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Creado por Emily Sutton
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| Nucleic Acids - questions and answers | On the front of the card is a question about nucleic acids. Try and answer it. Then check your answer with the model answer on the back of the card. Good luck! |
| 1) Describe the differences between the structure of DNA and RNA. | DNA is double stranded and helical, but RNA is only single stranded and not helical. DNA contains deoxyribose (C5H10O4) and has one less oxygen atom in pentose, whereas RNA has ribose (C5H10O5) that has one more oxygen atom in pentose. DNA also contains thymine, whereas RNA contains the base uracil instead. Furthermore, there is only one type of DNA but there are three types of RNA (mRNA, tRNA and rRNA). Finally DNA is a relatively long molecule but RNA is relatively short/small. |
| ii) a sample of DNA was analysed, 23% of the nucleotides contained guanine. Calculate the percentage of nucleotides which contained adenine. Show your working. | 23% guanine so 23% cytosine. 100 - 46 = 54% made up of thymine and adenine. Adenine = 54/2 = 27% |
| 2) Name the structural unit shown. | Nucleotide. |
| ii) Name component A. | Phosphate. |
| iii) Name component B for DNA and RNA. | DNA: deoxyribose RNA: ribose |
| iv) Name the four components in DNA, represented by C. | Guanine, cytosine, thymine, adenine |
| v) Describe how the structural units, drawn in part (a), are arranged in DNA molecules. | There is complimentary base pairing, so adenine and thymine pair and guanine and cytosine. Backbone/chain/polynucleotides are formed by alternating sugar phosphate groups. These two chains are connected by the base pairs joined by hydrogen bonds. Furthermore, the two chains are twisted to form a double helix. |
| vi) Describe the function of DNA molecules in cells | DNA forms a template for protein synthesis for mRNA copy. |
| 3) Compare DNA and mRNA. Name of sugar, number of carbon atoms in sugar, number of polynucleotide chains in molecule and location in cell. | DNA: deoxyribose, 5, 2, in the nucleus RNA: ribose, 5, 1, in the cytoplasm |
| This is due to base pairing. Adenine is complimentary to thymine. However, the amounts are not exactly identical due to experimental error. | |
| ii) Explain why the base sequence of the DNA samples taken from a rat's bone marrow would be the same as those taken from the muscle of the same rat. | DNA is passed on from parents during fertilisation and so is inherited. During the zygote formation, DNA from the same cell replicated via mitosis to form the bones and muscles. Due to DNA replication, all body cells have the same DNA, that is genetically similar with the same base sequence. |
| iii) Explain how a sample of DNA from a rat's sperm differs from that of a muscle cell from the same rat. | Sperm cell would have half as much DNA and is produced by meiosis, not mitosis like in the muscle cell. This means it allows for variation and genetic differences. |
| 4) What is meant by the term semi-conservative replication? | Each strand of DNA is used as a template to make a new DNA strand. The new DNA is made of an original strand linked to a new strand. |
| Nitrogenous bases. | |
| ii) If they wanted to show the relative position of DNA from different sample of bacteria, suggest two variables that would need to be controlled in the centrifugation process. | Spin at the same speed and same time. Same density/concentration of gel and the same temperature. |
| iii) These are the results. Explain why tubes A and B support semiconservative replication. | Tube A is all heavy N15. Tube B DNA is a mixture of heavy and light (N15 and N14) so in a intermediate position. DNA in tube B must therefore be made from one strand of heavy and one strand of light. If it was conservative replication there would be two bands in the light and heavy position. |
| iv) What would you expect to see in tubes C and D. | C: Intermediate and light in equal amounts (touching dotted line). D: Intermediate and light but more light than intermediate (shown as a thicker or wider line). |
| 5) What is the role of messenger RNA and ribosomes in protein synthesis? | Messenger RNA (mRNA) is produced within the nucleus of a cell and migrates to the cytoplasm, where it attaches to ribosomes and guides the building of the amino acid sequences that will compose proteins. Ribosomes are sites for the meeting and binding of mRNA and transfer RNA (tRNA). They are the structures where amino acids transported by tRNA are united by peptide bonds to form polypeptide chains (proteins). |
| 6) What is the difference between transcription and translation? | Transcription is the name given to the formation of RNA molecules from an open DNA chain used as a template. Translation is the creation of polypeptides (amino acids bound in sequence) and therefore of proteins based on information encoded in the mRNA molecule. |
| 7) What is the name of an RNA sequence that codifies one amino acid? | Codon. |
| 8) If a tRNA anticodon is CAA, what is its corresponding mRNA codon? | GUU |
| That's the end of the questions. Well done! Check the back of this card for a quick reminder about DNA and RNA. |
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