Changes

== Introduction ==

= '''Milk Composition''' =

 

 

 

 

 

== Milk Composition ==

* '''Inorganic Ash''' comprises 0.5-1.0% of milk.  This is the mineral content.

 

== Inorganic Ash ==

 

* Comprises 0.5-1.0% of milk.  This is the mineral content.

** Major components: calcium, phosphate, magnesium, sodium, potassium and chloride.  The concentration of calcium, phosphate and magnesium in milk is much greater than the plasma concentration (x14,x7 and x4 respectively).

** Major components: calcium, phosphate, magnesium, sodium, potassium and chloride.  The concentration of calcium, phosphate and magnesium in milk is much greater than the plasma concentration (x14,x7 and x4 respectively).

** Minor trace elements: iodine, zinc, cobalt etc are present in concentrations <1 part per million but are essential to the nutritional value of milk.

** Minor trace elements: iodine, zinc, cobalt etc are present in concentrations <1 part per million but are essential to the nutritional value of milk.

* '''Vitamins''' are present in trace amounts,but are important for nutritional value.

 

* Present in trace amounts,but are important for nutritional value.

** Major components: A and Riboflavin (B)

** Major components: A and Riboflavin (B)

** Minor components: E, K and the other B vitamins

** Minor components: E, K and the other B vitamins

* '''Fat''' comprises 1-30% of milk.  

 

 

* Comprises 1-30% of milk.  

** Synthesised in the smooth endoplasmic reticulem, then packaged into lipid droplets, which increase in size as they move towards the plasma membrane.  Eventually they pinch off and enter the milk as fat globules surrounded by membrane.

** Synthesised in the smooth endoplasmic reticulem, then packaged into lipid droplets, which increase in size as they move towards the plasma membrane.  Eventually they pinch off and enter the milk as fat globules surrounded by membrane.

** 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''' can be divided into two groups.

 

 

* Can be divided into two groups.

** '''Caseins''': precipitate at pH 4.5 or lower. They comprise 40-80% of total milk protein and exist in colloidal suspension complexed to calcium, phosphate and magnesium.  This allows the mineral concentration in milk to exceed that of plasma.  They have little secondary structure, so are easily digestable by Rennin.  They have a high content of nutritionally essential amino acids.

** '''Caseins''': precipitate at pH 4.5 or lower. They comprise 40-80% of total milk protein and exist in colloidal suspension complexed to calcium, phosphate and magnesium.  This allows the mineral concentration in milk to exceed that of plasma.  They have little secondary structure, so are easily digestable by Rennin.  They have a high content of nutritionally essential amino acids.

** '''Whey''': remain in solution at pH 4.5 or lower.  They comprise 20-60% of the total milk protein.  They are rich in α lactalbumin which is required for the synthesis of the milk carbohydrate lactose.  In ruminants, β lactoglobulin is also a majoy whey protein component, supplying the neonate with amino acids.

** '''Whey''': remain in solution at pH 4.5 or lower.  They comprise 20-60% of the total milk protein.  They are rich in α lactalbumin which is required for the synthesis of the milk carbohydrate lactose.  In ruminants, β lactoglobulin is also a majoy whey protein component, supplying the neonate with amino acids.

* '''Carbohydrate''': '''Lactose''' is the only carbohydrate in milk.  

 

== Carbohydrate:Lactose ==

 

* The only carbohydrate in milk.  

** Lactose is a '''dimer''' of '''glucose and galactose''', which are epimers.  Lacotse acts as a source of glucose to the neonate, as lactase in the gastrointestinal tract is capable of splitting the dimer.

** Lactose is a '''dimer''' of '''glucose and galactose''', which are epimers.  Lacotse acts as a source of glucose to the neonate, as lactase in the gastrointestinal tract is capable of splitting the dimer.

*** Synthesised on the golgi, then packaged into golgi vesicles which pinch off and migrate towards the plasma membrane.  At the plasma membrane, the contents of vesicles are released by exocytosis.

*** Synthesised on the golgi, then packaged into golgi vesicles which pinch off and migrate towards the plasma membrane.  At the plasma membrane, the contents of vesicles are released by exocytosis.

* In the '''Mare''', a measurement of '''calcium carbonate''' in mammary secretions can aid prediction of foaling onset.  If >200ppm, 51% of late pregnant mares will foal in 24 hours and 97% in 72 hours.  If <200ppm, 99% will not foal in the next 24 hours.

* In the '''Mare''', a measurement of '''calcium carbonate''' in mammary secretions can aid prediction of foaling onset.  If >200ppm, 51% of late pregnant mares will foal in 24 hours and 97% in 72 hours.  If <200ppm, 99% will not foal in the next 24 hours.

----

----

= Biosynthesis =

= '''Biosynthesis''' =

4. UDP is recycled

4. UDP is recycled

The mammary gland synthesised 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%).

1. Triacylglycerol from lipoproteins is broken down by '''lipoprotein lipase''' to three free fatty acids and glycerol.  These are then reassembled in cells to form new triacylglycerols.

1. Triacylglycerol from lipoproteins is broken down by '''lipoprotein lipase''' to three free fatty acids and glycerol.  These are then reassembled in cells to form new triacylglycerols.

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.