Other Carbohydrate Biosynthetic Pathways | Quizlet

What is the primary responsibility of the liver?

maintaining constant glucose level

Glucose produced by ____ or from glycogen ____ is released from the liver.

gluconeogenesis; breakdown

Glucose can be used by other tissues as an ____ source

energy

What kind of sugar is lactose?

disaccharide

Where is lactose produce and what is it produced by?

in the mammary gland by lactose synthase

What are the two subunits of lactose synthase?

galactosyltransferase and alpha-Lactalbumin

Galactosyltransferase catalyzes the reaction of ____ and ___

UDP-galactose; acetylglucosamine

The reaction between UDP-galactose and acetylglucosamine yields what?

N-acetyllactosamine

alpha-lactalbumin is a ___ gland protein with no ___ activity

mammary; catalytic

T/F: alpha-lactalbumin alters specificity of galactosyltransferase

true

When alpha-lactalbumin alters specificity of galactosyltransferase, it uses glucose as an ____ and forms ___ instead of acetyllactosamine

acceptor; lactose

alpha-lactalbumin triggers ___ by hormonal changes at parturition (childbirth) and promotes ___ synthesis for milk production.

synthesis; lactose

For lactose intolerance in infants, how is lactose hydrolyzed?

by beta-D-galactosidase

What does the hydrolyzation of lactose in infants allow to happen?

allows absorption into the bloodstream

How is galactose converted to glucose?

enzymatically

What is the main cause of lactose intolerance in adult mammals?

low levels of beta-D-galactosidase

Where does the ingested lactose moves to?

the colon

What generates large quantities of CO2, H2, and irritating organic acids, causing painful digestive upset in lactose intolerance?

bacterial fermentation

T/F: for populations that have historically relied on dairy products for nutrition throughout life, beta-D-galactosidase levels increase with age

false

What does the formation of glycosidic bonds entail?

link sugars to each other and to other molecules which requires free energy input

The needed energy for glycosidic bonds is acquired through synthesis of a ____ sugar from a monosaccharide and a _____ triphosphate

nucleotide; nucleoside

The nucleotide sugar synthesis leads to the release of ___

PPi

In mammals, what are most glycosyl groups donated by?

uridine diphosphate glucose (UDP-glucose)

T/F: almost all secreted and membrane-associated proteins of eukaryotic cells are not glycosylated

false

Oligosaccharides are covalently attached to proteins by what kinds of glycosidic bonds?

O or N

T/F: The most common O-glycosidic attachment involves the disaccharide core β-galactosyl-(1→3)-α-N-acetylgalactosamine linked to the OH group of either Ser or Thr

true

Where does O-linked oligosaccharide synthesis occur?

golgi apparatus

How does O-linked oligosaccharide synthesis occur?

By serial addition of monosaccharide units to a completed polypeptide, which requires nucleotide sugars as donors

T/F: in O-linked oligosaccharide synthesis, the first step is the transfer of N-acetyl-galactosamine (GalNAc)

true

In step one of O-linked oligosaccharide synthesis transfer of N-acetyl-galactosamine(GalNAc) is from UDP-GalNAc to a ___ (or ____) residue on the polypeptide by GalNAc _______

ser; thr; transferase

T/F: In O-linked oligosaccharide synthesis, the second step is stepwise subtraction of sugars. (ex: galactose, sialic acid, -acetylglucosamine, and fucose)

false

In N-linked oligosaccharide synthesis, N-acetyl-______samine is invariably ___-linked to the amide nitrogen of an ___ residue

gluco; beta; asn

In N-linked oligosaccharide synthesis, there could be Asn-X-___ or Asn-X-___ (X ≠ Pro; rarely Asp, Glu, Leu, or Trp)

ser; thr

In N-linked oligosaccharide synthesis, how does N-glycosylation occur?

cotranslationally

In N-linked oligosaccharide synthesis, what happens to proteins containing N-linked oligosaccharides before they are processed?

they are glycosylated

In N-linked oligosaccharide synthesis, where do initial glycosylation reactions take place?

ER membrane

T/F: In the late stages of N-linked oligosaccharide synthesis, sugar residues are sequentially added to the lipid carrier dolichol pyrophosphate

false

Dolichol is a long-chain polyisoprenol containing how many isoprene units?

17 to 21

Similar to nucleoside diphosphate, dolichol phosphate ______ a sugar residue for subsequent transfer

activates

The activation of a sugar for transfer by dolichol phosphate begins with the formation of (N-acetylglucosamine)2(mannose)9(glucose)3 on dolichol carrier, which is a process with how many steps?

12

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the first step is addition of N-acetyl____samine-1-P and N-acetyl____samine to dolichol-P

gluco; gluco

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the second step is the addition of ___ mannosyl residues from GDP-mannose (catalyzed by ___ different mannosyltransferases)

five; five

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the third step is membrane translocation of dolichol-PP-(N-acetylglucosamine)2(mannose)5 to where?

the lumen of the ER

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the fourth step is _____synthesis of dolichol-P-mannose from GDP-mannose and dolichol-P

cytosolic

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the fifth step is membrane translocation of dolichol-P-mannose to where?

the lumen of the ER

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the sixth steo is the addition of ____ mannosyl residues from dolichol-P-mannose in reactions (by ____ different mannosyltransferases)

four; four

T/F: In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the seventh step is cytosolic synthesis of dolichol-P-glucose

true

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the eighth step is membrane translocation of ____

dolichol-P-glucose

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the ninth step is addition of ___ glycosyl residues from dolichol-P-glucose

three

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the tenth step is the transfer of the oligosaccharide from dolichol-PP to the polypeptide chain at an ___ residue

Asn

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the eleventh step is the translocation of dolichol-PP to the cytoplasmic surface of the _____

ER membrane

In (N-acetylglucosamine)2(mannose)9(glucose)3 synthesis, the twelfth step is the ____ of dolichol-PP to dolichol-P

hydrolysis

In N-linked oligosaccharide synthesis, once the 14-residue oligosaccharide is linked to asn, _____ and ______ start trimming

glucosidases and mannosidases

T/F: In N-linked oligosaccharide synthesis, (Mannose)3(N-acetylglucosamine)2 core found in all N-linked oligosaccharides

true