BIO340 Cell Biology Study Guide: Chapters 1–5 (Proteins, DNA, Macromolecules, Energetics, Techniques)

Experimental Model Systems

Overview

Experimental model systems are organisms or cells used to study biological processes. They provide insight into cellular mechanisms and are chosen for their genetic tractability, ease of manipulation, and relevance to human biology.

• Common Model Organisms: Escherichia coli (bacteria), Saccharomyces cerevisiae (yeast), Drosophila melanogaster (fruit fly), Mus musculus (mouse), Arabidopsis thaliana (plant).

• Applications: Studying gene function, protein expression, cellular processes, and disease models.

• Advantages: Rapid growth, genetic manipulation, conservation of cellular pathways.

Biologically Relevant Non-Covalent Interactions

Types and Significance

Non-covalent interactions are essential for the structure and function of macromolecules. They include:

• Hydrogen Bonds: Attraction between a hydrogen atom and an electronegative atom (e.g., N, O).

• Van der Waals Forces: Weak, transient interactions between molecules.

• Ionic Bonds: Electrostatic attraction between oppositely charged ions.

• Hydrophobic Interactions: Nonpolar molecules aggregate to minimize contact with water.

• Significance: Stabilize protein folding, DNA double helix, membrane structure.

From Precursor to Macromolecule

Process and Key Terms

Macromolecules are synthesized from smaller precursors through specific reactions:

• Monomers: Building blocks (amino acids, nucleotides, monosaccharides, fatty acids).

• Polymerization: Formation of polymers (proteins, nucleic acids, polysaccharides, lipids).

• Condensation Reaction: Joins monomers, releases water.

• Hydrolysis: Breaks polymers, consumes water.

• Bonds: Peptide (proteins), phosphodiester (nucleic acids), glycosidic (carbohydrates), ester (lipids).

The Four Macromolecules

Significance in Cells

• Proteins: Enzymes, structural components, signaling molecules.

• Nucleic Acids: DNA (genetic information), RNA (gene expression, catalysis).

• Carbohydrates: Energy storage, cell structure, recognition.

• Lipids: Membrane structure, energy storage, signaling.

Energetics

Gibbs Free Energy and Reaction Direction

Cellular reactions are governed by thermodynamic principles:

• Gibbs Free Energy ($\Delta G$): Determines spontaneity of a reaction.

• Spontaneous Reaction: $\Delta G < 0$ (exergonic).

• Non-Spontaneous Reaction: $\Delta G > 0$ (endergonic).

• ATP Coupling: Endergonic reactions are driven by coupling to ATP hydrolysis.

Equation:

$\Delta G = \Delta H - T\Delta S$

• Enzymes: Lower activation energy ($E_a$), increase reaction rate, do not change $\Delta G$ or equilibrium.

• Activation Energy: Energy barrier to reaction; enzymes lower $E_a$.

Condensation vs. Hydrolysis: Condensation is typically endergonic; hydrolysis is exergonic.

Lipids

Categories and Biomembranes

• Three Main Categories:

  • Phospholipids: Major component of cell membranes.

  • Glycolipids: Membrane lipids with carbohydrate groups.

  • Steroids: Cholesterol and derivatives, membrane fluidity, signaling.

• Biomembranes: Composed of lipid bilayers, proteins, carbohydrates.

• Aggregate Structures: Micelles, bilayers, liposomes.

Amino Acids

Groups and Special Amino Acids

• Classification:

  • Nonpolar (hydrophobic)

  • Polar (hydrophilic)

  • Charged (acidic/basic)

• Three Special Amino Acids:

  • Cysteine: Forms disulfide bonds.

  • Proline: Causes kinks in polypeptide chain.

  • Glycine: Smallest, increases flexibility.

Protein Structure and Denaturation

Levels of Organization

• Primary Structure: Sequence of amino acids.

• Secondary Structure: Alpha helices, beta sheets (hydrogen bonds).

• Tertiary Structure: 3D folding (hydrophobic, ionic, disulfide bonds).

• Quaternary Structure: Multiple polypeptides assembled.

• Disulfide Bonds: Covalent bonds between cysteine residues, stabilize structure.

• Denaturation: Loss of structure due to heat, pH, chemicals; can revert to primary structure.

• Reduction: Breaking disulfide bonds.

Protein Modifications

Types and Functions

• Phosphorylation/Dephosphorylation: Addition/removal of phosphate groups; regulates activity.

• Ubiquitylation: Attachment of ubiquitin; targets proteins for degradation.

• Methylation: Addition of methyl groups; affects function and localization.

• Mechanisms: Enzymatic transfer (kinases, methyltransferases, ubiquitin ligases).

Protein Folding and Chaperones

Mechanisms and Examples

• Chaperones: Assist in proper folding, prevent aggregation.

• Pro-protein Concept: Inactive precursors activated by cleavage.

• Small Molecules: Cofactors, coenzymes aid folding/function.

• Examples: Immunoglobulin G, hemoglobin, proinsulin/insulin.

Protein Domains and Surface Shape

Functional Significance

• Domains: Distinct structural/functional units within proteins.

• Surface Shape: Determines interaction with other molecules.

Enzymes and ATP

Role in Reactions

• Enzymes: Catalyze reactions, lower activation energy, do not affect equilibrium or direction.

• ATP: Provides energy, drives endergonic reactions.

• Table 3-1: Common enzymes (Additional info: Examples include kinases, phosphatases, proteases, polymerases).

Nucleic Acids

Structure and Function

• Primary Sequence: Linear arrangement of nucleotides.

• Double Helix: Two strands, complementary base pairing.

• Directionality: 5' to 3' orientation.

Types of DNA Sequences in Eukaryotes

Classification and Function

• Introns: Non-coding regions, removed during RNA processing.

• Exons: Coding regions, expressed as protein.

• Regulatory Sequences: Control gene expression.

• Centromeres: Chromosome segregation.

• Telomeres: Chromosome end protection.

• Origins of Replication: Sites where DNA replication begins.

RNA Types

mRNA vs Functional/Non-Coding RNA

• mRNA: Messenger RNA, codes for proteins.

• Functional/Non-Coding RNA: tRNA, rRNA, snRNA, miRNA; roles in translation, regulation, splicing.

Chromatin Compaction

Dynamic Nature and Regulation

• Chromatin: DNA-protein complex, compaction regulates gene expression.

• Heterochromatin: Highly compacted, transcriptionally inactive.

• Euchromatin: Less compacted, transcriptionally active.

• Facultative Heterochromatin: Can switch between active/inactive.

• Permanent Heterochromatin: Always inactive.

• Histones: Proteins around which DNA wraps.

• Nucleosomes: DNA-histone complexes.

• DNA Loops: Higher-order structure.

Condensed DNA and Transcription

Relationship

• Condensed DNA: Less accessible, reduced transcription.

• Compacted State: Regulated by histone modifications.

Histone Marking

Methylation and Acetylation

• Methylation: Addition of methyl groups, often represses transcription.

• Acetylation: Addition of acetyl groups, often activates transcription.

DNA Replication

Process Overview

• Where: Nucleus (eukaryotes), cytoplasm (prokaryotes).

• How: Semi-conservative mechanism.

• Molecules Involved: DNA polymerase, helicase, primase, ligase.

• Order: Initiation at origins, unwinding, primer synthesis, elongation, ligation.

• Why: Accurate transmission of genetic information.

Chromatin Compaction Story

Process and Proteins

• Naked DNA: Wraps around histones to form nucleosomes.

• Euchromatin: Loosely packed, accessible for transcription.

• Heterochromatin: Further compacted, transcriptionally silent.

• Proteins Involved: Histones, chromatin remodeling complexes.

Protein Synthesis Story

From Amino Acids to Functioning Protein

• Key Interactions: Peptide bond formation, folding, stabilization by non-covalent and covalent bonds.

• Levels of Organization: Primary to quaternary structure.

• Additional Modifications: Phosphorylation, methylation, ubiquitylation.

• Roles: Coenzymes, chaperones assist folding and function.

Techniques and Tools

Overview

• Spectral Karyotyping: Chromosome visualization using fluorescent probes.

• Metabolic Labelling: Incorporation of labeled molecules to track cellular processes.

• Probe/Tag: Molecules used to detect or visualize targets.

• Fluorescently Tagged Probes: Enable visualization of specific molecules or structures.

• Subcellular Fractionation: Separation of cellular components by centrifugation.

Table: Common Enzyme Types (Inferred from Table 3-1)

Enzyme Type	Function	Example
Kinase	Adds phosphate group	Protein kinase A
Phosphatase	Removes phosphate group	Protein phosphatase 1
Protease	Cleaves peptide bonds	Trypsin
Polymerase	Synthesizes nucleic acids	DNA polymerase
Ligase	Joins DNA fragments	DNA ligase
Methyltransferase	Adds methyl group	DNA methyltransferase
Ubiquitin Ligase	Adds ubiquitin	E3 ligase

Additional info: Table entries inferred from standard cell biology enzyme classifications.