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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
What is a fluid mosaic model?
Cell membranes are a phospholipid bilayer
The membrane is also asymmetrical meaning that both sides are different. This is because one side is facing and outside environment and the other is facing an inside environment. Both of these environments are different so both sides of the membrane perform different functions.
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
Unsaturated fatty acids help keep the cell fluid. The kinks in the fatty acid chains prevent the phospholipids from packing too close to one another and become solid.
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
-Attachment Proteins
-Recognition Proteins
-Receptor Proteins
-Transport Proteins
Lipids and Proteins are free to move laterally through the membrane because it is only weak hydrophobic interaction that exist in the middle of the bilayer membrane
Diffusion and Osmosis
-Diffusion is the movement from an area of high concentration to an area of low concentration
-Passive Transport
-Simple Diffusion
-Facilitated Diffusion
-Channel proteins that transport ions are called ion channels
-In the case of ions, they diffuse across membranes down their electrochemical gradiants
-Some of these are gated channels that open in response to a stimulus
-Osmosis
-Osmosis is the diffusion of water
-When water moves from an area of high concentration to 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.
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 (less pressure)
-Hypotonic- having more water (More pressure)
-Isotonic- having an even amount (no pressure)
With Osmosis there is a net diffusion of water heading in the direction of hypertonic until equilibrium is met
-Equilibrium- having no pressure- isotonic
-Once an equilibrium is met the pressure is isotonic
For your quiz be able to label a jar as hypertonic, hypotonic, isotonic, and be able to say which direction the water will travel.
Plants that do not produce wood rely on turgor pressure for stability.
-The central vacuole fills with water which pushes against the cell wall making the plant turgid
-If the plant does not have water it becomes flaccid
-The cell membrane pulls away from the cell wall. This is called plasmolysis
-Active Transport
-Endocytosis
-Pinocytosis
-Phagocytosis
-Receptor-mediated endocytosis- this is a more selective version of endocytosis
-Exocytosis
Neurotransmitters
How cells know when to divide. The body releases growth factors which are a lipid based hormone. The growth factor diffuses through your blood stream and spreads throughout your body. The growth factor binds to any cells that have a growth factor receptor protein in their cell membrane. The receptor protein releases cyclin. The cyclin binds to cyclin dependent kinases (CDK). The CDK phosphorylates the proteins involved in mitosis. Phosphorylation means adding a phosphate group to a protein which is the way you activate proteins.
There are three major checkpoints for mitosis or cell division. These checkpoints are in place to make sure everything goes right. If something were to go wrong with cell division it could lead to cancer or other problems. There is a checkpoint between G1 and the S phase. If the cell is not ready to replicate its DNA it will not be allowed to enter the S phase. There is another checkpoint after G2 to make sure the cell is ready for mitosis. At this checkpoint the cell makes sure that the DNA was replicated properly. The last major checkpoint is after metaphase to make sure all the chromosomes lined up properly before they enter anaphase and are separated. Each one of these checkpoints requires phosphorylation by CDK's to move on.
Cancer
Cancer is caused by unregulated cell division. It is basically mitosis gone wrong.
There are many tumor suppressors inside our cells that help us fight against cancer. There are many ways that cancer can happen. Many of the ways that cancer is formed happens when one of our tumor suppressors breaks or mutates. This happens from damaged DNA.
Here are the normal working tumor suppressors
And here is what happens when these suppressors break or mutate
What is the Rb Gene?
The retinoblastoma protein (abbreviated pRb, RB or RB1) is a tumor suppressor protein that is dysfunctional in several major cancers.[1] One function of pRb is to prevent excessive cell growth by inhibiting cell cycle progression until a cell is ready to divide.
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