Cell Theory and Microscopy

• The current understanding of the cell is linked to advancements in imaging technology.

Development of Cell Theory

• Six defining characteristics of living organisms: growth, reproduction, energy requirement, waste production, cellular composition, and environmental response/adaptation.
• Aristotle initiated observation, recording, reasoning, and interpreting as key scientific steps.
• Abiogenesis (spontaneous generation) is the now-disproven theory that life arises from non-living matter.
• Redi's experiment disproved spontaneous generation by demonstrating that maggots come from flies laying eggs, not from non-living matter.

History of the Microscope & Cell Discovery

• Hans & Zacharias Janssen created the compound microscope around 1595 using 2 lenses and 9x magnification.
• Robert Hooke, using a light microscope, was the first to observe and name "cells" in cork in 1665.
• Hooke's microscope had 30x magnification.
• Antony Van Leeuwenhoek was the first to describe single-celled organisms, using a more powerful microscope (270x magnification) in the 1700s.
• Leeuwenhoek observed bacteria, protists, blood cells, pond water organisms, and sperm.
• The importance of cells to life wasn't recognized until the 1830s.
• Schwann and Schleiden stated that all organisms are composed of one or more cells.
• Virchow stated that all cells are produced from other cells.
• Pasteur's experiment confirmed that microorganisms exist in the air.
• Biogenesis states that living organisms arise only from other living organisms.

Types of Cells

• Subcellular structures only exhibit some characteristics of life, not acting as functional units like viruses, and prions.
• Viruses are proteins containing DNA and cannot reproduce without a host cell.
• Prions are normal proteins transformed into harmful particles that affect other proteins.
• Understanding cells is vital advancements in health & technology.
• Cancer is a disease involving uncontrolled division of abnormal cells.
• Understanding the genetic code enables gene mapping to identify and record gene locations, aiding in understanding genetic disorders.
• Cell cultures involve isolated cells in a nutrient-rich environment for research and tissue growth.
• Stem cells can differentiate into any cell type in the body and have potential for disease cures.
• Embryonic stem cells (from IVF, day 5 blastocysts) have the potential to become any cell type.
• Adult stem cells are more limited and "already programmed" to become specific cell types.

Microscopes

• Compound microscopes use multiple lenses and light to magnify objects, typically offering magnification from 4x to 2000x.
• Always hold the microscope with both hands.
• Secure the slide using stage clips.
• Begin with the lowest power objective lens.
• Adjust the iris and light source for optimal illumination.
• Use the coarse adjustment knob to initially focus, then fine adjustment knob for clarity.
• Rotate the nose piece to change objectives.
• Store the microscope with the objective lens at its lowest power.

Calculations with a Compound Microscope

• The ocular lens (eyepiece) typically magnifies 10x.
• Objective lenses (4x, 10x, 40x) bring the image into focus.
• Total Magnification = Objective Lens X Ocular Lens
• 1 mm = 1000 μm
• Field of View (FOV) is the visible area through a microscope.
• As total magnification increases, FOV decreases.
• FOV diameter cannot be accurately measured at medium or high power.
• Formula for FOV: M1D1 = M2D2
  • M1 = magnification at lowest power
  • M2 = magnification at medium/highest power
  • D1 = diameter at lowest power
  • D2 = diameter at medium/highest power
• Object Size = 1/𝑥 x ____mm (FOV) = ____mm

Scientific Drawings

• Title at the top (include magnification)
• Use pencil, avoid colour, shade only if necessary
• Label the parts/structures of the object
• Use a ruler to draw lines to connect the labels to the structures

Contrast & Staining

• Contrast is the ability to distinguish structures based on differences in light absorption.
• Staining can improve contrast, but usually on fixed (non-living) specimens.
• Resolution is the ability to distinguish closely spaced structures as distinct entities.
• Resolving Power of:
  • Unaided Eye = 0.1mm apart
  • CLM = 0.2 mm apart

Other Microscopes

• Electron microscopes use electron beams for detailed imaging.
• Electron-dense materials block electron passage.
• TEM (Transmission Electron Microscope) creates 2D images inside non-living specimens at magnifications up to 1,500,000x.
• SEM (Scanning Electron Microscope) creates 3D images of specimens (possibly alive) at magnifications up to 300,000x.
• Advantages of Light Microscope: Affordable, Easy to Use, Live Specimen, Portable, Colour
• Disadvantages: Limited resolving power & FOV, staining
• Uses for Electron Microscope: Higher mag, better res, (TEM) see inside specimen, 3-D image
• Mag = Zoom (how large spec. appears)
• Res = Distinguish between structures

Organelles

• Cells perform specialized tasks and have basic shared structures and functions.
• Organelles are specialized parts of a cell that carry out particular functions: growth, reproduction, waste removal, nutrient intake, and response to stimuli.

Cell Structures & Their Functions

• Cell Membrane: A protective barrier that allows transport of materials in and out of the cell, involved in cell-to-cell communication.
• Nucleus: Contains DNA (genetic material) and directs cellular activities.
• Lysosome: Contains enzymes that digest cell food/unwanted material into smaller components.
• Smooth Endoplasmic Reticulum (Smooth ER): Produces fats and oils (lipids) and transports them to other parts of the cell.
• Rough Endoplasmic Reticulum (Rough ER): Contains ribosomes and produces proteins, packages and transports them to other parts of the cell.
• Ribosome: Site where messenger RNA is read and assembly of proteins occurs.
• Mitochondria: Converts sugar into chemical energy through cellular respiration.
• Cell Wall: Rigid and supportive, giving plant cells their shape.
• Chloroplast: Converts sunlight and CO2 into glucose through photosynthesis.
• Cytoplasm: Jelly-like substance that fills the cell and suspends organelles and nutrients within.
• Golgi Apparatus: Receives, processes, sorts, and repackages materials from the ER into vesicles for transport.
• Vesicles: Stores and transports materials in and out of the cell.
• Vacuole: Sacs of cytoplasm used to control the amount of water in the cell.

Action vs. Organelle

• Intake of Nutrients: cell membrane/mitochondria
• Exchange of Gases: cell membrane/mitochondria/chloroplast
• Removal of Wastes: cell membrane/lysosome
• ER = attached to nucleus
• Instructions on making proteins come from DNA molecules, the DNA is a messenger → info is read & used in the ER to make proteins.
• Structure vs Function (Plant v Animal Cells)
• Plants have a rigid wall that animal cells don’t have
• Plants grow towards the sun (for photosynthesis)
• Animals = mobile (cell structure allows for more movement - less rigid) → Fluid

Cell Membrane

• The cell membrane surrounds all cells and organelles (except ribosomes).
• Composed of phospholipids, proteins, and carbohydrates
• Separates the intracellular fluid from the extracellular fluid
• It's an open system that freely exchanges materials and energy.
• It functions as a selective barrier, preventing unwanted materials from entering and allowing needed ones in.
• Known as the Fluid Mosaic Model and has proteins/carbohydrates embedded within.

Cell Membrane Function

• Biological Barrier - keeps foreign & unwanted particles out
• Selective Filter → Semi-permeable Membrane
• Transport of gases, nutrients, and wastes (constantly in flux)
• Ions
• Molecules

Phospholipids

• Membrane is composed of a Double Layer of phospholipids known as the Phospholipid Bilayer

• Composed of a head end & a tail end

• Each end reacts differently to water (Polarity)

• Head End: hydro-PHILIC (Water Loving)

  • composed of phosphate
  • Polar → (-) charge = (+) and (-) attracted

• Tail End: hydro-PHOBIC (Water fearing)

  • Composed of fat - fatty acids
  • Do not dissolve easily in water
  • Water molecules push away tail end

• Membranes are in constant motion (flux) - hence the name Fluid Mosaic Model.

Proteins

• Proteins embedded in the membrane carry out functions.
• Communication
• Chemical Reactions
• Protect cell from infection
• Move substances across membranes
• Markers to help with cell-to-cell recognition
• Attachment sites for messenger molecules (hormones)

Carbohydrates

• Carbohydrates are attached to lipids and proteins.
• Cell-to-cell communication
• Covid-19 is a virus that mimics a carbohydrate protein molecule (glycoprotein) and sneaks into the cell once inside, it replicates, forcing the cell to perform functions other than its intended ones.

Passive Transport

• Selective Transport (Selectively Permeable Membrane)
• Allows certain particles to pass through but excludes others

Particle Model Of Matter

• All matter is made up of tiny particles and in liquid or air these particles are in constant random motion known as Brownian Motion

Concentration Gradient

• The difference in concentration between two areas
• Molecules move down their concentration gradient from
• High Concentration to Low Concentration

Equilibrium

• Occurs when molecules are equally distributed
• No longer a difference in concentration
• Passive Transport is the transport of molecules across a membrane without energy input.

Three Types of Passive Transport

• Diffusion
• Osmosis
• Facilitated Diffusion

Diffusion

• Diffusion is the natural movement of particles from an area of high concentration to a low concentration.
• It's typical for small, uncharged molecules like oxygen and carbon dioxide.

Osmosis

• Osmosis is the diffusion of water across a cell membrane.
• Water molecules move along a concentration gradient from an area of high water concentration to an area of low water concentration
• More often talked about water movement as:
• Water moves from areas of low particle concentration to areas of high water concentration.

Solute/Solvent

• Solute: what is being dissolved in solution
• Solvent: what is doing the dissolving (usually more of it)
• Ex. Iced Tea:
• Solute: Sugar Crystals
• Solvent: Water

Hypotonic Solution

• A solution that loses water due to the movement of water from an area of high solute concentration to an area of low solute concentration
• A cell in a hypotonic solution will GAIN water because a hypotonic solution has less dissolved particles than the solution inside the cell

Hypertonic Solution

• A solution that gains water due to the movement of water from an are of low solute concentration to an area of high solute concentration
• A cell in a hypertonic solution will LOSE water because a hypertonic solution has more dissolved particles than the solution inside the cell

Isotonic Solution

• A solution that has an equal number of particles as the solution it is compared to so there is no net movement of water
• Water moving into the cell equals water moving out of the cell

Facilitated diffusion (Passive transport)

• Diffusion of molecules across a membrane through a transport protein
• Substances that are not soluble in liquids
• Does not use energy - always goes down concentration gradient
• Proteins are selective and recognize atoms/molecules by shape, size, or charge

Transport Proteins

• Membrane proteins that help move materials across the cell membrane
• Two types:
• Carrier proteins
• Channel Proteins

Carrier Proteins

• Protein molecule changes shape - molecule attaches to it and is released to other side
• Usually for macromolecules

Channel Proteins

• Tunnels in proteins that allows charged ions in and out of the cell
• Usually for ions

Key Facts for All Diffusion

• Particles move down their concentration gradient
• High concentration to Low concentration - NO ENERGY REQUIRED
• Diffusion help cells to survive by:
• Movement of needed particles into cell (H2O, O2, ions)
• Movement of prepare particles out (waste, CO2, hormones)
• In a solid substance, particles may vibrate but remain in a fixed position
• Particles in a liquid move faster than the particles in a solid
• When a liquid is cooled, its particles move more slowly
• Diffusion is the movement of particles from a region of high concentration to a region of low concentration
• Small polar molecules and ions: facilitated diffusion = channel proteins (tunnels move ions in/out)

Active Transport:

• Energy is required to transport materials across the cell membrane
• Energy input in the form of Adenosine Triphosphate (ATP)
• Molecules that are too big or have to move against their concentration gradient (low to high)
• Uses Channel and Carrier Proteins, these proteins act as more of a PUMP, pushing the particles across
• Proton Pump: Uses ATP to pump charged ions across cell membrane against its concentration gradient

Exocytosis & Endocytosis:

• Molecules that are too big to move across the cell membrane must be transported using vesicles
• Both Endo and Exocytosis require ATP

Endocytosis

• A vesicle (inside of cell) forms around the particle and the cell membrane pinches it off around it
• Phagocytosis: Cell EATING
• Pinocytosis: Cell DRINKING
• Receptor-mediated Endocytosis
• Receptors in cell membrane identify an item for transport, bind to trigger Endocytosis (ex. cholesterol)

Exocytosis

• The removal of substances by the cell (opposite of endocytosis)
• Waste, enzymes, hormones

Membrane Technology

• Kidney Dialysis
• Filtering of water using a membrane

Hemodialysis:

• artificial membrane in a external device connected to an ARTERY & VEIN

Peritoneal Dialysis:

• dialysis fluid is pumped into the PERITONEAL CAVITY (intestine lining) where rich supply of capillaries slowly filters blood
• Osmosis & reverse Osmosis Filtering of water using a membrane