OCR Biology A2 (Unit 2) Processes 3

Detailed, step by step flashcards to help you remember and understand lengthy processes in the last Unit of OCR Biology. These will help you gain marks for 8/9 mark questions. This section includes: PCR, The Nitrogen Cycle, Cloning animals, Meosis.

  • Created by: MJ
  • Created on: 04-06-13 14:14
DNA sample mixed with supply of DNA nucleotides and DNA Polymerase. Mixture heated to 95C, breaking the H bonds between complementary strands. So all strands in the mixture are now single stranded.
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Primers are added to the mixture and the temperature is lowered to 55C, allowing the primers to hydrogen bond to the samples at either end, forming sections of double strand DNA.
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DNA Polymerase can now bind to these strands, the temperature is raised to 72C - the optimum temperature for DNA Polymerase to function.
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DNA Polymerase adds free nucleotides to the unwound, single stranded DNA. When the DNA Polymerase meets the other end, a double strand is created. This can be repeated to exponentially increase DNA amount.
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Silencing Genes 1
Cells trim double stranded RNA to form small inhibitory RNA (siRNA). The siRNA is processed to the single strand antisense strand whilst the sense (coding strand) deintergrates. Several proteins are required.
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Anti sense strand RNA combine to produce RNA induced silencing complex. Complex binds with mRNA to destroy.
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Decomposers and Recycling: Nitrogen in air (What makes it, what is it used for)
Made by: Denitrification of Bacteria in anaerobic soil. Used by: Nitrogen fixation by Haber Process, Lightning. Rhizobium bacteria and bacteria in soil
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Organic Nitrogen in leguminous plants
Made by: Nitrogen fixation from Rhizobium bacteria, adsorption of ammonium ions/nitrates/nitrites, . Used by: Animals (eating), Death (nitrogen goes into soil)
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Organic Nitrogen in soil:
Made by: Death of plants/animals, Nitrogen fixation of bacteria in soil. Produces: Ammonium ions by decomposition and ammonification.
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Produced by excreting animals. Produces ammonium ions by ammonification and decomposition.
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Produced by: Decomposing Urea and dead plants/animals and ions from fertiliser. Used by oxidising bacteria (Nitrosomonass) to produce nitrates and adsorbed by plants for organic nitrogen
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Produced by: Oxidising bacteria (nitrosommass). Used by Nitrobacter oxidisation to Nitrates
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Produced by: Nitrobacter oxidising Nitrites. Produces: Nitrous oxide and nitrogen by denitrification and nitrates flow into rivers by leaching.
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Cloning animals: Splitting embryos
High value male and female eggs and sperm collected, fertilised and grown in vitro, 16 cell embryo split into several segments and implanted into surrogate mothers.
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Cloning animals: Enucleated eggs
Somatic cells cultured, ovum is enucleated (nucleus removed), somatic nucleus and enucleated ovum fused by electrofusion producing reconstructed cell with somatic nucleus and ovum cytoplasm
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Blastula placed in tied oviduct to develop, early embyro recovered and implant surrogate mother's uterus
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Meosis: Prophase 1
Chromatin condenses and shortens by supercoiling. They can take up stains and be seen under a microscope. The chromosomes come together to form homologous pairs, forming bivalents. Non sister chromatids wrap around each other forming chiasmata.
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Lengths of chromatid may be swapped between each other by crossing over. The nucleolus disappears and the nuclear envelope disintergrates. A spindle forms.
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Metaphase 1
Bivalents line up randomly at the equator of the spindle, attached at the centromere with chiasmata still present. Each member of pair facing a different pole, allowing independant segregration.
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Anaphase 1
Homologous chromosomes are pulled by spindle fibres to opposite poles, separating the bivalents, the centromeres dont divide. Chiasmata seperate but new lengths of chromatid stay with new chromatid
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Telophase 1
NOT PRESENT IN PLANTS. Two new nuclear envelopes form around chromosomes at each pole. The cell divides by cytokenesis. Brief interphase, chromosomes uncoil.
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Centrioles replicate and move to poles. Nuclear envelope breaks down. Chromatin condenses and supercoils and spindle forms.
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Metaphase 2
Chromosomes randomly arrange at equator of spindle and attach at centromere.
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Anaphase 2
Centromeres divide, chromatids are randomly segregrated by moving to opposite poles by spindle fibres
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Telophase 2
Nuclear envelope reforms around four new haploid daughter cells. In plants this is called a tetrad.
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Other cards in this set

Card 2




Primers are added to the mixture and the temperature is lowered to 55C, allowing the primers to hydrogen bond to the samples at either end, forming sections of double strand DNA.

Card 3




Preview of the front of card 3

Card 4




Preview of the front of card 4

Card 5


Silencing Genes 1


Preview of the front of card 5
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