Chapter 5

Dynamic Activities of Cells

Living things transform energy

Energy makes things happen• Energy-the capacity to do work, to make things happen• Forms of energy

– Radiant-solar energy– Chemical-food– Mechanical-motion– Electrical– Nuclear

• Heat– Motion of atoms, ions, or molecules (mechanical)– Low quality energy because it is too dispersed to do useful work

• Potential energy-stored energy• Kinetic energy-energy in action• Ex. Person climbing ladder to diving board and

diving into water.– Chemical-food– Kinetic-climbing ladder– Potential-higher altitude– Kinetic-diving to the water

• Measuring energy– Calorie-amount of heat required to raise the

temperature of 1g of water by 1o

C– Kilocalorie

• 1,000 calories• Calories listed on nutrition labels

Two laws apply to energy and its use

• The first law of thermodynamics– The law of conservation of energy-states that energy

cannot be created or destroyed, but it can be changed from one form to another

• The second law of thermodynamics– States that energy cannot be changed from one form

to another without a loss of usable energy• Energy flows through living things, it does not

cycle• The second law of thermodynamics tells us that

as energy conversion occurs, disorder (entropy) increases because it is difficult to use heat to perform more work

Cellular work is powered by ATP (adenosine triphosphate)

• ATP is a nucleotide-a monomer for DNA and RNA

• Phosphate groups are unstable• ATP can break down into ADP+P• ADP can break down into AMP+P• ATP beakdown and regeneration is the ATP

cycle• Exergonic reaction-releasing energy, performing

work• Endergonic reaction-energy is required,

constructing a building

ATP breakdown is coupled to energy-requiring reactions

• Coupled reactions occur in the same place, at the same time, and is such a way that an energy-releasing (exergonic) reaction drives an energy-requiring (endergonic) reaction

• Energy releasing reaction-hydrolysis of ATP

Enzymes speed chemical reactions

Enzymes speed reactions by lowering activation barriers

• Enzyme-typically a protein molecule that functions as an organic catalyst to speed a chemical reaction without itself being affected by the reaction

• A certain amount of energy (energy of activation) has to be put into a reaction and then the reaction will occur. An enzyme will lower the amount of energy required to start the reaction.

• Each enzyme has a specific reaction it speeds

• Substrate-reactants in an enzymatic reaction• Active site-part of the enzyme where substrate

forms an enzyme-substrate complex• Induced fit model-enzyme slightly changes

shape to achieve optimum fit with the substrate• Products are released after reaction is complete• Active site is then ready to bind with another

substrate molecule

Enzyme speed is affected by local conditions

• Substrate concentration-enzyme activity increases as substrate concentration increases

• Temperature-enzyme activity increases as temperature increases. If temperature is too high, the enzyme denatures and can no longer bind with substrate.

• pH-enzymes have optimal pH for reactions. Extreme pH can denature the enzyme

• Cofactors– Inorganic ions or nonprotein organic

molecules required by enzyme in order to be active

– Inorganic ions-copper, zinc, iron– Nonprotein organic molecules-coenzymes-

assist the enzyme and may accept or contribute atoms to the reaction

• Vitamins are required for synthesis of coenzymes. If vitamin is not available, enxymatic activity decreases.

– Inhibitor-reduces amount of product produced by an enzyme per unit time

Enzymes can be inhibited noncompetitively and competitively

• Metabolic pathway-series of linked reactions

• Noncompetitive inhibition-inhibitor binds to the enzyme at a location other than the active site

• Competitive inhibition-inhibitor and substrate compete for the active site of an enzyme

• Inhibition is benefitial because once sufficient end product of a metabolic pathway is present, it is best to inhibit further production to conserve raw materials and energy.

The plasma membrane has many and various functions

The plasma membrane is a phospholipid bilayer with embedded proteins

• Plasma membrane in both bacteria and eukaryotes are phospholipid bilayer

• Proteins are found within and along the membrane

• Cholesterol-supports the membrane• Phospholipids and proteins can have

cabohydrates attached. These are glycolipids and glycoproteins.

Proteins in the plasma membrane have numerous functions

•Channel proteins-allow molecule to move across the membrane

•Carrier proteins-combine with substance and help it move across the protein

•Cell recognition proteins-glycoproteins (have carbohydrates attached)-foreign cells have their own glycoproteins that enable the immune system to recognize them and mound a defense

•Receptor proteins-have a binding site for a specific molecule, protein then changes shape and causes a cellular response

•Enzymatic proteins-carry out metabolic reactions directly

•Junction proteins-form junctions between cells, assist cell-to-cell communications

Malfunctioning plasma membrane proteins

• Type 2 Diabetes-not enough carrier proteins for the amount of glucose in the blood

• Color blindness-lack functional red or green photopigment protein

• Cystic fybrosis-channel proteins that are not properly regulated

The plasma membrane regulates the passage of molecules into and out of cells

Diffusion across a membrane requires no energy

• Diffusion-molecules move from a high concentration to a low concentration. The molecules follow the concentration gradient until equilibrium is reached– Passive transport since no energy is required– Small molecules, such as CO2 and O2, can

diffuse through the plasma membrane

• Facilitated diffusion-water, glucose, amino acids, Na+, Cl-, and Ca2+ facilitated passage through membrane– Requires a transporter but no energy since it’s

moving down its concentration gradient– Transporter moves specific substances

Carrier proteins are slower than channel proteins

• Osmosis-diffusion of water from low solute to high solute– Isotonic solutions-solute concentration is the same on

both sides– Hypotonic solution-higher solute inside cell so water

moves into the cell• Lysis-cells bursting when in hypotonic solution• Plant cells-experience turgor pressure, which allows plants to

stand up

– Hypertonic solution-solute concentration higher outside cell, water moves out

Figure 5.10C

Active transport across a membrane requires a transporter and energy

• Active transport-molecules more across plasma membrane accumulating on one side of the cell. Moving against the concentration gradient so energy is required

Bulk transport involves the use of vesicles

• Endocytosis or exocytosis• Moves molecules too large to

be moved by carrier proteins such as polypeptides, polysaccharides, or polynucleotides

• Phagocytosis-large particle (like food) is taken in, common in unicellular organisms

• Pinocytosis-take in very small particles

• Receptor-mediated endocytosis. Allows bulk transport of specific substances.

In multicellular organisms, cells communicate

Extracellular material allows cells to join together and communicate

• Plant cells-– Plasmodesmata-numerous channels that

pass through the cell wall. This allows direct exchange of some materials between adjunct plant cells and, ultimately, all the cells of a plant.

• Animal cells– Anchoring junctions-

connect cells in tissues that stretch

– Tight junctions-prevent digestive juices from leaking

– Gap junctions-plasma membrane channels join

– Extra-cellular matrix-where junctions are not present

• Cartilage and bone