copyright © houghton mifflin company. all rights reserved.3–13–1 biochemistry biochemistry is...

Copyright © Houghton Mifflin Company. All rights reserved. 3–1

Biochemistry

Biochemistry is the study of chemical substances found in living systems and the chemical interactions of these substances with each other.

A biochemical substance is a chemical substance found within a living organism.


Biochemistry

Biochemistry Biochemistry


14.2 Intro to Carbohydrates

Carbohydrates are biomolecules that decom-pose to produce carbon and water. Their empirical formulas are approximately CH2O.

Carbohydrates are produced in plants by photosynthesis.

CO2 + H2Osunlight

chlorophyllenzymes

Carbohydrates + O2


14.2 Intro to 14 Carbohydrates

Carbohydrates are scarce in animals, but account for ~75% of dry mass in plants.

Uses of carbohydrates:

Oxidized to provide energy

Serve as stored form of chemical energy

Supply carbon for biosynthesis in cells

Form structures of some cells and tissues

Are markers on cell surfaces


14.3 Types of CarbohydratesCarbohydrates are polyhydroxy aldehydes,

polyhydroxy ketones, or substances that produce such compounds by hydrolysis.

C

C

OH

H OH

C HHO

C OHH

C OHH

CH2

C O

C

C

HHO

H OH

C OHH

CH2

Glucose,a polyhydroxy

aldehyde

Fructose,a polyhydroxy

ketone

OH

CH2 OH

OH


14.3 Types of CarbohydratesCarbohydrates are classified by size. Mono-

saccharides contain one polyhydroxycarbonyl unit. Larger carbohydrates contain chains of these units, linked by covalent bonds.

monosaccharide disaccharide

oligosaccharide (3 - 10 monosaccharide units)

polysaccharides contain many(sometimes >10,000)

monosaccharide units


14.4 Types of Monosaccharides

Monosaccharides are classified by

1. The type of carbonyl group:

Aldose or Ketose

2. The number of carbons:

Triose (3 carbons) Tetrose (4 carbons) Pentose (5 carbons) Hexose (6 carbons)

Competency XIII-1


14.4 Types of Monosaccharides

MonosaccharidesC

C

OH

H OH

C HHO

C OHH

C OHH

C OHH

H

C

C O

OHH

H

C

C

OHH

H OH

C OHH

H

Glucose, an aldohexose Ribulose, a ketopentose


14.5 Handedness

Shapes of molecules are incredibly important in biochemistry. Molecules that have the same formula but different shape are called isomers.

There are several types of isomers:

Constitutional Isomers

Stereoisomers Geometric Optical


14.5 Handedness

Types of isomers:

Constitutional isomers, or structural isomers, are isomers that differ in their bonding sequence or connectivity.

C

H3C

C

CH3

H

H

C C

CH3

CH3

H

H

H2C

H2C CH2

CH2

trans-2-butene cyclobutane 2-methylpropene


14.5 HandednessTypes of isomers:

Stereoisomers are isomers that differ only in how their atoms are oriented in space. The connectivity is the same in all the isomers. There are two types of stereoisomers.

Geometric isomers, or cis-trans isomers:

C

H3C

C

CH3

H

H

C

H

C

CH3

H

H3Ctrans-2-butenecis-2-butene


14.5 Handedness

Types of isomers:

Optical isomers are mol-ecules that interact with polarized light.

The simplest of these are nonsuperimposable mirror images of each other. They are called enantiomers.


14.5 Handedness

Molecules that can have enantiomers must have chiral centers.

Chiral centers are tetrahedral carbons with four different substituents. The substituents can be individual atoms or functional groups.

C

J

KC

J

KL LM M

1 2


14.5 Handedness

Pairs of molecules with nonsuperimposable mirror images are called enantiomers.


14.5 Handedness

Carbohydrates have many stereoiso-mers.

Glyceraldehyde, the simplest carbohy-drate, has enan-tiomers. It is an aldotriose.


14.5 HandednessEach enantiomer in a pair has the same prop-

erties unless it interacts with another chiral substance. Biological molecules are usually chiral.

H3C

O

C

HC H

H

CH3CH3

O

C

HCH

H

CH3

(S)-(+)-Carvone

odor of caraway

(R)-(−)-Carvoneodor of spearmint


14.5 HandednessCompounds can have more than one chiral

center. The number of stereoisomers is 2n, where n is the number of chiral centers.

C

C

OH

HO H

C HHO

C OHH

C OHH

CH2 OH

C

C

OH

H OH

C HHO

C HHO

C OHH

CH2 OH

C

C

OH

H OH

C HHO

C OHH

C OHH

CH2 OH

glucose mannose galactose


14.5 HandednessStereoisomers of compounds with more than

one chiral center that are not enantiomers (mirror images) are called diastereomers.

A B C D

A & B, C & D, pairs of enantiomers A is a diastereomer of C & D.

C

C

A

E

D

F

H

G

C

C

A

E

D

F

H

G

C

C

E

A

D

F

H

G

C

C

E

A

D

F

H

G


14.5 Handedness

In carbohydrates, handedness is shown in Fischer projections. The right-handed isomer is the D-(dextro) isomer; the left-handed isomer is the L-(levo) isomer.

C

C

C

OHH

OHH

H

O H

C

C

C

HO H

HOH

H

OH

D-glyceraldehydeL-glyceraldehyde

CHO

CH2OH

OHH

CHO

CH2OH

HHO


14.5 Handedness

In carbohydrates with many chiral centers, the carbon furthest from the carbonyl group is used for this designation.

Naturally occuring car-bohydrates are all D- isomers.

COH

H OH

HHO

OHH

OHH

CH2 OH

D-glucose

CO H

HHO

H OH

HO H

HO H

CH2HO

L-glucose


14.7 Cyclization

Monosaccharides contain carbonyl and hydroxyl groups. These react to form hemiacetals. The reactions are spon-taneous, intramolecular, and form cyclic products.

Ring size:

6 atoms pyranose

5 atoms furanose

O O

Pyran Furan


14.7 Cyclization

Ring size:

6 atoms pyranose

5 atoms furanose


14.7 Cyclization

Hemiacetals can form in two orientations:

36% 64%

C

C C

C

OCH

OHH

OH

OH

H

H

OH

CH2

H

OH

C

C C

C

OCOH

HH

OH

OH

H

H

OH

CH2

H

OH

α-D-glucose β-D-glucose


14.8 RXN’s of Monosaccharides

Aldoses are easily oxidized. Benedict’s test with Cu2+ can be used to detect them.

Tollens’ test, which produces metallic silver, is also useful.

C

C

HO

H OH

R

+ Cu2+

C

C

OHO

H OH

R

Cu2O

bluesol'n

reddishsolid


14.8 RXN’s of MonosaccharidesPositive Benedict’s test.


14.8 RXN’s of MonosaccharidesCarbonyl groups in monosaccharides can be

reduced to hydroxyl groups. The products are sugar alcohols.

COH

H OH

HHO

OHH

OHH

CH2 OH

D-glucose

H2

catalyst

CH2

H OH

HHO

OHH

OHH

CH2 OH

D-glucitol,a.k.a. sorbitol

OH


14.8 RXN’s of MonosaccharidesIn the presence of alcohols, monosaccharides

form cyclic acetals called glycosides.

C

C C

C

OCH

OH

OH

OH

H

H

OH

CH2

H

OH

C

C C

C

OCO

HH

OH

OH

H

H

OH

CH2

H

OH

methyl-α-D-glucoside

Glucose + CH3 OH

CH3

CH3

H3O1+ catalyst

methyl-β-D-glucoside


14.9 DisaccharidesDisaccharides contain two monosaccharide

units. They are bonded together through acetal/glycoside linkages. One monosac-charide supplies the carbonyl in hemiacetal form; the other provides the alcohol.

R

C

OH

OH

C

R

RRH

HO

+

hemiacetal alcohol

R

C

OH

R

OC

R

RH

acetal, a.k.a. glycoside

- H2O


14.9 DisaccharidesMaltose is composed of two glucose units

joined by an α(14) glycoside linkage.


14.9 DisaccharidesLactose is composed of galactose and glucose

units united in a β(14) linkage.

C

C C

C

OC

HH

OH

OH

H

OH

H

CH2

H

OH

C

C C

C

OCOH

HH

OH

OH

H

CH2

H

OH

β-D-galactose unit

D-glucoseα or β

O

H


14.9 Disaccharides

Lactose is the sugar found in milk.

Lactose intolerance occurs when a person does not produce the enzyme to hydrolyze the β(14) glycoside linkage. Infants and children have the enzyme, but many adults do not.


14.9 Disaccharides

Sucrose contains glucose and fructose units joined in an α,β(12) linkage.

C

C C

C

OC

H

OH

OH

H

H

OH

CH2

H

OH

C C

C

O

C

CH2 OH

CH2HO

H

OH

H

H

O

H

HO


14.10 Polysaccharides

The major polysaccharides are polymers of glucose. In cellulose, the glucose units are joined by β(14) glycoside linkages.



Cellulose is the major structural carbohydrate in plants.

Animals lack the enzyme cellulase, which catalyzes hydrolysis of the β(14) glyco-side linkages. They (we!) cannot metabo-lize cellulose for nutrition.

Grazing animals and termites have bacteria in their guts that produce the enzyme; these animals can feed on grass and wood.



Starches are also polymers of glucose. They are used for energy storage in plants. There are two forms, amylose and amylopectin.

Amylose is a straight-chain polymer in which glucose units are linked by α(14) glyco-side linkage.

Amylopectin is a branched-chain polymer. The branches are formed by α(16) link-ages.



Comparison of amylose and amylopectin structures.



Amylopectin, showing glycoside linkages.



Glycogen, sometimes called animal starch, is structurally similar to amylopectin.

Glycogen is formed when excess glucose is present in the blood; the process is called glycogenesis. Glycogen is stored in the liver and muscle tissue.

When blood glucose is low, glycogen is hydrolyzed to release glucose. The process is called glycogenolysis.

copyright © houghton mifflin company. all rights reserved.3–13–1 biochemistry biochemistry is...

Documents

handednesstypes of isomers

geometric isomers

optical isomers

structural isomers

cistrans isomers

types of stereoisomers

chiral substance

number of chiral centers