Chapter 3 : Structure & Function of Cells
Key concepts :
*A single cell is the smallest unit of life. Cells come only from preexisting cells
*Human cells are surrounded by a plasma membrane, which serves to contain the cellular structures and regulate the
kinds and quantities of molecules that can enter/exit the cell.
*The nucleus of a human cell contains the cell’s DNA. The genetic code of DNA specifies the amino acid sequences of
the proteins produced by the cell.
*Mitochondria, which are cell structures, produce usable energy in the form of ATP. Most of the energy for making ATP
comes from breakdown of glucose, which requires oxygen and results in the waste product carbon dioxide.
*Other cell structures use ATP to carry out cellular functions.
1. Cells are classified according to their INTERNAL organisation
(Outer organisation = Plasma membrane = the same for ALL cells)
EUKARYOTES : nucleus, cytoplasm, and organelles (HUMAN CELLS)
Plasma membrane
Nucleus = membrane-bound compartment, contains the cell’s genetic material and functions (some have >1)
Cytoplasm = cell material = gelfluid or cytosol containing microscopic structures with spec functions = organelles
PROKARYOTES (BACTERIA) : no nucleus or organelles
A plasma membrane, surrounded by a rigid cell way
Genetic material concentrated in particular region, but not specifically in a nuclues
2. Cell structure reflects cell function
Eukaryotic cells : very alike in structural features => All cellls carry out functions to maintain life AND strong link
between structure and function ! => Most of the structural differences differences in function !!
Cells remain small. WHY ? to stay efficient (uitzondering : egg of some species) :
The larger a cell gets, its metabolism will be limited by its ability to support itself across the plasma membrane. Some
cells have numerous microscopi projections of the plasma membrane called microvilli, to increase surface (Especially
cells for transport into/out of the body, eg. Digestice tract, tubules of the kidney)
Visualizing cells with microscopes
The light microscope (LM) : magnifies up to 1000x. Focus difficult if objects at different depth. Does not transmit
well thr thick samples, many cells can only be seen lf stained BUT the only one to use on living samples !
The transmission electron microscope (TM) : bombards a thin object with electrons. Wavelenghts of electrons
are shorter than visible light => magnifies up to 100.000x. Only 2-dimensional images, sample must be very thin.
The scanning electron microscope (SEM) : 3-dimensional image ! Object coated with metal => electrons cannot
penetrate ! Then scanned with a narrow beam of electrons => secondary electrons are given off & produe a visual
image of the object’s surface. Also 100.000x ! Black&White images but colorized !
3. A plasma membrane surrounds the cell
The plasma membrane is a LIPID BILAYER and consists of :
Phospholipids : Two layers of them = LIPID BILAYER. The nonpolar tails meet in center of the membrane. Layer 1 of
polar heads faces watery solution at outside cell, Layer 2 faces watery solution of cytoplasm.
Key concepts :
*A single cell is the smallest unit of life. Cells come only from preexisting cells
*Human cells are surrounded by a plasma membrane, which serves to contain the cellular structures and regulate the
kinds and quantities of molecules that can enter/exit the cell.
*The nucleus of a human cell contains the cell’s DNA. The genetic code of DNA specifies the amino acid sequences of
the proteins produced by the cell.
*Mitochondria, which are cell structures, produce usable energy in the form of ATP. Most of the energy for making ATP
comes from breakdown of glucose, which requires oxygen and results in the waste product carbon dioxide.
*Other cell structures use ATP to carry out cellular functions.
1. Cells are classified according to their INTERNAL organisation
(Outer organisation = Plasma membrane = the same for ALL cells)
EUKARYOTES : nucleus, cytoplasm, and organelles (HUMAN CELLS)
Plasma membrane
Nucleus = membrane-bound compartment, contains the cell’s genetic material and functions (some have >1)
Cytoplasm = cell material = gelfluid or cytosol containing microscopic structures with spec functions = organelles
PROKARYOTES (BACTERIA) : no nucleus or organelles
A plasma membrane, surrounded by a rigid cell way
Genetic material concentrated in particular region, but not specifically in a nuclues
2. Cell structure reflects cell function
Eukaryotic cells : very alike in structural features => All cellls carry out functions to maintain life AND strong link
between structure and function ! => Most of the structural differences differences in function !!
Cells remain small. WHY ? to stay efficient (uitzondering : egg of some species) :
The larger a cell gets, its metabolism will be limited by its ability to support itself across the plasma membrane. Some
cells have numerous microscopi projections of the plasma membrane called microvilli, to increase surface (Especially
cells for transport into/out of the body, eg. Digestice tract, tubules of the kidney)
Visualizing cells with microscopes
The light microscope (LM) : magnifies up to 1000x. Focus difficult if objects at different depth. Does not transmit
well thr thick samples, many cells can only be seen lf stained BUT the only one to use on living samples !
The transmission electron microscope (TM) : bombards a thin object with electrons. Wavelenghts of electrons
are shorter than visible light => magnifies up to 100.000x. Only 2-dimensional images, sample must be very thin.
The scanning electron microscope (SEM) : 3-dimensional image ! Object coated with metal => electrons cannot
penetrate ! Then scanned with a narrow beam of electrons => secondary electrons are given off & produe a visual
image of the object’s surface. Also 100.000x ! Black&White images but colorized !
3. A plasma membrane surrounds the cell
The plasma membrane is a LIPID BILAYER and consists of :
Phospholipids : Two layers of them = LIPID BILAYER. The nonpolar tails meet in center of the membrane. Layer 1 of
polar heads faces watery solution at outside cell, Layer 2 faces watery solution of cytoplasm.
