BIO 203 Lecture Notes - Lecture 4: Lipid Bilayer, Extracellular Fluid, Prokaryote

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Eukaryotic cells compared with prokaryotic cells
The cell theory is a fundamental organizing principle of biology that states the following:
The cell is the smallest unit of life
Cells make up all living things, including unicellular and multicellular organisms
New cells can arise only from preexisting cells
There are two basic cells types
Prokaryotic
eukaryotic
Difference between Prokaryotic and eukaryotic
Prokaryotic:
Structured simply
Typically smaller
Lack membrane-bound organelles
Include bacteria and archaea
Eukaryotic:
Structured complex
Typically larger
Have membrane-bound organelles
Found in plants, animals, fungi, protist
Cell size and microscopy
Cells vary in size, but they can never exceed the volume that can be nourished by
materials passing through the surface membrane
The small size of cells is dictated by a physical relationship known as the surface-to-
volume ratio
As a cell gets larger, its surface area increases far more slowly than its volume.
Most eukaryotic and prokaryotic cells are typically measured in micrometers, which
equal 10^-6
They can be seen through either light or electron microscopes
Micrographs are the photographs taken with the microscope
Although we begin life as only one cell, that cell differentiates into many specialized cells
These specialized cells have structures that reflect their particular functions
Plasma Membrane
The outer boundary of the cell
Controls the movement of substances in and out of the cell
The phospholipid bilayer separates the extracellular fluid from the material contained in
the cytoplasm inside the cell
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Proteins, cholesterol, and carbohydrates are also part of the membrane and give it
qualities of a fluid mosaic
Plasma Membrane
Functions of the structure of the plasma membrane:
Maintains structural integrity of the cell
Selectively permeable as it regulates the movement of substances into and out
of the cell
Glycoproteins provide recognition between cells
Receptors provide communication between cells
Cell adhesion molecules stick cells together to form tissues and organs
There are two types of movement across the plasma membrane:
Passive transport: movement across the membrane that doesn't require energy
(simple diffusion, facilitated diffusion, osmosis)
Active transport: movement across the membrane that requires energy
Simple diffusion
Movement of a substance following a concentration gradient, from high
concentration to low concentration
End result is an equal distribution of the substance in the two areas
Eliminates the concentration gradient
Facilitated diffusion
Movement of a substance from a region of higher concentration to a region of
lower concentration with the aid of a membrane protein
Osmosis
Movement of water across a selectively permeable membrane from a region of
higher water concentration to a region of lower water concentration
The water molecules move to dilute the solution
Endocytosis
A region of the plasma membrane engulfs the substance to be ingested and then
pinches off from the rest of the membrane, enclosing the substance in a vesicle,
which travels through the cytoplasm
Applied to large molecules
Two types of endocytosis:
Phagocytosis (cell eating): large particles or bacteria
Pinocytosis (cell drinking): droplets of fluid
Exocytosis
Large molecules are enclosed in membrane-bound vesicles, which travel to
plasma membranes, where they are released to the outside
Organelles
Inside the eukaryotic cells are membrane-bound organelles, which have different
functions
Organelles include
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