EXAM 2 Flashcards
Draw the structure of phosphatidylserine. Assume the fatty acids are saturated and are 16 carbons long. Don’t draw all 16 C’s. Use the -(CH2)n - shorthand. Remember to indicate the appropriate charges that would exist in a typical cell
Your friend isolates a new species of yeast that can grow at neutral pH using either ethanol (CH3CH2OH) or acetate (CH3COO-) as the yeast’s sole carbon source. She measures the initial rate of uptake as a function of concentration of each carbon source and obtain the following graphs:
Based on these graphs and your knowledge of membrane permeability, state the identity of molecules A and B (ethanol or acetate) and the most likely transport mechanism for each.
Briefly explain your answer.
Molecule A is using passive transport, looking at the first graph it is a steady rate of change and that is how passive transport is characterized. This is ethanol.
Molecule B is using facilitated transport, active transport changes concentration quickly and stops once it is reached. Also because it requires energy if it runs out it must stop. This is acetate.
Most mammalian cells have a voltage potential across their plasma membrane of -70 millivolts. Explain how this charge difference is generated.
Overall the charge difference is generated by ion concentration in and out of the cell. More specifically K+ leak channels are the main ones generating the voltage by constantly pushing out K+. Some is also done by the Na+/K+ transport.
If a cell finds itself with a voltage potential of -80 millivolts across its membranes, it will rapidly adjust itself back to a potential of -70 millivolts. How does it do this?
It will do this by using K+ leak channels to export K+. It will use Na+/K+ system to move 3 Na+ out and 2 K+ in. Then the K+ leak channels will export out more K+ until equilibrium is met.
Why does the citric acid cycle stop almost immediately when oxygen is removed?
Because it will have no where to transfer electrons.
In the absence of oxygen, yeast cells consume glucose at a high, steady rate. When oxygen is added, glucose consumption drops abruptly and is then maintained at the lower rate. Why is glucose consumed at a high rate in the absence of oxygen and at a low rate in its presence.
It is consumed at a high rate in the absence of oxygen because fermentation occurs breaking down a lot of glucose but not making much energy. When oxygen is added back it can return to normal respiration and wont have to use as much glucose.
Imagine a molecule of glucose being completely metabolized to CO2 and H2O in a yeast cell that is growing aerobically. Place the following events in the correct order, with step 1 occurring first and step 8 last. Obviously, many steps have been left out. It may be useful to think about whether the steps occur as part of glycolysis, the citric acid cycle, or electron transport, to place the steps in the general part of the whole process.
- addition of phosphate from ATP to glucose
- splitting of a 6 -carbon compound into two 3-carbon compounds
- generation of ATP in the cytoplasm by substrate-level phosphorylation
- Import pyruvate into the mitochondria
- addition of 2-carbon unit from acetyl CoA to oxaloacetate to form citrate, a 6-carbon-compound
- oxidation of NADH to NAD at the inner mitochondrial membrane
- pumping of protons across the inner mitochondrial membrane
- transfer of electrons to O2
You have patch-clamped a single voltage-gated ion channel in a membrane and have obtained the recording shown below. Sketch the recording you would expect to see if you repeat the experiment but this time your patch contained two molecules of the same voltage-gated ion channel (draw the recording to the right of the one given and use the same Y-axis scale). Briefly explain your results.
when 2 molecules of the same voltage-gated ion channel are patch clamped the result is 2x the current.
Briefly define the role of the following in photosynthesis:
Reaction center chlorophyll
Water
Photosystem 2
Cytochrome b6-f complex
Plastocyanin
Photosystem 1
NADPH
Ribulose 1,5-bisphosphate carboxylase (also known as rubisco)
Reaction center chlorophyll - absorbs light energy through resonance to be used by photosystem 2
Water - donates e- to be excited by light
Photosystem 2 - creates a strong proton gradient to be used ATPase or other work
Cytochrome b6-f complex - pumps proton in proton gradient, makes plastocyanin
Plastocyanin - electron carrier that takes e- to PSI
Photosystem 1 - uses the excited e- from PSII to synthesize NADPH
NADPH - used in calvin cycle to anabolize glucose
Ribulose 1,5-biphosphate carboxylase (also known as rubisco) - carbon fixation during the calvin cycle, attaches to CO2 to ribulose by temp forming a 6 carbon sugar
Describe the first four steps of glycolysis (just words, no structures are necessary), beginning with glucose, and ending with the formation of two 3-carbon compounds.
- glucose in phosphorylated by the enzyme hexokinase and with 1 ATP to form glucose-6 (adds P to H2O group)(other products ADP and H+)
- this is taken and the carbon bond is moved to form a pentane ring formation (fructose-6) this is catalyzed by phosphoglucoisomerase
- the other side of this is now phosphorylated using another ATP and this is catalyzed by phosphofructokinase. This also produces ADP and H+ (P is being added to other CH2O group)
- aldolase catalyzes the separation of this into 2 pyruvate molecules that are used for next steps
A. Suppose you discover a new single celled organism whose membranes mostly contain unsaturated fatty acids that are 12 carbons long. Which of the following types of organisms could this be? Circle your answer.
B. Explain why the answer you circled is the correct answer.
a. a bacterial cell that lives in cold environments
b. Bacterial membranes use fatty acids while archea often use isoprene, tetra ether, or diether, when the lipids are unsaturated this means it will be very fluid at high temperatures but will work well in cold environments.
Below is the structure of sodium dodecyl sulfate, a common detergent. Explain how it can remove greasy food residue from dishes. A diagram may be useful for your answer.
Detergents remove greasy food residue from dishes by creating micelles around oil drops because they are trying to hide their hydrophobic tails away. These micelles get washed away with water and your dishes are clean!
If you stub your toe, a nerve impulse will travel from your toe to the base of your spine, where it will be handed off to another nerve that will relay this information to your brain. Describe the role of the following proteins, ions, molecules, and structures during the transmission of a nerve impulse from your stubbed toe to the brain.
Acetylcholine -
Voltage gated Na+ channels -
Mechanically gated Na+ channels -
Voltage gated Ca+ channels -
Voltage gated K+ channels -
Ligand gated Na+ channels -
Acetylcholine - excitatory chemical found in neuromuscular junctions that send signals to muscles. would probably trigger muscles to pull away
Voltage-gated Na+ channels - are opened, inactivated, then closed and send the signal down the axon, dendrite, etc. and to the synapse
Mechanically-gated Na+ channels - open with the pressure/touch of stubbing your toe and let Na+ in
Voltage-gated Ca++ channels - open at synapses to signal the release of neurotransmitter from the presynaptic to the postsynaptic cleft. important for the electrical to chemical energy change
Voltage-gated K+ channels - allow for the repolarization of the cell to happen after the action potential was fired by opening to let K+ out
Ligand gates Na+ channels - are opened by acetylcholine and allow for Na+ to reuptake
