Can someone please explain what the core practicals are and how many we are supposed to know.... Our teacher only read them briefly off a piece of paper and I'm not sure if I have them all. :s-smilie:

They are on the specification which can be found on the edexcel website

Reply 383

arnab

11

Original post by M Kh

They are on the specification which can be found on the edexcel website

Hey can you please answer my question on post 380?

I don't undestand how H.I.V virus actually destroys the T-Helper Cells! I understand how it enters it but i don't understand what happens next after Virus rna is inserted into the Host cells DNA

Reply 384

M Kh

OP

Original post by -James-

Can someone please explain What an STR is, I just don't get it!

STRs - Short Tandem Repeats in the DNA. These are the non-coding, nonsense sections of the DNA (introns). About 99% (maybe 90%?) of the DNA is made up of these non-coding sections that DO NOT end up being translated. Although they are transcribed, they are usually removed from the mRNA molecule during post-transcriptional changes to the mRNA in the nucleus. Their function is not fully understood yet but they are inherited in the same way as the coding sections of the DNA (exons). Small sequences of about 50-100 base pairs are repeated around hundreds of times. Each person varies in regards to the number of these repeats they carry at each locus. Scientists use these to build up a unique pattern for an individual. So far, these are used in such a method for producing a DNA profile (more commonly known as DNA fingerprint) in paternity tests (for confirming father-child relationship), in crime investigations and also in confirming the identity of a dead person who cannot be recognised otherwise.

Hope this helps your understanding.

Reply 385

M Kh

OP

Original post by arnab

Hey can you please answer my question on post 380?

I don't undestand how H.I.V virus actually destroys the T-Helper Cells! I understand how it enters it but i don't understand what happens next after Virus rna is inserted into the Host cells DNA

HIV invade T helper cells. T killer cells then recognise and destroy some of the heavily infected T helper cells. This reduces the number of T helper cells in the body. You don't have to know the virus replication mechanism, as far as I know.

Reply 386

M Kh

OP

Original post by arnab

whats an STR? also care to answer my question in post380?

STRs - Short Tandem Repeats in the DNA. These are the non-coding, nonsense sections of the DNA (introns). About 99% (maybe 90%?) of the DNA is made up of these non-coding sections that DO NOT end up being translated. Although they are transcribed, they are usually removed from the mRNA molecule during post-transcriptional changes to the mRNA in the nucleus. Their function is not fully understood yet but they are inherited in the same way as the coding sections of the DNA (exons). Small sequences of about 50-100 base pairs are repeated around hundreds of times. Each person varies in regards to the number of these repeats they carry at each locus. Scientists use these to build up a unique pattern for an individual. So far, these are used in such a method for producing a DNA profile (more commonly known as DNA fingerprint) in paternity tests (for confirming father-child relationship), in crime investigations and also in confirming the identity of a dead person who cannot be recognised otherwise.

Hope this helps your understanding.

Reply 387

arnab

11

Original post by M Kh

HIV invade T helper cells. T killer cells then recognise and destroy some of the heavily infected T helper cells. This reduces the number of T helper cells in the body. You don't have to know the virus replication mechanism, as far as I know.

ohhh ok, i never knew that. So basically just know how h.i.v enters the cells and how it replicates and then just know that t-killer cells recoginse these cells and kills it, lowering the overall number of t-helpers cells in the body and hence lowering the immunity which in turn causes the diseases

Reply 388

M Kh

OP

Original post by arnab

Hey can either of you please help me with this :

I understand how H.I.V enters the body and how it replicates but i am really confused on how it actually causes the destruction of T-helper cells.

This is what i understand so far :

1. The virus bind to the CD4 receptors on the surface of T helper cells
2. They then combine with a second receptor allowing the envelope to fuse with the T helper cell membrane
3. the viral RNA then enters the cell

How the virus replicates:
-uses an enzyme called reverse transcriptase
- it makes a DNA copy of the RNA
- the DNA is copied to make a double strand that can be inserted into the human genome
- it is then integrated into the hot cell's genome using intergrase

HIV binds to cell receptors virus envelope fuses with cell surface membrane
- virus reverse transcription copies viral RNA into viral DNA
- intergrase inserts viral DNA into host DNA
- transcription occurs
- translation of virus envelope proteins
- virus envelope proteins are incorporated into the cell membrane
- the virus mRNA is translated
- virus particle budding becomes wrapped in cell membrane, forming the virus protein

The bold bits are the part that i don't understand at all! Can any of you or anyone else please explain it to how H.I.V virus, after entering the T-cells, actually causes the destruction of T-helper cells or do we not need to know about it?

You don't have to know about virus replication. But, for your understanding, it is not te actual replication of viruses that causes the T helper cells to be destroyed but when the T killer cells recognise and destroy some of the heavily infected T helper cells, the T helper cell count reduces.

Reply 389

totally lost

can someone plz state the definitions of a casual relationship, a casual link, a correlation :smile:

...thank u in advance ! :biggrin:

Reply 390

M Kh

OP

Original post by arnab

ohhh ok, i never knew that. So basically just know how h.i.v enters the cells and how it replicates and then just know that t-killer cells recoginse these cells and kills it, lowering the overall number of t-helpers cells in the body and hence lowering the immunity which in turn causes the diseases

Exactly.

Reply 391

M Kh

OP

Original post by totally lost

can someone plz state the definitions of a casual relationship, a casual link, a correlation :smile:

...thank u in advance ! :biggrin:

Causal link and causal relationship are both the same things. A causal link (or relationship) is one in which one factor causes the other.

On the other hand, a correlaton is when two factors change (or fluctuate) in step with one another.

Reply 392

This Honest

3

Original post by arnab

ohhh ok, i never knew that. So basically just know how h.i.v enters the cells and how it replicates and then just know that t-killer cells recoginse these cells and kills it, lowering the overall number of t-helpers cells in the body and hence lowering the immunity which in turn causes the diseases

Yup! Also symptoms as well such as TB, pneumonia...

Reply 393

M Kh

OP

Original post by arnab

heyy do we need to know any examples of primary sucession off by heart?

What do you mean by examples of primary succession?

Reply 394

M Kh

OP

Original post by This Honest

Yup! Also symptoms as well such as TB, pneumonia...

Outline the symptoms of TB and AIDS please.

Reply 395

vishalb

any predictions on which questions/core practical will come up?

Reply 396

vishalb

Original post by M Kh

Outline the symptoms of TB and AIDS please.

TB:
Loss of appetite
Weight loss
Coughing out blood
Fever
Fatigue - tiredness

AIDS:

Acute phase:
swollen lymph nodes
fever,
sweats,
headache,
more likely to get the cold/flu and it'll take longer to go away than usual

Chronic phase:
dormant diseases like TB or shingles may arise

Disease phase:
opportunistic infections would lead to death

Reply 397

C_Lauren

1

Original post by M Kh

What do you mean by examples of primary succession?

I would assume this means the process e.g. beginning with lichen or algae, these break up the rock and allow soil to form, conditions change making it suitable for other species to inhabit, wind blown moss spores start growing.

That's how most communities begin to evolve so I can't think of any other specific examples. If they ask a question on a specific species then just apply the above to that species obviously in more detail.

Ughhhhh why am I dreading this exam so much!?

Reply 398

C_Lauren

1

Any core practical predictions? Or anything in particular that hasn't come up in a while?

Reply 399

arnab

11

Original post by M Kh

What do you mean by examples of primary succession?

well there is an example in the CGP book about how primary sucession happens on a bare rock. i was just wondering if we needed to know any of it by heart!

Edexcel A2 Biology Unit 4 (6BI04) - 15 June 2012 - Official Exam Discussion Thread!!!

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