lec 16-Energy release from fat: 4BBY1013 Biochemistry

A set of vocabulary flashcards covering the biochemical processes of lipid storage, fatty acid activation, the carnitine shuttle, the β-oxidation pathway, and ketogenesis based on the 4BBY1013 lecture.

Adipose tissue

The tissue in which triglycerides are stored as large fat droplets in fat cells, providing a compact and large long-term fuel store.

Triglyceride (Triacylglycerol)

A fuel molecule formed by three fatty acids linked to a glycerol backbone via ester bonds.

Energy yield of Fat

On a weight basis, $1\,g$ of fat yields $38\,kJ$, which is significantly higher than the yield of protein ($21\,kJ$) or carbohydrate ($17\,kJ$).

Albumin

A plasma protein that binds to free fatty acids to transport them through the bloodstream to muscles, the heart, and the liver.

Glycerol

A water-soluble product of triglyceride breakdown that is converted to pyruvate via glycolysis or to glucose via gluconeogenesis in the liver.

Fatty acyl-CoA synthetase

An enzyme located in the cytosol that activates long-chain fatty acids by adding $CoA$ at the expense of $ATP$ (energetically equivalent to $2\,ATP$).

Coenzyme A (CoA)

A dinucleotide containing a vitamin and a sulphur-containing group that forms thioester bonds with carboxylic acids.

Carnitine shuttle

A system required to transport fatty acyl-CoA across the inner mitochondrial membrane using carnitine and two acyltransferase enzymes.

Carnitine acyltransferase I

The enzyme that transfers a fatty acid group to carnitine in the intermembrane space to create fatty acyl-carnitine.

$\beta$-oxidation

A series of four mitochondrial enzyme reactions that remove two-carbon units from a fatty acid chain as acetyl-CoA, while generating $NADH$ and $FADH_2$.

Acyl-CoA dehydrogenase

The first enzyme of $\beta$-oxidation that removes two hydrogen atoms to form a double bond, reducing $FAD$ to $FADH_2$.

Enoyl-CoA hydratase

The second enzyme of $\beta$-oxidation that catalyzes the addition of a water molecule ($H_2O$) across the double bond.

Hydroxyacyl-CoA dehydrogenase

The third enzyme of $\beta$-oxidation that removes two hydrogen atoms to reduce $NAD^+$ to $NADH + H^+$.

$\beta$-Ketoacyl-CoA thiolase

The fourth enzyme of $\beta$-oxidation that cleaves the bond and adds $CoA-SH$ to release acetyl-CoA and a shortened fatty acyl-CoA.

Palmitic acid ($16:0$) energy yield

A fatty acid that produces a net total of $106\,ATP$ molecules through the complete oxidation of its $16$ carbons via $\beta$-oxidation and the TCA cycle.

Propionyl-CoA-carboxylase

The enzyme that converts the last three-carbon unit (propionyl-CoA) of an odd-numbered fatty acid into methylmalonyl-CoA using $ATP$.

Ketogenesis

The process occurring in hepatocytes where excess acetyl-CoA is converted into ketone bodies because the concentration exceeds the capacity of the TCA cycle.

Ketone bodies

Molecules including acetoacetate and $\beta$-hydroxybutyrate that are released into the bloodstream to act as alternative fuels during starvation or Type I diabetes.