CHAPTER 6 CELLULAR

STRUCTURE

WHY STUDY CELLS?

Intro to Cells

Brief Hitory

Great researcher Based on

observation Viper venom! First to debunk

spontaneous generation

" I put in four flasks with wide mouths one sneak, some fish of river, four

small eels of Arno river and a piece of calf and I locked very well the mouths of the

flasks with paper and string. Afterward, I placed

in other four flasks the same things and left the

mouths of flasks open.Short time later the meat and the fishes inside the

open flasks became verminous, and after three

weeks I saw many flies around these flasks, but in

the locked ones I never seen a worm ".

- 1688

Lazzaro Spallanzani

1765Louis Pasteur

1862

"Omnis cellula e cellula"... 

"All cells only arise from pre-existing

cells".-Rudolf

Virchow

Cell Theory – original 1839

Schleiden and Schwann

All organisms are made up of cellsThe cell is the basic living unit of

organization for all organismsAll cells from pre-existing cells

Biogenesis -Not spontaneous generation or abiogenesis

   1. all known living things are made up of cells.    2. the cell is structural & functional unit of all living things.   3. all cells come from pre-existing cells by division.    4. cells contains hereditary information which is passed

from cell to cell during cell division.    5. All cells are basically the same in chemical composition.    6. all energy flow (metabolism & biochemistry) of life

occurs within cells.

The Modern Cell Theory:

Biological Diversity and Unity DNA is universal “language” Cells are most basic unit of

structure and function Lowest level of structure

capable of performing all

life activities and being

self-sustaining

Cells

Activities of Life

ReproductionGrowth and

developmentEnergy utilizationResponse to stimulihomeostasis

HOW DO WE STUDY CELLS?

Leewenhoek 1674

Robert Hooke 1665

Light microscope (LM) - visible light passes through specimen and then through glass lenses. lenses refract light - image is

magnified into the eye Specimen can be alive!

Microscopes

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

Resolving power = a measure of image clarity minimum distance 2 points can be

separated and still be viewed as two separate points

7X 45X 112.5X 225X

LIGHT MICROSCOPEminimum resolution is

about 2 microns (small bacterium)

magnify effectively to about 1,000 times

At higher magnifications, the image blurs

HOWBIG

ELECTRON MICROSCOPE1950’S2.0 nm resolution100X > than lightOrganellesOnly on dead cells

electron microscope (EM)- beam of electrons through the

specimen or onto its surface - shorter wavelengths of light

greater resolution

Transmission electron microscopes (TEMs)-study internal ultrastructure

electron beam through thin section of specimen image focused and magnified by electromagnets thin sections stained with atoms of heavy metals Dead; may leave debris/artifacts

Tracheal cells

Scanning electron microscopes (SEMs)- useful for studying surface structures surface covered with a thin film of gold beam excites electrons on surface secondary electrons collected and focused on screen

SEM has great depth of field, image seems 3-D

Dead,debris/artifacts

LM’s -less resolution but livingcytology- study of cell structuresCytology + biochemistry =

modern cell biology

ISOLATING ORGANELLESCell Fractionation

Separate organelles from cellUse varying densities of parts

•Ultracetrifuge

HEAVIEST? LIGHTEST?

•Ultracentrifuge – molecular level

•130,000 rpm

•Forces>1 million g’s

Why in a BIG thick lead-lined housing?

MicrocentrifugeBiotechnology research

Cells at protein and genetic level

Homogenization- disrupts cellUltracentrifuge- spins to separate

heavier pieces into pellet with lighter particles in supernatant

CELLSALIVE

AmoebasAnimals

Plant Cells

Cell characteristics – All Cells

Plasma membraneCytosol

Semi-fluid substance w/ “solutes” Cytoplasm = cytosol + organelles(euk’s)

Contain chromosomes w/ genes in DNARibosomes

Protein synthesis; carry out gene instructions

Types of Cells

Prokaryotic CellsNucleoid region1 main Circular

chromosome + plasmids

Ribosomes

Eukaryotic CellsNucleus; isolatedLinear chromosomesMembrane bound

organellesRibosomes

•Prokaryotic vs. Eukaryotic Cells

•Location of chromosomes

Human Cells

Remember the agar block lab?

Same time = same depth of diffusion

Limited by SA/ Vol ratio Volume increases by factor of 3; SA by 2

• Smaller objects have greater SA:Vol ratio

What cell organelle governs this?

Why is a huge single-cell organism not possible?

LIMITS TO SIZE---

Eukaryotes generally much bigger Logistics of carrying out metabolism sets

limits on cell size • SA to Volume ratio?

– smallest bacteria, mycoplasmas

» 0.1 to 1.0 micron

» Most bacteria 1-10 microns

– Eukaryotes typically 10-100 microns» Micron = 1 micrometer = 1/1,000,000 meter» 1000 microns = 1 millimeter» Human hair = apx. 20 microns

Size must be low to sustain life

• enough DNA to program metabolism

• enough ribosomes for protein synthesis

• enough enzymes for metabolism

• enough cellular components

plasma membrane functions as a selective barrier Controls movement in and out of cell maintains homeostasis - correct environment

bilayer of phospholipids + proteins Amphipathic

• hydrophyllic• hydrophobic

TOUR OF THE CELL

BUCKLE UP!

The Nucleus and

Ribosomes

contains most of genes in euk. Celllargest organelledouble membrane

unique environment

membranes fuse to form pores/envelope large macromolecules & particles pass unique chemical signals viruses may break code

Nucleus contains a eukaryotic cell’s genetic library

Nuclear lamina--nuclear side; lined by intermediate filaments

• maintains shape of nucleus

DNA and histone proteins = CHROMATIN

Nucleolus – rRNA synthesis

NUCLEUS - directs protein synthesis; synthesizes mRNA

Ribosomes contain rRNA and proteinA ribosome = two subunits combined to carry out

protein synthesis; no membrane!Free and Bound and prokaryotic

Ribosomes build a cell’s proteins

The Endomembrane

System

Endo-Membrane

system

membranous tubules and internal, fluid-filled spaces = cisternae; storage area

Lumen is center of ERcontinuous with N. E.

ER manufactures membranes and performs many other biosynthetic functions

2 connected regions of ER-- Smooth ER lacks

ribosomes Rough ER (bound

ribosomes)

Receives transports vesicles from ERModifies contentsWarehousing, sorting, and shippingAbundant in secretory cells Produces lysosomes and cell wall

The Golgi Apparatus finishes, sorts, and ships cell products

Endomembrane SystemSumanisc

lysosome - a membrane-bound sac of hydrolytic enzymes that digests macromolecules.

Lysosomes are digestive sacs

Vesicles and vacuoles (larger versions)membrane-bound sacs

Food vacuoles, from phagocytosis, fuse with lysosomes

Contractile vacuoles, in freshwater protists• pump excess water out of cell

Central vacuoles in plant cells; • Store water and solutes

Vacuoles have diverse functions in cell maintenance

Other Membranous Organelles

convert energy to usable forms for workMitochondria = sites of cell. respiration,

generate ATP from catabolism of sugars, fats, and other fuels in presence of oxygen

Chloroplasts - found in plants and eukaryotic algae; sites of photosynthesis convert solar energy to chemical energy and

synthesize new organic compounds from CO2 and H2O.

Mitochondria and chloroplasts are main energy transformers of cells

PLASTIDS - Amyloplasts/leucoplasts - store starch

in roots and tubers Chromoplasts store pigments Chloroplast

• produces sugar via photosynthesis

• color from chlorophyll pigment • in leaves and other green structures of plants and in eukaryotic algae

Peroxisomes - single membranecontain enzymes to break down H2O2

Some break fatty acids down for mitochondria for fuel Some detoxify alcohol and other harmful compounds

Glyoxysomes = Specialized peroxisomes,

in plants only, convert fatty acids to sugars in seeds

= easier energy and carbon source

The Cytoskeleton

CYTOSKELETON = a network of fibers throughout cytoplasm

maintains shape of the cell; oppose forcesorganizes structures and activities of cellprovides anchorage for organellesdynamic, dismantles and reassembles as

needed

cytoskeleton - major role in cell motility changes in cell location limited movements of parts of cell interacts with motor proteins- dynein In cilia and flagella also in muscle cells circulate materials

within cell by

cytoplasmic

streaming

kinesin Ciliaflagella

three main types of fibers in the cytoskeleton: microtubules microfilaments intermediate filaments

Actin

Actin and keratin

Cilia and Flagella are microtubules move unicellular and small multicellular

organisms thru water may move fluid over a surface

• EX: cilia sweep mucus carrying trapped debris from the lungs

Cilia usually in large #’s on cell surface flagella - usually just one or a few

Flagellum - undulatory movement Force - parallel to the flagellum’s axis

Cilia move like oars force perpendicular to cilia’s axis

•In animal cells, centrosome has a pair of centrioles, each with 9 triplets of microtubules arranged in a ring•centrioles replicate during cell division

“9 + 2”

Cilia and flagella

Basal bodyBasal body same structure as centriole

Site of controversy

bending driven by arms of motor protein called dynein

Hydrolysis of ATP causes bending of protein

Dynein arms

alternately grab,

move and release

outer microtubulesMicro-Tubulesliding

Motor protein

Microfilaments= thinnest fibers; solid, globular protein actin microfilament of actin subunits

resist tension = pullinginteract with myosin for muscle

contractionA contracting belt- divides cytoplasm

animal cells during cell division

microvilliincrease SA • lung tissue,•intestinal lining, etc;•Absorptive surfaces•anchored to intermediate filaments.

contraction causes amoeboid movement• Pseudopodia, cellular extensions, extend and contract

through assembly and contraction of actin subunits into microfilaments

In plant cells - actin-myosin interactions drive cytoplasmic streaming

a circular flow of cytoplasmspeeds the distribution of materials within the

cell.

Intermediate filaments - for bearing tension

built from keratinreinforce cell shape and

fix organelle location

Cell Surfaces and Junctions

cell wall - in prokaryotes, fungi, and some protists; multiple functions

In plants - protects, maintains shape, prevents excess uptake of water; turgor

supports plant against force of gravitythickness and composition differs from

species to species and among cell types

Plant cells are encased by cell walls

consists of microfibrils of cellulose in a matrix of proteins and other polysaccharides

mature cell wall consists of a primary cell wall, a middle lamella with sticky polysaccharides- pectin- holds cell together, and layers of secondary cell wall

glycoproteins, especially collagen, embedded in network of proteoglycans

fibronectins bind to integrin proteins in membrane to connect ECM to cytoskeleton microfilaments permit interaction of changes inside

and outside cell

Extracellular matrix (ECM) of animal cells

The ECM can regulate cell behavior Embryonic cells migrate along specific

pathways by matching the orientation of their microfilaments to the “grain” of fibers in the extracellular matrix.

ECM can influence activity of genes in nucleus via a combination of chemical and mechanical signaling pathways• This may coordinate all the cells within a tissue.

Connections between cellsPlant cells have plasmodesmata,

channels for direct exchange of cytosol

Intercellular junctions

Animal have 3 main types of intercellular links:

tight junctions, membranes are fused, form continuous belts around cells-prevents leakage of extracellular fluid

Desmosomes fasten cells together into strong sheets - keratin intermediate filaments

Gap junctions provide cytoplasmic channels between adjacent cells