Chapter 3 Cell Structure
Bacteria are found in all parts of the biosphere, including the human
body. Huge numbers inhabit our intestines, but most of these are
beneficial. A few can cause disease. Contamination of food with
disease-causing bacteria can result in food poisoning that is sometimes
What exactly is a cell?
1. Every living organism consists of one or more cells
2. The cell is the structural and functional unit of all organisms. A
cell is the smallest unit of life, individual y alive even as part of
a multi celled organism.
3. All living cells come from division of pre existing cells
4. Cells contain hereditary material, which they pass to their
offspring when they divide.
Cytoplasm – semifluid substance enclosed by a cell’s plasma membrane
Nucleus – of a cell is an organelle with two membranes that holds the
Organelle – structure that carries out a special metabolic function
inside a cell
Plasma membrane – a cell’s outermost membrane
Surface-to-volume ratio – a relationship in which the volume of an
object increases with the cube of the diameter, and the surface are
increases with the square.
1 1. Cells differ in size, shape and function, but all start out life with
a plasma membrane, cytoplasm and region of DNA. Most cells
have additional components
2. In eukaryotic cells, DNA is contained within a nucleus, which
is a membrane-enclosed organelle. All cell membranes,
including the plasma membrane and organelle membranes, are
selectively permeable and consist mainly of phospholipids
organized as a lipid bilayer. The surface-to-volume ratio
limits cell size.
3. By the cell theory, a.) all organisms consist of one or more
cells; b.) the cell is the smallest unit of life; c.)each new cell
arises from another preexisting cell; d.) and a cell passes
hereditary material to its offspring.
Take Home Message
How are all cells alike?
1. The cell is the fundamental unit of all life
2. All cells start life with a plasma membrane, cytoplasm and the
region of DNA, which in eukaryotic cells only, is enclosed by a
nucleus. The surface-to-volume ratio limits cell size and
influences cell shape
3. Different types of microscopes reveal different aspects of cell
2 3.3 The structure of cell membranes
Adhesion protein-plasma membrane protein that helps cells stick
Fluid mosaic – model of a cell membrane as a two dimensional fluid
of mixed composition
Receptor protein – plasma membrane protein that binds to a
particular substance outside of the cell
Recognition protein – plasma membrane protein that tags a cell as
belonging to self (one’s own body of species)
Transport protein – protein that passively or actively assists
specific ions or molecules across a membrane
1. A cell membrane can be described as a fluid mosaic, which
means it behaves like a two dimensional liquid of mixed
composition – lipids (maily phospholipids) and proteins.
2. The lipids are organized as a double layer in which the nonpolar
fatty acid tails of both layers are sandwiched between the polar
3. All cell membranes may have enzymes and transport
4. Plasma membranes can also incorporate receptor proteins,
adhesion proteins and recognition proteins.
Take home message
What is a cell membrane?
1. The foundation of all cell membranes is the lipid bilayer: Two
layers of phospholipids, tails sandwiched between heads.
2. Proteins that associate with lipid bilayers add various functions
to a membrane.
3 3.4 Introducing Prokaryotic Cells
biofilm - Community of microorganisms living within a shared mass
cell wall – semi rigid but permeable structure that surrounds the
plasma membrane of some cells
flagellum – long, slender cellular structure used for movement
pilus – a protein filament that projects from the surface of some
ribosome –organelle of protein synthesis
1. Bacteria and archaea informally grouped as prokaryotes are the
most diverse forms of life.
2. These single celled organisms have no nucleus, but all have DNA
and ribosomes. Many have a permeable but protective cell wall
and a sticky capsule, as well as motile structures (flagella) and
other projections (pili).
3. Bacteria and other microbial organisms often share living
arrangements in biofilms
Take home message
How are bacteria and archaea alike?
1. bacteria and archaea do not have a nucleus. Most kinds have a
cell wall around their plasma membrane. The permeable wall
reinforces and imparts shape to the cell body
2. The structure of bacteria and archaea is relatively simple, but
as a group these organisms are the most diverse forms of life.
4 3.5 Inside a Eukaryotic Cell
Endoplasmic recticulum (ER) – organelle that is a continuous system
of sacs and tubes extending from the nuclear envelope. Smooth ER
makes lipids and breaks down carbohydrates and fatty acids; ribosomes
on the surface of rough ER synthesize polypeptides
Golgi body – organelle that modifies polypeptides and lipids, then
packages the finished products into vesicles
Mitochondrion – eukaryotic organelle that produces ATP by aerobic
Lysosome – enzyme filled vesicle that breaks down cellular wastes and
Nuclear envelope –a double membrane that constitutes the outer body
of the nucleus. Pores in the membrane control which substances can
Peroxisome – enzyme filled vesicle that breaks down amino acids, fatty
acids and toxic substances
Vacuole – a fluid filled, empty looking organelle that isolates or
disposes of waste, debris, or toxic materials
Vesicle – small, membrane enclosed organelle; different kinds store,
transport, or break down their contents
Chloroplast – organelle of photosynthesis in the cells of plants and
Cilia – short movable structures that project from the plasma
membrane of some eukaryotic cells. ** cilia are usually more profuse
than flagella. The coordinated waving of many cilia propels cells
through fluid and stirs fluid around stationary cells.
5 Eukaryotic flagella are structures that whip back and forth to propel
cells such as sperm through fluid – they have a different structure and
type of motion than prokaryotic flagella.
Cytoskeleton – network of interconnected protein filaments that
support, organize and move eukaryotic cells and their internal
Intermediate filament – stable cytoskeletal element that structurally
supports cells and tissues
Microtubule – cytoskeletal element involved in movement; hollow
filament of tubulin subunits
Motor protein – type of energy using protein that interacts with
cytoskeletal elements to move the cell’s parts or the whole cell
Pseudopod – a temporary protrusion that helps some eukaryotic cells
move and engulf prey
1. All eukaryotic cells start out life with a nucleus and other