Cell Structure and Functionhhh.gavilan.edu/jcrocker/documents/Ch04_lecture_000.pdfmicrofilaments. mitochondrion. intermediate. filaments. ribosomes. endoplasmic. reticulum. microtubule.
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Copyright © 2009 Pearson Education, Inc..
Including some materialsfrom lectures by
Gregory AhearnUniversity of North Florida
Ammended byJohn Crocker
Chapter 4
Cell Structure and Function
Copyright © 2009 Pearson Education Inc.
What Is the Cell Theory?
Tenets of Modern Cell Theory• Every living organism is made of one or more
cells• The smallest organisms are made of single
cells while multicellular organisms are made of many cells
• All cells arise from pre-existing cells
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4.1 What Features Are Shared By All Cells?
Cells are the smallest unit of life.
Cells are enclosed by a plasma membrane.
Cells use DNA as a hereditary blueprint.
Cells contain cytoplasm, which is all the material inside the plasma membrane and outside the DNA-containing region.
Cells obtain energy and nutrients from their environment.
Copyright © 2009 Pearson Education Inc.
Copyright © 2009 Pearson Education Inc.
4.1 What Features Are Shared By All Cells?
Cell function limits cell size.• Most cells are small (1 to 100 um in diameter)• Cells need to exchange nutrients and wastes
with the environment• No part of the cell can be far away from the
external environment.• Diffusion of molecules across cell membranes
limits the diameter of cells.• As cells get bigger, their nutrient and waste
elimination needs grow faster than the membrane area to accommodate them.
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4.1 What Features Are Shared By All Cells?
The volume of cytoplasm grows faster than the plasma membrane area.
Fig. 4-2
Copyright © 2009 Pearson Education Inc.Fig. 4-1
frog embryo
most eukaryotic cells
mitochondrion
most bacteria
virus
proteinsdiameter of DNA double helix
chicken egg
atoms1 micrometer (m) = 1/1,000,000 m1 nanometer (nm) = 1/1,000,000,000 m
1 centimeter (cm) = 1/100 m1 millimeter (mm) = 1/1,000 m
Units of measurement:1 meter (m) = 39.37 inches
adult human
tallest treesDiameter
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100 m
10 m
1 m
10 cm
1 cm
1 mm
100 m
10 m
1 m
100 nm
10 nm
1 nm
0.1 nm
Relative sizes
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All Cells Share Common Features
A plasma membrane encloses all cells and regulates material flow
Cytoplasm is the fluid interior where a cell’s metabolic reactions occur• May contain organelles• Fluid portion (cytosol) contains water, salts,
and organic molecules
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Copyright © 2009 Pearson Education Inc.
All Cells Share Common Features
All cells use DNA (deoxyribonucleic acid) as a hereditary blueprint
All cells use RNA (ribonucleic acid) to copy DNA to make proteins
All cells obtain energy and nutrients from the environment
All cells use common building blocks to build the molecules of life
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Some Cell Types Have Cell Walls
Cell walls are stiff coatings on outer surfaces of bacteria, plants, fungi, and some protists
• Composed of polysaccharides like cellulose or chitin
• Support and protect fragile cells and are usually porous
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Cell Walls
Cell walls in plants may have multiple layers
• Primary cell walls in plants are outermost• Secondary cell walls are innermost• Cell walls of adjacent cells joined by middle
lamellae
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4.2 How Do Prokaryotic And Eukaryotic Cells Differ?
There are two kinds of cells.• Prokaryotic cells
• Are found only in two groups of single-celled organisms—the bacteria and archaea
• Eukaryotic cells• Are structurally more complex cells• Possess a membrane-enclosed nucleus• Probably arose from prokaryotic cells
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There Are Two Basic Cell Types
Prokaryotic• Before nucleus
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4.7 What Are The Features Of Prokaryotic Cells?
Prokaryotic cells are much smaller than eukaryotic cells (< 5 µm long)
Are very reproductively successful and so are more abundant
Have a simple internal structure
Surrounded by a stiff cell wall, which provides shape and protection
Can take the shape of rods, spheres, or helices
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Prokaryotic Cells
No nuclear membrane or membrane-bound organelles are present
Some have internal membranes used to capture light
Cytoplasm contains ribosomes used for protein synthesis
Cytoplasm may contain food granules
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Copyright © 2009 Pearson Education Inc.
Prokaryotic Cells
Single, circular chromosome of DNA
• Chromosome found coiled in an area called the nucleoid
Small rings of DNA (plasmids) are located in the cytoplasm
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Prokaryotic Cells
Some bacteria are propelled by flagella
Infectious bacteria may have polysaccharide adhesive capsules and slime layers on their surfaces
Pili and fimbriae are protein projections in some bacteria that further enhance adhesion
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Copyright © 2009 Pearson Education Inc.
There Are Two Basic Cell Types
Eukaryotic• True nucleus• Includes Protist, Fungi, Plant, and
Animal cells
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4.3 What Are The Main Features Of Eukaryotic Cells?
Eukaryotic cells are > 10 µm long
The cytoskeleton provides shape and organization
A variety of membrane-enclosed organelles perform specific functions
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Major Features
Nucleus: contains DNA
Mitochondria: produce energy
Endoplasmic reticulum: synthesizes membrane components and lipids
Golgi apparatus: molecule sorting center
Lysosomes: digest cellular membranes or defective organelles
Microtubules: make up the cytoskeleton
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Major Features
A generalized animal cell
Fig. 4-3mitochondrion
vesicle
cytoplasm
flagellum
lysosome
centrioleintermediatefilaments
Golgiapparatus
vesicle
nuclear pore
nuclear envelope
chromatin (DNA)nucleolus
nucleus
plasmamembrane
rough endoplasmicreticulum
ribosome
free ribosomesmoothendoplasmicreticulum
microtubules
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Major Features
Animal and plant cells differ with regards to cell walls, chloroplasts, plastids, central vacuoles, and centrioles
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Major Features
A generalized plant cell
Fig. 4-4
centralvacuole
mitochondrion
vesicle
plasmodesma
cell wall
plasmamembrane
intermediatefilaments
free ribosomeribosomes
nucleus
nucleolusnuclear porechromatinnuclearenvelope
roughendoplasmicreticulum
smoothendoplasmicreticulum
Golgiapparatus
chloroplast
microtubules(part of cytoskeleton)
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4.4 What Role Does The Nucleus Play?
The nucleus is the largest organelle in the cell.• It is bounded by a nuclear envelope.• It contains granular-looking chromatin.• It contains the nucleolus.
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The Nucleus
The nuclear envelope separates chromosomes from cytoplasm• Envelope is a double membrane with
nuclear pores for transport• Some smaller materials can move through
the pores, while others, such as DNA, are excluded.
• Outer membrane is studded with ribosomes
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The Nucleus
The nucleus
nucleus
nuclearpores
(b) Yeast cell
nuclearenvelope
nuclearpores
nucleolus
chromatin
(a) Structure of the nucleus
Fig. 4-5
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Copyright © 2009 Pearson Education Inc.
The Nucleus
The nucleus contains DNA in various configurations• Compacted chromosomes (during cell
division)• Diffuse chromatin (as DNA directs reactions
through an RNA intermediate by coding for proteins)
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Copyright © 2009 Pearson Education Inc.
The Nucleus
Darker area within the nucleus called the nucleolus• Functions as the site of ribosome synthesis• Ribosomes synthesize proteins• Ribosomes are composed of RNA and
proteins
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The Nucleus
Ribosome components are made at the nucleolus.• The nucleolus contains DNA, RNA, proteins,
and ribosomes in various stages of construction.
• This is the site where components of ribosomes are constructed.
• Ribosome components leave the nucleus and are assembled in the cytoplasm.
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4.5 What Roles Do Membranes Play In Eukaryotic Cells?
The plasma membrane isolates the cell, and alternately, helps it interact with its environment.• The phospholipid bilayer contains globular
proteins that regulate the transport of molecules into and out of the cell.
• Plant, fungi, and some protist cells also have a cell wall outside the plasma membrane, which acts as a protective coating.
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System of Membranes
The endoplasmic reticulum (ER) forms a series of enclosed, interconnected channels within cell• There are two forms of ER:
• Rough endoplasmic reticulum: is studded with ribosomes
• Smooth endoplasmic reticulum: has no ribosomes
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System of Membranes
Smooth ER has no ribosomes• Contains enzymes that detoxify drugs (in liver
cells) • Synthesizes phospholipids and cholesterol.• Together with rough ER are the sites of new
membrane synthesis for the cell.
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System of Membranes
Rough ER is studded with ribosomes on outside• Produces proteins and phospholipids destined
for other membranes or for secretion (export)• Together with rough ER are the sites of new
membrane synthesis for the cell.
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System of Membranes
Vesicles are membranous sacs that transport substances among the separate regions of the membrane system
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Copyright © 2009 Pearson Education Inc.
System of Membranes
The Golgi Apparatus is a set of stacked flattened sacs • Receive proteins from ER (via transport
vesicles) and sorts them by destination• Modify some molecules (e.g. proteins to
glycoproteins)• Package material into vesicles for transport
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Copyright © 2009 Pearson Education Inc.
System of Membranes
Three fates of substances made in the membrane system:
1. Secreted proteins made in RER, travel through Golgi, then are exported through plasma membrane – The following figure illustrates this process
for antibodies– Antibodies are proteins produced by white
blood cells to inactivate foreign disease- causing agents
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Copyright © 2009 Pearson Education Inc.
System of Membranes
2. Digestive proteins made in RER, travel through Golgi, and are packaged as lysosomes for use in cell• Lysosomes fuse with food vacuoles and
digest food into basic nutrients• In the cytoplasm, they digest defective
organelles or pieces of membrane into component parts that can be recycled.
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Copyright © 2009 Pearson Education Inc.
System of Membranes
3. Membrane proteins and lipids made in ER, travel through Golgi, and replenish or enlarge organelle and plasma membranes
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Copyright © 2009 Pearson Education Inc.
4.6 What Other Structures Play Key Roles In Eurkaryotic Cells?
Vacuoles
Mitochondria
Chloroplasts
Plastids
Cytoskeleton
Cilia and flagella
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Vacuoles
Fluid-filled sacs with a single membrane
Functions of vacuoles• Contractile vacuoles in freshwater organisms
used to collect and pump water out• Many plant cells have a large central vacuole.• Plant central vacuoles used in several ways
• Maintain water balance• Store hazardous wastes, nutrients, or
pigments• Provide turgor pressure on cytoplasm to
keep cells rigid
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Copyright © 2009 Pearson Education Inc.
Mitochondria Extract Food Energy
Mitochondria are round, oval, or tubular sacs of double-membranes• Inner membrane is folded into cristae• Intermembrane compartment lies between
inner and outer membranes• Matrix space within inner membrane
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Copyright © 2009 Pearson Education Inc.
Mitochondria Extract Food Energy
Function as the “powerhouses of the cell”• Mitochondria extract energy from food
molecules• Extracted energy is stored in high-energy
bonds of ATP• Energy extraction process involves anaerobic
and aerobic reactions
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Mitochondria Extract Food Energy
Mitochondria may be remnants of free-living prokaryotes (endosymbiotic hypothesis)
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Chloroplasts
Chloroplasts are specialized organelles surrounded by a double membrane• Outer membrane• Inner membrane encloses the stroma space
• Stacked hollow membranous sacs (grana) within stroma are called thylakoids
• The thylakoid membranes contain chlorophyll and other pigments that capture sunlight and with CO2 and water make sugar and O2 (photosynthesis)
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Copyright © 2009 Pearson Education Inc.
Plants Use Plastids for Storage
Plastids found only in plants and photosynthetic protists
Surrounded by a double membrane
Functions
• Storage for photosynthetic products like starch
• Storage of pigment molecules giving color to ripe fruit
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Copyright © 2009 Pearson Education Inc.
Cytoskeleton
The cytoskeleton provides shape, support, and movement.• All organelles in the cell do not float about the
cytoplasm, but instead, are attached to a network of protein fibers called the cytoskeleton.
Several type of protein fibers make up the cytoskeleton.• Microfilaments: thin fibers• Intermediate filaments: medium-sized fibers • Microtubules: thick fibers
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Cytoskeleton
Fig. 4-9
plasma membrane
microfilaments
mitochondrion
intermediatefilaments
ribosomes
endoplasmicreticulummicrotubule
vesicle
(a) Components of the cytoskeleton (b) Cell with stained cytoskeleton
microtubules (red)
nucleus
microfilaments (blue)
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Cilia and Flagella
Cilia and flagella are extensions of the plasma membrane
Cilia and flagella are composed of microtubules in a “9+2” arrangement formed by centrioles which become membrane-anchored structures called basal bodies
Cilia are short (10-25 µm) and numerous while flagella are long (50-75 µm) but few in any cell
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Copyright © 2009 Pearson Education Inc.
Cilia and Flagella
Long pairs of microtubules slide along each other (using ATP) causing movement of cilia and flagella
Functions• Cilia or flagella may be used to move cell
about• Cilia may be used to create currents of moving
fluid in their environment
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4.6 What Other Structures Play Key Roles In Eurkaryotic Cells?
Cilia provide force parallel to the plasma membrane, which can be described as a “rowing” motion.
Fig. 4-10a
return stroke
cilia liningthe trachea
plasma membranepower stroke
(a) Cilium
propulsion of fluid
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4.6 What Other Structures Play Key Roles In Eurkaryotic Cells?
Flagella provide a force perpendicular to plasma membrane, like the engine on a motorboat.
flagellumof humansperm
continuous propulsion
direction of locomotion
(b) Flagellum
propulsion of fluid
Fig. 4-10b
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Copyright © 2009 Pearson Education Inc.
Evolution of Membrane-Enclosed Organelles
The first eukaryotes (cells that possess membrane-bound organelles) appeared about 1.7 billion years ago
Several organelles (mitochondria, chloroplasts, centrioles) may have arisen when primitive cells engulfed certain types of bacteria (the endosymbiont hypothesis)
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Evolution of Mitochondria
Anaerobic, predatory prokaryotic cell engulfs an aerobic bacterium that it failed to digest
Predatory cell and bacterium gradually enter into a symbiotic relationship
Descendants of engulfed bacterium evolve into mitochondria
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Copyright © 2009 Pearson Education Inc.
Evolution of Chloroplasts
Mitochondria-containing predatory prokaryotic cell engulf a photosynthetic bacterium
Predatory cell and bacterium gradually enter into a symbiotic relationship
Descendants of engulfed bacterium evolve into chloroplasts
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Copyright © 2009 Pearson Education Inc.
Evidence for Endosymbionts
Many biochemical features are shared by eukaryotic organelles and living bacteria
Mitochondria, chloroplasts, and centrioles contain their own supply of DNA
Living intermediates (modern cells that host bacterial endosymbionts)• Pelomyxa palustris harbors aerobic bacteria• Paramecium harbors photosynthetic bacteria
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