Problem Set 2 (ch 7-13)

Question 1

The sequence shown below belongs to a DNA region transcribed by the RNA polymerase from a promoter on the left side to a terminator on the right side. This entire DNA segment is transcribed into RNA.

5′-AGCATGGCAATATCGTAGTA-3′

3′-TCGTACCGTTATAGCATCAT-5′

Asked what is the sequence of the RNA produced from this DNA, Jordan claims that it is:

3′-AGCATGGCAATATCGTAGTA-5′

Give two reasons why Jordan’s answer is incorrect.

Answer 1

First, the RNA molecule should have uracil instead of thymine bases. Second, the polarity of the molecule is incorrectly labeled. The correct RNA molecule produced, using the bottom strand of the DNA duplex as a template, would be:

5′-GGCAUGGCAAUAUUGUAGUA-3′

Question 2

The length of a particular gene in human DNA, measured from the start site for transcription to the end of the protein-coding region, is 5,000 nucleotides, but the length of the mRNA produced from this gene is 3,000 nucleotides. How is this possible?

Answer 2

The gene contains one or more introns.

Question 3

The following RNA sequence includes the beginning of the sequence encoding protein X. What would be the result of a mutation that changed a C (bolded and underlined below) into an A?

5′-AGGCUAUGAAUCGACACUGCGAGCCC . . .

Answer 3

The change creates a stop codon (TGA, or UGA in the mRNA) very near the beginning of the protein-coding sequence and in the correct reading frame (the beginning of the coding sequence is indicated by the ATG). Thus, the translation would terminate after only four amino acids had been joined together, and the complete protein would not be made.

Question 4

One strand of a section of DNA isolated from the bacterium E. coli reads:

5′-GTAGCCTACCCATAGG-3′

A. Suppose that an mRNA is transcribed from this DNA using the complementary strand as a template. What will be the sequence of the mRNA in this region (make sure you label the 5′ and 3′ ends of the mRNA)?

B. How many different peptides could potentially be made from this sequence of RNA, assuming that translation initiates upstream of this sequence?

C. What are these peptides? (Give your answer using the one-letter amino acid code.)

Answer 4

A. 5′-GUAGCCUACCCAUAGG-3′

B. Two. (There are three potential reading frames for each RNA. In this case, they are

GUA GCC UAC CCA UAG . . .

UAG CCU ACC CAU AGG . . .

AGC CUA CCC AUA GG? . . .

The center one cannot be used in this case, because UAG is a stop codon.)

C. VAYP; SLPIG

Note: PTHR will not be a peptide because it is preceded by a stop codon.

Question 5

In a diploid organism, the DNA encoding one of the tRNAs for the amino acid tyrosine is mutated such that the sequence of the anticodon is now 5′-CTA-3′ instead of 5′-GTA-3′. What kind of aberration in protein synthesis will this tRNA cause? Explain your answer.

Answer 5

If the DNA sequence specifying the anticodon is changed from 5′-GTA-3′ to 5′-CTA-3′, this tRNA will now pair with the 5′-UAG-3′ codon (instead of 5′ -UAC-3′). The UAG codon normally serves as a stop codon. Thus, this change will result in the amino acid tyrosine being incorrectly incorporated where there is a stop codon, resulting in the addition of amino acids at the end of proteins that normally would come to a stop because of the UAG codon in the mRNA. (Note that the tyrosine codons will NOT cause premature termination of translation, as tyrosine should continue to be incorporated into proteins, as there are additional tyrosine-tRNA genes in the cell that will provide a normal supply of tyrosine-tRNAs.)

Question 6

A neuron and a white blood cell have very different functions. For example, a neuron can receive and respond to electrical signals, while a white blood cell defends the body against infection. This is because

a. all of the proteins found in a neuron are completely different from the proteins found in a white blood cell.
b. the neuron and the white blood cell within an individual have the same genome.
c. the neuron expresses some mRNAs that the white blood cell does not.
d. neurons and white blood cells are differentiated cells and thus no longer need to transcribe and translate genes.

Answer 6

C

Different cell types express different mRNAs, leading to differences in protein expression. There are proteins common to all cells in multicellular organisms. Although it is true that the neuron and white blood cells within an individual have the same genome, this does not explain why these two cells have different functions. Differentiated cells still need to transcribe and translate genes.

Question 7

You work in a lab that studies the Ucb gene. You already know that the Ucb protein is normally produced when cells are exposed to high levels of both fructose (Fru) and maltose (Mal), two types of carbohydrates. SugX, SugY, and SugZ are proteins that bind to the promoter of the Ucb gene and regulate its transcription. SugX binds to the “X” site in the promoter region, SugY to the “Y” site, and SugZ to the “Z” site. You create binding-site mutations in the X, Y, and Z sites and measure the number of transcripts produced by the Ucb gene. Your results are summarized in the table below.

A) Which of the following proteins are likely to act as gene activators?

B) In the same scenario of the previous question, which of the following proteins are likely to act as gene repressors?

Answer 7

A) Both SugX and SugZ

B) SugY

Question 8

The figure below shows the phylogenetic tree of a family of plant species. Use the tree to answer the following questions.

A. When did species M and N share their last common ancestor and how much do their genome sequences divergence?

B. Compared to species P and S, are species M and N more or less closely related to each other?

C. If you were trying to discover nucleotide sequences with a very important function in species M, would you rather compare its genome with species N or with species Q?

Answer 8

A. M and N diverged 10 million years ago. There is an average of 2.0% nucleotide substitution in species M compared with species N (follow the path connecting the two species, which is twice the distance between each one and their common ancestor).

B. Neither more nor less. They show roughly the same degree of relatedness. The sequence divergence between species M and N is about 2.0%, the same as that between species P and S. Both pairs of species diverged 10 million years ago.

C. It is more informative to compare species that are separated by a greater evolutionary distance; thus, comparing species M and Q, which diverged 20 million years ago, will be better able to identify sequences that are likely to be important for function. Closely related species share many sequences by chance because there has been insufficient time for neutral mutations to accumulate.

Question 9

Which of the following mutations has the lowest chances of being selectively neutral?

a. A mutation that deletes 50% of a pseudogene.
b. A mutation that changes the CCC codon to the CCT codon in a protein-coding gene.
c. A mutation that changes the TCC codon to the AGT codon in a protein-coding gene.
d. A mutation that changes the TAT codon to the TAG codon in a protein-coding gene.

Answer 9

D

TAT codes for tryptophan, while TAG codes for a stop codon. This substitution is most likely to be detrimental to gene function. Although TCC and AGT look very different at the nucleotide level, both codons code for serine. Similarly, CCC and CCT will both code for proline. Pseudogenes do not make functional proteins, and thus removal of 50% of a pseudogene is likely to be neutral.

Question 10

Which of the following statements about the human genome is FALSE?

a. About 50% of the human genome is made up of mobile genetic elements.
b. More of the human genome comprises intron sequences than exon sequences.
c. About 1.5% of the human genome codes for exons.
d. Only the exons are conserved between the genomes of humans and other mammals.

Answer 10

D

About 5% of the human genome is highly conserved with other mammalian genomes, yet only about 1.5% of the human genome codes for exons.

Question 11

Consider the hypothetical protein Lng that can carry oxygen through the bloodstream. Mutation A and mutation B each cause Lng to be a very ineffective oxygen carrier, yet a Lng gene containing both mutations X and Y encodes a protein that carries oxygen even better than the original Lng protein. The chances that a single mutational event will generate both mutations X and Y are almost negligible. However, you discover an organism with a mutant Lng gene containing both mutations X and Y. Explain a simple way how that double-mutant Lng gene could have arisen during evolution.

Answer 11

The simplest way to evolve the new gene is by duplication and divergence. If the gene is duplicated, then the cell or lineage can maintain one functional, intact old copy of the original gene and can thus tolerate the disabling mutations in the other copy. The other copy can first be modified by the X or Y mutation that impairs its function; second, at some later time, the gene with the single mutation can acquire the additional mutation to yield the doubly mutant X + Y gene with the new or improved function.

Question 12

Cameron wants to amplify the DNA between the two double-stranded sequences shown in the figure below. Of the 8 primers listed below, which two primers should Cameron choose to amplify the DNA by PCR?

Answer 12

The appropriate PCR primers are primer 1 (5′-GACCTGTGGAAGC-3′) and primer 8 (5′-TCAATCCCGTATG-3′). The first primer will hybridize to the bottom strand and prime synthesis in the rightward direction. The second primer will hybridize to the top strand and prime synthesis in the leftward direction. (Remember that strands pair antiparallel.)

The middle two primers in each list (primers 2, 3, 6, and 7) would not hybridize to either strand. The remaining pair of primers (4 and 5) would hybridize, but would prime synthesis in the wrong direction—that is, outward, away from the central segment of DNA.

Question 13

How does the Cas9 system target where it produces a double-strand break in the DNA?

a. A guide RNA molecule is associated with Cas9 and will direct Cas9 to bind at sequences complementary to the guide RNA.
b. The Cas9 protein contains amino acids that can interact with specific sequences in the DNA, targeting Cas9 to those specific sites.
c. The Cas9 protein binds to a recombinase, allowing it to disable the gene of interest.
d. A guide RNA molecule associated with Cas9 provides the catalytic activity to cleave the DNA where Cas9 binds.

Answer 13

a

The guide RNA associated with Cas9 directs it to a segment of DNA with a complementary sequence. Researchers take advantage of this property by supplying an appropriate guide RNA to target Cas9 to wherever in the genome researchers may wish to make a cut to alter a gene.

Question 14

While many prokaryotic cells have a single membrane bilayer, all eukaryotic cells have a complex system of internal membrane-bound compartments. How might it be advantageous for the cell to have these additional compartments?

Answer 14

Compartmentalization using intracellular membranes allows eukaryotic cells to separate a variety of cell processes. Although this requires a higher degree of coordination, the cell also gains more control over these processes (examples include: the separation of transcription and translation; the separation of enzymes involved in protein modifications for secreted versus cytosolic substrates; the separation of proteolytic events in the lysosomes versus the cytosol; the separation of anaerobic metabolism in the cytosol and aerobic metabolism in the mitochondria).

Question 15

Explain the importance of glycolipids in the plasma membrane, identify where they are produced inside the cell, and describe the mechanism by which they are transported to the plasma membrane and presented to the extracellular environment.

Answer 15

Glycolipids are found on the surface of healthy cells and contribute to the cell’s defense against chemical damage and infectious agents. Glycolipids are produced by enzymes inside the Golgi apparatus. They are then transported to the plasma membrane through a process of vesicle budding. These secretory vesicles then fuse with the plasma membrane. The glycolipids that were facing the lumen of the Golgi apparatus will now face the extracellular environment.

Question 16

What chemical principles explain the observation that a protein-free lipid bilayer is a billion times more permeable to water than to a sodium ion?

Answer 16

Water is a small, uncharged molecule that diffuses directly across the membrane, despite needing to pass through a hydrophobic lipid core. In cells, ions pass through lipid bilayers via ion channels or transporters. Because ions carry a charge, they have strong electrostatic interactions with water molecules. There are no compensating interactions in the hydrophobic lipid core of the bilayer, which prevents ions from entering.

Question 17

True or False. If a statement is false, explain why it is false.

Facilitated diffusion can be described as the favorable movement of one solute down its concentration gradient being coupled with the unfavorable movement of a second solute up its concentration gradient.

Answer 17

False. This describes coupled transport, which is one type of active transport. Facilitated diffusion can also be called passive transport, in which a solute always moves down its concentration gradient.

Question 18

TRUE or FALSE. If a statement is false, explain why it is false.

Transporters undergo transitions between different conformations, depending on whether the substrate-binding pocket is empty or occupied.

Answer 18

True

Question 19

TRUE or FALSE. If a statement is false, explain why it is false.

The electrochemical gradient for K+ across the plasma membrane is small. Therefore, any movement of K+ from the inside to the outside of the cell is driven solely by its concentration gradient.

Answer 19

True

Question 20

TRUE or FALSE. If a statement is false, explain why it is false.

The net negative charge on the cytosolic side of the membrane enhances the rate of glucose import into the cell by a uniporter.

Answer 20

False. Glucose is an uncharged molecule, and its import is not directly affected by the voltage difference across the membrane if glucose is being transported alone. If the example given were the Na+/glucose symporter, we would have to consider the charge difference across the membrane.

Question 21

Describe the two components of an electrochemical gradient. Use your description to suggest which of the following is influenced by a larger electrochemical gradient: (1) Na+ moving into the cell; (2) K+ moving out of the cell. Explain your reasoning.

Answer 21

An electrochemical gradient is composed of two forces: the energy from the concentration gradient and the force derived from the charge differential across the membrane, referred to as the membrane potential.

There is a larger electrochemical gradient driving the movement of Na+ into the cell compared to the net force moving K+ out of the cell. In the case of Na+, the concentration gradient and the membrane potential both drive the movement of Na+ into the cell. In the case of K+, these two forces work in opposition, reducing the net magnitude of the electrochemical gradient.

Question 22

TRUE or FALSE. If a statement is false, explain why it is false.

The extracellular concentration of Ca2+ is approximately 104-fold higher than the concentration of Ca2+ in the cytosol.

Answer 22

True

Question 23

TRUE or FALSE. If a statement is false, explain why it is false.

The low cytosolic Ca2+ concentration sensitizes the cell to an influx of Ca2+, ensuring a rapid response to environmental stimuli.

Answer 23

True

Question 24

TRUE or FALSE. If a statement is false, explain why it is false.

Cytosolic Ca2+ concentration is kept low by the use of chelators such as EDTA.

Answer 24

False. Ca2+ concentrations in the cytosol are kept low by the action of ATP-driven calcium pumps in the endoplasmic reticulum membrane and the plasma membrane.

Question 25

TRUE or FALSE. If a statement is false, explain why it is false.

The primary mechanism by which Ca2+ acts as a signaling molecule is by increasing the net charge in the cytosol.

Answer 25

False. Ca2+ binds tightly to many proteins in the cell, which in turn changes their activity. This interaction is the primary mechanism by which Ca2+ signaling occurs.

Question 26

The movement of glucose into the cell, against its concentration gradient, can be powered by the co-transport of Na+ into the cell. Explain the thermodynamic factors governing this transporter. Under what conditions would transport of glucose slow or come to a halt?

Answer 26

The movement of Na+ ions from an area that has a high Na+ concentration to a new area of low Na+ concentration is energetically favorable because the net entropy in the system is increasing. As long as the difference in Na+ ion concentration across the membrane is large enough, the entropic factor will drive the import of glucose into the cell. This effect is amplified by the electrical component of the electrochemical gradient, the membrane potential, that drives Na+ in the same direction. If the magnitude of the Na+ electrochemical gradient was reduced (by reducing the membrane potential or concentration gradient) below that required to drive glucose against its concentration gradient, glucose import would cease.

Question 27

Describe the process by which gut epithelial cells use transporters to take up ingested glucose (against the concentration gradient) and to distribute glucose to other tissues by moving it back out of the cell (down the concentration gradient).

Answer 27

Gut epithelial cells use two different transporters to take glucose up from the gut and distribute it into the bloodstream and to other tissues. These transporters are located at opposite sides of the cell:

the apical side of the cell (which faces the gut) contains a Na+-glucose symporter. This symporter couples the entry of Na+ down its electrochemical gradient to the active import of glucose against its concentration gradient. The Na+-glucose symporter is restricted to the apical side of the cell by tight-junction complexes in the plasma membrane, which link neighboring epithelial cells together.

On the basolateral side of the cell, there is another transporter that facilitates the movement of glucose down its concentration gradient, out of the cell. This transporter is a uniporter that only transports glucose in one direction: from the cytosol to the extracellular matrix. The location of this uniporter is also restricted by the presence of the tight junctions so that the epithelial cell will not transport glucose back into the lumen of the gut.

Question 28

Because the Na+/K+ pump moves these ions at the same rate in opposing directions across the plasma membrane, it creates a net balance of charges on each side of the membrane (i.e., membrane potential = 0). Given this fact, explain how cells generate a membrane potential across the plasma membrane and suggest the consequences for cell functions if this capacity were handicapped.

Answer 28

The presence of K+ leak channels in the plasma membrane allows the free diffusion of K+ out of the cell. These channels create a voltage difference across the membrane (membrane potential ≠ 0). Without the “leak” capability in the membrane, the transport of glucose and other small molecules that depend on the electrochemical gradient would be reduced.

Question 29

Order and describe all the molecular events required for the propagation of an action potential. Is propagation along the axon bidirectional? Why or why not?

Answer 29

An initial event depolarizes the plasma membrane in the neuron, this change in membrane potential activates the voltage-gated Na+ channels, causing them to open. Na+ ions flood into the cytosol, locally depolarizing the membrane, which then activates resting Na+ channels further down the neuron. The action potential is only propagated in one direction because after the Na+ channels close and are inactivated, they cannot be immediately reactivated. The Na+ channels remain in this inactivated state until the membrane potential has returned to its resting negative value. The depolarized membrane returned to its resting potential by the opening of voltage-gated K+ channels (K+ flows out of the cell). These open in response to depolarization, but not as fast as the Na+ channels, and they stay open as long as the membrane remains depolarized.

Question 30

The stimulation of a motor neuron ultimately results in the release of a neurotransmitter at the synapse between the neuron and a muscle cell. How is the chemical signal converted into an electrical signal in the postsynaptic muscle cell?

Answer 30

Most neurotransmitter receptors function as ligand-gated ion channels. These ion channels open in response to the binding of a neurotransmitter. In the neuromuscular junction, the neurotransmitter acetylcholine binds to the acetylcholine receptor, which allows Na+ to enter the muscle cell, altering its membrane potential. In this way, a chemical signal (acetylcholine) is converted back into an electrical signal (change in membrane potential).

Question 31

Describe how synaptic signaling is influenced by the action of tranquilizers (such as Valium) compared to the effects of antidepressants (such as Prozac).

Answer 31

Tranquilizers bind to GABA-gated Cl- channels. They promote inhibitory signaling at the synapse. They do this by binding to GABA-gated Cl-channels, making GABA-gated channels open more easily in response to the inhibitory neurotransmitter GABA. This channel, when open, allows Cl− to flow into the neuron, making the cell more difficult to depolarize.

Antidepressants are used to enhance the neuronal signaling in neurons that have serotonin receptors. Prozac specifically blocks the reuptake of serotonin in the synaptic cleft. This results in a net increase in serotonin available for excitatory signaling to the postsynaptic neuron.

Question 32

For each of the following sentences, fill in the blank with the appropriate type of gating for the ion channel described.

1. The acetylcholine receptor in skeletal muscle cells is a/an __________ ion channel.
2. __________ ion channels are found in the hair cells of the mammalian cochlea.
3. __________ ion channels in the mimosa plant propagate the leaf-closing response.
4. __________ ion channels respond to changes in membrane potential.
5. Many receptors for neurotransmitters are __________ ion channels.

Answer 32

1. ligand-gated ion channel
2. mechanically/stress-gated ion channel
3. voltage-gated ion channel
4. voltage-gated ion channel
5. ligand-gated ion channel

Question 33

TRUE or FALSE. If a statement is false, explain why it is false.

CO₂ and H₂O are generated during the oxidation of food molecules.

Answer 33

True

Question 34

TRUE or FALSE. If a statement is false, explain why it is false.

Activated carrier molecules store heat energy for the cell to use later.

Answer 34

False. Activated carriers have high-energy bonds that can drive other reactions when broken. Heat may be released during these reactions and may increase the reaction rates, but is not a form of energy that is stored in biological systems.

Question 35

TRUE or FALSE. If a statement is false, explain why it is false.

Catabolism is a general term that refers to the processes by which large molecules are synthesized from smaller molecules.

Answer 35

False. Catabolism comprises the metabolic reactions that are involved in breaking large molecules into smaller molecules. Anabolism encompasses the reverse types of reactions: synthesizing larger molecules from smaller molecules.

Question 36

TRUE or FALSE. If a statement is false, explain why it is false.

The oxidation of sugar is an energetically favorable process.

Answer 36

True

Question 37

Although ATP and NADH are both important activated carrier molecules, ATP hydrolysis provides direct molecular energy for most biochemical reactions. Name two reasons why the mitochondria also need to generate high levels of NADH.

Answer 37

NADH is an activated carrier molecule used as a cofactor for many enzymes that catalyze redox reactions. NADH also donates electrons to the electron-transport chain, which is essential for the production of ATP.

Question 38

Compare and contrast the catabolism of carbohydrates, proteins, and fats. Specifically, highlight the similarities and differences in how they are broken down (extracellular, and intracellular) for conversion into acetyl-CoA, the entry point into the citric acid cycle.

Answer 38

The breakdown of all carbohydrates, proteins, and fats into smaller subunits occurs first in the stomach and small intestines.

Stage 1

• Carbohydrates are converted into simple sugars.
• Proteins are broken down into amino acids.
• Fats are cleaved into glycerol and fatty acid chains.

Once inside the cell, each of the simpler subunits is broken down further to produce 2-carbon acetyl groups joined to coenzyme A (via its SH group) to become acetyl CoA, which is a direct substrate for oxidation in the citric acid cycle.

Stage 2

• Glucose must be converted to pyruvate for transport into the mitochondrial matrix. This happens in the cytosol during a process called glycolysis, which produces two pyruvate molecules per glucose.
  
  • Two pyruvate molecules are transported into the mitochondrial matrix and converted into acetyl CoA.
• Both amino acids and fatty acids are transported directly into the mitochondrial matrix for conversion to acetyl CoA.
  
  • Amino acids require a deamination step prior to combination with coenzyme A.
  • Fatty acids are combined directly with coenzyme A, before undergoing a series of stepwise oxidation reactions that convert the entire fatty acid chain to the 2-carbon segments in acetyl CoA.

Question 39

Glycolysis and the citric acid cycle comprise two different sets of oxidation reactions. The reaction sequence for glycolysis is linear, whereas the reaction sequence for the citric acid cycle forms a circle. How does this difference in the arrangement of reactions influence the rate of these processes when an excess amount of a single intermediate is added?

Answer 39

Primarily, what is seen is that the citric acid cycle occurs more rapidly after the addition of any one of the intermediates. This means that if one intermediate is added, levels of all of them increase. In glycolysis, the intermediates downstream of the intermediate being added will be affected.

Question 40

Do you expect the cell to produce more ATP from one glucose molecule or from one fatty acid molecule? Explain your answer.

Answer 40

More ATP is produced from fat catabolism than from glucose catabolism. Most ATP is generated in the mitochondria, and the amount depends on the production of the NADH and FADH2 cofactors in the Krebs cycle. The Krebs cycle relies on the input of acetyl CoA. Each glucose molecule can be converted into two acetyl CoA molecules. A molecule of fat will have three fatty acid chains, with an average length of 12–16 carbons. Even if we assume very short fatty acid chains of six carbons each (the length of a glucose molecule), this would mean the production of three acetyl CoA molecules per chain, and nine total for the triacylglycerol.

Question 41

TRUE or FALSE. If a statement is false, explain why it is false.

The proteins of the electron-transport chain remove a pair of high-energy electrons from the cofactors NADH and FADH2, after which the electrons move across the inner mitochondrial membrane to maintain the voltage gradient.

Answer 41

False. Although the proteins of the electron-transport chain collect electrons from the NADH and FADH2 cofactors, these high-energy electrons go through a series of transfers along the electron-transport chain. The energy released with each transfer moves protons across the inner mitochondrial membrane. It is this proton gradient that provides the energy to synthesize ATP.

Question 42

Gluconeogenesis is a linear reaction pathway that the cell employs to generate glucose from pyruvate and is exactly the reverse of the reactions in the glycolytic pathway.

Answer 42

False. Gluconeogenesis can begin with pyruvate as a building block to make glucose, but there are three reactions in glycolysis that are irreversible because of a large free-energy barrier. Alternative enzymes and reaction pathways are used to bypass this problem, and they require the input of energy in the form of ATP and GTP.

Question 43

With respect to the amount of energy stored in molecules of the body, 6 g of glycogen is the equivalent of 1 g of fat.

Answer 43

True

Question 44

Glycogen phosphorylase cleaves glucose monomers from the glycogen polymer, phosphorylating them at the same time so that they can be fed unchanged into the glycolytic pathway.

Answer 44

False. When glycogen phosphorylase cleaves a glucose monomer from glycogen, the product is glucose 1-phosphate. Before it can be used in glycolysis, it needs to be isomerized to glucose 6-phosphate.

Question 45

Living systems run on a glucose economy even though the metabolism of fatty acids is a more efficient catabolic process. Explain this observation and suggest why no-carb diets are ill-advised.

Answer 45

Unlike glucose, fatty acids are transported directly into the mitochondrial matrix and readily converted into acetyl CoA molecules. A simple condensation reaction shortens the fatty acid by two carbons and generates acetyl CoA, NADH, and FADH2 in each reaction cycle.

There are multiple consequences of using lipids as your only energy source:

1. Several critical organs preferentially store or use glucose. Skeletal muscles store glycogen, the brain does not store energy, and it needs glucose. Without glucose in your system, you will feel weakness, fatigue, and dizziness.
2. There will be an accumulation of excess of free fatty acids in the absence of glucose, and this excess is broken down into ketones. Ketones in the bloodstream cause acidification of the blood. Ketoacidosis can be induced by extremely low-carb diets, lack of insulin in diabetic patients, or the consumption of extreme levels of alcohol without other sources of energy.

Question 46

Where do the following processes take place?

1. glycolysis
2. citric acid cycle
3. conversion of pyruvate to activated acetyl groups
4. oxidation of fatty acids to acetyl CoA
5. glycogen breakdown
6. release of fatty acids from triacylglycerols
7. oxidative phosphorylation

Answer 46

1. cytosol
2. mitochondrial matrix
3. mitochondrial matrix
4. mitochondrial matrix
5. cytosol
6. cytosol
7. inner mitochondrial membrane