Be101 Lecture 3: Structures and Functions Within the Cell

Flashcards covering animal and plant cell features, prokaryotic vs. eukaryotic cell comparisons, plasma membrane composition, protein types, passive and active transport mechanisms, and bulk vesicle transport.

What are the primary functions of the nucleus in an animal cell?

The nucleus is the storehouse for the cell's genetic information and the site for RNA synthesis.

What is the primary function of mitochondria in eukaryotic cells?

Mitochondria produce most of the ATP that serves as the energy currency of the cell.

What are the roles of the endoplasmic reticulum and Golgi apparatus?

The endoplasmic reticulum is involved in both protein and lipid synthesis. The Golgi apparatus modifies and sorts proteins and lipids as they move to their final destinations in or out of the cell.

What is the function of lysosomes in animal cells?

Lysosomes degrade macromolecules.

What is the cytoskeleton and what is its role in the cell?

The cytoskeleton is a network of protein filaments and other associated proteins that provide the cell with an internal structural framework.

What is the composition and function of the plant cell wall, and what do chloroplasts do?

The plant cell wall is a rigid barrier composed of polysaccharides. Chloroplasts enable plant cells to harness the energy of sunlight to synthesize sugars.

How do vacuoles contribute to the structural rigidity of plant cells?

Vacuoles are water-filled organelles that exert hydrostatic pressure (turgor pressure) against the cell walls, providing rigidity to the plant cell.

What cellular change causes a plant to wilt during dehydration?

Dehydration collapses the vacuoles, which relieves hydrostatic pressure against the cell wall and results in wilting.

How do prokaryotes and eukaryotes differ regarding the nucleus and internal organization?

Prokaryotes lack a nucleus (their DNA is organized in a nucleoid region) and contain no membrane-bound organelles (some contain plasmids). Eukaryotes have a membrane-bound nucleus and contain organelles.

Where do transcription and translation take place in prokaryotes versus eukaryotes?

In prokaryotes, both transcription and translation occur in the cytoplasm. In eukaryotes, transcription occurs in the nucleus and translation occurs in the cytoplasm.

What specific membrane lipid additions differentiate prokaryotic cell membranes from eukaryotic cell membranes?

Prokaryotic cell membranes contain hopanoids, whereas eukaryotic cell membranes contain sterols (cholesterol).

How do prokaryotes and eukaryotes compare in physical size and surface area-to-volume ratio?

Prokaryotes are small ($1\text{--}2\,\mu\text{m}$) with a high surface area-to-volume ratio, whereas eukaryotes are larger ($10\text{--}20\,\mu\text{m}$) with a low surface area-to-volume ratio.

How is the fluid mosaic model of membrane structure defined?

The fluid mosaic model consists of two components: lipids and proteins. The lipids form the matrix of the membrane, and the proteins carry out all the functions.

What are the hydrophilic and hydrophobic components of a phospholipid molecule?

The hydrophilic component consists of a polar group, a phosphate group, and glycerol. The hydrophobic component consists of two fatty acid chains.

Which three distinct lipid structures formed by phospholipids are shown in diagrams a, b, and c?

a. Micelle b. Bilayer c. Liposome

Why are the two halves of the plasma membrane bilayer not identical?

The outer surface contains glycolipids and carbohydrates (serving as cell labels and cell recognition), whereas the inner cytoplasmic surface contains proteins attached to the cytoskeleton.

How do the dissociation properties of peripheral membrane proteins differ from those of integral membrane proteins?

Peripheral membrane proteins are temporarily associated with the internal or external surface and can dissociate upon high or low pH or high temperature. Integral membrane proteins span the bilayer and can only dissociate through the action of detergents.

What are the functional classes of proteins present in the plasma membrane?

Channels (allow molecules/ions through), carriers (transfer molecules/ions across), receptors (allow attachment of specific molecules), enzymes (catalyze specific reactions), and anchors (attach to other proteins to maintain cell structure and shape, and aid in cell recognition).

Which types of molecules can freely diffuse directly across the phospholipid bilayer without the aid of membrane proteins?

Gases ($\text{O}_2$, $\text{CO}_2$), hydrophobic molecules (such as benzene), and small polar uncharged molecules ($\text{H}_2\text{O}$, ethanol).

Which molecules are unable to cross the lipid bilayer freely and require protein-mediated transport?

Large polar molecules (such as glucose) and charged molecules ($\text{Cl}^-$, $\text{Na}^+$, $\text{K}^+$).

What is diffusion, and what occurs when dynamic equilibrium is reached across a permeable membrane?

Diffusion is the net movement of solute from an area of higher solute concentration to an area of lower solute concentration. At equilibrium, there is no net movement of solute, but diffusion continues equally in both directions.

What is osmosis?

Osmosis is the diffusion of water across a semipermeable membrane that allows the passage of water but not solute.

Based on the diagram, what happens to red blood cells placed in hypertonic, isotonic, hypotonic, and very hypotonic solutions?

In a hypertonic solution the cell becomes shrunk; in an isotonic solution it remains normal; in a hypotonic solution it becomes swollen; and in a very hypotonic solution it becomes lysed.

How does facilitated diffusion differ from simple diffusion across the plasma membrane?

Simple diffusion occurs directly through the lipid bilayer, whereas facilitated diffusion transports solutes down their concentration gradient using transmembrane channel proteins or carrier proteins.

How does the sodium-potassium pump ($\text{Na}^+/\text{K}^+$ pump) illustrate primary active transport?

It expends ATP energy directly (hydrolyzing ATP to ADP) to move ions against their concentration gradients, pumping $\text{Na}^+$ out of the cell toward higher $\text{Na}^+$ and pumping $\text{K}^+$ into the cell toward higher $\text{K}^+$.

How does secondary active transport utilize the gradient created by primary active transport?

A primary active transport proton pump uses ATP to build an electrochemical proton gradient (higher outside the cell). An antiporter then uses the potential energy of this electrochemical gradient to drive a different molecule out of the cell against its concentration gradient.

What is exocytosis and how does it occur?

Exocytosis is the process of secreting macromolecules out of the cell by having intracellular vesicles formed by the Golgi apparatus fuse with the plasma membrane.

What are the three types of endocytosis shown in the diagram, and how do they function?

a. Phagocytosis: uptake of large particles or food into a vacuole via pseudopodia. b. Pinocytosis: nonspecific uptake of extracellular fluid or small solutes into a vesicle. c. Receptor-mediated endocytosis: specific uptake triggered by target molecules binding to receptors, forming a coated pit and coated vesicle.