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A2 Biology OCR June 2015 Revision Thread

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Hopefully unit 5 will be an average paper that tests our knowledge and application from a range of topics rather than just one module :erm:

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Original post by loperdoper
Just to check - you mean "Using the information in Fig. 5.1, list the three triplet codons that would cause termination of a polypeptide chain (stop codons) and explain why these codons have this effect."

The three triplet codons are just the ones that code for "stop" - so following the diagram, this is UAA, UAG, and UGA (read from the diagram).

They code for a "stop" because, whilst there is a tRNA with the complementary anticodon, there is no associated amino acid on the tRNA. This means the amino acid on the previous tRNA has nothing to create a peptide bond with, and the whole chain breaks away from the tRNA and therefore forms the primary structure.

Do we need to know the structure of polynucleotide nucleotide mRNA and tRNA like for eg tRNA has single polynucleotide strand ?
Original post by Student23478
Do we need to know the structure of polynucleotide nucleotide mRNA and tRNA like for eg tRNA has single polynucleotide strand ?


I would check the spec and see what they've said, but the end of f215 papers often is a series of questions where you make comparisons between two things - so I wouldn't be surprised if "what's the difference between DNA and (t/m)RNA" came up or similar.

It wouldn't be a bad idea to be aware of the structure of tRNA/mRNA, at least.
In the book (both CGP and official textbook) it says the sequencing reaction can only operate on a length of DNA that is 750bp. However, I do not understand why then the genome is cut into smaleer fragments of about 100000bp???
Confused on the whole sequencing genomes area. Is the BAC bit an overview of the whole sequencing, or a stage in sequencing the genome?

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Not looking forward to the exam.


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Original post by loperdoper
I would check the spec and see what they've said, but the end of f215 papers often is a series of questions where you make comparisons between two things - so I wouldn't be surprised if "what's the difference between DNA and (t/m)RNA" came up or similar.

It wouldn't be a bad idea to be aware of the structure of tRNA/mRNA, at least.


Yeah. Do we need to know examples for interspcfifc competition intra and predator prey relationships? So for predator prey you've for lynx predator and snowshoe then you've got the grey and (other coloured ) rabbits for inter what about intra eg??
Reply 3287
Avatar for mbcns
mbcns
I don't understand how pollarded/coppiced trees can grow because without their leaves, how do they photosynthesise?
And also in the Jan13 paper it asks why keeping shoots in the dark makes them grow more, the markscheme says something about light destroying auxin, or auxin being more evenly distrubuted around the plant. how does this work?
Thanks
What are the steps involved in the sequencing of a human genome?

Anyone???
Does anyone know what siRNA is and if we have to know about in the exam? I saw a couple of questions on it but can't find them anymore.
Thank you :smile:
Original post by Student23478
Yeah. Do we need to know examples for interspcfifc competition intra and predator prey relationships? So for predator prey you've for lynx predator and snowshoe then you've got the grey and (other coloured ) rabbits for inter what about intra eg??


Yes- its a good idea. Just done a past paper where you got marks for mentioning the names of animals. It would be good to learn specific examples for innate and learned behaviour too
Original post by mbcns
I don't understand how pollarded/coppiced trees can grow because without their leaves, how do they photosynthesise?
And also in the Jan13 paper it asks why keeping shoots in the dark makes them grow more, the markscheme says something about light destroying auxin, or auxin being more evenly distrubuted around the plant. how does this work?
Thanks


I don't know about the first part but for the second part... when sunlight is shining on a plant, the auxins move to the shaded side of the plant, causing the shaded side to elongate, therefore causing it to grow towards the light. If there is no light, who whole tip is shaded so the auxins will be evenly distributed at the shoot tip, causing it to grow directly upwards.
Reply 3292
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mbcns
Original post by raach.14
I don't know about the first part but for the second part... when sunlight is shining on a plant, the auxins move to the shaded side of the plant, causing the shaded side to elongate, therefore causing it to grow towards the light. If there is no light, who whole tip is shaded so the auxins will be evenly distributed at the shoot tip, causing it to grow directly upwards.


ahhh i get it now- thanks!
Original post by junaid95
What are the steps involved in the sequencing of a human genome?

Anyone???


Page 167 of the text book.

1) Genomes are mapped to identify which part of the genome they have come from (that doesn't make sense to me but whatever)
2) Samples are mechanically broken into smaller sections of around 100,000 base pairs (shotgun approach)
3) Each section is placed into an individual BAC (bacterial artificial chromosome)
4) BAC's transferred to E.coli cells which are grown in culture to make multiple copies of the sections, known as clone libraries
5) E.coli cells containing specific BAC's are removed and cultured separately.
6) The DNA is extracted from the cells and cut using restriction enzymes into smaller fragments
7) Fragments are separated by size using electrophoresis
8) Each fragment is sequenced using an automated process
9) A computer programme then compares overlapping regions from the cuts made by restriction enzymes, and use that to reassemble the whole BAC.

Although it doesn't say, I presume steps 5-9 are repeated for each BAC. Someone correct me if I'm wrong!

Also read page 172
(edited 8 years ago)
Hi!
Could someone help me with this please?
Is the polymerase chain reaction basically the same process at the Chain termination method? Except the CT method uses modified terminator nucleotides to create strands of different lengths?
Thanks! :smile:
Original post by Student23478
Also can someone give me the advantages of behaviours of innate and learning so classical operant habituation and innate reflexes kinesis and taxes??


Reflexes - avoid predators e.g earthworm withdraws underground in response to vibrations on the ground, also avoid being trampled on I guess

Kinesis - again avoid predation e.g woodlice move rapidly if exposed to light conditions, they do not actively seek damp and dark conditions, but they're movement will reduce when they have found them

Taxis - positive phototaxis enables plants to maximise photosynthesis

Habituation - animals don't waste energy responding to unnecessary stimulus

Imprinting - helps young learn survival skills from parents

Classical conditioning - not sure?

Operant conditioning - teaches animals right from wrong, not really sure?

Latent learning - animals retain information for a later date e.g. rabbits will explore burrows so that they can escape predators in the future

Insight learning - solving problems maximises survival rate
Original post by LMottram
Hi!
Could someone help me with this please?
Is the polymerase chain reaction basically the same process at the Chain termination method? Except the CT method uses modified terminator nucleotides to create strands of different lengths?
Thanks! :smile:


Where in the text book is the chain termination method?
Reply 3297
Avatar for Cdp3
Cdp3
2
Original post by shalalondon
Could someone please summarise/explain this point from spec to me, like what do you exactly need to know.
"Dicuss how the links btween a range of human behaviours and the dopamine receptor DRD4 may contribute to the understanding oh human behaviour."


So, basically dopamine is a neurotransmitter which affects certain behaviours, e.g. mood.
There are 5 different receptors for dopamine, the effects of dopamine vary depending on which receptor is binds to and each receptor is coded for by a different gene, so for D4 receptor, DRD4 codes for it.

Having many D4 receptors has a negative effect, it links to abnormal behaviour, in for example, Schizophrenia (a disorder impacting thinking, perception, memory and emotion), and there is certain pieces of evidence to prove this.
Reply 3298
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Cdp3
2
Can someone explain/summarise the biological and the phylogenetic species concept please?
Original post by Cdp3
Can someone explain/summarise the biological and the phylogenetic species concept please?


Biological is just the idea of the two organisms being able to breed together to produce fertile offspring. Though the zebra and horse can mate and produce a 'Zorse', the chromosome numbers mean that the the Zorse is infertile and can't reproduces, so they are therefor classed as different species.

Phylogenetic is based on evolutionary relationships through history. The closer the common ancestor, the more genetically related the organisms are likely to be to one another. This concept has it's issues as there's no clear say so as to classifying species.

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