Intro Bio 1 - CH. 5

• A glycosidic linkage formed by a condensation reaction between two hydroxyl groups.

• Can be broken by hydrolysis reaction (add H2O)

α-1,4-glycosidic linkage and β-1,4-glycosidic linkage, both between C-1 and C-4 carbons but differing in geometry.

• They both connect Carbon-1 of one sugar to Carbon-4 of another, but differ in direction at C-1: α points down, while β points up.

Starch has α-1,4-glycosidic linkages forming a helix, while cellulose has β-1,4-glycosidic linkages with every other glucose flipped, forming linear fibers.

Amylose is an unbranched starch with only α-1,4 linkages; amylopectin is a branched starch with α-1,6 linkages at branch points (abt 30 monomers).

• *Branched -splits off into a second chain instead of staying as one long line

Glycogen is a highly branched α-glucose polymer stored in animals, with branches about every 1 in 10 monomers, compared to starch's less frequent branching.

Cellulose is a structural polysaccharide forming the plant cell wall, providing strength and rigidity.

• Made of β glucose monomers linked by β-1,4 linkages; every other glucose is flipped --> linear model

Chitin is a structural polysaccharide in fungal cell walls and insect exoskeletons, composed of N-acetylglucosamine monomers linked by β-1,4 bonds (every other monomer is flipped)

• Bacterial cell wall polymer

• Long backbones of alternating polysaccharides

• Joined by B-1,4-glycosidic linkages

• Short amino acid chains form peptide bonds between adjacent strands

• Serve as precursors to other molecules, such as nucleotides and amino acids

• Provide fibrous structural materials

• Indicate cell identity

• Store chemical energy

Most organisms lack enzymes to break β-1,4 linkages, and the fibers formed exclude water, making hydrolysis challenging.

Carbohydrates store lots of energy because their C–H and C–C bonds have high potential energy; their electrons are held less tightly than in the C=O and C-O bonds of CO₂, where electrons have lower potential energy.

• Starch is hydrolyzed by amylase enzymes; glycogen is hydrolyzed by phosphorylase (into glucose).

• Yes, because they have a-glycosidic linkages (alpha linkages = easier to break → starch/glycogen can be quickly used for energy)

Glucose breakdown releases energy used to synthesize ATP, which powers cellular processes/other reactions like polymerization and muscle movement.

Sugars typically form ring structures in water, which affects their chemical reactivity and biological function.

Cell structure, cell identity, and energy storage

• Sugars

• Provide chemical energy in cells ; serve as building blocks for larger compounds; also played important role in chemical evolution (ex: ribose needed for nucleotide formation)

• Location of carbonyl group (end-aldose, middle-ketose)

• Number of carbon atoms present (triose, pentose, hexose)

• Spatial arrangement of their atoms (ex: diff arrangement of hydroxyl groups –OH)

• Linear & alternative ring forms

A chemical functional group consisting of a carbon atom double-bonded to an oxygen atom written as C=O

Because so many aspects of their structure are variable (ex: carbon #, aldose or ketose placement, etc.)

• They are complex carbohydrates and are polymers of monosaccharide monomers

• Two sugars/monosaccharides linked together 2

• Starch (plants, storage)

• Glycogen (animals; storage)

• Cellulose (plants; structural)

• Chitin (fungi & animals; structural)

• Peptidoglycan (bacteria; structural)

• Sugar is stored as starch in plants

• Composed of a-glucose monomers

• Forms a helix (amylose, amylopectin)

• Structural polysaccharide; forms long, straight chains w/ β-1,4 glycosidic linkages.

• Cellulose is found in plants, chitin in fungi & animals

Carbohydrates on the cell surface act like an “ID badge.” They are attached to proteins (glycoproteins) or lipids (glycolipids) and help cells recognize each other and communicate.