Bio test 1

Smallest to Largest

Chemical level - atoms + molecules

Cells (Atoms + molecules)

Cells form tissues

Tissues form organs

Organs form organ systems

Organ systems make up an organism

Isotonic Solutions

cells retain their normal size and shape in isotonic solutions (same solute/water concentration as inside cells; water moves in and out)

Hypertonic solutions

solutions that cause cells to shrink or shrivel due to loss of water

Hypotonic Solutions

water moves into the cell

Tissues are made up

similar cells with a common function.

Organs:

2 or more tissues organized into a structure

what living things do:

Maintain boundaries: We keep our internal environment separated from the external environment in a lot of ways.. we keep bacteria out, water in, water out, toxins out, and other goodies we like to keep to ourselves.

2. Movement.

3. Responsiveness (irritability):As things (or people) around us affect us, we can respond to the stimulus.

4. **Digestion:**Breaking down foodstuffs into things for our bodies to use.

5. **Metabolism:**Chemical reactions in cells :anabolic or catabolic

6. **Excretion:**We all get rid of wastes in various forms

7. **Reproduction:**Not necessary for individual survival, but of the species.

8. **Growth:**We start small and get larger, as do all living things.

Survival Needs

**Nutrients:**We need food nutrients for energy and most of our body processes.

2. **Oxygen:**Cellular respiration works best in most cases using oxygen.

3. **Water:**Most of our bodies are made of water- it provides a way to move things around our bodies, a medium for chemical reactions, and other great things.

4. **Body Temperature:**The chemical reactions in the body require heat to speed them along. That's why we build houses, and why other animals slow down when it gets too cold. If we get too cold our body processes stop, and that's not good for us!

5. **Atmospheric Pressure:**Ever see the Arnold movie "Total Recall"? When they went out on the surface of Mars their eyes popped out and their heads exploded. We don't KNOW that would happen to us today, but we do know we do need some pressure to hold us together as well as put oxygen into our blood and other things we will get to later.

Homeostasis

Internal conditions remain relatively constant despite changes in the external environment

ex. body temperature (98.6), blood pressure, blood sugar, blood PH. the internal environment is not UNCHANGING, but rather it remains within set ranges. What this means for us is that we keep our body temp fairly constant whether its 10 degrees out or 110. We keep our blood sugar relatively constant whether we are eating or fasting. We keep blood calcium levels relatively constant, our blood pH is relatively constant, as is blood oxygen, blood pressure, and about every other thing you can think of about our body.

Loss of homeostasis =

illness

Receptor:

:This is the sensor that sense the level of the variable. This measures the variable (body temp, blood sugar, etc) then sends impulses via afferent pathway to the control center.

Control center:

The control center determines the set point, analyzes the input from the receptor, and determines the output or if changes need to be made.

Effector

receives input via efferent pathways from the control center and changes the variable.

Negative Feedback Systems

shut off once things are back to the set point (ex. sweat, shivering). These are the most common in our body since they tend to reduce changes to the body- they keep homeostasis.

Positive Feedback Systems

increase in strength to reach a goal. Not as common. Big changes quickly. Ex. healing after getting a cut, labor. actually will increase the activity of the effector once changes in the variable have been made. These are usually reserved for body functions that need immediate, strong responses to achieve some goal.

homeostatic imbalances:

aging reduces efficiency of the control systems, pathogens disrupt them, injuries affect them and any imbalance is a sign of disease or illness.

Normal blood sugar = 90 mg/100 mls

If blood glucose levels are high, cells in the pancreas detect this + release the hormone insulin

Insulin goes to the liver + takes glucose + stores it as glycogen to lower blood sugar

Receptor: Pancreas Cells

Control center: Pancreas Cells

Effector: Liver

Glucose: Cells in the pancreas detect low blood glucose and release the hormone glucagon

Glucagon goes to your liver and it breaks down glycogen to release glucose

Receptor: Pancreas

Control center: Pancreas

Effector: Liver

Clotting: You trip on your feet, fall on your face and break blood vessels.

2. Platelets adhere to damage and release clotting factors.

3. These clotting factors cause more platelets to adhere, more platelets adhere and release factors. This is a

POSiTIVE feedback system- it strengthens itself because we don't want to wait 2 weeks to stop bleeding- we want to stop bleeding NOW to preserve homeostasis.

Atoms

Protons neutrons and electrons

Orbitals

First orbit is 2, second is 8, third also has 8

Carbon -

6 protons + 6 electrons

2 protons in first orbit, second has 4 - would like to have 8. Makes chemical bonds to have 8 electrons.

Covalent bonds -

atoms share electrons

ex. H2O - water

O - 2 electrons on first ring, 6 on second. Shares 2 electrons with 2 hydrogens.

Sharing can be equal: no charged areas

nonpolar covalent bond. Don't mix w/ water. Oils + fats are nonpolar or "hyrdrophobic" - water-fearing.

or unequal:

ex. H2O. Hydrogens are positive, oxygen is negative. Polar covalent bond. Dissolve in water. Hydrophillic.

Ionic Bonds

Electrons move from one atom to another.

ex. NaCl (salt).

Na - 11. 2 on first ring, 8 on second, 1 on third

Cl - 17. 2 on first ring, 8 on second, 7 on third.

Cl steals from Na. Na becomes positive and Cl becomes negative.

Hydrogen Bonds

Opposite charges attract. Polar molecules.

H2O. Oxygens are negative, hydrogens are positive.

Acids give off

Hydrogen (H+). Ex. Hydrochloric acid - HCl - H+ + Cl-

H2CO3 - Carbonic acid. H+ + HCO3- (bicarbonate ion)

Bases take

hydrogen (H+)

ex. HCO3- + H+. H2CO3

Acids increase

H+ concentrations

Bases lower

H+ concentrations

PH

measures the concentration of H+ or [H+]

PH = -log[H+]

[H+] = 10^-3 moles/liter = Ph = 3 (Acid). Ph is always the exponent.

Ph = 7 = [H] = 10^-7. Neutral.

PH above 7 is a base.

Buffer systems work to

prevent changes in PH

Blood PH = 7.4. Ex. Carbonic acid/bicarbonate buffer system.

(Side A) H2CO3 - (Side B) H+ (Carbonic acid) + HCO3- (bicarbonate ion)

PH should not change much.

More hydrogens -

Lower PH.

Excess hydrogen from drinking lemonade? Buffer system

gets rid of it. Removes excess H+ by going towards side A.

Replaces H+ by going towards

side B.

As you exercise, you produce lactic acid. The PH will

decrease. The buffer system will remove excess hydrogen by going towards side A.

Carbohydrates:

Energy. Hydrophillic.

Monosaccharides: single sugars. 5 or 6 member rings (O).

Disaccharides: 2 put together.

Polysaccharides: Long chains of monosaccharides together. Ex. Glycogen. Sugar.

Lipids:

Hydrophobic molecules.

triglycerides: fats + oils.

c-c-c (3 carbon glycerol)

| | | - fatty acids.

Saturated (fats - Solids) vs. Unsaturated (oils -Liquid).

Unsaturated - irregular shape.

C-C-C

| | | _

\\

Phospholipids - Charged molecule

P - Charged. Polar. Hydrophillic head.

|

c-c-c

| | | - Hydrophobic

Phospolipid bilayer. Hydrophic in the middle, hydrophillic tails

Steroids come from

cholesterol. 4 rings.

Proteins:

Long chains of amino acids.

R- Variable for amino acids.

H2N - C- C - OH

|

|. (O - acid)

(Amino Group)

Primary structure -

order of amino acids.

Secondary structure -

Local twists and folds

Tertiary structure -

complex. folding so the protein works. If you disrupt the structure, it does not work anymore - becomes denatured. Ex. cooking eggs. High fevers.

atom

smallest unit of an element.

Atoms consist of

a nucleus containing protons, neutrons, and electrons traveling around in orbits. This can be visualized as being similar to our solar system: A sun in the middle (nucleus) with orbitals moving around sun. These orbits contain a certain number of electrons, and different orbits are filled by different numbers of electrons:

i. 1st orbit: 2 electrons

ii. 2nd orbit: 8 electrons

iii. 3rd orbit: 8 electrons

Atoms will

always attempt to have the outermost orbit filled with the correct number of electrons.

Atoms have

no charge: so the number of electrons equals the number of protons. The number of protons is given by the atomic number of the atom.

An Ion is

an atom where an electron has been either lost or gained: it no longer has the same number of electrons as protons and so it carries either a positive or negative charge.

Chemical bonds form as

atoms attempt to make sure they have their orbitals filled: They will fill the first orbital first with 2 electrons, the second orbital with 8 electrons, and the 3rd orbital with 8 electrons.

There are 3 basic types of chemical bonds:

(1) covalent bonds, (2) ionic bonds, and (3) hydrogen bonds.

In covalent bonds, atoms share electrons to satisfy need of outer orbit:

An example of this is seen below as Carbon atoms will bind with 4 Hydrogen atoms. Note that the atomic number of carbon is 6: it uses 2 electrons to fill the innermost orbit. The remaining 4 electrons begin to fill the outer orbit but it only has 4: it needs four more to fill the orbit. Notice Hydrogen with an atomic number of 1 has only 1 electron. It needs 1 more to fill its outer orbit with 2 electrons. The carbon will share electrons with 4 hydrogens. Since they share, they all fill the outer orbit.

Non-Polar Covalent Bond

A non polar covalent bond is seen above: all the electrons are being shared equally and the resulting molecule of methane has no charged portions. CO2 in the picture below is also non polar.

Polar Covalent Bond

A polar covalent bond forms when the electrons aren't shared equally. This is what is happening in the water molecule seen below: The oxygen is larger and can keep the electrons more than the smaller hydrogenscan. As a result, the oxygen picks up a slightly negative charge, and the hydrogens are slightly positive.

Ionic Bonds

another way of assuring an atom has a completed outer orbital. In ionic bond one atom will take an electron from another to yield ions. NaCl is good example of an ionic bond.

a. Na has 11 electrons: 2 go in the first orbital, 8 go in the 2nd orbital, and we see there is 1 leftover.

b. Cl has 17 electrons: 2 electrons in the first,8 in the second, 7 in the third and it and wants 1 more to fill the orbital with 8.

c. NaCl bond as a crystal when dry, but when put into water, NaCl dissociate to Na+ and Cl-: Na has donated its extra electron, Cl needed on more electron and accepts the donated electron. Notice that now Na has a positive charge (since it lost a negative electron) and Clhas a negative charge (since it picked up a negative electron).

Hydrogen Bonds

are a little different since they don't complete the outer orbit of an atom. These are weak bonds caused by proton of hydrogen being attracted to a negatively charged molecule. If you remember the water molecule shown above, there were positive and negative parts to that molecule. A hydrogen bond is a simple attraction between positive and negative charges.

Although simple, they are important to our body in several ways.

i. hydrogen bonds allow for DNA double helix

ii. hydrogen bonds give water capillary action and surface tension

iii. hydrogen bonds allow some polar groups to be water soluble

Here we see how the positive and negative parts of the water molecule can create hydrogen bonds. The positive hydrogens are attracted to the negative oxygen atoms.

ACIDS

proton (H+) donors. Acids make the H+ concentration of a solution higher.Example: HCL (hydrochloric acid) H+ and Cl-another is H2 CO3 (carbonic acid) H+ + HCO3-

2. What this means is that if we put an acid into water, the concentration of hydrogen ions will increase. We can shorten that to read: [H+] - which indicates we are talking about the concentration of the hydrogen ion.

BASES

proton acceptors: these will remove H+ from the system and lower the [H+]: Example would be HCO3- which is the bicarbonate ion. If we put it into solution with hydrogen ions: HCO3- + H+ à H2CO3.

1. Notice in the above examples we had carbonic acid donating a hydrogen ion and acting as an acid. This results in formation of bicarbonate ions.

2. Bicarbonate ions act as a base and can accept the extra hydrogen ions. This results on the formation of carbonic acid.

The pH Scale

ur measurement of the concentration of H+in an aqueous solution. It looks complicated, but it really isn't that bad.

1. pH = -log[H+], so if the concentration of H+ is 10-7moles/liter, the pH =7 . This is a neutral solution such as pure water.

2. If you have a concentration of 10-3 moles/liter (molarity) of H+, then pH=3. This is an acidic solution.

3. If [H+] = 10-12, then pH is?

4. Yep, its pH= 12. This is a basic solution.

5. Notice from the diagram below that as Hydrogen ion levels increase we become more acidic. The pH will DROP!

6. As hydrogen ion levels decrease, we become more basic. The pH will INCREASE!

Buffer Solutions

are an important thing for our bodies. Buffers tend to reduce changes in the pH. Remember that our blood pH was an important factor in homeostasis, so its one of those things we like to keep pretty constant. Buffers help us do that. Buffer systems can work by absorbing excess H+ (we are too acidic) or by releasing H+when there are low levels (we are too basic).

a. The major buffer system in our blood involves carbonic acid and bicarbonate ions: H2 CO3 H+ + HCO3-

b. This is the carbonic acid/bicarbonate buffer system. This is constantly working in our blood to maintain our pH at about 7.4

As we exercise, lactic acid is produced, and since acids release H+ this will increase

[H+] in our blood. This would lower our pH if uncorrected. So, as the [H+] increases, it will associate with the bicarbonate ions to produce carbonic acid. In the equation above the reaction will be going toward the left; toward the formation of carbonic acid. So, our pH will not change much and we are buffered.

In extreme vomiting we lose many H+ from our body. As we lose H+ our pH would drastically

increase (we would be more basic) if not for carbonic acid dissociating into H+ and HCO3- to keep our pH buffered. The reaction above would be going to the right.. toward the formation of hydrogen and bicarbonate ions.

Organic Compounds

The are all based on carbon molecules: they can be found in rings and chains of carbon atoms.

2. These molecules contain functional groups or additions to the chains and rings such as:

1. NH2: amino groups: these are found in amino acids.

2. C=O: carbonyl group: these are found in ketones

3. OH: hydroxyl groups. These are found in sugars in the middle of rings and chains and alcohols if at the end of a chain.

4. HOC=O: carboxy group. These are found in organic acids such as amino acids and vitamins such as citric acid.

3. These molecules all have stereospecificity. This means that these molecules, like our hands, have right or left handedness. We can look at our right and left hand. We can count our fingers and our thumbs. They SOUND the same when we describe them, but looking at them we obviously have mirror image or opposite structures. Organic molecules come the same way: in right (D-form for dextrorotatory) or left (L-form for levorotatory) handed forms. Our bodies will only acknowledge and use L-amino acids and D-sugars.

Carbohydrates

Carbohydrates contain Carbon, Oxygen, and Hydrogen in a ration of 1 carbon, 2 hydrogens to 1 oxygen, for CH2O. These come in various levels of structure and are called saccharides. The levels are: (1) monosaccharides, (2) disaccharides, and (3) polysaccharides.

Monosaccharides

simple sugars like gucose and fructose. The mono part tells you its only 1 sugar molecule by itself. Some monosaccarides can be seen in the picture below:

Disaccharides

Disaccharides are two molecules put together. That is what the di- part of the word tells you. Table sugar is made of two monosaccarides: glucose and fructose. These can be seen in the picture below. the fructose and glucose molecules are put together by removing a water molecule (H2O)- a H atom from glucose and a OH group from the fructose. This process is called dehydration synthesis (dehydration = removal of water, synthesis=making). To break apart the sucrose we can simply add water back to split the molecule back into glucose and fructose. This is called hydrolysis (hydro = water, lysis = splitting or disrupting). These two processes are common mechanisms for making larger molecules in our bodies and for breaking large molecules down.

Enzymes are

proteins in our bodies that speed up these reactions.

Polysaccharides

Polysaccharides are many monosaccharides put together to form long chains (poly means many). Glycogen is a polymer of glucose that is used for storage of glucose in liver and in muscles. Here we see it below:

Lipids

These are insoluble molecules in polar solvents (water). Since they are insoluble in water, that also tells us that they are hydrophobic and also that they don't have charged aspects for the most part. Lipids come in 3 flavors:

1. triglycerides

2. Phosopholipids

3. Steriods

Triglycerides

fats and oils. They are made by the addition of a 3 carbon glycerol and 3 long fatty acid chains as seen below. Notice again that dehydration synthesis is the process creating these larger molecules.

Saturated and Unsaturated Fats

Lipids can be saturated fats and what this means is that each C in the fatty acid chain has 2 H on it: it is saturated with Hydrogens. This makes for very regular molecules with a consistent shape that pack very well at RT and form solids- these are the fats. When you read about anything about diet it will always tell you to try to avoid saturated fats. This is because in addition to packing well at room temperature on the counter, they also pack well in your arteries and cause clogging.

2. Lipids can also be unsaturated fats and what this means is that each C does not have 2H. This causes double bonds to form. Where the double bonds between the C form it creates kinks in the chain and irregular molecules. These irregular shapes don't fit together well and these stay more fluid at room temp- these are the oils. They don't pack well at room temperature and stay liquid on the counter. They also stay liquid in your arteries and tend to not cause clogging.

Phospholipids

These molecules are similar to triglycerides, but instead of 3 fatty acid chains, there are 2 fatty acid chains plus a molecule that has a phosphate on it. These are now polar molecules where the phosphates with hydrophobic ends where the fatty acids are. Molecules that are both hydrophobic and hydrophyllic can be called amphipathicmolecules.

This makes phospholipids very interesting molecules. In water, these have a hydrophyllic or polar end that wants to be in the water and a hydrophobic or non polar portion that tries to avoid the water. To keep both sides happy they will either form lipid bilayer sheets, liposomes or micelles. All these are successful at keeping the polar heads near the water and the hydrophobic tails away from the water.

Also notice in the phospholipid pictured above that the 2nd fatty acid chain is unsaturated. Notice how the double bond between carbon atoms puts a kink in the chain.

Steroids

another type of amphipathic lipid and they are all based on the cholesterol molecule seen below. These too have polar and nonpolar regions and vary from one another by the addition of different functional groups.

Proteins

These are all polymers (repeating units) of molecules of amino acids. All amino acids have same basic structure and are only different from each other by differences in the R group. There are over 20 variations of the R group which is shown in green below.

Amino Acids

Even though our bodies use more than 20 amino acids, we cannot synthesize all of them on our own and so we must be sure to get them in our diets. These are referred to as the essential amino acids.

Amino acids are held together by

peptide bonds to form peptides (small chains) and proteins (long chains). Here is how dehydration synthesis works again to form longer molecules from simple building blocks.

Proteins have various levels of structure and the simplest is called the

primary structure. The primary structure refers to order of amino acids in a chain. In secondary structure the chains begin to take simple shapes such as an alpha helix or a pleated sheet.

In the tertiary structure: chains fold back on itself to form more complex shapes.

4. In quaternary structure several chains may interact with each other to make more intricate complexes.

Denaturation

These structures are critical for protein function. If a protein should lose it's tertiary or quaternary structure the protein will lose it's function. This is a permanent loss of the protein and is referred to as denaturation.

Things that denature proteins would include:

1. Changes in the pH. both acid and bases can alter protein shape.

2. Temperature extremes. High fevers can change protein shapes which is why we avoid very high temperatures.

3. Heavy metals such as mercury

4. Toxins.

Again, once a protein has been denatured it cannot be fixed. This is what we do when we cook eggs: They go from clear and runny to white and solid- ever try to undo that? YOU CAN'T!!

Matthias Schleiden and Theodor Schwann proposed what we now call the

cell theory. It has a few basic parts which state:

1. Cells are the basic structural and functional component of living things

2. The organism's activity is dependent on both individual and collective activities of cells.

3. The principal of complimentarity states that biochemical activities of cells are dependent on subcellular components.

4. Finally, cells reproduce.

plasma membrane: the basics of the fluid mosaic model.

This model states that a membrane is basically a phospholipids bilayer as discussed in Chapter 2. In this bilayer are cholesterol (helps stiffen the membrane) as well as both integral and peripheral proteins.

2. Integral membrane proteins are difficult to remove from the plasma membrane- in fact they cannot be removed without destroying the membrane. Some of the integral proteins may also have sugar groups attached to make them glycoproteins.

3. Peripheral membrane proteins are only loosely associated with the membrane and can be removed without severe damage.

Plasma Membrane Specializations

Plasma membranes may have some unique specializations depending on their location and function of the cells. These specializations may include:

1. **Microvilli:**Fingerlike extensions to increase the surface area of cells: this is useful for cells that absorb or secrete.

Membrane Junctions

:

These are the ways that cells can be held together. The diagrams below illustrate the 3 basic types: (1) tight junctions, (2) desmosomes, and (3) gap junction.

Tight Junctions

Integral proteins in the cells membranes fit together like a zipper: nothing can pass between the cells. Tight junctions are good for places that we don't want things to get around the cells- the stomach cells are a good example because if the acid gets past it destroys the underlying tissue- this is what happens in an ulcer.

Desmosomes

These are anchoring junctions to hold cells together and consist of an anchoring protein in the cell membrane and then flexible wire-like protieins between these anchors. This gives cells the ability to resist being pulled apart. Desmosomes are found in areas subject to tension such as muscles and skin. There are forms of muscular dystrophy that are caused by a defect in a single protein found in the anchors in the cell membranes. These proteins fail, and the cells are torn apart and replaced with scar tissue. Over time, this results in all the muscle being destroyed and the person is no longer able to move.

Gap Junctions

These allow chemicals to pass from one cell into another-like tunnels between cells that allow small things like ions to pass. Gap junctions are found in cells where electrical connections are important such as cardiac muscle cells. They allow these cells to work together as a single unit to contract and pump blood.

The plasma membrane is involved in transport of materials in and out of the cell. This can require energy and be called

active transport, or require no energy and be considered passive transport.

Passive processes would include

diffusion of materials from high concentration to low concentration, and filtration where hydrostatic (water) pressure moves things across the membrane. The ion channels we will talk about in a bit are examples of passive transport.

Active processes use

ATP and include things like the Na+/K+ ATPase and bulk transport (endocytosis, phagocytosis, pinocytosis, exocytosis). We will talk about the Na+/K+ ATPase more in a bit since it is an important protein and an example of active transport.

Signaling Between Cells

how plasma membranes allow our cells to act like little batteries and have electrical properties useful for signaling between cells. This is one of the important plasma membrane processes and is found in the neurons, the muscle cells, and cardiac muscle cells.

membrane potentials.

Cells are like little batteries in that the inside of all cells is electrically negative compared to the outside of the cell. This is due primarily to the differences in concentration of positive and negative charges inside and outside of cells. Lets see what happens in our beaker shown below. What we have is a beaker with a difference in the Na Clconcentration on both sides. We have a membrane in the middle. The membrane shown above is permeable to Na+, but not Cl-. The concentration gradient will cause Na ions to move over to the B side because things will always tend to move from high concentration to low concentration. When the Na ions move, they take with them a positive charge. Notice how the B side is now positive when compared to the A side, which is now negative!

This difference in charge is called a voltage. It's basically the same thing you see in a battery with a positive pole and a negative pole! Our cells are like batteries! This gives us electrical energy useful for what cells need to do.

You will recall that membranes can be one of three types:

1. Impermeable membranes will not allow anything to cross (this is boring, might as well be a wall!)

2. Freely permeable membranes allow EVERYTHING to cross (this is also boring.. why bother with a membrane??)

3. Semi-permeable membranes are more interesting. They only allow certain things to cross so they are more like what our cells will do.

Equilibrium Potential

Let's apply this idea to our cells and look at the 2 major ions influencing our cells electrical activities:

For both Na and K we have what we call the equilibrium potential. This is the theoretical voltage that would be achieved if only one ion could cross the membrane. Let's start with K first. We find this in high concentrations inside the cell and lower concentrations outside.

Potassium and Sodium Equilibrium

Our cells have a set of what we call fixed negative charges. These are negative charges due to proteins and DNA that can't leave the cell. Potassium concentration is HIGH inside cells, lower outside. The concentration gradient forces K out. The electrical gradient (opposites attract) pull K back in. That's where those fixed negative charges come into play. Under these conditions, potassium is entering the cell due to the electrical attractions, but potassium content is higher in the cell than it is outside, causing potassium to leak out due to concentration gradients.

We can measure this voltage to see how negative our cells are on the inside. Since K+ leaks out, not enough can enter to neutralize the negative charges in cell. Our body doesn't have a high enough concentration of potassium to achieve this. If potassium is all we had moving, we would have a potential difference of about -90 mV. This means that the inside of the cell is negative about 90 millivoltswhen compared to the outside. This can also be called the equilibrium potential of potassium.

If we look at what sodium can do we get a different answer. Sodium can also leak into the cell in response to these electrical charges. It leaks much more slowly than potassium, but if it were the only ion moving it has aequilibrium potential of +60 mV. It is positive since there is much more sodium outside of the cell. In this case the concentration gradient is pushing Na into the cell, and the electrical charges are attracting Na+ into the cell as well. Both of these working together allow the cell to become positively charged on the inside if Na+ was the only ion involved.

Resting Membrane Potential

In real life, both Na+ and K+ ions are working together to create what we call the resting membrane potential of the cell. It balances out so cell membranes are anywhere from -65 to -85 mV when compared to the outside. That's going to depend on the cell type. It is closer to where K+ would like the membrane to be (-90mV) because there is more K+leaking out than Na+ leaking in.

At this point the curious student is wondering.. WHY do we have more K+ inside cells and more Na+ outside our cells? Well, the answer is found in what we call the sodium/potassium pump (Na+/K+ ATPase). This is an active transport process that will pump 3 Na+ out of the cell and put 2 K+ back in. It uses 1 ATP in the process and also generates some heat. THIS is what sets up the concentration gradients for the cells and gives them electrical properties.

Action Potential

Now that we know where the electrical properties of cells come from, we need to talk about what cells do with them. Cells normally rest at around -65 to -85 mV, but resting is boring. Some cells are electrically active and rely on ions moving in and out to bring activity to our bodies. Our neurons do this when we think, our muscles do this when they contract, our heart does this every time it beats. It is called the ACTION POTENTIAL and depends on Na+ and K+ movements. It can be divided up into 3 basic parts:

1. When a resting cell is stimulated, the first thing that happens is that Na+ is allowed to enter the cell rapidly. Remember the Na+ has a concentration gradient pushing Na+ into the cell, and the fixed negative charges pull Na+ in as well. The positive charges entering make the cell positive and this is called the depolarization phase.

2. Once the cell becomes positively charged, the Na+channels are closing and the K+ channels open.

3. This allows K+ to leave the cell so the cell returns to being negatively charged. Remember that the concentration gradient for K+ will push the ion out of the cell, but the electrical attraction tends to pull it back in. The positive charges leaving make the cell more negative again and this is called re-polarization

The diagram below shows these 3 basic steps along with some other things we will discuss later. For now, just notice that Na+ entry causes depolarization and K+ exit causes re-polarization.

Organelles

the components of the cell that determine its activities so are important little items.

Organelles

Ribosomes

Endoplasmic reticulum- both smooth and rough

Golgi apparatus

Lysozomes

Peroxisomes

Mitochondria

Centrioles

Cytoskeletal elements

cytoplasmic organelles

The cytoplasm is the gel solution which contains the other organelles and serves as a medium for a number of intracellular reactions.

Lysosomes are

vacuoles which contain digestive enzymes. These will fuse with endocytotic vacuoles. These digestive enzymes are important for the breakdown of lipids, proteins and polysaccharides brought into the cell via phagocytosis.

1. Primary lysosomes contain only enzymes.

2. Secondary lysosomes contain digestive enzymes and partially digested macromolecules.

3. Residual lysosomes contain undigested wastes which will be exocytosed or kept in the cell.

4. Cells can digest their own organelles (called autophagy) or release the digestive enzymes causing programmed cell death, or apoptosis. Think about this though.. would this be the MAIN function of this organelle? If it were, how long would we last if all our cells went around killing themselves??

Mitochondria

These organelles serve as the site of energy production.

1. The basic structure is an outer membrane and an inner membrane with many folds called christae, which extend into the inner portion and form the matrix. The christae and matrix consist of different compartments and have different functions.

2. Mitochondria have their own separate DNA, and protein synthesis apparatus, and can divide and replicate independently of what the cell is doing.

1. Mitochondrial DNA in mammals is a single circle containing 17,000 nucleotides.

2. Its structure is very different from the nuclear DNA. Nuclear DNA has genes which are interrupted by exons, while mtDNA is one continuous gene which is transcribed.

3. It has been suggested that since the DNA structure is so different than nuclear DNA, mitochondria evolved from an organism similar to bacteria and infiltrated mammalian cells and formed a symbiotic relationship that was beneficial to both organisms. More interesting mitochondria trivia lies in that an individual's mitochondria are inherited entirely from the mother, since sperm contain no mitochondria. This fact means that some genetic defects can be passed on through the mother, and do not affect the chromosomal DNA, only the mtDNA. Leber's optic neuropathy and other neuromuscular disorders.