Transport Across the Membrane. ^__^

Diffusion and Facilitated Diffusion.

Hydrophobic small and uncharged could pass through a membrane, but larger ones has more difficulty.

Simple Diffusion: Where molecules diffuse across the lipid bilayer through channel proteins in the direction of their concentration gradient.

Facilitated Diffusion: Where protein carrier molecules within the membrane assist the passage of substances across the membrane in the direction of the concentration gradient.

All methods above are passive, which means no cellular energy is required.

Concentration Gradient means that stuff from areas where there a lot goes into the areas where there's more little. Kinda to even things out a bit.

The bigger the difference between one side of molecule, the bigger/ more dramatic the net movement. [AN: So, basically, if there's more to shift, it puts more into doing it and gets the job done quicker, right?]

Diffusion is continued until equilibrium is reached.

It is chance that it hits are protein channel in facilitated, so wit ha higher concentration/amount of ions/molecules, the higher the chance of hitting the channel.

If they can pass through the lipid bilayer they are lipid soluble.

The larger the surface area, the more diffusion that can take place.

If the temperature is higher there is more kinetic energy, so the particles move quicker and there is more collisions. (Link this to before paragraph.)

Steepness of concentration gradient also affects it. If it is lower, diffusion will be less strong/quicker.

The membrane thickness affects the rate of diffusion too. The thicker the membrane, the longer it takes, as there's more to travel through.

Fick's Law states that the Rate Of Diffusion = (Surface Area x Steepness of Concentration Gradient) / Thickness of Membrane.

In facilitated diffusion there are CARRIER MOLECULES involved. When carier molecules have reached their limit, they can't transport any more. Eg, like only being able to fit two kids in a double buggy. Unless you take one out, only then can another take it's place.


Thoughts & Additions?
-Nin. ^_^

Triglycerides and all that jazz.

Obj- To be able to draw and label the components of a Triglyceride.

Lipids - Biochem of Biological Molecules.

Lipids are a diverse collection of substances. They are an excellent energy store. Hibernating animals use them to store nutrients as fats. They are found in seeds/the fruit of a plant.

They are used for:

1. Energy Storage.
   
2. Insulation - useful, conducts heat slowly.
   
3. Source of metabolic water- fats oxidised in respiration and make water. Deserts animals such as camels store fats as a source of this.

Lipids are not soluble in water, they are in organic liquids though, like ethanol.

A triglyceride, is glycerol, with 3 fats attached.

The difference between an oil and a fat is that an oil is a liquid at room temperature whereas a fat is a solid.

Glyderol is usually called a hydrocarbon, thanks to it's structure:

H
-
H- C - OH
-
H- C - OH
-
H- C - OH
-
H

If there are 3 hydrogens attached to a carbon, this structure is called a Methyl group. The -OH is a Hydroxyl group, wihch is the one found in alcohols. Therefore, Glycerol is a three carbon, alcohol molecule.

Fatty acids are hydrocarbons chains of varying length with a methyl group at one end and a carboxylic acid group at the other.

Methyl is a carbon with three single bonded hydrogens. Carboxylic acids is an 'Oh' single bonded to a carbon, with a double bonded oxygen.

COOH, means something is an acid.

Saturated fatty acid = Get a fat in triglyceride. (Yea, I don't get this bit of my note. Kersplain, someones?)

Unsaturated: Got double bonds, less saturated with 'H' atoms. Not as many particles that can move betweens each other can't become more squished and rigid, so becomes liquid, not solid. Also has a far lower melting point.

[AN: Surely with would mean Fats are saturated and Oils aren't? Yea? Comment and help???]

The more double bonds, the lower the melting point. [WHY?]

A triglyceride forms in a condensation reaction. If you're ever in doubt, write condensation reaction. Or at least, this is what my notes say. Lets go along with that one, shall we?

Anyway, it forms an 'o', or oxygen bond inbetween, which has a name, an esther bond.

To test for lipids, we use the Lipid Emulsion Test. To do this, we:

1. Take the material/sample, and put in the a test tube.
   
2. Add to this approx 2cm[cubed] of ethanol and shake. (Vigorously will do. xP)
   
3. Add 2cm[cubed] of water, and ...
   

If a MILKY EMULSION forms, this is a positive indictation of a lipid's presence.



Like usual, correct me, should I be wrong. I'm only an AS student, as I've said. (:
-Nin.

Magnification (Realllllly no notes whatsoever.)

Magnification = What you see/ Actual size.

The '/' represents divide, since, after like, 11 years around computers, I only just realised there's no divide sign on a keyboard.

Anyway, you can put it in a handy little triangle too. A bit the the distance speed time one at GCSE? It spells out IAM with the 'I' at the top, the 'A' on the left, bottom, and the 'M' on the right bottom. Cover up one letter to figure out which ever way round you need to put the equation for your question.

So yeah, short post.
-Nin

Cell fractionation and Ultracentrifugation.

Pg 41/42 in AQA Bio textbook. (They're the ones we use at QE, so if you're from there, that bit of info is for you.)

Obj- To describe the process and the resultant separation of cell components.

Cell fractionation is where cells are broken up and the organelles they contain are separated out.

1. HOMOGENATION: The cell is broken up by a homogeniser (big spinny thing, bit like a food liquidiser, only a little bit more high-tech. xP) The resultant fluid is called homogenate.
2. ULTRACENTRIFUGATION: Fragments of the homogenate are separated. rganelles get sedimented and seperated in order of density. (Not heaviness. Exam board people don't like heaviness. :D)

The three conditions of the whole thing are:

1. Temperature: Really low to prevent bacterial growth, but the main reason is to slow down any enzymes that may damage the organelles.
2. Isotonic Solution: Makes sure it has the same water protentail as the tissue to preven organelles from bursting or shrinking.
3. Buffered: Maintains a constant pH (Why???? )

The solid pellet at the bottom are centrifugation is called a supernatant.

It goes down a density gradient, For example: Nucleus, Mitochondria, Lysosomes, Membrane, Ribosomes.

The faster it is spun in centrifugation, the lighter the organelles that get separated/isolated, so it is spun with gradually increasing speed to get the denser ones first.

This is useful for finiding out the function, but not 100% perfect.

And remeber, correct me where I'm wrong. It helps. (:

-Nin.

The Electron Microscopeyyyy. ^_^

Obj- To describe the priciples and limitations of the Trasmission Electron Microscope, and the Scanning Electron Micrscope.

Cell surface membrane. Acts as a barrier (things go out and in). Smooth endoplasmic reticulum synthesises LIPIDS. (aka Fats.) [AN: See previous post, I asked about this part, yeah, probbem solved, will go back and correct in a bit.]

Magnification: Increases size, not deatil, only what you see increases in size.

Resolution: Allows you to see things close up, or closer together. Puts things into more detail.

The resolution depends on the wavelength of the illuminating source (i.e. the visible light from electrons.)

Resolution = 1/2 the Wavelength.

E.g. : A light has a wavelength of 500nm, the resolution would therefore be 250 nm.

Or: Electrons wavelength is 0.2nm, therefore, the resolution would be 0.1nm

Advantages of electron microscope:

• Greater resolution, see in more detail.
• Higher magnification (x500,000)

Disadvatages:

• Specimens are dead. *
• Artefacts (other things from outside, deposits, etc...) can be present.
• Preparation of the specimen is complex, and time consuming.
• Very expensive equiptment.
• Need a very specifically thin specimen.

*The tissue must be dead as it is in a vacuum. No oxygen, therefore, living organisms can't survive.

• Organelle shapes can be distored by this vacuum.
• See it from different angles, as it is 2D

Transmission Electron Miscroscope: Electron beam passes through specimen onto fluorescent plate onto photographic paper. 2D, and has higher resolution.

Scanning Electron Microscope: Electrons atr reflected from surface to get a 360 degree/ 3D view. Specimens can be thicker so electrons don't need to pass through. Lower resolution, 20nm. Still 10x better then light/optical, not better resoltion then a transmission electron microscope, but gives a much better image.

In the bit above, I /think/ the advantages/disadvantages are for the TEM only, as the SEM doesn't need a thin specimen, so yeah, once again, correct if wrong, or give extra info if you like. REmember, I'm only typing this up from my notes taken in class. ^___^

-Nin.

Organelles and other such bits. (:

Organelles are the bits that make the cell more efficient and designed for it's purpose.

Epithelial cells, which we are focusing on, are speificated to secrete and absorb in the small intestine. They line the small intestine in an epithelial layer, about 1mm in thickness. They have microvilli (little flappy hair type bits on the top, a bit like the tassley bits on the end of a scarf, I guess?) are there top increase surface area, so more can be absorbed.

Part of the cell...

Nucleus; They control activity in the cell, direct protein synthesis, contain cromatin (which is DNA and proteins, diffused together.) Cromatin condenses and becomes thicker into the usual chromosome shape.

It also makes RNA, which makes ribosomes.

Nuclear Envelope; Is a double membrane with little gaps along it called nuclear pores, these allow the nucleus to communicate with the cytoplasm.

Endo-plasmic Reticulum; Comes in two varieties, Rough and Smooth. Rough is named so becuase it has ribosomes attached on it. It transports material throughout the cell. Used for the synthesis of proteins and can be used as a passway for proteins after.

There are no ribosomes on the smooth endoplasmic reticulum. They transport, produce and store lipids, and some carbohydrates. In the liver the smooth endoplasmic reticulum aids with detoxification.

Boths need to produce enzymes and absorb, in relation the an epithelial cell, that is, as it's purpose is the absorb and produce.

Ribosomes; Can exist on their own or in chains (polyribosome) in the cytoplasm. Made by nucleolous. Made my two units, RNA & Protein, in a cottage loaf type shape.

In relation the the epithelial cells, they have 80's ribosomes, they are bigger and sediment faster.

Golgi Apparatus; Have vesicles on the end, ready to bud off. Made of flattened sacs, called cisternae. It collects the products of the cell, which I believe are lysosomes, not 100% sure, someone correct me if I'm wrong, repackages them into vesicles to transport around & out of the cell. Modifies proteins produced by the endoplasmic reticulum. Collection, Modification, Packaging & Distribution. (:

Lysosome; A lot of enzymes in them. One membrane thick, can contain up to 50 different enzymes. Used for breaking other things down, like other cells and worn down organelles. Releasesthe content to the outsidde of the cell by fusing with it. Phagocites (they engulf and digest bad bacteria) can help them along.

Mitochondrion; 1-10mm in length, double membrane. Space between membrane is the inner membrane space, forms folds, folds are called Cristae. These are the site of ATP production, enzyemes that form it are situated there, in aerobic respiriation. Inbetween the folds is a called the matrix. This is the site of the krebs cycles. Has it's on DNA & ribosomes, /can/ produce own protein. Epithelial need lots of them as they use lots of ATP which is stored in mitochondria. More christae = more ATP. ATP = Energy ^_^

Cells (:

Revise GCSE, label and desribe a typical cell function.

Animal: Have nucleus, cell membrane, and cytoplasm. The nucleus has the nuclear membrance & envelope, and it contains DNA and chromatin. There is the cell surface membrane around the outside. In the cytoplasm there are enyzmes to catalyse reactions, and ribosomes to make protiens. The pores around the nucleus allow connection to the rest of the cell, and mRNA to pass through. Mitochondria also exist in animal cells, which aid in respiration (aerobic).

Plant: Has a cell membrance, vacuole, cytoplasm, mitochondria (or mitochondrion, singularly.) Chloroplasts, a nucleus, and a cell wall for stability.