Carbohydrates

Alpha and Beta Conformations of Glucose

Glucose, a monosaccharide, can exist in two different ring forms known as alpha (α) and beta (β) anomers. These forms differ in the orientation of the hydroxyl group (-OH) attached to the first carbon (anomeric carbon) in the ring structure.

• Alpha (α) glucose: The -OH group on the anomeric carbon is positioned below the plane of the ring.

• Beta (β) glucose: The -OH group on the anomeric carbon is positioned above the plane of the ring.

• This difference affects the properties and biological roles of polysaccharides formed from glucose.

Carbons in a Triose

A triose is a monosaccharide containing three carbon atoms. The three carbons are typically numbered as C1, C2, and C3.

• Examples: Glyceraldehyde (an aldose triose), Dihydroxyacetone (a ketose triose).

Monosaccharides

Monosaccharides are the simplest carbohydrates, consisting of a single sugar unit. They vary by:

• Number of carbon atoms (triose, tetrose, pentose, hexose, etc.)

• Functional group (aldose: contains an aldehyde; ketose: contains a ketone)

• Arrangement of atoms (isomers)

Aldose vs. Ketose

The main difference between an aldose and a ketose is the location of the carbonyl group:

• Aldose: Carbonyl group is at the end of the carbon chain (as an aldehyde).

• Ketose: Carbonyl group is within the carbon chain (as a ketone).

• Example: Glucose (aldose), Fructose (ketose).

Polysaccharides: Types and Linkages

Polysaccharides are long chains of monosaccharide units linked by glycosidic bonds. The type of linkage and branching determines their structure and function.

• Starch: Storage polysaccharide in plants; composed of α-1,4 and α-1,6 glycosidic bonds (amylose and amylopectin).

• Glycogen: Storage polysaccharide in animals; highly branched with α-1,4 and α-1,6 glycosidic bonds.

• Cellulose: Structural polysaccharide in plants; composed of β-1,4 glycosidic bonds, forming straight, rigid fibers.

Polysaccharide Structure and Function

• Starch and Glycogen: Both serve as energy storage but differ in branching and solubility.

• Cellulose: Provides structural support in plant cell walls; indigestible by humans due to β-linkages.

Polysaccharides and Chemical Evolution

Polysaccharides played a role in the origin of life by providing structural frameworks and energy storage for early cells.

Starch vs. Glycogen

• Starch: Found in plants, less branched, stored in plastids.

• Glycogen: Found in animals, highly branched, stored in liver and muscle cells.

Cell Structure and Organelles

Prokaryotic, Eukaryotic, and Plant Cell Parts

• Prokaryotic cells: Lack a nucleus; have DNA, ribosomes, plasma membrane, and sometimes cell wall.

• Eukaryotic cells: Have a nucleus and membrane-bound organelles (e.g., mitochondria, ER, Golgi apparatus).

• Plant cells: Contain chloroplasts, large central vacuole, and cell wall in addition to typical eukaryotic organelles.

Where Bacterial DNA is Stored

• Bacterial DNA is stored in the nucleoid region, which is not membrane-bound.

Functions of Organelles

• Ribosomes: Protein synthesis.

• Rough ER: Protein synthesis and modification; studded with ribosomes.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Digestion and waste removal.

• Smooth ER: Lipid synthesis and detoxification.

Chloroplast Components

• Thylakoids: Membranous sacs where light-dependent reactions occur.

• Stroma: Fluid surrounding thylakoids; site of Calvin cycle.

• Grana: Stacks of thylakoids.

Lipids and Membranes

Phospholipids: Structure and Function

• Phospholipid: A lipid with a hydrophilic (polar) head and two hydrophobic (nonpolar) fatty acid tails.

• Function: Main component of cell membranes, forming a bilayer.

• Saturated vs. Unsaturated: Saturated fatty acids have no double bonds; unsaturated have one or more double bonds, affecting membrane fluidity.

Fats and Energy Storage

• Fats (Triglycerides): Composed of glycerol and three fatty acids; store energy efficiently.

• Stored in adipose tissue in animals.

Types of Lipids and Their Structure

• Fats (Triglycerides): Glycerol + 3 fatty acids.

• Phospholipids: Glycerol + 2 fatty acids + phosphate group.

• Steroids: Four fused carbon rings (e.g., cholesterol).

Plasma Membrane Permeability

• Small, nonpolar molecules (e.g., O2, CO2) pass easily.

• Large or charged molecules (e.g., ions, glucose) require transport proteins.

Osmosis and Tonicity

• Osmosis: Diffusion of water across a selectively permeable membrane.

• Hypertonic: Higher solute concentration outside the cell; water leaves the cell.

• Hypotonic: Lower solute concentration outside; water enters the cell.

• Isotonic: Equal solute concentration; no net water movement.

Types of Diffusion

• Simple diffusion: Movement of molecules from high to low concentration without energy input.

• Facilitated diffusion: Movement via transport proteins; no energy required.

• Active transport: Movement against concentration gradient; requires energy (ATP).

Identifying Macromolecules in a Figure

• Recognize structural features: ring structures (carbohydrates), long hydrocarbon chains (lipids), nitrogenous bases (nucleic acids), amino acid chains (proteins).

Summary Table: Types of Lipids

Additional info:

• Critical thinking questions may require application of these concepts to novel scenarios or data interpretation.