Chapter 6: A Tour Of the Cell. Hierarchy of Biological organization: Place in order from smallest to largest: Tissue Organisms Communities Organelles

Chapter 6: A Tour Of the Cell

Hierarchy of Biological organization: Place in order from smallest to largest:

TissueOrganismsCommunitiesOrganellesCellsBiospherePopulationsOrgan and Organ systemsEcosystemsMolecules

Hierarchy of Biological organization: 1. Molecules2. Organelles3. Cells4. Tissue5. Organs and Organ systems6. Organisms7. Populations8. Communities9. Ecosystems10. Biosphere

The Importance of Cells

The simplest formVery diverseStructural order – reinforcing the

themes of emergent propertiesCorrelation between structure and

functionInteractions with the Environment

How do biologists study cells:

Two methods: 1. Microscopy- investigations employing a

microscope2. Cell Fractionation- using the tools of

biochemistry

Microscopy: Investigations employing a microscope A. Two important parameters:

Magnification- the ratio of an object’s image size to its real size

Resolution- a measure of the clarity of the image; the minimum distance 2 points can be separated and still be distinguished as 2 points Resolution is inversely related to

wavelength

Microscopy: Investigations employing a microscope

B. Two types: Light microscopes (LMs) Electron Microscope (EM)

Light Microscopy:

Passing visible light through a lens, then a specimen, then to the eye. Lens refracts the light to magnify the image

Limited by the shortest wavelength of visible light used to illuminate the specimen.

Electron microscope:

Focuses a beam of electrons either on the surface or through a specimen

Much shorter wavelengths (remember the relationship between resolution and wavelength?)Resolution of about 2nm- a hundred- fold

improvement over light microscopes

Electron microscope:

Two types: Scanning Electron Microscope (SEM):Transmission Electron Microscope(TEM):

Scanning Electron Microscope(SEM)

Useful in detailed study of surface of specimenSpecimen is covered with a thin layer of goldGreat depth of field3-D like image

Transmission Electron Microscope (TEM):

Used to study internal structures of the cellUses electromagnets as lenses

Cell Fractionation:

Separating the organelles of a cellCentrifugeSeparates according to particle size and

densityUses force of gravityUltracentrifugeEnables the study of cell function and structure

Isolating Organelles by Cell Fraction

Goal of cell fractionationTo take cells apart and separate the major organelles

from one another

Centrifuge is usedSeparates cell by size and densityUltracentrifuges – the most powerful machines

Enables the study of cells’ composition and functionsEx. Cellular respiration

PCA: State the obvious- 1. distinguish between prokaryotic and eukaryotic. 2. Give two obvious differences.

Prokaryotic vs. Eukaryotic:

1. What are the basic features of all cells: Plasma membraneCytosolChromosomesRibosomes


2a. The nucleus: Prokaryote (pro = before, karyon =

kernel(nucleus)Domains Bacteria and Archaea

Eukaryote (Eu = true, karyon = kernel)Domain Eukarya


2b. DNA:Prokaryotes- DNA is concentrated in the nucleiod No membrane separates it from the rest of the cell

Eukaryotes- DNA is located in a double membrane


3. Cytoplasm:Present in both cellsEukaryotes contain multiple

organelles and prokaryotes do not Prokaryotes (as well as eukaryotes)

have ribosomes


For other features see diagram:

The nucleus: 1. contains genes (most of them)2. 5 micrometers in diameter3. Nuclear envelope: double membrane

structure(lipid bilayer)Nuclear pore complexNuclear lamina-array of proteins providing

shape and support for the nucleus

4. Nucleolus- synthesis of ribosomes5. Chromosomes- chromatin(complex of

DNA and proteins)

The Nucleus:

Function of: Directs protein synthesis by

transcribing mRNA

Ribosomes:

Protein factories23nm in diameterComposed of half RNA and half proteinOne large subunit and one small subunitSynthesized at the nucleolusHalf million ribosomes per cell

Endomembrane System:

Functions of:Protein synthesisTransport of proteinsMetabolism of lipidsMovement of lipidsDetoxification of poisons


Includes:Nuclear envelopeRough endoplasmic reticulumSmooth endoplasmic reticulumGolgi apparatusLysosomesVacuolesPlasma membrane (indirectly)

Endoplasmic Reticulum:

Endoplasmic = within the cytoplasmReticulum = little net

Continuous maze like sac(cisternae) surrounded by a SINGLE membrane

Lumen- internal cavity- provides storageContinuation of nuclear envelope

Lumen of nuclear envelope is continuous with lumen of ER


Two distinct regions:Rough endoplasmic reticulumSmooth endoplasmic reticulum


1. rough endoplasmic reticulumContains ribosomesSynthesizes proteins to be secreted

2. smooth endoplasmic reticulum Synthesis of lipids(for membranes)Metabolism of carbsDetoxificationShips proteins from RER to golgi apparatus

Endomembrane System: Golgi Apparatus:

A stack of flat, membranous sacHas a polarity or sideness:

Receives transport vesicles from the endoplasmic reticulum(Cis face)

Modifies, processes, sorts, packages and ships proteins(Trans face)

Produces secretory vesicles that pinch off, fuse with the plasma membrane and secreted by exocytosis

A stack of flat, membranous, polar sac

Golgi Apparatus cont…

Produces and modifies polysaccharides that will be secreted

Endomembrane system: Lysosomes:

Single membrane bound sac containing hydrolytic digestive enzymes

Used to digest macromoleculesSynthesized in the rough endoplasmic

reticulum, sent to the golgi apparatus and pinched off as a vesicle with over forty digestive enzymes

Recycle the cells organic materialLipid digestion enzyme in this organelle can

lead to Tay- Sachs disease


Peroxisomes: Single membrane organelles that function in the

synthesis of fatty acidsProduce hydrogen peroxide as a by-productFunction in detoxifying alcohol and other

poisons in the liverBreak down fatty acids into smaller molecules

which can be transferred to the mitochondria for cellular respiration

Break down molecules through oxidation

Endomembrane System:Glyoxosomes:

Specialized peroxisomesFound in fat storing tissues of plant seedsConvert fatty acids to sugars for the emerging

seedlingCapable of increasing in numbers by splitting in

two when they reach a certain size


Mitochondria: Double membrane organelle with a smooth

outer membrane and rough inner membrane (matrix)which contains inner foldings (cristae)

Only source of DNA that is different and separate from nuclear DNA

Contains ribosomes in its matrixFunctions in respiration and produces ATP

Metabolism of glucose and fatty acids


Chloroplasts: Belongs to a group of organelles called plastidsFunctions in the photosynthetic production of

glucose(used to make ATP)Convert light energy to chemical energyDouble membrane structure that contains

thylakoid sacsStacks of thylakoid membranes = granum(grana)

Stroma- fluid surrounding thylakoid, contains DNA, ribosomes and enzymes.


Mitochondria and Chloroplasts:Contain DNA, ribosomes and enzymesCan change shape, grow and occasionally split

into twomobile

Animals vs. Plant CellsSimilarities:

Nuclear envelope, nucleolusEndoplasmic reticulumRibosomesGolgi ApparatusMitochondriaPeroxisomeCytoskeletonCentrosome

Animals vs. Plant Cells Differences

Animal cells:LysosomesCentriolesFlagella

Plant cells: ChloroplastsCentral vacuoleCell WallPlasmodesmata

Cytoskeleton:

a network of protein fibers that plays a role in organizing the structure and activities of the cell:

Cytoskeleton:Role of:

1. mechanical support for the cell2. maintains shape of cell3. architecture4. anchors many organelles5. Involved in cell motility6.manipulates the plasma membrane to form

food vacuoles during phagocytosis7. regulation of biochemical activities in the cell

Cytoskeleton:

composed of:1. microtubules2. microfilaments3. intermediate filaments

Microtubules:

hollow tubules composed of the protein tubulin(α- tubulin, and β-tubulin)

25μm in diameter with 15μm lumenmaintains cell shape, cell motility,

chromosome and organelle movement

Types of Microtubules:

Centrosome – produce microtubulesCentrioles: found in animal cells only

found in centrosome composed of a ring of nine sets of triplet microtubules


Cilia- locomotor appendage25 µm in diameter, 2- 20µm in lengthon stationary cells, cilia move objects on the

cell surfacecilia propels cell in direction perpendicular to

cilia’s axis


Flagella: locomotor appendages much larger than ciliasame diameter as cilia(.25µm) but much longer

10-200µmpropels cell in same direction as flagellum’s

axisundulating, snake like motion


Basal body: anchors flagella or cilia to the cellstructurally identical to centriole

Types of microfilaments:

Actincan form 3-D structure to help support cell

shapemake up core of microvillifound in skeletal muscle cells and used for

muscle contraction

Myosinmotor proteins

Actin/ Myosin Interactions:

slide filament theory- results in muscle contraction

cytokinesisamoeboid movement- pseudopodia-

converts cytoplasm from sol(liquid) to gel cytoplasmic streaming

More on Intermediate Filaments: 1. specialized for bearing tension2.formed from a family of proteins including

keratins3. more permanent fixtures4. reinforcing shape of cell5. fix position of organelles6. make up nuclear lamina inside nucleus7. axons of nerve cells are strengthened by

intermediate filaments8. may serve as a frame work for entire

cytoskeleton

Extracellular components and connections

The Cell Wall (plants only): extracellular structure not found in animal cellsalso found in prokaryotes, fungi and some

protistscell wall thickness= 0.1 µm to several

micrometers


Role of the Cell Wall: protects the plant cellmaintains shapeprevents excessive uptake of waterresist force of gravity


cell wall design: polysaccharide cellulose microfibrils embedded

in a matrix of other polysaccharides and proteins

primary cell wall- cell wall secreted by the young plant

middle lamella: thin layer located between two adjacent plant cells

secondary cell wall: added between the plasma membrane and the primary cell wall


The Extracellular Matrix(ECM) of animal cellsGlycoproteins

Mainly collagenIntegrinFibronectin

functions in regulating passage of materialsExample: blood platelets


Intercellular Junctions: cell to cell communication through direct physical contactplasmodesmatatight junctionsdesmosomes:gap junctions:


plasmodesmata: perforations of the cell wallchemical communication between the cytosol of

one cell to the nextunify plants into a living columncontinuous from one cell to the nextallows water, solutes, specific proteins and

RNA molecules to move from cell to cell


Tight Junctions: series of connections between two animal cells that form a criss- cross pattern Interacts with proteins between cells


. Desmosomes: made from a complex series of proteins that extends into the intercellular spaceinteracting and interlocking network that binds

two cells togetheranchors plasma membrane


Gap Junctions: channel between two animal cells, forms a cytoplasmic bridgeactivity is regulated by Ca++high [Ca++]- gap junctions close

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter4/animation_-_endosymbiosis.html

Possible Essay Questions:

1. Discuss the endosymbiotic hypothesis. 2. Discuss the similarities and differences

between animal and plant cells.3. How does information flow through the

cell for proteins destined to be secreted by the cell.

4. How would you distinguish a prokaryotic cell from an animal cell. What are the similarities and differences?

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Chapter 6: A Tour Of the Cell. Hierarchy of Biological organization: Place in order from smallest to largest: Tissue Organisms Communities Organelles