Section 3 Other Carbohydrate Biosynthetic Pathways Part E

Lactose synthesis of Lactose which is a ?

• disaccharide

Disaccharide Lactose made up of?

• UDP-galactose and glucose

Lactose is synthesized in?

• mammary gland

Lactose Synthesis uses which enzyme?

• lactose synthase

Lactose synthase has 2 subunits

• Galactosyltransferase

• alpha-Lactalbumin

Galactosyltransferase is what type of subunit?

• Catalytic Subunit

what reaction does Galactosyltransferase catalyze?

• UDP-galactose and acetylglucosamine

What does Galactosyltransferase reaction yield?

• N-acetyllactosamine

Alpha-lactalbumin is a ?

• mammary gland protein

Alpha-lactabumin lacks a ?

• catalytic site

What does Alpha-lactaumin do?

• alters specificity of galatosyltransferase

What does altering the specificity of galactosyltransferase do?

• allows for formation of lactose instead of N-acetyllactosamine

• accepts glucose

how is alpha-lactalbumin synthesized?

• by trigger hormonal changes at parturition

What does alpha-lactalbumin synthesis promote?

• promotes lactose synthesis from milk production

Infants Lactose Tolerant through?

• lactose hydrolyzed by B-D-galatosidase then allowed by bloodstream absorption

Adults Lactose Intolerance due to?

• lower concentrations of B-D-galactosidase

• decreases with age unless historical diet of dairy products

Galactose enzymatically converted into?

• glucose

Glycosidic Bond Formation is

• linkage of sugars to each other or other molecules

Glycosidic Bond requires?

• free energy input

Where does energy input come from to form glycosidic bonds?

• synthesis of nucleotide sugar from monosaccharide and nucleoside triphosphate

The synthesis of nucleotide sugar causes the release of ?

• PPi

In mammals form where is the glycosyl group donated from ?

• UDP glucose

Glycosylation of Proteins occurs to?

• almost all secreted/membrane associated proteins of eukaryotic cells

Glycosylation of proteins means that proteins have what attached?

• a carbohydrate group

Oligosaccharides covalently attached to proteins through what linkages?

• O linked glycosidic bonds

• N linked glycosidic bonds

O linked glycosidic bonds occur in ?

• the Golgi apparatus

O linked glycosidic bonds are built through?

• serial addition of monosaccharides to polypeptide chain

B-galactosyl-(1→3)-alpha-N-acytylgalactosamine to OH of?

• Ser

• Thr

O linked glycosidic bond formation requires?

• nucleotide sugars as Donors

O linked synthesis is a 2 step process

1) transfer of N-acetyl-galactosamine (GalNAc)

2) stepwise addition of sugars

Step 1 O linked synthesis

• transfer of N-acetyl-galactosamine from UDP-N-Acetyl-galactosamine to Ser/thr on polypeptide

Step 1 of O linked synthesis is done by what enzyme?

• N-acetyl-galactosamine transferase

Step 2 of O linked synthesis

• stepwise addition of sugars

N-linked Synthesis is made by a ?

• N-Acetyl-glucosamine (GlcNAc) is B-linked to amide Nitrogen of Asparganine (Asn)

Aspargenine is usually linked with what other AA?

• Ser

• Thr

Aspargenine is Never linked with what other AA?

• proline

Aspargenine is sometimes linked with what other AA?

• Asp, Glu, Leu, Trp

N-Glycosylation occurs?

• cotranslationally, added as processed

Proteins with N-linked oligosaccharides typically ?

• glycosylated then processed

The initial glycosylation reaction occurs where?

• In the ER membrane

The Early stages of glycosylation occur through residues being added to lipid carrier called ?

• dolichol pyrophophate

Dolicol Pyrophophate is ?

• long chain polyisoprenol made up of 17-21 isoprene units

Dolichol phosphate does what ?

• activates sugar residue for subsequent transfer

12 step process of N-linked synthesis ends with formation of

• (N-Acetylglucosamine)2(mannose)9(glucose)3 on dolichol carrier

Step 1 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• addition of N-acetylglucosamine-1-P and N-acetylglucosamine to dolichol-P

  • In Cytosol

Step 2 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• Addition of 5 mannosyl residues from GDP-mannose (catalyzed by 5 different mannosyltransferases)

• In Cytosol

Step 3 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• Membrane Translocation of dolichol-PP-(N-Acetylglucosamine)2(mannose)5

• Lumen of ER

Step 4 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• Cytosolic synthesis of dolichol-P-mannose from GDP-mannose and dolichol-P

• in the cytosol

Step 5 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• membrane translocation of dolichol-P-mannose to the lumen of the ER

Step 6 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• addition of four mannosyl residues from dolichol-P-mannose in reactions by 4 different mannosyltransferases

• ER of the Lumen

Step 7 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• Cytosolic synthesis of dolichol-P-glucose

• In cytosol

Step 8 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• membrane translocation of dolichol-P-glucose

• into ER of the lumen

Step 9 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• addition of 3 glucosyl residues from dolichol-P-glucose

• In lumen of ER

Step 10 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• transfer of oligosaccharide from dolichol-PP to the polypeptide chain at an Asn residue

  • attachment in lumen of ER, nascent polypeptide

Step 11 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• translocation of dolichol-PP to the cytoplasmic surface of the ER membrane

  • integrated in membrane

Step 12 of (N-Acetylglucosamine)2(mannose)9(glucose)3 Synthesis

• hydrolysis of Dolichol-PP to Dolichol-P