that takes place in the mitochondria where fatty acids are broken down. The fatty acid enters the pathway when it binds to coenzyme A to form an acyl CoA. The acyl CoA then enters the mitochondrial matrix through the carnitine shuttle system. The acyl CoA undergoes a series of reactions involving dehydrogenases and hydratases that ultimately form acetyl CoA and reduce the fatty acid by two carbons.

1. β-oxidation.

2. • It is a catabolic reaction of fatty acid (FA) that take place inside
the mitochondria (in the matrix).
• The oxidation of FA take place on the β-carbon atom, hence
this process named β-oxidation.
β-Oxidation

3. Activation of FA
A FA enters the oxidative pathway only after it has
become activated by binding to coenzyme A (CoA)
(formation of acyl CoA.)

4. Transport of Acyl coA
• Acyl CoA enter the mitochondrial matrix via
carnitine shuttle system.
http://www.bioinfo.org.cn/book/biochemistry/chapt16/bio1.htm

5. Citrate
Inter citric acid cycle

6. Acyl-CoA dehydrogenase
Acyl-CoA
Trans-Δ2-enoylacyl-CoA
Enoyl-CoA hydratase
3-Hydroxyacyl-CoA
3-Hydroxyacyl-CoA dehydrogenase
3-Ketoxyacyl-CoA
Thiolase
Acyl-CoA (2) + Acetyl-CoA

7. Two component system in(TCS)
bacteria

8. TCS
• It’s a signaling system used by bacteria to transfer signals from
outside into cytoplasm to do that, sensors are required to detect
chemical and/or physical signals found in its environment.
• TCS consists of a sensor kinase (Histidine kinase HK) that responds
to specific signals by modifying the phosphorylated state of a
cognate response regulator
• The HK senses specific signals, and that leads to activation of the
kinase activity and autophosphorylation of a conserved histidine
residue. The phosphoryl group is subsequently transferred to a
cognate response regulator to activate its activities.

9. • Phosphorylation of a response regulator changes the
biochemical properties of its output domain, which can
participate in DNA binding and transcriptional control,
perform enzymatic activities, bind RNA, or engage in
protein–protein interactions.
• Sensor kinases are usually integral membrane proteins that
autophosphorylate from ATP at a conserved histidine
residue and then transfer the phosphoryl group to a
conserved aspartate in the response regulator

10. Histidine kinase receptor
(signal receptor)
Most bacterial TCSs consist of two proteins, a
sensor histidine kinase (HK) and a response
regulator (RR).

11. • Most RRs are transcription regulators and turn
on or off gene transcriptions in response to
the signals received by sensor HKs.