Transcript CHAPTER 4 A Tour of the Cell By Dr. Par Mohammadian

CHAPTER 4
A Tour of the Cell
By Dr. Par Mohammadian
Overview:
•Microscopes
•Cells
Prokaryotes
Eukaryotes
Animal Cells
Plants Cells
•Cell Junctions
• Microscopes
INTRODUCTION TO THE WORLD
OF THE CELL
• Using a microscope, Robert Hooke
discovered cells in 1665
• Cells are the building blocks of all life
• Organisms are either
– Single-celled, such as most bacteria
– Multicelled, such as plants, animals
Microscopes provide windows
to the world of the cell
The light microscope (LM) enables us to see the
overall shape and structure of a cell
• Micrograph: A photograph taken through a
microscope.
• LM 109X: The image under the light microscope
is 109 times the actual size of the organisms.
• Magnification: Increase in the apparent size of an
object.
• Resolving power: Measure of the clarity of an
image.
• Electron microscopes (EM) were invented in the
1950s
• They use a beam of electrons instead of light
• The greater resolving power of electron
microscopes
– allows greater magnification (0.2 nm vs. LM 0.2 µm)
– reveals cellular details
• LM remains the major tool to study living
organisms because in EM specimen must be
held in vacuum.
• Scanning electron
microscope (SEM)
used to study the
detailed architecture
of the surface of a
cell
• Transmission electron
microscope (TEM) is
useful for exploring
the internal structure
of a cell
Natural laws limit cell size
• At minimum, a cell must be large enough to
house the parts it needs to survive and reproduce
• The maximum size of a cell is limited by the
amount of surface needed to obtain nutrients
from the environment and dispose of wastes
• Cells
Prokaryotic Cells
Eukaryotic Cells
Animal Cells
Plant Cells
The Two Major Categories of Cells
• The countless cells on earth fall into two
categories
– Prokaryotic cells
– Eukaryotic cells
• Prokaryotic and
eukaryotic cells
differ in several
respects
• Prokaryotic cells
– Are smaller than eukaryotic cells and are simple
– Lack internal structures surrounded by membranes
– Lack a nucleus
• A prokaryotic cell is enclosed by a plasma
membrane (protects & shape of the cell) and is
usually encased in a rigid cell wall (further
protection)
– The cell wall may be
covered by a sticky
capsule (help glue
prok. to surfaces)
– Inside the cell
are its DNA and
other parts
Eukaryotic cells are partitioned into
functional compartments
• All other life forms (such as animals, plants,
protists, or fungi) are made up of one or more
eukaryotic cells
• These are larger and more complex than
prokaryotic cells
• Eukaryotes are distinguished by the presence of a
true nucleus
• The plasma membrane controls the cell’s contact
with the environment
• The cytoplasm contains
organelles
• Many organelles have
membranes as boundaries
– These compartmentalize the
interior of the cell
– This allows the cell to carry
out a variety of activities
simultaneously
• A plant cell has some structures that an animal
cell lacks:
– Chloroplasts
– A rigid cell wall
– Central vacuole
The nucleus is the cell’s genetic control center
• The largest organelle is usually the nucleus
• The nucleus is separated from the cytoplasm by
the nuclear envelope
• The nucleus is the cellular control center
– It contains the DNA that directs the cell’s activities
– Genes in the nucleus store information necessary to
produce proteins
MEMBRANE STRUCTURE AND FUNCTION
• The plasma membrane separates the living cell
from its nonliving surroundings
A Fluid Mosaic of Lipids and Proteins
• The membranes of cells are composed of
– Lipids
– Proteins
Cytoplasm
• The endomembrane system is a collection of
membranous organelles
– These organelles manufacture and distribute cell
products
– The endomembrane system divides the cell into
compartments
– Endoplasmic reticulum (ER) is part of the
endomembrane system
Rough endoplasmic reticulum makes
membrane and proteins
• The rough ER manufactures membranes
• Ribosomes on its surface produce proteins
1)
2)
3)
4)
Synthesized
polypeptide is
passed into ER
Sugars attach to
polypeptides
forming
glycoprotein
ER packages it in
tinny sacs called
transport vesicles
It buds off from the
ER & secretory
vesicles travel to
Golgi apparatus.
• The
“roughness” of
the rough ER is
due to
ribosomes that
stud the outside
of the ER
membrane
• The functions of the rough ER include
– Producing proteins
– Producing new membrane
Smooth endoplasmic reticulum has a variety of
functions
• Smooth ER synthesizes lipids
• In some cells, it regulates carbohydrate
metabolism and breaks down toxins and drugs
• Stores Ca ions
The Golgi apparatus finishes, sorts, and ships cell
products
• The Golgi apparatus consists of stacks of
membranous sacs
– These receive and modify ER products, then send
them on to other organelles or to the cell membrane
Lysosomes digest the cell’s food and wastes
• Lysosomes are
sacs of digestive
enzymes
• Lysosomal enzymes
–
–
–
–
digest food
destroy bacteria
recycle damaged organelles
function in embryonic
development in animals
Vacuoles
• Vacuoles are membranous sacs
– Two types are the contractile vacuoles of protists and
the central vacuoles of plants
–The vacuole has lysosomal and storage functions
CHLOROPLASTS AND MITOCHONDRIA:
ENERGY CONVERSION
• Cells require a constant energy supply to do all
the work of life
CHLOROPLASTS
• Chloroplasts are
the sites of
photosynthesis,
the conversion
of light energy
to chemical
energy
Mitochondria
• Mitochondria are the sites of cellular respiration,
which involves the production of ATP from food
molecules
THE CYTOSKELETON AND RELATED
STRUCTURES
The cell’s internal skeleton helps organize its
structure and activities
• A network of protein fibers makes up the
cytoskeleton
Maintaining Cell Shape
• One function of
the cytoskeleton
– Provide
mechanical
support to the
cell and
maintain its
shape
• The cytoskeleton can
change the shape of a cell
– This allows cells like
amoebae to move
• Microfilaments of actin enable cells to change
shape and move
• Intermediate filaments reinforce the cell and
anchor certain organelles
• Microtubules
– give the cell rigidity
– provide anchors for organelles
– act as tracks for organelle movement
Cilia and flagella move when microtubules bend
• Eukaryotic cilia and flagella are locomotor
appendages that protrude from certain cells
• A cilia or flagellum is composed of a core of
microtubules wrapped in an extension of the
plasma membrane
• Flagella propel the cell
in a whiplike motion
• Cilia move in a
coordinated back-andforth motion
• Some cilia or flagella
extend from
nonmoving cells
– The human windpipe is
lined with cilia
•Cell Junctions
EUKARYOTIC CELL SURFACES AND
JUNCTIONS
Cell surfaces protect, support, and join cells
• Cells interact with their environments and each
other via their surfaces
• Plant cells are supported by rigid cell walls made
largely of cellulose
– They connect by plasmodesmata, channels that allow
them to share water, food, and chemical messages
Plant Cell Walls and Cell Junctions
• Plant cells are encased by cell walls
– These provide support for the plant cells
Animal Cell Surfaces and Cell Junctions
• Animal cells lack cell walls
– They secrete a sticky covering called the extracellular
matrix
– This layer helps hold cells together
• Animal cells connect by various types of
junctions
– Tight junctions
– Adhering junctions
– Communicating junctions
• Tight junctions can bind cells together into
leakproof sheets
• Anchoring
junctions link
animal cells
• Communicating
junctions allow
substances to
flow from cell
to cell