NOTES: CH 6 – A Tour Of The Cell
Overview: The Importance of Cells
● All organisms
● The cell is the simplest collection of matter
● Cell structure is correlated to
● All cells are related by their
6.1 – Biologists use microscopes and the tools of biochemistry to study cells
MICROSCOPES
1) Light Microscope:
2) Electron Microscope (1950’s)
 Transmission Electron Microscope
 Scanning Electron Microscope
Light Microscope
 works by passing visible light through a thin section of specimen and then through glass lenses
 resolving power = 0.2 µm (size of small bacteria)

Electron Microscope (1950’s)
 uses electron beams which have shorter wavelengths of light
 resolving power = 0.2 nm (most cell structures)

1) Transmission Electron Microscope
- electrons transmitted through specimen are focused and image is magnified using electromagnets
2) Scanning Electron Microscope
- electron beam scans the surface of a specimen
**Disadvantages to EM:
 can only view dead cells (elaborate preparation)
 very expensive
WE CAN ALSO STUDY CELLS BY...
 Cell Fractionation =
 Centrifugation = spinning mixtures of cells and their parts at very high speeds; separates the components
6.2 – Eukaryotic cells have internal membranes that compartmentalize their functions
Types of CELLS:
● The basic structural and functional unit of every organism is one of two types of cells:
● Only organisms of the domains Bacteria and Archaea consist of prokaryotic cells
● Protists, fungi, animals, and plants all consist of eukaryotic cells (& are in the domain Eukarya)
ALL CELLS:
●
● have cytoplasm / cytosol
●
●
(make proteins)
material (DNA / chromatin / chromosomes)
CELLS CAN BE CLASSIFIED AS:
1) PROKARYOTES

(3.5 billion years)
2) EUKARYOTES
 “newer” cells (1.5 billion years)


.
.
 lack nucleus & membrane-bound organelles
 have a “
 genetic material in a single, circular molecule (PLASMID) in
region called NUCLEOID
 genetic material organized into CHROMOSOMES in
NUCLEUS


.
 Domains Bacteria and Archaea
”
& membrane-bound organelles
.
 Domain Eukarya, includes Kingdoms Protista, Fungi,
Plantae, Animalia
● although eukaryotic cells are larger than prokaryotes, there is a limit on cell size due to the logistics of carrying out cellular
metabolism
PLASMA MEMBRANE: the boundary of every cell
● The plasma membrane is a
nutrients, and waste to service the volume of the cell
● The general structure of a biological membrane is a
that allows sufficient passage of oxygen,
A Panoramic View of the Eukaryotic Cell:
● A eukaryotic cell has internal membranes that partition the cell into organelles
● Plant and animal cells have most of the same organelles
6.3 - The eukaryotic cell’s genetic instructions are housed in the NUCLEUS and carried out by the
ribosomes
● the nucleus contains most of the DNA in a eukaryotic cell
● ribosomes use the information from the DNA
The Nucleus: Genetic Library of the Cell
● the nucleus contains most of the cell’s genes and is usually the most conspicuous organelle
● the
encloses the nucleus, separating it from the cytoplasm
● houses the information / instructions for
…the “control center” of the cell
● averages
NUCLEAR ENVELOPE

- each of the 2 membranes is a phospholipid bilayer w/specific proteins
- is perforated by pores which regulate molecular traffic into and out of the nucleus
- RNA and proteins enter or leave the nucleus through these pores
- breaks down prior to cell division
CHROMATIN
 fibrous, threadlike complex of
CHROMOSOMES

 visible under microscope;
 form just prior to cell division;
 human cells have
NUCLEOLUS
 dense, spherical region in the nucleus
- visible when cell is NOT dividing
- may be 2 or more per cell
which make up chromosomes in eukaryotic cells
;
-
:
1) rRNA: transcribed in nucleolus
2) RNA produced elsewhere in nucleus
- ribosomal subunits pass through nuclear pores to the cytoplasm where assembly into ribosomes is completed
RIBOSOME
 cytoplasmic organelle;
- made of RNA and protein
- cells with high rates of protein synthesis have large numbers of nucleoli & ribosomes (e.g. human liver cells have millions)
● Ribosomes carry out protein synthesis in two locations:
-in the cytosol (
)
-attached to the outside of the endoplasmic reticulum (ER) or the nuclear envelope (
The Endomembrane System
**all structures are essentially compartments, closed off by their membranes from the cytoplasm
6.4 - The endomembrane system regulates protein traffic and performs metabolic functions in the cell
● Components of the endomembrane system:
-Nuclear envelope
-Lysosomes
-Endoplasmic reticulum
-Vacuoles
-Golgi apparatus
-Plasma membrane
● These components are either continuous or connected via transfer vesicles
● The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells
● The ER membrane is continuous with the nuclear envelope
ENDOPLASMIC RETICULUM (ER):
● extensive network of tubules and sacs
● used for transport and/or modification of proteins;
● can be
(ribosomes) or
(no ribosomes)
Rough ER:
● manufactures secretory proteins and membranes ;
● proteins made here may be modified (i.e. folded into their tertiary structure)
● usually closer in to nucleus than smooth ER
Smooth ER:
●
● participates in carbohydrate metabolism
●
● stores calcium ions (for muscle contraction)
The GOLGI APPARATUS: Shipping and Receiving Center
● The Golgi apparatus consists of flattened membranous sacs called cisternae
● Functions of the Golgi apparatus:
-Manufactures certain macromolecules
● cis face (forming face; faces the rough ER)
into transport vesicles
by accepting transport vesicles from the rough ER
● trans face (maturing face; faces the cell membrane) pinches off vesicles from the Golgi and transports molecules to other
sites.
)
Lysosomes: Digestive Compartments
● A lysosome is a membranous sac of
● Lysosomal enzymes can hydrolyze proteins, fats, polysaccharides, and nucleic acids
● Lysosomes also use enzymes to recycle organelles and macromolecules, a process called autophagy
● probably pinch off from the trans face of Golgi;
●
;
●
the cell’s own organic material;
● destroy cells
VESICLES / VACUOLES:
● membrane-enclosed sac used for
animal cells, vacuoles are small and look like vesicles
**Vacuoles in PLANTS have special characteristics:
-plants have a LARGE central vacuole that stores water and water-soluble organic compounds and inorganic ions (K + and Cl-);
-contain soluble pigments in some cells (red and blue pigments in flowers);
-play a role in plant growth by
;
-helps protect from predators by storing waste products that may also be poisonous compounds;
-are surrounded by a membrane called the
.
-some fresh-water protists have a
that pumps excess water from cell
MORE ORGANELLES…
6.5 - Mitochondria and chloroplasts change energy from one form to another
● Mitochondria are the
● Chloroplasts, found only in plants and algae, are the
● Mitochondria and chloroplasts are not part of the endomembrane system
● Peroxisomes are
MITOCHONDRIA:
●
.
● found in nearly all eukaryotic cells.
● the # in cells varies and is related to the cell’s metabolic activity
● inner membrane is convoluted and contains enzymes involved in cellular respiration
● inner membranes many infoldings are called CRISTAE; they increase the surface area for cellular respiration reactions to
occur
● region within inner membrane is the
.
CHLOROPLASTS: (a.k.a. “the organelles that feed the world”)
●
;
●
(convert light energy into chemical energy;
● found in eukaryotic algae, leaves and other green plant organs;
● can change shape, move and divide
● Chloroplast structure includes:
-Thylakoids,
-Stroma,
PEROXISOMES:
● contain special enzymes for specific metabolic pathways
● found in nearly all eukaryotic cells
● contain peroxide-producing enzymes that transfer hydrogen ions to oxygen producing hydrogen peroxide
● contain catalase enzyme which
6.6 - The CYTOSKELETON is a network of fibers that organizes structures and activities in the cell
● anchors and/or provides “tracks” for many organelles
● It is composed of three types of molecular structures:
-Microtubules
-Microfilaments
-Intermediate filaments
Components of the Cytoskeleton
● Microtubules are the thickest of the three components of the cytoskeleton
● Microfilaments, also called
, are the thinnest components
● Intermediate filaments are fibers with diameters in a middle range
Roles of the Cytoskeleton: Support, Motility, and Regulation
● the cytoskeleton helps to
and
● it interacts with motor proteins to
(
)
● inside the cell, vesicles can travel along “monorails” provided by the cytoskeleton
● recent evidence suggests that the cytoskeleton may help regulate biochemical activities
Microtubules:
● straight, hollow rods made of protein called
;
● can serve as “tracks” to guide organelle movement;
● involved in separation of chromosomes in cell division; make up
;
Cilia and Flagella
● Microtubules control the beating of cilia and flagella, locomotor appendages of some cells
● Cilia and flagella differ in their beating patterns
● FLAGELLA:
; usually found singly or in pairs;
● CILIA: shorter than flagella; usually present
; wavelike motion used to
● Cilia and flagella share a common ultrastructure:
-A core of microtubules sheathed by the plasma membrane
-A basal body that anchors the cilium or flagellum
-A motor protein called DYNEIN, which drives the bending movements of a cilium or flagellum
Microfilaments:
● can exist as single filaments or in bundles;
● formed from the protein
;
● help the cell (or parts of the cell) to contract;
● they stabilize cell shape;
● Involved in “pinching” contractions during cell division;
● Involved in forming “pseudopodia” that enable some cells to move.
Intermediate Filaments
● Intermediate filaments range in diameter from 8–12 nanometers, larger than microfilaments but smaller than microtubules
● They
and
● Intermediate filaments are more permanent cytoskeleton fixtures than the other two classes
Extracellular Structures:
6.7 - Extracellular components and connections between cells help coordinate cellular activities
● Most cells synthesize and secrete materials that are external to the plasma membrane
● These extracellular structures include:
- The extracellular matrix (ECM) of animal cells
● CELL WALL:
-semirigid structure outside of cell membrane of
;
-consists of
fibers + complex polysaccharides & proteins
-provides support, limits cell’s volume, and protects against fungi and/or microorganism infection.
Cell Walls of Plants
● Plant cell walls may have multiple layers:
-Primary cell wall: relatively thin and flexible
-Middle lamella: thin layer between primary walls of adjacent cells
-Secondary cell wall (in some cells): added between the plasma membrane and the primary cell wall
● Plasmodesmata are channels between adjacent plant cells
The Extracellular Matrix (ECM) of Animal Cells:
● Animal cells lack cell walls but are covered by an elaborate extracellular matrix (ECM)
● Functions of the ECM:
-Support
-Adhesion
-Movement
-Regulation
 EXTRACELLULAR MATRIX:
-fibrous proteins such as
and glycoproteins are secreted by and surround cells;
-
;
-helps filter materials passing between different tissues;
-orients cell movement during development;
-
.
Intercellular Junctions
● Neighboring cells in tissues, organs, or organ systems often adhere, interact, and communicate through direct physical contact
● Intercellular junctions facilitate this contact
Plants: Plasmodesmata
● Plasmodesmata are channels that perforate plant cell walls
● Through plasmodesmata,
(and sometimes proteins and RNA) can pass from cell to cell
Animals: Tight Junctions, Desmosomes, and Gap Junctions
● At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid
● Desmosomes (anchoring junctions)
● Gap junctions (
into strong sheets
) provide cytoplasmic channels between adjacent cells
The Cell: A Living Unit Greater Than the Sum of Its Parts
● Cells rely on the integration of structures and organelles in order to function
● For example, a macrophage’s ability to destroy bacteria involves the whole cell, coordinating components such as the
cytoskeleton, lysosomes, and plasma membrane