Ch. 19.2: Lipid metabolism

what is the dynamic state of lipids in the body

catabolism (breakdown) and anabolism (synthesis) are constantly happening

what are the 6 functions of lipids?

1) fats can be oxidized to CO2 for ATP (krebs)

2) make up glycolipids and phospholipids

3) contribute to lung alveolar integrity

4) solubilize & store fat-soluble vitamins (ADEK)

5) help synthesize prostaglandins, sex hormones, and adrenal hormones

6) provide energy

how are triglycerides stored in the body

in all tissues

adipose tissue: a special fat tissue made of adipocytes (fat cells that will synthesize fat & store it for later use)

what is the difference between fat storage and fat catabolism?

1) fat storage

• occurs in energy surplus

• glucose, proteins & fat → fat storage

2) fat catabolism

• occurs in energy deficiency

• fat storge → energy

what is the role of insulin?

increases fat storage

in adipocyte

released after a meal

what is the role of epinephrine

decrease fat storage when body is under stress

limits the ability of adipocytes to store fat

what is the role of cortisol

decreases fat storage

what is the role of glucagon

decreases fat storage

what is the role of growth hormone

decreases fat storage

so what 4 hormones decrease fat storage

cortisol, epinephrine, glucagon, growth hormone

how does triglyceride deposition vary between ruminants and monogastric animals?

1) monogastric: composition of TGs deposited in the body are similar to the ones consumed (eat saturated fats = deposit saturated fats)

2) ruminants: composition can be different because unsaturated fats are saturated in the rumen (so saturated fats are deposited when unsaturated fats are consumed)

how long are fat-soluble vitamins and cholesterol stored?

~30-90 days

how does lipid production in mammary tissue differ between ruminants and monogastrics?

1) monogastrics: milk fat is primarily derived from GLUCOSE

2) ruminants: milk fat is primarily derived from VFAs (ACETATE)

what are the 4 sources of acetyl-CoA?

1) CHOs

2) Proteins (amino acids)

3) VFAs in ruminants (glucose → pyruvate → lactic acid or A-CoA)

4) Degraded fats

what tissues does fatty acid synthesis take place

liver, kidney, brain, lungs, mammary gland

where in the cell does fatty acid synthesis take place

cytosol

how are fatty acids formed

1) fatty acid synthase adds 2 carbons at a time in the form of acetyl CoA

2) repeat until the fatty acid is 16 carbons long

what is the enzyme that performs fatty acid synthesis

fatty acid synthase

how is fatty acid synthase regulated

1) excess energy = ^^ fat synthesis

2) deficient energy = vv fat synthesis

how are fats broken down

1) 2 carbons at a time, beta oxidation

2) triglyceride + tissue lipase = glycerol + fatty acid

what tissues break down fats

muscle, connective tissue, liver, kidney, and adipose tissue

what body parts rely heavily on fatty acid oxidation

liver, heart, and resting skeletal muscle

whats the step by step of beta oxidation

1) 1 mole of acetate (2 carbons) is removed as acetyl CoA

2) process repeats until the fat is completely broken down

• original fat has even number of C: breaks down into just acetyl CoAs

• original has ODD number of C: breaks into mostly acetyl CoA and 1 propionyl CoA (3 C)

3) acetyl CoA enters the kreb cycle and produces energy

where does beta oxidation occur in the cell

mitochondria

how many ATP do you get from 1 acetyl-CoA in the krebs cycle

12

how much ATP is produced from one step of beta oxidation (removing 1 acetyl-coa)

5 (1 NADH and 1 FADH2)

when can ketosis occur

when an animal has a high energy demand, like a lactating ewe or high producing dairy cow

how does ketosis work

increase energy demand (milk production) → increased beta oxidation → increased acetyl CoA → acetyl CoA overloads the krebs cycle and backs it up → so acetyl CoA is converted to ketones → blood pH decreases → metabolic acidosis

what are the 3 examples of ketones

1) acetoacetic acid

2) beta-hydroxybutyric acid

3) acetone

what ketone is toxic in large amounts

acetoacetic acid

what are the symptoms of ketosis

weak, trembling, acetone breath (acidic)

what are the remedies for ketosis

calcium gluconate or sodium propionate

• these are buffers that increase the pH of the blood and provide glucose to shut down beta oxidation (& thus decrease amt of acetyl CoA)