Biology HW Q's Exam 2

When cells are initially placed in hypertonic solutions:

cell volume decreases.

Approximately how many ATP does one NADH molecule produce?

2.5

A lysosomal enzyme works best at a pH of:

5

As a cat pounces on a mouse, her muscles burn 10 units of chemical potential energy (which the cat previously gained from eating). However, the pounce itself only required 4 units of kinetic energy. In this conversion from potential to kinetic energy, how many units of energy were dissipated as heat?

6

In response to seasonal changes in temperature, many organisms must alter the composition of their plasma membranes to maintain the proper degree of fluidity. As summer turns to fall and eventually into winter, which of the following would you predict occurs in the plasma membranes of organisms that do not regulate their body temperature?

A decrease in phospholipid fatty acid tail length and a decrease in tail saturation.

The hydrolysis of _____ is an exergonic reaction that drives many endergonic reactions in a cell.

ATP

You are studying the transport of a substance into skin cells. You find it only moves into the cells when ATP is present. How is the protein moving through the membrane?

Active transport

If a mutation rendered the signal recognition particle nonfunctional, what would be the MOST obvious effect on the cell?

All proteins normally secreted by the cell would remain in the cytosol.

The sodium-potassium pump is an example of: (Hint, this was discussed towards the end of the lecture.)

An active transport

Which of the following would most dramatically decrease membrane fluidity?

An increase in phospholipid fatty acid chain length and an increase in saturation.

Why does active transport require ATP?

An input of energy is needed to allow the movement of molecules from an area of low concentration to one of higher concentration.

Building a protein by adding amino acids to the polypeptide chain is an example of:

Anabolism

How do eukaryotic plant and animal cells differ from one another?

Animal cells do not have chloroplasts and cell walls, and plant cells do.

_________ are specialized channels for the transfer of water molecules into and out of the cell.

Aquaporins

Why are reduction reactions called reductions if they result in a gain of electrons?

Because initially, people noticed that heating rusty metal with a carbon source (i.e., charcoal) resulted in the material losing weight. While it was later found that the 'rusty metal' gained electrons, the mass of electrons is so small that their gain had virtually no impact on the overall weight.

What transporters allow hydrophilic molecules to move across cell membranes?

Both channels and carriers

Which of these reactions summarizes aerobic cellular respiration?

C6H12O6 + 6 O2 ➝ 6 CO2 + 6 H2O + energy

Cellular respiration is a series of ______ reactions. (Hint: Think back to the thermodynamic lectures.)

Catabolic

Which of the following statements violates the laws of thermodynamics?

Cells increase the total energy in the universe when they produce ATP.

Which of the following accurately describes the path traveled by a new protein as it is synthesized and released from the cell?

Cytosol → ER → Golgi → vesicle → plasma membrane → external environment

Which of the following is TRUE about exergonic reactions?

Energy is released from the reactants.

Which of these equations is/are endergonic? (Select all that apply) Equation 1: ATP + H2O → ADP + Pi ΔG1 = -7 kcal/mol Equation 2: phosphoenolpyruvate + H2O → pyruvate + Pi ΔG2 = -14.8 kcal/mol Equation 3: glucose + Pi → glucose-6-phosphate + H2O ΔG3 = +3.3 kcal/mol Equation 4: ADP + Pi → ATP + H2O ΔG3 = +7 kcal/mol

Equation 3 and Equation 4

Imagine that you are talking with one of your friends. He states that evolution has actually violated the second law of thermodynamics because complex living organisms are more ordered than the nucleic acids, amino acids, and other molecules that compose them. Why doesn't evolution contradict the second law of thermodynamics?

Even though evolution may decrease the entropy of living organisms, it increases the entropy of the Earth (or the universe) as organisms release heat.

Which of the following describes ATP hydrolysis? (Select all that apply.)

Exergonic Often coupled to a reaction that has a positive ΔG Spontaneous

T/F: A change in pH can disrupt the ionic bonds in a molecule, affecting the primary structure and subsequently enzyme function.

False

T/F: Bacteria use lysosomes to digest material in the cell.

False

T/F: Enzymes get used up during chemical reactions, and so subsequently there must be enough enzymes present for the reaction to continually proceed.

False

T/F: If an enzyme reaction has a ∆G<0, then the reaction must happen at an observable rate.

False

T/F: The mitochondria and chloroplast are part of the endomembrane system

False

T/F: When glucose is broken down in a cell, all of the energy it stores is released simultaneously, not in a stepwise process.

False

Where would a protein lacking an ER signal sequence be translated?

Free ribosomes in the cytosol

Which of the following have cell walls?

Fungal cells, plant cells, bacterial cells

What type of sugar would have the smallest weight?

Glucose (a monosaccharide)

Endergonic

absorbs free energy (+ΔG)

When physicians perform organ transplants, they make sure that there is a match between the donor (the person donating the organ) and the recipient (the person receiving the organ). What feature of the cell is being matched?

Glycyoproteins in the plasma membrane

Disorders of which organelle are often associated with defects in transport from compartment to compartment, resulting in poor sorting of protein components within the cell?

Golgi Apparatus

What is the main difference between starch and cellulose? (Hint: To exclude one possibility you will need to look carefully at the lecture slides.)

Humans and other animals don't have the necessary enzymes to break down the sugars in cellulose, meaning that they obtain no digestive benefit from them.

Synthesis of a protein destined to function in the nucleus occurs: (Hint: use the signalling diagram handout.)

In the cytosol

At low temperatures, how does cholesterol influence the fluidity of a membrane and why does it have this influence? (Hint: The book goes into more detail with regards to how cholesterol influences membrane properties.)

It increases fluidity by preventing tight packing of the phospholipid fatty acid tails.

What would happen to the pH inside a lysome if the proton pump stopped working?

It would change to resemble the pH of the cytoplasm, meaning more basic.

Which one of the following represents the REDUCED form of the two major electron carriers? (Hint: The same process that applies to NADH, applies to FADH2. See the textbook.)

NADH and FADH2

While it is often stated that the phosphate bonds in ATP are "high energy," it takes a relatively low amount of energy to break the bond. What makes the phosphate bonds easy to break?

Negative charges on phosphate groups repel each other.

RNA molecules are transported from the nucleus to the cytoplasm in eukaryotes through:

Nuclear pores

Which stage of cellular respiration is responsible for producing the most ATP?

Oxidative Phosphorylation

The __________ forms of the electron carriers NAD+/NADH and FAD/FADH2 have high potential energy. (Hint: See textbook for more information about FAD.)

Reduced

In intestinal epithelial cells, a transport protein moves glucose into the cytoplasm against its concentration gradient at the same time that it transports Na+ into the cell down its electrochemical gradient. Which of the following CORRECTLY describes this co-transport of glucose and sodium?

Secondary active transport by a symporter.

What organelle is the primary site of lipid synthesis?

Smooth ER

What happens to a red blood cell when placed in distilled water?

Swells and bursts open

What property do enzymes effect?

The activation energy of a reaction

Which of the following statements is a consequence of the second law of thermodynamics?

The amount of useable energy resulting from a reaction will always be less than the total energy available in the starting materials.

Which of the following reactions is MOST likely to be exergonic?

The digestion of protein from food into amino acids

Imagine that you have two blades of grass. One is from a normal plant, and the other is from a mutant plant that cannot produce vacuoles. How will the structures of these two blades of grass compare?

The grass blade from the mutant plant will appear limp compared to that from the normal plant.

Imagine that you walk out of your warm house on a cold winter's day. What is different between the air inside and outside of your house in this scenario?

The molecules in the warm air of your house are moving faster than those outside.

Why does a phospholipid on the cytoplasmic side of the cell membrane rarely flip to the extracellular side in aqueous environments?

The polar head group cannot pass through the nonpolar interior.

If the reaction of ATP -> ADP + Pi (a phosphate group), releases 31 kJ/mol of energy, what most be true about the backwards reaction ADP + Pi -> ATP?

The reaction absorbs 31 kJ/mol of energy.

Which one of the following statements about the formation of a peptide bond is INCORRECT? (Hint, think about how entropy changes in this process.)

The reaction is spontaneous.

Which of the following is true about spontaneous chemical reactions?

The reactions are exergonic.

In ________, large molecules are broken down and ATP is produced.

catabolism

How do enzymes work to speed up reactions? (Select all that Apply)

They provide a favorable microenvironment for the reaction to occur. They lower the activation energy of a reaction. They orient substrates making it easier for them to interact. They strain substrate bonds to make them easier to break.

T/F: If a reaction has a ∆Gº>0, and you start with only reactants, products will form. (Hint: Think about the difference between ∆Gº and ∆G; see bonus slide in lecture notes.)

True

Put the following events in the CORRECT sequence for a protein that will be secreted from the cell. 1. SRP binds to the growing polypeptide chain and to the ribosome. 2. Translation resumes. 3. SRP binds to its receptor. 4. The signal sequence is cleaved. 5. Protein synthesis begins in the cytosol. 6. Translation pauses.

_1__Protein synthesis begins in the cytosol. __2__SRP binds to the growing polypeptide chain and to the ribosome. __5__Translation resumes. __6__The signal sequence is cleaved. __3__Translation pauses. __4__SRP binds to its receptor.

What is the hydrophilic component of cholesterol?

a hydroxyl group

With which of the following is a signal-recognition particle (SRP) capable of interacting?

a signal sequence in a protein destined for the ER, an SRP receptor, a ribosome

The reactions in the pathways of glycolysis and the citric acid cycle break down glucose into smaller molecules. While we haven't covered the details of these reactions it is clear they:

are catabolic pathways.

Transmembrane proteins MUST have:

both a signal sequence and a signal-anchor sequence.

Where are ribosomes found inside a cell?

both in the cytosol and attached to the rough endoplasmic reticulum

You have entered a 5K race. As you finish the last 500 yards, your body has converted _____ energy to _____ energy with the loss of _____.

chemical potential; kinetic; heat

Which of the following reactions would you predict could be coupled to ATP synthesis from ADP + Pi? (Hint: You will need to find the delta G for ATP synthesis in units of kcal/mol, not J/mol. The textbook may help.)

creatine phosphate + H2O -> creatine + Pi, delta G -10.3 kcal/mol

The synthesis of ATP from ADP and Pi is a(n) _____ reaction with _____ ΔG.

endergonic; a positive

The process of a vesicle fusing with the plasma membrane and depositing its contents into the cytoplasmic space is referred to as:

endocytosis

The first law of thermodynamics states that:

energy cannot be created or destroyed.

The controlled release of cellular material stored in membrane-bound vesicles to the outside of the cell is an example of:

exocytosis

In cellular respiration, oxygen:

gains electrons and is an oxidizing agent.

Which of the following reactions would you predict could be coupled to ATP hydrolysis? (Hint: You will first need to find the delta G for ATP hydrolysis in units of kcal/mol, the textbook will help. Then pick the most sensible answer from the perspective of a cell.)

glutamic acid + NH3 -> glutamine, delta G +3.4 kcal/mol

Membrane phospholipids: (Hint: Look carefully at their molecular structure.)

have both polar and non-polar regions.

Suppose that three critical amino acids in a specific enzyme's active site are arginine, lysine, and histidine. Which of the following characteristics would you predict the substrate to possess to bind this enzyme's active site? (Hint: The table of amino acids in Fig. 4.2 of the textbook will help.)

hydrophilic, with a negative charge

Where is the SRP receptor located in a cell?

in the membrane of the rough endoplasmic reticulum

Which of the following has the MOST entropy, individual nucleotides or a nucleic acid?

individual nucleotides

Which eukaryotic organelle is associated with the breakdown of macromolecules?

lysosome

The chemical bonds of carbohydrates and lipids have high potential energy because:

many of these bonds are C-C and C-H bonds

Imagine you have radioactively labeled a protein in the lumen of the endoplasmic reticulum. Where would you predict the labeled protein will end up?

outside the cell in the lumen of a vesicle in the lumen of the Golgi apparatus (All of these choices are correct.)

The Golgi apparatus is responsible for at least a portion of a eukaryote's:

modification of proteins synthesized in the ER, modification of lipids synthesized in the ER, targeting of proteins to their final destinations, carbohydrate synthesis.

Spontaneous reactions have a __________ ΔG

negative

Where are lysosomal enzymes synthesized?

on the rough endoplasmic reticulum

In which of the following regions of the cell can protein synthesis occur in eukaryotes? (Select all that apply.)

rough endoplasmic reticulum Cytoplasm

In aerobic respiration, glucose is _____ to CO2 and oxygen is _____ to water.

oxidized; reduced

When a carbohydrate such as glucose is in the presence of oxygen, it has a great deal of _____ energy.

potential

Which one of the following is moved from one side of a lysosomal membrane to the other by a transport protein in the lysosomal membrane?

protons and broken-down macromolecules

A proton pump is needed in the lysosomal membrane because:

protons cannot move across a membrane on their own. the interior of the lysosome needs to be acidic. protons are being moved from low to high concentration (All of these choices are correct)

Which stage of aerobic respiration occurs immediately after pyruvate is produced? (Hint: You are going to need to know the four main stage of respiration. This is covered at the beginning of the lecture.)

pyruvate oxidation

Exergonic

releases free energy (-ΔG)

Reactions in which there is a negative change in free energy (-ΔG) are:

spontaneous and exergonic.

What is glycosylation?

the addition of sugars to lipids or proteins

Gibbs free energy is defined as:

the amount of energy available to do work.

Which of the following reactions is MOST likely to be exergonic?

the digestion of protein from food into amino acids

The second law of thermodynamics states that:

there is an increase in disorder in the universe over time.

Free Energy

ΔG

Enthalpy (chemical bond energy)

ΔH

Entropy (measure of disorder)

ΔS