Daily Newsletter: September 14, 2012 - Evolution Friday

Daily Newsletter

September 14, 2012 Evolution Friday

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The evolution of the cell, especially the development from prokaryote to eukaryote, is an important topic as it demonstrates core differences between living organisms. Archaea, Bacteria, and Eukarya are dramatically different from each other, but even within these domains, there are vast differences in cell types. When studying the development of cellular differences and structures, and thus studying the evolution of cells, biologists often look toward existent organisms that do not fit the typical cellular model. Anomalous structures give us insight into possible evolutionary steps.
For example, the genus Symbiodinium is an algae of the phyllum Dinoflagellata. These algae are known to live inside the cells of cnidarians (corals and jellyfish). Within the cell, they algae will deliver photosynthetic products to the cnidarians. Sound familar? How does this cell "know" to become symbiotic? Are there signals between the two cells? Does this mimic the entry of a Cyanobacteria into a cell where it became the chloroplast?
Then there is the bacterial phyllum Planctomycetes which researchers suspect is the "missing-link" between prokaryotic and eukaryotic cells, i.e., the development of a nucleus. Beyond membrane alterations, this is a bacteria that reproduces by budding (the daughter cell has a reduced cytoplasm). Other bacteria reproduce by binary fission, which results in two daughter cells with equal cytoplasm.
The bacterium Bdellovibrio is of interest in that it is a predator of other bacteria. This organism hunts other bacteria, enters their cell wall, then devours them. This is a very unusual characteristic. Not only in the recognition of prey, but in the entire life cycle. This is a complexity that we do not see in other bacterial groups.

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Daily Challenge

Review the following diagram showing proposed steps in the evolution of the eukaryotic cell.

In your own words, discuss the origin of the eukaryotic cell. Using the examples above, and any others you find, how can we provide evidence of these evolutionary steps or stages. Some claim that the Archaea are the ancestors of the Eukarya, but if so, why are there so many differences, espeically when it comes to phospholipids? How easy would it be to change the phospholipids a cell uses?

Link to Forum

Daily Newsletter: September 13, 2012 - The Mitochondria

Daily Newsletter

September 13, 2012 The Mitochondria

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The mitochondria is known as the power house of the cell, for this is where eukaryotic cells experience oxidative phosphorylation and ATP production. We will come back to ATP in a latter newletter, but you should note that phosphorylation of proteins is a powerful activator of enzymes (allowing them to work). Everything from pump systems, cellular movement, and even muscle contraction relies on ATP.
Like the structure of the nuclear envelope, the mitochondria is a double membrane bound structure, but the origin of the nuclear envelope and mitochondria are very different. It is hypothesized that the nuclear envelope formed from the infolding (invagination) of the cell membrane. The mitochondria, in contrast, is two separate and distinct membranes.
The Endosymbiotic Theory is used to explain the development of the mitochondria. (Question: why should we consider this a theory?) Before we get to the endosymbiotic theory, we need to first look at the structure of the mitochondria:
We have an outer membrane and an inner membrane. Between the two membranes is the Intermembranous Space. The inner membrane is highly folded into Cristae (Question: why would you fold a membrane?). The inner compartment, bounded by the inner membrane, is known as the mitochondrial matrix.
With the structure in mind, how does this differ from the nuclear envelope?

• The outer membrane displays eukaryotic proteins.
• The inner membrane displays prokaryotic proteins.
• The intermembranous space stores hydrogen ions, so is acidic.
• The matrix contains a circular bacterial DNA molecule and 70s (prokaryotic) ribosomes.
• The mitochondria is self-replicating (the DNA can make copies).

NOTE: Remember that phospholipid bilayer membranes allow you to create seperate fluid compartments. Here we have three fluid compartments: Intracellular, Intermembranous, matrix. Are these three fluid compartments have different chemical or electrochemical concentrations?
NOTE: The inner membrane seperates the intermembranous space (acid) from the matrix. We find that there is a H⁺ gradient across this membrane. Pumps along this membrane maintain the gradient by pumping H⁺ ions from the matrix into the intermembranous space. Pores along the inner membrane allow H⁺ ions to move back into the matrix. REMEMBER: when ions move down their electrochemical gradient across a membrane, work is done. There is a proton motive force across the inner membrane (this is the name we give to this type of H⁺ electrochemical gradient. 

QUESTION: Why do we not consider the outer membrane to have an electrochemical gradient?
 
The endosymbiotic theory describes the mitochondria as a bacterial symbiont that was engulfed by a "proto-eukaryotic" cell. A relationship formed between the two cells, with the mitochondria taking over ATP production, and the "proto-eukaryotic" cell loosing the ability.

Genenomic analysis of the mitochondria shows that it comes from the bacterial Order Rickettsiales, which means that it is related to the intracellular parasite Rickettsia rickettsii (Rocky Mountain Spotted Fever). Mitochondrial genes are inherited matrilineally, and are the basis of human population genetics studies of the mitochondrial genome.

Like the Mitochondria, the cholorplast is an endosymbiont that exists in eukaryotic photosynthetic cells (such as plant cells). Photosynthetic cells will have both mitochondria (extract energy) and chloroplasts (build reduced organic compounds). The function of the chloroplast is to use light energy to reduce carbon (carbon fixation) in order to produce reduced carbon compounds, such as glucose. The chloroplast, like the mitochondria, has two membranes, one eukaryotic in structure and ond prokaryotic. The chloroplast is also self-replicating, and has baterial ribosomes and genophore (DNA).

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Daily Challenge

Write about the mitochondria, the endosymbiotic hypothesis and human mitochondrial genetics. Explore these topics, and feel free to go deeper on any feature of the mitochondria that interests you. One question I want you to focus on is why is the mitochondrial genome reduced (smaller) than other members of the Rickettsiales? In your discussion, you must answer the question: Why do we not consider the outer membrane to have an electrochemical gradient?
Link to Forum

Daily Newsletter: September 11, 2012 - The Nucleus

Daily Challenge

September 11, 2012 - The Nucleus

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Admistrative: Milestone Paper

Your first Milestone Paper is due to be loaded next week. Remember that you can use any information written in your daily challenge to help build this paper.

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The nucleus defines the eukaryotic cell. Why would we say that? Remember yesterdays discussion about prokaryotes and eukaryotes? The principle differences is the presence or absence of a nucleus. Eukaryotes have a nucleus, while the prokarotes don't. Presence of a nucleus also implies the ability to create internal membranes.
The nucleus is a central structure present in eukaryotic cells, and is the site where we find the cell's DNA. It is a highly regulated structure, and one function is to ensure the protection and stability of the cell's genetic information. We also consider the nucleus an organelle.

The nucleus is a double membrane bound structure, which means that there are two lipid bilayers that make up the nuclear envelope.The outer layer of the nuclear envelope gives rise to the endomembranous system, which includes the Endoplasmic Reticulum and the Golgi Apparatus.

To gain access to the inside of the nucleus, you must first move through nuclear pores. Remember that phospholipid bilayers are selectively permeable. The nuclear pores are large. The purpose here is not to control ion movment, but macromolecule movement. For example, messager RNA (mRNA) will need to leave the nucleus so that proteins can be made in the cytoplasm. mRNA is a large linear macromolecule, so to move it from the nuclear compartment to the cytoplasm, you have to pass the mRNA through nuclear pores. These pores are regulated so that only specifically tagged macromolecules can move though. So the goal is not to protect the DNA from small molecules, but provide protection from macromolecules. Click on the link for more information on the nuclear pore complex.
Inside of the nucleus, you will find a region known as the nucleolus. In micrographs (pictures generated from microscopes), you will see the nucleolus staining differently than the rest of the nucleus. It appears denser. This is a region of active transcription (making RNA). Ribosomal RNA, Transfer RNA, and Small Nuclear RNA is continually being transcribed (synthesized) in this area, hence the reason for the difference in appearance.
The job of the nucleus is to protect the cells DNA. We will discuss DNA in more detail later, but for now know that it holds the code (in the form of nucleotides) for how to create the different forms of RNA, and thus how to create proteins. Changes in DNA will change the resulting protein's primary structure (sequence of amino acids). As we learned earlier, changes to the primary structure will affect the secondary and tertiary structures, and thus, the function of the protein. DNA needs to be protected from oxidizing agents, digestive agents, and any other harmful macromolecule.
NOTE: prokaryotes do not have a nucleus! The DNA of a prokaryote is found in the cytoplasm of the cell. As DNA has a tendency to stain differently than the rest of the cytoplasm, we can generally visualize the region of the cell where the DNA is found. In prokaryotes, this region is referred to as a nucleoid.

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Daily Challenge

In your own words, describe the structure and function of the nucleus, including the action of the nuclear pores.
Link to Formum

Daily Newsletter: September 10, 2012 - Cell Theory and Domains

Daily Newsletter

September 10, 2012 Cell Theory and Domains

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The fundamental unit of life is the cell. This is one of characteristics of life, and is a foundational principle of biology. Based on the discussions from last week, you see that for life to exist, we must first create a barrier that seperates and inside fluid compartment from the outside (external) fluid compartment. This allows us to create electrochemical gradients that will be necessary for life functions. When that membrane seperating inside from outside is disrupted and broken, life functions cease. While the cell membrane may be the defining structure of the cell, the cell is more than just the cell membrane.
This week, we turn our attention to cellular structure, and begin to look at the life functions of a cell. The first step is to recognize that all life is made up of cells, and that all living cells come from pre-existing cells. The following phrase, highlighted in yellow, is the core of the modern cell theory. This theory, which we credit to the work of Matthais Schleiden (1838) and Theodor Schwann (1839), was based upon growing microscopic work in the early 1800's. Work, even into the modern day, has provided robust evidence to support this theory, and has helped in some refinements.
What is interesting about the cell theory are the implications, e.g., a complex organism, such as man, is made up of millions of individual, and seemingly independent, cells. The overall organism, is an expression of the total activity of each of these cells. This has led to people studying communication between cells, for how do you coordinate the action of millions of individual cells? Another study is how the individual metabolic operations of cells can sum to the overall metabolic operation of an organism. As you can see, the idea of the cell being the fundamental unit of life has rather important implications for biology.
When we look at life, we begin to notice that there are different types of cells. The most basic difference between cells is the presence or absence of a nucleus. Prokaryotic cells lack a nucleus, while eukaryotic cells contain a nucleus. The nucleus, which will will cover in more depth later this week, is an internal comparment that contains the cells DNA. An internal compartment means that there is a membrane barrier that seperates the contents of the compartment from the rest of the cell. Like the cell membrane, these internal compartments are surrounded by protein containing phospholipid bilayers (fluid mosaics). As the cell membrane seperates the extracellular fluid from the intracellular, so to do these internal membranes create new fluid compartments. Just like the cell membrane, these internal membranes are selectively permeable, and allow for internal spaces with different chemical concentrations.
The presence or absence of a nucleus is a major taxonomic feature for organisms, and the ability to form and maintain internal compartments has many implications for the organism (some of which we will discuss this week). One of the major differences is in size. Remember all the proteins found on the cell membrane? An important thing to remember is that there are a termendous number of metabolic reactions that occur at the membrane, as well as the import and export of ions. We have to have enough membrane to satisfy our metabolic needs. The larger the volume of the cell, the smaller the surface area, so cells have to remain small. That is, unless you have the ability to make internal membranes. Internal membranes increase the available surface area...so eukaryotic cells, which are able to make internal membranes, can be larger than prokaryotic cells.
Living organisms are divided into three domains: Eukarya, Archaea and Bacteria. Eukarya contains all cells that are eukaryotic (nucleus containing). The Archaea and Bacteria are prokaryotic. The division of organisms into three domains was based on genetic and biochemical analysis conducted over the previous 30 years. Each domain represents a unique cellular structure.

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Daily Challenge

Members of all three domains are based on the fundamental unit of the cell. For today's challenge, you are to discuss the differences that led to the three domains being declared unique from one another.
Link to Forum

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Reflection

Cells are the fundamental unit of life, but over the past four years, virologists have been saying that the definition of life should be expanded to include acellular structures such as viruses. Currently, viruses and other acellular structures are considered to be biological agents; i.e., structures that can affect the genetics and metabolism of a cell, but are not technically living. What would be the logic behind expanding the definition of life to include viruses? What problems would it create?

Daily Newsletter: September 6, 2012 - Cell Recognition and Junctions

Daily Newsletter

Cell Recognition and Junctions

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Cells must have the ability to sense their environment, and part of this is to be able to sense and recognize other cells. In a multicellular organism, individual cells must be able to recognize other cells that are part of the same organism, and must be able to anchor to them. Ultimately, mutlicellularity requires cells to have some system whereby cells are anchored to each other.

For example: Would you be able to move if your muscles were not somehow anchored to the bone? Would your skin be a defensive structure if it separated when you pulled it? Would your cardiovascular system be able to transport blood if the pressure would rip open the vessels?

In terms of recognition, we also have to have the ability to determine if something is part of the "SELF" or foreign. We will find that the ability for cells to recognize each other will be an important concept in many areas of biology, most notably, immunology. The Major Histocompatability Complex Class I and II are two protein complexes (quaternary proteins) that are part of our "self recognition" system. The figure to the right shows a cartoon of MHC I, which is found on every nucleated cell in the body. MHC will become important in discussions on immunology. For now, remember that it is a cellular marker in our self recognition system.
When we talk about cell signaling, we will come back to the concept of cellular receptors, many of which are membrane bound proteins. Their job will be to pick up chemical signals around the cell, and then cause a response inside of the cell.
A linked topic to cellular recognition is cellular junctions. Cellular Junctions are points where two cells are anchored together through proteins and glycoproteins. There are numerous types of junctions, and some are specific to a group of organisms. The following three cellular junctions are associated with different animals, and provide a good foundation in the function of cellular junctions.
Tight Junctions - This is a cell junction found in vertabrates that holds cells tightly together, causing them to form a water proof layer. Water (and solutes) is not able to move through the intercellular (between cell) spaces. Instead solutions must pass through the cell (we regulate what moves through). This is important in organs like the stomach, intestines, and bladder.
Desmosomes - This type of cellular junction is designed to adhere cells together in a manner that is many times described as "spot-welding". Keratin plauges (waterproof structural protein) hold adhesion (anchoring) proteins. The adhsion holding plauges from different cells connect to form an incredibly strong and durable junction. The goal is to create a series of very strong connections between neighboring cells without creating a waterproof layer. These are found in areas of animal tissue that need to resist shearing or tearing forces.
Gap Junctions - The previous two types of junctions were designed to hold the cell membranes of two cells together. While this also occurs with the gap junction, the ultimate goal is different. With the gap junction, cells are connecting their cytoplasm, forming a continuous cytosol (cellular solution) between the neighboring cells. This is critical for rapid movement of ions between cells. This type of junction is used to communicate electrical changes (action potentials/nerve impuses) from one cell directly to another cell. The gap junction will come up again in discussions about action potential, neural function, and heart muscles.

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Daily Challenge: Junctions and Recognition

Explain why cellular junctions and cellular recognition are important to multicellular organisms. Use MHC and desmosomes as examples of cellular recognition proteins and junction proteins. Also discuss how we are using membrane bound proteins to make these recognition points and junctions. Do you think you are born with all the recognition points and junctions, or can you change them over time?

Link to Forum

Daily Newsletter: September 5, 2012 - Active Transport

Daily Newsletter

September 5, 2012 Active Transport

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Administrative Note

Please note that I have added a number of tutorials for you to use. Some are step by step guides, while others are video lectures. Each one has interesting content that can help you as you go through this section of material, or in some cases, throughout biology. I encourage you to review them. There will also be an optional forum where you can comment about what you learned from the Video lectures.

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In active transport, cells are moving substances across the membrane, but against the chemical concentration gradient. Chemicals are move from areas of low concentration to areas of higher concentration. To move against a concentration gradient requires energy to overcome the inherent Brownian motion of the molecule. This always requires protein (enzyme) pumps. The word pump implies an active process that moves against a natural gradient or flow. (consider: passive transport proteins are called channels, pores or carriers, while active transport proteins are called pumps)
The most commonly discussed pumps will be the ion pumps. There are two pumps that all biology students must become familiar with as they are critically important and are discussed in many different biology courses.

• Sodium-Potassium ATPase (also known as the Na⁺/K⁺ pump).
  • This helps to establish and maintain the Sodium and Potassium gradients of a cell.
  • Sodium should be at high concentrations outside of the cell (extracellular)
  • Potassium should be a high concentrations inside of the cell (intracellular)
  • This combined gradient helps to establish the Resting Membrane Potential of many cells (an electrical charge across the membrane).
• Proton Pumps
  • This pump system help to establish and maintain a proton (hydrogen ion) gradient.
  • In Eukaryotes, this will be found along the inner mitochondrial membrane.
  • In Prokaryotes, this will be found along the cell membrane.
  • This is a critical electrochemical gradient for cellular energy.

With both of these pump systems, we are creating electrochemical gradients, and both represent potential energy.
All active transport systems require energy to work. Primary active transport will utilize ATP, while secondary active transport will utilize either reducing power (redox reactions) or an established electrochemical gradient.
Primary Active Transport: The addition of the phosphate causes a conformational change in the proteins structure. Remember, you are adding a -2 charge to a specific location on the protein; this will change the electrical profile of the protein, causing the proteins folding pattern to change. Note that both Na⁺ and K⁺ are moving against their electrochemical gradients.
Secondary Active Transport: As with active transport, there will be a conformational change in the protein (aka, the folding pattern, and hence shape, will change). The cause of this shape alteration will either result from a redox reaction or an established electrochemical gradient. In the image below, we see the entry of one ion (sodium) causing the expulsion of a second ion (amino acid) in an antiport system. How do you know that sodium is the "motive force"? Look at the Na⁺ concentration gradient; sodium is moving down the electrochemical gradient.

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Important Memes

When an ion moves down it's electrochemical gradient, across a membrane, work (kinetic energy) is done. The electrochemical gradient is a seperation of charged particles (ions) on either side of the membrane. When we speak of a Sodium (Na⁺) gradient, we are actually referring to an electrochemical gradient. Movement of ions down an electro chemical gradient is akin to hooking up a battery in a circuit, you get kinetic genery (work is done). Until then, the electrochemical gradient acts a potential energy.
When you add something to a protein, the protein changes shape. This is a general rule that you should remember. Whether it is the substrate of an enzyme, an ion, or a phosphate, as things are added, the protein's shape changes.

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Daily Challenge: Na⁺/K⁺ pump

Using diagrams and text, describe the operation of the Na⁺/K⁺ pump. Explain it! Your goal is to show an understanding of primary active transport, how proteins change shape, and how ions have not only a chemical gradient, but also an electrical gradient.

Daily Newsletter: September 4, 2012 Phospholipid Bilayer & Passive Transport

Daily Newsletter

September 4, 2012 The Phospholipid Bilayer & Passive Transport

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The basic structure of the cellular membrane is composed of Phospholipids. You will recall the introduction to phospholipids found in Daily Newsletter: August 29, 2012 - Carbohydrates and Lipids. The amphipathic nature of phospholipids means that they will naturally associate with one another. Specifically, the hydrophobic tails want to be with other hydrophobic compounds, and exclude polar compounds (Hydrophobic Exclusion-This is a good concise discussion of the topic by Stephen T. Abedon, Ph.D. at Ohio State). Below is a brief movie that shows what happens when phospholipids in water begin to interact.

Phospholipid Movie: Bilayer formation through molecular self-assembly

The resulting phospholipid bilayer is polar (hydrophilic) on the outside, while the middle is non-polar (hydrophobic). The sides interact with water, but the middle excludes polar substances. This creates a selectively permeable barrier, and is the basis of the membranes function. Changing phospholipids and adding sterols (like cholesterol) will change the integrity and stability of this basic membrane structure.
Selective permeability means that only certain classes of chemical can make it through the phsopholipid bilayer. For other chemicals, we need to provide a protein to serve as a pore, channel or transporter.
In general, there are two ways that a chemical can be moved across the membrane: Down the chemical's concentration gradient (diffusion), or Against the chemical's concentration gradient. When a chemical moves down it's concentration gradient, we do not need to add energy to the process. The concentration gradient and the kinetic energy of the molecule (Brownian Motion) provided the needed energy. We call this form of movement Passive Transport.

There are three basic forms of passive transport through the membrane:

1. Diffusion - Using the inherent Brownian motion of molecules, chemicals move from points of high concentration to points of low concentration.

• Every chemical has a unique concentration gradient.
• The concentration gradient of one molecule will not interfer with the concentration gradient of another molecule.
• What interfers is the ability to move across the cellular membrane (phospholipid bilayer).
• Molecules with high polarity, ions, and large molecules are excluded by the phospholipid tails, and thus can not cross.
• Water*, CO₂, O₂, and nonpolar compounds (lipids) can cross though diffusion.
• Water moves through very slowly; water moves across more readily due to porins (protein pores) possessed by cells to make sure water and small polar compounds can cross readily.

Osmosis - The movement of water across a selectively permeable membrane.

• Water goes to where the party is, meaning it will move to a compartment that has a higher solute concentration.
• Since we are talking about two fluid compartments on either side of a membrane, we are ultimately talking about relative solute concentrations.
• REMEMBER: you are looking at two fluid compartments, so when we are looking at osmosis, we are discussing the movement of water across a selectively permeable membrane from one fluid compartment to a second fluid compartment.
• In biology we always use the inside of the cell as our reference, so:
  • An isotonic fluid has the same solute concentration as the inside of the cell.
  • A hypertonic solution has a solute concentration that is higher than the solute concentration inside the cell.
  • A hypotonic solution has a solute concentration that is lower than the solute concentration inside the cell.

• Remember that we are looking at solute concentrations, not the concentration of a single chemical.
  • Diffusion gradients are specific for each chemical.
  • Osmosis is determined by total solute concentration on each side of a selectively permeable membrane.

Facilitated Diffusion - Ultimately, this is diffusion, but the cell has had to provide a passage for the chemical. So, this only applies to chemicals that can not normally pass through the phospholipid bilayer.

• The cell provides a protein channel or pore for the chemical to pass through.
• Each channel or pore is specific to a single chemical or set of chemicals.
• Since this is an protein (enzyme) mediated action, the ability to transport follows standard enzyme kinetics.
• The core idea about facilitated diffusion following enzyme kinetics is that diffusion becomes limited by the number of channels or pore available.
• Note: You will generally build up a large concentration of a compound on one side of the membrane. We will refer to this as a steep gradient (high on one side, low on the other).
• The facilitator proteins will allow molecules from the HIGH side to move toward the LOW side; hence the use of the word diffusion.
• Rarely will the channel or pore (facilitator) allow transport in the reverse direction for the same ion.

In each case, the cell does not need to expend energy to move the chemical across the membrane. The motive force is built in to the chemical gradients. Remember, the cell membrane is going to provide an internal vs. an external space (compartment). Each side of the membrane will have a unique chemical profile. As such, there will be concentration gradients across the membrane.

Osmosis Movie

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Important Memes

Occassionly, there will be a phrase that I want you to remember to help you as you move through biology.

1. Water goes to where the party is! (This is a great way to remember in what direction water will flow across a selectively permeable membrane in response to changes in osmolarity, aka, solute concentration).
2. The phospholipid bilayer establishes the structure of the membranes, but the proteins provide the function. (The proteins embedded in the membrane will determine the functional capabilities of the membrane).
3. When something is added to a protein, the protein changes shape.

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Daily Challenge: Passive transport

In your own words, describe passive transport. Concentrate on osmosis and facilitated diffusion by providing an example that illustrates each action. Make sure you use an example that uses a cell (not beakers, flasks, etc...).

Daily Newsletter: September 3, 2012 - The Nature of the Cell

Daily Newsletter

September 3, 2012 The Nature of the Cell

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The cell theory describes the importance of the cells to biologists. How important is it? Well the first part of the cell theory answers that: All known living things are made up of one or more cells. But what ultimately is a cell? What takes place in one? Why are they so important?

It will take a few discussions to get to all these questions, but there is a starting point. As a basic description, the cell is a self-managing, self-contained chemical factory. Cells take in materials, use these for energy and building blocks, and then produce materials to keep the cell healthy, harvest nutrients, eliminates waste, and produces products. The cell has many components to accomplish these tasks: DNA for management, chemical signals to send messages, enzymes for chemical activity, etc....

Let's look at the analogy of a chemical factory: Inside a factory, there are going to be different processing places for different chemicals. There are going to be pathways of pipes going between vats and other structures. Taking a further look back, there is a building, with trucks coming and going.


Inside of the cell, chemical reactions will be taking place. Outside the cell, chemical reactions are taking place. Are they the same chemical reactions? One of the foundations of cells is that the inside of a cell is a spatial area with a defined concentration of a variety of chemicals that is distinct and different from the chemical concentrations found outside of the cell.

So, there is an inside and outside of a cell, and they are different.

You will hear me say again and again that the cell membrane is the defining structure of a cell. Why? Because it establishes the boundary. When you have a cell membrane, you can have an inside as opposed to an outside of a cell. If you loose that membrane, you start moving to a full equilibrium between the inside and outside of the cell. If you loose the membrane, or it gets holes, the cell dies. The cell dies when you cease to have an inside vs. an outside.

The fastest way to kill a cell is to poke holes in it.

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Daily Challenge: The cell membrane
Today, I want you to discuss the basic structure and functions of the cell membrane, focusing on this idea that it provides the essential, and foundational, separation between the inside and outside.