The Cell Membrane

Functions of the Cell Membrane

     -Selectively isolates the cell from the external environment

     -Regulate the exchange of essential substances between the cell and the extracellular fluid

     -Communication between cells

     -Create attachments within and between cells

     -Regulate biochemical reactions

Cell membranes are a phospholipid bilayer

A phospholipid has a hydrophilic (Water liking) Head and a hydrophobic (Water hating) Tail

     -These two features of a phospholipid are extremely important. they are the reason that cells can exist.

     -The cell membrane is like a drop of oil floating in water. It is not very strong and can easily tear open.

     -The chemical properties of lipids is what allows some things in and others not...also known as selectively permeable

Activity:

     -Lets go outside to blow bubbles

     -In many ways a cell membrane is like a soap bubble

     -It is a phospholipid

     -It has a hydrophobic side and a hydrophilic side

     -Its natural properties drive it to form a sphere (bubble)

Membrane Proteins

     -The phospholipid bilayer is not the only thing that makes up the cell membrane.

     -There are also membrane proteins embedded in the bilayer

We call these proteins Integral Proteins

Here are some types of the integral proteins

 Attachment Proteins

     -Attachment proteins attach the cell to other cells. It is what holds them in place. You would not want your heart cells floating off.

Recognition Proteins

     -A recognition protein is like a name tag. Most cells have a name tag. Heart cells say hello my name is heart. Skin cells say hello my name is skin. Your blood type is a recognition protein.

Receptor Proteins

     -A receptor protein receives signals and messages. This is where hormones will bind and other messages sent throughout the body.

     -A ligand is the specific molecule that binds to and activates the receptor protein

Transport Proteins

     -Transport proteins transport things in and out of the cell. Since many things cannot cross the phospholipid bilayer, the transport proteins bring in and remove what the cell needs.

     -There are passive transport proteins that do not require energy and then there are active transport proteins that do require energy.

Read this Case study about Cystic Fibrosis

Cell: Cystic Fibrosis

Cystic fibrosis (CF) affects approximately 30,000 people in the United States, with about 1,000 new cases reported each year. The genetic disease is most well known for its damage to the lungs, causing breathing difficulties and chronic lung infections, but it also affects the liver, pancreas, and intestines. Only about 50 years ago, the prognosis for children born with CF was very grim—a life expectancy rarely over 10 years. Today, with advances in medical treatment, many CF patients live into their 30s.

The symptoms of CF result from a malfunctioning membrane ion channel called the cystic fibrosis transmembrane conductance regulator, or CFTR. In healthy people, the CFTR protein is an integral membrane protein that transports Cl– ions out of the cell. In a person who has CF, the gene for the CFTR is mutated, thus, the cell manufactures a defective channel protein that typically is not incorporated into the membrane, but is instead degraded by the cell.

The CFTR requires ATP in order to function, making its Cl– transport a form of active transport. This characteristic puzzled researchers for a long time because the Cl– ions are actually flowing down their concentration gradient when transported out of cells. Active transport generally pumps ions against their concentration gradient, but the CFTR presents an exception to this rule.

In normal lung tissue, the movement of Cl– out of the cell maintains a Cl–-rich, negatively charged environment immediately outside of the cell. This is particularly important in the epithelial lining of the respiratory system. Respiratory epithelial cells secrete mucus, which serves to trap dust, bacteria, and other debris. A cilium (plural = cilia) is one of the hair-like appendages found on certain cells. Cilia on the epithelial cells move the mucus and its trapped particles up the airways away from the lungs and toward the outside. In order to be effectively moved upward, the mucus cannot be too viscous; rather it must have a thin, watery consistency. The transport of Cl– and the maintenance of an electronegative environment outside of the cell attract positive ions such as Na+ to the extracellular space. The accumulation of both Cl– and Na+ ions in the extracellular space creates solute-rich mucus, which has a low concentration of water molecules. As a result, through osmosis, water moves from cells and extracellular matrix into the mucus, “thinning” it out. This is how, in a normal respiratory system, the mucus is kept sufficiently watered-down to be propelled out of the respiratory system.

If the CFTR channel is absent, Cl– ions are not transported out of the cell in adequate numbers, thus preventing them from drawing positive ions. The absence of ions in the secreted mucus results in the lack of a normal water concentration gradient. Thus, there is no osmotic pressure pulling water into the mucus. The resulting mucus is thick and sticky, and the ciliated epithelia cannot effectively remove it from the respiratory system. Passageways in the lungs become blocked with mucus, along with the debris it carries. Bacterial infections occur more easily because bacterial cells are not effectively carried away from the lungs.

Diffusion

     -Diffusion is the movement from an area of high concentration to an area of low concentration

-In order to understand diffusion we need to remember that atoms are always moving. Hot atoms move fast. Because atoms are always moving they tend to bounce off each other. Once they collide and bounce off each other they then head in the opposite direction. All of this bouncing off of each other causes atoms to spread out. This is diffusion.

SO WHAT! Who cares about diffusion?

Diffusion is the reason everything in biology works. At the heart of almost all biological processes is diffusion.

     -Passive Transport (Does not require energy)

     -Simple Diffusion

     -Facilitated Diffusion (Diffusion that needs a little help)

     -Osmosis (Diffusion of water)

Demonstration:

-The teacher sprays body spray in the front of the classroom and then continues to lecture. As the students become able to smell it they raise their hands. This continues until the body spray can be smelled from the back of the room.

      -How did the spray make it to the back of the room?

Real World Application:

     -When you wear cologne or perfume do you spray it on your clothes or on your skin? Why do you do that? Do you have a reason for doing one or the other?

     -Heat speeds up the rate of diffusion because the hotter a molecule is the more energy it has. The molecules can travel faster when they are heated up.

     -If you spray perfume on your skin, your skin heats the perfume causing it to diffuse faster which means it can reach further distances faster. If you are in a room and perfume is on your skin then everyone in the room can smell you. The draw back is that the perfume does not last as long because the rate of diffusion is happening so fast.

     -If you spray perfume on your clothes the perfume will stay with you much longer but only people right next to you can smell you.

Osmosis

Osmosis is the Diffusion of Water

     -When water moves from an area of high concentration to low concentration

Some words we need to know:

     -Solvent-Usually water-the substance there is more of. the liquid doing the dissolving.

     -Solute-The other substance in the mixture of the solvent and the solute. Usually the stuff mixed in with water

     -Hypertonic- having less water (More pressure)

     -Hypotonic- having more water (Less pressure)

     -Isotonic- having an even amount (Same pressure)

     -Equilibrium- having same pressure- isotonic

Active Transport (Requires energy)

     -Endocytosis (When cells engulf things)

     -Pinocytosis (When a cell engulfs a large drop of water)

     -Phagocytosis (When a cell eats)

     -Exocytosis (When a cell sends things outside)

Cells

Cells are made up of Organelles

It is important to know each organelle and their function

Golgi Apparatus - Packages, labels, and ships anything made in the cell

Nucleus - Where genetic information is stored (DNA)

Nucleolus - Where ribosomes are made

Plasma Membrane - The membrane around a cell (phospholipid bilayer)

Mitochondria - Where ATP (cell energy is made)

Endoplasmic Reticulum

Smooth ER - Makes lipids and also detoxifies things

Rough ER - The location where proteins are made

Ribosomes - Makes proteins

Cytoplasm - The space in the cell between the membrane and the nucleus

Cytoskeleton - Holds the structure of the cell

Vacuole - Cell storage

Vesicle - Cell transport

Lysosome - A vesicle filled with digestive enzymes for breaking things down

Centriole - For cell division

Chloroplast - Does photosynthesis

Cell Wall - Around the membrane for protection

Flagella - A tailed used for movement

Cilia - Hair like structures for movement

Read this Case Study

Cell: The Free Radical Theory

The free radical theory on aging was originally proposed in the 1950s, and still remains under debate. Generally speaking, the free radical theory of aging suggests that accumulated cellular damage from oxidative stress contributes to the physiological and anatomical effects of aging. There are two significantly different versions of this theory: one states that the aging process itself is a result of oxidative damage, and the other states that oxidative damage causes age-related disease and disorders. The latter version of the theory is more widely accepted than the former. However, many lines of evidence suggest that oxidative damage does contribute to the aging process. Research has shown that reducing oxidative damage can result in a longer lifespan in certain organisms such as yeast, worms, and fruit flies. Conversely, increasing oxidative damage can shorten the lifespan of mice and worms. Interestingly, a manipulation called calorie-restriction (moderately restricting the caloric intake) has been shown to increase life span in some laboratory animals. It is believed that this increase is at least in part due to a reduction of oxidative stress. However, a long-term study of primates with calorie-restriction showed no increase in their lifespan. A great deal of additional research will be required to better understand the link between reactive oxygen species and aging.