CNGNGE JOHN MCMURRY CHAPTER 21 Biomolecules: Carbohydrates T HI R D EDITION Organic Chemistry with Biological applications
CHAPTER 21 Biomolecules: Carbohydrates
Carbohydrates Carbohydrate Broad class of polyhydroxylated aldehydes and ketones commonly called sugars 。 Synthesized by green plants during photosynthesis 重 Name derived from glucose Glucose was the first simple carbohydrate obtained in pure form ·brae0Y8ot8e8h6n是eoe,as ~50%of the dry weight of earth's biomass consists of glucose polymers HO HH OH O H-C-OH hO. HO-C-H or H-C-OH HHH OHH OH H-C-OH CH2OH Glucose(dextrose), a pentahydroxyhexanal
Carbohydrate ▪ Broad class of polyhydroxylated aldehydes and ketones commonly called sugars ▪ Synthesized by green plants during photosynthesis ▪ Name derived from glucose ▪ Glucose was the first simple carbohydrate obtained in pure form ▪ Molecular formula of glucose, C6H12O6 , was thought to be a “hydrate of carbon, C6 (H2O)6 ” ▪ ~ 50% of the dry weight of earth’s biomass consists of glucose polymers Carbohydrates
Carbohydrates Carbohydrates act as chemical intermediates by which solar energy is stored and used to support life on earth 6C02+6H20 Sunlight 602+C6H1206 → Cellulose,starch Glucose
Carbohydrates act as chemical intermediates by which solar energy is stored and used to support life on earth Carbohydrates
21-1 Classification of Carbohydrates Carbohydrates are classed as simple or complex 量 Simple sugars,or monosaccharides Carbohydrates like glucose and fructose that cannot be converted into more simple sugars by hydrolysis Complex carbohydrates Made up of two or more simple sugars Sucrose is a disaccharide comprised of one glucose and one fructose Cellulose is a polysaccharide comprised of several thousand linked glucose units CH2OH HO HOCH2- Hao 1Glucose 1Fructose CH2OH HOHO Sucrose (a disaccharide) CH2OH 0 CH2OH 0 -3000 Glucose HO OH HO 一0之 OH Cellulose (a polysaccharide)
Carbohydrates are classed as simple or complex ▪ Simple sugars , or monosaccharides ▪ Carbohydrates like glucose and fructose that cannot be converted into more simple sugars by hydrolysis ▪ Complex carbohydrates ▪ Made up of two or more simple sugars ▪ Sucrose is a disaccharide comprised of one glucose and one fructose ▪ Cellulose is a polysaccharide comprised of several thousand linked glucose units 21-1 Classification of Carbohydrates
Classification of Carbohydrates Monosaccharides are classified as aldoses or ketoses -ose suffix designates a carbohydrate aldo-prefix identifies an aldehyde carbonyl group in the sugar keto-prefix identifies a ketone carbonyl group in the sugar Number of carbons indicated by the numerical prefix tri-, tetra-,pent-,hex- CH2OH Hc≥0 CH2OH C=0 H-C-OH C=0 Hc0 HO-C-H HO-C-H HO-C-H H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH H-C-OH CH2OH CH2OH CH2OH CH2OH Glucose Fructose Ribose Sedoheptulose (an aldohexose) (a ketohexose) (an aldopentose】 (a ketoheptose)
Monosaccharides are classified as aldoses or ketoses ▪ -ose suffix designates a carbohydrate ▪ aldo- prefix identifies an aldehyde carbonyl group in the sugar ▪ keto- prefix identifies a ketone carbonyl group in the sugar ▪ Number of carbons indicated by the numerical prefix tri-, tetra-, pent-, hexClassification of Carbohydrates
21-2 Depicting Carbohydrate Stereochemistry: Fischer Projections Fischer projections Suggested by Emil Fischer(1891) Method to project a tetrahedral carbon onto a flat surface Tetrahedral carbon represented by two crossed lines Horizontal lines come out of the page -Vertical lines go back into page Press flat Fischer projection
Fischer projections ▪ Suggested by Emil Fischer (1891) ▪ Method to project a tetrahedral carbon onto a flat surface ▪ Tetrahedral carbon represented by two crossed lines ▪ Horizontal lines come out of the page ▪ Vertical lines go back into page 21-2 Depicting Carbohydrate Stereochemistry: Fischer Projections
Depicting Carbohydrate Stereochemistry: Fischer Projections A Fischer projection of(R)-glyderaldehyde Bonds out of page CHO CHO CHO H H-C-OH H -OH Bonds CH2OH HO CH2OH CH>OH into page (R)-Glyceraldehyde (Fischer projection) Cengag Learring.All Fights Reerved
A Fischer projection of (R)-glyderaldehyde Depicting Carbohydrate Stereochemistry: Fischer Projections
Depicting Carbohydrate Stereochemistry: Fischer Projections Rules for manipulating Fischer projections: A Fischer projection can be rotated on the page by 180°，but not by90°or270° Only a 180 rotation maintains the Fischer convention by keeping the same substituent groups going into and coming out of the plane 180° CHO CH2OH H OH same as HO -H CH2OH CHO (R)-Glyceraldehyde (R)-Glyceraldehyde
Rules for manipulating Fischer projections: ▪ A Fischer projection can be rotated on the page by 180°, but not by 90° or 270° ▪ Only a 180° rotation maintains the Fischer convention by keeping the same substituent groups going into and coming out of the plane Depicting Carbohydrate Stereochemistry: Fischer Projections
Depicting Carbohydrate Stereochemistry: Fischer Projections A 90 rotation breaks the Fischer convention by exchanging the groups that go into and come out of the plane A 90 or a 270 rotation changes the representation to the enantiomer CH090 H OH Not HOCH2- -CHO same as CH2OH OH (R)-Glyceraldehyde (S)-Glyceraldehyde
▪ A 90° rotation breaks the Fischer convention by exchanging the groups that go into and come out of the plane ▪ A 90° or a 270° rotation changes the representation to the enantiomer Depicting Carbohydrate Stereochemistry: Fischer Projections
Depicting Carbohydrate Stereochemistry: Fischer Projections A Fischer projection can have one group held steady while the other three rotate in either a clockwise or a counterclockwise direction Effect is to simply rotate around a single bond Hold steady CHO CHO OH same as HO CH2OH →CH20H H (R)-Glyceraldehyde (R)-Glyceraldehyde
▪ A Fischer projection can have one group held steady while the other three rotate in either a clockwise or a counterclockwise direction ▪ Effect is to simply rotate around a single bond Depicting Carbohydrate Stereochemistry: Fischer Projections