Cell Biology Final Exam Study Guide: Cytoskeleton, Cell Division, and Molecular Biology

Lecture 21: Cytoskeleton and Microtubules

Functions and Organization of Cytoplasmic and Axonemal Microtubules

Microtubules are dynamic polymers of tubulin that play essential roles in cell structure, intracellular transport, and cell division.

• Cytoplasmic microtubules: Involved in maintaining cell shape, vesicle transport, and organelle positioning.

• Axonemal microtubules: Found in cilia and flagella, responsible for motility.

• Microtubule organizing centers (MTOCs): Sites where microtubule nucleation occurs, such as the centrosome.

• Critical concentration: The tubulin concentration at which microtubule assembly and disassembly are balanced.

• GTP cap: Stabilizes the growing end of a microtubule; loss of the cap leads to rapid depolymerization (catastrophe).

Example: The mitotic spindle is formed by microtubules emanating from centrosomes (MTOCs) during cell division.

Microtubule-Associated Proteins (MAPs) and Regulation

• MAPs: Proteins that bind to microtubules and regulate their stability and interactions (e.g., tau, MAP2).

• Motor proteins: Kinesin and dynein move cargo along microtubules using ATP.

• Regulatory proteins: CLASP, XMAP215, and stathmin modulate microtubule dynamics.

Additional info: WASP proteins are involved in actin nucleation, not microtubules, but may be referenced for cytoskeletal cross-talk.

Lecture 22: Motility Systems and Transport

Types of Motility Systems

Cells use various motility systems for movement and intracellular transport.

• Microtubule-based motility: Cilia and flagella use axonemal microtubules for movement.

• Actin-based motility: Muscle contraction, cell crawling, and cytokinesis.

Transport Mechanisms

• Kinesin: Moves cargo toward the plus end of microtubules (anterograde transport).

• Dynein: Moves cargo toward the minus end (retrograde transport).

• ATP hydrolysis: Provides energy for motor protein movement.

Example: Axonal transport in neurons relies on kinesin and dynein to move vesicles and organelles.

Structure and Function of Cilia and Flagella

• Axoneme: The core structure of cilia and flagella, composed of a "9+2" arrangement of microtubules.

• Basal body: The MTOC for cilia and flagella, similar to the centriole.

Additional info: The axoneme's dynein arms generate sliding forces for motility.

Lecture 23: Cell Cycle and Division

Phases of the Cell Cycle

The cell cycle consists of distinct phases that regulate cell growth and division.

• G1 phase: Cell growth and preparation for DNA synthesis.

• S phase: DNA replication.

• G2 phase: Preparation for mitosis.

• M phase: Mitosis and cytokinesis.

Regulation of the Cell Cycle

• Cyclins and cyclin-dependent kinases (CDKs): Control progression through the cell cycle.

• Checkpoints: Ensure proper DNA replication and division (e.g., G1/S, G2/M).

• MPF (Maturation Promoting Factor): A complex of cyclin and CDK that triggers mitosis.

Example: The spindle assembly checkpoint prevents anaphase until all chromosomes are properly attached to the spindle.

Apoptosis and Cancer

• Apoptosis: Programmed cell death, important for development and tissue homeostasis.

• Cancer: Results from uncontrolled cell division due to mutations in cell cycle regulators.

Exam I Review: Biomolecules and Enzymes

Structure and Function of Biomolecules

Cells are composed of four major classes of biomolecules: proteins, carbohydrates, nucleic acids, and lipids.

• Proteins: Polymers of amino acids; perform structural, enzymatic, and regulatory functions.

• Carbohydrates: Polymers of monosaccharides; provide energy and structural support.

• Nucleic acids: DNA and RNA; store and transmit genetic information.

• Lipids: Hydrophobic molecules; form membranes and store energy.

Peptide Bonds and Protein Structure

• Peptide bond: Covalent bond between amino acids in a protein.

• Primary structure: Sequence of amino acids.

• Secondary structure: Alpha helices and beta sheets.

• Tertiary structure: Overall 3D shape.

• Quaternary structure: Assembly of multiple polypeptides.

Example: Hemoglobin is a quaternary protein composed of four subunits.

Enzyme Kinetics and Inhibition

• Enzyme: Biological catalyst that speeds up chemical reactions.

• Competitive inhibition: Inhibitor binds to the active site, blocking substrate.

• Non-competitive inhibition: Inhibitor binds elsewhere, altering enzyme activity.

• Uncompetitive inhibition: Inhibitor binds only to the enzyme-substrate complex.

Equation:

$V = \frac{V_{max}[S]}{K_m + [S]}$

Additional info: $K_m$ is the substrate concentration at half-maximal velocity.

Exam II Review: Molecular Biology and Gene Expression

DNA and RNA Structure

• DNA: Double helix, deoxyribose sugar, bases A, T, C, G.

• RNA: Single-stranded, ribose sugar, bases A, U, C, G.

• 5' and 3' ends: Refer to the orientation of the sugar-phosphate backbone.

Transcription and Translation

• Transcription: Synthesis of RNA from DNA template by RNA polymerase.

• Translation: Synthesis of protein from mRNA template at the ribosome.

• RNA processing: Includes capping, splicing, and polyadenylation.

Gene Regulation

• Promoters: DNA sequences where RNA polymerase binds to initiate transcription.

• Enhancers: Regulatory DNA elements that increase transcription.

• Transcription factors: Proteins that regulate gene expression by binding DNA.

Post-Translational Modifications

• Phosphorylation: Addition of phosphate groups to proteins, altering activity.

• Ubiquitination: Tags proteins for degradation.

Table: Comparison of DNA and RNA

Feature	DNA	RNA
Sugar	Deoxyribose	Ribose
Bases	A, T, C, G	A, U, C, G
Strands	Double	Single
Function	Genetic storage	Genetic expression

Additional info:

• RNA polymerase III transcribes tRNA and 5S rRNA genes.

• Post-transcriptional control includes alternative splicing and RNA editing.