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Milk Composition & Synthesis
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Milk Composition & Synthesis
Study Questions & References


Study Questions and References

Study Questions

1. It is possible to transplant the mammary gland of a goat to the neck of the goat and the gland will produce milk (this is true, if done carefully). What about transplanting the lactating mammary gland of a cow to the neck of a sow? Assuming that this could be done successfully, would the composition of the milk produced by that transplanted gland be like sow milk, like cow milk, or like some combination of the two? Assume that the transplanted cow udder would not be rejected by the immune system of the sow and that it would be capable of producing milk. Consider the following in addressing this question : how the individual components of milk are synthesized, how the composition of the milk from the transplanted gland would compare with the composition of sow milk (the recipient of the transplant) and with the composition of cow milk (the donor of the transplant), and why the milk composition would be similar or different in each case. Be sure that you can explain in detail why you have come to these conclusions and to offer specific examples to illustrate your answers.

2. You have a very keen eye for biochemistry. You are able to observe a single glucose molecule in the blood of a lactating mammal. You do not know what type of mammal it is. You have taken a personal interest in this particular glucose molecule. Discuss all potential origins of the glucose molecule which would explain how it might end up in the mammary gland, and discuss all potential fates of the glucose molecule if it is taken up by the lactating mammary epithelial cell. Discuss all alternative origins, metabolic pathways, and fates of the glucose molecule. How does it end up as part of milk or contributing to the synthesis and secretion of milk? Discuss and explain any metabolic pathways involved. How are the various points of participation of this glucose molecule in milk synthesis and secretion regulated?

3. How might you go about altering the fatty acid composition of milk from the following species:

  • pig
  • human
  • cow
  • rabbit

References

Mammary Carbohydrates and Lactose Synthesis

See Kuhn, Ch. 6 in Mepham, 1983, Biochemistry of Lactation, Elsevier.

Saavedra, JM and Perman JA 1989 Current Concepts in lactose malabsoption and intolerance. Ann. Rev. Nutrition 9:475

For general references on milk proteins and their synthesis see:

Mercier and Gaye, 1983, Ch. 7 in Biochemistry of Lactation, T. B. Mepham ed, p.177

Mercier and Gaye, 1982, J. Dairy Sci. 65:299

Burgoyne RD, Duncan JS 1998 Secretion of milk proteins. J. Mammary Gland Biology and Neoplasia 3:275-286.

Some More References on Lactose Synthesis and a-Lactalbumin :

Brew, K, Grobler, J.A. (1992) a-Lactalbumin. In Advanced Dairy Chemistry, Volume 1, Proteins. P. F. Fox, Ed. Elsevier Science Publishers Ltd, New York.

Das Gupta, N.A., Alexander, L.J., Beattie, C.W. (1992) The sequence of a porcine cDNA encoding a-lactalbumin. Gene 110:265-266.

Dhiman, T.R., Satter, L.D. (1993) Protein as the first-limiting nutrient for lactating dairy cows fed high proportions of good quality alfalfa silage. J. Dairy Sci. 76:1960-1971.

Hayssen, V., Blackburn, D.G. (1985) a-Lactalbumin and the origins of lactation. Evolution 39:5 1147-1149.

Kuhn, N.J., Wooding, F.B.P., White, A. (1980) Properties of galactosyltransferase-enriched vesicles of Golgi membranes from lactating-rat mammary gland. Eur. J. Biochem. 103:377-385.

McKenzie, H.A., White, F.H. (1991) Lysozyme and a-lactalbumin: structure, function, and interrelationships. In: Advances in Protein Chemistry 41:173-315.

Mitranic, M.M., Paquet, M.R., Moscarello, M.A. (1988) The interaction of bovine milk galactosyltransferase with lipid and a-lactalbumin. Bioch Biophys Acta 956:277-284.

Rao, D. R., Hegarty, H. M., Larson, B. L. (1975) Effect of cell density on lactose synthesis in bovine mammary cell cultures. J. Dairy Sci. 58:159-163.

Vilotte, J.L., Soulier, S. (1992) Isolation and characterization of the mouse a-lactalbumin-encoding gene interspecies comparison, tissue- and stage-specific expression. Gene 119:287-292.

Zhao, F.-Q., Moseley, W.M., Tucker, H.A., Kennelly, J.J. (1996) Regulation of glucose transporter gene expression in mammary gland, muscle, and fat of lactating cows by administration of bovine growth hormone and bovine growth hormone-releasing factor. J. Anim. Sci. 74:183-189.


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