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The breakdown of fatty acids, called fatty acid oxidation    or beta (β)-oxidation    , begins in the cytoplasm, where fatty acids are converted into fatty acyl CoA molecules. This fatty acyl CoA combines with carnitine to create a fatty acyl carnitine molecule, which helps to transport the fatty acid across the mitochondrial membrane. Once inside the mitochondrial matrix, the fatty acyl carnitine molecule is converted back into fatty acyl CoA and then into acetyl CoA ( [link] ). The newly formed acetyl CoA enters the Krebs cycle and is used to produce ATP in the same way as acetyl CoA derived from pyruvate.

Breakdown of fatty acids

This figure shows the reactions that break down fatty acids. The top panel shows the conversion of fatty acids into carnitine. The bottom panel shows the conversion of carnitine into acetyl-CoA.
During fatty acid oxidation, triglycerides can be broken down into acetyl CoA molecules and used for energy when glucose levels are low.

Ketogenesis

If excessive acetyl CoA is created from the oxidation of fatty acids and the Krebs cycle is overloaded and cannot handle it, the acetyl CoA is diverted to create ketone bodies    . These ketone bodies can serve as a fuel source if glucose levels are too low in the body. Ketones serve as fuel in times of prolonged starvation or when patients suffer from uncontrolled diabetes and cannot utilize most of the circulating glucose. In both cases, fat stores are liberated to generate energy through the Krebs cycle and will generate ketone bodies when too much acetyl CoA accumulates.

In this ketone synthesis reaction, excess acetyl CoA is converted into hydroxymethylglutaryl CoA (HMG CoA)    . HMG CoA is a precursor of cholesterol and is an intermediate that is subsequently converted into β-hydroxybutyrate, the primary ketone body in the blood ( [link] ).

Ketogenesis

This pathway shows the production of beta-hydroxybutyrate from acetyl-CoA.
Excess acetyl CoA is diverted from the Krebs cycle to the ketogenesis pathway. This reaction occurs in the mitochondria of liver cells. The result is the production of β-hydroxybutyrate, the primary ketone body found in the blood.

Ketone body oxidation

Organs that have classically been thought to be dependent solely on glucose, such as the brain, can actually use ketones as an alternative energy source. This keeps the brain functioning when glucose is limited. When ketones are produced faster than they can be used, they can be broken down into CO 2 and acetone. The acetone is removed by exhalation. One symptom of ketogenesis is that the patient’s breath smells sweet like alcohol. This effect provides one way of telling if a diabetic is properly controlling the disease. The carbon dioxide produced can acidify the blood, leading to diabetic ketoacidosis, a dangerous condition in diabetics.

Ketones oxidize to produce energy for the brain. beta (β)-hydroxybutyrate    is oxidized to acetoacetate and NADH is released. An HS-CoA molecule is added to acetoacetate, forming acetoacetyl CoA. The carbon within the acetoacetyl CoA that is not bonded to the CoA then detaches, splitting the molecule in two. This carbon then attaches to another free HS-CoA, resulting in two acetyl CoA molecules. These two acetyl CoA molecules are then processed through the Krebs cycle to generate energy ( [link] ).

Questions & Answers

what are the functions of the liver
Emorut Reply
detoxification formation of blood in the fetus blood reservoir regulations of the body temperature
ibrahim
regulation of the body temperature in the sense that the liver reduce some of the activities so has to maintain the amount of heat generations in the body
ibrahim
detoxification of blood
marzia
1. Regulate blood clotting. 2. Detoxify harmful substances. 3. Stores and release glucose when necessary. 4. Produce certain proteins for blood plasma. 5. Produce bile which helps in fat metabolism. 6. It stores iron needed for erythropoiesis and also helps in haemolysis
Adoma
It regulate blood clotting by producing clotting factors like vitamin k
Adoma
metaboilism produce bile
Tahir
production of heat
Aradhana
explain the advantages and disadvantages of learning anatomy using systemic and regional. help please😫🙏🙏💓
Enock Reply
hello which is the longer tater
Daniel Reply
the inflammation of spinal cord is called
Francis Reply
TM partial transver myelitis
Ayan
Transverse myelitis
Amit
transverse mylitis
Gopi
T M means transeverse myelitis
Ayan
TM
babita
Example of irregular bones in the upper limb
Daniel
what is anatomy
Bruce Reply
is the study of human structure or various parts of the body
Adoma
What is the chordae tendineae and where is located? Where is the Aorta located?
Sovilace Reply
What is the meaning of aponuerosis
Veronica Reply
a sheet of pearly white fibrous tissue that takes the place of a tendon in flat muscles having a wide area of attachment.
Hassan
example of epitheliam tissue
Nirob Reply
what is systemic anatomy
Friday Reply
it's a study of organ structure
Amarachi
definition of anatomy and physiology
Kapil Reply
in anatomy we study about structure of human body........ in physiology we study about function
Zahid
Explain the anatomy
Junaid
structure of heart
Anusha
explain biology
saviour
biology is the science of life. biologists study the structure, function, growth, origin, evolution and distribution of living organisms.
Kadence
how is albino affected
Ujam Reply
what are the important stuff in the papillary layer
Ujam
Melanie's is responsible for the change in the color of the skin
Ujam
what happened when they are badly severed
Ujam
what happened when they are badly severed
Ujam
Examples of glial cells?
Nesh Reply
glial cell s help in the attractive foces of motion in the cellular network
Ujam
What is glial cell?
Esther
what is gland
Nirob
a gland is a group of cells or group of similar cells that secretes substances
Veronica
what is homeostasis
Laura Reply
homeostasis- The ability to maintain relatively stable internal conditions even though the outside world changes continuously. i,e, maintaining normal values in your body such as Adequate blood levels,blood pressure, heart activity and blood pressure.
Williams
thank you
Laura
Give atleast three reasons to study anatomy and physiology
George Reply
It helps to know about the body structure properly and administer proper care for the patient
Opeyemi
what's augmentin
Aphet Reply
augmentin is a type of combination antibiotic.
wintana

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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