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How Do Glucose Molecules Enter A Cell?

Diffusion And Transport

Diffusion And Transport

Chapter 1 This chapter deals with the processes by which substances move in solutions, particularly how they move through cell membranes. There are three basic processes for such movement: As we shall see, some of these are passive processes, requiring no external energy. Others are active processes--they oppose some passive process, requiring external energy. Some substances move by only one of these process, whereas others can use several of them. Let's examine the behavior of ions in solution in some detail. If we place some salt, NaCl, into one of two compartments separated by a removable partition, as shown in Figure 1-1, and add equal volumes of water to both compartments, we can determine how solutes move in solutions. Within a few minutes after removal of the partition, the solutions in both compartments will contain salt, and the solutions will have the same concentrations. The salt must have moved throughout the compartments; this movement is called diffusion. Molecules in solution at temperatures above absolute zero are in random motion, so-called Brownian motion. The direction of motion of any one molecule can be changed by collision with another molecule or the side of the vessel, but once in motion the molecule will travel in a straight line until a collision occurs. The higher the temperature, the greater is the velocity of movement; the higher the concentration of the solution, the greater is the likelihood of a collision. Some collisions will result in molecules moving toward the interface between the two compartments and crossing it. The probability that a given molecule will cross the interface is therefore proportional to both temperature and the concentration of the solution. Thus, the flux from one compartment to the other, J, is given by: J = kC(1 Continue reading >>

How Does Glucose Get Into The Cells?

How Does Glucose Get Into The Cells?

There are many ways. Glucose is too large to dissolve through the membrane but there are integral proteins (termed GLUT ) that utilize glucose concentrations to move glucose in passively. Glucose in the GI tract can also enter the cell through secondary active transport where sodium gradient inside the cell drives a trans-membrane protein to import glucose with it. Red blood cells contain primarily GLUT 1, allowing them to absorb glucose from the bloodstream to make energy through glycolysis. Muscle and fat cells contain a lot of GLUT 4, a protein that is fond main in vesicles in cell cytoplasm. Insulin allows GLUT 4 vesicles to fuse with the cell membrane to increase the number of GLUT transporters found on the cell membrane, thus increasing glucose uptake into fat and muscle (as well as other ) cells. Glucose molecules are simply diffused across the cell membrane due to its low molecular weight. But the proper question is “How do they stay there inside the cell?” Its blocking from existing the cell is due to a reaction of phosphorylation carried out by an enzyme called hexokinase, which add a phosphate group to the 6th carbon converting it into glucose-6-phosphate which is now negatively charged and let’s be aware of that lipid bi-layer cell membrane have phospholipid also making it negatively charged also. Now the same charges pushes each other away keeping the phosphorylated glucose molecule inside the cell. Continue reading >>

In And Out Of Cells

In And Out Of Cells

All living organisms are made up of cells. Cells may be eukaryotic (in animals and plants) or prokaryotic (bacterial cells). They: absorb or produce food reproduce are sensitive to and respond to changes in their environment control the chemical reactions taking place inside them In this way they have the properties that characterise life. All eukaryotic cells have a cell surface membrane (also known as a plasma membrane). It is very fragile and its role is to hold the cell together and to help control what substances can get in and out. It is partially permeable, allowing only some substances to pass through it. The membrane has a complex structure consisting of a phospholipid bi-layer and different types of proteins. Phospholipids These layers are constantly moving, creating small pores which allow small particles to pass through by diffusion and osmosis. Some of the lipids in the cell surface membrane are triglycerides. These are molecules formed from glycerol by reaction with fatty acids, phosphoric acid or simple sugars. Each glycerol molecule has three hydroxyl groups. However, the majority of lipids in the membrane are phospholipids. In these, two hydroxyl groups of a glycerol molecule form esters with fatty acids. The third hydroxyl group forms a phosphate. A phospholipid molecule has one part that is attracted to water (it's said to be hydrophilic) and one part that repels water (it's said to be hydrophobic). In the bi-layer, the hydrophilic parts are on the outside, attracted by the water in the cell and water in the fluid surrounding the cell. The hydrophobic parts are in the middle of the membrane. Proteins There are many different types of proteins associated with the phospholipid bi-layer. Some lie in just one of the phospholipids layers (extrinsic protein Continue reading >>

Selective Permeability Definition

Selective Permeability Definition

Selective permeability is a property of cellular membranes that only allows certain molecules to enter or exit the cell. This is important for the cell to maintain its internal order irrespective of the changes to the environment. For example, water, ions, glucose and carbon dioxide may need to be imported or exported from the cell depending on its metabolic activity. Similarly, signaling molecules may need to enter the cell and proteins may need to be released into the extracellular matrix. The presence of a selectively permeable membrane allows the cell to exercise control over the quantum, timing and rate of movement of these molecules. Movement across a selectively permeable membrane can occur actively or passively. For example, water molecules can move passively through small pores on the membrane. Similarly, carbon dioxide released as a byproduct of respiration quickly diffuses out of the cell. Some molecules are actively transported. For example, cells in the kidney expend energy to reabsorb all the glucose, amino acids and vitamins from the glomerular filtrate even against the concentration gradient. Failure of this process leads to the presence of glucose or the byproducts of protein metabolism in urine; a tell tale sign of diabetes. Structure of Selectively Permeable Membranes Cell membranes are not easily visualized using light microscopes. Therefore, hypotheses about their existence only arose in the late 19th century, nearly two hundred years after the first cells has been observed. At various points, different models have attempted to explain how the structure of the membrane supports its function. Initially, the membrane was supposed to be a simple lipid layer demarcating the cytosol from the extracellular region. Afterwards, models included semipermeable Continue reading >>

Transport Across Cell Membranes

Transport Across Cell Membranes

Facilitated Diffusion of Ions Ligand-gated ion channels. External Ligands Internal Ligands Mechanically-gated ion channels Voltage-gated ion channels The Patch Clamp Technique Facilitated Diffusion of Molecules Active Transport Direct Active Transport The Na+/K+ ATPase The H+/K+ ATPase The Ca2+ ATPase of skeletal muscle ABC Transporters Indirect Active Transport Symport Pumps Antiport Pumps Some inherited ion-channel diseases Osmosis Hypotonic Solutions Isotonic Solutions Hypertonic Solutions All cells acquire the molecules and ions they need from their surrounding extracellular fluid (ECF). There is an unceasing traffic of molecules and ions in and out of the cell through its plasma membrane Examples: glucose, Na+, Ca2+ In eukaryotic cells, there is also transport in and out of membrane-bounded intracellular compartments such as the nucleus, endoplasmic reticulum, and mitochondria. Examples: proteins, mRNA, Ca2+, ATP 1. Relative concentrations Molecules and ions move spontaneously down their concentration gradient (i.e., from a region of higher to a region of lower concentration) by diffusion. Molecules and ions can be moved against their concentration gradient, but this process, called active transport, requires the expenditure of energy (usually from ATP). 2. Lipid bilayers are impermeable to most essential molecules and ions. The lipid bilayer is permeable to water molecules and a few other small, uncharged, molecules like oxygen (O) and carbon dioxide (CO). These diffuse freely in and out of the cell. The diffusion of water through the plasma membrane is of such importance to the cell that it is given a special name: osmosis. Lipid bilayers are not permeable to: ions such as K+, Na+, Ca2+ (called cations because when subjected to an electric field they migrate towa Continue reading >>

Facilitated Diffusion And Active Transport Of Glucose

Facilitated Diffusion And Active Transport Of Glucose

Concept 4 Review Whether a cell uses facilitated diffusion or active transport depends on the specific needs of the cell. For example, the sugar glucose is transported by active transport from the gut into intestinal epithelial cells, but by facilitated diffusion across the membrane of red blood cells. Why? Consider how different these two environments are. Epithelial cells lining the gut need to bring glucose made available from digestion into the body and must prevent the reverse flow of glucose from body to gut. We need a mechanism to ensure that glucose always flows into intestinal cells and gets transported into the bloodstream, no matter what the gut concentration of glucose. Imagine what would happen if this were not so, and intestinal cells used facilitated diffusion carriers for glucose. Immediately after you ate a candy bar or other food rich in sugar, the concentration of glucose in the gut would be high, and glucose would flow "downhill" from the gut into your body. But an hour later, when your intestines were empty and glucose concentrations in the intestines were lower than in your blood and tissues, facilitated diffusion carriers would allow the glucose in blood and tissues to flow "downhill," back into the gut. This would quickly deplete your short-term energy reserves. Because this situation would be biologically wasteful and probably lethal, it is worth the additional energy cost of active transport to make sure that glucose transport is a one-way process. By contrast, erythrocytes (red blood cells) and most other tissues in your body move glucose by facilitated diffusion carriers, not by active transport. Facilitated diffusion makes sense in this context because the environment is different for red blood cells and the gut. Whereas the gut experiences Continue reading >>

21. If 8 Glucose Molecules Enter Glycolysis, The Net Products Will Be How Many Pyruvate ...

21. If 8 Glucose Molecules Enter Glycolysis, The Net Products Will Be How Many Pyruvate ...

21.)Glycolysis break glucose down to form two pyruvates.This process occurs in the cytosol of a cell.Glycolysis produces 4 ATPs and 2 NADH, but uses 2 ATPs in the process for a net gain of 2 ATP and 2 NADH. In The First Stage of Glycolysis Glucose (6Carbon) is broken down into 2 PGALs (3Carbon) This requires two ATPs. In The Second Stage of Glycolysis 2 PGALs (3C) are converted to 2 pyruvates This creates 4 ATPs and 2 NADHs Thus, the net ATP production of Glycolysis is 2 ATPs ,2 NADH and 2 pyruvates.So if 8 molecules of glucose enter glycolysis,the pesult has to be multiplied by 8, i.e. 16pyruvates and 16 net ATPs. 17.) In aerobic conditions, the process of glycolysis converts one molecule of glucose into two molecules of pyruvate (pyruvic acid), generating energy in the form of two net molecules of ATP. In humans, aerobic conditions produce pyruvate and anaerobic conditions produce lactate.Starting with glucose, 1 ATP is used to donate a phosphate to glucose to produce glucose 6-phosphate.During energy metabolism, glucose 6-phosphate becomes fructose 6-phosphate. An additional ATP is used to phosphorylate fructose 6-phosphate into fructose 1,6-disphosphate by the help of phosphofructokinase. Fructose 1,6-diphosphate then splits into two phosphorylated molecules with three carbon chains which later degrades into pyruvate. Thus converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+.which has 3 carbon atoms.and its 2 molecules will have 2x3=6 carbons still in case of doubts feel free to ask me. Show all Review by this student She was clear in her explanation and yet she still helped me get the answer. How Chegg Tutors works: 1 2 3 Continue reading >>

How Do Organisms Generate Energy?

How Do Organisms Generate Energy?

Enzymes of Glycolysis Yeast 20, J.A. Barnett, A history of research on yeast 6: the main respiratory pathway, 1015-44 (2003). All cells need energy, which they get through ATP, an inherently unstable molecule that must continually be produced. Though ATP can be produced in different ways, nearly all living cells can harness ATP through glycolysis, the stepwise degradation of glucose, and other sugars, obtained from the breakdown of carbohydrates without the need for molecular oxygen (anaerobic). Glycolysis is an ancient, universal pathway that probably developed before there was sufficient oxygen in the atmosphere to sustain more effective methods of energy extraction. When aerobic organisms evolved, they simply added more efficient energy extraction pathways onto glycolysis, breaking down the end products from glycolysis (pyruvate) still further through the tricarboxylic acid cycle. Yet, aerobic cells can still rely predominantly on glycolysis when oxygen is limiting, such as in hard working muscle cells where glycolysis ends in the production of lactate, causing muscle fatigue. The aerobic and anaerobic processes are kept separate in eukaryotic cells, with glycolysis occurring in the cytoplasm, and the aerobic tricarboxylic acid cycle occurring in the mitochondria. Glycolysis During glycolysis, glucose is broken down in ten steps to two molecules of pyruvate, which then enters the mitochondria where it is oxidised through the tricarboxylic acid cycle to carbon dioxide and water. Glycolysis can be split into two phases, both of which occur in the cytosol. Phase I involves splitting glucose into two molecules of glyceraldehyde-3-phosphate (G3P) at the expense of 2 ATP molecules, but allows the subsequent energy-producing reactions to be doubled up with a higher net gain Continue reading >>

How Do Substances Move Across A Selectively Permeable Membrane?

How Do Substances Move Across A Selectively Permeable Membrane?

BIOL 1406 PreLab 5.2 A selectively permeable membrane is a membrane that allows some substances to pass through easily, while other substances pass through very slowly or not at all. All cell membranes, including the plasma membrane, are selectively permeable. In the exercise below, you will learn about 2 types of diffusion across selectively permeable membranes: Simple diffusion refers to diffusion of substances without the help of transport proteins. Facilitated diffusion refers to diffusion of substances with the help of transport proteins. Use the interactive exercise below to learn more about simple diffusion and facilitated diffusion. Your Turn Assume there is a higher concentration of each of the following substances in the extracellular fluid surrounding a cell than in the cell’s cytoplasm. Predict whether the substance would be more likely to enter the cell by simple diffusion or by facilitated diffusion, and explain why. Is O2 more likely to enter the cell by simple diffusion or facilitated diffusion: Explain why: Hint Check your answer. Is glucose more likely to enter the cell by simple diffusion or facilitated diffusion: Explain why: Hint Check your answer. Is Na+ more likely to enter the cell by simple diffusion or facilitated diffusion: Explain why: Hint Check your answer. Is insulin (a protein) more likely to enter the cell by simple diffusion or facilitated diffusion: Explain why: Hint Check your answer. Is estrogen (a lipid) more likely to enter the cell by simple diffusion or facilitated diffusion: Explain why: Hint Check your answer. Are hydrogen ions more likely to enter the cell by simple diffusion or facilitated diffusion: Explain why: Hint Check your answer. Dialysis tubing is composed of a selectively permeable membrane. However, its selectivit Continue reading >>

Metabolism Of Molecules Other Than Glucose

Metabolism Of Molecules Other Than Glucose

You have learned about the catabolism of glucose, which provides energy to living cells. But living things consume more than just glucose for food. How does a turkey sandwich, which contains various carbohydrates, lipids, and protein, provide energy to your cells? Basically, all of these molecules from food are converted into molecules that can enter the cellular respiration pathway somewhere. Some molecules enter at glycolysis, while others enter at the citric acid cycle. This means that all of the catabolic pathways for carbohydrates, proteins, and lipids eventually connect into glycolysis and the citric acid cycle pathways. Metabolic pathways should be thought of as porous—that is, substances enter from other pathways, and other substances leave for other pathways. These pathways are not closed systems. Many of the products in a particular pathway are reactants in other pathways. Carbohydrates So far, we have discussed the carbohydrate from which organisms derive the majority of their energy: glucose. Many carbohydrate molecules can be broken down into glucose or otherwise processed into glucose by the body. Glycogen, a polymer of glucose, is a short-term energy storage molecule in animals (Figure 1). When there is plenty of ATP present, the extra glucose is converted into glycogen for storage. Glycogen is made and stored in the liver and muscle. Glycogen will be taken out of storage if blood sugar levels drop. The presence of glycogen in muscle cells as a source of glucose allows ATP to be produced for a longer time during exercise. Figure 1 Glycogen is made of many molecules of glucose attached together into branching chains. Each of the balls in the bottom diagram represents one molecule of glucose. (Credit: Glycogen by BorisTM. This work has been released into Continue reading >>

(fig. 11-3.1, Lodish)

(fig. 11-3.1, Lodish)

1. Transport may involve ions, which are of central importance in the functioning of cells. Of particular imporance is the fact that concentrations of Na+ and Cl- are high outside the cell (as they are in sea water!!!!) and concentrations of K+ and trapped organic anions are high within cells.. Component Intracellular Concentration (mM) Extracellular Concentration (mM) Na+ 5-15 145 K+ 140 5-15 Cl- 5-15 110 Organic ions high 0 2. Carrier proteins are important for transport of many types of substances across both external and internal cell membranes. Simple, "Fick's Law", diffusion, down a concentration gradient from high to low concentration, is only found for small hydrophobic molecules, such as steroid hormones, and gases. These substances move across membranes without the aid of a protein channel. Transport across membranes is mostly through protein channels. Diffusion shows net movement from high concentration to low concentration. Net movement up the concentration gradient, from low to high concentrations, must have energy supplied from somewhere. (fig. 11-3.2, Lodish) (fig. 11-3.3, Lodish) Glucose is moved into cells by facilitated diffusion through a uniport transporter protein that shows enzyme-like kinetics. There is a maximum rate of transport (flux), even if the concentration difference between the two sides of the membrane is very high. (fig. 11-4, Lodish) Most mammalian cells use the GLUT1 uniport transporter protein to moved glucose across cell membranes. All GLUT proteins likely have 12 alpha-helical, membrane-spanning, segments. In animal cells, such as those lining our intestine, glucose and other solutes may be moved into cells by symport cotransport with an ion, usually Na+. Here is a cartoon of the facilitated diffusion cotransport system. Glucose mo Continue reading >>

How Does Glucose Move Into A Cell?

How Does Glucose Move Into A Cell?

Eat a bowl of cereal or a piece of fruit and your body will convert the carbohydrates in your meal to glucose--the form of sugar cells in the body rely on for quick energy. Glucose circulates through the blood stream, powering your muscles, organs, and brain. But how exactly does your body use glucose? Video of the Day Your body relies on molecules called glucose transporters (GLUT is the scientific term) to deliver the sugar to cells. GLUT molecules tend to specialize: GLUT2, for example, delivers glucose to the digestive tract, liver, and pancreas; GLUT3 keeps the central nervous system and the brain running; GLUT4 serves the heart, muscles and fat cells. And GLUT1? It's a general transporter that can fill in where needed. When cells require energy, the GLUT molecule on the cell's surface will bind with blood glucose and usher it into the cell. After reaching the inside of the cell, the cells machinery converts the sugar into energy. You've probably heard about the hormone insulin in connection with blood sugar before: After all, many people with diabetes rely on insulin shots to help control their blood sugar. Insulin primarily assists GLUT4--the transporter that serves muscle and fat cells. Insulin can boost the number of transponders on fat cells especially, and it can increase the rate at which fat cells' transponders bind with sugar. When you have high levels of glucose in the blood, insulin can urge fat cells to absorb the excess sugar and store it as fat. The Hazard of too Much Sugar People who overeat carbohydrate-rich foods like breads, pasta, and cereal or regularly down colas and other sweet drinks, can overtax the body's ability to process glucose. The pancreas--which produces insulin--can fail to secrete enough of the hormone to meet the body's needs. Ins Continue reading >>

Active And Passive Transport

Active And Passive Transport

Active and passive transport are biological processes that move oxygen, water and nutrients into cells and remove waste products. Active transport requires chemical energy because it is the movement of biochemicals from areas of lower concentration to areas of higher concentration. On the other hand, passive trasport moves biochemicals from areas of high concentration to areas of low concentration; so it does not require energy. Comparison chart Active Transport versus Passive Transport comparison chart Active Transport Passive Transport Definition Active Transport uses ATP to pump molecules AGAINST/UP the concentration gradient. Transport occurs from a low concentration of solute to high concentration of solute. Requires cellular energy. Movement of molecules DOWN the concentration gradient. It goes from high to low concentration, in order to maintain equilibrium in the cells. Does not require cellular energy. Types of Transport Endocytosis, cell membrane/sodium-potassium pump & exocytosis Diffusion, facilitated diffusion, and osmosis. Functions Transports molecules through the cell membrane against the concentration gradient so more of the substance is inside the cell (i.e. a nutrient) or outside the cell (i.e. a waste) than normal. Disrupts equilibrium established by diffusion. Maintains dynamic equilibrium of water, gases, nutrients, wastes, etc. between cells and extracellular fluid; allows for small nutrients and gases to enter/exit. No NET diffusion/osmosis after equilibrium is established. Types of Particles Transported proteins, ions, large cells, complex sugars. Anything soluble (meaning able to dissolve) in lipids, small monosaccharides, water, oxygen, carbon dioxide, sex hormones, etc. Examples phagocytosis, pinocytosis, sodium/potassium pump, secretion of a Continue reading >>

Facilitated Diffusion

Facilitated Diffusion

The cell membrane, also called the plasma membrane, of eukaryotic cells is composed of a phospholipid bilayer. These phospholipids are composed of a polar head, made up of a phosphate group, and two non-polar fatty acid tails. This amphipathic nature of phospholipids creates a semi-permeable membrane, fluid enough to allow for the growth and movement of the cell, but solid enough to hold the shape of the cell. The phospholipids of the membrane are arranged tail to tail, creating a protective, hydrophobic region in-between the bilayer. This hydrophobic area prevents many types of molecules from entering the cell; including large, polar or charged molecules. This is an important feature for the regulation of substances and concentrations within and without of the cell; however, it poses a problem because most vital molecules are unable to pass through the membrane via simple diffusion. Water, for example, is vital to a cells survival. Water is also a polar molecule. How, then, does the cell allow water and similar molecules to pass in and out? By using a process termed facilitated diffusion. There are many ways for a cell to transport molecules across its membrane. Diffusion is an example of passive transport. Passive means that no energy is required. Facilitated diffusion is a specific type of passive transport specific to large molecules, such as glucose, polar molecules, such as water, or ions, such as Na+. Facilitated diffusion is performed by various types of proteins that are embedded within the cell membrane. While there are hundreds of different proteins throughout the cell, only two types are found associated with facilitated diffusion: channel proteins and carrier proteins. Channel proteins typically are used to transport ions in and out of the cell. Channel pro Continue reading >>

Movement Of Substances Across Cell Membranes

Movement Of Substances Across Cell Membranes

Diffusion Diffusion is the spontaneous movement of a substance down its concentration gradient from higher to lower concentration. If you have a bottle of perfume and take the cap off. The perfume molecules will waft out and diffuse into the air where there is a lower concentration of them. All atoms and molecules are in motion, the only way you could stop all motion is to cool things down to absolute zero (-273.15 C or 0K). On the bottom of b25 , look at the diffusion thing and read it. Factors that affect the RATE of diffusion 1. Difference in concentration between the inside and outside of the cell. The bigger the difference between concentrations, the diffusion will be faster. 2. The size of the chemical substance. O2 is two atoms. Glucose is 24 atoms big. Protein is massive. Oxygen can easily diffuse across a cell membrane. Sugar can kind of, that’s why it’s assisted by a transporter protein to facilitate it. The proteins don’t move at all. 3. Temperature. Higher temps = molecules move faster. ‘Nuff said. 4. Whether the chemical substance is water-soluble or lipid soluble. The lipid soluble goes through faster because the cell membrane is phospholipids and can easily diffuse through a fatty membrane. The effect of osmosis on cells Osmosis is simply the diffusion of water. Anytime water flows in or out, it’s called osmosis. The water flows to wherever there is more solute. 1. The cytoplasm of a cell is 80% water, but not completely. Anything that’s not water are called solutes, such as electrolytes. If we surround the cell with a fluid that’s similarly 80% water and 20% “other stuff” on the outside of the cell. The “other stuff” don’t even have to be the same things as the inside of the cell. With osmosis we only care about the concentration Continue reading >>

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