A&P Chapter 3

• Tight junctions: impermeable junction that encircles the cell and prevent molecules from passing through the intercellular space. (between epithelial cells lining the digestive tract).
• Desmosomes: Anchoring junctions bind adjacent cells together and help form an internal tension reducing network of fibers. (abundant in tissues subjected to great mechanical stress, such as skin and heart muscle)
• Gap Junctions: communicating junctions allow ions and small molecules to pass from one cell to the next for intercellular communication. (present in electrically excitable tissues, such as the hear and smooth muscle, where ion passage from cell to cell helps synchronize their activity)

• The tendency of molecules or ions to move from an area where they are in higher concentration to an area where they are in lower concentration.
• Non-polar and lipid soluble substances diffuse directly though the lipid bilayer

• A type of passive transport process
• 1. binds to protein carriers in the membrane and is ferried across, or
• 2. moves through water filled protein channels.
• The rate of diffusion is controllable

A water-specific channel constructed by transmembrane proteins that water is able to move freely and reversibly though

The total concentration of all solute particles in a solution

the back pressure exerted by water against the membrane.

The tendency of water to move into the cell by osmosis

The ability of a solution to change the shape or tone of cell by altering their internal water volume

Cells immersed in hypertonic solutions lose water and shrink; or crenate

Cells placed in a hypotonic solution plump up rapidly as water rushes into them

• Primary active transport: the energy to do work comes directly from hydrolysis of ATP
• Secondary active transport: transport is driven indirectly by energy stored in ionic gradients created by operation of primary active transport pumps. All are coupled systems.

in active transport when the two transported substances are moved in the same direction.

• Ejects 3 sodium ions out of the cell
• Carries 2 potassium ions into the cell

Signaling chemicals that bind specifically to plasma membrane receptors

shelflike inner membrane folds of the mitochondria

• 1. Ligand (1st messenger) binds to the receptor
• 2. The activated receptor binds to a G protein and activates it.
• 3. Activated G protein activates (or inactivates) effector protein by causing its shape to change
• 4. Activated effector enzymes catalyze reactions that produce 2nd messengers in the cell
• 5. Second messengers activate other enzymes or ion channels.
• 6. Kinase enzymes transfer phosphate groups from ATP to specific proteins and activate a series of other enzymes that trigger various cell responses.

• Contain their own DNA, RNA, and ribosomes and are able to reproduce themselves.
• When cellular requirements for ATP increase, the mitochondria synthesize more cristae or simply pinch themselves in half (fission) to increase their number and then grow to normal size.

• Free ribosomes: make soluble proteins that function in the cytosol
• Membrane bound ribosomes: synthesize proteins destined either for incorporation into cell membranes or for export from the cell

• Lipid metabolism, cholesterol synthesis
• synthesis of steroid based hormones
• absorption, synthesis and transport of fats
• detoxification of drugs
• breakdown of stored glycogen to form free glucose
• calcium storage

• the principal "traffic director" for cellular protein.
• Major function is to modify, concentrate, and package the proteins and lipids made at the rough E.R.

• Most important function is to neutralize dangerous free radicals.
• Numerous in kidney and liver cells

• small region of cytoplasm near the nucleus in the cell where most microtubules radiate from.
• Centrosome is a region; centromere is the organelle

act as internal guy wires to resist pulling forces exerted on the cell

• Nuclear envelope (membrane): contain nuclear pores
• nucleoli: not membrane bound; sites where ribosomal subunits are assembled
• Chromatin: fundamental units are nucleosomes- consist of flattened disc-shaped cores or clusters of eight histone proteins connected like beads on a string by a DNA molecule.

unwinds the double helix and exposes the bases

Positions complementary nucleotides along the template strand and the covalently links them together

Constructed in segments in the opposite direction of the leading strand and requires that a primer initiate replication of each segment

Normal cells stop proliferating when the begin touching

noncoding, often repetitive segments that range from 60 to 100,000 nucleotides

amino acid specifying the informational sequences

The process of converting DNA base sequence to the complimentary base sequence of mRNA molecule

• 1. Initiation
• 2. elongation
• 3. termination

the information carried by mRNA is decoded and used to assemble polypeptides.

• elongates the mRNA strand one base at a time
• unwinds the DNA helix in front of it and rewinds the helix behind it

Remove introns from the newly formed RNA