Chapter 5

30

-In amylopectin, branching occurs at about one out of every _______ glucose residues.

glycoprotein

A ____________ is a protein that is similarly linked to carbohydrates - usually relatively short oligosaccharides.

glycolipid

A _____________ is a lipid that has been glycosylated, meaning it has one or more covalently bonded carbohydrates.

polysaccharides

All cells are enclosed by a membrane, and the cells of most organisms are also surrounded by a protective layer of material called a cell wall. -In plants, bacteria, fungi, and many other groups, the cell wall is composed primarily of one or more ______________.

five, carbons

Although these monosaccharides are represented as linear chains, it's actually rare for sugars consisting of ________ or more _________ to exist in this form.

aldose ketose

Although these two sugars share the same molecular formula (C3H6O3), their molecular structures are different. The carbonyl group that serves as one of the monosaccharides' distinguishing features can be found either at the end of the molecule, forming an aldehyde sugar (an ________), or within the carbon chain, forming a ketone sugar (a _______)

hydrogen bonds

As a result, cellulose forms long, parallel strands that are joined by _________ _______. The interacting cellulose fibers are strong and give the cell structural support.

identification

As a result, they are capable of displaying information to other cells through their structure. -More specifically, polysaccharides act as an _________ badge on the outer surface of the plasma membrane that surrounds a cell.

polar

Based on this observation, it's not surprising that sugars are _________ molecules that form hydrogen bonds with water and are easily dissolved in aqueous solutions.

arrangement

Besides varying in the location of the carbonyl group and the total number of carbon atoms present, monosaccharides can vary in the spatial __________ of their atoms. -While these two aldose sugars have the same molecular formula, they differ in the spatial arrangement of the hydroxyl group on the fourth carbon.

identity, structural, carbon

Candy-bar wrappers promise a quick energy boost, and ads for sports drinks claim that their products provide the "carbs" needed for peak activity. -If you were to ask friends or family members what carbohydrates do in your body, they would probably say something like "They give you energy." -And you'd agree, but only after pointing out that carbohydrates are also used in cell _____________, as a _________ material, and as a source of _________ atoms for the synthesis of other complex molecules.

sexual reproduction

Carbohydrates are at the root of one of the most important events in the life cycle of many multicellular organisms - _______ ________.

structural, identity, energy

Carbohydrates have diverse functions in cells: In addition to serving as precursors to larger molecules, they 1. provide fibrous __________ materials 2 indicate cell __________ 3. store chemical _________.

linear, hydrogen bonds

Cellulose -The geometry of the linkage is such that each glucose residue in the chain is flipped in relation to the adjacent residue. -The flipped orientation is important because: 1. It generates a _______ molecule, rather than the helix seen in starch. 2. It permits multiple ______ _______ to form between adjacent, parallel strands of cellulose.

structural

Cellulose and chitin, along with the modified polysaccharide peptidoglycan, are key __________ compounds. -They form fibers that give cells and organisms strength and elasticity.

B-glucose, B

Cellulose is a polymer made from ___-_________ monomers joined together by ___-1,4-glycosidic linkages.

NAG

Chitin is similar to cellulose, but instead of consisting of glucose residues, the monosaccharide involved is one called N-acetylglucosamine (______).

helical, 10

Glycogen is a _________ polymer of a-glucose and is nearly identical to the branched form of starch. -However, instead of an a-1,6-glycosidic linkageoccuring in about 1 out of every 30 residues in amylopectin, a branch occurs in about 1 out of every ___ glucose subunits.

cell-cell recognition

Glycolipids and glycoproteins are key molecules in what biologists call _____-_____ _________ and (______-______) signaling.

insoluble, hydrolysis

In addition to being tough, structural carbohydrates are durable. -Almost all organisms produce enzymes that cleave the a-glycosidic linkages in starch and and glycogen molecules, but only a few organisms have enzymes capable of digesting cellulose, chitin, or peptidoglycan. -These fibers tend to be ___________ due to the strong interactions between strands consisting of B-1,4-glycosidic linkages. -The exclusion of water within these fibers makes their ____________ more difficult so they are resistant to degradation and decay.

amino acids

In addition, sugars frequently give the raw "carbon skeletons" that are used as building blocks in the synthesis of important molecules -Your cells are using sugars right now as a starting point for the synthesis of ____ ______.

carbonyl, hydroxyl

In aqueous solution they spontaneously form ring structures when the _______ group bonds to a carbon with a _______ group.

glucose

In humans, for example, glycogen is stored in the cells of liver and muscle tissues. When you start exercising, enzymes begin breaking glycogen into ________ monomers, which are then processed in muscle cells to supply energy.

starch

In plant cells, some monosaccharides are polymerized and stored for later use in the form of ___________.

cellulose

In plants, the major component of the cell wall is ____________.

starch, glycogen, cellulose, chitin, peptidoglycan

Let's now consider the structures of the most common polysaccharides found in organisms today: _________, _________, __________, and _________, along with a modified polysaccharide called ________________.

1,4 1,4

Maltose and lactose illustrate two of the most common glycosidic linkages, called the a-__,__ -glycosidic linkage and the B-__,__-glycosidic linkage. -The numbers refer to the carbons on either side of the linkage, indicating that both linkages are between the C-1 and C-4 carbons. -Their geometry, however, is different: a and B refer to the contrasting orientations of the C-1 hydroxyls - on oppositesides of the plane of the glucose rings (i.e.,"below" vs "above" the plane)

condensation, hydroxyl, glycosidic

Monosaccharides polymerize when a __________ reaction occurs between two ___________ groups, resulting in a covalent bond called a ___________ linkage. -The inverse reaction, hydrolysis, cleaves these linkages

peptidoglycan

Most bacteria, like all plants and fungi, have cells walls. The primary structural component of bacterial cell walls consists of a polysaccharide called ____________.

substrate,

One of the basic functions that carbohydrates perform in organisms is to serve as a _________ for synthesizing more-complex molecules. -Recall that RNA contains the 5-carbon sugar ribose. -The sugar itself acts as a subunit of each of these monomers.

NAG, NAM, B-1,4

Peptidoglycan is the most complex of the polysaccharides discussed so far. -It has a long backbone formed by _______ and N-acetymuramic acid (______) that alternate with each other and are linked by ___-___,___ glycosidic linkages. -In adition, a short chain of amino acids is attached at the C-3 carbon of NAM.

pentose

Ribose, which acts as a building block for nucleotides, has five carbons and is called a __________.

monomers

Similar to proteins and nucleic acids, the structure and function of larger carbohydrates depends on the types of ___________ involved and how they are linked together.

complex carbohydrates

Simple sugars covalently link to form chains of varying lengths called __________ __________.

a-glucose, B-glucose

So there are two possible forms of glucose: ___-_______ and ___-______.

potential energy

So, because C-C and C-H bonds have much higher _______ ________ than C-O bonds have, carbohydrates store much more chemical energy than carbon dioxide does.

monomers, linkages

Some polysaccharides exhibit enormous structural diversity, because their component ___________ - and the __________ between them - vary a lot.

a-glucose, helix

Starch consists entirely of ___-________ joined by glycosidic linkages. -Most of these linkages are between C-1 and C-4 carbons, and the angle of these bonds causes the chain of glucose residues to coil into a _______.

amylose amylopectin

Starch is made up of 2 types of polymers. -One is an unbranched molecule called __________, which contains only a-1,4-glycosidic linkages. -The other is a branched molecule called _____________. -Branching occurs when a glycosidic linkage forms between a C-1 carbon and C-6 carbon (an a-1,6 linkage).

energy, building blocks

Sugars are fundamental to life. They provide chemical _________ in cells and furnish some of the molecular ________ ________ required for the synthesis of larger, more complex compounds.

carbonyl, carbons, hydroxyl

Summary Many distinct monosaccharides exist because so many aspects of their structure are variable: aldose or ketose placement of the ________ group, the number of _________, and the different arrangements of _______ groups in space. -Ring forms of the same molecule also have alternative forms. -These variations give each monosaccharide a unique structure and function.

hexose

The glucose that's coursing through your bloodstream right now is a six-carbon sugar, or a ________.

carbonyl

The number of carbon atoms present also varies among monosaccharides. By convention, the carbons in a monosaccharide are numbered consecutively, starting with the end nearest the ________ group.

carbonyl, hydroxyl

The presence of a ________ group along with multiple polar ________ groups means that even the simplest sugars have many reactive and hydrophilic functional groups.

monosaccharides, oligosaccharides, polysaccharides

The term carbohydrate, or sugar, encompasses the monomers called _______________, small polymers called _____________, and the large polymers called _____________.

B-glucose

The two forms exist in equilibrium, but ___-________ is more common because it is slightly more stable.

store, support

The variation in how polysaccharides are formed allows organisms to use them in radically different ways. For example, polysaccharides may be used to ________ chemical energy in the cells of plants or provide structural _________ in the exoskeletons of insects.

two

There is an important difference, however. Peptide bonds and phosphodiester linkages form between the same locations in their monomers, giving proteins and nucleic acids a standard backbone structure, but this is not the case for carbohydrates. -Because glycosidic linkages form between hydroxyl groups, and because every monosaccharide contains at least ______ hydroxyls, the location and geometry of glycosidic linkages can vary widely among oligosaccharides and polysaccharides.

B-1,4 flipped, hydrogen bonds

These NAG monomers are joined by ___-___,____-glycosidic linkages. -As in cellulose, the geometry of these bonds results in every other residue being ______ in orientation. -The NAG subunits in chitin also form ________ _______ between adjacent strands to produce a stiff protective armor.

disaccharide

These chains range in size from short oligosaccharides to long polysaccharides. -When just two sugars link together, the resulting molecule is known as a _____________.

sugars

This same type of transformation from light energy to chemical energy occurs in cells today, but instead of making formaldehyde, cells produce _________. -For example, plants harvest the energy in sunlight and store it in the bonds of carbohydrates the process known as photosynthesis.

energy

This unit highlights the four types of macromolecules that were key to the evolution of the cell: Proteins, nucleic acids, carbohydrates, and lipids. Understanding the structure and function of macromolecules is a basic requirement for exploring how life began and how organisms work. Proteins and nucleic acids could satisfy 3 of the 5 fundamental characteristics of life: information, replication, and evolution. Carbohydrates play an important role in a fourth characteristic - ____________.

trioses

Three-carbon sugars are called __________.

atoms, hydroxyls

When glucose forms a ring, the C-1 carbon forms a bond with the oxygen atom of the C-5 hydroxyl. The hydrogen displaced from the C-5 hydroxyl is transferred to the C-1 carbonyl. This transfer preserves the number of ______ and _______ between the ring and linear forms.

peptide

When molecules of peptidoglycan align, ________ bonds link the amino acid chains on adjacent strands. These links serve the same purpose as the hydrogen bonds between the parallel strands of cellulose and chitin in the cell walls of other organisms.

below, above

When the ring structure is formed in sugars, the position of the newly formed C-1 hydroxyl group will be fixed in one of two possible orientations: _____ or _____ the plane of the ring.

Glycosidic linkages

__________ _______ hold monomers together, just like the peptide bonds and phosphodiester linkages do for proteins and nucleic acids.

Chitin

__________ is a polysaccharide that stiffens the cell walls of fungi. -It's also found in a few types of protists and in many animals. -It is, for example, the most important component of the external skeletons of insects and crustaceans.

Cellulose, glycogen, starch

__________ is the most abundant organic compound on Earth today, and chitin is probably the second most abundant by weight. -Virtually all organisms depend on ________ or _________ to store chemical energy, but despite their current importance to life, polysaccharides probably played little to no role in the origin of life.

Monosaccharides

____________, or simple sugars, are the monomers of carbohydrates.

glycogen

______________ performs the same storage role in animals that starch performs in plants.

Monosaccharides

______________ were important during chemical evolution, early in Earth's history, too. For example, the sugar called ribose is required for the formation of the nucleotides that make up nucleic acids.