1. (7 pts) [Fill in the blanks] Proteins destined for the outside of the cell are synthesized on __RIBOSOMES_, which are assembled in the __NUCLEOLUS__ region of the __NUCLEUS_, attached to the _ENDOPLASMIC RETICULUM__ in which they are _POST-TRANSLATIONALLY MODIFIED_, packaged and transferred to the _GOLGI BODY_ where they are further packaged and delivered to the surface via _TRANSITION VESICLES_.
2. (9 pts) Hollow cytoplasmic rods called _MICROTUBULES_, composed of _TUBULIN_, play a role in controlling (a) the _STRUCTURE_ (function) of a cell because of their ability to _ASSEMBLE/DISASSEMBLE_, (b) the _MOTILITY_ (function) of a cell because of their arrangement in the 9 + 2 structure of _CILIA_ and _FLAGELLA_, and (c) the _CELL DIVISION_ (function) of the cell because of their 9 x 3 arrangement in _CENTRIOLES_.
3. (6 pts) Eukaryotic cells use compartments (membrane organelles) and a fibrous cytoskeleton to regulate function.
(a) Give one specific example of the control of a process that involves separation by compartments.
· enzymes in lysosomes
· substrates separated from enzymes (cytoplasmic vs mitochondria).
· separation of stomach environment from circulation
(b) Postulate a regulatory means (physical or chemical) by which the dynamics of the cytoskeleton could be controlled. (What are the dynamics?)
The dynamics are the assembly/disassembly of microfilaments for examples. Regulatory means include change in (1) ionic strength to compete with ionic interactions, change (2) hydrophobic environment to replace hydrophobic interface betweeen subunits using chemical modification that removes charge thus diminishing ability to assemble through ionic interactions or add polar molecules that competes with hydrogen bonding associating subunits.
4. (4 pts) Give two examples of protein quaternary structure.
· hemoglobin
· ribosomes
· microfilaments
· microtubules
5. (5 pts)[Circle the appropriate choice and fill in the blank.] In an ideal exergonic reaction, the standard free energy change would be negative resulting from decreasing enthalpy and increasing entropy.
The hydrolysis of ATP is an exergonic reaction used in _coupled (endergonic)_ reactions to make thermodynamically unfavorable reactions proceed.
6. (5 pts) The reactions of living cells are never at equilibrium.
(a) Explain how this fact can be used to control the direction of glycolysis.
mass action: the system is always trying to move toward equilibrium, thus the direction will depend on the direction away from equilibrium you have moved.
(b) Why is this fact essential to allow the pathway to proceed in either direction?
The use of mass action to overcome non-spontaneous reaction in either direction defined by:
delta G = delta Go + RT ln[P]/[S]
7. (10 pts) Plants vs Animals
(a) Light provides energy to what common process that is in both plant and animal cells?
electron transport chain
(b) Give one effect that the lack of light in plants and the lack of oxygen in animals have in common (include the ultimate function of the common pathways in your answer).
ultimate function in both is to convert energy to useful form for synthesis or work (ATP/NADPH). Loss of light or O2 stops production of products necessary for synthesis.
8. (5 pts) One regulatory method controlling the direction of metabolism (anabolism vs catabolism) is the energy need of the cell. What guiding principle defines the energy state of the cell?
ATP + ADP = constant
NADH + NAD+ = constant
FADH2 + FAD = constant
if ATP is high then ADP is low. High ATP indicates that energy metabolism is not needed thus glycolysis does not need to move forward until regenration of more ADP takes place.
9. (16 pts) [Fill in the blanks.] Aerobic glycolysis is the breakdown of _GLUCOSE_ to _PYRUVATE_ and takes place in the _CYTOPLASM_ of the cell. The end product is metabolized further to _ACETYL-COA_ and simultaneously transported into the __MATRIX_ of the _MITOCHONDRIA_ where its carbons are further metabolized to _CARBON DIOXIDE_ in the _CITRIC ACID CYCLE_ pathway. The byproducts of this metabolism are _ATP_, _NADH_, and _FADH2_. Two of these byproducts are further metabolized through the _ELECTRON TRANSPORT CHAIN_ that is located in the _INNER MEMBRANE_ of the _MITOCHONDRIA_ and result in the formation of a _PROTON_ gradient that provides the energy for _ATP_ synthesis.
10. (6 pts) On the following diagram of the metabolic pathway thus far studied, indicate where the primary input of (a) monosaccharides, (b) proteins, and (c) fats enter this scheme.
I = (a)
II = (b)
III = (c)
11. (6 pts) "...research finds that anaerobic exercise burns over 500% more fat than aerobic exercise" says an advertisement in the Sunday newspaper.
(a) Explain how this is possible using the general balance of metabolic pathways (a general diagram would be appropriate).
under anaerobic conditions, fats are metabolized to produce a large amount of NADH. Without oxygen, NADH must be converetd back to NAD by other methods, i.e. synthesis of proteins for example.
(b) Why is it recommended that this "exercise" only be done for 5-10 minutes a day?
under extended anaerobic conditions, the yield of ATP is too low to support muscle activity or cellular work. In addition extended build up of lactic acid will cause tissue damage.
12. (9 pts) [Fill in the blanks] Enzymes are _CATALYSTS_ that effect the _RATE_ of a reaction without being consumed by the reaction. Enzymes function by lowering the _ACTIVATION_ energy while not affecting the _FREE_ energy of the reaction by combining with the _SUBSTRATE_ to form a complex in the region of the protein called the _ACTIVE SITE_.
13. (6 pts) It is observed that as the concentration of G-6-P increases, the activity (velocity) of the enzyme (E) decreases.
(a) What type of inhibition does this demonstrate?
Competitive (feedback) inhibition
(b) Under what cellular conditions would you expect the concentration of G-6-P to increase?
system at rest where there is a surplus of ATP or NADH. Thus no need for glycolysis and glycolysis slows down, building up intermediates including G-6-P. Another possibility is a rapid increase in circulating glucose that rapidly form g-6-P with insufficient downstream need.
14. (6 pts) A pesticide functions by covalently modifying a specific enzyme.
(a) The specificity of the pesticide results from its initial binding to the _ACTIVE SITE_ region of the enzyme.
(b) Show a graphical representation of this type of "inhibition".
(c) What other cellular method (process) parallels this type of regulation?
GENETIC REGULATION OF PROTEIN SYNTHESIS OR ANY PROCESS THAT CONTROLS
THE CONCENTRATION OF ENZYME IN THE CELL.