Introduction to Genetic Engineering
4) Cellular Structural Proteins and Nucleic Acids
Nucleic Acids
DNA is a double helix formed by the repetition of four molecules called bases: adenine, guanine, cytosine, and thymine. These bases contain nitrogen. The size of a DNA molecule is measured in bases, kilobases, or megabases. DNA is shaped like a spiral staircase. Its railings are formed by each of the two strands, with monotonous successions of the four components of the DNA alphabet: A, C, G, and T. The steps of the staircase are chemical bonds that make the structure stable. In this arrangement, if a base in one railing is A, the other must be T, and if one is C, the other must be G, and vice versa. The consequence is that a certain message in one strand always corresponds to a defined one in the other. If the sequence order in one of the two railings is A, T, G, C, A, in the other, the complement will be T, A, C, G, T (nucleotides).
Proteins (Amino Acids)
Proteins are another type of molecular building block. There are 20 different amino acids essential for the synthesis of all proteins in living beings. There is a correlation between genes and proteins, where each 3-letter combination in DNA corresponds to a specific amino acid. For example, the triplet TGC encodes the amino acid threonine, while CGT and AAA encode alanine and phenylalanine, respectively. Therefore, the DNA sequence T, G, C, C, G, T, A, A, A will encode the protein sequence Thr-Ala-Phe, which in turn defines the functions and characteristics of the protein. Any cell of a living being uses a pair of molecular mechanisms, referred to as transcription and translation. In the first, the DNA sequence encoding the gene is transcribed into an intermediary molecule called messenger RNA (mRNA). This mRNA is a complementary copy of the DNA strand containing the gene sequence, although this RNA is formed by A, C, G, and instead of T, it contains uracil (U). In the case mentioned above, the DNA sequence TGCCGTAAA is transcribed to the mRNA sequence ACGGCAUUU.
5) Difference Between Genetically Modified and Conventional Crops
In genetically modified (GM) crops, genetic engineering has been used in the design, while conventional processes have been used in conventional crops. This difference has three important consequences:
- Increased directionality: Genetic engineering is no longer limited to randomly mutating or crossing genes but allows for the selection, molecular identification, and insertion of specific genes into a genome.
- Concrete results: Given the potential of these techniques, genetic engineering yields much faster results.
- Species barrier leap: This mainly affects the application of genetic engineering to improve plants or animals for food production.
6) Three Risks and Three Advantages of Genetic Engineering
Risks
Among the environmental and health risks, three types stand out:
- Possible transfer of foreign genes from transgenic varieties to wild varieties.
- Loss of agricultural biodiversity associated with the cultivation of transgenic plants, as farmers tend to use the best-performing cultivars preferentially.
- Harmful effects that certain transgenic plants resistant to insects may have on populations of insects other than those they are designed to protect against.
Advantages
(Advantages not provided in the original text)
7) Plasmids in Genetic Engineering
a) What is a plasmid?
Plasmids are extrachromosomal DNA molecules, either circular or linear, that replicate and transcribe independently of normal chromosomal DNA. They are present in bacteria and some eukaryotic organisms like yeast.
b) In what type of cells are they naturally located?
In bacteria and eukaryotic organisms.
c) What are their applications in genetic engineering?
Plasmids (recombinant vectors) used in genetic engineering are commercially available in solution packages. These plasmids have an antibiotic resistance gene to allow for the separation of bacteria that have incorporated the plasmid from those that have not. If bacteria are grown in a culture medium with antibiotics, bacteria without plasmids will die, while those with plasmids will be resistant to antibiotics and will develop.
8) DNA, mRNA, and Protein Sequence
If a DNA molecule has the sequence AATGTTA-CAATGGATCCGTTGCAT, what will be the messenger RNA sequence that it generates? What will be the protein sequence formed by translating said mRNA?
Information: The codons AAC, CAA, CUA, GGA, GUA, UAC, and UGU encode the amino acids asparagine, glutamine, leucine, glycine, valine, tyrosine, and cysteine, respectively.
Answer:
mRNA sequence: UUACAAU-GUUACCUAGGCAACGUA
Protein sequence: Leucine-Glutamine-Leucine-Glycine-Asparagine-Tyrosine-Cysteine-Valine
10) Mutants in Our Diet
All the foods we eat are mutants because they come from the artificial selection of wild organisms. For example, Brussels sprouts.
13) Restriction Enzymes
What are they and how do they work?
Restriction enzymes are enzymes that cut DNA at very specific sites. These sites are palindromic DNA sequences. As a consequence, they generate sticky ends in the DNA.
14) Protoplasts and DNA Transfer
What is a protoplast? What advantage does it present compared to a normal bacterial cell in DNA transfer processes?
It is easier to transform a protoplast than a normal cell. Protoplasts are microbial cells that have had their cell walls temporarily removed, thus facilitating the entry of transforming DNA. Afterward, the cell wall can be regenerated.