Comprehensive Study Guide: Carbohydrates, Nucleic Acids, Lipids, Membranes, and Biosignaling

Carbohydrates: Structure and Function

Fischer and Haworth Projections

Carbohydrates can be represented in different structural forms. Fischer projections are linear representations, while Haworth projections depict cyclic forms.

• Conversion: Be able to convert between Fischer and Haworth projections for monosaccharides.

• Example: D-glucose in Fischer projection can be cyclized to form α- or β-D-glucopyranose in Haworth projection.

Physicochemical Properties of Homopolysaccharides

Homopolysaccharides are polymers composed of one type of monosaccharide.

• Examples: Cellulose, chitin, amylose, amylopectin, glycogen.

• Functions: Energy storage (glycogen, starch), structural support (cellulose, chitin).

Glycoconjugates and Glycan Attachment

Glycoconjugates are molecules where carbohydrates are covalently linked to proteins or lipids.

• Attachment: Glycans can be N-linked (to asparagine) or O-linked (to serine/threonine).

• Function: Cell recognition, signaling, and structural roles.

Lectins and Glycan Recognition

Lectins are proteins that bind specific carbohydrate structures.

• Role: Mediate cell-cell interactions, immune response.

• Example: Selectins in inflammation.

DNA Structure: Major and Minor Grooves

DNA double helix contains major and minor grooves formed by the arrangement of base pairs.

• Importance: Protein binding and regulation of gene expression.

Attachment Sites of Sugars in Nucleotides

The sugar in nucleotides attaches to the base at specific positions (N9 in purines, N1 in pyrimidines).

• Significance: Determines the structure and function of nucleic acids.

Nucleic Acids: Structure and Function

Palindromic DNA Sequences

Palindromic sequences read the same 5' to 3' on both strands and are important in restriction enzyme recognition.

• Example: 5'-GAATTC-3' (EcoRI site).

Factors Affecting DNA Stability

• Temperature: High temperature can denature DNA.

• Base Composition: GC-rich regions are more stable due to three hydrogen bonds.

RNA vs. DNA

RNA and DNA differ in structure and function.

• RNA: Ribose sugar, uracil base, single-stranded.

• DNA: Deoxyribose sugar, thymine base, double-stranded.

• Types of RNA: mRNA, tRNA, rRNA.

Nucleic Acid Recognition by Proteins

• Recognition: Proteins bind specific DNA/RNA sequences via motifs (helix-turn-helix, zinc finger).

Polymerase Chain Reaction (PCR)

PCR amplifies DNA using cycles of denaturation, annealing, and extension.

• Equation: $N = N_0 imes 2^n$ (where N is final DNA copies, N_0 is initial, n is cycles)

Lipids: Structure and Properties

Fatty Acids and Lipid Classes

• Fatty Acids: Long hydrocarbon chains with a carboxyl group.

• Glycerophospholipids: Glycerol backbone, two fatty acids, phosphate group.

• Glycosphingolipids: Sphingosine backbone, fatty acid, carbohydrate group.

• Steroids: Four fused rings, e.g., cholesterol.

Factors Affecting Membrane Fluidity

• Chain Length: Shorter chains increase fluidity.

• Saturation: Unsaturated fatty acids increase fluidity.

Membranes and Membrane Proteins

Membrane-Associated Proteins

• Integral Proteins: Span the membrane.

• Peripheral Proteins: Attached to membrane surface.

Hydropathy Plots

Hydropathy plots predict membrane-spanning regions in proteins based on hydrophobicity.

Membrane Transport Mechanisms

• Diffusion: Passive movement down concentration gradient.

• Active Transport: Requires energy input.

• Facilitated Transport: Uses carrier proteins.

• Symport/Antiport: Coupled transport of molecules in same/opposite directions.

Bacterial Potassium Channel Selectivity

• Basis: Selectivity filter allows K+ ions but excludes Na+ due to size and coordination.

Channel and Transporter Function

• Activation/Inactivation: Channels open/close in response to signals; e.g., voltage-gated channels.

• ATPases: Use ATP hydrolysis to pump ions (e.g., Na+/K+ ATPase).

Membrane Transport Energetics

• Free Energy Change: $\Delta G = RT \ln \frac{[C]_2}{[C]_1}$ (for uncharged solutes)

• Electrochemical Potential: Includes both concentration and electrical gradient.

Biosignaling

GPCR Signaling

• GPCRs: G protein-coupled receptors transmit signals via G proteins.

• Second Messengers: cAMP, Ca2+, IP3.

• Desensitization: Prolonged stimulation reduces receptor response.

Receptor Tyrosine Kinase Signaling

• RTKs: Receptors with intrinsic kinase activity; phosphorylate tyrosine residues.

• Difference from GPCRs: RTKs directly activate intracellular signaling cascades via phosphorylation.

Fatty Acid Nomenclature

• Shorthand: Number of carbons:number of double bonds (e.g., 18:1 for oleic acid).

Summary Table: Major Biomolecule Classes

Class	Structure	Function
Carbohydrates	Monosaccharides, polysaccharides	Energy, structure, recognition
Nucleic Acids	DNA, RNA	Genetic information, protein synthesis
Lipids	Fatty acids, phospholipids, steroids	Membranes, energy storage, signaling
Proteins	Amino acid polymers	Catalysis, structure, transport

Additional info: Academic context and definitions have been expanded for clarity and completeness.