day #1: microscopy and cell structure
TRANSCRIPT
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PowerPoint Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Microscopy and Cell Structure
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Life in Its Diverse Forms– Diversity is the hallmark of life.
• The diversity of known life includes 1.8 million species.
• Estimates of the total diversity range from 10 million to over 200 million species.
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Grouping Species: The Basic Concept– Biodiversity can be
both beautiful and overwhelming.
– Taxonomy is the branch of biology that names and classifies species.
• It formalizes the hierarchical ordering of organisms.
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Taxonomy
• Classifying lifeSpecies Genus Family Order Class Phylum Kingdom Domain
Mammalia
Ursusameri-canus(Americanblack bear)
Ursus
Ursidae
Carnivora
Chordata
Animalia
Eukarya
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The Three Domains of Life
• At the highest level, life is classified into three domains
– Bacteria
– Archaea
– Eukarya
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• Domain Bacteria and domain Archaea
– Consist of prokaryotes
• Domain Eukarya, the eukaryotes
– Includes the various protist kingdoms and the kingdoms Plantae, Fungi, and Animalia
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• Life’s three domains
100 µm
0.5 µm
4 µmBacteria are the most diverse and widespread prokaryotes and are now divided among multiple kingdoms. Each of the rod-shapedstructures in this photo is a bacterial cell.
Protists (multiple kingdoms)are unicellular eukaryotes and their relatively simple multicellular relatives.Pictured here is an assortment of protists inhabiting pond water. Scientists are currently debating how to split the protistsinto several kingdoms that better represent evolution and diversity.
Kingdom Plantae consists of multicellula eukaryotes that carry out photosynthesis, the conversion of light energy to food.
Many of the prokaryotes known as archaea live in Earth‘s extreme environments, such as salty lakes and boiling hot springs. Domain Archaea includes multiple kingdoms. The photoshows a colony composed of many cells.
Kindom Fungi is defined in part by thenutritional mode of its members, suchas this mushroom, which absorb nutrientsafter decomposing organic material.
Kindom Animalia consists of multicellular eukaryotes thatingest other organisms.
DOMAIN ARCHAEA
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Comparison of Bacteria, Archaea, and Eucarya
Three domains of living organisms
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How does classification differ from identification?
Classification is the taxonomy, identification is the process of characterizing an isolate to determine which taxon it belongs to
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How are prokaryotes identified?
Microscopic examinationCulture characteristics or phenotypeBiochemical testsNucleic acid analysissymptoms
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Parts of the Microscope
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In microscopy, we often speak of resolution
• What is meant by resolution?
The minimum distance between two objects that can still be observed as separate entities
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Lenses and Magnification• The total magnification is the product of all
lenses used
• The eyepiece magnifies 10x
• The scanning objective is 4x
• What is the total magnification when viewing a specimen with the scanning objective?
• The 10x or 20x objectives are called low power lenses
• The 40x objective is the high power lens
• The 100x objective is the oil immersion lens
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Why is oil needed for the high power objective?Light rays are
refracted as they pass through air
Oil and glass have the same refractive index, so the light rays are not bent
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Exercise 1: Use of the Microscope
Review the parts of the compound microscope
Observe a slide of human blood and identify the different cell types
At what magnification are you viewing the cells?
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The Microscopic World of Cells
Organisms are either: Single-celled, such as most bacteria and protists Multicelled, such as plants, animals, and most fungi
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Cells were first discovered in 1665 by Robert Hooke.
The accumulation of scientific evidence led to the cell theory.
All living things are composed of cells. All cells are formed from previously existing cells.
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The Importance of Cells
All organisms are made of cellsThe cell is the simplest collection of matter
that can live
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The Two Major Categories of Cells
• The countless cells on earth fall into two categories:
– Prokaryotic cells
– Eukaryotic cells
• Prokaryotic and eukaryotic cells differ in several respects.
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Comparing Prokaryotic and Eukaryotic Cells
All cells have several basic features in common
• They are bounded by a plasma membrane
• They contain a semifluid substance called the cytosol
• They contain chromosomes
• They all have ribosomes
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Prokaryotic cells
Do not contain a nucleus
Have their DNA located in a region called the nucleoid
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Figure 4.4
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• Prokaryotic cells
– Are smaller than eukaryotic cells.
– Lack internal structures surrounded by membranes.
– Lack a nucleus.
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Eukaryotic cells
Contain a true nucleus, bounded by a membranous nuclear envelope
Are generally quite a bit bigger than prokaryotic cells
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A Panoramic View of Eukaryotic Cells
• An idealized animal cell
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• An idealized plant cell
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Exercise #2: Analysis of cells
Prepare and analyze a prokaryotic cell under the microscope
Prepare and analyze a eukaryotic animal cell
Prepare and analyze a eukaryotic plant cell
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Prokaryotic cells in yogurt
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Cytoplasmic Streaming in Elodea
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Membrane Structure
• The plasma membrane separates the living cell from its nonliving surroundings.
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The plasma membrane
Functions as a selective barrier
Allows sufficient passage of nutrients and waste
Carbohydrate side chain
Figure 6.8 A, B
Outside of cell
Inside of cell
Hydrophilicregion
Hydrophobicregion
Hydrophilicregion
(b) Structure of the plasma membrane
Phospholipid ProteinsTEM of a plasmamembrane. Theplasma membrane,here in a red bloodcell, appears as apair of dark bandsseparated by alight band.
(a)
0.1 µm
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The Plasma Membrane:A Fluid Mosaic of Lipids and Proteins
• The membranes of cells are composed mostly of:
– Lipids
– Proteins
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• The lipids belong to a special category called phospholipids.
• Phospholipids form a two-layered membrane, the phospholipid bilayer.
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The plasma membrane
Functions as a selective barrier
Allows sufficient passage of nutrients and waste
Carbohydrate side chain
Figure 6.8 A, B
Outside of cell
Inside of cell
Hydrophilicregion
Hydrophobicregion
Hydrophilicregion
(b) Structure of the plasma membrane
Phospholipid ProteinsTEM of a plasmamembrane. Theplasma membrane,here in a red bloodcell, appears as apair of dark bandsseparated by alight band.
(a)
0.1 µm
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Fats
Fats
• Are constructed from two types of smaller molecules, a single glycerol and usually three fatty acids
(b) Fat molecule (triacylglycerol)
H HH H
HHH H H
H H HH
HH
HOH O HC
C
C
H
H OH
OH
H
HH
HH
H H HH
H HH
H HH
H
HCCCCC
CCCCC
CC
CCC C
Glycerol
Fatty acid(palmitic acid)
HH
H
H
H H HH
HH
HH
HH
H HH
HH H
HHHHHHHHHHHHHHHH
H
HH H H H H H H H H H H H H H
H
HHHHHHHHHHHHHH
H H H H H H H H H H H H H H HH
HHHHHHHHHHHHHHH
HO
OO
O
OC
C
C C C C C C C C C C C C C C C C C
C
CCCCCCCCCCCCCCCC
C C C C C C C C C C C C C C CO
O
(a) Dehydration reaction in the synthesis of a fatEster linkage
Figure 5.11
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Fatty acids
• Vary in the length and number and locations of double bonds they contain
Fats
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Saturated fatty acids
Have the maximum number of hydrogen atoms possible
Have no double bonds
(a) Saturated fat and fatty acid
Stearic acid
Figure 5.12
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Have one or more double bonds
(b) Unsaturated fat and fatty acidcis double bondcauses bending
Oleic acid
Figure 5.12
Unsaturated fatty acids
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Phospholipids
Phospholipids
• Have only two fatty acids
• Have a phosphate group instead of a third fatty acid
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Phospholipid structure
Consists of a hydrophilic “head” and hydrophobic “tails”
CH2
OPO OOCH2CHCH2
OO
C O C O
Phosphate
Glycerol
(a) Structural formula (b) Space-filling model
Fatty acids
(c) Phospholipid symbol
Hyd
roph
obic
tails
Hydrophilichead
Hydrophobictails
–
Hyd
roph
ilic
hea d CH2 Choline
+
Figure 5.13
N(CH3)3
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The structure of phospholipids
Results in a bilayer arrangement found in cell membranes
Hydrophilichead
WATER
WATER
Hydrophobictail
Figure 5.14
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SteroidsSteroids
• Are lipids characterized by a carbon skeleton consisting of four fused rings
One steroid, cholesterol
• Is found in cell membranes
• Is a precursor for some hormones
HO
CH3
CH3
H3C CH3
CH3
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Figure 4.7a
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• Most membranes have specific proteins embedded in the phospholipid bilayer.
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• Membrane phospholipids and proteins can drift about in the plane of the membrane.
• This behavior leads to the description of a membrane as a fluid mosaic:
– Molecules can move freely within the membrane.
– A diversity of proteins exists within the membrane.
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Cell Surfaces
• Most cells secrete materials for coats of one kind or another
– That are external to the plasma membrane.
• These extracellular coats help protect and support cells
– And facilitate interactions between cellular neighbors in tissues.
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• Plant cells have cell walls,
– Which help protect the cells, maintain their shape, and keep the cells from absorbing too much water.
• Animal cells have an extracellular matrix,
– Which helps hold cells together in tissues and protects and supports them.
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Collagen
Fibronectin
Plasmamembrane
EXTRACELLULAR FLUID
Micro-filaments
CYTOPLASM
Integrins
Polysaccharidemolecule
Carbo-hydrates
Proteoglycanmolecule
Coreprotein
Integrin
Figure 6.29
A proteoglycan complex
Inner Life of the Cell
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Exercise #3: Constructing a Fluid Mosaic Model
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Membrane Function
• Working cells must control the flow of materials to and from the environment.
– Membrane proteins help with this task.
• Membrane proteins perform a variety of functions.
Membrane Selectivity
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Passive Transport: Diffusion Across Membranes
• Molecules contain heat energy.
– They vibrate and wander randomly.
• Diffusion is one result of the movement of molecules.
– Molecules tend to spread into the available space.
– Diffusion is passive transport; no energy is needed.
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• Another type of passive transport is facilitated diffusion, the transport of some substances by specific transport proteins that act as selective corridors.
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Osmosis and Water Balance in Cells
• Osmosis is the passive transport of water across a selectively permeable membrane.
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• A hypertonic solution
– Has a higher concentration of solute.
• A hypotonic solution
– Has a lower concentration of solute.
• An isotonic solution
– Has an equal concentration of solute.
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Water Balance in Animal Cells
• The survival of a cell depends on its ability to balance water uptake and loss.
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Active Transport: The Pumping of Molecules Across Membranes
• Active transport requires energy to move molecules across a membrane.
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Case Study : Osmosis is Serious Business
Case Study Collection
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Exercise #4: Transport Across the Cell Membrane