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Ch. 6: A Tour of the Cell - Coggle Diagram
Ch. 6: A Tour of the Cell
Extracellular components &
connections between cells
Cell Walls of Plants
The cell wall is an extracellular structure that
distinguishes plant cells from animal cells
Prokaryotes, fungi, and some protists also have cell
walls
Functions
protects the plant cell
maintains cell
shape
prevents excessive uptake of water
made of cellulose fibers
embedded in other polysaccharides and protein
Plant cell walls may have multiple layers
Primary cell wall
: Relatively thin and flexible, secreted first
Middle lamella
: Thin layer between primary walls, containing polysaccharides called pectins
Secondary cell wall (in some cells)
: Added between the plasma membrane and the primary cell wall
The Extracellular Matrix (ECM) of Animal Cells
Animal cells lack cell walls but are covered by an
elaborate extracellular matrix (ECM)
made up of
glycoproteins
such as collagen
proteoglycans
fibronectin
Fibronectin
and other ECM proteins bind to
receptor proteins in the plasma membrane called
integrins
ECM has an influential role in the lives of cells
can regulate a cell’s behavior by
communicating with a cell through integrins
ECM around a cell can influence the activity of
genes in the nucleus
Mechanical signaling may occur through
cytoskeletal changes that trigger chemical signals
in the cell
Cell Junctions
Neighboring cells in tissues, organs, or organ
systems often adhere, interact, and communicate
through direct physical contact
Plasmodesmata
in Plant Cells
Plasmodesmata are channels that connect plant
cells
Through plasmodesmata, water and small solutes
(and sometimes proteins and RNA) can pass from
cell to cell
Three types of cell junctions
At
tight junctions
, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid
Desmosomes
(anchoring junctions) fasten cells together into strong sheets
Gap junctions
(communicating junctions) provide cytoplasmic channels between adjacent cells
Most cells synthesize and secrete materials to the
outside of the cell
These extracellular materials and structures are
involved in many essential cellular functions
Microscopes & Biochemistry
Microscopy
Microscopes were invented in 1590 and further refined during the 1600s
Microscopes are used to visualize cells
Cells are usually too small to be seen by the naked
eye
In a
light microscope (LM)
, visible light is passed
through a specimen and then through glass lenses
Lenses refract (bend) the light so that the image is
magnified
Cell Fractionation
takes cells apart and
separates the major organelles from one another
A useful technique for studying cell structure and function
differential centrifugation
Centrifuges fractionate cells into their
component parts
which spins test tubes holding mixtures of disrupted cells at a series of increasing speeds
enables scientists to determine
the functions of organelles
Biochemistry and cytology help correlate cell
function with structure
Parameters of Microscopy
Magnification
the ratio of an object’s image
size to its real size
can magnify effectively to about
1,000 times the size of the actual specimen
Resolution
the measure of the clarity of the image
the minimum distance of two distinguishable
points
Contrast
visible differences in brightness between
parts of the sample
Types of Microscopes
Light Microscope
New advances
Labeling individual cells with fluorescent markers
improves the level of detail that can be seen
Confocal microscopy and deconvolution microscopy
provide sharper images of three-dimensional tissues
and cells
The resolution of standard light microscopy is too
low to study
organelles
, the membrane-enclosed
structures in eukaryotic cells
Electron Microscopes
used to see organelles in detail
rather than focusing light, the
electron microscope (EM)
focuses a beam of electrons through the specimen or onto its surface
2 basic types
Scanning electron microscopes (SEMs)
focus a
beam of electrons onto the surface of a specimen,
providing images that look 3-D
Transmission electron microscopes (TEMs)
focus a beam of electrons through a specimen
used mainly to study the internal
structure of cells
cryo-electron microscopy
new type of TEM
allows specimens to be preserved at extremely low temperatures
Mitochondria & Chloroplasts
are the organelles that convert energy to forms that cells can use for work
Mitochondria
are the sites of cellular respiration,
the metabolic process that uses oxygen to
generate ATP
Chloroplasts
found in plants and algae, are the
sites of photosynthesis
Evolutionary Origins
Mitochondria and chloroplasts have similarities with
bacteria
These similarities led to the
endosymbiont theory
Theory suggests that an early ancestor of eukaryotes
engulfed an oxygen-using nonphotosynthetic
prokaryotic cell
The engulfed cell formed a relationship with the
host cell, becoming an endosymbiont
endosymbionts evolved into mitochondria
At least one of these cells may have then taken up
a photosynthetic prokaryote, which evolved into a
chloroplast
Similarities between mitochondria and chloroplasts
that supports theory
Enveloped by a double membrane
Contain free ribosomes and circular DNA molecules
Grow and reproduce somewhat independently in cells
Mitochondria
Chemical Energy Conversion
found in nearly all eukaryotic cells
has a smooth outer membrane and an inner
membrane folded into
cristae
inner membrane creates two compartments
intermembrane space
mitochondrial matrix
Some metabolic steps of cellular respiration are
catalyzed in the mitochondrial matrix
Cristae present a large surface area for enzymes
that synthesize ATP
Chloroplasts
Capture of Light Energy
contain the green pigment
chlorophyll
,
as well as enzymes and other molecules that
function in photosynthesis
are found in leaves and other green
organs of plants and in algae
Chloroplast structure
Thylakoids
, membranous sacs, stacked to form a
granum
Stroma
, the internal fluid
The chloroplast is one of a group of plant
organelles, called
plastids
Another type of plastids is
amyloplast
, a colorless organelle that stores starch (amylose), particularly in roots and tubers
Chromoplast
, which has pigments that give fruits and flowers their orange and yellow hues
Peroxisomes
are
oxidative
organelles
is not known how peroxisomes are related to
other organelles
are specialized metabolic
compartments bounded by a single membrane
contain enzymes that remove hydrogen
atoms from various substances and transfer them
to oxygen
This forms hydrogen peroxide
Functions of peroxisomes
Some use oxygen to break fatty acids into smaller molecules, eventually used for fuel for respiration
In the liver, they detoxify alcohol and other harmful compounds
Glyoxysomes
in the fat-storing tissues of plant seeds, convert fatty acids to sugar to feed the emerging seedling
Two Types of Cells
Eukaryotic
Domain Eukarya
Protists
Animals
Fungi
Plants
DNA in a nucleus that is bounded by a double
membrane
Membrane-bound organelles
Cytoplasm
in the region between the plasma
membrane and nucleus
larger than
prokaryotic cells
Prokaryotic
Domains
Bacteria
Archae
No nucleus
Nucleoid
DNA in an unbound region
No membrane-bound organelles
Cytoplasm
bound by the plasma membrane
smaller than eukaryotic cells
The basic structural and functional unit of every
organism is one of two types of cells: prokaryotic or
eukaryotic
Comparing Prokaryotic and Eukaryotic Cells
All cells share certain basic features
Plasma membrane
is a selective barrier that
allows sufficient passage of oxygen, nutrients, and
waste to service the volume of every cell
Semifluid substance called
cytosol
Chromosomes (carry genes)
Ribosomes (make proteins)
Panoramic View of Eukaryotic Cell
has internal membranes that
divide the cell into compartments—the organelles
cell’s compartments provide different local
environments so that incompatible processes can
occur in a single cell
basic fabric of biological membranes is a
double layer of phospholipids and other lipids
Plant and animal cells have most of the same
organelles
Eukaryotic cell’s genetic
instructions
The nucleus contains most of the DNA in a
eukaryotic cell
Ribosomes use the information from the DNA to
make proteins
The Nucleus
Information Central
nucleus
contains most of the cell’s genes and
is usually the most conspicuous organelle
nuclear envelope
encloses the nucleus,
separating it from the cytoplasm
is a double membrane; each
membrane consists of a lipid bilayer
Pores
lined with a structure called a pore complex
regulate the entry and exit of molecules from the
nucleus
The nuclear side of the envelope is lined by the
nuclear lamina
composed of proteins
maintains the shape of the nucleus
In the nucleus, DNA is organized into discrete units
called
chromosomes
Each chromosome contains one DNA molecule
associated with proteins, called
chromatin
The
nucleolus
, located within the nucleus, is the
site of
ribosomal RNA (rRNA) synthesis
Ribosomes
Protein Factories
Ribosomes
are complexes made of ribosomal
RNA and protein
build proteins in two locations
In the cytosol (free ribosomes)
On the outside of the endoplasmic reticulum or the nuclear envelope (bound ribosomes)
Endomembrane system
regulates protein traffic and performs metabolic
functions
consists of
Nuclear envelope
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Vacuoles
Plasma membrane
These components are either continuous or
connected via transfer by vesicles
Endoplasmic Reticulum
The
endoplasmic reticulum (ER
) accounts for
more than half of the total membrane in many
eukaryotic cells
is continuous with the nuclear
envelope
2 distinct regions of ER
Smooth ER
, which lacks ribosomes
Functions
Synthesizes lipids
Detoxifies drugs and poisons
Stores calcium ions
Rough ER
whose surface is studded with ribosomes
Functions
Has bound ribosomes, which secrete
glycoproteins
(proteins covalently bonded to carbohydrates)
Distributes
transport vesicles
, secretory proteins surrounded by membranes
Is a membrane factory for the cell
Golgi Apparatus
Shipping and Receiving
Center
consists of flattened
membranous sacs called cisternae
Functions
Modifies products of the ER
Manufactures certain macromolecules
Sorts and packages materials into transport vesicles
Lysosomes
Digestive Compartments
is a membranous sac of hydrolytic
enzymes that can digest macromolecules
Lysosomal enzymes work best in the acidic
environment inside the lysosome
Hydrolytic enzymes and lysosomal membranes are
made by rough ER and then transferred to the
Golgi apparatus for further processing
Some types of cell can engulf another cell by
phagocytosis
; this forms a food vacuole
fuses with the food vacuole and digests
the contents
also use enzymes to recycle the
cell’s own organelles and macromolecules,
a process called
autophagy
Vacuoles
Diverse Maintenance Compartments
are large vesicles derived from the ER
and Golgi apparatus
perform a variety of functions in different
kinds of cells
Food vacuoles
are formed by phagocytosis
Contractile vacuoles
, found in many freshwater
protists, pump excess water out of cells
Central vacuoles
plays a major role in the growth
of plant cells
found in many mature plant
cells, contain a solution called sap
It is the plant cell’s main repository of inorganic
ions, including potassium and chloride