BASIC LESSONS IN GENETICS

·      Genetics is the field of biology devoted to understanding how characteristics are transmitted from parents to offspring.

·      Genetics was founded with the work of Gregor Johann Mendel. His work is with Pisum sativum. The pea characteristics that Mendel observed were plant height, flower position along stem, pod color, pod appearance, seed texture, seed color,  and flower color.

·      Heredity is the transmission of characteristics from parents to offspring.

·      P generation refers to the true-breeding parents. F1 generation or filial generation is the offspring of the P generation. If you cross the F1 the second filial generation or F2 is the result.

·      Dominant is the trait appearing while recessive is the trait that is masked

·      Law of Segregation states that a pair of factors is segregated or separated during the formation of gametes

·      Law of Independent Assortment states that factors separate independently of one another during the formation of gametes.

·      Most of Mendel’s findings agree with what biologists now know about molecular genetics.

·      Molecular genetics is the study of the structure and function of chromosomes and genes.

·      Chromosome is a threadlike structure made up of DNA.

·      Gene is the segment of DNA on a chromosome that controls a particular hereditary trait

·      Both chromosomes and genes occur in pairs. Each of two or more alternative forms of a gene is called an allele. Mendel’s factors are now called alleles. Letters are used to represent alleles. Capital letters refer to dominant alleles, and lowercase letters refer to recessive alleles.

Mendel’s law of independent assortment is supported by the independent segregation of chromosomes to gametes during meiosis. Therefore, the law of independent assortment is observed only for genes located on separate chromosomes or located far apart on the same chromosome.

ORGANS FOR TRANSPLANT

Transplantation of a human kidney, heart, liver, pancreas, lung, and other organs is now possible due to two major breakthroughs.

First, solutions have been developed that preserve donor organs for several hours. This made it possible for one young boy to undergo surgery for 16 hours, during which time he received five different organs.

Second, rejection of transplanted organs is now prevented by immunosuppressive drugs; therefore, organs can be donated by unrelated individuals, living or dead. Even so, rejection is less likely to happen if the donor’s tissues “match” those of the recipient—that is, their cell surface molecules should be similar to one another. Living individuals can donate one kidney, a portion of their liver, and certainly bone marrow, which quickly regenerates.

After death, it is still possible to give the “gift of life” to someone else—over 25 organs and tissues from the same person can be used for transplants at that time. A liver transplant, for example, can save the life of a child born with biliary atresia, a congenital defect in which the bile ducts do not form. Dr. Thomas Starzl, a pioneer in this field, reports a 90% chance of complete rehabilitation among children who survive a liver transplant. (He has also tried animal-to-human liver transplants, but so far, these have not been successful.) So many heart recipients are now alive and healthy that they have formed basketball and softball teams, demonstrating the normalcy of their lives after surgery.

One problem persists: The number of Americans waiting for organs now stands at over 80,000 and is getting larger by the day. Although it is possible for people to signify their willingness to donate organs at the time of their death, only a small percentage do so. Organ and tissue donors need only sign a donor card and carry it at all times. In many states, the back of the driver’s license acts as a donor card. Age is no drawback, but the donor should have been in good health prior to death. Organ and tissue donation does not interfere with funeral arrangements, and most religions do not object to the donation.

Family members should know ahead of time about the desire to become a donor because they will be asked to sign permission papers at the time of death.

Especially because so many Americans are waiting for organs and a chance for a normal life, researchers are trying to develop organs in the laboratory. Just a few years ago, scientists believed that transplant organs had to come from humans or other animals. Now, however, tissue engineering is demonstrating that it is possible to make some bio-artificial organs—hybrids created from a combination of living cells and biodegradable polymers. Presently, lab grown hybrid tissues are on the market. For example, a product composed of skin cells growing on a polymer are used to temporarily cover the wounds of burn patients. Similarly, damage cartilage can be replaced with a hybrid tissue produced after chondrocytes are harvested from a patient. Another connective tissue product made from fibroblasts and collagen is available to help heal deep wounds without scarring. Soon to come are a host of other products, including replacement corneas, heart valves, bladder valves, and breast tissue.

The ultimate goal of tissue engineering is to produce fully functioning transplant organs in the laboratory. After nine years, a Harvard Medical School team headed by Anthony Atala has produced a working urinary bladder. After testing the bladder in laboratory animals, the Harvard group is ready to test it in humans, whose own bladders have been damaged by accident or disease,

or will not function properly due to a congenital birth defect. Another group of scientists has been able to grow arterial blood vessels in the laboratory. Tissue engineers are hopeful that they will one day produce more complex organs such as a liver or kidney.

CELLULAR RESPIRATION

·      Cellular respiration is the complex process in which cells make ATP by breaking down organic compounds. Energy in ATP is used by cells to do work.

·      Cellular respiration can be divided into two stages:

1.     Glycolysis – organic compounds are converted into three C molecules of pyruvic acd, producing a small amount of ATP and NADH (an electron carrier molecule). It is an anaerobic process because it does not require the presence of oxygen.

2.     Aerobic Respiration – if oxygen is present in the cell’s environment, pyruvic acid is broken down and NADH is used to make a large amount of ATP through the process known as aerobic respiration.

·         If oxygen is not present in the cell’s environment, pyruvic acid can enter in to another anaerobic pathway called fermentation.

 GLYCOLYSIS

·      Glycolysis is a biochemical pathway in which one 6-C molecule of glucose is oxidized to produce two 3-C molecules of pyruvic acid. It is a series of chemical reactions catalyzed by specific enzymes.

·      The major steps in Glycolysis are:

1.     Two phosphate groups are attached to one molecule of glucose, forming new 6-C compound that has two phosphate groups. The phosphate groups are supplied by two molecules of ATP, which are converted into two molecules of ADP.

2.     The 6-C compound is split into 3-C molecules of glyceraldehydes-3-phosphate (G3P). Recall that G3P is also produced by the Calvin cycle in photosynthesis.

3.     The two G3P molecules are oxidized, and each receives a phosphate group. The product of this step is two molecules of a new 3-C compound. This is also accompanied by reduction of two molecules of NAD⁺ to NADH.  (Counter part of NADP in light reaction). NAD⁺ is an organic molecule that accepts electrons during redox reactions.

4.      The phosphate groups added in steps 1 and 3 re removed from the 3-C compounds which produce two molecules of pyruvic acid. Each phosphate group Is combined with a molecule of ADP to make a molecule of ATP. Since there were four phosphate groups added, four molecules of ATP are produced.

·      Notice that two ATP molecules were used in step 1 but four were produced in step 4. Therefore, Glycolysis has a net yield of two ATP molecules for every molecule of glucose that is converted into pyruvic acid.

·      Fermentation is the combination of Glycolysis and additional pathways which regenerate NAD⁺. The additional pathways in fermentation do not produce ATP; however, recycled NAD⁺ from NADH. Thus allow for the continued production of ATP.

FERMENTATION

·      There are many fermentation pathways, and they differ in terms of enzymes that are used and the compounds that are made from pyruvic acid. Two common fermentation pathways result n the production of lactic acid and ethyl alcohol.

·      Lactic acid fermentation, an enzyme converts pyruvic acid made during Glycolysis into another 3-C compound called lactic acid. It involves the transfer of one hydrogen atom from NADH and addition of one free proton, H⁺ to pyruvic acid. Thus, the regeneration of NAD⁺ in lactic acid fermentation helps to keep Glycolysis operating.

·      Lactic acid fermentation by microorganisms plays an essential role in manufacture of many dairy products – cheese, buttermilk, yogurt, sour cream. In muscle, lactic acid makes the cells’ cytosol more acidic that reduce the capacity of the muscle cells to contract resulting to muscle fatigue, pain and cramps. Eventually, the lactic acid diffuses into the blood and is transported to the liver, where it can be converted back to pyruvic acid.

·      Alcoholic fermentation converts pyruvic acid into ethyl alcohol which requires two steps

1.     Carbon dioxide molecule is removed from pyruvic acid, leaving a 2-C compound

2.     Two hydrogen atoms are added to the 2-C compound to form ethyl alcohol

·      Like lactic acid fermentation, NAD⁺ is also regenerated in this process.

·      Alcoholic fermentation by yeast cells is the basis of the wine and beer industry.

·      The efficiency of Glycolysis in providing energy or ATP can be determined if one compared the amount of energy available in glucose with the amount of energy contained in the ATP that is produced by Glycolysis.

·      Scientists have calculated that the complete oxidation of a standard amount of glucose releases 686 kcal. The production of a standard amount of ATP from ADP absorbs a minimum of about 7 kcal, depending on the conditions inside the cell.

·      Efficiency of Glycolysis = Energy required to make ATP

                                              Energy released by oxidation of glucose

                    = (2 X 7 kcal/686 kcal) x 100% = 2%

CITRIC ACID/KREB’S CYCLE

·      The Krebs cycle is a biochemical pathway that breaks down acetyl CoA, producing CO₂, hydrogen atoms, and ATP.

·      The cycle has five main steps:

1.     A 2-C molecule of acetyl CoA combines with a 4-C compound, oxaloacetic acid to produce a 6-C compound, citric acid. Notice that this reaction regenerates coenzyme A.

2.     Citric acid releases a CO₂ molecule and a hydrogen atom to form a 5-C compound. By losing a hydrogen atom with its electron, citric acid is oxidized. The electron in the hydrogen atom is transferred to NAD⁺, reducing it to NADH.

3.     The 5-C compound formed also releases a CO₂ molecule and a hydrogen atom, forming a 4-C compound. Again NAD⁺ is reduced to NADH. Notice that in this step a molecule of ATP is also synthesized from ADP.

4.     The 4-C compound formed releases a hydrogen atom to form another 4-C compound. This time, the hydrogen atom is used to reduce  FAD to FADH₂. FAD or flavin adenine dinculeotide, is a molecule very similar to NAD⁺. Like NAD⁺, FAD accepts electrons during redox reactions.

5.     The 4-C compound formed releases a hydrogen atom to regenerate oxaloacetic acid, which keeps the Krebs cycle operating. The electron in the hydrogen atom reduces NAD⁺ to NADH.

ELECTRON TRANSPORT SYSTEM

·      In the electron transport chain, these electrons are passed along a series of molecules embedded in the inner mitochondrial membrane.

1.     NADH and FADH₂ give up electrons to the electron transport chain. NADH donates electrons at the beginning, and FADH₂ donates them farther down the chain. These molecules also give up protons (hydrogen ions, H⁺.

2.     The electrons are passed down the chain. As they move from molecules to molecules, they lose energy.

3.     The energy lost from the electrons is used to pump protons from the matrix, building a high concentration of protons between the inner and outer membranes. Thus, a concentration gradient is also created, as the protons carry a positive charge.

4.     The concentration and electrical gradients of protons drive the synthesis of ATP by chemiosmosis, the same process that generates ATP in photosynthesis. ATP synthase molecules are embedded in the inner membrane, near the electron transport chain molecules. As protons move through ATP synthase and down their concentration and electrical gradients, ATP is made from ADP and phosphate.

5.     Oxygen is the final acceptor of electrons that have passed down the chain. Oxygen also accepts protons that were part of the hydrogen atoms supplied by NADH and FADH₂. The protons, electrons and oxygen all combine to form water.

·      Cellular respiration can produce up to 38 ATP molecules from the oxidation of single molecules of glucose. Thus, up to 39 percent of the energy released by the oxidation of glucose can be transferred to ATP. However, most eukaryotic cells produce only about 36 ATP molecules per molecule of glucose.

Cellular respiration uses the processes of Glycolysis and aerobic respiration to obtain energy from organic compounds.

PHOTOSYNTHESIS

·      Autotrophs use photosynthesis to make organic compounds from carbon dioxide and water. Heterotrophs cannot make their own organic compounds from inorganic compounds and therefore depends on autotrophs

·      Photosynthesis converts light energy into chemical energy through series of reactions known as biochemical pathways. Almost all life depends on photosynthesis.

·      Photosynthesis occurs in two stages. In the light reactions, energy is absorbed from the sunlight and converted into chemical energy; in the Calvin cycle, carbon dioxide and chemical energy are used to form organic compounds.

·      The light reactions of photosynthesis begin with the absorption of light by chlorophyll a and accessory pigments in the thylakoids.

·      Excited electrons that leave chlorophyll a travel along two electron transport chains, resulting in the production of NADPH. The electrons are replaced when water is split into electrons, protons and oxygen in the thylakoid. Oxygen is released as a by-product of photosynthesis.

·      As electrons travel along the electron transport chains, protons move into the thylakoid and built up a concentration gradient. The movement of protons down this gradient of protons and through ATP synthase results in the synthesis of ATP through chemiosmosis.

·      The dark reaction of photosynthesis or also known as Calvin Cycle happens without the presence of light energy.

·      The ATP and NADPH produced in the light reactions drive this second stage of photosynthesis. Carbon dioxide is incorporated in this cycle through the process of carbon fixation.

·      The Calvin Cycle produces a compound called G3P. Most of the G3P molecules are converted into RuBP to keep the Calvin cycle operating. However, some G3P molecules are used to make other organic compounds, including amino acids, lipids and carbohydrates.

·      Plants that fix carbon using only the Calvin cycle are known as C₃ plants. Some plants that evolved in hot, dry climates fix carbon through alternative pathways – the C₄ and CAM pathways. These plants carry out carbon fixation and the Calvin cycle either in different cells or at different times.

·      The rate of photosynthesis increases and then reaches a plateau as light intensity or carbon dioxide concentration increases. Below a certain temperature, the rate of photosynthesis increases as temperature increases. Above that temperature, the rate of photosynthesis decreases as temperature increases.

BIOGEOCHEMICAL CYCLE

·      As energy and matter flow through an ecosystem, matter must be recycled and reused. Substances such as water, carbon, nitrogen, sulphur and phosphorus each pass between the living and non living words through biogeochemical cycles.

·      The energy from the sub causes water to move into the atmosphere. This is called evaporation. Water moving from the atmosphere to the earth is called precipitation.

·      In the carbon-oxygen cycle there are two basic life processes involved – respiration and photosynthesis.

1. During cellular respiration, glucose is oxidized and carbon dioxide is released.
2. During photosynthesis, green plants use the carbon dioxide and energy from the sun to make oxygen, glucose and water.

·      When plants and animals die, the organic compounds of their bodies are broken down by microorganisms. One of the end products that eventually form is carbon dioxide.

·      In spite of the abundance of nitrogen in the atmosphere, plants cannot change the element nitrogen into compounds they need. The nitrogen must be in the form of nitrate. Synbiotic bacteria can change atmospheric nitrogen into ammonium compound

·      Bacteria of decay break down the protein of dead organisms to ammonia or ammonium compounds. Some bacteria cause nitrogen to return to the atmosphere by breaking down ammonia in the soil.

·      Phosphorus is present in the soil in the form of phosphate. Through weathering, phosphate rocks contribute to the amount of phosphate in the soil. Phosphate is taken in by plants and passed on to the food chain when plants and animals die. The bacteria converts the dead bodies into phosphates and return them into the soil. Guano deposits are also sources of phosphate.

Sulfur and phosphorus cycles are both lithosphoric cycles. Sulfur comes from several sources – volcanoes, the action of soil microorganisms – combustion of fossil fuels such as oil, gas, and coal. When fuel is burned, oxygen combines to form oxides. When oxides reach the atmosphere, they combine with rain and form sulphuric acid, which in turn falls to the ground as acid precipitation.