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Biology 11
Chapter 3: Cell Structure and Function
Eukaryotic Cells
Eukaryotic cells are structurally complex, distinguished by the presence of a nucleus, which
contains the genetic material. They also contain organelles, which are sub-cellular structures
with defined functions.
• Structures include the plasma membrane, cytoplasm, cell wall, nucleus, ribosomes,
endoplasmic reticulum, Golgi body, lysosomes, vesicles, mitochondria, chloroplasts, and
cytoskeleton
• Animals, plants, fungi, and protists are composed of eukaryotic cells
Plasma Membrane and Cytoplasm
All cells are surrounded by a plasma membrane (cell membrane)
consisting of a phospholipid bilayer embedded with protein molecules.
The cell membrane separates the living contents of the cell from the
surrounding environment.
Inside the cell is a semi-fluid medium called the cytoplasm, composed
of water, salts, and dissolved organic molecules.
The cell membrane regulates the entrance and exit of molecules into
and out of the cytoplasm.
Cell Walls
Some eukaryotic cells have permeable but protective cell
walls in addition to cell membranes. Many plant cells have
primary and secondary cell walls.
• primary cell walls contain cellulose
• secondary cell walls contain lignin; some fungi have
chitin
Biology 11
The Nucleus
The nucleus stores genetic information.
• Chromatin contains DNA and proteins
• Condensed chromatin forms chromosomes
• The nuclear envelope separates the nucleus from the
cytoplasm and contains nuclear pores
Ribosomes
Ribosomes are responsible for protein synthesis.
• Composed of large and small subunits, as well as rRNA
• Associate with mRNA during protein synthesis
• Can be found as polyribosomes (several associated with a
single mRNA)
The Endomembrane System
The endomembrane system is the transportation and processing centre of the cell. It consists of
• The nuclear envelope
• The endoplasmic reticulum (ER): a system of membranous channels and sacs, where
proteins are synthesized and processed (rough ER) and phospholipids are made (smooth
ER)
• The Golgi apparatus: the “shipping centre” of the cell
• Lysosomes and vacuoles (larger storage units, more prominent in plant cells)
Biology 11
The Golgi Apparatus
• The Golgi apparatus: flattened sacs where collection, packaging, and distribution of
proteins and lipids occurs
• Produces lysosomes, which contain hydrolytic digestive enzymes and act as the garbage
disposal for the cell
Peroxisomes
Peroxisomes, similar to lysosomes, are membrane-bound vesicles that
enclose enzymes.
• Typically peroxisomes contain enzymes that produce hydrogen
peroxide, which is a toxic molecule that is broken down by an
enzyme to oxygen and water
• Peroxisomes are most prevalent in cells that synthesize and
break down fats, for example in the liver
Energy-Related Organelles
Chloroplasts and mitochondria specialize in converting energy to a form the cell can use.
• chloroplasts use solar energy to synthesize carbohydrates (photosynthesis)
Biology 11
•
mitochondria break down carbohydrates to produce energy in the form of ATP (cellular
respiration)
Chloroplasts
• Present in plant and algae cells
• Bound by two membranes that enclose the fluid-filled stroma
• Within the stroma are thylakoids stacked as grana (chlorophyll in the thylakoid used for
photosynthesis)