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| Question | Answer |
| Complete the sentences: Nucleotides join together to form _______________. The nucleotides join up between the ___________ group of one nucleotide and the ________ of another. This forms a __________________ ________ (consisting of the phosphate group and two ester bonds). The chain of sugars and phosphates is known as the __________ - ____________ ______________ | Nucleotides join together to form POLYNUCLEOTIDES. The nucleotides join up between the PHOSPHATE group of one nucleotide and the SUGAR of another. This forms a PHOSPHODIESTER BOND (consisting of the phosphate group and two ester bonds). The chain of sugars and phosphates is known as the SUGAR-PHOSPHATE BACKBONE. |
| What is the structure of DNA? |
2 polynucleotide strands joined together by hydrogen bonding between the bases by complementary base pairing
Double-helix shape
Two hydrogen bonds form between A + T
Three hydrogen bonds between C + G
Two polynucleotide strands are antiparallel
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| Outline the method of purifying DNA | 1. Break up the cells in sample 2. Make up a solution of detergent, salt and distilled water 3. Add the broken up cells 4. Incubate the solution in a water bath at 60°C for 15 minutes 5. Put solution in an ice bath to cool mixture down 6. Filter mixture using filter paper and funnel. Transfer a sample of of filtered mixture to a clean boiling tube 7. Add protease enzymes 8. Slowly dribble cold ethanol down the side of the tube, so that it forms a layer on top of the DNA-detergent mixture 9. If you leave the tube for a few minutes, the DNA will form a white precipitate, which can be removed using a glass rod |
| In DNA purification, why is the DNA-detergent mixture put into a warm water bath? | The detergent in the mixture breaks down the cell membranes. The temperature should be high enough to stop enzymes in the cell from working properly and breaking down the DNA |
| In DNA purification, why is salt in the mixture? | The salt binds to the DNA and causes it to clump together |
| In DNA purification, what is the role of protease? | These will break down some proteins in the mixture (e.g. proteins bound to the DNA) |
| Complete the sentences: The enzyme __________ unzips the DNA strands by breaking the __________ bonds between the _______ |
The enzyme HELICASE unzips the DNA strands by breaking the HYDROGEN bonds between the BASES
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| Complete the sentences: At the _________ strand, the ________________ nucleotides (free nucleotides) are attached to the __________ strand (in a 5’ to 3’ direction) continuously |
At the LEADING strand, the PHOSPHORYLATED nucleotides (free nucleotides) are attached to the TEMPLATE strand (in a 5’ to 3’ direction) continuously
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| Complete the sentences: At the ________ strand, fragments of nucleotides (_________ fragments) are added _____________ (5’ to 3’). This is because the DNA is being constantly ________ , the phosphorylated ____________ have to keep back-tracking up the strand when the nucleotides are added in the 5’ to 3’ direction. |
At the LAGGING strand, fragments of nucleotides (OKAZAKI fragments) are added DISCONTINUOUSLY (5’ to 3’). This is because the DNA is being constantly UNZIPPED, the phosphorylated NUCLEOTIDES have to keep back-tracking up the strand when the nucleotides are added in the 5’ to 3’ direction.
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| Complete the sentences: DNA ____________ catalyses the addition of new ____________ bases | DNA POLYMERASE catalyses the addition of new NUCLEOTIDE bases |
| Complete the sentences: _________ eventually joins up the okazaki fragments at the _______ strand |
LIGASE eventually joins up the okazaki fragments at the LAGGING strand
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| Complete the sentences: Two DNA molecules now exist, with one of the 2 strands of each molecule being the original (__________) DNA. This is ______-_______________replication. | Two DNA molecules now exist, with one of the 2 strands of each molecule being the original (PARENT) DNA. This is SEMI-CONSERVATIVE replication. |
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