Download - Chapter 5 Cell Structure
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Chapter 5 Cell Structure
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Warning!!
Much of this chapter is covered in Biology I so the pacing will be rapid.
Focus on what is new to you while you review what is already familiar.
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“Faith is a fine invention when
gentlemen can see, but microscopes are
prudent in an emergency.”
Emily Dickinson
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Cell Biology or Cytology
Cyto = cell - ology = study of
Should use observations from several types of microscopes to make a total picture of how a cell is put together.
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Light Microscope - LM
Uses visible light to illuminate the object.
Relatively inexpensive type of microscope.
Can examine live or dead objects.
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Light Microscope
Occular Lens
Objective Lens
Stage with specimen
Light Source
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Resolution
Ability to detect two discrete points as separate from each other.
As Magnification increases, resolution decreases.
LM working limits are 100 - 1000X.
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Limitations - LM
Miss many cell structures that are beyond the magnification of the light microscope.
Need other ways to make the observations.
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Light Microscope Variations
Fluorescence: uses dyes to make parts of cells “glow”.
Phase-contrast: enhances contrasts in density.
Confocal: uses lasers and special optics to focus only narrow slides of cells.
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Electron Microscopes
Use beams of electrons instead of light.
Invented in 1939, but not used much until after WWII.
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TEM SEM
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Advantages
Much higher magnifications. Magnifications of 50,000X or
higher are possible. Can get down to atomic level
in some cases.
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Disadvantages
Need a Vacuum. Specimen must stop the
electrons. High cost of equipment. Specimen preparation.
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Transmission Electron Microscope - TEM
Sends electrons through thinly sliced and stained specimens.
Gives high magnification of interior views. Many cells structures are now visible.
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TEM Limitations
Specimen dead. Specimen preparation uses
extreme chemicals so artifacts are always a concern.
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Scanning Electron Microscope - SEM
Excellent views of surfaces. Produces 3-D views. Live specimens possible.
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Other Tools for Cytology
Cell Fractionation Chromatography Electrophoresis
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Cell Fractionation
Disrupt cells. Separate parts by
centrifugation at different speeds.
Result - pure samples of cell structures for study.
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Cell Fractionation
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Chromatography
Technique for separating mixtures of chemicals.
Separates chemicals by size or degree of attraction to the materials in the medium.
Ex - paper, gas, column, thin-layer
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Electrophoresis
Separates mixtures of chemicals by their movement in an electrical field.
Used for proteins and DNA.
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History of Cells
Robert Hooke - Observed cells in cork.
Coined the term "cells” in 1665.
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History of Cells 1833 - Robert Brown,
discovered the nucleus. 1838 - M.J. Schleiden,
all plants are made of cells. 1839 - T. Schwann,
all animals are made of cells. 1840 - J.E. Purkinje, coined
the term “protoplasm”.
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Cell Theory
All living matter is composed of one or more cells.
The cell is the structural and functional unit of life.
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R. Virchow
“Omnis cellula e cellula” All cells are from other cells.
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Types of Cells
Prokaryotic - lack a nucleus and other membrane bounded structures.
Eukaryotic - have a nucleus and other membrane bounded structures.
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Both Have:
Membrane Cytosol Ribosomes (but the size is
different)
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Prokaryotic Eukaryotic
Nucleus
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Prokaryotic
Eukaryotic
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Why Are Cells So Small?
Cell volume to surface area ratios favor small size.
Nucleus to cytoplasm consideration (control).
Metabolic requirements.
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Basic Cell Organization
Membrane Nucleus Cytoplasm Organelles
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Animal Cell
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Plant Cell
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Membrane
Separates the cell from the environment.
Boundary layer for regulating the movement of materials in/out of a cell.
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Cytoplasm or Cytosol
Cell substance between the cell membrane and the nucleus.
The “fluid” part of a cell. Exists in two forms: gel - thick sol - fluid
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Organelle
Term means "small organ” Formed body in a cell with a specialized function.
Important in organizational structure of cells.
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Organelles - function
Way to form compartments in cells to separate chemical reactions.
Keeps various enzymes separated in space.
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You must be able to:
Identify the major organelles Give their structure Give their function
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Nucleus
Most conspicuous organelle. usually spherical, but can be
lobed or irregular in shape.
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Structure
Nuclear membrane Nuclear pores Nucleolus Chromatin
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Nuclear Membrane
Double membrane separated by a 20-40 nm space.
Inner membrane supported by a protein matrix which gives the shape to the nucleus.
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Nuclear Pores
Regular “holes” through both membranes.
100 nm in diameter. Protein complex gives shape. Allows materials in/out of
nucleus.
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Nucleolus
Dark staining area in the nucleus.
0 - 4 per nucleus. Storage area for ribosomes.
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Chromatin
Chrom: colored - tin: threads DNA and Protein in a “loose”
format. Will form the cell’s chromosomes.
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Nucleus - Function
Control center for the cell. Contains the genetic
instructions.
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Ribosomes
Structure: 2 subunits made of protein and rRNA. No membrane.
Function: protein synthesis.
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Subunits
Large: 45 proteins 3 rRNA molecules
Small: 23 proteins 1 rRNA molecule
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Locations
Free in the cytoplasm - make proteins for use in cytosol.
Membrane bound - make proteins that are exported from the cell.
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Endomembrane System
Membranes that are related through direct physical continuity or by the transfer of membrane segments called vesicles.
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Endomembrane System
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Endoplasmic Reticulum
Often referred to as ER. Makes up to 1/2 of the total
membrane in cells. Often continuous with the
nuclear membrane.
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Structure of ER
Folded sheets or tubes of membranes.
Very “fluid” in structure with the membranes constantly changing size and shape.
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Types of ER
Smooth ER: no ribosomes. Used for lipid synthesis,
carbohydrate storage, detoxification of poisons.
Rough ER: with ribosomes. Makes secretory proteins.
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Golgi Apparatus or Dictyosomes
Structure: parallel array of flattened cisternae. (looks like a stack of Pita bread)
3 to 20 per cell. Likely an outgrowth of the ER
system.
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Function of Golgi Bodies
Processing - modification of ER products.
Distribution - packaging of ER products for transport.
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Golgi Vesicles
Small sacs of membranes that bud off the Golgi Body.
Transportation vehicle for the modified ER products.
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Lysosome
Single membrane. Made from the Golgi
apparatus.
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Function
Breakdown and degradation of cellular materials.
Contains enzymes for fats, proteins, polysaccharides, and nucleic acids.
Over 40 types known.
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Lysosomes
Important in cell death. Missing enzymes may cause
various genetic enzyme diseases.
Examples: Tay-Sachs, Pompe’s Disease
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Vacuoles
Structure - single membrane, usually larger than the Golgi vesicles.
Function - depends on the organism.
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Protists
Contractile vacuoles - pump out excess water.
Food vacuoles - store newly ingested food until the lysosomes can digest it.
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Plants
Large single vacuole when mature making up to 90% of the cell's volume.
Tonoplast - the name for the vacuole membrane.
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Function
Water regulation. Storage of ions. Storage of hydrophilic
pigments. (e.g. red and blues in flower petals).
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Function: Plant vacuole
Used to enlarge cells and create turgor pressure.
Enzymes (various types). Store toxins. Coloration.
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Microbodies
Structure: single membrane. Often have a granular or
crystalline core of enzymes.
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Function
Specialized enzymes for specific reactions.
Peroxisomes: use up hydrogen peroxide.
Glyoxysomes: lipid digestion.
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Enzymes in a crystal
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Mitochondria
Structure: 2 membranes. The inner membrane has more surface area than the outer membrane.
Matrix: inner space. Intermembrane space: area
between the membranes.
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Inner Membrane
Folded into cristae. Amount of folding depends
on the level of cell activity. Contains many enzymes. ATP generated here.
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Function
Cell Respiration - the release of energy from food.
Major location of ATP generation.
“Powerhouse” of the cell.
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Mitochondria
Have ribosomes (small size). Have their own DNA. Can reproduce themselves. May have been independent
cells at one time.
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Chloroplasts
Structure - two outer membranes.
Complex internal membrane. Fluid-like stroma is around
the internal membranes.
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Inner or Thylakoid Membranes
Arranged into flattened sacs called thylakoids.
Some regions stacked into layers called grana.
Contain the green pigment chlorophyll.
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Function
Photosynthesis - the use of light energy to make food.
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Chloroplasts
Contain ribosomes (small size). Contain DNA. Can reproduce themselves. Often contain starch. May have been independent
cells at one time.
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Plastids
Group of plant organelles. Structure - single membrane. Function - store various
materials.
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Examples
Amyloplasts/ Leucoplasts - store starch.
Chromoplasts - store hydrophobic plant pigments such as carotene.
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Ergastic Materials General term for other
substances produced or stored by plant cells.
Examples: Crystals Tannins Latex Resins
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Cytoskeleton
Network of rods and filaments in the cytoplasm.
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Functions
Cell structure and shape. Cell movement. Cell division - helps build cell
walls and move the chromosomes apart.
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Components
Microtubules Microfilaments Intermediate Filaments
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Microtubules
Structure - small hollow tubes made of repeating units of a protein dimer.
Size - 25 nm diameter with a 15 nm lumen. Can be 200 nm to 25 m in length.
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Tubulin
Protein in microtubules. Dimer - and tubulin.
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Microtubules
Regulate cell shape. Coordinate direction of
cellulose fibers in cell wall formation.
Tracks for motor molecules.
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Microtubules
Form cilia and flagella. Internal cellular movement. Make up centioles, basal
bodies and spindle fibers.
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Cilia and Flagella
Cilia - short, but numerous. Flagella - long, but few. Function - to move cells or to
sweep materials past a cell.
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Cilia and Flagella
Structure - 9+2 arrangement of microtubules, covered by the cell membrane.
Dynein - motor protein that connects the tubules.
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Dynein Protein
A contractile protein. Uses ATP. Creates a twisting motion
between the microtubules causing the structure to bend or move.
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Centrioles
Usually one pair per cell, located close to the nucleus.
Found in animal cells. 9 sets of triplet microtubules. Help in cell division.
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Basal Bodies
Same structure as a centriole. Anchor cilia and flagella.
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Basal Body
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Microfilaments
5 to 7 nm in diameter. Structure - two intertwined
strands of actin protein.
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Microfilaments are stained green.
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Functions
Muscle contraction. Cytoplasmic streaming. Pseudopodia. Cleavage furrow formation. Maintenance and changes in
cell shape.
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Intermediate Filaments
Fibrous proteins that are super coiled into thicker cables and filaments 8 - 12 nm in diameter.
Made from several different types of protein.
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Functions
Maintenance of cell shape. Hold organelles in place.
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Cytoskeleton
Very dynamic; changing in composition and shape frequently.
Cell is not just a "bag" of cytoplasm within a cell membrane.
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Cell Wall
Nonliving jacket that surrounds some cells.
Found in: Plants Prokaryotes Fungi Some Protists
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Plant Cell Walls
All plant cells have a Primary Cell Wall.
Some cells will develop a Secondary Cell Wall.
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Primary Wall
Thin and flexible. Cellulose fibers placed at
right angles to expansion. Placement of fibers guided by
microtubules.
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Secondary Wall
Thick and rigid. Added between the cell
membrane and the primary cell wall in laminated layers.
May cover only part of the cell; giving spirals.
Makes up "wood”.
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Middle Lamella
Thin layer rich in pectin found between adjacent plant cells.
Glues cells together.
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Cell Walls
May be made of other types of polysaccharides and/or silica.
Function as the cell's exoskeleton for support and protection.
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Extracellular Matrix - ECM
Fuzzy coat on animal cells. Helps glue cells together. Made of glycoproteins and
collagen. Evidence suggests ECM is
involved with cell behavior and cell communication.
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Intercellular Juctions
Plants-Plasmodesmata
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Plasmodesmata
Channels between cells through adjacent cell walls.
Allows communication between cells.
Also allows viruses to travel rapidly between cells.
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Intercellular Juctions
Animals: Tight junctions Desmosomes Gap junctions
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Tight Junctions
Very tight fusion of the membranes of adjacent cells.
Seals off areas between the cells.
Prevents movement of materials around cells.
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Desmosomes Bundles of filaments which
anchor junctions between cells.
Does not close off the area between adjacent cells.
Coordination of movement between groups of cells.
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Gap Junctions
Open channels between cells, similar to plasmodesmata.
Allows “communication” between cells.
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Summary
Answer: Why is Life cellular and what are the factors that affect cell size?
Be able to identify cellular parts, their structure, and their functions.