Day #1: Microscopy and Cell Structure

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint Lectures for Biology, Seventh Edition

Neil Campbell and Jane Reece

Lectures by Chris Romero

Microscopy and Cell Structure


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.


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.


Taxonomy

• Classifying lifeSpecies Genus Family Order Class Phylum Kingdom Domain

Mammalia

Ursusameri-canus(Americanblack bear)

Ursus

Ursidae

Carnivora

Chordata

Animalia

Eukarya


The Three Domains of Life

• At the highest level, life is classified into three domains

– Bacteria

– Archaea

– Eukarya


• Domain Bacteria and domain Archaea

– Consist of prokaryotes

• Domain Eukarya, the eukaryotes

– Includes the various protist kingdoms and the kingdoms Plantae, Fungi, and Animalia


• 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


Comparison of Bacteria, Archaea, and Eucarya

Three domains of living organisms

http://www.ucmp.berkeley.edu/alllife/threedomains.html

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

How are prokaryotes identified?

Microscopic examinationCulture characteristics or phenotypeBiochemical testsNucleic acid analysissymptoms


Parts of the Microscope


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

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

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?

The Microscopic World of Cells

Organisms are either: Single-celled, such as most bacteria and protists Multicelled, such as plants, animals, and most fungi

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.

The Importance of Cells

All organisms are made of cellsThe cell is the simplest collection of matter

that can live

Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings

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.


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


Prokaryotic cells

Do not contain a nucleus

Have their DNA located in a region called the nucleoid

Figure 4.4


• Prokaryotic cells

– Are smaller than eukaryotic cells.

– Lack internal structures surrounded by membranes.

– Lack a nucleus.


Eukaryotic cells

Contain a true nucleus, bounded by a membranous nuclear envelope

Are generally quite a bit bigger than prokaryotic cells


A Panoramic View of Eukaryotic Cells

• An idealized animal cell


• An idealized plant cell


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


Prokaryotic cells in yogurt


Cytoplasmic Streaming in Elodea


Membrane Structure

• The plasma membrane separates the living cell from its nonliving surroundings.


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

The Plasma Membrane:A Fluid Mosaic of Lipids and Proteins

• The membranes of cells are composed mostly of:

– Lipids

– Proteins

Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings

• The lipids belong to a special category called phospholipids.

• Phospholipids form a two-layered membrane, the phospholipid bilayer.


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


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


Fatty acids

• Vary in the length and number and locations of double bonds they contain

Fats


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


Have one or more double bonds

(b) Unsaturated fat and fatty acidcis double bondcauses bending

Oleic acid

Figure 5.12

Unsaturated fatty acids


Phospholipids

Phospholipids

• Have only two fatty acids

• Have a phosphate group instead of a third fatty acid


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


The structure of phospholipids

Results in a bilayer arrangement found in cell membranes

Hydrophilichead

WATER

WATER

Hydrophobictail

Figure 5.14


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

Figure 4.7a


• Most membranes have specific proteins embedded in the phospholipid bilayer.


• 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.


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.


• 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.


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

http://www.youtube.com/watch?v=Y3Sx-Rj8oV4


Exercise #3: Constructing a Fluid Mosaic Model


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


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.


• Another type of passive transport is facilitated diffusion, the transport of some substances by specific transport proteins that act as selective corridors.


Osmosis and Water Balance in Cells

• Osmosis is the passive transport of water across a selectively permeable membrane.


• 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.


Water Balance in Animal Cells

• The survival of a cell depends on its ability to balance water uptake and loss.


Active Transport: The Pumping of Molecules Across Membranes

• Active transport requires energy to move molecules across a membrane.

Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings


Case Study : Osmosis is Serious Business

Case Study Collection

http://www.sciencecases.org/


Exercise #4: Transport Across the Cell Membrane

Day #1: Microscopy and Cell Structure

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