The Cell: The Basic Unit of Life All cells come from
preexisting cells and have certain processes, molecules, and
structures in common. Surrounded and separated from external
environment by a lipid bilayer membrane
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The Cell: The Basic Unit of Life Microscopes are needed to
visualize most cells Eggs notable exception Light or electron
microscopes allow observation of greater detail than light
microscopes do.
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Categories of Cells Eukaryotic membranous organelles nucleus,
ER, Golgi, vesicles, mitochondria, plastids cytoskeleton actin,
myosin, tubulin Prokaryotic circular chromosome no membranous
organelles
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Prokaryotic Cell Features Prokaryotic cell organization is
characteristic of the kingdoms Eubacteria and Archaebacteria.
Prokaryotic cells lack internal compartments. All prokaryotes have
plasma membrane nucleoid region with DNA cytoplasmic ribosomes Some
prokaryotes have cell wall outer membrane and capsule
photosynthetic membranes mesosomes.
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Prokaryotic Organelles Ribosome Large & small subunits 3
core molecules of RNA (rRNAs) and ~40 proteins 23S rRNA + 5S rRNA =
50S large ribosomal subunit 16S rRNA = 30S small ribosomal subunit
Assembles on mRNA Associates with tRNAs to decode mRNA and
synthesize proteins 23S rRNA molecule is catalytic component that
joins amino acids to for polypeptides
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Prokaryotic Cells Some prokaryotes have rotating flagella for
movement. Pili are projections by which prokaryotic cells attach to
one another or to environmental surfaces.
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The Cell: The Basic Unit of Life Eukaryotic cell organization
is characteristic of the other four kingdoms animalia, protista,
plantae, fungi. Eukaryotic cells have many membrane-enclosed
compartments, including a nucleus containing DNA.
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Animal Eukaryotic Cell Figure 4.7 Part 1 figure 04-07a.jpg
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Plant Eukaryotic Cell Figure 4.7 Part 2 figure 04-07b.jpg
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Eukaryotic Organelles - Nucleus Contains most of the cells DNA
Chromatin DNA bound by proteins Discrete units - chromosomes
Surrounded by nuclear envelope Double membrane system Pores Outer
membrane contiguous with ER Nucleolus Subdomain where transcription
rRNA and assembly of ribosomes occurs
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Eukaryotic Organelles - Endomembrane System The endomembrane
system groups together interrelated membranes and compartments.
Coordinated function to produce, process, and transport
materials
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Endoplasmic Reticulum Contiguous with the outer nuclear
membrane Rough endoplasmic reticulum Associated with ribosomes
synthesize proteins to be transported out of the cell or into other
cellular membranes Smooth endoplasmic reticulum Not associated with
ribosomes Location of lipids biosynthesis
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Golgi Apparatus Modifies proteins to be secreted or
incorporated into lysosomes/endosomes Proteins enter the Golgi in
vesicles from the ER Three subregions of Golgi cis, medial,
trans
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Golgi, Lysosomes & Endosomes Lysosomes Contain hydrolytic
enzymes to break down biomolecules into constitutive monomeric
units Endosomes Bud off from plasma membrane Contain materials to
be degraded or to be incorporated into the cell
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Mitochondria and Chloroplasts figure 04-14.jpg
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Energy Processing Organelles Mitochondria Enclosed by an outer
membrane and an inner membrane Inner membrane highly convoluted to
provide large surface area Cristae Contain enzymes that carry out
cellular respiration and generate ATP Chloroplasts Enclosed by an
outer membrane and an inner membrane 3 rd internal membrane system
thylakoid Contain pigments and enzymes that carry out
photosynthesis Generate ATP, NADPH, & O 2 Synthesize sugars
from ATP, NADPH & CO 2
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Organelles that Process Energy Mitochondria and chloroplasts
contain their own DNA and ribosomes and can make most of their own
tRNAs and some of their own proteins.
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Organelles that Process Energy The endosymbiont theory of the
evolutionary origin of mitochondria and chloroplasts originated
when large prokaryotes engulfed, but did not digest, smaller ones.
Mutual benefits permitted symbiotic relationship to evolve into
eukaryotic organelles of today. Mitochondria eubacterial origin
Chloroplast - cyanobacterium Chromosome Circular, intron-less genes
bacterial-like ribosomes Sensitivity to antibiotics, bacterial size
double membrane
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Other Membraneous Organelles Peroxisomes Glyoxysomes contain
special enzymes and carry out specialized chemical reactions inside
the cell. Vacuoles a membrane-enclosed compartment of water and
dissolved substances. They take in water and enlarge, providing
pressure to stretch the cell wall and structural support for a
plant.
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The Cytoskeleton The cytoskeleton within the cytoplasm of
eukaryotic cells provides shape, strength, and movement. It
consists of three major types of protein fibers.
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The Cytoskeleton Actin cytoskeleton Microfilaments consist of
two chains of actin units forming a double helix. Microfilaments
strengthen cellular structures and provide movement in animal cell
division, cytoplasmic streaming, and pseudopod extension. They
occur as individual, bundled, or networked fibers.
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The Cytoskeleton Intermediate filaments are formed of keratins
and add strength to cell attachments in multicellular
organisms.
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The Cytoskeleton - Microtubules Chains of dimers of the protein
tubulin, Cilia and flagella both have a characteristic 9 + 2
pattern of microtubules.
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The Cytoskeleton - Microtubules Movements of cilia and flagella
are due to binding of the motor protein dynein to microtubules.
Microtubules also bind motor proteins that move organelles through
the cell. Centrioles, made up of triplets of microtubules, are
involved in the distribution of chromosomes during nuclear
division.
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Extracellular Structures Materials external to the plasma
membrane provide protection, support, and attachment for cells in
multicellular systems. Cell walls of plants consist principally of
cellulose. They are pierced by plasmodesmata that join the
cytoplasm of adjacent cells In multicellular animals, the
extracellular matrix consists of different proteins many of which
are proteoglycans. Collagen - bone and cartilage Fibronectin basal
membranes of epithelia Laminin
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CHAPTER 5 Cellular Membranes
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Membrane Composition and Structure Biological membranes consist
of lipids, proteins, and carbohydrates. fluid mosaic model
describes a phospholipid bilayer in which membrane proteins move
laterally within the membrane.
Membrane Composition and Structure Membrane Proteins Integral
membrane proteins are inserted into the phospholipid bilayer.
Peripheral proteins attach to its surface by ionic bonds, H-bonds,
and/or polar interactions.
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Membrane Composition and Structure The two surfaces of a
membrane can have different properties due to different
phospholipid compositions, exposed domains of integral membrane
proteins, and peripheral membrane proteins. Defined regions (rafts)
of a plasma membrane may have different membrane proteins. Proteins
projecting from the external surface of the plasma membrane
function in communication & recognition signals between
cells.
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Cell Adhesion Cells recognize and bind to each other by means
of membrane proteins protruding from the cell surface.
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Cell Adhesion - Categories of Adhesive Junctions Tight
junctions prevent passage of molecules around cells define
functional regions of the plasma membrane ZO-1, actin cytoskeleton
Desmosomes Allow strong adhesion between cells Desmin, intermediate
filaments Adherins Junctions Allow strong, but reversible adhesion
between cells of the same type Cadherin, catenins, actin
cytoskeleton Focal Adhesions Allow temporary attachment to ECM for
motility Integrins, actin cytoskeleton Gap junctions provide
channels for chemical and electrical communication between cells
Connexins
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5.6 Part 1 Figure 5.6 Part 1 figure 05-06a.jpg Adherins
junction similar to desmosome Tight junction Desmosome
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5.6 Part 2 Figure 5.6 Part 2 figure 05-06b.jpg Focal
adhesions
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Transmembrane Movement of Substances table 05-01.jpg
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Passive Processes of Membrane Transport Two types of passive
movement unaided diffusion through the lipid bilayer, facilitated
diffusion through protein channels, or by means of a carrier
protein Solutes diffuse across a membrane from a region of greater
solute concentration to a region of lesser concentration.
Equilibrium is when the concentrations are equal The rate of
diffusion of a solute across a membrane is directly proportional to
the concentration gradient across the membrane. For unaided
diffusion to occur requires lipid solubility
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Passive Processes of Membrane Transport Osmosis Diffusion of
water Osmosis occurs when the solutes on either side of a membrane
can not pass through the membrane H 2 O is slightly lipid soluble H
2 O passes through membrane toward equilibrium
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Passive Processes of Membrane Transport Tonicity Relative
concentrations of two solutions Hypo lower [solute] relative to
some solution Hyper higher [solute] relative to some solution Iso
equal [solute] relative to some solution Often tonicity of solution
is relative to tonicity of cell For a cell: hypotonic solutions -
cells tend to take up water hypertonic solutions cells tend to lose
water isotonic equal rate of water movement (dynamic
equilibrium)
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5.8 Figure 5.8 figure 05-08.jpg
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Passive Processes of Membrane Transport The cell walls of
plants and some other organisms prevent cells from bursting under
hypotonic conditions. Turgor pressure develops under these
conditions and keeps plants upright and stretches the cell wall
during cell growth.
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Passive Processes of Membrane Transport Channel proteins
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Passive Processes of Membrane Transport Carrier proteins figure
05-10.jpg
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Active Transport Active transport means that energy is required
to move substances across a membrane Any movement against a
concentration gradient will require active transport Energy sources
ATP Counter gradient
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Active Transport Active transport requires integral membrane
proteins Active transport proteins uniports, symports,
antiports
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Primary Active Transport Energy from the hydrolysis of ATP
Binding of ATP alters protein configuration allowing binding to
substrate on one side of membrane Hydrolysis of ATP is possible
after substrate bound Hydrolysis of ATP alters configuration of
protein to release substrate on opposite side of membrane
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Secondary Active Transport Couples the passive movement of one
solute down its concentration gradient to the movement of another
solute up its concentration gradient. Energy from ATP is used
indirectly to establish the concentration gradient of the counter
gradient resulting in movement of the first solute.
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Endocytosis and Exocytosis Endocytosis transports
macromolecules, large particles, and small cells into eukaryotic
cells by means of engulfment and vesicle formation from the plasma
membrane. Exocytosis materials in vesicles are secreted from the
cell when vesicles fuse with the plasma membrane. In
receptor-mediated endocytosis, a specific membrane receptor binds
to a particular macromolecule
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Other Membranes Functions Sites for recognition and processing
of extracellular signals, Sites for energy transformations, Sites
for organizing chemical reactions.
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Membranes Are Dynamic Although not all cellular membranes are
identical, ordered modifications in membrane composition accompany
the conversions of one type of membrane into another type.