OCR 2010 A2 Biology Unit 2 - Control, Genome and Environment

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uer23

Can someone please tell me what exactly we need to know for Body plans/Homeobox genes and Apoptosis ?

Homebox genes code for the basic structural formation(body plan) of the organism i.e from zygote to a whole organism.
These genes are function the same in any organism (argh cant think remember the exact word which I am looking for starts from "p&quot in nature.These work by coding for transcription factor proteins which attach onto their respective places in the DNA.These allows certain part to get transcribed hence you get the resulting changes.
Some genes of these kind are: Antp and ubx.Where ubx codes for the inhibition of the growth of wings in the T3 segment.
While the Antp codes for the formation of 3 pairs of leg in each Body segment.

Apoptosis: Programmed destruction of cells during the development of the organisms body.

Reply 1601

cfc18

ibysaiyan

Yep thats right ! but dont forget that homeobox genes code for proteins called transcribtion factors. for example one homeobox gene can code for several transcription factors that can bind to lenths of dna thus being able to switch on or off several genes involved in formation of limbs.
we also need to know that homeobox genes are very similar in animals e.g. homeobox gene that codes for ear formation in a mouse can be inserted into a flie and the flie grows an ear.
this suggests the mouse and flie shared a common ancestor about half a billion years ago.

edit : i just realised you talked about transcription factors lol stupid me

Reply 1602

Falcon91

ibysaiyan

Apoptosis: Programmed destruction of cells during the development of the organisms body.

You also need to know the process of Apoptosis itself:
-Enzymes break down the cytoskeleton
-Cell cytoplasm becomes thick and organelles become tightly packed
-Cell membrane distorts and small parts/bits called blebs form
-The chromatin condenses and DNA fragments
-The cell then fragments into many different vesicles
-The vesicles undergo phagocytosis which disposes of the waste from the cell

Can be controlled by hormones, cytokines produced by the immune system and Nitric Acid (which can induce apoptosis).

Side Notes - Hows your revision going for everyone?

Ive covered it all (as in this unit) and lokoed at some of the AS content. Just need to go over stuff from F214 and i should be ready (hopefully)

Reply 1603

cfc18

Falcon91

Thanks for that , i only took brief notes about adaptosis from the green book.
ive written all my notes and learnt most things just need 2 weeeks to crack on with past papers then should be ready hopefully. :yes:

Reply 1604

s_a_r_a

is it me or is the genetic stuff the hardest topic on the syllabus!!!!
i just cant get my head around it arghhhhhh!
HELP PLEASE :confused:

Reply 1605

aimz08

Discuss how the links between a range of human behaviours and the dopamine receptor DRD4 may contribute to the understanding of human behaviour....

Help anyone?

Reply 1606

Liverpool F.C.™

s_a_r_a

is it me or is the genetic stuff the hardest topic on the syllabus!!!!
i just cant get my head around it arghhhhhh!
HELP PLEASE :confused:

genetics is a pain in the arse.

Reply 1607

chuck111

Hey guys

I was wondering if someone could explain the chain termination method for sequencing DNA, i missed the lesson on it and im finding it hard to get my head around -.-

Reply 1608

Sakujo

chuck111

Hey guys

I was wondering if someone could explain the chain termination method for sequencing DNA, i missed the lesson on it and im finding it hard to get my head around -.-

Each DNA nucleotide have a fluorescent marker of a different colour added, A,T,C,G each have a seperate colour. They are also modified so that DNA polymerase falls off the DNA chain when they are added and growth stops. DNA needed to be sequence is sheared into single strand fragments, primes added, DNA polymerase and the whole thing is run like PCR. Double strand fragments of different sizes produce terminating with a fluorescent nucleotide. A process similar to electrophoresis occurs, where the frgaments are run through a machine with the smallest moving the fastest and therefore read first then the next smallest and so on until all the fragments are through. This allows you to know the DNA sequence, as you just read off the nucleotide colour so it would go red, blue, red which might mean ATA for example.

Reply 1609

Sakujo

explain the role of isolating mechanisms in the evolution of new species, with reference to ecological (geographic), seasonal (temporal) and reproductive mechanisms;

Eh? :lolwut:

Reply 1610

chuck111

Sakujo

explain the role of isolating mechanisms in the evolution of new species, with reference to ecological (geographic), seasonal (temporal) and reproductive mechanisms;

Eh? :lolwut:

Isnt it like:

Geographical-Physical barrier divides a population of a species, conditions slightly different on each side , due to these different conditions different characteristics start to become common due to natural selection, allele frequencies change + random mutations will lead to changes in the phenotype, Eventually the separated species cannot breed together to produce fertile offspring leading to two different secies being formed

Reproductive- Happens when changes in alles and phenotypes of the two populations prevent them from breeding together.
Can happen by:
Seasonal changes-Develop different mating seasons/ become sexually active at different times of the year
Mechanical-Changes in genitalia prevent mating
Behavioural-New mating rituals that might be unattractive to rest of populaton

hopefully thts right and answered your question

Reply 1611

uer23

chuck111

...

Hey chuck, any chance you making them revision cards for F215 ?

Reply 1612

chuck111

Sakujo

thanks alot :smile:

ive summarised the points in my revision guide and i think it goes into far too much detail, which isnt even in the text book:

"

•

Fragments of the DNA to be sequenced are produced by the use of four dideoxynucleoside triphosphate (ddNTP)

•

DNA denatured to separate it into two strands

•

In the presence of ample supply of each of the four ddNTP(each marked with a fluorescent marker A,T,C,G), DNA is replicated by DNA polymerase, using a primer to begin the process

•

Low concentration of the ddNTP is used so that it will be added only rarely to the lengthening chain

•

In separate reactions each of the three other ddNTP’s is added to identify strands of DNA

•

Adding the products of all four reactions together produces a set of fragments that end at nucleotides with different bases and differ in length by one nucleotide

are we really supposed to go into tht much detail?

Reply 1613

chuck111

uer23

Hey chuck, any chance you making them revision cards for F215 ?

lol making them as we speak :P

Reply 1614

Sakujo

chuck111

thanks alot :smile:

ive summarised the points in my revision guide and i think it goes into far too much detail, which isnt even in the text book:

"

•

Fragments of the DNA to be sequenced are produced by the use of four dideoxynucleoside triphosphate (ddNTP)

•

DNA denatured to separate it into two strands

•

In the presence of ample supply of each of the four ddNTP(each marked with a fluorescent marker A,T,C,G), DNA is replicated by DNA polymerase, using a primer to begin the process

•

Low concentration of the ddNTP is used so that it will be added only rarely to the lengthening chain

•

In separate reactions each of the three other ddNTP’s is added to identify strands of DNA

•

Adding the products of all four reactions together produces a set of fragments that end at nucleotides with different bases and differ in length by one nucleotide

are we really supposed to go into tht much detail?

No I don't think so, I'm using the official OCR book, the purple one and it doesn't mention half the stuuf you have.

•

Fragments of the DNA to be sequenced are modified to throw off DNA polymerase when added to a chain.

•

DNA denatured to separate it into two strands

•

In the presence of modified DNA nucleotides(each marked with a fluorescent marker A,T,C,G), DNA is replicated by DNA polymerase, using a primer to begin the process

•

Produces a set of fragments that end at nucleotides with different bases and differ in length by one nucleotide

•

Fragments run through a machine (like electrophoresis) which uses a laser to identify the colour sequence and therefore the base pair sequence of the DNA

Modified to what I think we should know.

Reply 1615

chuck111

Sakujo

No I don't think so, I'm using the official OCR book, the purple one and it doesn't mention half the stuuf you have.

•

Fragments of the DNA to be sequenced are modified to throw off DNA polymerase when added to a chain.

•

DNA denatured to separate it into two strands

•

In the presence of modified DNA nucleotides(each marked with a fluorescent marker A,T,C,G), DNA is replicated by DNA polymerase, using a primer to begin the process

•

Produces a set of fragments that end at nucleotides with different bases and differ in length by one nucleotide

•

Fragments run through a machine (like electrophoresis) which uses a laser to identify the colour sequence and therefore the base pair sequence of the DNA

Modified to what I think we should know.

ok cheers, because I was like wth when i read the detail in the revision book :smile:

i thought the revision book was supposed to simplify stuff not the text book :P

Reply 1616

ViolinGirl

uer23

Can someone please tell me what exactly we need to know for Body plans/Homeobox genes and Apoptosis ?

I doubt we need to know the fly example, so I haven't bothered learning it, but knowing them (OCR) they could throw in anything, so if I have time I may learn it, just in case.

We need to know that the development in body plans is similar in many types of organisms, and that this development is controlled by homeobox genes that are arranged in hox clusters. They have a set amount of base sequences that are used to transcribe polypeptides of which contain transcription factors and these can bind to genes and initiate their transcrition while regulating the expression of other genes. They are also involved in the polarity of the organism and the positioning of the organs. In embryo development they govern the fate and identities of cells/tissues, and they are expressed in the same way as the devleopment of the organism, from anterior to posterior. There are certain factors that can influence the way that these genes work, for example by taking in an excess amount of vitamin A in the diet, this can interfere with the nomal working of the homeobox genes, and and can birth defects, in particular cranial deformities.

Aptosis is programmed cell death that occurs in multicellular organisms. It is also important in the regulation of body plans, because there is extensive division and proliferation of cells, followed by sorting of these cells, and killing of the ones that are not necessary. Unlike, necrosis, apoptosis doesn't damage cells, because no enzymes are released in the process.

The process is tightly regulated by a number of signals that are both inside and outside of cells. These include:
Cytokines
Hormones
Growth Factors
Nitric Oxide

If too much apoptosis occurs --> cell loss and degeneration
If too little apoptosis occurs---> tumours

THe process:
1. The cell cytoskeleton is broken down by enzymes.
2. THe cell cytoplam becomes dense with organelles tightly packed.
3. Cell membrane changes to form bits called blebs.
4 Chromatin condenses, and DNA fragments.
5. Cell breaks into vesicles.
6. Vesicles are uptaken by phagocytosis and disposed of without damaging other cells.

It happens very fast.

Reply 1617

ViolinGirl

Sakujo

explain the role of isolating mechanisms in the evolution of new species, with reference to ecological (geographic), seasonal (temporal) and reproductive mechanisms;

Eh? :lolwut:

seasonal/temporal --> unable to mate due to change in breeding seasons, mating behaviors.