Chapter 4
Cells and Cell Theory
Page 1
Historical Observations
Robert Hooke (1665): First to observe cells using a microscope.
Mathias Schleiden (1838) and Theodor Schwann (1839): Proposed the Cell Theory.
Cell Theory Principles
Organisms are composed of one or more cells where heredity and metabolism occur.
Cells are the smallest living things and the basic unit of an organism.
Cells arise only from the division of previous cells.
Cell Size and Structure
Page 2
Cell Size Limitations
Cell size: 1 unit= radius surface area=12.57
Most cells are small and round due to diffusion reliance.
Factors Affecting Diffusion Rate
Surface area
Temperature
Concentration gradient
Distance
Nonpolar materials can pass freely inside the cell
Cells are semi permeable
Page 3
Surface Area-to-Volume Ratio
Small round cells have advantages over larger cells.
As cell size increases, volume increases faster than surface area, slowing diffusion.
Some large cells adapt by having multiple nuclei (e.g., muscle cells) or elongated shapes (e.g., neurons).
Microscopy
Page 4
Visibility of Cells
Most cells are less than 50 μm in diameter; not visible to the naked eye.
Resolution
It’s the minimal distance of two points apart that can be two separate points
Minimum distance for the naked eye to distinguish two points is 100 μm.
Page 5
Types of Microscopes
Light Microscopes
Use visible light and two magnifying lenses.
Resolve structures 200 nm apart.
Limited resolution
Electron Microscopes
Use electron beams.
Resolve structures 0.2 nm apart.
Types include Transmission and Scanning Electron Microscopes.
Cellular Components
Page 6
Size Scale of Cellular Components
Most cells are microscopic; cell membranes are 5 nm thick.
Light microscopes resolve structures 200 nm apart; electron microscopes resolve 0.2 nm.
Page 7
Basic Structural Similarities in All Cells
Nucleoid or nucleus (where DNA is located).
Cytoplasm (semifluid matrix of organelles and cytosol).
Ribosomes (synthesize proteins).
Plasma membrane (phospholipid bilayer with proteins).
Prokaryotic Cells
Page 8
Characteristics of Prokaryotic Cells
Simplest organisms with a wall and membrane covering the cytoplasm.
Two domains: Archaea and Bacteria.
Archaea has sugar and proteins
Bacteria is made with peptidoglycan susceptible to antibiotics
Lack a membrane-bound nucleus, DNA in nucleoid.
has ribosomes
Page 9
Organelles in Prokaryotes
Some contain organelles like magnetosomes for navigation found in magnetotactic bacteria
May have infoldings of the plasma membrane for reaction aggregation.
Page 10
Bacterial Microcompartments (BMCs)
Cellular compartments bounded by a semipermeable protein shell.
Functions include isolating metabolic processes and storage.
Page 11
Cytoskeletons in Prokaryotes
Possess molecules related to actin and tubulin influencing cell shape.
Cell wall determines strength and shape.
Page 12
General Prokaryotic Cell Structure
Nucleoid visible as a dense region.
Some have pili and flagella for movement, rotating it using the power of a proton gradient.
Bacteria cell walls
Composed of peptidoglycan, different glom plants
Maintain shape and prevent excessive uptake or loss of water
Archaea cells
Lack peptidoglycan
Thermally protected by hydrocarbons attaching to glycerol at both ends
Eukaryotic Cells
Page 16
Animal vs. Plant Cells
Animal Cells
Have plasma membrane, cytoskeleton, and most organelles.
No cell wall, chloroplasts, or large vacuoles.
Plant Cells
Have plasma membrane, cell wall, chloroplasts, and large vacuoles.
Thylakoids is the sit for light driven atp
Glyoxysome is fat to sugar conversion though glyoxylate cycle
Page 19
Nucleus Structure
Repository of genetic information.
Contains nucleolus for ribosomal RNA synthesis.
Surrounded by a nuclear envelope with pores for material movement.
Page 22
Endomembrane System
Largest internal membrane
Comprises the endoplasmic reticulum (ER) and Golgi apparatus.
Rough ER synthesizes proteins
SER (Smooth ER)
no bound ribosomes
most membrane lipids are formed here
Ca2+ is stored here
performs modification of substances
Page 24
Golgi Apparatus
Stacks of membranes for sorting and distributing proteins and lipids.
Cis face (front) and trans face (back) membranes have different compositions
protiens are made in the SER/RER in cis and converted to glycoprotiens/lipids by carb additions and rhen pinched off trans face
Page 25
Lysosomes
Organelles containing hydrolytic enzymes for degrading cellular debris.
activated by fusing with phagcytosis or a worn our organelle
this activated the lysosomal membrane
low pH activates the hydroltyic enzymes
Page 26
Peroxisomes
Contain enzymes for fatty acid oxidation and detoxification.
Page 27
Vacuoles
Membrane-bound structures for storage and maintaining osmotic pressure.
Cellular Processes
Page 30
Mitochondria
Semiautonomous organelles involved in sugar metabolism and ATP production.
Page 31
Chloroplasts
Organelles in plants for photosynthesis, containing thylakoids with chlorophyll.
Page 32
Endosymbiosis Theory
Proposes that eukaryotic organelles evolved from symbiotic prokaryotes.
Cytoskeleton and Cell Movement
Page 33
Cytoskeleton
Network of protein fibers (actin, microtubules, intermediate filaments) for support and movement.
Page 34
Centrioles
Organelles involved in microtubule organization during cell division.
Cell Interactions
Page 44
Cell-to-Cell Interactions
Surface proteins allow cells to identify and communicate with each other.
Page 45
Types of Cell Connections
Adhesive junctions: Mechanically attach cells.
Tight junctions: Prevent leakage between cells.
Communicating junctions: Allow signal passage between cells.
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