biochem chapter 10

What do Fischer projections convey?

3D information in 2D

In Fischer projections, atoms in horizontal bonds are positioned where?

In front of the plane of the page

In Fischer projections, atoms in vertical bonds are positioned where?

Behind the plane of the page

What designates D or L in Fischer projections?

The farthest asymmetric carbon from aldehyde or ketone

Which side indicates D in Fischer projections?

Right side

Which side indicates L in Fischer projections?

Left side

Isomers with identical molecular formulas but differ in the order of attachment of atoms.

constitutional isomers

Atoms connected in the same order, but differ in spatial arrangement.

stereoisomers

Nonsuperimposable mirror images, such as D and L configurations with a single asymmetric carbon.

enantiomers

Isomers that are not mirror images of each other and have multiple asymmetric carbons.

diastereomers

Isomers that differ in configuration at only a single asymmetric center.

epimers

Isomers that differ at a new asymmetric carbon atom formed on ring closure.

anomers

What can an aldehyde react with to form a hemiacetal?

An alcohol

What is the cyclic form of glucose called?

Pyranose

How many atoms are in the ring structure of a pyranose?

Six atoms

What is the designation for the anomeric carbon with OH above the ring?

It has a β designation.

What percentage of sugars exists in an open chain form?

<1%

What reaction forms a hemiacetal?

An aldehyde reacts with an alcohol.

What is the characteristic of Haworth projections?

They are not really planar.

What is the approximate ratio of α to β forms of sugars?

~1/3 α and ~2/3 β.

What are the two orientations of substituents on carbon ring atoms in the chair form?

axial and equatorial

Which conformation does β-D-glucopyranose adopt preferentially?

Chair conformation

Why does β-D-glucopyranose prefer the chair conformation?

Axial positions are occupied by hydrogens, reducing steric hindrance.

What can a ketone react with to form a hemiketal?

An alcohol

What is the name of the five-atom ring formed by the ketose fructose?

Furanose

What type of carbon is involved in the formation of a hemiketal?

Anomeric carbon

What does cyclic hemiacetal formation create?

Another asymmetric carbon

What are the anomeric forms of fructose?

α and β forms

What does the orientation of the hydroxyl at C2 determine in fructose?

The α and β forms

What are monosaccharides known to be?

Reducing agents

What is the free aldehyde in monosaccharides?

Reactive

What type of sugars react with oxidizing agents?

Reducing sugars

What does glucose form when it reacts with hemoglobin?

Glycosylated hemoglobin (hemoglobin A1c)

Is fructose a reducing sugar?

yes

What is formed between the anomeric carbon atom and a hydroxyl group of another molecule?

An O-glycosidic bond which results in a glycoside.

What is formed between the anomeric carbon atom and an amine?

An N-glycosidic bond.

What type of linkages do carbohydrates form to phosphates?

Ester linkages.

How are monosaccharides joined to alcohols and amines?

Through glycosidic bonds.

What do oligosaccharides contain?

≥2 monosaccharides linked by O-glycosidic bonds

What is maltose composed of?

Two molecules of glucose

What do glycosyltransferases catalyze?

The formation of glycosidic bonds.

What activates monosaccharide substrates for glucosyltransferases?

Attachment to uridine diphosphate (UDP).

What do enzymes on the outer surface of the small intestinal epithelium cleave?

Common disaccharides

Which disaccharides are reducing sugars?

lactose and maltose

What is a polysaccharide called if all its monosaccharides are the same?

Homopolymer

What are the two types of starch in plants?

Amylose and amylopectin

What enzyme hydrolyzes starches?

α-amylase

What type of bonds link most glucose units in glycogen?

α-1,4-glycosidic bonds

What type of bonds form branches in glycogen?

α-1,6-glycosidic bonds

How often are branches formed in glycogen?

Every 10 glucose units

What type of bonds do glycogen and starch have?

α-1,4-glycosidic bonds.

What do the α-1,4-glycosidic bonds of starch and glycogen form?

Compact hollow cylinders for storage.

What type of linkage does cellulose have?

β-1,4-glycosidic bond.

What are the three main classes of glycoproteins?

glycoproteins, proteoglycans, mucoproteins

What is the main component of glycoproteins by weight?

the protein

What are proteoglycans attached to?

glycosaminoglycans

What is the main composition of proteoglycans by weight?

carbohydrates

what do proteoglycans do

They play structural roles such as in cartilage.

What are mucins predominantly made of?

carbohydrate

How are proteins attached to carbohydrates in mucins?

The protein is attached by N-acetylgalactosamine.

What is a common function of mucins?

Mucins often act as lubricants, such as mucus.

To which amino acids can carbohydrates be linked in proteins?

Asparagine, serine, or threonine

What is the common core of N-linked polysaccharides?

A pentasaccharide core consisting of three mannoses, a six-carbon sugar, and two N-acetylglucosamine units.

What additional components can be attached to the N-linked polysaccharide core?

Additional monosaccharides

What are glycosaminoglycans composed of?

Repeating units of a disaccharide

What do glycosaminoglycans contain?

One amino sugar derivative and one negatively charged unit

Give an example of glycosaminoglycan. What is its function?

Chitin - exoskeleton of insects and crustaceans

What role do proteoglycans play in the extracellular matrix?

They serve as lubricants and have structural roles

What are mucopolysaccharidoses?

Pathological conditions from inability to degrade glycosaminoglycans

what is a hemiacetal group

a carbon bonded to an oh and an or

what does a reducing sugar contain

a hemiacetal group