Biol5 processes

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  • Created on: 12-06-15 12:41


1. DNA helicase separates the DNA strands

2. RNA polymerase uses the template strand to add free complementary nucleotides, creating a molecule of pre-mRNA

3. Introns are then spliced out of pre-mRNA to give a molecule of mRNA


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1. A ribosome joins to the end of the mRNA molecule

2. This causes a molecule of tRNA, carrying the amino acid that is complementary to the first triplet/ codon to join

3. A second tRNA carrying the amino acid that is complementary to the second codon then joins

4. These amino acids are joined together using an enzyme and ATP

5. The process continues as the ribosome moves along the strand, building up a polypeptide

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In Vitro gene cloning

1. The DNA, primers and DNA polymerase are added to a vessel

2. The mixture is heated to 95 degrees, which causes the DNA strands to separate

3. The mixture is then cooled to 55 degrees allowing primers to join

4. DNA polymerase begins copying the DNA, starting from the primers

5. The temperature is increased to 72 degrees which is the optimum temperature for DNA polymerase to begin adding nucleotides

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In Vivo gene cloning- Producing DNA fragments

1. The relevant mRNA is extracted from the cell

2. cDNA is made from this mRNA using reverse transcriptase

3. The second strand of the DNA is built up using free complementary nucleotides and DNA polymerase

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In Vivo gene cloning- Inserting the fragments

1. The most common vector is a plasmid; the same restriction endonuclease is used to cut the fragment of DNA and the plasmid

2. The plasmid and DNA fragments are added together so that the fragments become incorporated into the plasmid, this join is made permanent using DNA ligase

3. The plasmids are now mixed with a host cell (bacterial cells) in a calcium medium which makes the cells more permeable

4. The bacterial cells take up the plasmids

5. 'successful' cells are identified using fluorescent markers or antibiotic resistance

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Action potentials

1. A stimulus causes the Na+ ion channels to open and Na+ floods the axon 

2. The influx of sodium ions causes yet more Na+ channels to open (positive feedback) which further depolarises the axon

3. Once +40mV has been reached the Na+ ion channels close and K+ ion channels open

4. This causes K+ ions to diffuse out of the axon, repolarising the axon and restablishing resting potential at 65mV

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1. The action potential reaches the synaptic knob

2. This causes calcium ion channels to open and calcium ions flood the synapse

3. This causes acetylcholine to be released into the synaptic cleft via exocytosis

4. The acetylcholine diffuses across the synaptic cleft and binds with receptors on the post synaptic membrane

5. This causes a new action potential to be generated

6. The acetylcholine is hydrolysed by acetylcholinesterase

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Muscle contraction

1. The action potential travels through the sarcoplasm via t-tubules

2. This causes calcium ion channels to open and calcium ions flood the sarcoplasm

3. This causes tropomyosin to stop blocking the myosin binding sites on the actin filament

4. The myosin heads are now in the cocked position due to the ADP molecule attached to them

5. The myosin heads bind to the actin filament forming cross-bridges

6. The myosin heads flex in unison, pulling the actin filament along

7. The myosin heads detach when a molecule of ATP attaches to them

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