BIOL 251 - Chapter 3 (Cells: Plasma Membranes)

Structure, Transport, Membrane Potentials, and Interactions

prefix: cyto- and suffix: -cyte

cell - the smallest unit of life

Despite differences in function, cells have 3 basic parts:

• 1) Plasma membrane: outermost boundary, selectively permeable

• 2) Cytoplasm: intracellular fluid

• Mostly water, but also contains salts and organic molecules

• 3) Nucleus*: controls cellular activities (technically some do not)

Fluid Mosaic Model

describes the general structure of the plasma membrane

• Plasma membranes consist of a phospholipid bilayer with proteins randomly dispersed in it

• Importance: separates the intracellular fluid (ICF) from the

extracellular fluid (ECF)

Chemical Composition of Cell Membranes

1) Lipids

2) Proteins

3) Carbohydrates

Chemical Composition of Cell Membranes

1) Lipids

A) Phospholipids: forms basic structure of membrane

• Polar Phosphate head: hydrophilic portions contact intracellular or extracellular fluid

• Nonpolar Fatty acid tails (2): hydrophobic portions that face the inside of the membrane

• What effect does this have on water-soluble molecules?

• B) Cholesterol: provide structural support to “stiffen” the membrane

Chemical Composition of Cell Membranes

2) Proteins

constitute most of the specialized membrane functions

2 types of membrane proteins by location:

• A) Integral proteins

• B) Peripheral proteins

2 types of membrane proteins by location:

A) Integral Proteins

embedded in the plasma membrane

• Transmembrane proteins span the entire width of the membrane

2 types of membrane proteins by location:

B) peripheral proteins

loosely attached to integral protein

• Are not found in the lipid bilayer

6 types of proteins by function:

A) Transport proteins

B) Receptor proteins

C) Enzymes

D) Cell-Cell recognition proteins

E) Attachment proteins

F) intercellular junctions

6 types of proteins by function:

A) Transport proteins

Transport proteins: move substances in and/or out of cells

• Substances are selectively moved into or out of the cell

• What does “selectively” mean?

6 types of proteins by function:

B) Receptor Proteins

can relay messages to cell interior when bound or exposed to certain chemical messengers

• Most receptor proteins are very specific

• How?

• When bound to chemical messenger → protein changes shape, leading to series of changes inside the cell

6 types of proteins by function:

C) Enzymes

proteins that catalyze chemical reactions

6 types of proteins by function:

D) Cell-cell recognition proteins

allow body cells to recognize other body

• What types of cells in the body would need to use this type of protein? Why?

6 types of proteins by function:

E) Attachment Proteins

helps hold some membrane proteins in place or maintains cell shape

• Can be located inside of the cell or outside, depending on function

6 types of proteins by function:

F) intercellular junctions

proteins used to link cells together

• Major functions: allows cells to adhere to one another & interact

with one another temporarily or permanently

Chemical Composition of Cell Membranes

3) Carbohydrates

Extracellular surface is dotted with short-branching carbohydrates attached to lipids or proteins

• Creates the glycocalyx

glycocalyx

• Different cell types have different arrangements → allows for identification by other body cells

• Can also act as a barrier → prevents very large substances from entering cell