Download CHAPTER 4 The Organization of Cells

CHAPTER 4
The Organization of Cells
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
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.
Categories of Cells
 Eukaryotic
 membranous organelles
• nucleus, ER, Golgi,
vesicles, mitochondria,
plastids
 cytoskeleton
• actin, myosin, tubulin
 Prokaryotic
 circular chromosome
 no membranous organelles
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.
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
Prokaryotic Cells
• Some prokaryotes have rotating flagella for movement.
• Pili are projections by which prokaryotic cells attach to one
another or to environmental surfaces.
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.
Animal Eukaryotic Cell
Figure 4.7 – Part 1
figure 04-07a.jpg
Plant Eukaryotic Cell
figure 04-07b.jpg
Figure 4.7 – Part 2
Eukaryotic Organelles - Nucleus
• Contains most of the cell’s
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
Eukaryotic Organelles - Endomembrane System
• The endomembrane system groups together
interrelated membranes and compartments.
• Coordinated function to produce, process, and
transport materials
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
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
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
Mitochondria and Chloroplasts
figure 04-14.jpg
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
3rd internal membrane system – thylakoid
Contain pigments and enzymes that carry out photosynthesis
Generate ATP, NADPH, & O2
Synthesize sugars from ATP, NADPH & CO2
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.
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
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.
The Cytoskeleton
• The cytoskeleton within the cytoplasm of eukaryotic cells provides
shape, strength, and movement. It consists of three major types of
protein fibers.
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.
The Cytoskeleton
• Intermediate filaments are formed of keratins
and add strength to cell attachments in
multicellular organisms.
The Cytoskeleton - Microtubules
• Chains of dimers of
the protein tubulin,
• Cilia and flagella
both have a
characteristic 9 + 2
pattern of
microtubules.
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.
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
CHAPTER 5
Cellular Membranes
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.
Lipid Bilayer Structure
figure 05-02.jpg
Figure 5.2
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.
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.
Cell Adhesion
• Cells recognize and bind to each other by means
of membrane proteins protruding from the cell
surface.
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
figure 05-06a.jpg
Tight junction
Desmosome
5.6 – Part 1
Figure 5.6 – Part 1
Adherins junction similar to desmosome
figure 05-06b.jpg
5.6 – Part 2
Focal adhesions
Figure 5.6 – Part 2
Transmembrane Movement of
Substances
table 05-01.jpg
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
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
• H2O is slightly lipid soluble
• H2O passes through membrane toward
equilibrium
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)
figure 05-08.jpg
5.8
Figure 5.8
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.
Passive Processes of Membrane Transport
• Channel proteins
Passive Processes of Membrane
Transport
 Carrier proteins
figure 05-10.jpg
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
Active Transport
• Active transport requires integral membrane
proteins
• Active transport proteins
• uniports,
• symports,
• antiports
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
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.
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
Other Membranes Functions
• Sites for recognition and processing of
extracellular signals,
• Sites for energy transformations,
• Sites for organizing chemical reactions.
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.