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Flashcards · Biology

DNA and Protein Synthesis

94 cards from 6 lessons

  1. What does DNA stand for?

    Deoxyribonucleic acid.

  2. What is a polymer?

    A long molecule made of many repeating units.

  3. What is a nucleotide?

    The repeating unit of DNA, made of a sugar, a phosphate group and a base.

  4. Name the four bases in DNA.

    Adenine (A), thymine (T), cytosine (C) and guanine (G).

  5. Which base pairs with A?

    T (thymine).

  6. Which base pairs with C?

    G (guanine).

  7. What holds the two strands of DNA together?

    Hydrogen bonds between the paired bases.

  8. What forms the backbone of a DNA strand?

    Alternating sugar and phosphate groups.

  9. What is the shape of DNA?

    A double helix.

  10. What is the complementary strand of A A T C G?

    T T A G C.

  11. A DNA sample has 22% cytosine. What percentage is guanine?

    22%, because C pairs with G.

  12. A DNA sample has 18% thymine. What percentage is cytosine?

    32% (A is 18%, so C + G is 64%, and C is half of that).

  13. Why is it useful that hydrogen bonds are weak?

    The strands can be separated, to copy the DNA or read a gene.

  14. Why is DNA still stable if the hydrogen bonds are weak?

    There are millions of them holding the helix together.

  15. Who built the first model of the DNA double helix, in 1953?

    Watson and Crick, using X-ray data from Rosalind Franklin.

  16. What is the common error with the pairing rule?

    Pairing A with C or T with G. A pairs with T, and C with G, every time.

  17. What is a genome?

    The entire DNA of an organism.

  18. Roughly how many base pairs are in the human genome?

    About 3 billion.

  19. Roughly how many genes are in the human genome?

    About 20 000.

  20. When did the Human Genome Project start and finish?

    It started in 1990 and finished in 2003.

  21. What was the aim of the Human Genome Project?

    To find the order of all of the bases in human DNA.

  22. Do all of the human genome's bases make up genes?

    No. Only a small part is genes, and the rest is non-coding DNA.

  23. How similar is the DNA of two different people?

    More than 99% identical.

  24. Give one use of the genome project in medicine.

    Finding the genes that cause inherited disorders, or predicting a person's risk of a disease.

  25. What is personalised medicine?

    Treatment chosen according to a patient's own genes.

  26. Name one gene linked to a higher risk of breast cancer.

    BRCA1.

  27. Give one concern about genetic testing.

    Privacy, discrimination by insurers or employers, or worry about the results.

  28. Why was the number of human genes a surprise?

    There are only about 20 000, not many more than in a mouse.

  29. What does "sequencing" mean?

    Finding the order of bases in a piece of DNA.

  30. What is gene therapy?

    Treating a disorder by replacing or changing the faulty gene.

  31. What do scientists mean by "a variant" of a gene?

    A different version of the gene, with a different base sequence.

  32. Why was all of the Human Genome Project data made freely available?

    So that scientists anywhere could use it to help research and medicine.

  33. Why is the fruit mashed?

    To break open the cells and cell walls.

  34. What does detergent do in DNA extraction?

    It breaks down the cell membranes and the nuclear membrane, releasing the DNA.

  35. What is the purpose of salt in the extraction solution?

    It helps the DNA to clump together.

  36. Why is the mixture filtered?

    To remove the solid pieces of fruit and cell wall.

  37. Why is ethanol added?

    DNA is insoluble in ethanol, so it comes out of the solution.

  38. Why is the ethanol ice-cold?

    The cold helps the DNA to separate, and slows enzymes that could break it down.

  39. What does the DNA look like when it appears?

    White, stringy strands, like cobwebs.

  40. Where do the DNA strands appear?

    At the boundary between the filtrate and the ethanol layer.

  41. How can the DNA be removed?

    Lifted out with a glass rod or cocktail stick.

  42. Why are strawberries a good fruit to use?

    They have eight copies of each chromosome, so they have a lot of DNA.

  43. Name one hazard in the experiment.

    Ethanol is flammable and harmful.

  44. How should you add the ethanol?

    Slowly, down the side of the tilted tube, so it floats as a layer on top.

  45. Name one control variable in the experiment.

    The mass of fruit, the volumes of solution or the mixing time.

  46. Is the extracted DNA pure?

    No. It also contains proteins and other cell material.

  47. Why is an experiment like this usually qualitative?

    The amount of DNA is hard to measure, so results are mostly descriptions.

  48. What mistake do students make about the precipitate?

    Saying the DNA dissolves in ethanol. It does not, which is why it appears.

  49. What are proteins made from?

    Amino acids joined in chains.

  50. How many different amino acids are used to make proteins?

    20.

  51. What is a polypeptide?

    A long chain of amino acids.

  52. What is a triplet?

    A group of three bases that codes for one amino acid.

  53. How many different triplets can four bases make?

    64.

  54. What does the order of bases in a gene decide?

    The order of amino acids in the protein.

  55. What happens to a polypeptide chain after it is made?

    It folds into a specific three-dimensional shape.

  56. Why is the shape of an enzyme important?

    The substrate must fit into the active site, so a change in shape stops it working.

  57. A gene has a coding region of 300 bases. How many amino acids are coded for?

    100.

  58. A protein has 80 amino acids. How many bases code for it, at least?

    240.

  59. Can two different triplets code for the same amino acid?

    Yes. There are 64 triplets but only 20 amino acids.

  60. Give two examples of proteins and their functions.

    Enzymes speed up reactions, and antibodies bind to pathogens (or haemoglobin carries oxygen).

  61. Do bacteria use the same genetic code as humans?

    Yes, which is why bacteria can be made to produce human insulin.

  62. What is the mistake in saying "one base codes for one amino acid"?

    It takes a triplet of three bases to code for one amino acid.

  63. Why can a protein with a different order of amino acids behave differently?

    The different order can change how it folds, and so its shape and function.

  64. What is transcription?

    Making an mRNA copy of a gene.

  65. What is translation?

    Using the code in mRNA to build a polypeptide at a ribosome.

  66. Where does transcription take place?

    In the nucleus.

  67. Where does translation take place?

    At a ribosome in the cytoplasm.

  68. What is the job of RNA polymerase?

    To make a complementary mRNA strand from the coding DNA.

  69. Where does RNA polymerase bind?

    To non-coding DNA in front of the gene.

  70. What is mRNA?

    A single strand copy of a gene that carries the code to a ribosome.

  71. What is a codon?

    Three bases on mRNA that code for one amino acid.

  72. What is the job of tRNA?

    To carry an amino acid to the ribosome, matching the codon with its anticodon.

  73. Which base replaces thymine in RNA?

    Uracil.

  74. What would the mRNA be for the DNA coding sequence T A C?

    A U G.

  75. How does RNA differ from DNA in its strands?

    RNA is a single strand, DNA is two strands.

  76. What happens to the polypeptide once it is complete?

    It is released and folds into a protein.

  77. Why is mRNA needed?

    DNA cannot leave the nucleus, but the ribosomes are in the cytoplasm.

  78. Why do different cells make different proteins, if they have the same genes?

    Different genes are transcribed in different cells.

  79. What is a common mistake about transcription and translation?

    Mixing them up. Transcription makes mRNA, and translation makes the protein.

  80. What is a genetic variant?

    A difference in the base sequence of DNA between individuals.

  81. What causes a genetic variant?

    A mutation.

  82. What is a substitution?

    One base swapped for a different base.

  83. What is a frameshift?

    An insertion or deletion that changes how all of the following triplets are read.

  84. How can a variant in non-coding DNA change the phenotype?

    It changes how well RNA polymerase binds, so the amount of protein made changes.

  85. Does a non-coding variant change the protein itself?

    No. It changes the quantity of the protein, not its structure.

  86. How can a variant in coding DNA change the phenotype?

    It changes the amino acids, so the protein's shape and activity change.

  87. Why might a substitution have no effect on a protein?

    Several triplets code for the same amino acid, so the amino acid may not change.

  88. What is the cause of sickle cell disease?

    A single base change in the haemoglobin gene, so valine replaces glutamic acid.

  89. What happens to red blood cells in sickle cell disease?

    They are distorted into a sickle shape at low oxygen levels.

  90. Give an example of a variant in non-coding DNA.

    Lactase persistence, where a variant near the gene keeps it switched on in adults.

  91. What does a stop codon in the wrong place do?

    It cuts the polypeptide short, so it usually does not work.

  92. What happens if exactly three bases are deleted?

    One amino acid is lost, but the rest of the triplets are read correctly.

  93. Do all variants change the phenotype?

    No. Many have no effect on it.

  94. A variant makes RNA polymerase bind more strongly. What is the effect?

    More mRNA is made, so more protein is produced.