cell structure and biology advanced placement biology chapter 6 mr. knowles liberty senior high...
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Cell Structure and Biology
Advanced Placement Biology
Chapter 6
Mr. Knowles
Liberty Senior High School
History of the Cell• 1665- Robert Hooke described
cork as composed of cellulae (cell).• A few years later-Anton van
Leeuwenhoek described live cells.• 1838 and 1839- Schleiden and
Schwann developed the cell theory.
Schleiden and Schwann- Cell Theory
• All organisms are composed of cells or at least one.
• Cells are the smallest unit of life (a collection of metabolic processes + heredity).
• All cells come from other cells. None spontaneously arise.
• Different types of microscopes– Can be used to visualize different sized
cellular structures
Una
ide
d e
ye
1 m
0.1 nm
10 m
0.1 m
1 cm
1 mm
100 µm
10 µ m
1 µ m
100 nm
10 nm
1 nm
Length of somenerve and muscle cells
Chicken egg
Frog egg
Most plant and Animal cells
Smallest bacteria
Viruses
Ribosomes
Proteins
Lipids
Small molecules
Atoms
NucleusMost bacteriaMitochondrion
Lig
ht m
icro
sco
pe
Ele
ctro
n m
icro
sco
pe
Ele
ctro
n m
icro
sco
pe
Figure 6.2
Human height
Measurements1 centimeter (cm) = 102 meter (m) = 0.4 inch1 millimeter (mm) = 10–3 m1 micrometer (µm) = 10–3 mm = 10–6 m1 nanometer (nm) = 10–3 mm = 10–9 m
Use different methods for enhancing visualization of cellular structures
TECHNIQUE RESULT
Brightfield (unstained specimen). Passes light directly through specimen. Unless cell is naturally pigmented or artificially stained, image has little contrast. [Parts (a)–(d) show a human cheek epithelial cell.]
(a)
Brightfield (stained specimen). Staining with various dyes enhances contrast, but most staining procedures require that cells be fixed (preserved).
(b)
Phase-contrast. Enhances contrast in unstained cells by amplifying variations in density within specimen; especially useful for examining living, unpigmented cells.
(c)
50 µm
Figure 6.3
Differential-interference-contrast (Nomarski). Like phase-contrast microscopy, it uses optical modifications to exaggerate differences indensity, making the image appear almost 3D.
Fluorescence. Shows the locations of specific molecules in the cell by tagging the molecules with fluorescent dyes or antibodies. These fluorescent substances absorb ultraviolet radiation and emit visible light, as shown here in a cell from an artery.
Confocal. Uses lasers and special optics for “optical sectioning” of fluorescently-stained specimens. Only a single plane of focus is illuminated; out-of-focus fluorescence above and below the plane is subtracted by a computer. A sharp image results, as seen in stained nervous tissue (top), where nerve cells are green, support cells are red, and regions of overlap are yellow. A standard fluorescence micrograph (bottom) of this relatively thick tissue is blurry.
50 µm
50 µm
(d)
(e)
(f)
• The scanning electron microscope (SEM)
– Provides for detailed study of the surface of a specimen
TECHNIQUE RESULTS
Scanning electron micro-scopy (SEM). Micrographs takenwith a scanning electron micro-scope show a 3D image of the surface of a specimen. This SEM shows the surface of a cell from a rabbit trachea (windpipe) covered with motile organelles called cilia. Beating of the cilia helps moveinhaled debris upward toward the throat.
(a)
Cilia
1 µm
Figure 6.4 (a)
• The transmission electron microscope (TEM)
– Provides for detailed study of the internal ultrastructure of cells
Transmission electron micro-scopy (TEM). A transmission electron microscope profiles a thin section of a specimen. Here we see a section through a tracheal cell, revealing its ultrastructure. In preparing the TEM, some cilia were cut along their lengths, creating longitudinal sections, while other cilia were cut straight across, creating cross sections.
(b)
Longitudinalsection ofcilium
Cross sectionof cilium
1 µm
Figure 6.4 (b)
Cell fractionation is used to isolate(fractionate) cell components, based on size and density.
First, cells are homogenized in a blender tobreak them up. The resulting mixture (cell homogenate) is thencentrifuged at various speeds and durations to fractionate the cellcomponents, forming a series of pellets.
• The process of cell fractionation
APPLICATION
TECHNIQUE
Figure 6.5
Tissuecells
Homogenization
Homogenate1000 g(1000 times theforce of gravity)
10 min Differential centrifugation
Supernatant pouredinto next tube
20,000 g20 min
Pellet rich innuclei andcellular debris
Pellet rich inmitochondria(and chloro-plasts if cellsare from a plant) Pellet rich in
“microsomes”(pieces of plasma mem-branes andcells’ internalmembranes)
Pellet rich inribosomes
150,000 g3 hr
80,000 g60 min
Figure 6.5
• A smaller cell– Has a higher surface to volume ratio, which
facilitates the exchange of materials into and out of the cell
Surface area increases whiletotal volume remains constant
5
1
1
Total surface area (height width number of sides number of boxes)
Total volume (height width length number of boxes)
Surface-to-volume ratio (surface area volume)
6
1
6
150
125
12
750
125
6
Figure 6.7
(b) A thin section through the bacterium Bacillus coagulans (TEM)
Pili: attachment structures onthe surface of some prokaryotes
Nucleoid: region where thecell’s DNA is located (notenclosed by a membrane)
Ribosomes: organelles thatsynthesize proteins
Plasma membrane: membraneenclosing the cytoplasm
Cell wall: rigid structure outsidethe plasma membrane
Capsule: jelly-like outer coatingof many prokaryotes
Flagella: locomotionorganelles ofsome bacteria
(a) A typical rod-shaped bacterium
0.5 µmBacterial
chromosome
Figure 6.6 A, B
Prokaryote vs. Eukaryote• Archaebacteria and Eubacteria.• Lack membrane-bound
organelles.• DNA in a nucleoid region.• Have plasma membrane.• Cell wall of peptidoglycan.• Use 70S ribosome.• Unique flagella-flagellin
protein.
• Animalia, Plantae, Protista, Fungi.
• Have true membrane-bound organelles.
• DNA in a nucleus.• Have plasma membrane.• Plants and some protists have
a cell wall of cellulose.• Use different ribosomes.
• A animal cell:
Rough ER Smooth ER
Centrosome
CYTOSKELETON
Microfilaments
Microtubules
Microvilli
Peroxisome
Lysosome
Golgi apparatus
Ribosomes
In animal cells but not plant cells:LysosomesCentriolesFlagella (in some plant sperm)
Nucleolus
Chromatin
NUCLEUS
Flagelium
Intermediate filaments
ENDOPLASMIC RETICULUM (ER)
Mitochondrion
Nuclear envelope
Plasma membrane
Figure 6.9
• A plant cell:
In plant cells but not animal cells:ChloroplastsCentral vacuole and tonoplastCell wallPlasmodesmata
CYTOSKELETON
Ribosomes (small brwon dots)
Central vacuole
Microfilaments
Intermediate filaments
Microtubules
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
ChromatinNUCLEUS
Nuclear envelope
Nucleolus
Chloroplast
PlasmodesmataWall of adjacent cell
Cell wall
Golgi apparatus
Peroxisome
Tonoplast
Centrosome
Plasma membrane
Mitochondrion
Figure 6.9
• 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
What is the function of organelles?
• To compartmentalize chemical reactions that may proceed simultaneously.
• To provide membranes on which to catalyze reactions.
Nuclear Envelope– Encloses the nucleus, separating its contents from the
cytoplasm
Figure 6.10
Nucleus
NucleusNucleolus
Chromatin
Nuclear envelope:Inner membrane
Outer membrane
Nuclear pore
Rough ER
Porecomplex
Surface of nuclear envelope.
Pore complexes (TEM). Nuclear lamina (TEM).
Close-up of nuclearenvelope
Ribosome
1 µm
1 µm
0.25 µm
1. The Nucleus• Largest organelle, centralized in animal cells.• Stores and protects the cell’s genetic
information.• Surrounded by two phospholipid bilayer
membranes-nuclear envelope.• Where both layers are fused - nuclear pores
+ transport protein.
A REAL Fantastic Voyage to the Nucleus!
The Nucleolus• Site within the nucleus of ribosomal
subunits are manufactured- rRNA + ribosomal proteins.
• Ribosomes leave the nucleus as subunits through the nuclear pore and are later reassembled.
• May be free (in the cytoplasm) or attached to the ER (rough ER).
– Carry out protein synthesis
ER
Ribosomes Cytosol
Free ribosomes
Bound ribosomes
Largesubunit
Smallsubunit
TEM showing ER and ribosomes Diagram of a ribosome
0.5 µm
Figure 6.11
Endoplasmic Reticulum (ER)
Endoplasmic Reticulum (ER)• Means “little net within the cytoplasm”• Internal membrane system with a lipid
bilayer + proteins.• Weaved in sheets- forming channels.• Outer membrane of the nuclear envelope is
continuous with the ER membrane.• Some regions have embedded ribosomes.
The ER Membrane– Is continuous with the nuclear envelope
Smooth ER
Rough ER
ER lumen
Cisternae
RibosomesTransport vesicle
Smooth ER
Transitional ER
Rough ER 200 µm
Nuclearenvelope
Figure 6.12
Two Types of (ER)1. Rough ER: heavily studded with ribosomes-
protein synthesis. Proteins have signal sequences which direct to a docking site on the surface of the ER.
2. Smooth ER: lack ribosomes; have enzymes embedded in membrane for carbohydrate and lipid synthesis.
3. Both secrete finished products in transport vesicles.
Functions of Smooth ER
The smooth ER:
–Synthesizes lipids
–Metabolizes carbohydrates
–Stores calcium
–Detoxifies poison
The Golgi Complex• Flattened stacks of membranes in
the cytoplasm-cisternae.• Collection, packaging and
distribution of proteins and lipids.• Transport vesicles from RER and
SER fuse with the Golgi membrane.
Golgiapparatus
TEM of Golgi apparatus
cis face(“receiving” side ofGolgi apparatus)
Vesicles movefrom ER to Golgi Vesicles also
transport certainproteins back to ER
Vesicles coalesce toform new cis Golgi cisternae
Cisternalmaturation:Golgi cisternaemove in a cis-to-transdirection
Vesicles form andleave Golgi, carryingspecific proteins toother locations or tothe plasma mem-brane for secretion
Vesicles transport specificproteins backward to newerGolgi cisternae
Cisternae
trans face(“shipping” side ofGolgi apparatus)
0.1 0 µm16
5
2
3
4
Functions of the Golgi Apparatus
Figure 6.13
The Golgi Complex• Proteins (from RER) may have short sugar chains
added--> glycoproteins.• Lipids (from SER) may have short sugar chains
added-->glycolipids.• Both collect at flattened ends-cisternae.• Cisternae membranes pinch off the glycoproteins and
glycolipids into secretory vesicles (liposomes).• Liposomes may fuse with plasma membane or
organelle membranes.
Lysosomes carry out intracellular digestion by
– Phagocytosis
Figure 6.14 A(a) Phagocytosis: lysosome digesting food
1 µm
Lysosome containsactive hydrolyticenzymes
Food vacuole fuses with lysosome
Hydrolyticenzymes digestfood particles
Digestion
Food vacuole
Plasma membraneLysosome
Digestiveenzymes
Lysosome
Nucleus
Lysosomes• Membrane-bound organelle with digestive
enzymes.• Breakdown protein, nucleic acid, carbos,
lipids.• Digest old organelles and invading bacterial
cells.• Digestive enzymes only active at low pH.
Autophagy
Figure 6.14 B (b) Autophagy: lysosome breaking down damaged organelle
Lysosome containingtwo damaged organelles 1 µ m
Mitochondrionfragment
Peroxisomefragment
Lysosome fuses withvesicle containingdamaged organelle
Hydrolytic enzymesdigest organellecomponents
Vesicle containingdamaged mitochondrion
Digestion
Lysosome
Lysosomes• Inactive lysosomes-Primary Lysosomes, high
pH, enzymes are inactive.• Once fused with food vacuole- pump H+ into
compartment- active, Secondary Lysosomes.• Involved in normal cell death and programmed
cell death (apoptosis).• Ex. Tadpole tail tissue; webbing between human
fingers.
Peroxisomes: Oxidation• Peroxisomes:
– Produce hydrogen peroxide and convert it to water.
Chloroplast
Peroxisome
Mitochondrion
1 µmFigure 6.19
Plasma membrane expandsby fusion of vesicles; proteinsare secreted from cell
Transport vesicle carriesproteins to plasma membrane for secretion
Lysosome availablefor fusion with anothervesicle for digestion
4 5 6
Nuclear envelope isconnected to rough ER, which is also continuous
with smooth ER
Nucleus
Rough ER
Smooth ERcis Golgi
trans Golgi
Membranes and proteinsproduced by the ER flow in
the form of transport vesiclesto the Golgi
Nuclear envelop
Golgi pinches off transport Vesicles and other vesicles
that give rise to lysosomes and Vacuoles
1
3
2
Plasmamembrane
Relationships among organelles of the endomembrane system
Figure 6.16
Mitochondrion (ia)• Rod-shaped organelle, 1-3 micrometers long.• Bounded by two membranes- outer is smooth;
inner is folded into continuous layers-cristae.• Two compartments- matrix-inside the inner
membrane and intermembrane space between the two membranes.
• Enzymes for oxidative metabolism are embedded in the inner membrane.
Mitochondria are enclosed by two membranes– A smooth outer membrane– An inner membrane folded into cristae
Mitochondrion
Intermembrane space
Outermembrane
Freeribosomesin the mitochondrialmatrix
MitochondrialDNA
Innermembrane
Cristae
Matrix
100 µmFigure 6.17
Mitochondria• Contain a circular piece of DNA for many of
the proteins in oxidative metabolism.• Also has its own rRNA and ribosomal
proteins--> own protein synthesis.• Involved in its own replication.• Circular DNA? Two membranes? Own Genes?
Own replication?• What does that sound like?
Chloroplasts– Are found in leaves and other green organs of
plants and in algae.
Chloroplast
ChloroplastDNA
Ribosomes
Stroma
Inner and outermembranes
Thylakoid
1 µm
Granum
Figure 6.18
Chloroplasts• Algae and plants have organelles for photosynthesis.• Two membranes- outer and inner membranes.• A closed, stacked network of membranes-granum
(a).• Fluid-filled space around grana-stroma.• Disc-shaped structures-thylakoids.• Light-capturing enzymes are embedded on
thylakoids.
Chloroplasts• Have DNA which encode many enzymes
necessary for photosynthesis.• Do all plant cells have chloroplasts?• May lose internal structure-leucoplasts.• A leucoplast that stores starch-amyloplast.
Found in root cells.• A leucoplast that stores other pigments-
chromoplasts.
Centriole• Barrel-shaped organelles in animals and
protists, NOT plants.
• Usually found in pairs around the nuclear membrane.
• Hollow cylinders made of microtubules (protein). Have their own DNA.
• Help move chromosome during cell division.
Some Other Organelles
• Central Vacuole or Tonoplast: in plants, for protein, water, and waste storage.
• Vesicles: in animals, usually smaller sacs used for storage and transport of materials.
Central Vacuoles– Are found in plant cells– Hold reserves of important organic
compounds and water
Central vacuole
Cytosol
Tonoplast
Centralvacuole
Nucleus
Cell wall
Chloroplast
5 µmFigure 6.15
Cytoskeleton– Is a network of fibers extending throughout the
cytoplasmMicrotubule
0.25 µm MicrofilamentsFigure 6.20
Actin Filaments• Made of globular protein
monomers- actin• Actin monomers polymerize to
form actin filaments• Filaments are connected to
proteins within the plasma membrane.
Actin Filaments
• Actin filaments are thinner, cause cellular movements like ameboid movements, cell pinching during division.
• Provide shape for the cell.
Actin that function in cellular motility– Contain the protein myosin in addition to actin
Actin filament
Myosin filament
Myosin motors in muscle cell contraction. (a)
Muscle cell
Myosin arm
Figure 6.27 A
Amoeboid Movement– Involves the contraction of actin and myosin
filamentsCortex (outer cytoplasm):gel with actin network
Inner cytoplasm: sol with actin subunits
Extendingpseudopodium
(b) Amoeboid movementFigure 6.27 B
Cytoplasmic Streaming– Is another form of locomotion created by
microfilamentsNonmovingcytoplasm (gel)
Chloroplast
Streamingcytoplasm(sol)
Parallel actinfilaments
Cell wall
(b) Cytoplasmic streaming in plant cellsFigure 6.27 C
So you want to see some actin in action?
Microtubules• 2 globular monomers- tubulin and
tubulin polymerize to form 13 protofilaments
• Filaments form wide, hollow tubes- microtubules.
• Form from nucleation centers (near nucleus) and radiate out.
Microtubules• Constantly polymerize and
depolymerize- GTP-binding at ends.
• Ends are + (away from center) or - (toward center).
• Cellular movements and intracellular movement of materials and organelles.
Microtubules• Use specialized motor proteins to
move organelles along the microtubule.
• Kinesins- move organelles toward the + end (toward cell periphery)
• Dyneins- move them toward the - end (toward the center of cell)
Intermediate Filaments
• Most durable protein filament- tough fibrous filaments of overlapping tetramers of protein (rope-like).
• Between actin and microtubules in size. Stable
• Ex. of Fibers- vimentin and keratin
Intermediate Filaments
• Anchored to proteins embedded into plasma membrane.
• Provide mechanical support to cell.
Structural Support…that’s what I’m talking about!
Plant Cell Walls– Are made of cellulose fibers embedded in other
polysaccharides and protein– May have multiple layers
Central vacuoleof cell
Plasmamembrane
Secondarycell wall
Primarycell wall
Middlelamella
1 µm
Centralvacuoleof cell
Central vacuole
Cytosol
Plasma membrane
Plant cell walls
PlasmodesmataFigure 6.28
Plants: Plasmodesmata• Plasmodesmata
– Are channels that perforate plant cell walls
Interiorof cell
Interiorof cell
0.5 µm Plasmodesmata Plasma membranes
Cell walls
Figure 6.30
The Extracellular Matrix (ECM) of Animal Cells
• Animal cells– Lack cell walls– Are covered by an elaborate matrix, the ECM
The ECM– Is made up of glycoproteins and other
macromolecules
Collagen
Fibronectin
Plasmamembrane
EXTRACELLULAR FLUID
Micro-filaments
CYTOPLASM
Integrins
Polysaccharidemolecule
Carbo-hydrates
Proteoglycanmolecule
Coreprotein
Integrin
Figure 6.29
A proteoglycan complex
Types of Intercellular Junctions in animals
Tight junctions prevent fluid from moving across a layer of cells
Tight junction
0.5 µm
1 µm
Spacebetweencells
Plasma membranesof adjacent cells
Extracellularmatrix
Gap junction
Tight junctions
0.1 µm
Intermediatefilaments
Desmosome
Gapjunctions
At tight junctions, the membranes ofneighboring cells are very tightly pressedagainst each other, bound together byspecific proteins (purple). Forming continu-ous seals around the cells, tight junctionsprevent leakage of extracellular fluid acrossA layer of epithelial cells.
Desmosomes (also called anchoringjunctions) function like rivets, fastening cellsTogether into strong sheets. IntermediateFilaments made of sturdy keratin proteinsAnchor desmosomes in the cytoplasm.
Gap junctions (also called communicatingjunctions) provide cytoplasmic channels fromone cell to an adjacent cell. Gap junctions consist of special membrane proteins that surround a pore through which ions, sugars,amino acids, and other small molecules maypass. Gap junctions are necessary for commu-nication between cells in many types of tissues,including heart muscle and animal embryos.
TIGHT JUNCTIONS
DESMOSOMES
GAP JUNCTIONS
Figure 6.31