Lec 2_Attributes of the Cell

8/3/2019 Lec 2_Attributes of the Cell

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ology 11 Lecture 2 JPQ/TLS/LBU//CCB/JJMP

Copyright © 2005 Pearson Education, Inc. publishingas Benjamin Cummings

General Attributes of the Cell


Overview: The Importance of Cells

• All organisms are made of cells

• The cell is the simplest collection of matter

that can live• Cell structure is correlated to cellular function

• All cells are related by their descent from earliercells


Size range of cells


Prokaryotes vs Eukaryotes

• domains Bacteria and Archaea – prokaryotic cells

• domain Eukarya (protists, fungi, animals, andplants) – eukaryotic cells


• Basic features of all cells:

– Plasma membrane

– Semifluid substance called the cytosol

– Chromosomes (carry genes)

– Ribosomes (make proteins)



• Prokaryotic cells have no nucleus

• In a prokaryotic cell, DNA is in an unbound regioncalled the nucleoid

• Prokaryotic cells lack membrane-bound organelles





A typicalrod-shapedbacterium

A thin section through thebacterium Bacillus coagulans (TEM)

0.5 µm

Pili

Nucleoid

Ribosomes

Plasma

membrane

Cell wall

Capsule

Flagella

Bacterialchromosome



ANIMAL CELL TYPES



PLANT CELL TYPES


• selective barrier that allows passage ofoxygen, nutrients, and wastes for the whole

volume of the cell

Cell Parts: Plasma membrane





• contains most of the DNA in a eukaryotic cell

Cell Parts: Nucleus

Close-up of nuclearenvelope

Nucleus

Nucleolus

Chromatin

Nuclear envelope:Inner membraneOuter membrane

Nuclear pore

Porecomplex

Ribosome

Pore complexes (TEM) Nuclear lamina (TEM)

1 µm

Rough ER

Nucleus1 µm

0.25 µm

Surface of nuclear envelope


• particles made of ribosomal RNA and protein

• carry out protein synthesis in two locations:

– cytosol (free ribosomes)

– outside of the endoplasmic reticulum (ER) orthe nuclear envelope (bound ribosomes)

Cell Parts: RibosomesRibosomes

0.5 µm

ER Cytosol

Endoplasmicreticulum (ER)Free ribosomes

Bound ribosomes

Largesubunit

Smallsubunit

Diagram of

a ribosome

TEM showing ER

and ribosomes


• Components : – Nuclear envelope

– Endoplasmic reticulum – Golgi apparatus – Lysosomes – Vacuoles – Plasma membrane

• These components are either continuous orconnected via transfer by vesicles

Cell Parts: Endomembrane system


• accounts for more than half of the total membranein many eukaryotic cells

• continuous with the nuclear envelope

• two distinct regions of ER:

– Smooth ER

– Rough ER

Cell Parts: Endoplasmic Reticulum




Ribosomes

Smooth ER

Rough ER

ER lumen

Cisternae

Transport vesicle

Smooth ER Rough ER

Transitional ER

200 nm

Nuclearenvelope


Functions of Smooth ER

– Synthesizes lipids

– Metabolizes carbohydrates

– Stores calcium

– Detoxifies poison


– produces proteins and membranes, which aredistributed by transport vesicles

– membrane factory for the cell

Functions of Rough ER


• consists of flattened membranous sacs calledcisternae

• Functions:

– modifies products of the ER

– manufactures certain macromolecules

– sorts and packages materials into transportvesicles

Cell Parts: Golgi apparatus

trans face(“shipping” side of Golgi apparatus) TEM of Golgi apparatus

0.1 µm

Golgiapparatus

cis face(“receiving” side of Golgi apparatus)

Vesicles coalesce toform new cis Golgi cisternaeVesicles also

transport certainproteins back to ER

Vesicles movefrom ER to Golgi

Vesicles transport specificproteins backward to newerGolgi cisternae

Cisternalmaturation:Golgi cisternaemove in a cis -to- trans direction

Vesicles form andleave Golgi, car ryingspecific proteins toother locations or tothe plasma mem-brane for secretion

Cisternae


• membranous sac of hydrolytic enzymes

• enzymes can hydrolyze proteins, fats,polysaccharides, and nucleic acids

• use enzymes to recycle organelles andmacromolecules, a process called autophagy

Cell Parts: Lysosomes




Phagocytosis: lysosome digesting food

1 µm

Plasmamembrane

Food vacuole

Lysosome

Nucleus

Digestiveenzymes

Digestion

Lysosome

Lysosome containsactive hydrolyticenzymes

Food vacuolefuses withlysosome

Hydrolyticenzymes digestfood particles

Autophagy: lysosome breaking downdamaged organelle

1 µm

Vesicle containingdamaged mitochondrion

Mitochondrionfragment

Lysosome containingtwo damaged organelles

Digestion

Lysosome

Lysosome fuses withvesicle containingdamaged organelle

Peroxisomefragment

Hydrolytic enzymesdigest organellecomponents


• vesicles and vacuoles are membrane-bound sacswith varied functions

• a plant cell or fungal cell may have one or severalvacuoles

Cell Parts: Vacuoles


• food vacuoles are formed by phagocytosis

• contractile vacuoles , found in many freshwaterprotists, pump excess water out of cells

• central vacuoles , found in many mature plantcells, hold organic compounds and water

Cell Parts: Vacuoles

5 µm

Central vacuole

Cytosol

Tonoplast

Centralvacuole

Nucleus

Cell wall

Chloroplast


The Endomembrane System: A Review

• a complex and dynamic player in the cell’scompartmental organization




Nuclear envelope

Nucleus

Rough ER

Smooth ERNuclear envelope

Nucleus

Rough ER

Smooth ER

Transport vesicle

cis Golgi

trans Golgi

Nuclear envelope

Nucleus

Rough ER

Smooth ER

Transport vesicle

cis Golgi

trans Golgi

Plasmamembrane


Mitochondria and chloroplasts change energyfrom one form to another

• mitochondria are the sites of cellular respiration

• chloroplasts , found only in plants and algae, arethe sites of photosynthesis

• mitochondria and chloroplasts are not part of theendomembrane system

• peroxisomes are oxidative organelles


• are in nearly all eukaryotic cells

• with smooth outer membrane and an inner

membrane folded into cristae• inner membrane creates two compartments:

intermembrane space and mitochondrial matrix

Cell Parts: MitochondriaMitochondrion

Intermembrane space

Outermembrane

Innermembrane

Cristae

Matrix

100 nmMitochondrialDNA

Freeribosomesin themitochondrialmatrix





• member of a family of organelles called plastids

• contain chlorophyll, as well as enzymes and othermolecules that function in photosynthesis

• found in leaves and other green organs of plantsand in algae

• structure includes: – thylakoids, membranous sacs – stroma, the internal fluid

Cell Parts: Chloroplasts

Chloroplast

ChloroplastDNA

RibosomesStroma

Inner and outermembranes

Granum

Thylakoid1 µm


• specialized metabolic compartments bounded bya single membrane

• produce hydrogen peroxide and convert it to water

Cell Parts: Peroxisomes

Chloroplast

Peroxisome

Mitochondrion


• a network of fibers extending throughout thecytoplasm

• organizes the cell’s structures and activities,anchoring many organelles

• composed of three types of molecular structures: – microtubules – microfilaments

– intermediate filaments

Cell Parts: Cytoskeleton

Microtubule

Microfilaments0.25 µm


Roles of the Cytoskeleton

• helps to support the cell and maintain its shape

• interacts with motor proteins to produce motility

• vesicles can travel along “monorails” provided bythe cytoskeleton

• may help regulate biochemical activities




Vesicle

Receptor for

motor protein

Microtubuleof cytoskeleton

Motor protein(ATP powered)

ATP

0.25 µmMicrotubule Vesicles


Components of the Cytoskeleton






Centrosomes and Centrioles

• In many cells, microtubules grow out from acentrosome near the nucleus

• The centrosome is a “microtubule -organizingcenter”

• In animal cells, the centrosome has a pair ofcentrioles, each with nine triplets of microtubulesarranged in a ring




0.25 µm

Microtubule

Centrosome

Centrioles

Longitudinal sectionof one centriole

Microtubules Cross sectionof the other centriole


Cilia and Flagella

• Microtubules control the beating of cilia andflagella, locomotor appendages of some cells

• Cilia and flagella differ in their beating patterns


5 µm

Direction of swimming

(a) Motion of flagella

Direction of organism’s movement

Power stroke Recovery stroke

(b) Motion of cilia15 µm


• Cilia and flagella share a common ultrastructure:

– a core of microtubules sheathed by the plasmamembrane

– a basal body that anchors the cilium orflagellum

– a motor protein called dynein, which drives thebending movements of a cilium or flagellum

0.5 µm

Microtubules

PlasmamembraneBasal body

Plasmamembrane

0.1 µm

Cross section of basal body

Triplet

Outer microtubuledoublet

0.1 µm

Dynein armsCentralmicrotubuleCross-linkingproteins insideouter doublets

Radialspoke


• How dynein “walking” moves flagella and cilia: – Dynein arms alternately grab, move, and

release the outer microtubules – Protein cross-links limit sliding – Forces exerted by dynein arms cause doublets

to curve, bending the cilium or flagellum




Dynein “walking”

Microtubuledoublets ATP

Dynein arm

LE 6-25b

Wavelike motion

Cross-linkingproteins insideouter doublets

ATP

Anchoragein cell

Effect of cross-linking proteins

Microfilaments (actinfilaments)

Microvillus

Plasma membrane

Intermediate filaments

0.25 µm

• form a 3Dnetwork justinside theplasmamembrane tohelp support thecell’s shape

• bundles ofmicrofilamentsmake up thecore of microvilliof intestinal cells

Microfilaments(Actin filaments)

Muscle cell

Actin filament

Myosin filamentMyosin arm

Myosin motors in muscle cell contraction

• microfilaments that function in cellular motility contain theprotein myosin in addition to actin

Cortex (outer cytoplasm):gel with actin network

Amoeboid movement

Inner cytoplasm: solwith actin subunits

Extendingpseudopodium

• localized contraction brought about by actin and myosinalso drives amoeboid movement

• pseudopodia (cellular extensions) extend and contractthrough the reversible assembly and contraction of actinsubunits into microfilaments

Nonmovingcytoplasm (gel)

Cytoplasmic streaming in plant cells

Chloroplast

Streamingcytoplasm(sol)

Cell wallParallel actinfilaments

Vacuole

• actin-myosin interactions and sol-gel transformations drivecytoplasmic streaming

• speeds distribution of materials within the cell





Intermediatefilaments

• support cellshape and fixorganelles inplace

• are morepermanentcytoskeletonfixtures thanthe other twoclasses

Microvillus

Plasma membrane

Microfilaments (actinfilaments)

Intermediate filaments

0.25 µmCopyright © 2005 Pearson Education, Inc. publishingas Benjamin Cummings

Extracellular components

• materials that are external to the plasmamembrane

• synthesized and secreted by most cells• include:

– cell walls of plants

– extracellular matrix (ECM) of animal cells

– intercellular junctions


Cell Walls of Plants

• protects the plant cell, maintains its shape, andprevents excessive uptake of water

• made of cellulose fibers embedded in otherpolysaccharides and protein


Cell Walls of Plants

• may have multiple layers:

– primary cell wall : relatively thin and flexible

– middle lamella : thin layer between primarywalls of adjacent cells

– secondary cell wall (in some cells): addedbetween the plasma membrane and theprimary cell wall

• plasmodesmata are channels between adjacentplant cells

Centralvacuoleof cell

PlasmamembraneSecondarycell wall

Primarycell wall

Middlelamella

1 µm

Central

vacuoleof cell

Central vacuoleCytosol

Plasma membrane

Plant cell walls

Plasmodesmata


The Extracellular Matrix (ECM) of Animal Cells

• animal cells lack cell walls but are covered by anelaborate extracellular matrix (ECM)

• made up of glycoproteins and othermacromolecules

• Functions of the ECM: – support – adhesion – movement – regulation




EXTRACELLULAR FLUID ProteoglycancomplexCollagen

fiber

Fibronectin

Integrin Micro-filaments

CYTOPLASM

Plasmamembrane

Polysaccharidemolecule

Carbo-hydrates

Coreprotein

Proteoglycanmolecule

Proteoglycancomplex


Intercellular Junctions

• neighboring cells in tissues, organs, or organsystems often adhere, interact, and communicatethrough direct physical contact

• intercellular junctions facilitate this contact


Plants: Plasmodesmata

• channels that perforate plant cell walls

• for passage of water and small solutes (andsometimes proteins and RNA) from cell to cell

Interiorof cell

Interiorof cell

0.5 µm Plasmodesmata Plasma membranes

Cell walls


Animals: Tight Junctions, Desmosomes,and Gap Junctions

• at tight junctions , membranes of neighboring cellsare pressed together, preventing leakage of

extracellular f luid• desmosomes (anchoring junctions) fasten cells

together into strong sheets

• gap junctions (communicating junctions) providecytoplasmic channels between adjacent cells

Tight junctions preventfluid from movingacross a layer of cells

Tight junction

0.5 µm

1 µm

0.1 µm

Gap junctionExtracellularmatrix

Spacebetweencells

Plasma membranesof adjacent cells

Intermediatefilaments

Tight junction

Desmosome

Gapjunctions





The Cell: A Living Unit Greater Than the Sum of Its Parts

• cells rely on the integration of structures andorganelles in order to function

• for example, a macrophage’s ability to destroybacteria involves the whole cell, coordinatingcomponents such as the cytoskeleton, lysosomes,and plasma membrane

5 µ m

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Lec 2_Attributes of the Cell