Carbohydrates

Molecules

• Monomers

  • A small molecule that can bind chemically to other molecules

• Polymers

  • A large molecule that’s formed when monomers link together chemically in a chain

• Macromolecules

  • Complex molecule composed of repeating units of smaller molecules covalently linked together

Structure of Carbohydrates

• Carbohydrates/Saccharides are divided into three chemical groups:

1. Monosaccharides (simple sugars)

   1. Alpha glucose, beta glucose, galactose, fructose

2. Disaccharides (double sugars)

   1. Sucrose, malatose, lactose

3. Polysaccharides (complex sugars)

   1. Starch, glycogen, cellulose, chitin

Carbohydrates

• A large biological molecule consisting only of carbon, hydrogen, and oxygen

• General empirical formula is (CH2O)n, where n is the number of carbons in the molecule, represents carbohydrates

Carbohydrates Role

Energy Source

• Carbohydrates broken down to mainly glucose are the preferred source of energy for our body, as cells in our brain, muscle, and all other tissues directly use monosaccharides for their energy needs

• Monosaccharides are directly absorbed by the small intestine into the bloodstream, where they are transported to the cells in need

Membrane Carbohydrates

• Structural role as a physical barrier

• Participate in cell recognition

Structural Support

• Diff carbohydrates, particularly those in the form of polysaccharides, contribute to the building of cellular structure

• In plants particularly, cellulose creates a solid wall around the plant cells, giving the plant its structure

Biochemical Synthesis

• Carbohydrates release carbon atoms as they break down

• These serve as the raw material for much of an organism’s biochemistry, as the carbon can then join w other chemicals in the body

Monosaccharides

• Simple carbohydrates that consist of 1 monomer subunits

• Contains 6 carbon atoms, 12 hydrogen atoms, and 6 oxygen atoms

• An energy source, building blocks (monomer)

• Most monosaccharide names end w the suffix -ose

  • Ex. Glucose, fructose, galactose, ribose, deoxyribose

• Glucose is an important source of energy (aka blood sugar)

• Fructose is commonly found in fruits and known as fruit sugar

• Galactose is found in milk products

• Ribose and deoxyribose are sugar components of DNA (C5H10O5)

• Monosaccharides are classified based on:

  • The position of their carbonyl group

  • The number of carbons in the backbone

Carbonyl groups - monosaccharides

• Monosaccharides can be distinguished by their carbonyl group

• Glucose, fructose, and galactose are isomers, meaning they have the same chemical formula (C6H12O6) but a diff atom arrangment

  

# of carbons - monosaccharides

• Monosaccharides can be distinguished by the # of carbons

• Ribose and Deoxyribose are a pentose sugar (5 carbons)

• Glucose is a hexose sugar (6 carbons)

In solutions

• Monosaccharides form a ring structure when dissolved in water

• The hydroxyl group on carbon 1 can end up either above or below the ring

• α-glucose - below the ring

• β-glucose  - above the ring

Dry State

• Monosaccharides are linear in a dry state

Disaccharides

• Formed when two monosaccharide molecules join in a dehydration rxn to form a glycosidic bond

  • An H2O molecule is removed in the process

• Used as energy storage and as a building block for larger molecules

• Some important disaccharide molecules include:

  • Sucrose (table sugar)

  • Maltose (grain sugar)

  • Lactose (milk sugar)

• These types of disaccharide formed depends on the monomers involved & their form (alpha or beta)

Polysaccharides

• A long chain of monosaccharides linked by glycosidic bonds is a polysaccharide

• The chain may be branched or unbranched and it may contain different types of monosaccharides

• Primary examples include:

  • Starch

  • Glycogen

  • Cellulose

• Starch and glycogen are examples of storage for carbohydrates

• Cellulose and chitin are examples of a structural complex carbohydrates

• Disaccharides and polysaccharides can be broken down into smaller, simpler sugars via hydrolysis

  • A chemical rxn using water to break bonds to form two or more new substances

Starch

• 2-6 thousand glucose molecules bonded together forming amylose (unbranched, coiled α-glucose chain) or amylopectin (branched α-glucose chain)

• Storage molecules used by plants

• Glucose made through photosynthesis can be stored as a starch polymer

Glycogen

• The storage form of glucose in humans and other vertebrates and is comprised of monomers of glucose

• Stored in liver and muscle cells

• Whenever blood glucose levels decrease, glycogen breaks down to release glucose

• Good for long-term source of energy

  

Cellulose

• Structural component of plant cell walls that provides support

• Straight chain of β-glucose monomers w β 1-4 linkages

  • Linkages cause inversion of every other monomer

• Form bundles of fibres

• Humans cannot digest cellulose bc we lack the enzymes in our digestive systems to break down the bonds within cellulose

• The linear shape of cellulose allows it to interact w water

Chitin

• Exoskeleton of insects and crustaceans

• Contains a glucose-like monomer w a nitrogen group at C-2

Lactose Intolerance

• Lactase is an enzyme that breaks down the glycosidic bond in lactose

• Although almost all babies are born w the ability to produce lactase, some people lose that as they get older

  • Lactose intolerant lmao