USABO

Cell Biology

What is the complete pathway taken by a protein destined for secretion, starting from the nucleus?

$$\text{Nucleus} \rightarrow \text{Rough ER} \rightarrow \text{Transport Vesicle} \rightarrow \text{Golgi Apparatus (cis to trans)} \rightarrow \text{Secretory Vesicle} \rightarrow \text{Plasma Membrane}$$

How do unsaturated fatty acids affect cell membrane fluidity at low temperatures, and what structural feature causes this?

They increase fluidity. Double bonds in unsaturated fatty acid tails introduce kinks that prevent phospholipids from packing tightly together.

How does cholesterol act as a temperature buffer in animal cell membranes?

• At high temperatures, it restrains phospholipid movement and reduces fluidity.

• At low temperatures, it hinders close packing and prevents solidification.

What is the fundamental difference in energy source between Primary Active Transport and Secondary Active Transport?

• Primary Active Transport uses direct ATP hydrolysis.

• Secondary Active Transport uses the potential energy stored in an electrochemical gradient (created by primary active transport).

What is the formula for Water Potential ($\Psi$), and in which direction does water naturally flow?

• Formula: $\Psi = \Psi_s + \Psi_p$ (Water potential = Solute potential + Pressure potential)

• Flow direction: Water flows from higher water potential ($\Psi$) to lower water potential ($\Psi$).