BIO 101 - Cell Membrane Structure and Function

Filtration

Movement of substances across the membrane due to pressure, such as blood pressure.

Channel protein

allows a particular molecule or ion to cross the plasma membrane freely.

phospholipid bilayer

two layers of phospholipids. -This bilayer has a consistency of olive oil.

If the intercellular (outside the cell) fluid has a 64% NaCL concentration and the intracellular (inside the cell) fluid has a 14% NaCl concentration, will water move in or out of the cell? Which is hypotonic and which is hypertonic?

water will move in. Inter is hyper and intra is hypo.

extracellular matrix

-animal cells have it -a meshwork of fibrous proteins and polysaccharides. -They are found in intercellular spaces and allow adherence of cells. -help in support and lend strength to the cell, neither interferes with the operation of the plasma membrane.

cell wall

-plant cells have it -a framework of cellulose fibrils called pectic substance (a type of protein). -They allow the cell wall to stretch. -help in support and lend strength to the cell, neither interferes with the operation of the plasma membrane.

two types of transport:

1. passive transport 2. active transport

Cell junctions allow interaction between cells:

4 major types (3 found in animal cells and 1 found in plant cells).

glycoprotein

A special kind of protein found in cell membranes. -These are proteins with carbohydrates attached to them. -They make cell to cell recognition possible and serve as the "fingerprints" of the cell. -Cholesterol also works in this fashion too. -Some plasma proteins allow for passage of substances across the membrane.

Active Transport

Cell uses its own ATP to move material across its membrane. Often against a concentration gradient.

Passive transport

Cells do not use their own ATP to move material across the cell membrane. Usually substances move from a higher concentration to a lower concentration.

Facilitated diffusion:

Movement of substances across a membrane from a higher concentration to a lower concentration with the aid of a carrier molecule. -Carrier molecule does not use the cell's ATP. -Examples: sugars (glucose) and amino acids.

Diffusion

Movement of substances from a higher concentration of the substance to a lower concentration of that substance. -Example: lipid soluble molecules and gases.

Osmosis

Movement of water from a higher concentration of water to a lower concentration of water across a semi-permeable membrane.

Carrier molecules:

Substances move across membranes with the aid of carrier molecules (also called permease systems) which does require using the cell's ATP.

cytosol

The internal and external environments of cells are largely fluid and within the cell it is called cytosol. -The cell (plasma) membrane surrounds the cytosol.

1. Animal cells

a. desmosome (adhesion junctions) b. tight junction c. gap junction

Proteins

are either partially or wholly embedded in the cell membrane. Composition of proteins varies among cells.

Cell membranes

are semi-permeable, which means that the membrane structure determines what can move across the membrane. -Cells can either use ATP or not in moving substances across the membrane. -There are two types of transport, separated based on whether or not the cell expends any of its own energy to move substances across its membrane.

Pinocytosis

cell drinking, engulfment of liquids

Phagocytosis

cell eating, engulfment of solids

c. gap junction

channel proteins connect adjacent cells together.

isotonic solution:

concentration of solute and water is the same on both sides of the plasma membrane.

hypertonic solution

concentration of solute is greater and the concentration of water is less than that of the cell, cells tend to lose water.

hypotonic solution:

concentration of solute is lesser and the concentration of water is greater than that of the cell, cells tend to gain water.

The Fluid-Mosaic Model

describes the structure of the plasma membrane as a mosaic of components —including phospholipids, cholesterol, proteins, and carbohydrates—that gives the membrane a fluid character. Plasma membranes range from 5 to 10 nm in thickness.

Phospholipids

have a nonpolar, hydrophobic end (tail) and a polar, hydrophilic end (head).

cholesterol

is a major membrane lipid and also has hydrophilic/hydrophobic ends. -They are believed to makes the membrane more impermeable to most biological molecules.

Receptor protein:

is shaped in such a way a specific molecule can bind to it.

glycolipids

lipids which have a hydrophilic head and are made up of a variety of sugars. -They function as receptor sites for the cell, cell markers, and possibly play a role in growth.

plasmodesmata

numerous narrow channels connect the cytoplasm between neighboring cells. -Tubular portion of the ER extends through these narrow channels from one cell to the next. -Plasma membrane surrounds the channels. -Plasmodesmata allow direct exchange of material between plant cells.

Exocytosis

opposite of endocytosis - substances move out of cells, vesicle fuses with the plasma membrane and discharges its contents into the intercellular spaces.

Cell membranes are made up of a

phospholipid bilayer

2. Plant cells

plasmodesmata

a. desmosome (adhesion junctions)

protein filaments between adjacent plasma membranes hold cells together.

Tonicity

refers to the solute concentration of a solution.

Carrier protein:

selectively interacts with a specific molecule or ion so that it can cross the plasma membrane.

Endocytosis:

substances to large to be taken into the cell by protein carriers may enter by:

b. tight junction

tiny proteins between the plasma membrane bind adjacent cells together.