Unit 2: Cell Structure and Function

Prokaryotic vs Eukaryotic Cells (Nucleus, size, DNA, organelles, cell division, cell wall, examples)

Feature	Prokaryotic Cells	Eukaryotic Cells
Nucleus	No true nucleus, DNA is in the nucleoid region	Have a true nucleus with a nuclear membrane
Size	smaller	Larger
DNA	Circular, located in the nucleoid	Linear, contained in the nucleus
Organelles	Lack membrane-bound organelles	Contain membrane-bound organelles (e.g., mitochondria, ER, Golgi)
Cell Division	Binary fission	Mitosis or meiosis
Cell Wall	Present (made of peptidoglycan)	Only in plants/fungi (made of cellulose or chitin)
Examples	Bacteria	Plants, animals, fungi

Nucleus

stores DNA, and controls cell activities (growth, metabolism, and reproduction)

the manager

Mitochondria

powerfouse of the cell, produces ATP via cellular respiration

the power plant

ribosomes

synthesizes proteins

factory workers

Rough ER

synthesizes proteins

“rough because of ribosomes”

assembly line with workers

Smooth ER

synthesizes lipids, detoxifies drugs and poisons

no ribosomes

oil refinery / detox center

Golgi Apparatus

modifies, sorts, packages, and ships proteins and lipids for secretion or delivery to other organelles

post office

lysosomes

breaks down waste and foreign substances

Mostly in animal cells

garbage disposal

vacuoles

storage (water, food waste)

chloroplasts (plant cells)

carry out photosynthesis (solar → chemical energy)

solar panel

cell membrane (plasma membrane)

controls what enters and exists the cell, provides structural support

selectively permeable

security gate

centrosomes and centrioles (animal cells)

organizes microtubules during cell division

• The centrosome is like the whole "command center" for organizing the cell’s skeleton (the cytoskeleton).

• Centrioles are little cylinder-shaped structures inside the centrosome that are especially important for mitosis and meiosis.

cytoskeleton

provides structural support, intracellular transport

frame

peroxisomes

break down fatty acids and detoxifies harmful substances, including hydrogen peroxide

hazmat team

what structures are shared by prokaryotes and eukaryotes?

plasma membrane: controls what enters/leaves the cell

cytoplasm: where reactions happen

ribosomes: makes proteins

DNA: carries genetic info

Compare and contrast the organelles in prokaryotes, eurkaryotic plant cells, and eukaryotic animal cells

Organelle/Structure	Prokaryotes	Plant Cells	Animal Cells

Plasma Membrane

✅

✅

✅

Cytoplasm

✅

✅

✅

Ribosomes

✅ (smaller)

✅ (larger)

✅ (larger)

DNA

✅ (circular)

✅ (linear, in nucleus)

✅ (linear, in nucleus)

Cell Wall

✅ (peptidoglycan)

✅ (cellulose)

❌

Chloroplasts

❌

✅

❌

Mitochondria

❌

✅

✅

Large Central Vacuole

❌

✅

❌ (small vacuoles only)

Lysosomes

❌

Rare

✅

Centrioles

❌

❌ (usually)

✅

Flagella

✅ (simple)

Rare (only sperm of some plants)

Some (ex: sperm cells, complex)

Fluid mosaic model

Components:

Phospholipid Bilayer: Forms the basic structure

Integral proteins (span across the membrane) act as channels, transporters, or receptors.

Peripheral proteins (sit on the surface) are involved in signaling or maintaining cell shape.

Carbohydrates: Attached to proteins or lipids, these play a role in cell recognition and communication (e.g., glycoproteins or glycolipids).

Cholesterol: Scattered throughout the membrane, cholesterol helps maintain membrane fluidity and stability, especially in fluctuating temperatures.

Key functions of Plasma Membrane

Selective Permeability: lets some substances in (water and ocygen) but blocks others (like toxins or larger molecules)

Communication: The proteins and carbohydrates allow for cell signaling

Structural Support: the membrane helps give the cell shape

Analogy

Phoshplipid bilayer: the gate → controls what goes in and out

Proteins: the guards → helps decide whats allowed through, communicate to the outside world

Carbohydrates: the signs → help identify the cell and its purpose

Cholesterol: the stabalizers → help the maintain fluidity and integrity of the membrane, especially at varying temperatures.

Passive transport

doesnt require energy (ATP) to move substances acros the plasma membrane

List and explain the types of passive transport

1. Diffusion: the movement of molecules from an area of higher concentration to an area of lower concentration.

   • only small nonpollar molecules can diffuse easily through the phosphlipid bilayer

   • ex: O2, CO2

2. Osmosis: the diffusion of water molecules across semipermeable membrane from an area of lower solute concentration to an area of higher solute concentration

   • water naturally moves to balance solute concentrations on both sides of the membrane (dilute a more concentrated solution)

   • can occur through special channels called aquaporins

   • ex: if you place a cell in fresh water, water will move into the cell (because the vells internal concentration is high) and cause the cell to swell

3. Facilitated diffusion: movement of molecules from an area of a higher concentration to an area of lower concentration

   • some molecules are too large, polar, or charged to pass through the bilayer so they need assistance fromt ransport proteins

     • channel proteins: like a tunnel that allows specific molecules or ions to pass through. (Ex: aquaporins, ion channels)

     • carrier proteins

       • change shape once molecule binds to move specific molecules across the membrane. (ex: glucose transporter)

active transport

requires energy (ATP) to move substances across the membrane (usually against their concentration gradient)

List and expain the types of active transport

• Primary Active Transport: Directly uses ATP to transport molecules against their concentration gradient via pump proteins. (Ex: sodium-potassium pump)

• Secondary Active Transport: Does not directly use ATP; instead, utilizes the energy from the primary active transport process to move other substances against their concentration gradient.

  • Example: Sodium-glucose cotransporter: It uses the gradient of sodium ions (created by the sodium-potassium pump) to bring glucose into the cell.

• Bulk Transport: Involves the movement of large quantities of materials into (endocytosis) or out of (exocytosis) the cell, using vesicles.

  • phagocytosis: cell engulfs large solid particuls (cell eating)

  • pinocytosis: cell engulfs liquids (cell drinking).

Tonicity (isotonic, hypertonic, hypotonic)

the ability of a solution to affect the movement of water across a cell membrane.

1. Isotonic solution: same concentration of solutes inside and outside the cell, resulting in no net movement of water.

2. Hypertonic solution: higher concentration of solutes outside the cell, causing water to move out and the cell to shrink.

3. Hypotonic solution: lower concentration of solutes outside the cell, leading to water moving in and the cell swelling.

Surface Area to Volume Ratio

Formulas will be given!

SA: V → Surface Area / Volume (which describes how the size of an object affects its efficiency in exchanging materials with the environment.)

• As a cell grows larger, its volume increases at a faster rate than its surface area.

• Smaller cells have a higher SA:V ratio, meaning more surface area is available for exchange relative to the volume.

  • more effficient at exchanging materials

  • cells like bacteria are small → efficient nutrients asorbtion and waste removal

• Larger cells have a lower SA:V ratio, meaning there's less surface area available for exchange relative to the volume.

  • found in multicellular organisms

  • compensate for lower SA:V ratio with folding membranes to increase surface area and specialized structures

If a cell were to get too large, it might struggle to bring in enough nutrients or expel waste products quickly enough to survive, so they tend to stay small