Concept discussion

[alondouek]

Here's some more questions I have:
- Do we need to know that adenine and guanine are purines, and that cytosine and thymine are pyrimidines?

It's good to know, but not necessarily necessary; an easy way to remember is this:

Cytosine and Thymine are Pyramidines - they all have y's; hence guanine and adenine are purines.

- Do we need to know the significance of the 3' and 5' ends of a nucleotide strand?

Absolutely, 100% you need to. This becomes very important when you start doing DNA replication. You may need to identify the directionality of replication of a DNA strand (5' end to 3' end IIRC). You'll also learn about upstream (towards the 5' end) and downstream (towards the 3' end) of a sequence.

[Stick]

Absolutely, 100% you need to. This becomes very important when you start doing DNA replication. You may need to identify the directionality of replication of a DNA strand (5' end to 3' end IIRC). You'll also learn about upstream (towards the 5' end) and downstream (towards the 3' end) of a sequence.

I meant this in terms of early Unit 3 Biology. I'll make sure that when it comes up later in Unit 4 that I take note of it.

[alondouek]

Fair enough; my teacher taught us DNA replication in Unit 3, obviously I don't know if it's standard in other schools

[Stick]

By early Unit 3, I mean chapter 1 of Nature of Biology.

[alondouek]

In which case, the best advice I can offer is this:

[Stick]

Well it turns out I made a note of both of my questions in my Biology bound reference two months ago without even realising it. I must've known I would forget it.

[Yacoubb]

Here's some more questions I have:
- Do we need to know that adenine and guanine are purines, and that cytosine and thymine are pyrimidines?
- Do we need to know the significance of the 3' and 5' ends of a nucleotide strand?
[/quote]

1) All you really have to know is that Adenine + Guanine are purines, and that Cytosine and Thymine are pyrimidine. It isn't even in the textbook so that should be adequate, as this sort of stuff is more Chem orientated.

2) Yes. You need to know that DNA always replicates from 5' to 3' in anti-parrallel directions. That is, if one side of the DNA strand is 3' from the top to 5' from the bottom, the other side of the DNA molecule will be 5' from the top to 3'. You don't need to know about that completely now, its more when you do unit 4 genetics and you start to look at Replication Forks + how DNA replicates!

Hope that was somewhat helpful. Lol I'm going through the concepts of the textbook which is why I know that. Don't worry about something that sounds too Chemistry-ish. It is often not relevant. Though a good point to add is that you need to know questions like the one below. This was in the 2012 Bio exam 1.

Question 5
A particular DNA double helix is 100 nucleotide pairs long and contains 25 adenine bases.
The number of guanine bases in this DNA double helix would be
A. 25
B. 50
C. 75
D. 100

Knowing that 100 pairs long = 200 bases is essential. This is because of there are 25 adenine bases, there must be 25 complementary Thymine bases. 200 - (25 adenine + 25 thymine) = 150 bases left. You now know that the remaining bases are made up of Guanine and Cytosine nitrogenous bases. Divide 150 by 2, to get 75 guanine and 75 cytosine. Therefore the answer is C. So it is possible you'll get a question like this that just requires you to dissect it based on your knowledge of complementary base pairs. It may also come as a percentage.

So it says there are 30% guanine bases in DNA. How many adenine (in percentage form).
You just know that 30% guanine equates to 30% cytosine. This means (100 - 60) = 40% made up of Adenine and Thymine. Divide it by 2, and you get 20%.

That is about all you'll need to know. Do some practice where you find complementary base pairs for DNA or RNA sequences, and learn differences between DNA + RNA.

Hope that helps.

[Stick]

I like that question. You're right though, it doesn't necessarily have much to do with the Chemistry of DNA, it's more the understanding of how bases work (which is part of chapter 1). Thanks!

[Yacoubb]

I like that question. You're right though, it doesn't necessarily have much to do with the Chemistry of DNA, it's more the understanding of how bases work (which is part of chapter 1). Thanks!

Yeah like in the 2012 Chem Exam there was a DNA molecule that asked what the two types of bonds were: you don't have to know that for Bio because that then investigates the Chemistry component of DNA. So glad that Chem complements Bio in certain things, because its a bit easier I imagine to work through.

[pi]

It's good to know, but not necessarily necessary; an easy way to remember is this:

Cytosine and Thymine are Pyramidines - they all have y's; hence guanine and adenine are purines.

I remember from some podcast as "imagine a glass pyramid that's very pointy, it can CUT you. Hence, pyrimidines are Cytosine, Thymine and Uracil"

[Yacoubb]

Let's start with Cell Organelles

Okay so we have two main types of cells:
a) Eukaryotic: possess a distinct nucleus housing hereditary information DNA + organelles held in a membrane.
b) Prokaryotic: lack a nucleus [DNA is dispersed in cytosol] and organelles not held in membrane.

Essential difference between animal + plant cells:
Plants cells possess a cell wall, chloroplasts (some) and vacuoles that store cell sap and other dissolved solution. Animals do not possess these distinct structure/organelles respectively.

One thing to note is that mentioning chloroplasts on its own is inaccurate, because not all plant cells on a plant have chloroplasts in them (non-photosynthetic cells). Instead, mentioning a cell wall as the PRIMARY difference between them is correct because even some animal cells possess vacuoles.

Let's begin with organelles and writing their functions:

I'll start:

Plasma membrane: the boundary of all cells that controls the entry and exit of substances into and out of a cell. It is primarily composed of lipids, forming the phospholipid bi-layer, and protein molecules, forming channels for the transport of lipophobic (i.e. substances that are insoluble in the phospholipid bi-layer) across the plasma membrane.

Five main methods of transport of substances include:
a) Diffusion - passive transport
b) Facilitated diffusion or mediated transport - passive transport
c) Osmosis - passive transport
d) Active Transport - active transport
e) Vesicular Transport (endo/exocytosis) active transport.

The difference between active + passive transport is that active transport requires an input of energy to take place, wheras passive transport occurs with the absense of an energy source.

[Scooby]

Okay so we have two main types of cells:
a) Eukaryotic: possess a distinct nucleus housing hereditary information DNA + organelles held in a membrane.
b) Prokaryotic: lack a nucleus [DNA is dispersed in cytosol] and organelles not held in membrane.

I probably wouldn't say that the DNA in prokaryotic cells is dispersed. Most of it is contained within the nucleoid. It's not as if it's all just floating randomly around the cytoplasm

Essential difference between animal + plant cells:
Plants cells possess a cell wall, chloroplasts (some) and vacuoles that store cell sap and other dissolved solution. Animals do not possess these distinct structure/organelles respectively.

One thing to note is that mentioning chloroplasts on its own is inaccurate, because not all plant cells on a plant have chloroplasts in them (non-photosynthetic cells). Instead, mentioning a cell wall as the PRIMARY difference between them is correct because even some animal cells possess vacuoles.

If you're asked to describe a difference between animal and plant cells, mentioning that plant cells contain a large and central vacuole but that animal cells don't is fine. Just make sure you mention that it's large and central 

The point you made about chloroplasts is a good one! It's definitely a common mistake

Plasma membrane: the boundary of all cells that controls the entry and exit of substances into and out of a cell. It is primarily composed of lipids, forming the phospholipid bi-layer, and protein molecules, forming channels for the transport of lipophobic (i.e. substances that are insoluble in the phospholipid bi-layer) across the plasma membrane.

Also carbohydrates (eg. glycolipids and glycoproteins)

The difference between active + passive transport is that active transport requires an input of energy to take place, wheras passive transport occurs with the absense of an energy source.

Active transport also allows substances to be moved against the concentration gradient, whereas passive transport doesn't


I'm just being picky though. Good job! 

[Yacoubb]

Could you kindly tell me what the function of glycolipids and glycoproteins are?!

[alondouek]

Glycolipids (lipids with an attached carbohydrate):

• Function as cellular markers that are utilised in intercellular signalling
• Provide energy for metabolic processes

Glycoproteins (proteins with glycans that are attached to polypeptide chains) have numerous functions; they can act as structural, immunological, transportational, hormonal and enzymatic molecules (this is not a complete list of functions). Examples of a glycoprotein are collagen (structural), immunoglobins (immunological) and TSH (hormonal - this is an important hormone in VCE-level homeostasis; learn it )

[Yacoubb]

Thank you very much. I need to make those fine-tuning adjustments for a good result so I appreciate the constructive criticism.

So really glycolipids act as signalling molecules for intracellular activity + provide energy for metabolic processes, whereas glycoproteins have diverse structural, immunological, enzymatic or transportational. Thanks so much.

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?

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.