Concept discussion

[alondouek]

glycoproteins have diverse structural, immunological, enzymatic or transportational.

This may just be a type, but it should be: "...glycoproteins have a diverse range of functions; including structural, immunological, enzymatic or transportational roles".

So really if we were asked to draw a plasma membrane, you must include:
* Phospholipid bi-layer
* Protein molecules forming protein channels
* Glycolipids attached to lipid segment of cell membrane
* Glycoproteins attached to the protein molecule
* Fully labelled diagram + a little diagram to demonstrate the hydrophilic phosphate head and hydrophobic fatty acid tails of a phospholipid.

^ That would be sufficient, right?? Unless of course it specifies something like the arrangement of phospholipids in the fluid-mosaic model?

There have been a couple of "diagram the phospholipid bilayer" questions in past VCAA exams; they're never very specific in the given solution, so you could probably get away with a correctly-oriented bilayer with a couple of embedded protein channels. Everything MUST be labelled unless otherwise specified. You can be as detailed as you want, but it's important not to spend too much time on a diagram in the exam.

Functions of cholestrol in plasma membrane:
* gives the plasma membranes more flexibility
* promotes more stability
* increases fluidity of plasma membrane in cold environments
* CAN SOMEONE ADD SOME MORE THINGS PLEASE? much appreciated.

A question like this would be a great opportunity to throw in the term 'fluid mosaic model'.

In temperatures that are above the norm for a cellular environment, cholesterol stops fatty acid tails from coming into contact, thereby maintaining the structure of the membrane.

[Yacoubb]

Summary of cholestrol function:
* gives flexibility
* gives stability
* maintains shape of membrane in cold climates by preventing fatty acid tails from becoming compact together.
* fluid-mosaic model is retained

^ would that be sufficient for the functions of cholestrol in the plasma membrane.

[alondouek]

Summary of cholestrol function:
* gives flexibility
* gives stability
* maintains shape of membrane in cold climates by preventing fatty acid tails from becoming compact together.
* fluid-mosaic model is retained

^ would that be sufficient for the functions of cholestrol in the plasma membrane.

These are very general, so you'd need to elaborate on the first two points. My definition of the function of cholesterol would be:

"In the fluid mosaic model of the plasma membrane, cholesterol maintains fluidity and integrity of the phospholipid bilayer. Moreover, cholesterol molecules within the bilayer make it less permeable to water-soluble substances.

Cholesterol keeps the plasma membrane at optimal fluidity. At high temperatures, cholesterol makes the plasma membrane less permeable to small molecules by increasing rigidity. Conversely, at low temperatures, cholesterol makes the bilayer more fluid to prevent damage to the cell from the cold."

[Yacoubb]

Yeah elaboration is essential; I merely placed points for its function. I would then obviously have to elaborate depending in the question. Do I have to include cholestrol in the diagram of plasma membrane or perhaps even mention it?!

[alondouek]

Probably not, it's a bit difficult to accurately represent cholesterol in the bilayer diagrammatically. Here's wikipedia's version, you don't have to be anywhere near this accurate.

[Yacoubb]

Yeah I thought so. Okay so I'm going to place the definition for my five methods of transport across plasma membranes + please give me constructive criticism.

Diffusion:
The passive transport of a substance across the semi-permeable plasma membranes from an area of high solute concentration to low solute concentration along a plasma membrane.

Facilitated Diffusion
The passive transport of a substance that cannot readily diffuse across phospholipid bi-layer, and is thereby transported by a carrier molecule across the plasma membrane via the protein channel along a concentration gradient (area of high solute concentration to low solute concentration.

Active Transport
The endergonic movement of a substance across the plasma membrane from an area of low solute concentration to an area of high solute concentration, against a concentration gradient.

Osmosis
The net movement of water molecules across the semi-permeable plasma membrane from an area of low solute concentration to high solute concentration.

Endocytosis
The bulk transport of large, solid particles (phagocytosis) or dissolved substances (pinocytosis) into a plasma membrane by engulfment of the material.

Exocytosis
The bulk, vesicular transport of a substance across a plasma membrane by fusing with the membrane and being secreted or voided outside the cell.

Please give me some constructive criticism; my aim is to improve and do so accordingly Much appreciated guys!!

[alondouek]

Yeah I thought so. Okay so I'm going to place the definition for my five methods of transport across plasma membranes + please give me constructive criticism.

Diffusion:
The passive transport of a substance across the semi-permeable plasma membranes from an area of high solute concentration to low solute concentration along a plasma membrane.

"Along a plasma membrane"? I think you either mean 'along the concentration gradient' or 'across the plasma membrane'. The first statement is a handy piece of info to mention. Also, when you say "semi-permeable plasma membranes", you can make it singular ('membrane') for the purpose of a definition.

Facilitated Diffusion
The passive transport of a substance that cannot readily diffuse across phospholipid bi-layer, and is thereby transported by a carrier molecule across the plasma membrane via the protein channel along a concentration gradient (area of high solute concentration to low solute concentration.

Read over to remove typos ([the] phospholipid bilayer). Also consider saying "therefore transported via a carrier molecule (often protein-based) across etc..." - better, briefer and more specific is what examiners like. "via the protein channel" - IIRC not all forms of facilitated diffusion utilise protein channels specifically.

Active Transport
The endergonic movement of a substance across the plasma membrane from an area of low solute concentration to an area of high solute concentration, against a concentration gradient.

Instead of saying "the endergonic movement", simply begin with "the movement...". You can state that the process is endergonic at the end, and why it is endergonic (an input of energy is required) - you want to be as specific as is reasonably possible. Otherwise this is a pretty good definition.

Osmosis
The net movement of water molecules across the semi-permeable plasma membrane from an area of low solute concentration to high solute concentration.

Good definition. You might want to mention that osmosis is a form of passive transport, and that no carrier molecules are required (water molecules pass through gaps in the bilayer).

Endocytosis
The bulk transport of large, solid particles (phagocytosis) or dissolved substances (pinocytosis) into a plasma membrane by engulfment of the material.

You need to mention that bulk transport is a form of active transport, as an energy input is required.

Exocytosis
The bulk, vesicular transport of a substance across a plasma membrane by fusing with the membrane and being secreted or voided outside the cell.

"Vesicular bulk transport" is better phraseology. Maybe don't mention vesicles so early, leave it for later in the definition when you're discussing the technicalities of exocytosis, i.e. "fusing with the membrane to form a vesicle etc...". Again, mention that exocytosis is a form of active transport.

[Yacoubb]

Here are the modified ones:

Diffusion
The passive transport of a substance across a semi-permeable plasma membrane from an area of high solute concentration to an area of low solute concentration, along a concentration gradient.

Facilitated diffusion
The passive transport of a substance across the plasma membrane via the protein channel from an area of high solute concentration to an area of low solute concentration, along a concentration gradient.

Active transport
The transport of substances across a semi-permeable plasma membrane from an area of low solute concentration to an area of high solute concentration against a concentration gradient. Active transport is an energy-requiring (active) form of transport.

Vesicular transport
The bulk transport of a substance into and out of a cell that occurs by the fusion of transport vesciles with the semi-permeable plasma membrane.

[alondouek]

Here are the modified ones:

Diffusion
The passive transport of a substance across a semi-permeable plasma membrane from an area of high solute concentration to an area of low solute concentration, along a concentration gradient.

Facilitated diffusion
The passive transport of a substance across the plasma membrane via the protein channel from an area of high solute concentration to an area of low solute concentration, along a concentration gradient.

Active transport
The transport of substances across a semi-permeable plasma membrane from an area of low solute concentration to an area of high solute concentration against a concentration gradient. Active transport is an energy-requiring (active) form of transport.

Vesicular transport
The bulk transport of a substance into and out of a cell that occurs by the fusion of transport vesciles with the semi-permeable plasma membrane.

Ya these are good. One things is, is with the active transport one you're going to want to throw in the word 'endergonic' instead of "(active)" - you don't use part of the word you're defining in the actual definition, ever!

Also, I'm not sure why you suddenly have a definition for "vesicular transport". Keep separate definitions for endo- and exocytosis.

[Yacoubb]

These are just handy ones I've constructed just from knowledge of reading through the textbook + looking at the transportation of molecules that can occur in various ways. My next mission is basically to differentiate between which organelles are found in eukaryotes/prokaryotes (e.g. prokaryotes anaerobically respire due to the absence of mitochondria, the organelle where Kreb's Cycle and the Electron Transport chain take place in the complete process of aerobic respiration). Knowing these sort of things (i.e. the organelles in relation to prokaryotes and eukaryotes) is helpful for these sorts of questions.

Maybe some assistance?

[Yacoubb]

Okay so I thought that we should start looking at some organelles. I'll start with Mitochondria:

Mitochondria are membrane-bound organelles found exclusively in eukaryotic cells that are the principle site of cellular respiration (specically aerobic respration) and ATP production. The mitochondrion in cells contains cristae and a matrix.

Cristae
Inner-membrane folds that increase the surface area of the mitochondria.

Matrix
Contains fluid that is actually enclosed by the cristae.

It is important than when describing a cell with this organelle found in them, you should emphaise whether it is singular (mitochondrion) or mitochondria They are most abundant in cells that have high enery needs. E.g. kidney tubule cells, muscle cells like the heart, etc.

Feel free to add to that:

Oh, and perhaps let us discuss mitochondria in relation to the endosymbiotic theory of evolution. Things to support that it was once a prokaryotic organism:
* had a plasma membrane, supporting double-membrane in which it is held in within cytosol of eukaryotic cells.
* the presence of ribosomes within the mitochondria.
* mtDNA (mitochondrial DNA) present in them!
Feel free to add

[Scooby]

Cristae
Inner-membrane folds that increase the surface area of the mitochondria.

Matrix
Contains fluid that is actually enclosed by the cristae.

The cristae are the "compartments" created in the intermembrane space by the folding of the inner mitochondrial membrane

The matrix is the space within the inner mitochondrial membrane, and is filled with fluid. It's not really right to say that it's "enclosed by the cristae" though

[Yacoubb]

So really to explore the structure of mitochondria:
- Cristae:
the compartments in the intermembrane structure of the mitochondrion that is actually formed by the folding of the inner mitochondrial membrane.

- Matrix:
the space within the inner mitochondrial membrane filled with fluid.

I'd just like to clarify what I said above ^ and also what I wrote in that large paragraph regarding the endo-symbiotic theory of evolution + its function?!

[Scooby]

Yeah, those definitions are better 

Also... might want to clear up one of your points about evidence for endosymbiosis

"...had a plasma membrane, supporting double-membrane in which it is held in within cytosol of eukaryotic cells" doesn't really make sense

Essentially, there was once an independent prokaryotic cell, which, while it was just floatin' around, was engulfed by a eukaryotic cell and encased within a vesicle. But it wasn't digested. The cell membrane of this prokaryote became the inner mitochondrial membrane; the membrane of the vesicle became the outer mitochondrial membrane

Or at least that's the theory of endosymbiosis. Biologists think that the reason the mitochondria has a double membrane is because a prokaryotic cell (which had a single cell membrane) was endocytosed by a eukaryotic cell

[Yacoubb]

Essentially, there was once an independent prokaryotic cell, which, while it was just floatin' around, was engulfed by a eukaryotic cell and encased within a vesicle. But it wasn't digested. The cell membrane of this prokaryote became the inner mitochondrial membrane; the membrane of the vesicle became the outer mitochondrial membrane

That is so interesting; so basically the inner-membrane of a mitochondrion is beleived to be the plasma membrane of the prokaryote + the vesicle that the mitochondrion was held in when engulfed, but not digested, by eukaryotic cells, is believed to have formed the outer-membrane of the mitochondria. That is quite interesting.

It's like chloroplasts. I guess you can say that chloroplasts are made up of the grana (small discs containing the green-pigment chlorophyll) and stroma (containing enzymes for photosynthesis and other dissolved substances in solution form). Can we say the inner membrane is believed to be the plasma membrane, whilst the outer membrane is believed to be that of the vesicle it was held in when engulfed, but not digested?

Just making sure that the double-membrane theory can be applied to both chloroplasts AND mitochondria