SNAB Biology Unit 4

Transcription is when DNA is copied into mRNA

• RNA polymerase attaches onto the DNA at the beginning of the gene in the nucleus of the cell and breaks the hydrogen bonds; this causes the DNA to unwind and leaves 2 seperate strands of RNA.
• One of the strands is used as a template (antisense strand); the RNA polymerase lines up free RNA nucleotides with their complementary base pairs (base T is replaced with a U in RNA).
• The nucleotides are then joined together to form an mRNA strand; then the RNA polymerase moves along the DNA strands and re-joins them with hydrogen bonds so the strands can coil back into a double helix.
• When the RNA reaches a stop codon, it detaches from the DNA.
• The mRNA moves out from the nucleus through a nuclear pore, and moves through the cytoplasm where it attaches to a ribosome to start the Translations stage.

The scientific community accept theories and ideas because they have shared and discussed them, so they can validate them; this is done in 3 main ways:

• Scientific journals allow scientists to publish their work and findings and share new ideas, theories, experiments and conclusions. These journals also allow other scientists to repeat experiments and see if they get the same results - if the same results come up over and over again, the evidence can be seen as reliable.
• Peer review is when other scientists from the same area of work read and review a scientist's work before it can be published in a journal. The reviewer has to check that the work is valid and supports the conclusions drawn from the results - this method is used by the scientific community to make sure that any scientific evidence published is valid and that the experiments are carried out to the highest possible standard.
• Scientific conferences are where many scientists meet to discuss each others work, and the conference is usually led by a scientist who has interesting results and will do a lecture/presentation on them. Other scientists can ask questions and discuss the results with them face to face, and so it is an easy way for the latest theories and evidence to be shared, discussed and validated.