CHEM161 Lecture#11 Exam#2

N- linked glycans are linked via a beta-glycosidic bond to the amide N of asparagine. Draw asparagine with an N-linked oligosaccharide bonded to it.

Glucose attached to the side chain amide Nitrogen from asparagine.

ANSWER: Arrows are pointing to the reducing ends and dots represent the non-reducing ends

In the picture, which end are the arrows pointing at and what do the dots at the end of each branch represent? the reducing ends or non-reducing ends?

ANSWER: a. amylopectin b. glycogen

In the picture, which is amylopectin and which is glycogen?

What are oligosaccharides most often attached to?

polypeptides and glycoproteins

What are glycans also known as?

polysaccharides

What are larger glycans called that are hundreds or thousands of monomers?

polysaccharides

What are two interchangeable terms that are described as a large number of monosaccharides connected by glycosidic linkages?

polysaccharides and glycans

What is the core of proteoglycans?

proteins

What can hold water 1000x its weight and provides lubrication for joints and cartilage?

proteoglycan aggregates

Why is glycogen more compact and easily mobilized than other polysaccharides such as amylopectin? (compare branch points)

Amylopectin has branch point every 20-25 residues. Glycogen has branch points every 8-12 residues.

Why is chitin indigestible to mammals?

Because mammals cannot breakdown beta(1,4) bonds

Describe the three steps in which glycosylation occurs during protein synthesis.

1. As the polypeptide leaves the ribosome and is translocated throughout the cell for further folding, an oligosaccharide chain of 14 residues is attached to an asparagine residue. 2.The oligosaccharide is trimmed by enzymes called glycosidases. 3. Additional monosaccharide residues are attached by enzymes called glycosyltransferases producing a glycoprotein with a mature oligosaccharide

Fill in the blanks: The major types of heteroglycans are 1. N- and O-linked ___ 2. ___ of the Extra Cellular Matrix 3. glycan components of ___ and GPI anchors

1. heteropolysaccharides 2. glycosaminoglycans 3. glycolipids

Cellulose are made up of approximately ___ glucose units.

12,000

Amylopectin is one of the homopolysaccharides of starch and its molecular weight it up to ___ ___

200 million

Starch is a source of carbohydrates in humans. Glycogen is also a carbohydrate in humans. It is a storage molecule in vertebrates. Where can glycogen be found in the greatest abundance in humans? Provide the %.

8-10% in liver cells and 2-3% in muscle cells

Where can glycoaminoglycans be found?

Can be found in connective tissue and lubrication of joints

How does cellulase allow fungi, bacteria, and protozoa to use wood as a source of glucose?

Cellulase is the enzyme that hydrolyzes (breaks down) the beta(1,4) linkages of cellulose.

Compare the linkages of cellulose and starch

Cellulose have beta(1,4) linkages and starch has alpha(1,4) linkages

Which class of polysaccharide are high-molecular-weight carbohydrate polymers that contain more than one type of monosaccharide? homoglycans or heteroglycans?

Heteroglycans

Which class of polysaccharide are found in starch, glycogen, cellulose and chitin? Homoglycans or Heteroglycans?

Homoglycans

What is the difference between homoglycans and heteroglycans?

Homoglycans are made of one type of monosaccharide. Heteroglycans are made of two or more types of monosaccharides.

ANSWER: 1. alpha(1,4) linkage 2. The C4 side of the main chain and branch are the non-reducing ends. The reducing end is at the C1 side of the main chain. 3. alpha(1,6) linkage

In this amylopectin structure, 1. What kind of linkage is the main branch? 2. Which is the reducing end and non-reducing end? 3. What kind of linkage is the branch?

What type of bonds attache the GAG chains to the protein core of proteoglycans?

N- and O- glycosidic bonds

When does glycosylation of a protein occur?

N-Glycosylation begins while a protein is being synthesized to help determine how the protein is folded.

In addition to mannose, galactose and N-acetylglucosamine residues, what do O-linked oligosaccharides contain?

N-acetyl neu raminic acid (NANA)

Chitin is a structural homopolysaccharide. What is the monomer called and what linkage does it have?

N-acetylglucosamine monomer that forms beta(1,4) linkages

Proteins can be linear but not branched. How is this different from polysaccharides?

Polysaccharides can be linear and branched.

What are long chains of glycoaminoglycans called?

Proteoglycans

Compare the terms proteoglycan and glycoprotein.

Proteoglycans have more glycans than proteins. Glycoproteins have more proteins than glycans (carbohydrates).

What animals can live symbiotically with microorganisms that produce cellulase? The bacteria in their gut breaks down the cellulose not the animal.

Ruminants and termites

Homoglycans: Starch and glycogen are energy ___ molecules. Homoglycans: Chitin and cellulose are ___ molecules.

Starch and glycogen are energy storage molecules while chitin and cellulose are structural molecules.

What is the main difference between storage homosaccharides and structural homosaccharides?

Storage homosaccharides have alpha(1,4)linkages and structural homosaccharides have beta(1,4) linkages

What does it mean when the branch point is said to be at alpha(1,6) linkage?

The alpha anomeric carbon of the branch is bond to C6 of the main chain.

There are three amino acids that oligosaccharides can bind to. Which amino acid do N-linked oligosaccharides bind to? Which parts bind?

The side chain amide nitrogen of asparagine replaces the OH on the anomeric carbon of modified glucose.

There are three amino acids that oligosaccharides can bind to. Which amino acids do O-linked oligosaccharides bind to? Which parts bind?

The side chain hydroxyl group of serine or threonine replaces the OH on the anomeric carbon of modified galactose.

How is cellulose important?

They form dietary fiber, wood, paper and textiles.

What is special about glycosidases and glycosyltransferases?

They highly specific for the identities of the monosaccharides and the positions of the glycosidic bonds.

What is in example of a type of proteoglycan that can be found in abundance in cartilage?

aggrecan

Hyaluronic acid and ___ form huge noncovalent aggregates

aggregan

What interacts strongly with collagen in the ECM of cartilage giving it strength and resilience?

aggregan

The branching of glycogen is similar to that of amylopectin in that the branches bind at ___ linkages at the branchpoint.

alpha(1,6)

Which homopolysaccharide of glucose is branched with alpha (1,6) branch points occurring every 20-25 residues? amylose or amylopectin

amylopectin

Which homopolysaccharide forms an unbranched left-handed helix? amylopectin or amylose

amylose

Which homopolysaccharide of glucose is an unbranched polymer of alpha(1,4) linked residues? amylose or amylopectin

amylose

Which is a starch in potatoes? amylose or amylopectin

amylose

What are the two homopolysaccharides of glucose that starch is a mixture of?

amylose and amylopectin

Cellulose is a polymer of D-glucopyranoside linked by ___ glycosidic bonds.

beta(1,4)

Humans can only break alpha(1,4) linkages. Since we cannot produce cellulase, we cannot break ___.

beta(1,4) linkages

What could be 1%-85% of the total weight of a glycoprotein?

carbohydrate

What are attached to the protein core of proteoglycans?

carbohydrates such as GAG chains (glycoaminoglycan chains)

Homoglycan: Cellulose is the primary component of plant ___ ___.

cell wall

Where can chitin be found?

cell walls in mushrooms, in exoskeletons of insects such as spiders and also crabs

What enzyme do fungi, bacteria, and protozoa secrete which allows them to use wood as a source of glucose?

cellulase

What are the two structural polysaccharides?

chitin and cellulose

Where can proteoglycan be found?

found on cell surfaces or are secreted to the extracellular matrix

Homoglycans: Chitin is part of the cell wall of ___ and arthropod exoskeleton.

fungi

What forms meshwork with fibrous proteins to form extracellular matrix? a. glycoaminoglycans b. proteoglycans c. glycoproteins d. lectins

glycoaminoglycans

What are linear polymers with disaccharide repeating units? (Two sugar units that repeat over and over that have amino groups attached to them)

glycoaminoglycans (GAGs)

About half of mammalian proteins are proteoglycan or glycoproteins?

glycoproteins

What is commonly defined as proteins that are covalently linked to carbohydrates through N- and O- linkages?

glycoproteins

Hyaluronic acid, chondroitin sulfate, dermatan sulfate, heparin/heparin sulfate, and keratan sulfate are five classes of ___.

glycosaminoglycans

During protein synthesis, what are the two processing enzymes? What do each do?

glycosidases - trim oligosaccharides glycosyltransferases - attach monosaccharide residues to oligosaccharides.

Name the three major types of asparagine-linked oligosaccharides.

high mannose, hybrid, complex

What two classes can polysaccharides be divided into?

homoglycans and heteroglycans

Microfibrils in cellulose are held together by ___ bonds.

hydrogen

Cellulose is unbranched. The 12,000 glucose units are held together by hydrogen bonds to form sheetlike strips called ___.

microfibrils

Steel wire is used to describe the strength and structure of ___ bundles in cellulose because it is tough and inflexible with a tensile strength.

microfibrils

Are glycoproteins more protein than glycans or are they more glycan than protein?

more protein than glycan

What are smaller glycans made of 10-15 monomers called?

oligosaccharides

What the two main energy storage polysaccharides?

starch and glycogen

What makes cellulose a difficult substrate to act on?

the fibrous structure and water-insolubility

Homoglycans can be found in starch. Starch is a mixture of ___ homopolysaccharides of glucose.

two

Is Amylose in an unbranched polymer or branched polymer.

unbranched

Is cellulose branched or unbranched?

unbranched

Out the four types of homoglycans, which ones are unbranched and which are branched?

unbranched: starch (amylose), cellulose and chitin. branched:starch (amylopectin), glycogen

Only some bacteria glycosylate few of their proteins. However, ___ proteins are heavily glycosylated to help evade the immune system.

viral