Chapter 5 Study Guide

Describe the structure of an enzyme‐substrate interaction.

Substrate molecules bind to enzymes at specific active sites thus activating the enzyme. The enzyme then reduces the activation energy required for a bond to form between the substrate molecules, so bonding (the reaction) proceeds at a faster rate.

Explain how the properties of phospholipids spontaneously form membranes.

When mixed with water, phospolipids spontaneously form membranes because the tails are hydrophobic (don't like water) and the heads are hydrophillic (like water because slightly polar). This causes the tails to move inside the layer and the heads to be on the outside.

Distinguish between hypertonic, hypotonic, and isotonic solutions.

hypotonic: a solution which contains more solute than solvent (example: a lot of salt(solute) dissolved in water(solvent)) hypertonic: a solution which contains more solvent than solute (example: purified water--there's almost no solute dissolved in the solvent(water)) isotonic: a solution in which the solute and solvent are equally distributed--a cell normally wants to remain in an isotonic solution, where the concentration of the liquid inside of it equals the concentration of the liquid outside of it

Explain how osmosis can be defined as the diffusion of water across a membrane.

Osmosis is the result of diffusion across a semi-permeable membrane. If two solutions of different concentration are separated by a semi-permeable membrane, then the solvent will tend to diffuse across the membrane from the less concentrated to the more concentrated solution. This process is called osmosis.

Activation Energy

the minimum quantity of energy that the reacting species must possess in order to undergo a specified reaction.

explain how enzymes speed up chemical reactions.

A+ By acting as organic catalysts .

Distinguish between exocytosis, endocytosis, phagocytosis, and receptor‐mediated endocytosis.

Endocytosis occurs when a substance is brought into the cell. Phagocytosis is a type of endocytosis, and is called cell eating. Pinocytosis is cell drinking, another type of endocytosis.

Explain how animal and plant cells change when placed into hypertonic or hypotonic solutions.

Hypotonic: means the water is more concentrated on the outside compared to the inside. ie, there are more solutes found on the inside. Water moves from an area of high concentration to an area of low concentration. This can be thought of a attempt to balance out the concentrations. If this occurs over a semipermeable membrane, this is called osmosis. Animal cell: The water moves into the cell, if the concentration gradient is high (ie, there is a large difference in the concentrations of water) water will continue to move into the cell until the cellular membrane can no longer stay together and the cell bursts. Plant cell: The water moves into the cell as before, however, due to the presence of the cell wall the cell does not burst. This results in a turgid cell, and the turgidity of the plant itself (as plants do not have a skeletal system). This can be seen as if you remove a water source from a plant it wilts, as the cells are no longer turgid and cannot keep a rigid shape.

Define and compare kinetic energy, potential energy, chemical energy, and heat.

Potential Energy is any type of stored energy; it isn't shown through movement. Potential energy can be chemical, nuclear, gravitational, or mechanical. Kinetic Energy is the energy of movements: the motion of objects (from people to planets), the vibrations of atoms by sound waves or in thermal energy (heat), the electromagnetic energy of the movements of light waves, and the motion of electrons in electricity. Chemical energy is stored in the bonds between atoms. (See here for more about atoms.) This stored energy is released and absorbed when bonds are broken and new bonds are formed — chemical reactions. Chemical reactions change the way atoms are arranged. Like letters of the alphabet that can be rearranged to form new words with very different meanings, atoms go through chemical reactions to be reorganized to form new compounds with vastly different properties. Each compound has its own chemical energy associated with the bonds between the atoms it contains. Heat and thermal energy are directly related to temperature. We can't see individual atoms vibrating, but we can feel their kinetic energies as temperature, which is a reflection of the energy with which atoms vibrate. When there's a difference between the temperature of the environment and a system within it, thermal energy is transferred between them as heat.

Describe the process of feedback inhibition.

The term feedback inhibition refers to a situation in which the substances at the end of a long series of reactions inhibits a reaction at the beginning of the series of reactions. It is the process by which the accumulated end product of a biochemical pathway stops synthesis of that product.

Describe the three main types of cellular work driven by ATP.

The three major types of cellular work is Chemical Work, Mechanical Work, and Transport Work.

Relate the structure of phospholipid molecules to the structure and properties of cell membranes.

By the definition of phospholipid, there is a phosphate (PO43-) functional group attached the opposite side as the two fatty acids. This side turns outward on the membrane forming a phospholipid bilayer. This lipid bilayer keeps ions, proteins, and other various molecules (esp. water, phosphate is hydrophilic whereas the fatty acids are hydrophobic) where they are needed.

Explain how the cellular environment affects enzyme activity.

Cellular environment affects enzyme activity because at extremes of pH or temperature, either high or low, the native structure of the enzyme will be compromised, and the molecule will become inactive.

Define diffusion and describe the process of passive transport.

Diffusion is the tendency of molecules to spread into an available space. Passive transport is a movement of biochemicals and other atomic or molecular substances across cell membranes.

Explain how competitive and noncompetitive inhibitors alter an enzyme's activity.

The inhibitor has a similar shape to the usual substrate for the enzyme, and competes with it for the active site. However, once it is attached to the active site, nothing happens to it. It doesn't react - essentially, it just gets in the way. Basically they are competing against the enzyme substrate molecules for the active site, if the competitive enzyme combines with active site of the enzyme, this means that there is a limited number of active site of the enzyme available for the enzyme substrate molecules. this subsequently decreases the enzyme activity. A non-competitive inhibitor does not attach itself to the active site, but attaches on the allosteric site of the enzyme. By attaching there it changes the shape of the active site, so that i is not complementary to the enzyme substrate.Because there isn't any competition involved between the inhibitor and the substrate, increasing the substrate concentration won't help. so the difference would be the following:- the competitive inhibitor competes against the enzyme substrate for the active site whereas the non-competitive inhibitor does the competitive inhibitor attaches to the active site whereas the non-competitive inhibitor binds to the alloseric site.

Describe the structure and diverse functions of cell membranes.

2 Plasma Membrane Structure and Function 1. The plasma membrane is a phospholipid bilayer with embedded proteins. 2. Phospholipids have both hydrophilic and hydrophobic regions; nonpolar tails (hydrophobic) are directed inward, polar heads (hydrophilic) are directed outward to face both extracellular and intracellular fluid. 3. The proteins form a mosaic pattern on the membrane. 4. Cholesterol is a lipid found in animal plasma membranes; it stiffens and strengthens the membrane. 5. Glycolipids have a structure similar to phospholipids except the hydrophilic head is a variety of sugar; they are protective and assist in various functions. 6. Glycoproteins have an attached carbohydrate chain of sugar that projects externally. 7. The plasma membrane is asymmetrical; glycolipids and proteins occur only on outside and cytoskeletal filaments attach to proteins only on the inside surface. A. Carbohydrate Chains 1. In animal cells, the glycocalyx is a "sugar coat" of carbohydrate chains; it has several functions. 2. Cells are unique in that they have highly varied carbohydrate chains (a "fingerprint"). 3. The immune system recognizes foreign tissues that have inappropriate carbohydrate chains. 4. Carbohydrate chains are the basis for A, B, and O blood groups in humans. B. Fluidity of the Plasma Membrane 1. At body temperature, the phospholipid bilayer has the consistency of olive oil. 2. The greater the concentration of unsaturated fatty acid residues, the more fluid the bilayer. 3. In each monolayer, the hydrocarbon tails wiggle, and entire phospholipid molecules can move sideways. 4. Phospholipid molecules rarely "flip flop" from one layer to the other. 5. Fluidity of the phospholipid bilayer allows cells to be pliable. 6. Some proteins are held in place by cytoskeletal filaments; most drift in the fluid bilayer. C. The Functions of the Proteins 1. Plasma membrane and organelle membranes have unique proteins; red blood cells (RBC) plasma membrane contains 50+ types of proteins. 2. Membrane proteins determine most of the membrane's functions. 3. Channel proteins allow a particular molecule to cross membrane freely (e.g., Cl− channels). 4. Carrier proteins selectively interact with a specific molecule so it can cross the plasma membrane (e.g., Na+ K+ pump). 5. Cell recognition proteins are glycoproteins that allow the body's immune system to distinguish between foreign invaders and body cells. 6. Receptor proteins are shaped so a specific molecule (e.g., hormone) can bind to it. 7. Enzymatic proteins carry out specific metabolic reactions.

Explain how ATP functions as an energy shuttle.

ATP, or Adenosine triphosphate, has (as the name implies) three phosphate groups bound to one adenosine nucleotide (RNA version). Each of these phosphate groups carries an overall negative charge, making the triple phosphate tail similar to a coiled up spring, containing lots of energy. When an exergonic pathway, such as cellular respiration, releases energy, it often results in the creation of ATP. The ATP can now give up some of that energy to help endergonic reactions, such as active transport across the membrane, through a process known as "phosphorylation." This is when the ATP gives one of it's phosphates or "phosphorylates" along with energy, to another molecule, allowing a reaction to reach the energy of activation. The ATP is now ADP, adenosine diphosphate.

Compare the processes of active transport and facilitated diffusion.

The transport process a cell uses depends on its specific needs. For example, red blood cells rely on facilitated diffusion to move glucose across membranes, whereas intestinal epithelial cells use active transport to take in glucose from the gut. Facilitated diffusion is effective for red blood cells because the concentration of glucose in the blood is stable and higher than the cellular concentration. On the other hand, active transport is needed in the gut because there are large fluctuations of glucose concentration as a result of eating.

Explain how transport proteins facilitate diffusion.

many polar molecules and ions impeded by the lipid bilayer of the membrane diffuse passively with teh help of transport proteins that span the mebrance, that is calld facillitated diffusion. there are channel proteins and carrier proteins channel proteins: provide corridors that allow a specific molecule or ion cross the membrane, they hydrophillic passageways provided by these proteins allow water molecules or small ions to flow very quickly form one side of the membrane to the other a kind of channel proteins are aquaporins that facilitate the massive amounts of diffusion that occur in plant cells and in animal cells such as red blood cells other channels are ion channels and gated channels carrier proteins: undergo a subtle change in shpae that translocates the solute-binding site across the membrane