Download CHAPTER 3: CELL STRUCTURE AND FUNCTION

CHAPTER 3: CELL STRUCTURE AND FUNCTION
LECTURE OUTLINE
3.1 The Cellular Level of Organization
The cell marks the boundary between the nonliving and the living. Cells can be classified as
either prokaryotic or eukaryotic. The cell theory states that all organisms are made up of basic
living units called cells, and that all cells come only from previously existing cells.
Cell Size
Cells are quite small. This allows nutrients to enter and wastes to exit a cell at its surface.
Plasma Membrane and Cytoplasm
All cells are surrounded by a plasma membrane composed of a phospholipid bilayer with
embedded proteins. Inside the cell is a semifluid medium called the cytoplasm composed
of water, salts, and dissolved organic molecules.
3.2 Prokaryotic Cells
Prokaryotic cells lack a membrane-bounded nucleus. The domains Archaea and Bacteria consist
of prokaryotic cells. Although prokaryotes are structurally simple, they are much more
metabolically diverse than eukaryotes.
3.3 Eukaryotic Cells
Eukaryotic cells are structurally very complex. The principal distinguishing feature of eukaryotic
cells is the presence of a nucleus.
Cell Walls
Some eukaryotic cells have a permeable but protective cell wall.
Organelles of Animal and Plant Cells
We will use the term organelle to include any well-defined subcellular structure.
The Nucleus
The nucleus stores genetic material which governs the characteristics of the cell and its
metabolic functioning. Chromatin consists of DNA and associated proteins.
Ribosomes
Ribosomes are small organelles where protein synthesis occurs.
The Endomembrane System
The endomembrane system consists of the nuclear envelope, the endoplasmic reticulum,
the Golgi apparatus, and several vesicles.
The Endoplasmic Reticulum
The endoplasmic reticulum is a complicated system of membranous channels and
saccules that is physically continuous with the outer membrane of the nuclear
envelope. It is responsible for the synthesis, processing, and modification of
proteins. The rough ER (RER) is studded with ribosomes. The smooth ER does
not have ribosomes and synthesizes phospholipids and performs various other
functions.
The Golgi Apparatus
The Golgi apparatus is referred to as the post office of the cell because it collects,
sorts, packages, and distributes materials such as proteins and lipids.
Lysosomes
Lysosomes contain hydrolytic digestive enzymes.
Vacuoles
A vacuole is a large membranous sac that is larger than a vesicle. Vacuoles store
substances.
Peroxisomes
Peroxisomes are membrane-bounded vesicles that enclose enzymes. The enzymes
present in a peroxisome depend on the function of the cell.
Energy-Related Organelles
Chloroplasts use solar energy to synthesize carbohydrates, and carbohydrate-derived
products are broken down in mitochondria to produce ATP molecules.
Chloroplasts
Plant and algal cells contain chloroplasts which allow them to carry on
photosynthesis.
Mitochondria
All eukaryotic cells contain mitochondria.
The Cytoskeleton
The protein components of the cytoskeleton maintain cell shape and allow the cell and its
organelles to move.
Actin Filaments
Actin filaments play a structural role when they form a dense, complex web just
under the plasma membrane. They are involved in movement of the cell and its
organelles when they interact with motor molecules.
Intermediate Filaments
These perform a structural role in the cell.
Microtubules
Microtubules are organized by the centrosome. They are associated with motor
molecules.
Centrioles
Centrioles are composed of microtubule triplets. In animal cells, centrioles play
a role in the formation of the mitotic spindle.
Cilia and Flagella
Cilia and flagella are hairlike projections that can move either in an undulating
fashion or like an oar.
3.4 Origin and Evolution of the Eukaryotic Cell
The fossil record suggests that the first cells were prokaryotes. Scientists believe that eukaryotic
cells evolved from prokaryotic cells in a particular manner. This theory is called the
endosymbiotic theory.