Bio 160

Unit 2 – 1 Week Two- Lecture One

Cellular Functions

• Thermodynamics and energy– is the capacity to do work

• Kinetic - actual work• Potential - stored work• Heat - given off from the movement of

molecules• Chemical - stored for cells

– Thermodynamic laws- energy transformations• 1st law- energy can neither be created nor

destroyed, but it may change form• 2nd law- law of entropy- energy transformation

results in chaos of randomness. (entropy)

– Implication for the 1st law• Energy that comes to us from the sun can be

transferred into many different forms through different systems

– Implications for the 2nd law• As one environment becomes more organized, all

around it becomes disorganized• Disorganized energy is heat

– A cell creates an ordered space, increasing the entropy around it, so it can not be transfer or transform energy 100% efficiently, therefore energy can not be transferred 100% through a system. Most is given off as heat

• Chemical reactions store or release energy– Endergonic reactions require energy to be put

into the system, then stores energy in the chemical products. (ex. Photosynthesis)

– Exergonic reactions release energy out of the system from energy rich bonds being broken in the reactants. (ex. Cellular respiration)

• Cellular Metabolism- all of the endergonic and exergonic reactions of a cell– ATP- adenosine triphosphate powers nearly

all forms of cellular work• Obtained from food molecules• Energy coupling reactions for cellular metabolisms

are run by ATP– ATP is a little unstable, so it can be broken down to ADP

through hydrolysis» A phosphate is removed, releasing energy

(dephosphorylation)

» Exergonic reaction» Phosphorylation- ADP receives a phosphate

converting it to ATP, energizing it to perform work» Dephosphorylated ATP is converted to ADP:

adenosine diphosphate by the removal of a phosphate, releasing energy for the cell to do work.

– During cell respiration ADP is phosphorylated through dehydration synthesis and converted back to ATP. Therefore it is renewable source.

– Enzymes control the rate of chemical reactions without being consumed or changed in any way. (Biological catalyst protein)

• Works by lowering the energy barrier or the energy of activation energy needed to start a reaction

• The enzyme has no effect on the amount of energy content of reactants or products, just on the rate of the reaction.

• Enzymes are very specific in where they work– Use a “lock and key” mechanism. The active site on the

enzyme must have the appropriate “fit” with receptor site on the protein substrate

• Enzymes require a specific environment to function optimally. (Temp, pH, salinity, etc.)

– Some enzymes also require a non-protein cofactor or coenzyme (organic molecule) to function properly.

• Enzymes may be blocked from their substrates by inhibitor chemicals

– Competitive inhibitor- competes with the enzymes normal substrate, tying up the enzyme

– Non Competitive inhibitor- binds to the enzyme outside of the active site, changing the shape of the enzyme, preventing the enzyme from fitting with its own substrate

– Inhibitors regulate cell reaction rates by slowing it down» Negative feedback regulation of metabolism

Cellular Membranes

• Cellular Membranes control cellular metabolic functioning– Phospholipid bilayer made of a mosaic of

different small fragments that can move laterally in the membrane

• Membranes are selectively permeable, allowing certain substances in and out, but not others.

– Types of movement across cell membranes• Passive Mechanisms allow movement without the

use of energy

• Diffusion- molecules moving from areas of [] to [] through random molecular motion

• Passive Transport- diffusion of a substance across a membrane along a [ ] gradient until equilibrium is reached

• Osmosis- diffusion of water molecules across a selectively permeable membrane

– When water molecules can move across a membrane but the solute cannot, different concentrations of solutes may result

» Hypertonic- a solution with a higher [ ] of solutes in it that the surrounding solution is considered to by hypertonic it its solution

» Hypotonic- A solution with a lower [ ] of solutes in it than the surrounding solution is said to be hypotonic to its solution

» Isotonic- the [ ] of solute is the same on both sides of the membrane

» In all of the solutions, water will cross the s.p. membrane to reach equal concentrations. The direction of osmosis is determined only by the difference in total solute [ ].

» Water balance is controlled by osmoregulation

• Facilitated diffusion- a special protein embedded in the cell membrane called a transport protein regulates the diffusion of larger molecules down their [ ] gradients, thereby facilitating the diffusion

– Active transport mechanisms require cell energy to move substances across the membrane. Uses ATP phosphorylation to activate transport protein

» Exocytosis- cellular expulsion of molecules using cellular energy

» Endocytosis- cellular intake of macromolecules using cellular energy

─ pinocytosis-cellular intake of fluid droplets

─ phagocytosis- engulfing of large particles from outside the cellular membrane

─ receptor- mediated endocytosis- engulfing of specific molecules through the use of receptor proteins

Cellular Respiration

• The process of creating ATP the organism needs by using the materials the body takes in– Overall process

– Cells only use 40% of energy released from glucose. Other 60% lost as heat

– During the chemical conversion process of the reaction, e- are released from one set of molecules and are attached to others, giving off energy in the process

• Accomplished by H atoms moving places (fig. 6.4)– H carried by NAD+ (nicotinamide adenine dinucleotide)

through an oxidation-reduction (redox) reaction» 2 hydrogens and 2 e-’s are first peeled off of a

glucose molecule in an oxidation reaction (loss of e-)

» The H and 2 e- are shuttled through the oxidation by NAD+ coenzymes and dehydrogenase enzyme

» NAD+ becomes reduced, picking up H+ and 2 e- becoming NADH. The other H+ goes into the fluid surrounding the cell

» The energy from the redox reaction is released when NADH releases its e- carriers to become NAD+ again

− the NADH stores the energy for the cell

− The e- carriers “fall” down a series of energy level carriers like a stair step

−Called electron transport chain (e- “dance”)

−The e- carrier proteins (levels) are imbedded in mitochondrial membranes of the cristae

• 2 mechanisms to generate ATP– Chemiosmosis- uses concentration gradients

and ATP synthatase proteins found in membranes to generate most of their ATP

– Substrate level phosporylation- without a membrane, transfers a phosphate group from an organic molecule to ADP, happens in the conversion of glucose to CO2 in the Kreb’s cycle

• 3 stages of Cell Respiration (fig. 6.8)– Glycolysis- splitting of sugar anaerobically

• Occurs in cytoplasm without oxygen needed\• Oxidizes glucose into pyruvic acid through 9 chemical steps• 2 separate stages of glycolysis

– First stages are preparatory and consume energy» ATP is used to split one glucose into 2 smaller sugars that are

primed to release energy

• Since the prep phase uses 2 ATP, only 2 ATP are the end product generated by glycolysis– Produced through substrate- level phosphorylation– 2 molecules of NAD+ are reduced to NADH

• 2 ATP are available for immediate use by the cell• NADH must enter electron transport system for E to be released

– Must have O2 to release E

– Second stages release energy» Happens in tandem» NADH is produced when a sugar molecule is

oxidized and 4 ATP are generated

• Total end products of glysolysis: 2 ATP + Heat + 2 pyruvic acid

– Kreb’s Cycle- aerobic respiration• Pyruvic acid must be groomed to enter the Kreb’s

Cycle– It is oxidized while a molecule of NAD+ is reduced to

NADH– A C atom is removed and released in CO2

– Coenzyme A joins with what is remaining of the pyruvic acid to form AcetylCoenzyme A

– The acetyl part then enters the kreb’s cycle, the coenzyme A splits off and is recycled

• Kreb’s cycle happens in the cristae of the mitochondria

– Acetyl fragment combines with the oxaloacetic acid already in the mitochondria

– This forms citric acid. A molecule of CO2 is released and NAD+ is reduced to NADH, which releases an e- to the electron transport system

– Citric acid is converted to alpha- ketoglutaric acid, phosphorylated to produce ATP and NAD+ is reduced to NADH, again releasing an e- to the electron dance. Four-carbon succinic acid results.

– At succinic acid, enzymes rearrange chemical bonds FAD, a related hydrogen carrier similar to NAD, is reduced to FADH, releasing more e- to the electron dance. Malic acid is formed (FAD= flavin adenine dinucleotide)

– At malic acid NAD+ is reduced to NADH and a H+ ion, adding more e- to the dance. Malic acid is converted to oxaloacetic acid, which is ready to accept a new acetyl group for another turn at the cycle

• End products of Kreb’s: 36 ATP + CO2 + HEAT– 2 ATP are from substrate- level phophorylation

– Approx 34 ATP are formed by chemiosmotic phosphorylation

» The electron transport chains are built into the convoluted cristae of the mitochondria, there are many sites for the electron dance to occur

• Electron transport system is third stage of cellular respiration

• Pathways for dietary carbohydrates, lipids and proteins– Carbohydrates break down into sugars that eventually

break down into glucose and then goes into glycolysis• Quick access energy

– Lipids are broken down through hydrolysis into fatty acids and glycerol

• Fatty acids may be stored as fat, be converted into ketone bodies (acetone) and further broken down to enter the Kreb’s or eliminated, or undergo beta- oxidation and be converted straight into Acetyl Co A

• Glycerol may be converted into Acetyl Co A and enter the Kreb’s or be converted to glucose and undergo glycolysis

• Yields high energy when used but likes to be stored rather than used

• 2x as much ATP as in the same amount of starch

– Proteins undergo hydrolysis to break into amino acids that are then broken into deaminated portions which can go to fat, glucose, and acetyl Co A to enter glycolysis/Krebs cycles. The other portion of the amino acid is the NH2 (Ammonia) group, which is excreted through urea

• Long term energy- takes long time to digest

• Food Molecules are used for other stuff besides Kreb’s Cycle– Used for biosynthesis (uses ATP to do so)

• Produces proteins, lipids, and polysaccharides• Used for growth and repair