Biology 1107 Unit 2

Why is it advantageous for the plasma membrane to be fluid in nature?

Fluidity allows greater flexibility to the cell and motion of membrane components required for transport.

An experiment was set up to determine the movement of molecules through a dialysis-tubing bag into water. A dialysis-tubing bag containing 5% lactose and 5% fructose was placed in a beaker of distilled water, as illustrated. After four hours, fructose is detected in the distilled water outside of the dialysis-tubing bag, but lactose is not. What conclusions can be made about the movement of molecules in this experiment?

Fructose, being a monosaccharide, diffused through the dialysis bag into the distilled water. However, lactose, being a disaccharide, could not diffuse through the dialysis bag.

If a peripheral membrane protein were synthesized inside the lumen of the ER, would it end up on the inside or outside of the plasma membrane?

The vesicle travels from the Golgi to the plasma membrane to release the protein outside.

The hydrolysis of one ATP molecule releases 7.3kcal/mol of energy (ΔG=−7.3kcal/mol). If it takes 2.1kcal/mol of energy to move one Na+ across the membrane (ΔG=+2.1kcal/mol), what is the maximum number of sodium ions that could be moved by the hydrolysis of one ATP molecule?

three

Which of the following bodily process would most likely be hindered by a lack of water in the body?

digestion

Macrophages ingest and digest many pathogens. Which organelle plays a major role in the activity of macrophages?

lysosome

Look at each of the processes shown, and decide if it is endergonic or exergonic. In each case, does enthalpy increase or decrease, and does entropy increase or decrease?

A ball rolling down the hill doesn't affect the order of system; therefore, the entropy would remain unchanged.

Based on what you know about plant and animals cells, which of the following events are most likely to have occurred?

A host cell that gave rise to modern plants ingested both aerobic and photoautotrophic bacteria, while a host cell that gave rise to modern animals ingested aerobic bacteria only.

Why is it beneficial for cells to use ATP rather than directly use the energy stored in the bonds of carbohydrates to power cellular reactions? What are the greatest drawbacks to harnessing energy from the bonds of several different compounds?

ATP is readily available in the form of a single unit. The cell would need to tailor each reaction to each energy source if it harvested energy from different compounds.

In individuals with normally functioning CFTR protein, which substances are transported via active transport?

Cl-

What would be the most direct result of blocking structure Z in the graphic?

Cytochrome c would not pass electrons from complex III to complex IV.

Why does water move through a membrane?

Difference in concentration of solute and solvent

How do the differences in amino acid sequence lead to different protein functions?

Different amino acids provide different geometric configurations and thus varied functions.

Which of the following best describes how the citric acid cycle relates to glycolysis, oxidative phosphorylation, and chemiosmosis?

Glycolysis produces pyruvate, which is converted to acetyl-CoA and enters the citric acid cycle. This cycle produces NADH and FADH2, which donate electrons to the electron transport chain to pump protons and produce ATP through chemiosmosis. Production of ATP using an electron transport chain and chemiosmosis is called oxidative phosphorylation.

Energy transfers take place constantly in every day activities. Think of two scenarios: cooking on a stove and driving. Explain how the second law of thermodynamics applies to these scenarios.

Heat is lost into the room while cooking and into the metal of the engine during gasoline combustion.

You have been identifying the sequence of a segment of a protein. The sequence to date is: leucine-methionine-tyrosine-alanine-glutamine-lysine-glutamate. You insert arginine between the leucine and methionine. What effect would this have on the segment?

Inserting arginine places a positively charged amino acid in a portion that is non-polar, creating the possibility of a hydrogen bond in this area.

Dinitrophenol is a compound that can directly shuttle protons across biological membranes. What effect would this drug have on energy generation?

It dissipiates the electrochemical proton gradient across the mitochondrial membrane, hindering ATP production.

Explain why mitochondria are considered the powerhouse of the cell.

Most of the ATP is produced in mitochondria by oxidative phosphorylation.

Explain how the formation of NAD+ differs between aerobic and anaerobic respiration.

NAD+ is formed by a fermentation process in anaerobic respiration by the conversion of pyruvate into lactate and by simple oxidation of NADH in aerobic respiration.

What role does NAD+ play in redox reactions?

NAD+, an oxidizing agent, can accept electrons and protons from organic molecules and get reduced to NADH.

Why do phospholipids tend to spontaneously orient themselves into something resembling a membrane?

Phospholipids are amphipathic molecules. The polar head faces towards water and the nonpolar fatty acid tails face towards other fatty acid tails.

List four components of a plasma membrane and explain their function.

Phospholipids: form the bilayer; Carbohydrates: help in adhesion; Cholesterol: provide flexibility; Integral proteins: form transporters; Peripheral proteins: part of the cell's recognition sites.

Which of the following statements most directly supports the claim that different species of organisms use different metabolic strategies to meet their energy requirements for growth, reproduction, and homeostasis?

Plants generally use starch molecules for storage while animals use glycogen and fats for storage.

What happens when potential energy is turned into kinetic energy?

Potential energy will be expressed in the form of heat, movement or work.

In the following general reaction, explain how electrons are transferred and the role of each species. RH + NAD+ → NADH + R

RH acts as a reducing agent and donates its electrons to the oxidizing agent NAD+, forming NADH and R.

Cellular respiration breaks down glucose and releases carbon dioxide and water. Which steps in the oxidation of pyruvate produces carbon dioxide?

Removal of a carboxyl group from pyruvate releases carbon dioxide. The pyruvate dehydrogenase complex comes into play.

Where do the electrons moving along the membrane in the figure come from, and where do the electrons end up?

The electrons are released by NADH and FADH2 and finally accepted by oxygen to form water.

Explain how the nucleus and the endomembrane system work together for protein synthesis.

The endomembrane system processes and ships proteins specified by the nucleus. In the nucleus, DNA is used to make RNA which exits the nucleus and enters the cytoplasm of the cell. The ribosomes on the rough ER use the RNA to create the different types of protein needed by the body.

Salmonella is one of the most common food borne illnesses. When salmonella bacteria are engulfed by a white blood cell during phagocytosis, it secretes a protein that prevents the fusion of the encased bacteria with the lysosome of the cell. What effect would this have?

The bacteria will survive and possibly will cause illness.

You are looking at a sample under a light microscope and observe a new type of cell. You come to the conclusion that it is a bacterium and not a eukaryotic cell. What would you observe to come to this conclusion?

The cell does not have a nucleus.

Paramecium are unicellular protists that have contractile vacuoles to remove excess intracellular water. In an experimental investigation, Paramecium were placed in salt solutions of increasing osmolarity. The rate the contractile vacuole contracted to pump out excess water was determined and plotted against osmolarity of the solutions, as shown in the graph. Which of the following is the correct explanation for the data?

The contraction rate increases as the osmolarity decreases because the amount of water entering the Paramecia by osmosis increases.

In the context of cell biology, what do we mean by "form follows function?" What are at least two examples of this concept?

The form of the structure is dictated by its function. For example, the arms of humans and the wings of bats serve different functions, and thus their forms are adapted to those functions.

Why does the immune system attack a transplanted organ?

The immune system does not recognize the glycoproteins and glycolipids on the surface of the organ.

Inhibitors of microtubule assembly, vinblastine for example, are used for cancer chemotherapy. How does an inhibitor of microtubule assembly affect cancerous cells?

The inhibitors restrict the separation of chromosomes, thereby stopping cell division.

Explain why glucose cannot pass directly through the cell membrane.

The plasma membrane is selectively permeable to polar molecules, and a transport protein is required.

What happens to the proteins that are synthesized on free ribosomes in the cytoplasm? Do they go through the Golgi apparatus?

The proteins do not go through the Golgi apparatus and remain free in the cytosol.

Describe the position of the transition state on a vertical energy scale, from low to high, relative to the position of the reactants and products, for both endergonic and exergonic reactions.

The transition state of the reaction exists at a higher energy level than the reactants. Activation energy is always positive regardless of whether the reaction is exergonic or endergonic.

How does the sodium-potassium pump contribute to the net negative charge of the interior of the cell?

The sodium-potassium pump forces out three (positive) Na+ ions for every two (positive) K+ ions it pumps in, thus the cell loses a net positive charge of one at every cycle of the pump.

Tremetol, a metabolic poison found in the white snake root plant, prevents the metabolism of lactate. When cows eat this plant, it is concentrated in the milk they produce. Humans who consume the milk become ill. Symptoms of this disease, which include vomiting, abdominal pain, and tremors, become worse after exercise. Why do you think this is the case?

Tremetol inhibits enzymes that convert lactate into less harmful compounds. Exercise worsens this by producing more lactate.

During aerobic cellular respiration, oxygen gas is consumed at the same rate as carbon dioxide gas is being produced. In order to provide accurate volumetric measurements of oxygen gas consumption, the experimental setup should include which of the following?

a substance that removes carbon dioxide gas

One type of mutation in the CFTR protein blocks the channel, preventing the transport of ions. Which of the following is most likely to be observed in the lungs of patients with this type of mutation?

dehydrated mucus

Compare the four types of RNA by structure and function.

mRNA is a single stranded transcript of DNA. rRNA is found in ribosomes. tRNA transfers specific amino acids to a developing protein strand. miRNA regulates the expression of mRNA strands.

How does the change in Gibbs free energy (ΔG) differ between the catalyzed versus uncatalyzed reaction?

ΔG is the same for the catalyzed and uncatalyzed reactions.