MCB 252 EXAM 3

Metastasis

When a primary tumor breaks away to other body parts via inappropriate cell adhesion and movement

Tissue Cell Properties

1. Specialized Shapes: cells morph depending on function, & maintains homeostasis and differentiation

2. Cell Adhesion: cells sticking together

3. Extracellular Matrix (ECM): outer secreted proteins that bring cells into organized tissue via homeostasis

Eukaryotic Gene Structures

• Eukaryotic genes have many enhancers which allows for many genes

• Enhancers act over a distance

• Eukaryotic genes specifically in fruit flies have an Eve gene (evens skipped) on every odd gene within the 14 para-segmented embryo because there are 7 distinct modular enhancers that each activate transcription

Protein Domains

• protein structures varying by 3 amino acid sequences

• allows for exon shuffling & avoids clashing because N- and C- termini point in opposite directions

• Ex: TFIIIA has 9 zinc fingers varying by 3 amino acids each

• Ex: Ig domains making up antibodies

Gene Families

• Gene groups formed via duplication and divergence

• independent mutations

• sometimes leads to pseudogenes (non-functional genes)

• Ex: steroid hormones & hemoglobin tetramer

Actin Properties

• Actin is an ATPase (hhydrolyzes ATP —> ADP +Pi)

• G-actin = monomers

• F-actin = polymers (requires ATP + Mg 2+)

• Held together via protein-protein interactions

Decoration Experiment

Scientists added S1 (myosin head) domains to actin filaments to determine directionality and found that + end grows faster than - end

Nucleation

• Forms nucleus using trimolecular reactions of monomers (slow reaction)

• </= Cc : only monomers (F-actin depolymerizes)

Elongation

• Lengthens filaments by adding monomers to both ends of filaments

• Adding a preformed filament eliminates need for nucleus since it transitions from trimolecular to bimolecular reaction

• >Cc : filaments + monomers (F-actin polymerization)

Steady State

• No net F-actin assembly (length doesn’t change)

• Some free G-actin

• (+ end) G-actin < (- end) G-actin

• Rates are still constant due to treadmilling; still polymerizing, just at a constant rate

ATP hydrolysis

1. Supplies energy for treadmilling in steady state reactions

2. Makes actin polymers non-homogenous (ends have different Cc values)

   1. Rate of polymerization is faster at - end

   2. (+ end) = ATP & (- end) = ADP (majority of polymer)

   3. There’s no ATP at equilibrium

Actin Destabilizers

1. Cytochalzin = prevents addition by binding to + end

2. Latrunculin = prevents monomers from binding by binding to G-actin beforehand

Actin Stabilizers

Phalloidin = Binds & stabilizes filaments (prevents depolymerization)

• The + end pushes membrane forward

ActA Protein

• A bacterial protein that directly contacts Arp 2/3 complex to nucleate branched filaments

• Capping occurs when filaments stop pushing on the membrane

• necessary for movement of comet tails

• proves polymerization is necessary and sufficient to drive movement

Polymerization Driving Movement

1. Actin Flexing: Bends/flexes to add monomers

2. Pushing the Membrane Bound Proteins: Rho provides a slight gap for formin to build actin and push the membrane forward

3. Rectified Diffusion (Brownian Ratchet): Actin briefly diffuses from membrane to add monomers, and these small molecular movements stem from thermal fluctuations

Cell Movement Pathways

1. Cdc42: Activated by GTP —> WASP via RBD —> Arp 2/3

2. Rac: Activated by GTP —> WAVE via RBD —> Arp 2/3

3. Rho: Activated by GTP —> formin FH1 (profilin) & FH2 (ring) domains bind via RBD

Regulatory Proteins

1. Sequestering G-actin = Thymosin B4

2. Nucleation = Formin & Arp 2/3

3. Elongation = Formin & Profilin

4. Disassembly = Cofilin & Gelson

5. Assembly/Disassembly Prevention: (+ end) = CapZ & (- end) = Tropomodulin