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7-Biology of Lactation > Slide Set 10: Milk Fat Biosynthesis > Flashcards

Slide Set 10: Milk Fat Biosynthesis Flashcards

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1
Q

How much blood in the mammary tissue is needed for 1L of milk?

A

500L of blood

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2
Q

Does rumen has enzymes?

A

No only bacteria

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3
Q

What is the main feature of bacteria in the rumen?

A

Digest fibrous materials

- cellulose and hemi-cellulose

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4
Q

Structural CHO is called

A

silage

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5
Q

Non-structural CHO is called

A

concentrate

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6
Q

What is the dietary CHO digested into by the bacteria of the rumen?

A

3 volatile fatty acids:

  • butyrate
  • propionate
  • acetate
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7
Q

What is the main source of energy for cows and humans?

A

for cows - butyrate

for humans - glucose

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8
Q

How is acetate related to milk fat percentage?

A

Higher the acetate higher the milk fat percentage

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9
Q

What is the main gluconeogenic volatile fatty acid?

A

propionate

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10
Q

Why is propionate important?

A
  • for lactose biosynthesis

- for development of the cell wall of the rumen

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11
Q

Where is dietary fat digested?

A

in the small intestine both in humans and ruminants

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12
Q

What is the composition of VLDL?

A

50% TG
22% Cholesterol
18% Phospholipids
9% Protein

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13
Q

What is the composition of Chylomicrons?

A

83% TG
8% Cholesterol
7% Phospholipids
2% Protein

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14
Q

Which lipoprotein is responsible for carrying lipids in humans and cows?

A

in humans it is chylomicrons

in cows it is VLDL

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15
Q

Mammary gland can only synthesize _________ chain fatty acids

A

medium and short chain

C4-C14

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16
Q

What are the sources of milk fatty acids?

A
  • Blood plasma lipids (50%)

- De novo synthesis in the mammary gland (50%)

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17
Q

What are the sources of blood plasma lipids?

A
  • diet (80%)

- adipose tissue (20%)

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18
Q

What are the pathways of fatty acid synthesis in the mammary gland?

A
  • fatty acid oxidation (B-oxidation)

- Malonyl-CoA pathway

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19
Q

Where is B-oxidation take place and what is the end product?

A

in the mitochondria

only short chain fatty acids

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20
Q

Where does Malonyl-CoA pathway take place and what is the end product?

A

in the cytoplasm

elongation up to C16

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21
Q

What is the main pathway of de novo milk fatty acid synthesis?

A

Malonyl-CoA pathway

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22
Q

What are the two steps of Malonyl-CoA pathway?

A
  1. Formation of malonyl-CoA from Acetyl-CoA

2. Step wise elongation by addition of Malonyl-CoA

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23
Q

What is the equation for formation of malonyl-CoA from Acetyl-CoA?

A

Acetyl CoA + ATP + CO2 —> Malonly-CoA + ADP + Pi

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24
Q

What is the name of the enzyme required for the formation of malonyl-CoA from Acetyl-CoA?

A

Acetyl-CoA carboxylase

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25
Q

What is the equation for step wise elongation by addition of Malonyl-CoA?

A

Acetyl-Coa + 7Malonyl-CoA + 14 (NADPH + H+) —> Palmitate + 7CO2 + 14NADPH + 8CoA + 6H20

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26
Q

What is the name of the enzyme required for the step wise elongation by addition of Malonyl-CoA?

A

Fatty acid synthetase

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27
Q

Explain the steps of the Malonyl-CoA pathway

A
  • Acetyl CoA is carboxylated to malonyl CoA
  • Malonyl CoA joins an acyl carrier protein
  • Malonyl acyl complex attaches to acetyl CoA molecule to form β-hydroxybutyrate
  • Hydrogenation of β-hydroxybutyrate produces butyryl Protein complex
  • Addition of a second malonyl CoA increases chain length to C6
  • More malonyl CoA molecules are added until C16
28
Q

Complete elongation produces ____

A

C16

no further elongation beyond that

29
Q

How is are the fatty acids with less than C16 are synthesized in the mammary gland?

A

Premature termination of chain elongation by thioesterase II will produce medium & short chain fatty acids

30
Q

What is the enzyme that is required for the premature termination of chain elongation?

A

thioesterase II

31
Q

Explain the fatty acid biosynthesis in the mammary gland of monogastric mammals

A
  • the glucose uptake of monogastric animals are much higher than ruminants
  • glucose will be metabolized into pyruvate through glycolysis the pyruvate then enters the mitochondria and converted into acetyl-coA
  • Acetyl-CoA cannot diffuse the membrane so the acetyl coA will be carried to the cytosol as citrate
  • citrate will be cleaved into acetyl-coA and oxaloacetate in the cytosol
  • this break down will take place by an enzyme called citrate lyase
  • then Acetyl-CoA can be used for a primary source of fatty acid synthesis
  • Acetyl-CoA will go into malate and will generate NADPH PENTOSE MONOPHOSTPHATE PATHWAY main source of NADPH for fatty acids
32
Q

What is the main sources of Acetyl-CoA in ruminants?

A

acetate and B-HBA

33
Q

What is the main source of Acetyl-CoA in non-ruminants?

A

produced in the mitochondria from pyruvate

34
Q

What is the main source of reducing equivalent (NADPH) in ruminants?

A

conversion of isocitrate to a-ketogluterate

35
Q

What is the main source of reducing equivalent (NADPH) in non-ruminants?

A

from oxaloactetate

36
Q

What are the two sources of fatty acids for the biosynthesis of milk TG?

A
  1. Blood lipids (dietary lipids and adipose tissue)
  2. De novo synthesis (within the mammary
    gland)
37
Q

Where does milk TG biosynthesis take place?

A

In the SER

38
Q

What are the two pathways for TG biosynthesis?

A
  1. Glycerol 3 phosphate

2. Monoacylglycerol (monoglyceride)

39
Q

What is the major pathway for milk TG biosynthesis?

A

Glycerol 3 phosphate pathway

40
Q

What are the 3 sources of glycerol for milk TG biosynthesis?

A
  1. Glucose via glycolytic pathway intermediates (70%)
  2. Free glycerol from blood plasma (10%)
  3. Plasma lipids, following lipolysis at the mammary cell capillary wall (20%)
41
Q

Where does desaturation of stearic acid (C18:0) occur?

A

small intestine and mammary gland (more active in the mammary gland)

42
Q

What is the main objective of desaturation of stearic acid?

A

the main objective is to maintain milk fat fluidity

43
Q

What is the enzyme needed for desaturation of stearic acid? What is the end product?

A

desaturase

C18:0 to C18:1

44
Q

What happens if the cow consumes a high fat diet?

A

High levels of fats in diets, depress intake and reduce ruminal digestibility

45
Q

_________ fats are more detrimental to ruminal microbes than ______ fats (tallow)

A

Polyunsaturated fats (oils)

saturated fats

46
Q

Explain the metabolism of dietary fat in the rumen

A
  • dietary fat (mainly polyunsaturated) enters the rumen and gets hydrolyzed into polyunsaturated fatty acids (C18:3)
  • Polyunsaturated fatty acids then go through isomerization and biohydrogenation into saturated fatty acids (C18:0) and partially unsaturated fatty acids
  • then saturated fatty acids (C18:0) and partially unsaturated fatty acids are transported to the small intestine from the reticulo-rumen as mostly saturated FA
47
Q

for the ruminal bacteria it is very import process to detoxify fatty acids as a defense mechanism. And it requires 2 steps:

A
  1. isomerization conversion cis to trans. Most fatty acids in nature are in cis. trans only found in the rumen bc of the bacteria
  2. biohydrogenation
48
Q

How are unsaturated fatty acids converted to saturated fatty acids by the ruminal microbes?

A
  1. Hydrolysis of triglycerides to fatty acids
  2. Isomerization
  3. Hydrogenation
49
Q

What are the end product of fat metabolism in the rumen?

A
  1. Saturated fatty acids (e.g. stearic acid, C18:0)
  2. Partially saturated & isomerized fatty acids (e.g. cis-9, trans-11
    C18:2)
  3. Branched and odd number fatty acids of microbial origin
50
Q

The extent to which dietary fat can alter milk fatty acid composition depends on:

A

o Fatty acid composition of dietary fat
o Degree of biohydrogenation in the rumen
o Influence of dietary fat on rumen microbes

51
Q

What are the effects of high dietary fat on milk fatty acid composition?

A

Ø Decrease concentrations of short & medium chain fatty acids
Ø increase concentrations of long chain fatty acids
Ø increase concentration of PUFA (in some
conditions
Ø Decrease milk fat percentage (high levels)

52
Q

What are the problems associated with milk high in PUFA?

A
  • Milk with high levels of PUFA (C18:2 & C18:3) is more susceptible to autoxidation (short shelf life)
  • Produces softer butter (oil off at low temperature)
  • Requires separate collection and processing systems
  • Modifications of processing facilities involved in production of dairy products (butter & cheese)
  • A better alternative is to decrease the ratio of C16:0 to C18:1 without excessive increase in C18:2 and C18:3
53
Q

What are health-promoting compounds found in milk?

A
  • Conjugated linoleic acid (CLA)
  • Butyric acid,
  • Sphingomyelin
  • B-carotene
  • Omega-3 DHA
54
Q

What are the two approaches to improve the quality of milk fatty acids?

A
  1. Increase the concentration of polyunsaturated fatty acids of feed origin (Omega-3 fatty acid)
  2. Increase fatty acid content of animal origin (e.g. CLA)
55
Q

Why is CLA health-promoting?

A
  • The only fatty acid shown to inhibit carcinogenesis
  • Potent at very low concentration
  • Ability to prevent diabetes
56
Q

What are some nutritional strategies to increase CLA content in milk?

A
  • Unsaturated fatty acid content of the diet
  • High forage : concentrate ratio
  • Source of dietary fat (substrate)
  • Level of fat supplementation
  • All factors that affect ruminal fermentation may affect CLA biosynthesis and trans fatty acid
57
Q

How does dietary fat affect human milk?

A

Dietary fat intake does not affect total amount of fat in breast milk, however it influences the fatty acid composition

58
Q

Foremilk vs Hindmilk

A

• Fore milk has a lower fat content than hind milk.
o As the infant continues to breastfeed over the next several minutes, the fat content increases.
• Hind milk is thought to facilitate satiety in the infant.

59
Q

What are the PUFAs found in the human milk

A

DHA & AA

60
Q

What does DHA concentration depend on?

A

DHA concentration varies according to diet (high with fish rich-diet).

61
Q

What does AA concentration depend on?

A

AA concentration of breast milk is stable (derived from C18:2)

62
Q

Cholesterol content of human milk vs formula based cow milk

A

Cholesterol content of breast milk is higher than formula-based cow milk

63
Q

What are the health effects of human milk cholesterol?

A

Exposure to breast milk cholesterol may have long term benefits for cardiovascular health

64
Q

What is the importance of DHA?

A
  • Primary structural component of the human brain, cerebral cortex, skin, and retina
  • Enhances the development of visual system (high levels in photoreceptors)
  • Improve cognitive ability of infants
  • Breast fed infants have higher levels of DHA than formula fed infants
  • Breast fed infants accumulate DHA in the cortex, whereas formula fed infants maintain the same level found at birth
65
Q

Breastmilk vs Formula Milk

A
  • Baby formula was fortified with essential fatty acid precursors (linoleic and linolenic acids)
  • In 2001, formula companies added DHA and AA to narrow the nutrient gap between breast milk and formula
  • Added DHA was derived from algae and AA was extracted from soil fungi
  • Human fatty acids are structurally different from plant FA (may cause digestive problems)

7-Biology of Lactation (16 decks)

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