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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 is plasma
Chukwu Reply
functions of plasma membrane
Dinyando Reply
what is heparin
Lawrence Reply
why is it anatomy
Tenacious Reply
hello
ASIMENU
hi
asare
hws life
Tenacious
anatomy is the scientific study of the body's structure
Lawrence
great
Lawrence
good night
Kaaya
anatomy is the study of form, physiology is the study of function
Patrick
anatomy is the study of the structure of the body and the physical relationship between it constituent part
Florence
what is heparin
Lawrence
what is the trunk
Tenacious
trunk is define as a person's or animal's body apart from the limp and head
Lawrence
The trunk is part of the axial skeleton
Patrick
supine or dorsal position is used in clinical setting when patient is placed in position, to examine what?
Dinyando Reply
what do nurses/doctors detect when a patient is placed on dorsal position?
Dinyando
What is coroid process?
kelvin Reply
describe special situation with implications in medical ethics.
kelvin
what is the difference between anatomy and physiology
Dinyando Reply
anatomy is the study of human body . and physiology is the study of the brain
Maryiam
ok
Varun
hi friends
Varun
hi!
kelvin
hello
Maryiam
sorry I cant see the full question
Jessica Reply
what was the question?
evelyna
what is spine as a bone marking?
John
similar to a crest but raised more
evelyna
pointed process
evelyna
slender
evelyna
pointed projection i meant
evelyna
what fills the hallow space in the middle of bones? thanks
John
marrow
evelyna
bone marrow
evelyna
hey you gotta read a book
evelyna
i just happen to take this bone chapter in my book last week so i remember
evelyna
yeah i should. how about the correct match of the number of tarsal, metatarsal and phalanges?
John
10, fingers and toes, u know this
Patrick
what is the difference between basal laminal and basal membrane
Nartey Reply
I think they r the same
Patrick
If one is missing the opsin which detects wavelengths of approximately 560 nm what color would they be unable to see?
Alicia Reply
how do I explain into details the epithelial tissue
Sir Reply
Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the epidermis, the outermost layer of the skin. There are three principal shapes of epithelialcell: squamous, columnar, and cub
DJ
thank you
Sir
explain how the intestinal irritation results in diarrhoea
Sir
what is cerebrospinal fluid
nitesha Reply
Cerebrospinal fluid is a clear, colorless body fluid found in the brain and spinal cord. It is produced by the specialised ependymal cells in the choroid plexuses of the ventricles of the brain, and absorbed in the arachnoid granulations.
DJ
cerebrospinal fluid is the fluid present in the brain and spinal cord
olusoga
it is whitish in colour
olusoga
what are the function of the blood
Hannah Reply
to transport oxygen in hemoglobin and nutrients
Thembani
ok
Hannah
describe the pulmonary circulation
Hannah
Which of the following structures contains membranes with mucus glands and blood vessels to help humidify and warm air?
Sheika Reply
thoracic pump for blood, and lymphatic flow for mucus membranes .
Rugiatu
explanation shortly about organizaton of human body
Maulidi Reply
the human body is the entire structure of a human being.it is composed of many different types of cells that together create tissues and subsequently organ systems.they ensure homeostasis and viability of the human body
Chundu

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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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