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15 Cards in this Set
- Front
- Back
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How many hydrogen bonds does adenine form with thiamine? |
Two |
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How many hydrogen bonds does cytosine form with guanine? |
Three |
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What is meant by the terms 'major groove' and 'minor groove'? |
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What is the difference between DNA in prokaryotes and eukaryotes? |
Prokaryotes have a single, circular chromosome, eukaryotes have linear chromosomes with the ends protected by telomeres |
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What is a telomerase? |
Specialised form of reverse transcriptase that carries an internal RNA template to direct DNA synthesis. Forms the telomeres by extending the 3' end with repeating units. |
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How is DNA condensed? |
DNA strand wraps around histones to form nucleosomes, nucleosomes form solenoids, structure arranges itself on a protein scaffold, protein scaffold further condenses |
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What is the nucleosome core made up of? |
Eight histone molecules: two of each of H2A, H2B, H3 and H4 |
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What is the purpose of H1? |
Stabilizes the nucleosome structure by sitting outside it |
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Name four covalent modifications to histone tails and their effects |
-Acetylation of lysine groups neutralises the positive lysine group. Regulates transcription. -Methylation of side chains (lysine, argentine etc) to regulate transcription. -Phosphorylation of hydroxy groups (serine and threonine) to regulate transcription Ubiquitination can lead to protein degradation
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What is a solenoid? |
A stack of nucleosomes with a left handed turn |
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What holds the base of the chromosome loop in place on the protein scaffold? |
Structural maintenance of chromosome proteins (SMC proteins) |
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What is supercoiling? |
The creation of loops in DNA via superhelical tension |
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What is the difference between positive and negative supercoiling? |
Positive = in front of the polymerase Negative = Behind the polymerase |
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Explain the equation Lk = Tw + Wr |
Lk = linking number, the number of times the DNA twists around each other when the axis is flat. It is a constant for a particular strand.
Tw = the number of twists in a DNA molecule
Wr = Number of twists in the supercoil
Both Tw and Wr can change to maintain Lk |
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What is a topoisomerase? |
Enzymes which break phosphodiester bonds in DNA to relieve superhelical tension. |
