Glycolipids PDF

Glycolipids Level: 1st level Semester: 1st semester Module: BSF112 Module  Prepared by Dr. Shaymaa M. Abdelrahman Medical Biochemistry Department  Learning outcomes By the end of the lectures, the students will be able to: Identify definition of glycolipids Ident...

Glycolipids Level: 1st level Semester: 1st semester Module: BSF112 Module  Prepared by Dr. Shaymaa M. Abdelrahman Medical Biochemistry Department  Learning outcomes By the end of the lectures, the students will be able to: Identify definition of glycolipids Identify functions of glycolipids Enumerate types of glycolipids  What are glycolipids? Glycolipids are lipids with a carbohydrate attached by a glycosidic bond. Glycolipids are complex (compound) lipids containing carbohydrate.  Importance in diet Glycolipids are present in high concentrations in the brain, egg yolk, liver and kidney. They are not essential dietary components. Glycolipids are amphipathic Glycerol & sphingosine Types of glycolipids Types of glycosphingolipids Neutral glycosphingolipids: cerebrosides & globosides. Acidic glycosphingolipids: They are negatively charged at physiologic PH. This negative charge provided by (NANA, sialic acid) in gangliosides, or by sulfate groups in sulfatides.  Cerebrosides They are called simple glycolipids. Upon hydrolysis they give: 1) Sphingosine. 2) Fatty acid. 3) Sugar (usually galactose or glucose). Functions: 1) Cerebrosides are present in many tissues especially in the brain and myelin of nerve fibers. 2) Cerebrosides act as insulators of nerve impulses. Gaucher’s disease: 1) Accumulation of cerebrosides in phagocytes due to deficiency of β glucocerebrosidase enzyme. 2) Manifestations: mental retardation, hepatomegaly and bone disorders.  Gangliosides They are called complex glycolipids, because they contain in addition to hexose, one or more sialic acid molecules. Upon hydrolysis they give: 1) Ceramide (sphingosine and fatty acid) 2) Hexoses (glucose and galactose) 3) Hexosamines: Sialic acid (N-acetylneuraminic acid) N-acetylgalactosamine Functions: 1) They act as receptors at cell membrane. 2) They are present in high concentrations in brain. Degradation by hexosaminidase enzyme. Tay sachs disease: 1) Accumulation of gangliosides in brain and intestine due to deficiency of hexosaminidase enzyme. 2) Manifestations: mental retardation, hepatomegaly, blindness and death in early life. Globosides They contain sphingosine base, fatty acid and many glucose and galactose units (ceramide oligosaccharides). They are present in heart and kidney. Sulfatides Their structure consists of a ceramide backbone linked to a sulfated galactose sugar molecule.  Formative questions All of the following are constituents of ganglioside molecule except a. Glycerol b. Sialic acid c. Hexose sugar d. Sphingosine  Formative questions Glycosphingolipids are a Cerebrosides are composed of combination of a. Sphingosine, fatty acid, a. Ceramide with one or more glycerol and phosphoric acid sugar residues b. Sphingosine, fatty acids, b. Glycerol with galactose galactose c. Sphingosine with galactose c. Glycerol, fatty acids, galactose d. Sphingosine with phosphoric acid d. Glycerol, fatty acids, galactose, sphingol  Formative questions Gangliosides derived from glucosyl ceramide contain in addition one or more molecules of a. Sialic acid b. Glycerol c. Diacylglycerol d. Hyaluronic acid  Formative questions Cerebrosides contain all of the Hexosaminidase A is deficient following except in a. Galactose a. Tay-Sachs disease b. Sulphate b. Gaucher’s disease c. Sphingosine c. Niemann-Pick disease d. Fatty acid d. Fabry’s disease  Formative questions Glycolipid are made up of Gangliosides are complex which of the following? glycosphingolipids found in a. Proteins and lipids a. Liver b. Carbohydrates and lipids b. Brain c. Proteins and carbohydrates c. Kidney d. Lipids and nucleic acids d. Muscles  Formative questions In cell membrane, Which of the following are carbohydrates in glycolipids included in the types of are oriented glycolipids? a. Towards outside a. N-acetylgalactosamine b. Towards inside b. N-acetylglucosamine c. Towards outside and inside c. Xylose d. Randomly distributed d. Cerebrosides