Tuesday, February 15, 2000

Midterm Exam #2

Biology 113

Name: _____________________________________

Œ   Place your name at the top of each page.

�   There are 29 questions (three for each lecture + two extra mitosis questions)

Ž   Each question is worth the same amount

� Remember to distinguish compared items by linking descriptions with terms (e.g., the sky isblue).

�   Unless requested, do not multiply out expressions (e.g., stop at 2*500³ rather than 2.5x10⁸).

‘ I encourage you to ask questions during the exam, but do so discretely.

’   Remember to use safe, i.e., unambiguous & well-articulated answers whenever possible.

“   Above all, avoid jumping to profoundly incorrect conclusions: make sure you actually read a question (all of it) before you answer, and then make sure you are actually answering what is being asked.

(1) __________ are more structurally diverse and more permanently assembled.

(a) Actin filaments

(b) Intermediate filaments

(c) Microfilaments

(d) Microtubules

(e) Polytubulin

A: (b) intermediate filaments (chapter 7)

(2) __________ is a complex of DNA and protein that, though present in large amounts in the nucleus of an interphase eukaryotic cell, is not visible through a light microscope.

A: Chromatin (chapter 12)

(3) __________ is an exergonic process by which ions may be transported across a cell membrane.

(a) Active transport

(b) Exocytosis

(c) Facilitated diffusion

(d) Passive diffusion

(e) Pinocytosis

A: (c) Facilitated diffusion; exergonic meaning occurs spontaneously without an imput of energy (once membrane protein is in place; this contrasts with active transport which involves an input of energy) and capable of transporting ions (passive diffusion is not); pinocytosis and exocytosis are both complex, energy-requiring processes (chapter 8)

(4) An electrical charge differential between the inside of a cell and the outside of a cell (i.e., across the plasma membrane) is known as a/the __________. Note that I am not asking for the name of the larger phenomenon that includes both the electrical charge differential and a chemical gradient.

A: Membrane potential (chapter 8)

(5) Another name for free-living Gram-negative-like bacteria that photosynthesize in a manner that is very similar to that of the chloroplasts of green plants is __________.

A: cyanobacterial (blue-green algae) (chapter 7)

(6) By what mechanisms do animal cells secrete proteins such as insulin into the extracellular environment? (looking for a one-word answer)

A: Exocytosis (chapter 8)

(7) Complete this reaction of glycolysis: C₃-P + NAD⁺ + __________ à __________ + NADH + H⁺

A: Pi, P-C₃-P (chapter 9)

(8) Complete this reaction:

                      pyruvate + __________ + coenzyme A à acetyl CoA + __________ + __________ + H⁺

A: Coenzyme A, CO₂, NADH (chapter 9)

(9) Considering both substrate-level phosphorylation and the oxidative phosphorylation that eventually occurs, how many ATPs does one turn of the Kreb’s cycle generate? (assume standard ATP estimations from chemiosmosis)

A: 3 NADH, 1 FADH₂, and one substrate-level phosphorylation per turn of the Kreb’s cycle, for a total of 3x3 + 1x2 + 1 ATP = 12 (chapter 9)

(10) Describe the mechanism of the sodium-potassium pump beginning just after the release and diffusion of the sodium ions out of the pump and ending with the diffusion of the sodium ions back into the pump. Be sure to use correct stoichiometries and please do not describe the pump in any more detail than I’ve asked for (i.e., if you include descriptions of the rest of the pump’s mechanism, e.g., after sodium ion diffusion into the pump, then I will assume that you don’t understand the process well enough to not talk about these steps so consequently will dock points for this extra effort). Please be clear and neat in your explanations.

A: Three potassium ions diffuse into the pump from the extracelular environment; their binding triggers a relaxation of the conformation of the protein to the shape that was present prior to ATP hydrolysis; the completion of this conformational relaxation finds the potassium ions translocated to the intracellular side of the membrane, upon which they are released from the pump and they diffuse away into the cytoplasm (chapter 8)

(11) During what phase of mitosis does cell lengthening begin to occur?

A: Anaphase is the phase that I am looking for, but metaphase is also an acceptable answer (i.e., see photos on pp. 210-211 of your text) (chapter 12)

(12) During what phases of mitosis are nucleoli not at all present?

A: During prometaphase, metaphase, and anaphase nucleoli are not present with a cell (chapter 12)

(13) From what do most common autotrophs obtain their carbon and energy (note that this is asking two questions and requires two answers)?

A: Light and CO₂ (chapter 10)

(14) Given that a signal has been released by one (sending) cell, what then are the three subsequent (general) steps of cell signaling?

1.

2.

3.

A: Reception, transduction, response (chapter 11)

(15) How many double helices of DNA does an individual sister chromatid (half of a sister chromatid pair) contain?

A: One double helix of DNA per sister chromatid (two per sister chromatid pair) (chapter 12)

(16) In substrate-level phosphorylation, what is the phosphate donor?

A: A substrate (i.e., not a proton-motive force) (chapter 9)

(17) Microtubules radiate out from a single __________, supporting the interphase cell structure.

A: centrosome (chapter 7)

(18) Name a protein or protein-containing complex (other than the various microtubules or the tubulin protein) that is directly associated with chromosomes during metaphase.

A: Kinetochores (chapter 12)

(19) Other than ATP, what commonly is employed by cells to directly power active transport (if you use a specific example, make sure that you include the type of organism in which you would expect to find this specific example employed)?

A: Electrochemical gradients are employed to power cotransport; specific examples include sodium or potassium gradients in animal cells or hydrogen ion gradients in plant, bacteria, and fungal cells;  note that a failure to employ the term gradient (or its equivalent) is necessary to answer this question correctly (chapter 8)

(20) Other than location, what do secreted proteins and membrane proteins have in common that distinguishes them from the soluble proteins that are found in the cytoplasm.

A: secreted and membrane proteins are both synthesized by bound ribosomes whereas soluble proteins  (chapter 7)

(21) There are at least three ways that cells may communicate. One involves the diffusion of substances between cells over either short distances or over long distances (paracrine or synaptic signaling and hormones, respectively). A second involves the direct contact between the proteins found on the surfaces of two cells such that the occurrence of that contact signals one or both participating cells via a transduction of that contact information through the plasma membrane(s) into the adjacent cytoplasm(s). What is the third means by which cells may communicate?

A: The (a) third way that cells may is via the free diffusion of chemicals from one cell’s cytoplasm to another via junctions that directly link the cytoplasms of adjacent cells (chapter 11)

(22) What are cysternae?

A: found in the cytoplasm are synthesized by free ribosomes) the cysternae are networks of ER sacs and tubules (chapter 7)

(23) What is the name given to the electrochemical gradient generated in the course of cellular respiration?

A: proton-motive force (chapter 9)

(24) What kind of enzyme catalyzes reactions such as:  H-C-OH + NAD⁺ à C=O + NADH + H⁺

A: Dehydrogenases (chapter 9)

(25) What portion of the endomembrane system is involved in the detoxification of many especially hydrophobic drugs? Be reasonably specific.

A: smooth endoplasmic reticulum (chapter 7)

(26) What specific, non-electron-transport chain, multi-molecular complex is involved in both cyclic and non-cycle photophorylation?

A: Photosystem I (chapter 10)

(27) What steps are typically involved in G-protein-linked receptor signal transduction? Consider only those steps that directly involve the G protein. By my count, following ligand binding and the resulting receptor conformational change, there are approximately 8 steps including the various binding and diffusion steps. (you may want to use the back of this sheet to pull together your thoughts before answering below)

A: G-protein-linked receptor signal transduction involves (starting following ligand binding): (i) binding of G protein to receptor, (ii) loss of GDP from G protein, (iii) gain of GTA by G protein (thereby activating it), (iv) diffusion along membrane toward subsequent protein in signal transduction pathway, (v) binding to subsequent protein, (vi) activation of subsequent protein, (vii) hydrolysis of GTP to GDP, and (viii) diffusion of G protein away from subsequent protein. (chapter 11)

1.

2.

3.

4.

5.

6.

7.

8.

(28) Why would you expect that the oligosaccharides of an integral membrane glycoprotein would project into the extracellular environment rather than into a cell’s cytoplasm?

A: Oligosaccharides are added to proteins within the lumen of the endomembrane system, which is equivalent to the extracellular environment in terms of membrane asymmetries; given minimal flipping of integral membrane glycoproteins, one would predict minimal presence of the oligosaccharide component of glycoproteins projecting into the cytoplasm (chapter 8)

(29) Write the portion (chemical reaction) of photosynthesis’ light reaction—occurring at the end of the non-cyclic pathway—that involves in particular the addition of reduced electrons to the electron carrier that ultimately is employed during the Calvin cycle.

A: 2e^- + 2H⁺ + NADP⁺ + energy (supplied by the electrons) à NADPH + H⁺ (chapter 10)