yolk

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yolk

1. the substance in an animal ovum consisting of protein and fat that nourishes the developing embryo
2. a greasy substance secreted by the skin of a sheep and present in the fleece

Yolk

 

(deutoplasm), a nutritive substance that accumulates in the ovum of animals and man in the form of granules or membranes that sometimes merge into a solid yolk mass (in insects, bony fish, and birds).

Yolk has been discovered in the ova of all animals and man, but its quantity and distribution vary considerably. In ova with a small amount of yolk, the yolk particles are distributed evenly throughout the cytoplasm (isolecithal ova). In ova with a large amount of yolk, the yolk particles are concentrated either in the vegetative part of the ovum (telolecithal ova) or in the central part of the cytoplasm, around the nucleus (centrolecithal ova). The type of egg cleavage depends on the quantity and distribution of the yolk. Chemically there are three principal varieties of yolk: protein, fat, and carbohydrate. However, in most animals the yolk granules have a complex chemical composition and contain proteins, fats, carbohydrates, ribonucleic acid, pigments, and mineral substances. For example, in the mature hen’s egg, the yolk contains 23 percent neutral fat, 16 percent protein, 11 percent phospholipids, 1.5 percent cholesterol, and 3 percent minerals. Various organelles of the ovum participate in the synthesis and accumulation of the yolk: the Golgi apparatus, endoplasmic reticulum, and mitochondria. In many animals the protein component of the yolk is synthesized outside the ovary and enters the growing ovum by means of pinocytosis. In some invertebrate animals the yolk may also accumulate in special cells of the ovary—the yolk cells, on which the developing embryo is nourished.

T. B. AIZENSHTADT

yolk

[yōk]
(biochemistry)
Nutritive material stored in an ovum.
The yellow spherical mass of food material that makes up the central portion of the egg of a bird or reptile.
References in periodicals archive ?
Baking with Liggy Ingredients For the pastry: 1 egg yolk 100g cubed salted butter 150g plain white flour 50g caster sugar For the filling: 2tbsp ground almonds 2 tbsp caster sugar 250g dessert apples 400g bramley apples 150g of blueberries 1 medium egg yolk Method Begin by making the pastry.
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With an electric mixer, beat 12 egg yolks (retaining the whites in a separate bowl) until pale and foamy, then add 200g caster sugar, finely grated zest of four lemons (and their juice) and 150g chopped walnuts, mix until smooth.
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London, August 5 ( ANI ): The more egg yolks people eat, the worse effect it has on blood vessels, a new study has revealed.
1 WHAT YOU NEED For parfait: 100g soft cooked Christmas pudding, 3 egg yolks, 60g caster sugar, 175ml double cream, dark rum to taste.
1 Their estimate: The cholesterol in a single egg yolk raises blood cholesterol by 5.