🧫 CHAPTER 4 STUDY NOTES: CELLS (PROKARYOTIC vs EUKARYOTIC)

1. 🔬 Prokaryotic vs Eukaryotic Cells (Overview)

Similarities

  • Both have:

    • DNA

    • Ribosomes

    • Plasma membrane

    • Similar chemical reactions (metabolism)

Differences

Feature

Prokaryotes

Eukaryotes

Nucleus

❌ No nucleus

✅ True nucleus

Organelles

❌ No membrane-bound organelles

✅ Many organelles

Size

Smaller

Larger

DNA

Circular, single chromosome

Linear chromosomes

Cell wall

Peptidoglycan (bacteria)

Cellulose/chitin/none

2. 🦠 Prokaryotic Cells (Bacteria)

Basic Features

  • Unicellular

  • Reproduce by binary fission

  • Classified by:

    • Shape

    • Metabolism

    • Nutrition

    • Biochemical activity

3. 📏 Size, Shape, Arrangement

Size

  • Very small (microscopic range; usually ~0.2–2 μm wide, 2–8 μm long)

Shapes

  • Coccus = spherical

  • Bacillus = rod-shaped

  • Spiral = twisted

Special forms

  • Pleomorphic = multiple shapes

  • Arrangements:

    • Staphylo- = clusters

    • Strepto- = chains

4. 🧬 External Structures

Glycocalyx

  • Sticky outer layer (capsule or slime layer)

  • Functions:

    • Prevents phagocytosis (immune evasion)

    • Helps attachment

    • Prevents drying out

Flagella / Archaella

  • Used for movement

  • Structure:

    • filament + hook + basal body

  • Movement: rotation like a motor

  • Types of movement:

    • Positive taxis = toward stimulus

    • Negative taxis = away

Axial Filaments (Spirochetes)

  • Internal flagella

  • Allow corkscrew motion

Fimbriae & Pili

  • Fimbriae → attachment

  • Pili → DNA transfer (conjugation) + twitching motility

5. 🧱 Cell Wall

Function

  • Protects cell

  • Prevents osmotic lysis

  • Gives shape

Peptidoglycan

  • Made of:

    • NAG + NAM sugars

    • amino acid cross-links

Gram-Positive Cell Wall

  • Thick peptidoglycan

  • Teichoic acids present

  • No outer membrane

Gram-Negative Cell Wall

  • Thin peptidoglycan

  • Outer membrane contains:

    • LPS (lipopolysaccharide)

  • Porins allow small molecules through

  • LPS = endotoxin (toxic to humans)

Gram Stain Mechanism

  • Gram+ → retains crystal violet → purple

  • Gram− → loses stain → pink/red

Atypical Cell Walls

  • Mycoplasma → no cell wall

  • Archaea → pseudopeptidoglycan

  • Acid-fast bacteria → mycolic acid (waxy layer)

Cell wall damage

  • Lysozyme destroys peptidoglycan

  • Protoplast = Gram+ cell without wall

  • Spheroplast = Gram− partially stripped wall

  • Penicillin blocks wall synthesis

6. 🧫 Plasma Membrane

Structure

  • Phospholipid bilayer (fluid mosaic model)

  • Proteins embedded

Function

  • Selectively permeable

  • Controls entry/exit of substances

  • Contains enzymes for metabolism

7. 🚪 Transport Across Membrane

Passive Transport (no energy)

  • Simple diffusion → high to low

  • Facilitated diffusion → uses protein channels

  • Osmosis → water movement

Active Transport (requires ATP)

  • Low → high concentration

  • Uses carrier proteins

Group Translocation

  • Molecule chemically changed during transport

8. 🧫 Cytoplasm

  • Gel-like fluid inside cell

  • Contains:

    • DNA

    • Ribosomes

    • enzymes

    • inclusions

  • No cytoplasmic streaming in prokaryotes

9. 🧬 Nucleoid & DNA

  • Nucleoid = DNA region (no nucleus)

  • Plasmids = extra circular DNA

10. 🧪 Ribosomes

  • Prokaryotes: 70S ribosomes

  • Function: protein synthesis

  • Antibiotic target

11. 📦 Inclusions

Storage structures:

  • Glycogen (energy)

  • Lipids

  • Sulfur granules

  • Gas vacuoles (buoyancy)

  • Magnetosomes (orientation)

12. 🧫 Endospores

  • Dormant survival structures

  • Formed during harsh conditions

  • Extremely resistant (heat, chemicals)

Why important:

  • Survival advantage

  • Can reactivate when conditions improve

13. 🧬 Eukaryotic Cells Overview

Key features

  • Nucleus

  • Organelles

  • Larger size

  • 80S ribosomes

14. 🧫 Eukaryotic Cell Structures

Cell wall (if present)

  • Plants/algae: cellulose

  • Fungi: chitin

  • Yeast: glucan + mannan

Plasma membrane

  • Phospholipid bilayer + sterols

  • Allows:

    • diffusion

    • active transport

    • endocytosis (phagocytosis, pinocytosis, receptor-mediated)

Cytoplasm

  • Includes cytoskeleton

  • Cytoplasmic streaming occurs

Ribosomes

  • 80S (larger than prokaryotes)

Organelles

Nucleus

  • Contains chromosomes

ER

  • Rough ER → proteins

  • Smooth ER → lipids

Golgi

  • Modifies, packages, secretes proteins

Lysosomes

  • Digestive enzymes

Vacuoles

  • Storage (especially plants)

Mitochondria

  • ATP production

  • Have DNA + 70S ribosomes

Chloroplasts

  • Photosynthesis

  • DNA + 70S ribosomes

Peroxisomes

  • Break down fatty acids

  • Catalase breaks down hydrogen peroxide

Centrosome

  • Organizes spindle fibers

  • Contains centrioles (9 triplet microtubules)

15. 🌱 Evolution of Eukaryotes

  • Endosymbiotic theory:

    • Mitochondria and chloroplasts were once free bacteria

16. ⚡ Key Functional Comparisons

Diffusion vs Facilitated diffusion

  • Both passive

  • Facilitated uses protein channels

Facilitated vs Active transport

  • Facilitated: high → low

  • Active: low → high (uses energy)

Active transport vs Group translocation

  • Active: moves molecule

  • Group: chemically modifies molecule

17. 🧠 IMPORTANT CONCEPTS FROM QUESTIONS

Gram-positive vs Gram-negative

  • Gram+: thick wall, no outer membrane

  • Gram−: outer membrane + endotoxin

Penicillin effect

  • Works best on Gram+ (blocks peptidoglycan)

  • Gram− protected by outer membrane

Osmosis situations

  • Hypotonic → water enters → cell may lyse

  • Hypertonic → water leaves → cell shrinks

Endospores

  • Advantage: survival in extreme conditions

  • Dormant until environment improves

Fimbriae

  • Function = attachment (NOT motility)

Toxins

  • Gram− outer membrane LPS = toxic to humans

18. 🧠 HIGH-YIELD STUDY SUMMARY

MUST KNOW:

  • Gram + vs Gram − structure + staining

  • Endospore function

  • Ribosome differences (70S vs 80S)

  • Membrane transport types

  • Organelles and functions

  • Endosymbiotic theory

  • Bacterial shapes + arrangements

1. 🔬 Prokaryotic vs Eukaryotic Cells (Overview)

Similarities

  • Both have:

    • DNA

    • Ribosomes

    • Plasma membrane

    • Similar chemical reactions (metabolism)

Differences

Feature

Prokaryotes

Eukaryotes

Nucleus

❌ No nucleus

✅ True nucleus

Organelles

❌ No membrane-bound organelles

✅ Many organelles

Size

Smaller

Larger

DNA

Circular, single chromosome

Linear chromosomes

Cell wall

Peptidoglycan (bacteria)

Cellulose/chitin/none

2. 🦠 Prokaryotic Cells (Bacteria)

Basic Features

  • Unicellular

  • Reproduce by binary fission

  • Classified by:

    • Shape

    • Metabolism

    • Nutrition

    • Biochemical activity

3. 📏 Size, Shape, Arrangement

Size

  • Very small (microscopic range; usually ~0.2–2 μm wide, 2–8 μm long)

Shapes

  • Coccus = spherical

  • Bacillus = rod-shaped

  • Spiral = twisted

Special forms

  • Pleomorphic = multiple shapes

  • Arrangements:

    • Staphylo- = clusters

    • Strepto- = chains

4. 🧬 External Structures

Glycocalyx

  • Sticky outer layer (capsule or slime layer)

  • Functions:

    • Prevents phagocytosis (immune evasion)

    • Helps attachment

    • Prevents drying out

Flagella / Archaella

  • Used for movement

  • Structure:

    • filament + hook + basal body

  • Movement: rotation like a motor

  • Types of movement:

    • Positive taxis = toward stimulus

    • Negative taxis = away

Axial Filaments (Spirochetes)

  • Internal flagella

  • Allow corkscrew motion

Fimbriae & Pili

  • Fimbriae → attachment

  • Pili → DNA transfer (conjugation) + twitching motility

5. 🧱 Cell Wall

Function

  • Protects cell

  • Prevents osmotic lysis

  • Gives shape

Peptidoglycan

  • Made of:

    • NAG + NAM sugars

    • amino acid cross-links

Gram-Positive Cell Wall

  • Thick peptidoglycan

  • Teichoic acids present

  • No outer membrane

Gram-Negative Cell Wall

  • Thin peptidoglycan

  • Outer membrane contains:

    • LPS (lipopolysaccharide)

  • Porins allow small molecules through

  • LPS = endotoxin (toxic to humans)

Gram Stain Mechanism

  • Gram+ → retains crystal violet → purple

  • Gram− → loses stain → pink/red

Atypical Cell Walls

  • Mycoplasma → no cell wall

  • Archaea → pseudopeptidoglycan

  • Acid-fast bacteria → mycolic acid (waxy layer)

Cell wall damage

  • Lysozyme destroys peptidoglycan

  • Protoplast = Gram+ cell without wall

  • Spheroplast = Gram− partially stripped wall

  • Penicillin blocks wall synthesis

6. 🧫 Plasma Membrane

Structure

  • Phospholipid bilayer (fluid mosaic model)

  • Proteins embedded

Function

  • Selectively permeable

  • Controls entry/exit of substances

  • Contains enzymes for metabolism

7. 🚪 Transport Across Membrane

Passive Transport (no energy)

  • Simple diffusion → high to low

  • Facilitated diffusion → uses protein channels

  • Osmosis → water movement

Active Transport (requires ATP)

  • Low → high concentration

  • Uses carrier proteins

Group Translocation

  • Molecule chemically changed during transport

8. 🧫 Cytoplasm

  • Gel-like fluid inside cell

  • Contains:

    • DNA

    • Ribosomes

    • enzymes

    • inclusions

  • No cytoplasmic streaming in prokaryotes

9. 🧬 Nucleoid & DNA

  • Nucleoid = DNA region (no nucleus)

  • Plasmids = extra circular DNA

10. 🧪 Ribosomes

  • Prokaryotes: 70S ribosomes

  • Function: protein synthesis

  • Antibiotic target

11. 📦 Inclusions

Storage structures:

  • Glycogen (energy)

  • Lipids

  • Sulfur granules

  • Gas vacuoles (buoyancy)

  • Magnetosomes (orientation)

12. 🧫 Endospores

  • Dormant survival structures

  • Formed during harsh conditions

  • Extremely resistant (heat, chemicals)

Why important:

  • Survival advantage

  • Can reactivate when conditions improve

13. 🧬 Eukaryotic Cells Overview

Key features

  • Nucleus

  • Organelles

  • Larger size

  • 80S ribosomes

14. 🧫 Eukaryotic Cell Structures

Cell wall (if present)

  • Plants/algae: cellulose

  • Fungi: chitin

  • Yeast: glucan + mannan

Plasma membrane

  • Phospholipid bilayer + sterols

  • Allows:

    • diffusion

    • active transport

    • endocytosis (phagocytosis, pinocytosis, receptor-mediated)

Cytoplasm

  • Includes cytoskeleton

  • Cytoplasmic streaming occurs

Ribosomes

  • 80S (larger than prokaryotes)

Organelles

Nucleus

  • Contains chromosomes

ER

  • Rough ER → proteins

  • Smooth ER → lipids

Golgi

  • Modifies, packages, secretes proteins

Lysosomes

  • Digestive enzymes

Vacuoles

  • Storage (especially plants)

Mitochondria

  • ATP production

  • Have DNA + 70S ribosomes

Chloroplasts

  • Photosynthesis

  • DNA + 70S ribosomes

Peroxisomes

  • Break down fatty acids

  • Catalase breaks down hydrogen peroxide

Centrosome

  • Organizes spindle fibers

  • Contains centrioles (9 triplet microtubules)

15. 🌱 Evolution of Eukaryotes

  • Endosymbiotic theory:

    • Mitochondria and chloroplasts were once free bacteria

16. ⚡ Key Functional Comparisons

Diffusion vs Facilitated diffusion

  • Both passive

  • Facilitated uses protein channels

Facilitated vs Active transport

  • Facilitated: high → low

  • Active: low → high (uses energy)

Active transport vs Group translocation

  • Active: moves molecule

  • Group: chemically modifies molecule

17. 🧠 IMPORTANT CONCEPTS FROM QUESTIONS

Gram-positive vs Gram-negative

  • Gram+: thick wall, no outer membrane

  • Gram−: outer membrane + endotoxin

Penicillin effect

  • Works best on Gram+ (blocks peptidoglycan)

  • Gram− protected by outer membrane

Osmosis situations

  • Hypotonic → water enters → cell may lyse

  • Hypertonic → water leaves → cell shrinks

Endospores

  • Advantage: survival in extreme conditions

  • Dormant until environment improves

Fimbriae

  • Function = attachment (NOT motility)

Toxins

  • Gram− outer membrane LPS = toxic to humans