Biochemistry Overview

Section 18.1: Biochemistry—An Overview

• Definition of Biochemistry

  • Study of chemical substances in living organisms and their interactions.

• Types of Biochemical Substances

  • Bioinorganic Substances: Water and inorganic salts.

  • Bioorganic Substances: Carbohydrates, lipids, proteins, and nucleic acids.

• Life Sustaining Interactions

  • Isolated bioinorganic and bioorganic substances do not sustain life; their interactions within cells do.

Section 18.2: Occurrence and Functions of Carbohydrates

• Carbohydrates in Plants

  • Over half of organic carbon in plants is carbohydrate material.

  • Carbohydrates account for 75% of dry plant material, produced via photosynthesis.

  • Types of Carbohydrates:

    • Cellulose: Structural element.

    • Starch/Glycogen: Energy reservoir.

• Functions in the Human Body

  • Provide energy through oxidation.

  • Serve as short-term energy reserves (glycogen).

  • Supply carbon for synthesizing proteins, lipids, and nucleic acids.

  • Form structural components of DNA and RNA.

  • Participate in cell recognition processes when linked to proteins and lipids.

Section 18.3: Classification of Carbohydrates

• Types of Carbohydrates:

  • Monosaccharides: Single units (e.g., glucose, fructose).

  • Disaccharides: Two monosaccharide units (e.g., sucrose, lactose).

  • Oligosaccharides: 3-10 monosaccharide units.

  • Polysaccharides: Many monosaccharide units (e.g., starch, cellulose).

• Monosaccharide Classification:

  • Based on carbon atoms (triose, tetrose, pentose, hexose).

  • Based on functional groups (aldoses and ketoses).

Section 18.4: Chirality: Handedness in Molecules

• Chirality in Biological Molecules

  • Most biological molecules exhibit "handedness" (isomerism).

  • Chiral centers are carbon atoms attached to four different groups.

• Mirror Images

  • Chiral molecules have nonsuperimposable mirror images.

  • Mirror image: Reflection of an object in a mirror

    •Classes of objects based on mirror images

    –Superimposable mirror images: Images that coincide at all points when the images are laid upon each other

    •Achiral molecule

• Nonsuperimposable mirror images: Images where not all points coincide when the images are laid upon each other

• Chiral molecule (handedness)

Section 18.5: Stereoisomerism: Enantiomers and Diastereomers

• Types of Stereoisomers:

  • Enantiomers: Non-superimposable mirror images.

  • Diastereomers: Not mirror images.

• Chiral Centers: Presence of chiral centers generates stereoisomerism.

Section 18.6: Designating Handedness Using Fischer Projection Formulas

• Fischer Projection: Two-dimensional notation for spatial arrangement around chiral centers.

• Tetrahedral Geometry: Groups attached to chiral centers assume tetrahedral arrangements.

Section 18.7: Properties of Enantiomers

• Differences in Properties:

  • Enantiomers have similar physical properties except for their interaction with polarized light.

  • Dextrorotatory: Rotates light clockwise.

  • Levorotatory: Rotates light counterclockwise.

Section 18.8: Classification of Monosaccharides

• Monosaccharide Types:

  • Aldoses: Contain an aldehyde group.

  • Ketoses: Contain a ketone group.

Section 18.9: Biochemically Important Monosaccharides

• D-Glucose: Most abundant and important for human nutrition.

• D-Galactose: Milk sugar, important for brain tissue.

• D-Fructose: Sweetest sugar, found in fruits.

• D-Ribose: Component of RNA and ATP.

Section 18.10: Cyclic Forms of Monosaccharides

• Cyclic Structures: Formed by the reaction of carbonyl and hydroxyl groups.

• Anomers: Cyclic monosaccharides differing in substituent position on the anomeric carbon.

Section 18.11: Haworth Projection Formulas

• Haworth Projection: Two-dimensional notation for cyclic monosaccharides.

• α and β Configurations: Determined by the position of the –OH group on C1.

Section 18.12: Reactions of Monosaccharides

• Key Reactions:

  • Oxidation to acidic sugars.

  • Reduction to sugar alcohols.

  • Glycoside formation.

  • Phosphate ester formation.

  • Amino sugar formation.

Section 18.13: Disaccharides

• Formation: Two monosaccharides react to form a disaccharide via glycosidic linkage.

• Examples:

  • Maltose: Composed of two glucose units.

  • Lactose: Composed of galactose and glucose.

  • Sucrose: Composed of glucose and fructose.

Section 18.14: Oligosaccharides

• Definition: Carbohydrates with 3-10 monosaccharide units.

• Examples: Raffinose and stachyose, found in various vegetables.

• Blood Types: Determined by oligosaccharides on red blood cells.

Section 18.15: General Characteristics of Polysaccharides

• Types:

  • Homopolysaccharides: One type of monosaccharide.

  • Heteropolysaccharides: Different monosaccharides.

• Characteristics: Not sweet, limited solubility, and various functions (storage, structural).

Section 18.16: Storage Polysaccharides

• Starch: Storage form in plants, composed of amylose and amylopectin.

• Glycogen: Storage form in animals, highly branched.

Section 18.17: Structural Polysaccharides

• Cellulose: Major component of plant cell walls, indigestible by humans.

• Chitin: Provides rigidity to exoskeletons of arthropods.

Section 18.18: Acidic Polysaccharides

• Definition: Polysaccharides with repeating disaccharide units containing amino sugars.

• Examples: Hyaluronic acid and heparin.

Section 18.19: Dietary Considerations and Carbohydrates

• Dietary Role: Carbohydrates constitute over 50% of the diet.

• Types:

  • Simple Carbohydrates: Sugars.

  • Complex Carbohydrates: Starches and fibers.

Section 18.20: Glycolipids and Glycoproteins: Cell Recognition

• Glycolipids: Lipids with carbohydrate units.

• Glycoproteins: Proteins

Properties of Enantiomers

Dextrorotary and Levorotatory Compounds

• Enantiomers are optically active, i.e., they arecompounds that rotate the plane of polarized light

• Dextrorotatory compound: Chiral compoundthat rotates light towards right (clockwise; +)

• Levorotatory compound: Chiral compound thatrotates light towards left (counterclockwise; -)

• There is no correlation between D, L and +, -

– In D and L system, the structure is viewed

– + and – can be determined using a polarimeter

Interactions Between Chiral Compounds

• Right- and left-handed baseball players cannotuse the same glove (chiral) but can use thesame hat (achiral)

– Two members of the enantiomer pair (chiral) reactdifferently with other chiral molecules

• Enantiomeric pairs have same solubility inachiral solvents like ethanol and have differentsolubility in chiral solvent like D-2-butanol

D-Ribose

• Part of a variety of complex molecules which include:

– RNA

– ATP

– DNA

• Five-membered cyclic form

Cyclic Hemiacetal Forms of D-Glucose

• Dominant forms of monosaccharides with 5 or more C atoms

– Cyclic structures are in equilibrium with open chain forms

• Cyclic structures are formed by the reaction of carbonyl group (C=O) with hydroxyl (–OH) group on carbon 5

2 forms of D-Glucose:

– α-form where the –OH of C1 and CH2OH of C5 are on opposite sides

– β-form where the –OH of C1 and CH2OH of C5 are on the same side

Anomers

• Cyclic monosaccharides that differ only in the position of the substituents on the anomeric carbon atom

Cyclic Forms of Other Monosaccharides

• Intramolecular cyclic hemiacetal formation and the equilibrium between various forms are not restricted to glucose

• All aldoses with five or more carbon atoms establish similar equilibria, but with different percentages of the alpha, beta, and open-chain forms

• Fructose and other ketoses with a sufficient number of carbon atoms also cyclize.

Pyranose and Furanose

• Pyranose - Cyclic monosaccharide containing a six-atom ring

• Furanose - Cyclic monosaccharide containing a five-atom ring

• Their ring structures resemble the ring structures in the cyclic ethers pyran and furan, respectively

Haworth projection formula: Two-dimensional structural notation that specifies the three-dimensional structure of a cyclic form of a monosaccharide

Determined by the position of the –OH group on C1 relative to the –CH2OH group that determines D or L series

– In a β configuration, both of these groups point in the same direction

– In an α configuration, the two groups point in opposite directions

OH Group Position

he specific identity of a monosaccharide is determined by the positioning of the other –OH groups in the Haworth projection formula

– Any –OH group at a chiral center that is to the right in a Fischer projection formula points down in the Haworth projection formula– Any –OH group to the left in a Fischer projection formula points up in the Haworth projection formula

Reactions of Monosaccharides

• Five important reactions of monosaccharides:

– Oxidation to acidic sugars

– Reduction to sugar alcohols

– Glycoside formation

– Phosphate ester formation

– Amino sugar formation

• Glucose will be used as the monosaccharide reactant

• Other aldoses, as well as ketoses, undergo similar reactions

Oxidation to Produce Acidic Sugars

• The redox chemistry of monosaccharides is closely linked to the alcohol and aldehyde functional groups

• Oxidation can yield three different types of acidic sugars depending on the type of oxidizing agent used

– Aldolic acid - Formed when weak oxidizing agents such as Tollens and Benedict’s solutions oxidize the aldehyde end

– Reducing sugar: Carbohydrate that gives a positive test with Tollens and Benedict’s solutions

Reactions of Monosaccharides

Oxidation to Produce Acidic Sugars

• Strong oxidizing agents can oxidize both ends of a monosaccharide at the same time (the carbonyl group and the terminal primary alcohol group) to produce a dicarboxylic acid

– Such polyhydroxy dicarboxylic acids are known as aldaric acids

• In biochemical systems, enzymes can oxidize the primary alcohol end of an aldose such, without oxidation of the aldehyde group, to produce an alduronic acid

Reduction to Produce Sugar Alcohols

• The carbonyl group in a monosaccharide (either an aldose or a ketose) is reduced to a hydroxyl group using hydrogen as the reducing agent

– The product is the corresponding polyhydroxy alcohol called sugar alcohol or alditol

– Sorbitol - Used as a moisturizing agent in foods and cosmetics and as a sweetening agent in chewing gum

Glycoside Formation

• Glycoside: Acetal formed from a cyclic monosaccharide by replacement of carbon –OH group with an –OR group

– Glucoside - Glycoside produced from glucose

– Galactoside - Glycoside produced from galactose

– Exist in both α and β forms

Phosphate Ester Formation

• Hydroxyl groups of a monosaccharide can react with inorganic oxyacid to form inorganic esters

• Phosphate esters of various monosaccharides are stable in aqueous solution and play important roles in the metabolism of carbohydrates

Amino Sugar Formation

• Amino sugar - Formed when one of the of a monosaccharide is replaced with an amino group

• In naturally occurring amino sugars, the C2hydroxyl group is replaced by an amino group

• Amino sugars and their N-acetyl derivatives are important building blocks of polysaccharides such as chitin and hyaluronic acid

Maltose (MaltSugar)

• Structurally made of 2 D-glucose units, one of which must be α-D-glucose, linked via an α(14)glycosidic linkage

• Digested easily by humans because of an enzyme that can break α(14) linkages• Baby foods are rich in maltose

Cellobiose

• Produced as an intermediate in the hydrolysis of the polysaccharide cellulose– Contains two D-glucose monosaccharide units, one of which must have a β configuration, linked through a β(14) glycosidic linkage

• Cannot be digested by humans

Lactose

• Made up of β-D-galactose unit and a D-glucose unit joined by a β(14) glycosidic linkage

• Milk is rich in the disaccharide lactose• Lactase hydrolyzes β(14) glycosidic linkages

Lactose Intolerance or Lactase Persistence

• Lactose is the principal carbohydrate in milk

– Human mother’s milk - 7%–8% lactose

– Cow’s milk - 4%–5% lactose

• Lactose intolerance is a condition in which people lack the enzyme lactase needed to hydrolyze lactose to galactose and glucose

• Deficiency of lactase can be caused by a genetic defect, physiological decline with age, or by injuries to intestinal mucosa.

Lactose Intolerance or Lactase Persistence

• When lactose is undigested, it attracts water causing fullness, discomfort, cramping, nausea, and diarrhea

• Bacterial fermentation of lactose further along the intestinal tract produces acid (lactic acid) and gas, adding to the discomfort.

Sucrose (Table Sugar)

• The most abundant of all disaccharides and found in plants

• Produced commercially from the juice of sugarcane and sugar beets

– Sugar cane contains up to 20% by mass sucrose

– Sugar beets contain up to 17% by mass sucrose

Oligosaccharides

• Carbohydrates that contain 3–10 monosaccharide units bonded to each other via glycosidic linkages

• Generally present in association with other complex molecules

– Raffinose - Made of 1 galactose, 1 glucose, and 1fructose

– Stachyose - Made of 2 galactose, 1 glucose, and 1fructose units

• Commonly found in onions, cabbage, broccoli, and whole wheat.

Blood Types and Oligosaccharides

• Human blood is classified into four types– A, B, AB, and O

– The basis for the difference is the type of sugars(oligosaccharides) present

– Blood of one type cannot be given to a recipient with blood of another type– A transfusion of wrong blood type can cause the blood cells to form clumps, a potentially fatal reaction– People with type O blood are universal donors, and those with type AB blood are universal recipients

Blood Types and Oligosaccharides

• In the United States, type O blood is the most common and type A the second most common

• The biochemical basis for the various blood types involves oligosaccharides present on plasma membranes of red blood cells• The oligosaccharides responsible for blood groups are D-galactose and its derivatives =

Other Oligosaccharides

• Solanine, a potato plant toxin, is a oligosaccharide found in association with an alkaloid

– Bitter taste of potatoes is due to relatively higher levels of solanine

General Characteristics of Polysaccharides

The Polymer Chain

• Polysaccharides are polymers of many monosaccharide units bonded with glycosidic linkages• Two types:

– Homopolysaccharide

– Heteropolysaccharide

General Characteristics of Polysaccharides

Characteristics of Polysaccharides

• Polysaccharides are not sweet and do not show positive tests with Tollen’s and Benedict’s solutions, whereas monosaccharides are sweet and show positive tests

• Limited water solubility

• Examples:

– Cellulose and glycogen

- Storage polysaccharides

– Chitin - Structural polysaccharide

– Hyaluronic acid - Acidic polysaccharide

Storage Polysaccharides

Starch

• Storage polysaccharide: Polysaccharide that isa storage form for monosaccharides and used as an energy source in cells

• Starch

– Glucose is the monomeric unit

– Storage polysaccharide in plants.

Types of Polysaccharides Isolated From Starch

• Amylose– Unbranched-chain polymer and accounts for15%–20% of the starch

– Has α(14) glycosidic bonds

• Amylopectin– Branched chain polymer and accounts for 80%–85%of the starch]

– Has α(14) and α(16) glycosidic bonds

– Up to 100,000 glucose units are present

– Amylopectin is digested more readily by humans (canhydrolyze α linkages but not β linkages)

Glycogen

• Glucose storage polysaccharide in humans and animals

• Contains only glucose units

• Branched chain polymer with α (14) glycosidic bonds in straight chains and α(16) in branches

• Three times more highly branched than amylopectin in starch• Contains up to 1,000,000 glucose units

Glycogen

• Excess glucose in blood is stored in the form of glycogen

Structural Polysaccharides

Cellulose

• Linear homopolysaccharide with β(14)glycosidic bond

• Contains up to 5000 glucose units with molecular mass of 900,000 amu

– Cotton has 95% cellulose and wood 50% cellulose

• Humans do not have enzymes that hydrolyzeβ(14) linkages and so they cannot digest cellulose

– Animals also lack these enzymes, but they can digest cellulose due to the presence of cellulase-producing bacteria

Cellulose

• It serves as dietary fiber in food and readily absorbs water resulting in softer stools

– 20–35 g of dietary fiber is desired everyday

Chitin

• Similar to cellulose structurally and functionally

• Linear polymer with all β(14) glycosidic linkages

– It has an N-acetyl amino derivative of glucose

• Function is to give rigidity to the exoskeletons of crabs, lobsters, shrimp, insects, and other arthropods

Acidic polysaccharides

• Polysaccharides with a repeating disaccharide unit containing an amino sugar and a sugar with a negative charge due to a sulfate or a carboxyl group

• They are heteropolysaccharides, i.e., different monosaccharides exist in an altering pattern• Examples: Hyaluronic acid and Heparin

Hyaluronic Acid

• Alternating residues of N-acetyl- β-D-glucosamine and D-glucuronate

• Highly viscous and serve as lubricants in the fluid of joints as well as vitreous humor of the eye.

Heparin

• Polysaccharide with 15–90 disaccharide residues per chain

• Blood anticoagulant

Dietary Considerations and Carbohydrates

Nutrition

• Foods high in carbohydrate content constitute over 50% of the diet of most people of the world

– Corn in South America

– Rice in Asia

– Starchy root vegetables in parts of Africa

– Potato and wheat in North America

• Balanced dietary food should contain about 60%of carbohydrate

Classes of Dietary Carbohydrates

• Simple carbohydrates: Dietary monosaccharides or disaccharides

– Sweet to taste and commonly referred to as sugars

– Constitute 20% of the energy in the US diet

• Complex carbohydrates: Dietary polysaccharides

– Include starch and cellulose, which are normally not sweet to taste

Glycolipids and Glycoproteins: Cell Recognition

• Glycolipid: Lipid molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it

• Glycoprotein: Protein molecule that has one or more carbohydrate (or carbohydrate derivative) units covalently bonded to it– Such carbohydrate complexes are very important in cellular functions such as cell recognition

Biochemistry Overview Mind Map

Central Idea

• Biochemistry: The Study of Chemical Substances in Living Organisms

Main Branches

1. Definition of Biochemistry

• Study of chemical substances in living organisms and their interactions.

2. Types of Biochemical Substances

• Bioinorganic Substances

  • Water

  • Inorganic salts

• Bioorganic Substances

  • Carbohydrates

  • Lipids

  • Proteins

  • Nucleic acids

3. Life Sustaining Interactions

• Isolated substances do not sustain life; interactions within cells do.

4. Carbohydrates Overview

• Occurrence in Plants

  • Over half of organic carbon in plants is carbohydrate.

  • 75% of dry plant material from photosynthesis.

• Functions in the Human Body

  • Energy provision

  • Short-term energy reserves

  • Carbon supply for synthesis

  • Structural components of DNA/RNA

  • Cell recognition processes

5. Classification of Carbohydrates

• Types

  • Monosaccharides

  • Disaccharides

  • Oligosaccharides

  • Polysaccharides

• Monosaccharide Classification

  • Based on carbon atoms

  • Based on functional groups

6. Chirality and Stereoisomerism

• Chirality in Biological Molecules

  • Chiral centers and mirror images

• Types of Stereoisomers

  • Enantiomers

  • Diastereomers

7. Fischer Projection and Handedness

• Fischer Projection for spatial arrangement

• Tetrahedral geometry around chiral centers

8. Properties of Enantiomers

• Similar physical properties

• Dextrorotatory and levorotatory interactions with polarized light

9. Biochemically Important Monosaccharides

• D-Glucose

• D-Galactose

• D-Fructose

• D-Ribose

10. Cyclic Forms of Monosaccharides

• Formation via carbonyl and hydroxyl group reactions

• Anomers and their significance

11. Reactions of Monosaccharides

• Key reactions: oxidation, reduction, glycoside formation, etc.

12. Disaccharides

• Formation