Lecture 5 - Cell Structure
Page 1: Introduction
Cell Structure: Lecture 5, focussing on organisms and their environment.
Acknowledgment of Indigenous Lands: Recognizes the Mi’kmaq People and the responsibilities of being treaty people.
Page 2: Overview of Cells
Definition of Cells: Simplest functional unit of a living organism.
Cell Theory (mid-1800s):
All living organisms are composed of one or more cells.
Cells are the smallest unit of life.
New cells arise only from pre-existing cells through cell division.
Over 200 types of cells in the human body (example: epithelial cells).
Key components of a cell:
Nucleus (contains genetic material),
Mitochondria (energy production),
Cytoskeleton (structure & movement),
Plasma membrane (boundary of the cell).
Page 3: Cell Biology Essentials
Plasma Membrane: Acts as a barrier, provides attachment, and enables cell communication.
Nucleus: Houses genetic material (DNA).
Cytoplasm Components:
Cytosol (liquid part).
Organelles (e.g. mitochondria).
Cytoskeleton: Provides support and motility.
Page 4: Genetic Material
DNA (Deoxyribonucleic acid):
Stores genetic information (blueprints).
Self-replicating and hereditary (passed from parents).
Stable and long-lived.
RNA (Ribonucleic acid):
Converts genetic information into proteins.
Generally single-stranded and fragile.
Proteins (collectively known as proteome): Provide structure and function to the body.
Examples:
Contractile Proteins (muscles).
Cell Signaling Molecules (neurons).
Antibodies (immune cells).
Structural Proteins (bones).
Page 5: Keith Porter and Cell Structure
Keith Porter (1912-1997): Renowned for contributions to cell biology.
Achievements: BA in Biology & Chemistry from Acadia University in 1934; recognized for work with Transmission Electron Microscopy.
Discovered and described various parts of the cell, including the endoplasmic reticulum.
Page 6: Types of Cells
Prokaryotic Cells (examples: bacteria):
Lack internal compartmentalization and membrane-enclosed nucleus.
Smaller in size (1-10 µm).
Eukaryotic Cells:
Possess internal compartmentalization (membrane systems) including:
Nucleus (contains DNA).
Sarcoplasmic reticulum.
Mitochondria (energy).
Examples of Eukaryotic Cells: Plant cells, which have:
Nucleoid (DNA),
Cell membrane,
Cell wall.
Cytoplasm.
Ribosomes (synthesize polypeptides).
Animal cells lack a cell wall.
Page 7: (Duplicate Content: Same as Page 6)
Repeat of information regarding Prokaryotic and Eukaryotic cells.
Page 8: Viruses
SARS CoV-2 Spike Protein:
Contains membrane and genetic material (RNA).
Characteristics of Viruses:
Not classified as cells; lack cell membranes and organelles.
Can’t reproduce independently; must use a host cell.
Quote: "A virus is a piece of nucleic acid surrounded by bad news." - Peter Medawar.
Page 9: Eukaryotic Cell Structure
Components of Eukaryotic Cells:
Nucleus: Contains chromatin, nucleolus, and nuclear envelope.
Internal membranes help in compartmentalization and organelle formation, isolating functions.
Chromatin: DNA packaged around proteins (histones).
Nucleolus: Major site for ribosomal RNA assembly into ribosomes used for protein synthesis.
Page 10: Endoplasmic Reticulum (ER)
Structure: Network of membranes with two types:
Rough ER: Contains ribosomes for protein synthesis; packages proteins into vesicles.
Smooth ER: Lacks ribosomes; involved in detoxification, calcium storage, and various metabolic processes.
Page 11: Golgi Complex
Golgi Apparatus:
Layers of flat membrane sacs, zonally organized:
cis (closest to ER).
medial (middle layer).
trans (furthest from ER).
Functions in processing, modifying, sorting, and secreting molecules.
Creates secretory vesicles for transporting cargo out of the cell.
Page 12: Plasma Membrane
Fluid-Mosaic Model: Phospholipid bilayer that separates the cell from the external environment.
Proteins Embedded: Facilitate transport, communication, and adhesion.
Receptors, like the ACE2 receptor, are crucial for signaling.
Page 13: Angiotensin II
Signaling Molecule: Binds to Angiotensin II Type 1 Receptor, influencing blood pressure and inflammation.
Interaction with ACE2 can reduce these effects.
Cells modulate the number of these receptors based on signaling needs, which implicates pharmaceuticals (e.g., ACE inhibitors) in blood pressure treatment.
Page 14: Viral Interaction with Receptors
Structural similarities between SARS COVID spike proteins and Angiotensin II.
Spike proteins interact with ACE2, facilitating viral entry into the cell via fusion of viral and plasma membranes.
Examining ACE2 modulation as a treatment for COVID with mixed effectiveness.
Page 15: Mechanism of SARS CoV-2 Binding
Mechanism of viral entry:
Spike proteins bind to ACE-2 receptor.
Outer viral covering fuses with the host plasma membrane, allowing RNA entry into host cells.
Page 16: Life Cycle within Host Cell
SARS-CoV-2 lifecycle steps inside host's cell:
Entry through ACE2 receptors.
Use of host ribosomes for viral protein synthesis.
Host ER modifies viral proteins.
Golgi complex packages the proteins for release.
New viruses released from the host's membrane.
Page 17: Organelles
Definition of organelles: Subcellular structures with unique functions.
Examples:
Nucleus, Endoplasmic Reticulum, Golgi Complex, Mitochondria (energy provider, own genome), Chloroplasts (in plants, own genome, photosynthesis).
Endosymbiosis Theory: Chloroplasts and mitochondria originated from bacteria engulfed by eukaryotic cells.
Page 18: Unique Organisms
Elysia chlorotica: A sea slug with symbiotic chloroplasts (kleptoplasty).
Page 19: Cytosol
Role of cytosol in metabolic pathways:
Site for chemical breakdown and synthesis processes involving enzymes.
Contains ribosomes for protein synthesis, distinct from rough ER ribosomes.
Page 20: Cytoskeleton
Described as the cell’s highway, connecting organelles:
Microtubules: For structure and transport.
Intermediate Filaments: Provide shape and rigidity.
Actin Filaments: Dynamic structure, aiding in cellular movement with motor proteins (e.g., kinesin, myosin, dynein).
Page 21: Summary of Cell Components
Animal Cell Structures:
Nucleus: Organizes genetic material.
Nuclear Envelope: Double membrane surrounding nucleus.
Rough ER: Site of protein synthesis and sorting.
Nucleolus: Ribosome assembly site.
Ribosomes: Protein synthesis.
Smooth ER: Detoxification and lipid synthesis.
Mitochondrion: ATP production site.
Plasma Membrane: Regulates substance movement and cell signaling.
Cytoskeleton: Maintains shape and aids in movement.
Golgi Apparatus: Modification and secretion of proteins and lipids.