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Focuses on the development of Genetically Modified Organisms (GMOs) to improve crop yield, nutrition, and pest resistance.
What if a plant could produce its own pesticide, or a grain of rice could prevent blindness in millions of children? We are no longer just breeding plants; we are rewriting their genetic code to solve global crises.
One of the most successful applications of biotechnology is Bt-crops. These plants contain genes from the soil bacterium Bacillus thuringiensis. This bacterium produces Cry proteins (crystal toxins). When an insect larvae ingests the plant tissue, the alkaline environment of its midgut () activates the toxin. The activated toxin binds to specific receptors on the gut epithelium, creating pores that lead to ion imbalance, gut paralysis, and eventual death of the pest. Because humans have highly acidic stomachs ( to ), these proteins are degraded before they can cause harm, making Bt-crops a targeted biological pesticide.
Quick Check
Why is the specific pH of the insect gut critical for the effectiveness of Bt-toxin?
Answer
The Cry proteins are pro-toxins that require an alkaline (high pH) environment to be chemically activated into their toxic form.
To manage weeds without killing crops, scientists developed herbicide-resistant varieties, such as 'Roundup Ready' crops. These plants are engineered to withstand glyphosate, a broad-spectrum herbicide. Glyphosate normally kills plants by inhibiting the enzyme EPSPS (5-enolpyruvylshikimate-3-phosphate synthase), which is essential for synthesizing aromatic amino acids. Transgenic crops express a version of the EPSPS enzyme derived from Agrobacterium that is insensitive to glyphosate. This allows farmers to spray entire fields with herbicide; the weeds die, but the transgenic crop continues to synthesize proteins and grow normally.
Consider a farmer who loses 30% of their crop to weeds. 1. Without GMOs: The farmer spends 300 in yield. Total loss/cost = 50 on glyphosate and 70. 3. Result: The farmer saves $330 per acre, demonstrating the immediate economic incentive for GMO adoption.
Quick Check
What specific enzyme is targeted by glyphosate, and how do GMOs bypass this?
Answer
Glyphosate targets the EPSPS enzyme; GMOs bypass this by expressing a bacterial version of EPSPS that the herbicide cannot bind to.
Biofortification is the process of increasing the nutritional value of crops through genetic engineering. Golden Rice was developed to combat Vitamin A Deficiency (VAD), which causes blindness in hundreds of thousands of children annually. Scientists inserted two genes—psy (from daffodils) and crtI (from a bacterium)—into the rice genome. these genes complete the metabolic pathway for **-carotene** (provitamin A) biosynthesis in the rice endosperm (the edible part). This turns the rice grains a distinct yellow-orange color, providing a vital nutrient source in regions where rice is the primary staple.
If a child requires of Vitamin A daily and Golden Rice contains of -carotene per gram (with a conversion rate of 12:1 to Vitamin A): 1. Calculate Vitamin A per gram: . 2. Calculate required rice consumption: of rice. 3. Conclusion: A small bowl of Golden Rice can provide nearly 100% of the daily requirement for a child.
Widespread GMO use faces criticism regarding gene flow and pest resistance. Gene flow occurs when pollen from transgenic crops fertilizes wild relatives, potentially creating 'superweeds.' Furthermore, constant exposure to Bt-toxin exerts selective pressure on insects, leading to the evolution of resistant populations. To combat this, farmers use the Refuge Strategy: planting a percentage of non-Bt crops alongside Bt-crops. This ensures that some non-resistant insects survive and mate with any rare resistant mutants, diluting the resistance genes in the population and delaying the onset of widespread resistance.
Assume resistance is a recessive trait (). 1. In a 100% Bt field, only insects survive. They mate with each other, making 100% of the next generation resistant. 2. In a field with a 20% refuge, many susceptible insects () survive. 3. A rare resistant mutant () is much more likely to mate with a susceptible insect () from the refuge than another insect. 4. The resulting offspring () are susceptible to the Bt-toxin, effectively 'resetting' the resistance clock in the population.
Which condition is required for the activation of the Bt-toxin within an organism?
What is the primary ecological concern regarding 'gene flow' in GMO cultivation?
Golden Rice was engineered primarily to increase the total caloric yield of rice crops in Asia.
Review Tomorrow
In 24 hours, try to explain the 'Refuge Strategy' and why it relies on the genetics of recessive traits to work.
Practice Activity
Research a local agricultural crop in your region and find out if a transgenic version exists and what specific trait was modified.