cell varieties

Overview of Cells and Their Structures

Microscale Organization

• Units of measurement relevant to cell biology

  • Cells typically measured in micrometers (μm)

  • Microscopic structures range from 0.2 μm to 100 μm

  • Examples: E. coli is 1 μm; frog eggs around 1 mm; ostrich eggs approximately 28 cm

Progeria Disease

• Understanding Progeria

  • Definition: A genetic mutation leading to dysfunctional protein affecting cell nucleus shape

  • Symptoms: Early aging onset around two years of age, signs include balding and wrinkled skin

  • Lifespan: Average of 14 years

  • Prevalence: Rare, affecting around 400 children worldwide

The Cell Nucleus

• Key Features and Functions

  • Structure: An organelle found in all eukaryotic cells

  • Role: Differentiates eukaryotic from prokaryotic cells and stores genetic information (DNA)

  • Processes: Hosts transcription (RNA synthesis) and replication (DNA synthesis)

  • Shape: Affected in progeria; surrounded by a nuclear envelope with two membranes

  • Nuclear lamina: Structural support provided by lamin proteins; contains nuclear pores for molecular transport

Nucleolus

• Structure and Function

  • Definition: Dense spherical structure within the nucleus

  • Functions:

  • Ribosomal RNA synthesis

  • Ribogenesis—assembly of ribosomes

Genome Organization

• Inside the Nucleus

  • Composition: 46 DNA molecules in human cells

  • Organization: DNA combines with proteins to form chromatin fibers

  • Mitosis/Meiosis: Chromatin condenses into visible chromosomes

  • Interphase: Each chromosome occupies a specific territory inside the nucleus

Eukaryotic Cell Compartments

• Membrane-Enclosed Organelles

  • Definition: Organelles are membrane-enclosed compartments with specific functions, distinct from the nucleus

  • Types of Organelles:

  • Chloroplasts (plants/algae only)

  • Large central vacuoles (plants/algae)

  • Structure: Cytoplasm consists of cytosol (fluid) and organelles

  • Cytoskeleton: Network of proteins supporting cell structure

Endoplasmic Reticulum (ER)

• Classification: Rough ER and Smooth ER

  • Rough ER:

  • Role: Protein synthesis, chemical modifications, post-translational modifications, folding

  • Smooth ER:

  • Role: Glycogen degradation, lipid and steroid synthesis, calcium ion storage

  • Structure: Network of membranes and lumen

Golgi Apparatus

• Functions and Structure

  • Composition: Flattened membranous sacs called cisternae and vesicles

  • Functional Regions:

  • Cis face (receiving)

  • Medial face (processing/modifying)

  • Trans face (shipping)

  • Roles:

  • Modification and sorting of proteins from RER

  • Glycosylation and cutting precursor proteins

Endosomes

• Function

  • Structure: Membrane-bound vesicles

  • Role: Sorting internalized substances for degradation via lysosomes or recycling back to the plasma membrane

Lysosomes

• Functionality

  • Definition: Organelles with a more acidic interior (pH = 5)

  • Contents: Digestive enzymes for macromolecule breakdown (proteins, polysaccharides, nucleic acids, lipids) and old organelles

  • Role of autophagy: Recycling cellular components

The Endomembrane System

• Components

  • Includes: Nuclear envelope, ER, Golgi apparatus, endosomes, lysosomes, vesicles, and plasma membrane

  • Interaction: Vesicles transport substances between components, maintaining interconnectedness

Mitochondria

• Function

  • Definition: Sites of cellular respiration and energy transformation

  • Structure: Two membranes (outer and inner), inner membrane forms cristae

  • Spaces: Intermembrane space and mitochondrial matrix

Chloroplasts

• Photosynthesis

  • Structure: Surrounded by two membranes, containing thylakoid membranes

  • Functional Aspect: Light-dependent reactions occur in thylakoid membranes, with stroma interior

Peroxisomes

• Toxicity Management

  • Structure: Lipid bilayer surrounding compartments

  • Function: Degradation of toxic peroxides, like hydrogen peroxide (H2O2), utilizing catalase

  • Chemical reaction: $2H<em>2O</em>2 → 2H<em>2O + O</em>2$

Vacuoles

• Plant Cells

  • Role: Storage compartments; occupy 90% of plant cell volume

  • Functions:

  • Support through water pressure

  • Reproductive pigments

  • Digestion of stored proteins

  • Storage of toxic molecules and waste

Compartmentalization's Importance

• Functions and Benefits

  • Enhances: Chemical concentration leading to efficient reactions

  • Conditions: Provides favorable environments for processes (e.g., acidic Lysosomes)

  • Regulation: Separation of processes such as transcription and translation aids gene regulation

Prokaryotic Cells vs Eukaryotic Cells

• Key Differences

  • Prokaryotic cells: Lack a true nucleus, smaller in size compared to eukaryotic cells

  • Example Sizes: Prokaryotic cells (0.2–2 μm) vs Eukaryotic cells (10–100 μm)

  • Common Features: All prokaryotic cells have cell membrane, nucleoid, cytoplasm, and ribosomes

Specialized Features in Prokaryotic Cells

• Additional Structures

  • Cell Wall: Composed of peptidoglycan, providing structural support

  • Capsules: Polysaccharide layer offering protection and aiding in adhesion

  • Cytoskeleton: Composed of filamentous proteins homologous to those in eukaryotic cells, involved in cell division and morphology

Nutritional Requirements of Prokaryotic and Eukaryotic Cells

• Energy and Carbon Sources

  • Categories: Phototrophs, Chemotrophs, and Lithotrophs

  • Examples:

  • Photoautotrophs (Plants)

  • Chemoheterotrophs (Animals)

  • Lithotrophs (Inorganic compound users)

Learning Objectives

• Understand Cell Differences

  • Variability in cell structures, size limitations, nutritional differences

  • Compare prokaryotic and eukaryotic cells, including subtypes like archaea and bacteria

  • Importance of compartmentalization in eukaryotic cells, including depiction of organelles

  • Illustrate connections and communications between organelle interiors and exterior aspects of cells.