Biology by Bradford
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The subtopic in the middle and nine tasks round it: label three diagrams, complete a table, put a process in order and fill 42 gaps. The whole subtopic is higher level. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
Proteins that bind to specific base sequences in DNA and control its transcription are . Some bind at the , just before the gene, where they help attach. Others bind at an , which can be thousands of bases away, and raise the rate at which the gene is transcribed.
On DNA, these tags are added to the base . In a promoter they transcription of the gene downstream. On histones they may do the same or the reverse, it. Neither kind changes the .
| Lactose, in E. coli | Oestradiol, a hormone | |
|---|---|---|
| Binds to | a | a |
| Then | the protein lets go of the DNA | the pair binds to the DNA |
| Target genes | ||
| Result | enzymes made to lactose | e.g. uterus lining thickens |
Number the steps in order.
Copying the gene into mRNA is ; building the polypeptide is .
Tags that stay in place through are passed to daughter cells; tags that survive can reach offspring, changing their phenotype with no change to the DNA. Most tags are from sperm and egg, but not all. So a , from a lion father and a tiger mother, grows far bigger than either parent, while a , from a tiger father and a lion mother, does not.
Monozygotic twins develop from one , so their are identical and any difference between them comes from the . The older the twins, the more their tag patterns differ, as the graph shows. Air pollution is one factor known to change the tags on DNA.
Enzymes called break mRNA down. In human cells one mRNA may last a few minutes or several . The longer it lasts, the more often it is , so controlling its breakdown controls how much is made.
No cell expresses all of its genes, and the pattern it does express decides how it . Setting up these patterns as an organism develops is : the phenotype of the cells changes, but not their .
1234Copying the gene into mRNA is transcription; building the polypeptide is translation.
Proteins that bind to specific base sequences in DNA and control its transcription are transcription factors. Some bind at the promoter, just before the gene, where they help RNA polymerase attach. Others bind at an enhancer, which can be thousands of bases away, and raise the rate at which the gene is transcribed.
Enzymes called nucleases break mRNA down. In human cells one mRNA may last a few minutes or several days. The longer it lasts, the more often it is translated, so controlling its breakdown controls how much protein is made.
No cell expresses all of its genes, and the pattern it does express decides how it differentiates. Setting up these patterns as an organism develops is epigenesis: the phenotype of the cells changes, but not their genotype.
On DNA, these tags are added to the base cytosine. In a promoter they repress transcription of the gene downstream. On histones they may do the same or the reverse, activate it. Neither kind changes the base sequence.
Tags that stay in place through mitosis are passed to daughter cells; tags that survive meiosis can reach offspring, changing their phenotype with no change to the DNA. Most tags are removed from sperm and egg, but not all. So a liger, from a lion father and a tiger mother, grows far bigger than either parent, while a tigon, from a tiger father and a lion mother, does not.
Monozygotic twins develop from one zygote, so their genomes are identical and any difference between them comes from the environment. The older the twins, the more their tag patterns differ, as the graph shows. Air pollution is one factor known to change the methyl tags on DNA.
| Lactose, in E. coli | Oestradiol, a hormone | |
|---|---|---|
| Binds to | a repressor | a receptor |
| Then | the protein lets go of the DNA | the pair binds to the DNA |
| Target genes | switched on | switched on |
| Result | enzymes made to digest lactose | e.g. uterus lining thickens |