Utilization of fats and amino acids as fuels

• To utilize triglycerides as fuel, they must be:

• Broken down

• Transported

• Activated

• oxidized

• To utilize proteins as fuel, they must be:

• Broken down into amino acids

• Amino group removed (transferred)

• Carbon skeleton will enter pathways at appropriate points

• Triglycerides broken down by lipoprotein lipase, which is activated by hormones such as glucagon, cortisol, growth hormone

• Transported in the blood via serum albumin

• Trapped in the cell by the addition of CoA. This takes the equivalent of 2 ATPs.

• Transported into the matrix of the mitochondrion

• Undergoes oxidation. Chain is shortened by 2 carbon units (acetyl coA) with each oxidation cycle. One NADH + H+ and one FADH2 produced each time.

• Acetyl coAs go into the TCA cycle, NADH &FADH to the ET chain

Krebs Cycle

How many turns of oxidation would occur for a 12 carbon fatty acid? How many acetyl CoAs, NADHs and FADHs would be produced?

Acetyl CoA

Turns of the oxidation cycle?

Acetyl CoAs produced?

NADHs and FADH2s produced?

TOTAL ATPs?

• The term glucogenic is used to describe amino acids whose carbons are converted to glucose by way of the gluconeogenesis pathway.

• Many amino acids also have pathways which lead to acetylCoA or to acetoacetyCoA, from which fats or ketone bodies can be made. These are called ketogenic amino acids. Only two of these (leucine and lycine) are not also glucogenic. Yes, you can get fats from proteins, either directly in the case of ketogenic amino acids or less directly through gluconeogenesis and glycolysis in the case of glucogenic amino acids.

Proteins are generally used sparingly, and mainly in order to conserve or replenish blood glucose.

                                                                                                                              

(can be used by the brain as an alternative to glucose)

Amino Acid Essential? Glucogenic? Ketogenic?Alanine No Yes NoArginine No Yes NoAsparagine No Yes NoAspartate No Yes NoCysteine No Yes NoGlutamate No Yes NoGlutamine No Yes NoGlycine No Yes NoHistidine Yes Yes NoIsoleucine Yes Yes YesLeucine Yes No YesLycine Yes No YesMethionine Yes Yes NoPhenylalanine Yes Yes YesProline No Yes NoSerine No Yes NoThreonine Yes Yes YesTryptophan Yes Yes YesTyrosine Yes Yes YesValine Yes Yes No