1 chapter 4 general features of cells prepared by brenda leady, university of toledo
TRANSCRIPT
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Cell theory
1. All living things are composed of one or more cells
2. Cells are the smallest units of living organisms
3. New cells come only from pre-existing cells by cell division
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Microscopy
MagnificationRatio between the size of an image produced
by a microscope and its actual size Resolution
Ability to observe two adjacent objects as distinct from one another
ContrastCan be enhanced using dyes
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Light microscopeUses light for illuminationResolution 0.2 µm
Electron microscopeUses an electron beamResolution 2 nm
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Electron microscopes
Transmission electron microscopy (TEM)Thin slices stained with heavy metalsSome electrons are scattered while others
pass through to form an image Scanning electron microscopy (SEM)
Sample coated with heavy metalBeam scans surface to make 3D image
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Prokaryotic cells
Simple cell structure Lack a membrane-enclosed nucleus 2 categories- bacteria and archaea
Both smallBacteria- abundant, most not harmfulArchaea- less common, often found in
extreme environments
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Typical bacterial cell
Plasma membrane- barrier Cytoplasm- contained inside plasma
membrane Nucleoid- region where genetic material
found Ribosomes- involved in protein synthesis
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Many structures are located outside the plasma membraneCell wall- support and protectionGlycocalyx- traps water, protectionAppendages- pilli (attachment), flagella
(locomotion)
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Eukaryotic cells DNA housed inside nucleus Eukaryotic cells exhibit compartmentalization Organelle- subcellular structure or membrane-
bounded compartment with its own unique structure and function
Shape, size, and organization of cells vary considerably among different species and even among different cell types of the same species
The Proteome Determines the Characteristics of a Cell How does a single organism produce different types
of cells? Identical DNA in different cells but different proteomes The proteome of a cell determines its structure and
function Gene regulation, amount of protein, amino acid
sequence of a particular protein and protein modification can influence a cell’s proteome
Proteomes in healthy cells are different from the proteomes of cancerous cells
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Cytosol
Region of a eukaryotic cell that is outside the cell organelles but inside the plasma membrane
Cytoplasm includes everything inside the plasma membraneCytosol, the endomembrane system and the
semiautonomous organelles
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Metabolism
Cytosol is central coordinating region for many metabolic activities of eukaryotic cells
Catabolism- breakdown of a molecule into smaller components
Anabolism- synthesis of cellular molecules and macromolecules
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Translation
Process of polypeptide synthesis Information within a gene is ultimately
translated into the sequence of amino acids in a polypeptide
Ribosome- site of synthesis Transfer RNA (tRNA)- brings amino acids Messenger RNA (mRNA)- information to make
a polypeptide
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Cytoskeleton
Network of three different types of protein filaments Microtubules
Dynamic instability Centrosome or microtubule-organizing center in animals
Intermediate filaments Tend to be more stable than microtubules and actin
filaments, which readily polymerize and depolymerize Actin filaments
Also known as microfilaments
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Motor Proteins Category of cellular proteins that use ATP as a source of
energy to promote movement Three domains called the head, hinge, and tail Walking analogy
Ground is a cytoskeletal filament, your leg is the head of the motor protein, and your hip is the hinge
Three different kinds of movements Motor protein moves the cargo from one location to another Motor protein can remain in place and cause the filament to move Motor protein attempting to walk (both the motor protein and
filament restricted in their movement) exerts a force that causes the filament to bend
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Flagella and cilia
Flagella usually longer than cilia and present singly or in pairs
Cilia are often shorter than flagella and tend to cover all or part of the surface of a cell
Share the same internal structure Microtubules, dynein, and axoneme Movement involves the propagation of a
bend, which begins at the base of the structure and proceeds toward the tip
Sheetz and Spudich Show That Myosin Walks Along Actin Filaments Early researchers proposed the sliding-filament model
based on work with living cells in vivo 1983, Michael Sheetz and James Spudich devised an
approach to study myosin in vitro Nitella cells were used as a source of actin filaments Myosin was purified and attached to a fluorescently
labeled bead Confirmed that myosin is a motor protein that uses ATP
to walk along actin filaments All that is needed for movement are actin, myosin, and ATP
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Endomembrane system
Network of membranes enclosing the nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles
Also includes plasma membrane May be directly connected to each other or
pass materials via vesicles
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Nuclear envelope
Double-membrane structure enclosing nucleus
Outer membrane of the nuclear envelope is continuous with the endoplasmic reticulum membrane
Nuclear pores provide passageways Materials within the nucleus are not part of
the endomembrane system
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Nucleus
ChromosomesComposed of DNA and proteinChromatin
Primary function involves the protection, organization, and expression of the genetic material
Ribosome assembly occurs in the nucleolus
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Endoplasmic reticulum
Network of membranes that form flattened, fluid-filled tubules or cisternae
ER membrane encloses a single compartment called the ER lumen
Rough endoplasmic reticulum (rough ER) Studded with ribosomes Involved in protein synthesis and sorting
Smooth endoplasmic reticulum (smooth ER) Lacks ribosomes Detoxification, carbohydrate metabolism, calcium balance,
synthesis and modification of lipids
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Golgi apparatus
Also called the Golgi body, Golgi complex, or simply Golgi
Stack of flattened, membrane-bounded compartments, which are not continuous with the ER
Vesicles transport materials between stacks Three overlapping functions
Secretion, processing, and protein sorting
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Lysosomes Contain acid hydrolases that perform
hydrolysis Many different types of acid hydrolases to
break down proteins, carbohydrates, nucleic acids, and lipids
AutophagyRecycling of worn-out organelles through
endocytosis
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Vacuoles
Functions of vacuoles are extremely varied, and they differ among cell types and even environmental conditions
Central vacuoles in plants for storage and support
Contractile vacuoles in protists for expelling excess water
Phagocytic vacuoles in protists and white blood cells for degradation
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Plasma membrane
Boundary between the cell and the extracellular environment
Membrane transport in and out of cellSelectively permeable
Cell signaling using receptors Cell adhesion
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Semiautonomous organelles
Can grow and divide to reproduce themselves, but they are not completely autonomous because they depend on other parts of the cell for their internal components
Mitochondria, chloroplasts, and peroxisomes
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Mitochondria
Outer and inner membrane Intermembrane space and mitochondrial matrix
Primary role is to make ATP Also involved in the synthesis, modification,
and breakdown of several types of cellular molecules
Can also generate heat in brown fat cells
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Chloroplasts Photosynthesis
capture light energy and use some of that energy to synthesize organic molecules such as glucose
Found in nearly all species of plants and algae
Outer and inner membrane with an intermembrane space
Third membrane, the thylakoid membrane, forms flattened tubules that stack to form a granum (plural, grana)
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Peroxisomes
Relatively small organelles found in all eukaryotic cells
Origin remains controversial General function to catalyze certain chemical
reactions, typically those that break down molecules by removing hydrogen or adding oxygen
Reaction by-product is hydrogen peroxide (H2O2) Catalase breaks down H2O2 without forming
dangerous free radicals