DNA (Deoxyribonucleic Acid): The molecule that carries genetic information in all living organisms. It consists of two strands forming a double helix structure.
Genes: Specific sequences of nucleotides within DNA that code for proteins.
Structure of DNA:
Nucleotides: Building blocks of DNA, each consisting of a sugar, a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, guanine).
Base Pairing: Adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G).
21.2 Protein Synthesis
Protein Synthesis: The process by which cells make proteins based on the information in DNA.
Transcription: In the nucleus, DNA is transcribed into mRNA (messenger RNA).
Translation: In the cytoplasm, ribosomes translate the mRNA code into a sequence of amino acids to form a protein.
Codons: Triplets of bases in mRNA that correspond to specific amino acids.
21.3 Genetic Code
The Genetic Code: The set of rules by which the sequence of bases in DNA is translated into proteins.
Each sequence of three nucleotides (codon) in mRNA codes for one specific amino acid.
There are 64 possible codons (since 4 bases × 4 bases × 4 bases = 64), but only 20 amino acids, so some amino acids are coded by more than one codon.
21.4 Mutations
Mutation: A change in the DNA sequence that can affect protein production.
Point Mutation: A change in a single nucleotide base (e.g., substitution, insertion, or deletion).
Frameshift Mutation: Insertion or deletion of a base that shifts the reading frame, changing all subsequent amino acids.
Silent Mutation: A mutation that does not change the amino acid sequence.
Nonsense Mutation: A mutation that creates a stop codon, leading to an incomplete protein.
21.5 Biotechnology
Biotechnology: The use of living organisms or biological systems to develop products or processes for specific uses.
Applications of Biotechnology:
Genetic Engineering: The manipulation of an organism’s DNA to achieve desirable traits.
Recombinant DNA: DNA molecules formed by combining genes from different organisms.
Genetically Modified Organisms (GMOs): Organisms whose DNA has been altered for desired traits (e.g., pest-resistant crops, insulin-producing bacteria).
Cloning: Creating an organism that is genetically identical to another (e.g., therapeutic cloning for stem cell research).
Gene Therapy: Inserting, altering, or removing genes within an organism’s cells to treat disease.
21.6 Applications of Genetic Engineering
Medicine:
Production of Insulin: Genetically modified bacteria can produce human insulin for the treatment of diabetes.
Gene Therapy: Inserting a healthy gene into a patient’s cells to treat genetic disorders.
Agriculture:
GM Crops: Crops can be genetically modified to improve yield, resist pests, or tolerate environmental stresses.
Golden Rice: A genetically engineered rice that contains vitamin A to combat vitamin A deficiency.
Forensics:
DNA Profiling: Used in criminal investigations and paternity testing.
21.7 Ethical Issues in Biotechnology
Ethical Concerns:
GMOs in Agriculture: Concerns about the long-term environmental impact and health risks.
Cloning and Stem Cell Research: Issues surrounding the morality of cloning and using embryonic stem cells for research.
Gene Therapy: Ethical debates over the alteration of human genes and the potential for “designer babies.”