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Ocr f215: 27/1/11

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writing notes to myself/internet just to make it stick - mainly all essay predictions

Lac operon

If non lactose is present - repressor binds to operator and inhibits transcription

When lactose is present it binds to lac repressor changing its shape so it can longer bind to the operator site.
RNA Polymerase can now begin the transcription of the structural genes - B Galactosidase and Lactose
permease

Succession
Primary occurs on previously uninhabited land that has been newly expose eg bare rock from earthquake
Secondary occurs on land cleared of all plants but still has soil present eg after forest fire

Bare rock succession example -
Pioneer species first species to colonise - adapted to harsh condition eg lichen
Die and decay breaking down rock - humus produced - little layer of soil

Little soil means water retained and nutrients - bigger plants can colonise that are better adapted to environment eg small flowering plants

As more plants die and compose each seral stage has more soil - larger species can colonise with longer roots ect - they are better adapted than previous species. Each seral stage become more complex/diverse

Climax community is reached where ecosystem is supporting largest and most complex of species (not forgetting animals) - equilibrium is reached (steady state)

Oak tree is typical British climax species in woodland.

Reply 201

Casper266

Original post by Summerdays

Have you guys attempted the specimen?

Yeah didn't find it too bad.. Managed to get a B which I'm happy with.. Made me revise more on the parts I got wrong :smile:

what about you?

Reply 202

SwordStream

Protein synthesis - formation of a protein/polypeptide

Transcription

RNA polymerase binds to start of DNA to be copied - hydrogen bonds between bases break separating two strands
One strand acts as a template to make mRNA copy

RNA polymerase lines up free nucleotides alongside template stands - complementary base pairing (except U replaces T)

Joined together making mRNA that is a complementary copy of the template strand and therefor the protein to be made

Hydrogen bonds reform between DNA stands and it coils back into d helix

RNA polymerase reaches stop codon and mRNA is stopped being made and detaches from DNA

mRNA moves out of nucleus through nuclear pore and attaches to ribosome

Translation - happens at ribosome in cytoplasm

mRNA attaches to a ribosome - tRNA has amino acid binding site and an anticodon

tRNA with anticodon complementary to the first codon attaches to first codon

tRNA with anti condon complementary to second codon attaches to second codon

the two amino acids carried by the tRNA molecules are bound by peptide bond

the first tRNA molecules moves away leaving amino acid behind - 3rd tRNA binds to anticodon and peptide bond forms between 2nd and 3rd amino acid

This process continues until stop codon is reached - a polypeptide chain is created and moves away from ribosome............

Reply 203

Adventure10

Original post by mathsclown

Nice with the B, I would of been over the moon !
Ehm good question and seriously not sure so to be on safe side, we should learn them not to tough

p + q = 1
p^2 + 2pq + q^2 = 1
And the assumptions made when carrying it out are just: any mating is random, population is large, no genotype has a selective advantage and errr there is no mutation, migration or genetic drift

My thoughts exactly :smile:

And thanks, I had to redo my Chemistry this year (I got a C when I needed a B) so as I had the time I thought I'd have a go at this paper again.

Reply 204

ibysaiyan

I AM BACK... :P gonna do last 3 hour revision

Reply 205

aimz08

3 Hour cram.

Apoptosis: aka programmed cell death
Occurs in soft tissue and skeleton
May be triggered by a change in the body plan.
Controlled by cytokines produced by immune system, hormones, growth factors etc
This control can be inhibited by protein inhibitors.

Enzymes break down cell cytoskeleton
Cell Shrinks
Chromatin Condenses
Condensed chromatin is not transcribed

Too much apoptosis leads to degeneration
Too little apoptosis leads to tumours

Reply 206

SwordStream

Standard growth curve - normally followed by growth of microorganisms in closed culture

Log phase - microorganisms adapting to new env. or producing enzymes etc..
no energy for reproduciton used - growth slow

Exponential phase - growth fast, doubles at regular interval - culture conditions most favourable

Stationary phase - death rate same as reproduction rate
mircobes die because not enough room/food sparse (intraspecific comp)

decline (DEATH) phase - death rate exceeds reproduction rate - food very sparse and waste products are at toxic levels

Reply 207

ibysaiyan

Original post by SwordStream

aka sigmoid growth curve

Reply 208

SwordStream

Gene technologies - used to study genes and their functions

Polymerase chain reaction (PCR)

1) DNA sample mixed with free nucleotides, DNA polymerase and primers.

2) Mixture heated to 95C to break hydrogen bonds

3) Then cooled to about 50C so primers anneal to start of DNA fragment

4) Heated again to about 72C and DNA polymerase lines up free floating nucleotides along each template by complementary base pairing, producing new DNA strands

Cycle 1 produces 4 stands 2 produces 8 etc...

Reply 209

aimz08

Cloning of plants

Plants natural cloning
Vegetative propogation... plants grow structures on their non-reproductive tissues e.g. leaves, stems roots, which grow into a new plant.
An example: In the roots of elm trees, lie dormant sucker buds.
These sucker buds are activated when there is any stress to the tree e.g. disease, damage
These may be far away from the tree itself - to prevent the new trees from the original stress
Suckers begin to form and eventually a new plant is created identical to the original.

Plants artificial cloning
Tissue culture. Stem cells (unspecialised cells)are taken from the roots of a plant,
these are then sterilised to kill off any microrganisms as these would compete with the stem cells for nutrients.
The stem cells are grown in a culture medium containing growth factors (e.g. auxins) and nutrients (e.g. glucose)
The cells divide and grow into a small plant which is then placed in soil to grow into a full plant identical to original
Micropropogation allows cloning of many plants quickly. Stem cells are taken from the developing clone and subcultured in other mediums

Advantages: Can save plants from extinction, plants that take too long to germinate can be grown quickly, desireable genetic characteristics always passed on

Disadvantages: Disadvantageous characteristics also passed on, expensive, reduced variation - one disease could kill whole crop

Reply 210

aimz08

Animal cloning
Reproductive - whole organism, used to clone animals to test drugs as it removes genetic variable making it more reliable
Non-reproductive a.k.a theraputic - cells, tissues or organs created from embryonic stem cells, can replace damaged tissue without rejection issues

Both use nuclear transfer: Egg cell taken from organism X and organism Y.
X's egg cell becomes enucleated (Removing nucleus) and insert Y's nucleus
Egg Cell stimulated to divide and grow genetically identical embryo to Y

In reproductive: it is placed in a surrogate mother
In non-reproductive: stem cells harvest from embryo

Advantages: Desirable genetic characteristics, Infertile organisms can reproduce
Disadvantages: Undesirable genetic characteristics, difficult, expensive, cloned org may not live as long
Human cloning is illegal in the UK - ethical issues: lower quality of life, disturbance of family structure, destroyed embryos

Reply 211

aimz08

Argh genomes & gene technologies now

Reply 212

ibysaiyan

Original post by aimz08

Argh genomes & gene technologies now

I have finished everything just doing behaviour.. god I hate it ;/

Reply 213

aimz08

Original post by ibysaiyan

I have finished everything just doing behaviour.. god I hate it ;/

Did you do F214?
I reckon I managed to get an A :smile:

But this module I'm probably resitting in june!

If I had a high B at AS, and two A's in the coursework and F214 what do you reckon I need to get in F215 to get an A or B overall?

Reply 214

ibysaiyan

Original post by aimz08

Did you do F214?
I reckon I managed to get an A :smile:

But this module I'm probably resitting in june!

If I had a high B at AS, and two A's in the coursework and F214 what do you reckon I need to get in F215 to get an A or B overall?

I did it last year got 95% ish.. but I so want 90% on this f215 module.Ah That's good to hear :smile:

Hmm I am guessing about 70 for a B ? in f215 :P

(edited 13 years ago)

Reply 215

aimz08

Original post by ibysaiyan

I did it last year got 95% ish.. but I so want 90% on this f215 module.Ah That's good to hear :smile:

Hmm I am guessing about 70 ? in f215 :P

I honestly don't care what I get as long as I get into one of the uni's I've applied for.
So glad I didnt get into medicine - Can't stand sciences anymore :P

Any predictions? I'm just going through the list someone posted earlier...essay type questions. Can't do much else now.

p.s. good luck for tomorrow ...doubt you need it as much as me though :P

Reply 216

Chunkeymonkey62

Hey guys Ive just realised how pointless this exam is to me.

If I get 0/150, Ill get a B in A Level Biology and if I get 130/150, Ill still get a B in A Level Biology. :frown:

Reply 217

aimz08

Original post by Chunkeymonkey62

Hey guys Ive just realised how pointless this exam is to me.

If I get 0/150, Ill get a B in A Level Biology and if I get 130/150, Ill still get a B in A Level Biology. :frown:

How do you work it out?

Reply 218

ibysaiyan

Original post by Chunkeymonkey62

Hey guys Ive just realised how pointless this exam is to me.

If I get 0/150, Ill get a B in A Level Biology and if I get 130/150, Ill still get a B in A Level Biology. :frown:

Impossible.... lol
60 ums is for a grade....