Question

. If you are asked to amplify exon 3 of beta hemoglobin gene how you would do this?

. PCR revolutionized molecular biology-explain.

. ​​​​​​​Describe events occurring in the C4 cycle of photosynthesis.

Why C4 cycle is a good adaptation for certain plants.

Answer 1

1) To amplify specific region of the given gene, Polymerase Chain Reaction (PCR) technique can be used. For this, first we need to know the sequence of the beta haemoglobin gene. This could be found out by performing FASTA analysis on NCBI. Once, the sequence is known, then primers have to be designed complementary to the sequences present in exon 3. By using softwares, 8-14bp forward and reverse primers are designed. Also, we need to find out the appropriate set of restriction endonucleases to get DNA fragment of appropriate length containing the exon.

Now, PCR is set up. The reaction mixture will have buffer, dNTPs. primers and water. The template and the taq polymerase enzyme will be added in the end. The PCR steps will occur and amplify the required gene.

2) Polymerase Chain Reaction makes it easier to get multiple copies of specific regions of DNA. One can easily amplify the tiny amount of DNA. This is inexpensive and donot consumes much time. These copies hold immense importance in forensic analysis as well as the biotechnology applications. The amplified DNA can be used to study genetic diseases, therapies, tissue transplants, DNA fingerprinting, crime investigation etc. It offers tremendous opportunity for scientists, doctors, health care workers to study the intricacies of genetic material.

3) In C4 plants, calvin cycle and light dependent reactions occur separately. Calvin cycle occurs in bundle sheath cells present around veins of leaf and light reactions occur in mesophyll cells of spongy tissue. The events that occur are:

• Fixation: In the mesophyll cells, carbon dioxide is taken in and it reacts with phosphoenol pyruvate (PEP) to form oxaloacetate. This reaction is catalyzed by PEP carboxylase.
• Transport: Then the oxaloacetate is converted to malate. Malate is transported to the bundle sheath cells.
• Here, it breaks down to form pyruvate and carbon dioxide. Carbon dioxide enters calvin cycle. Here, it is fixed by enzyme Rubisco and converted to sugar.
• Regeneration: ATP is hydrolyzed and pyruvate converts backs to phosphoenol pyruvate. 4) C4 plants keep their stomata close since they are efficient in taking up carbon dioxide. This reduces water loss from the plant. Thus, they can survive drought and have high water efficiency. Photorespiration, which is energy consuming process do not occur since PEP carboxylase is not sensitive to oxygen while Rubisco can bind to it. This increases photosynthesis rate. C4 cycle is more prominent in monocots like grasses.