bio 160
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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