BIO 203 Lecture Notes - Lecture 4: Lipid Bilayer, Extracellular Fluid, Prokaryote
43 views5 pages
21 Feb 2019
School
Department
Course
Professor
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
● 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