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Milk Composition and Biosynthesis- Anatomy & Physiology (view source)
Revision as of 17:49, 7 December 2010
, 17:49, 7 December 2010moved Lactation - Milk Composition and Biosynthesis- Anatomy & Physiology to Milk Composition and Biosynthesis- Anatomy & Physiology
== Milk Composition ==
= Milk Composition =
* Milk separates into two phases:
* Milk separates into two phases:
== Inorganic Ash ==
=== Inorganic Ash ===
* Comprises 0.5-1.0% of milk. This is the mineral content.
* Comprises 0.5-1.0% of milk. This is the mineral content.
== Vitamins ==
=== Vitamins ===
* Present in trace amounts,but are important for nutritional value.
* Present in trace amounts,but are important for nutritional value.
== Fat ==
=== Fat ===
* Comprises 1-30% of milk.
* Comprises 1-30% of milk.
** Globules consist mainly of triacylglycerols surrounded by a membrane containing cholesterol and phospholipid. The membrane is derived from the mammary gland plasma membrane as the globules pinch off. Globules also contain the fat soluble vitamins (D,K,E)
** Globules consist mainly of triacylglycerols surrounded by a membrane containing cholesterol and phospholipid. The membrane is derived from the mammary gland plasma membrane as the globules pinch off. Globules also contain the fat soluble vitamins (D,K,E)
== Protein ==
=== Protein ===
* Can be divided into two groups, caseins and whey.
* Can be divided into two groups, caseins and whey.
Proteins are synthesised on the rough endoplasmic reticulem and migrate to the golgi, where they are processed and complexed with minerals. Golgi vesicles containing the proteins pinch off and migrate towards the plasma membrane where their contents is released by exocytosis.
Proteins are synthesised on the rough endoplasmic reticulem and migrate to the golgi, where they are processed and complexed with minerals. Golgi vesicles containing the proteins pinch off and migrate towards the plasma membrane where their contents is released by exocytosis.
=== Caseins ===
==== Caseins ====
* Precipitate at pH 4.5 or lower.
* Precipitate at pH 4.5 or lower.
* They have little secondary structure, so are easily digestable by Rennin. They have a high content of nutritionally essential amino acids.
* They have little secondary structure, so are easily digestable by Rennin. They have a high content of nutritionally essential amino acids.
=== Whey ===
==== Whey ====
* Remain in solution at pH 4.5 or lower.
* Remain in solution at pH 4.5 or lower.
** In ruminants, β lactoglobulin is also a majoy whey protein component, supplying the neonate with amino acids.
** In ruminants, β lactoglobulin is also a majoy whey protein component, supplying the neonate with amino acids.
=== Minor Milk Proteins ===
==== Minor Milk Proteins ====
* Albumin
* Albumin
* Immunoglobulin
* Immunoglobulin
* Enzymes
* Enzymes
== Carbohydrate:Lactose ==
=== Carbohydrate:Lactose ===
* The only carbohydrate in milk.
* The only carbohydrate in milk.
== Colostrum ==
= Colostrum =
* The milk produced in the first few days after birth. It is especially rich in protein, vitamin A and fat to enhance chances of survival of the neonate. It contains less potassium and lactose than milk.
* The milk produced in the first few days after birth. It is especially rich in protein, vitamin A and fat to enhance chances of survival of the neonate. It contains less potassium and lactose than milk.
** Fat is important for energy generation and thermal insulation.
** Fat is important for energy generation and thermal insulation.
== Biosynthesis ==
= Biosynthesis =
=== Synthesis of Lactose ===
[[Image:Synthesis of Lactose.jpg|thumb|right|150px|Synthesis of Lactose,Copyright RVC 2008]]
1. In the cytosol of the mammary cell, glucose is converted to UDP- glucose. UDP glucose is then epimerised by the enzyme '''epimerase''' to form UDP galactose.
1. In the cytosol of the mammary cell, glucose is converted to UDP- glucose. UDP glucose is then epimerised by the enzyme '''epimerase''' to form UDP galactose.
4. UDP is recycled
4. UDP is recycled
=== Synthesis of the Fat Component ===
[[Image:Milk Fat and Protein Synthesis.jpg|thumb|right|150px|Synthesis of the Fat and Protein Component,Copyright RVC 2008]]
The mammary gland synthesises triacylglycerol from glycerol and three fatty acids. The fatty acids originate from triacyclglycerol in plasma lipoproteins (60%) or from synthesis in the mammary gland (40%).
The mammary gland synthesises triacylglycerol from glycerol and three fatty acids. The fatty acids originate from triacyclglycerol in plasma lipoproteins (60%) or from synthesis in the mammary gland (40%).
3. In '''ruminants''', the enzyme citrate lyase is lacking, so Acetyl CoA from glucose metabolism cannot be used for fatty acid synthesis. However, they have an abundant supply of '''acetate, butyrate and β hydroxybutyrate''' from the digestion of carbohydrate in the rumen. These are therefore used as the precursors for the synthesis of acyl CoA. '''Acyl CoA''' and '''gylcerol-3-phosphate''' then combine to form triacylglycerol.
3. In '''ruminants''', the enzyme citrate lyase is lacking, so Acetyl CoA from glucose metabolism cannot be used for fatty acid synthesis. However, they have an abundant supply of '''acetate, butyrate and β hydroxybutyrate''' from the digestion of carbohydrate in the rumen. These are therefore used as the precursors for the synthesis of acyl CoA. '''Acyl CoA''' and '''gylcerol-3-phosphate''' then combine to form triacylglycerol.
=== Synthesis of Protein ===
[[Image:The Lactating Mammary Cell.jpg|thumb|right|150px|The Lactating Mammary Cell,Copyright RVC 2008]]
1. Polypeptide chains are synthesised on the rough endoplasmic reticulem from amino acids in the blood.
1. Polypeptide chains are synthesised on the rough endoplasmic reticulem from amino acids in the blood.
=== FIL protein ===
==== FIL protein ====
* Produced in milk synthesis
* Produced in milk synthesis
[[Category:Female Reproduction]]