Anatomy 25 cytology - cell membrane

Palsma membrane - The outer boundary of the cell, the "shell".

Cytoplasm - contains organelles, surrounds nucleus.

Nucleus - controls cellular activity.

Cell membrane is made of a lipid bilayer consisting or phospholipids with hydrophobic fatty acid chains pointing towards each other and charged hydrophilic heads pointing to watery outside and inside of the cell membrane.

Proteins that are imbedded in or strongly attached to the lipid bilayer.

Transmembrane integral proteins span the entire lipid bilayer. They can allow or deny certain things to pass the lipid bilayer.

Some of these transmembrane proteins are choloesterol which allow the cell membrane to remain flexible at a range of temperatures.

Are attached to the outer surface of the cell membrane.

Some of these are simple sugars, carbohydrates. These give the cell a kind of unique identifier and allow it to be recognized as that particular kind of cell by the rest of the body.

The cell coat. Glycocalyx means "sugar covering".

Some of these are simple sugars, carbohydrates. These give the cell a kind of unique identifier and allow it to be recognized as that particular kind of cell by the rest of the body.

The stickiness of the glycocalyx also helps the cells stick together to bind when they need to.

Some membrane proteins act as receptors. They are able to bind to specific molecules outside of the cell and pull them in for whatever the cell needs them for.

The cells picking up extracellular mollecules are in this way also able to communicate with th rest of the body.

Connexon proteins between two bonded cells have a channel between them through which stuff can be transferred.

Band of proteins that wraps around the top ( apical? ) portion of two cells to hold them togeher.

Sort of spot weld points between cells. Intermediate filaments inside the cell attach to cytoplasmic placques inside the cell which attach to cadherins which transvers the cell wall and connect to cadherins of another cell, holding the cell together.

Intermediate filaments->cytoplasmic plaque->|cell membrane| ->cadherins

IF>CP>CM>C }I|=

These are the things a cell membrane can do!

Small, uncharged particles, fat-soluble drugs ( -lipid-bilayer ).

Tendency for molecules to pass from areas of higher concentration to lower concentration.

Only certain things can pass through a cell membrane. If a particle or molecule is small enough and if it is fat-soluble ( -lipid-bilayer ) it may pass through.

Some particles or molecules will diffuse through a protein channel, in this case shape, size, and electrical charge are limitations to what can pass through the protein channel.

Diffusion that does not act only by way of difference in concentration. Fascilitated diffusion uses a intergral ( trans-membrane ) carrier protein to move polar, charged molecules which cannot move through cell membrane by regular osmosis through cell membrane.

A substrate attaches to the carrier protein and the carrier protein then reorients itself ( changes shape, moves ) to move the substrate to the inside of the cell.

This process requires energy which is gained from the breakdown of ATP to ADP.

Water passing through a semi-permeable membrane.

The process of particles and large mollecules being pulled into a cell.

For these larger molecules and particles which cannot pass through transport proteins or lipid bilayer the cell membrane sort of caves inward ( invaginates? ), holding the particle in a sort of bubble ( coated pit ). The opening of the bubble then seals the cell membrane again and the bubble then releases the particle into the cytoplasm.

Phagocytosis = "cell eating".

Psuedopods reach out.

The cell membrane pokes out little pseudopods that reach out and surround the partcle, seal it off forming a phagosome, pull it in, and seal off the opening created by the pseudopods moving into the cytoplasm.

White blood cells are really good at this, surrounding a foreign body, pulling it into itself, then KILLING IT! DUN Dun dunnnn....

Pinocytosis - "cell drinking"

Cell membrane indents in.

The cell membrane kind of caves in, sucking in some of the extracelular fluid along with it.

This process is used by cells lining the intestines to pull in nutrients.

1. Substrates bind to receptors on the outside of the cell membrane.

2. Clathrin ( a protein ) inside the cell is then signaled to attach to the inside of the cell membrane at the site that the substrate has attached to. The clathrin then help pull the substrate and cell membrane in in a kind of bubble called a coated pit.

3. The pit seals off, the cell membrane reseals. The pit is now a bubble containing "stuff" and is called a coated vescicle.

4. The clathrin detach from the coated vescicle turning it into an endosome.

5. Endosome then fuses with a lysosome ( lysosomes contain acid hydrolase enzymes which break stuff down ).

6. The lysosome digests the "stuff" and either uses it or expells it.

7. Clathrin carry receptors back to the cell membrane.

Flask ( chemistry flask ) shaped indentations in the cell membrane which are coated with caveolin proteins.

These work kind of like receptor mediated endocytosis to move spcific substrates, very small molecules into and around in the cell.

Moving stuff from the inside to the outside of the cell.

Removal of waste products from cells.

Production of useful materials by cells.

Microvilli ( microvillus - sing. ) are long, fingerlike projections on the cell membrane of some cells. They serve to increase the surface area of the cell. They are found in the small intestine ( as well as other areas ) where the greater surface area makes for greater nutrient absorbtion.

They do not move around on their own, they contain actin - microfilaments that allow the microvilli to change or maintain shape.

Cilia are much larger than microvilli and also unlike microvilli they move around.

They have a quick whip / beat like motion followed by a slow recovery motion.

They serve to move stuff along the surfaces they occupy.

They line mucous membranes in your nose and serve to remove debris from your nose.

Flagellum are cilia, they are the tails on sperms that whip back and forth to propell the sperm along its merry way.

Cillia have 9 doublet pairs of microtubules in a circle connected to each other by dynein. In the middle of this circle are 2 more microtubules that are not conncted.

The basal body ( base ) of the cillia is made up of a triplet centriole - 9 sets of 3 microtubes, and produces the cilium. Rootlets anchor the cilium in place.