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CHAPTER 5
THE WORKING CELL
Why Cellular Functions Matter
« Both nerve gas and insecticides work by crippling a vital enzyme. « For thousands of years, people have used osmosis to preserve food through salt and sugar curing. « You'd have to walk more than two hours to burn the calories in half of a pepperoni pizza.
Nanotechnology Biology and society
Harnessing Cellular Structures
Nano – A meter to 1 billion parts Cellular structures even the smallest cell, such as one from the human pancreas, Is a miniature machine of startling complexity. Imagine a tiny movable car bowls of carbon atoms for wheels, arrest 3-dimensional relief map of the world carved into an object 1000 times more than a grain of sand. These are real world examples of nanotechnology manipulation of materials at molecular scale. Researchers at Cornell University are attempting to harvest the energy producing capabilities of human sperm cells. Sperm cell generates energy by breaking down sugars and other molecules that has to its packed plasma membrane. Enzymes within the cell carry out a
process called glycolysis. During glycolysis, the energy released from the breakdown of glucose is used to produce molecules of ATP
within the living sperm. The ATP produced during glycolysis and other processes provides the energy that propels the sperm for the female reproductive tract. In attempt to harness this energy producing sperm the Cornell researchers attached three glycolysis enzymes to a computer chip. The end signs continued to function in this artificial system, producing energy from sugar. Hope is that a larger set of enzymes can eventually be used to power microscopic robots. Nano robots could use glucose from the bloodstream to power the delivery of drugs to body tissues, among many other possible tasks.
Three processes common to all living cells
« The use of enzymes to speed chemical reactions « transport regulation by the plasma membrane. « Energy metabolism
Cells need following to function
« Energy « Plasma membrane « Enzymes
Some Basic Energy Concepts
Conservation of energy
What is energy?
Energy is the capacity to cause change. Chemical energy from food is converted into kinetic energy. « Kinetic energy is the energy of motion
« Potential energy is stored energy. An object has potential energy because of its location or structure. « The principal of conservation of energy states that energy can't be created or destroyed. « Energy can only be converted from one form to another Machines and organisms can transform kinetic energy of motion to potential energy stored energy and vice versa. And all such energy transformations, total energy is conserved. Energy cannot be created or destroyed. A power plant does not make energy; it merely converts it from one form (such as energy stored as coal) to a more conventional form (such as electricity). Machines and organisms can transform potential energy and vice versa.
Heat
Every energy conversion releases some randomized energy in the form of heat. Entropy is a measure of disorder
or randomness
The kinetic energy is converted to heat when the diver hits the water. Heat - a type of kinetic energy contained in the random motion of Adams in molecules. The friction between the body and its surroundings generate heat in the air and then in the water. All energy conversions generate heat. Releasing heat does not destroy energy. He is energy and it's most disordered, chaotic form, the energy of aimless molecular movement. Entropy as a measure of the amount of disorder, or randomness in system. Every time Energy is converted from one form to another, entropy increases. The energy when the diver is climbing up the ladder and back down increases entropy. The diver emits heat to the surroundings. Each climb to the top of the platform uses additional stored food energy. This conversion also creates heat and therefore increases entropy. In each energy transformation total energy is conserved, however usable energy is not conserved, some energy is lost as heat.
Chemical Energy
Molecule share varying amounts of potential energy in the arrangement of their atoms. Organic compounds are
relatively rich in such chemical energy.
Molecules of food, gasoline and other fuels have a form of potential energy called chemical energy, w hich arises from the arrangement Adams and can be released by chemical reaction. Carbohydrates, facts and gasoline have structures that make them rich in chemical energy. Living cells and auto engines use the same basic process to make the chemical energy stored in their fuels available for work. Both cases
- process breaks down organic fuel into smaller waste molecules that have much less chemical energy than the fuel molecules thereby releasing energy that can perform work. And both a car and a cell chemical energy of organic fuel molecules is harvested using oxygen. This chemical breakdown releases energy stored in the fuel molecules and produces carbon dioxide and water. The released energy can be used to perform only about 25% of the energy sitting automobile Engine extracts from its fuel is converted to kinetic energy of the cars movement. Most of the rest is converted to heat, so much so that without the radiator dispersing the heat into the atmosphere the engine would melt. Cells use oxygen and reactions that release energy from fuel molecules. As in car engine, the "exhaust" from such a reaction and cells is mostly carbon dioxide and water. The combustion is called cellular respiration. Which is a more gradual and efficient "burning" of the fuel compared with explosive combustion in an automobile engine.
Phosphate Transfer
When ATP drives work in cells by being converted to ADP the released phosphate group doesn’t just fly off into space. ATP energizes other molecules and cells by transferring phosphate groups to those molecules. Want to target molecule excepts the third phosphate group, it becomes energized and can perform the work in the cell.
The ATP Cycle
Your cells spend ATP continuous. Fortunately, it is a renewable resource. ATP can be restored by adding a phosphate group back to the ADP. That takes energy, wake re-compressing a spring. And that’s where food enters the picture the chemical energy that cellular respiration harvest from sugars and other organic fuels is put to work regenerating himself supply ATP. Cellular network spends ATP, which is recycled went ADP and phosphate are combined using energy released by cellular respiration. Enzymes A living organism contains a vast collection of chemicals, and countless chemical reactions constantly changing organism’s molecular
makeup. The total of all chemical reactions in an organism is called metabolism. Metabolic reactions usually require the assistance of
enzymes, proteins that speed up chemical reactions without being consumed by those reactions. Activation energy For a chemical reaction to begin call Chemical bonds in the reactant molecules must be broken. For chemical reactions, sell has to spend a little energy to make more. The energy that must be invested to start a reaction is called activation energy because it activates the reactants and triggers the chemical reaction. Enzyme enable metabolism To occur. If you think of activation energy as a barrier to a chemical reaction, it enzymes function is to lower that barrier. It does so by reducing the amount of the activation energy required to break the bonds of reactant molecules. This can be described as a friend offering to help you clean your room, you start and end same place whether solo or assistant, but your friends help bluish or activation energy making it more likely you’ll proceed.
Nanotechnology THE PROCESS OF SCIENCE
Can Enzymes Being Engineered?
Like all other proteins, enzymes are encoded by genes. Observations of genetic sequences suggest that many of our genes were formed through a type of molecular evolution: Our ancestral gene duplicated, and the two copies diverged over time, via random genetic changes, eventually becoming distinct genes for enzymes with different functions.
ATP
Motor protein preforming mechanical work Moving a muscle fiber
Question: can laboratory message minutes this process through artificial selection? Hypothesis: formed by a group of researchers at two California research biotechnology companies. An artificial process couldn’t be used to modify the gene that codes for the enzyme lactase ( which breaks down sugar lactose) into a new gene coding for a new enzyme with a new function. Experiment: they used a procedure called directed evolution. In this process, many copies of the gene for the starting lactose enzyme were mutated at random. Researchers tested the enzymes resulting from the mutated jeans determine which enzyme best displayed new activity. Results: indicated that directed evolution had produced a new enzyme with a novel function. These results show that directed evolution is another example of how scientist can mimic the natural processes of cells for their own purposes. Directed evolution of an enzyme: during seven rounds of directed evolution, the lactase enzyme gradually gained a new function.
Structure/Function Enzyme activity
Enzyme is very selective in the reaction it capitalizes. Based on enzymes ability to recognize certain reactant molecule, which is called
the enzyme substrate
The region of the enzyme called the active site has a shape and chemistry that fits the substrate molecule. Usually a pocket or groove
surface of the enzyme. Substrate slips into docking station, site shape changes lately to embrace the substrate and catalyzed the reaction.
This interaction is called induced fit because the entry of this substrate induces the enzyme to change shape slightly, making the fit
snugger. Similar to handshake. As your hand makes contact with another hand it changes shape slightly to make a better fit. Products aren’t send released from the active site, the enzyme can except another molecule of substrate. Functioning repeatedly is Keith.
Enzyme Inhibitors
Certain molecules can inhibit a metabolic reaction but bonding two an enzyme and disrupting its function. Some of these enzyme inhibitors our substrate impostors that Plug up the active site. (you can not shake a person’s hand if someone puts a banana in it first). Other inhibitors bind enzyme at a remote site but the binding changes the enzymes shape (imagine trying to shake hands when someone is tickling your ribs, causing you to clinch your hand) any header disrupts the enzyme by altering its shape. A clear example of the link between structure and function « Both nerve gas and insecticides work for crippling vital enzyme « Sometimes the binding of an inhibitor is reversible. Example: Cell is producing more of a certain product than it needs, that product may reversibly inhibit an enzyme required for its production. Feedback regulation keeps the cell from wasting resources. « Penicillin blocks the active site of an& the bacteria use in making cell walls. « Ibuprofen inhibits an enzyme involved in sending pain signals « Many cancer drugs inhibit enzymes that promotes cell division « Many toxins in poisons also work as inhibitors. Nerve gases (a form of chemical warfare) irreversibly bind to the active site of an enzyme vital to transmitting nerve impulses, leading to rapid paralysis and death. « Many pesticides are toxic to insects because they inhibit the same enzyme
Osmosis and Water Balance
The diffusion of water across a selectively permeable membrane it’s called osmosis. A solute is a substance that is dissolved any
liquid solvent , and resulting mixture is called a solution.
Imagine a solution of salt water (salt is the is the solute, water is the solvent, salt water is the solution) with a membrane separating the two solutions with different concentrations of the solute. The solution with the higher concentration of salute it Is said to be:
Hypertonic: solution with the higher concentration of solute.
Hypotonic: solution with the lower levels absolute concentration is aid to be Hypotonic to the other.
Therefore, water will diffuse across the membrane along its concentration gradient from an area of higher water concentration (hypotonic solution) to one of lower water concentration (hypertonic solution) this reduces difference in solute concentrations and changes the volumes of the two solutions. Osmosis is used to preserve food. Salt is often a place to meet to carry them. Salt causes water to move out of food spoiling bacteria and fungi. Food can also be preserved in honey because of high sugar concentration draws water out of food. When the solute concentrations are the same on both sides of the membrane, water molecules will move at the same rate in both directions, so there will be no net change in solute concentrations.
Isotonic: solution of equal solute concentration for example many marine animals, such as sea stars and crabs are isotonic to see
water, so that overall, they neither gain or lose water from the environment. In hospitals, intravenous (IV) fluids administered to patients must be isotonic to blood cells to avoid harm. Water Balance in Animal Cells: The survival of a cell depends on its ability to balance water uptake and loss. For an animal cell to survive a hypertonic or hypotonic environment, animal must have a way to balance The uptake and loss of water. Osmoregulation – the control of water balance. Example: a freshwater fish has kidneys and gills and work constantly to prevent an excess buildup of water in the body. Humans can suffer consequences of osmoregulation failure. Dehydration can cause fatigue and even death. Drinking too much water called hyponatremia or “water intoxication” can also cause death over diluting necessary ions. Water Balance in Plant Cells: Problems of water balance are somewhat different for cells that have rigid cell walls, such as those from plants, fungi many prokaryotes and some protists. A plant cell immersed and isotonic solution is flaccid, in the plant belts. In contrast, plant cell is turgid (very firm) and healthiest in a hypotonic environment, buffet net and flow of water. Turgor it’s necessary for plants to retain their upright posture and the extended state of their leaves. However, in a hypertonic environment, a plant cell it is no better off than an animal cell. As a plant cell loses water, it shrivels, and it’s plasma membrane pulls away from the cell wall. This usually kills the cell. Thus, plant cells thrive in a hypotonic environment, whereas animal cells thrive and an isotonic one.
Active Transport: The Pumping of Molecules Across Membranes
In contrast to passive transport, Active transport requires the cell expend energy to move molecules across a membrane. Cellular energy usually provided by ATP against the concentration gradient–that is, and the direction that is opposite the way it would naturally flow. Movement against a force, Rolling a boulder uphill against gravity, requires a considerable expenditure of energy. Active transport allows the cells to maintain internal concentrations of small solutes that differ from environmental concentration. For example animal nerve cell has a higher concentration of potassium ions and a lower concentration of sodium ions. The plasma membrane helps maintain these differences by pumping sodium out of the cell and potassium into the cell. This particular case of active transport (called the sodium - potassium pump) is final to the nervous system of most animals. Exocytosis and Endocytosis: Traffic of Large Molecules
Large molecules such as proteins are too big to fit through the membrane. There traffic into and out of the cell depends on the ability
of the cell to package large molecules inside sacs called vesicles. Earlier example of this: during protein production by the cell,
Secretory proteins exit the cell from transport vesicles that fuse with the possible membrane, spilling the contents outside the cell. That
process exocytosis. When you cry, for example cells in your tears glands use exocytosis to export the salty tears. In your brain, the
exocytosis of Neurotransmitter chemicals such as dopamine help neuron communicate. In endocytosis, a cell takes material in via vesicles that bud inward. For example, a process called phagocytosis (“cellular eating”) , a cell engulfs a particle and packages it within a food vacuole. In Another example, a cell “gulps” droplets of fluid into vesicles. Endocytosis can also be triggered by the bonding of certain external molecules to specific receptor proteins built into the plasma membrane. This finding causes the local region of the membrane to form a vesicle that transports the specific substance into the cell. In human liver cells, this process is used to take up cholesterol from the blood. Inherited defect in the receptors on liver cells can lead to an inability to process cholesterol, which can lead to a heart attack at age is as young as five. Cells of your immune system used endocytosis to engulf and destroy invading bacteria and viruses. Because all cells have a plasma membrane, it is logical to infer that membranes first formed in the evolution of life on earth.
Nanotechnology EVOLUTION CONNECTION
The Origin of Membranes Scientist has been able to demonstrate that many other molecules important to life conform spontaneously. Phospholipids, the key ingredients in all membranes, were probably among the first organic compounds that formed from chemical reactions on the early earth. Once formed, they could self-assemble into simple membranes. The mixture of phospholipids and water is shaken, for example, the phospholipids organized into bilayers, forming water filled bubbles of membrane. This assembly requires neither genes nor other information by on the properties of the phospholipids themselves. The tendency of lipids and water to spontaneously form membranes has led biomedical engineers to produce liposomes (a type of artificial vesicle) that can in case particular chemicals. In the future these engineered liposomes may be used to deliver nutrients to medications to specific sites within the body. As of 2012 12 drugs has been approved for delivery via liposomes, including one that targets fungal infections, influenza and hepatitis.
