Concepts
The Key structure and function of a cells overall shape and
composition, as well as individual cell components, are closely
related.
Molecular zip codes aid material transport within a cell.
The cells cytoskeleton provides a structural framework within
the cell, and plays a role in cell division, movement, and
transport.
2011 Pearson Education, Inc.
Key Concepts
Cells are highly dynamic and integrated; within a cell, thousands
of chemical reactions occur every second, molecules are
constantly moving across the plasma membrane, cell products are
transported along protein fibers, and elements of the cells
internal skeleton grow and shrink.
2011 Pearson Education, Inc.
Grouping Cells
According to morphology, there are two broad groupings of life:
1. Prokaryotes, which lack a membrane-bound nucleus
2. Eukaryotes, which have such a nucleus
According to phylogeny, or evolutionary history, there are three
domains:
1. Bacteria
prokaryotic
2. Archaea
3. Eukarya eukaryotic
2011 Pearson Education, Inc.
Prokaryotic Cells Structural Overview
All prokaryotes lack a membrane-bound nucleus.
Recent advances in microscopy reveal complexity in prokaryotic
structure.
Archaeal cell structure is relatively poorly understood.
Bacterial cells vary greatly in size and shape, but most bacteria
contain several structural similarities:
Plasma membrane
A single chromosome
Ribosomes, which synthesize proteins
Stiff cell wall
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Prokaryotic Cells Genetic Information
Most prokaryotic species have one supercoiled circular
chromosome found in the nucleoid region of the cell.
The chromosome contains a long strand of DNA and a few
supportive proteins.
In addition to the large chromosome, many bacteria contain
plasmids.
Small, supercoiled, circular DNA molecules
Plasmids usually contain genes that help the cell adapt to
unusual environmental conditions.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Prokaryotic Cells Internal Structure
In addition to the nucleoid chromosome and plasmids, other
structures are contained within the cytoplasm:
All prokaryotic cells contain ribosomes, consisting of RNA
molecules and protein, for protein synthesis.
Many prokaryotes have internal photosynthetic membranes.
Some prokaryotes have membrane-enclosed organelles.
The inside of many prokaryotic cells is supported by a
cytoskeleton of long, thin protein filaments.
2011 Pearson Education, Inc.
Bacterial Organelles
Recently, internal compartments in many bacterial species were
discovered.
These compartments qualify as organelles (little organs).
An organelle is a membrane-bound compartment inside the
cell that contains enzymes or structures specialized for a
particular function.
Organelles are common in eukaryotic cells.
Each type of bacterial organelle is found in certain species.
Bacterial organelles perform an array of tasks.
2011 Pearson Education, Inc.
Prokaryotic Cells External Structure
Some prokaryotes have tail-like flagella on the cell surface that
spin around to move the cell.
Most prokaryotes have a cell wall.
Bacterial and archaeal cell walls are a tough, fibrous layer that
surrounds the plasma membrane.
Many species have an additional layer outside the cell wall
composed of glycolipids.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
An Introduction to Eukaryotes
Eukaryotes range from microscopic algae to 100-meter-tall
redwood trees.
Many eukaryotes are multicellular, others are unicellular.
Most eukaryotic cells are larger than most prokaryotic cells.
2011 Pearson Education, Inc.
Eukaryotic Cells
The relatively large size of the eukaryotic cell makes it difficult for
molecules to diffuse across the entire cell.
This problem is partially solved by breaking up the large cell
volume into several smaller membrane-bound organelles.
The compartmentalization of eukaryotic cells offers two primary
advantages:
1. Separation of incompatible chemical reactions
2. Increasing the efficiency of chemical reactions
2011 Pearson Education, Inc.
Eukaryotes and Prokaryotes Compared
Four key differences between eukaryotic and prokaryotic cells have
been identified:
1. Eukaryotic chromosomes are found inside a membranebound compartment called a nucleus.
2. Eukaryotic cells are often much larger.
3. Eukaryotic cells contain extensive amounts of internal
membrane.
4. Eukaryotic cells feature a diverse and dynamic cytoskeleton.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
The Nucleus
The nucleus is large and highly organized.
STRUCTURE:
The nucleus is surrounded by a double-membrane nuclear
envelope.
The nucleus has a distinct region called the nucleolus.
FUNCTION:
Information storage and processing
Contains the cells chromosomes
Ribosomal RNA synthesis (in the nucleolus)
2011 Pearson Education, Inc.
Rough Endoplasmic Reticulum
STRUCTURE:
The rough endoplasmic reticulum (rough ER, RER) is a
network of membrane-bound tubes and sacs studded with
ribosomes.
The interior is called the lumen.
The rough ER is continuous with the nuclear envelope.
FUNCTION:
Ribosomes associated with the rough ER synthesize
proteins.
New proteins are folded and processed in the rough ER
lumen.
2011 Pearson Education, Inc.
Golgi Apparatus
STRUCTURE:
The Golgi apparatus is formed by a series of stacked flat
membranous sacs called cisternae.
FUNCTION:
The Golgi apparatus processes, sorts, and ships proteins
synthesized in the rough ER.
Membranous vesicles carry materials to and from the
organelle.
2011 Pearson Education, Inc.
Ribosomes
STRUCTURE:
Ribosomes are non-membranous (they are not considered
organelles).
Have large and small subunits, both containing RNA molecules
and protein
Ribosomes can be attached to the rough ER or free in the
cytosol, the fluid part of the cytoplasm.
FUNCTION:
Protein synthesis
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Peroxisomes
STRUCTURE:
Peroxisomes are globular organelles bound by a single
membrane.
FUNCTION:
Center of oxidation reactions
Specialized peroxisomes in plants called glyoxysomes are packed
with enzymes that oxidize fats to form a compound that can be
used to store energy for the cell.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Lysosomes
STRUCTURE:
Lysosomes are single-membrane-bound structures containing
approximately different 40 digestive enzymes.
Lysosomes are found in animal cells.
FUNCTION:
Lysosomes are used for digestion and waste processing.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
How Are Materials Delivered to Lysosomes?
Materials are delivered to the lysosomes by three processes:
Phagocytosis
Autophagy
Receptor-mediated endocytosis
Endocytosis is a process by which the cell membrane can pinch off
a vesicle to bring outside material into the cell.
In addition to phagocytosis and receptor-mediated endocytosis,
a third type of endocytosis called pinocytosis brings fluid into
the cell.
2011 Pearson Education, Inc.
Mitochondria
STRUCTURE:
Mitochondria have two membranes; the inner one is folded
into a series of sac-like cristae. The solution inside the cristae
is called the mitochondrial matrix.
Mitochondria have their own DNA and manufacture their own
ribosomes.
FUNCTION:
ATP production is a mitochondrions core function.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Cytoskeleton
The cytoskeleton, composed of protein fibers, gives the cell shape
and structural stability, and aids cell movement and transport of
materials within the cell.
In essence, the cytoskeleton organizes all of the organelles and
other cellular structures into a cohesive whole.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Structure and Function at the Whole-Cell Level
An organelles membrane and its enzymes correlate with its
function, and cell structure (e.g., the type, size, and number of
organelles) correlates with cell function.
Cells are dynamic living things with interacting parts and
constantly moving molecules.
2011 Pearson Education, Inc.
How Dynamic Are Eukaryotic Cells?
Your bodys cells use, and synthesize, approximately 10 million
ATP molecules per second.
Cellular enzymes can catalyze >25,000 reactions per second.
Each membrane phospholipid can travel the breadth of its organelle
or cell in under a minute.
The hundreds of trillions of mitochondria inside you are replaced
about every 10 days, for as long as you live.
The fluid plasma membranes composition is constantly changing.
2011 Pearson Education, Inc.
The Endomembrane System
The endomembrane system is composed of the smooth and rough
ER and the Golgi apparatus, and is the primary system for protein
and lipid synthesis.
Ions, ATP, amino acids, and other small molecules diffuse
randomly throughout the cell, but the movement of proteins and
other large molecules is energy demanding and tightly regulated.
2011 Pearson Education, Inc.
The Dynamic Cytoskeleton
The cytoskeleton is a complex network of fibers that helps
maintain cell shape by providing structural support. The
cytoskeleton is dynamic; it changes to alter the cells shape, to
transport materials in the cell, or to move the cell itself.
There are three types of cytoskeletal elements:
Actin filaments (microfilaments)
Intermediate filaments
Microtubules
2011 Pearson Education, Inc.
Actin Filaments
Actin filaments are the smallest cytoskeletal elements.
Actin filaments form by polymerization of individual actin
molecules.
Actin filaments are grouped together into long bundles or dense
networks that are usually found just inside the plasma membrane
and help define the cells shape.
2011 Pearson Education, Inc.
Actin-Myosin Interactions
Actin filaments can also be involved in movement by interacting
with the motor protein myosin.
Actin-myosin interactions can cause cell movements such as cell
crawling, cytokinesis, and cytoplasmic streaming.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Intermediate Filaments
Intermediate filaments are defined by size rather than
composition. Many types of intermediate filaments exist, each
consisting of a different protein.
Intermediate filaments provide structural support for the cell. They
are not involved in movement.
Intermediate filaments form a flexible skeleton that helps shape the
cell surface and hold the nucleus in place.
2011 Pearson Education, Inc.
Microtubule Structure
Microtubules are large, hollow tubes made of tubulin dimers (twopart compounds).
Microtubules have polarity, are dynamic, and usually grow at their
plus ends.
Microtubules originate from the microtubule organizing center
and grow outward, radiating throughout the cell.
Animal cells have just one microtubule organizing center called the
centrosome. Centrosomes contain two bundles of microtubules
called centrioles.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Microtubule Function
Microtubules provide stability and are involved in movement; they
may also provide a structural framework for organelles.
Microtubules can act as railroad tracks; transport vesicles
move through the cell along these microtubule tracks in an
energy-dependent process.
Microtubules require ATP and kinesin for vesicle transport to
occur. Kinesin is a motor protein that converts chemical energy in
ATP into mechanical work.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Cilia and Flagella: Moving the Entire Cell
Flagella are long, hairlike projections from the cell surface that
move cells.
Bacterial flagella are made of flagellin and rotate like a
propeller.
Eukaryotic flagella are made of microtubules and wave back
and forth.
Closely related to eukaryotic flagella are cilia, which are short,
filament-like projections.
Cells generally have just one or two flagella but may have many
cilia.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Cilia and Flagella Structure
The axoneme of cilia and flagella is a complex 9 + 2
arrangement of microtubules connected by links and spokes.
The axoneme attaches to the cell at a structure called the basal
body.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
A Motor Protein in the Axoneme
The motor protein dynein forms the arms between doublets and
changes shape when ATP is hydrolyzed to walk up the
microtubule.
When the dynein arms on just one side of the axoneme move, cilia
and flagella bend instead of elongating because the links and
bridges constrain movement of the microtubule doublets.
2011 Pearson Education, Inc.
2011 Pearson Education, Inc.
Chapter Summary
Taken together, the data reviewed in this chapter can be summed
up in six words: Cells are dynamic, highly integrated
structures.
2011 Pearson Education, Inc.