Carbohydrates

Biopolymers

Large biological molecules: carbohydrates, nucleic acids, proteins

Monomer of carbohydrates

Monosaccharides (ex. glucose, fructose, galactose)

Condensation reaction

Connection of two monomers together, resulting in water leaving

Carbohydrate Condensation

2 monosaccharides → Disaccharide + H2O

Hydrolysis Reaction

Water is added to polymer, breaking it apart (consumes water instead of releasing)

Composition of Carbohydrates

C,H, and O; hydroxyl group and carbonyl group (ketone or aldehyde)

Formula for monosaccharides

C_x(H₂O)_x

Primary function of carbohydrates

Provide energy to organisms

2 types of carbs (sugars):

1. Simple - mono and disaccharides

2. Complex - polysaccharides

What is a carbohydrate with a ketone called?

Ketose (-ROR)

What is a carbohydrate with an aldehyde called?

Aldose (-ROH); glucose is an aldose

Ways of drawing carbohydrates:

1. Fischer projection (straight-chain)

2. Cyclic (how they are found in nature)

Stereoisomers of carbohydrates

1. Alpha - hydroxyl next to oxygen faces DOWN

2. Beta - hydroxyl next to oxygen faces UP

Common name for glucose

Hexose/dextrose

Photosynthesis

• Sunlight is used by plants to produce glucose

  • 6CO₂ + 6H₂O + Sunlight → Glucose + 6O₂

ATP Synthesis (Cellular Respiration)

• Used by animals to convert glucose into ATP (energy)

  • Glucose + 6O₂ → 6CO₂ + 6H₂O + ATP

Glucose

6-carbon sugar with alpha hydroxyl

Fructose

Isomer of glucose stored and metabolized into glucose in liver (STORED)

Stored form of glucose

Fructose; converted by liver into glucose

What foods contain fructose?

Fruit, honey, and syrup

Galactose

Isomer of glucose that ISN’T common in nature

Which monosaccharide can pass through the bloodstream?

ONLY glucose, all carbohydrates MUST be converted to glucose

Which organ converts fructose and galactose into glucose?

The liver

All monosaccharides:

1. Glucose

2. Fructose

3. Galactose

4. Ribose

5. Deoxyribose

Ribose

5-carbon sugar that forms RNA (rRNA); gain little in diet

Deoxyribose

5-carbon structure used for DNA formation; we CAN make this

All disaccharides:

1. Maltose

2. Sucrose

3. Lactose

Maltose

2 glucose molecules to form alpha bond; fermentation reaction

Sucrose

1 glucose and 1 fructose form alpha bond

Lactose

1 glucose and 1 galactose form beta bond

Why do people have a lactose intolerance?

Lactose has a beta bond needing to be broken by enzyme lactase, which some people don’t produce

Methods to start hydrolysis:

• Heat - would kill humans

• Acid - take too long

• Enzymes (-ase)

  • Ex. Lactase, maltase, sucrase (AKA invertase)

What is the other name for sucrase?

Invertase

Primary lactose maldigestion

• Inherited inability to produce lactase

  • Production stops after 3-5 years old

• The majority of people have this

• Mutation allows for production after loss

Secondary lactose maldigestion

Temporary decrease in lactose production that increases with age

Can lactose intolerant eat yogurt?

Yes, low amount of lactose because bacteria converts lactose into lactic acid

Cheese and lactose intolerance

• Lactose is in whey (water + lactose + protein) due to bacteria

• Hard cheese - less lactose

• Soft cheese - more lactose

Sugar beet/cane Preparation

1. Wash and cut

2. Extract juice

3. Evaporate and concentrate its syrup

4. Crystals fall from syrup, leaving molasses

Brown sugar composition

Sucrose + maltose

Honey

Contains mostly sugar (fructose and glucose) and phytochemicals

Functions of sugars in food preparation:

1. Sweeten foods

2. Preserve foods

3. Crystallization Agents (candies)

4. Caramelizing Agents

5. Fermentation (bread-making)

Which sugar is the most sweet?

Fructose

Which sugar is the least sweet?

Lactose

How do sugars preserve foods?

60% of sugar kills bacteria by osmosis (loss of water from cell)

How can you make milk sweeter?

Add lactase enzyme to break lactose into glucose and galactose

Sugar alcohols

• Instead of carbonyl, a sugar has an extra hydroxyl group (making it an alcohol)

• -ol ending

  • Ex. Sorbitol

Benefits of sugar alcohols

• Not metabolized by bacteria, preventing tooth decay

• Cooling sensation due to endothermic reaction (heat-absorbing)

  • Xylitol

• Less calories

Side effects of sugar alcohols

• Bloating, diarrhea, flatulence (laxative effect)

• Not absorbed by small intestine

Oligosaccharides

3-10 monosaccharides (raffinose and stachyose)

What foods contain oligosaccharides?

Beans and legumes (high in fiber foods)

Digestion of oligosaccharides

• CAN’T be digested, no enzyme

  • Fibers

• Metabolized by bacteria, resulting in gas in large intestine

Polysaccharides

10+ monosaccharides that can be digestible or non-digestible

Digestible polysaccharides

• Starch from plants

• Glycogen from animals

Non-digestible polysaccharides

Fibers (soluble and insoluble) - definition is non-digestible polysaccharides

Starch

(Glucose)_x, many glucose molecules connected by alpha bonds

2 types of starch:

1. Amylose (straight chain)

2. Amylopectin (branched)

Glycogen

Highly branched stored form of glucose in liver and muscles; holds more water

Why don’t we want to store so much glycogen?

It has more water, which would make us fat and give us less energy

Cellulose

Polysaccharide found only in plant cell wall, not digestible by humans (fiber)

Pectins

Polysaccharide in cell walls of fruits called “sugar acids”; fibers to humans

Use of pectins in food:

Used to make jams because they form strong gels in sugar due to dehydration

What makes fibers indigestible?

They all contain beta bonds which we don’t have enzymes for

Insoluble Fibers

Not fermented (Cellulose, hemicellulose, lignin)

Soluble Fibers

Can be fermented, giving calories (Gums and pectins)

Carbohydrate gums

• Soluble polysaccharides from plants that thicken and stabilize food

  • Traps color and flavor

• Used as additives

  • Salad dressing, candies, agar

Uses of complex polysaccharides in food:

• Structure

• Binding (bringing 2 things together that usually wouldn’t)

• Thickening (gelatinization)