Aerobic respiration is the major process used by oxygen- requiring organisms to generate energy. During respiration, glucose is metabolized to generate chemical energy in the form of ATP:C6H12O6 + 6O2 6CO2 + 6H2O + 36ATPThe biochemical machinery necessary for cellular respiration is found in the mitochondria, small organelles scattered throughout the cytoplasm of most eukaryotic cells. The number of mitochondria per cell varies by tissue type and cell function.Mitochondria are unusual in that they have their own genetic systems that are entirely separate from the cell's genetic material. However, mitochondrial replication is still dependent upon the cell's nuclear DNA to encode essential proteins required for replication. Despite this fact, mitochondria seem to replicate randomly, out of phase with both the cell cycle and other mitochondria.The nature of the mitochondrial genome and protein synthesizing machinery has led many researchers to postulate that mitochondria may have arisen as the result of the ingestion of a bacterium by a primitive cell millions of years ago. It is postulated that the two may have entered into a symbiotic relationship and eventually became dependent on each another; the cell sustained the bacterium, while the bacterium provided energy for the cell. Gradually, the two evolved into the present-day eukaryotic cell, with the mitochondrion retaining some of its own DNA. This is known as the endosymbiotic hypothesis. Because mitochondrial DNA is inherited in a non-Mendelian fashion (mitochondria are inherited from the maternal parent, who supplies most of the cytoplasm to the fertilized egg), it has been used to look at evolutionary relationships among different organisms.In which of the following phases of the cell cycle could mitochondrial DNA replicate?I). G1II). SIII). G2IV. M
Answer(s): D
In the passage you're told that mitochondria replicate in a seemingly random pattern out of phase with both other mitochondria and the cell itself. And remember that mitochondrial DNA must replicate in order for the mitochondrion itself to replicate. So basically, it can be inferred that mitochondrial DNA replicates throughout all of the phases of the cell cycle: G1, S, G2, and M. So, choice D is correct. During the G1 phase, the cell undergoes intense biochemical activity. During the S phase, or synthesis phase, the nuclear DNA replicates.During the G2 phase, the nuclear DNA condenses and the structures used during mitosis begin to assemble.During the M phase, or mitotic phase, mitosis occurs. Finally, the nuclear DNA segregates to opposite poles of the cell, the replicated organelles, mitochondria included, also segregate, along with the nuclear DNA, and the cell divides, forming two identical daughter cells.
Aerobic respiration is the major process used by oxygen- requiring organisms to generate energy. During respiration, glucose is metabolized to generate chemical energy in the form of ATP:C6H12O6 + 6O2 6CO2 + 6H2O + 36ATPThe biochemical machinery necessary for cellular respiration is found in the mitochondria, small organelles scattered throughout the cytoplasm of most eukaryotic cells. The number of mitochondria per cell varies by tissue type and cell function.Mitochondria are unusual in that they have their own genetic systems that are entirely separate from the cell's genetic material. However, mitochondrial replication is still dependent upon the cell's nuclear DNA to encode essential proteins required for replication. Despite this fact, mitochondria seem to replicate randomly, out of phase with both the cell cycle and other mitochondria.The nature of the mitochondrial genome and protein synthesizing machinery has led many researchers to postulate that mitochondria may have arisen as the result of the ingestion of a bacterium by a primitive cell millions of years ago. It is postulated that the two may have entered into a symbiotic relationship and eventually became dependent on each another; the cell sustained the bacterium, while the bacterium provided energy for the cell. Gradually, the two evolved into the present-day eukaryotic cell, with the mitochondrion retaining some of its own DNA. This is known as the endosymbiotic hypothesis. Because mitochondrial DNA is inherited in a non-Mendelian fashion (mitochondria are inherited from the maternal parent, who supplies most of the cytoplasm to the fertilized egg), it has been used to look at evolutionary relationships among different organisms.Scientists have demonstrated that human mitochondrial DNA mutates at a fairly slow rate. Because mitochondria play such an important role in the cell, these mutations are most likely to be:
Answer(s): A
This question tests your knowledge of the things that can go wrong during the replication of mitochondrial DNA, or any DNA for that matter, and the consequences. In addition, you've got to apply this knowledge to the role that mitochondria play in the cell. Mitochondria are responsible for cellular energy production they supply the cell with ATP. Mitochondrial DNA directs the synthesis of mitochondrial proteins, which ultimately play a major role in cell survival. Since mitochondria are so essential to eukaryotic cell life, one would therefore expect replication of its DNA to be highly accurate. Mutations that would cause a dramatic change in its DNA and its ability to produce proteins needed for ATP formation would be lethal to the cell. Since mutations do occur, the most likely type to occur would be one that causes the least damage. A point mutation fits the bill. Point mutations are defined as those in which only nitrogenous base is affected; for example, a cytosine is substituted for an adenine during replication. Point mutations are not usually lethal because of the redundancy of the genetic code; that is, each amino acid is typically coded for by more than one codon. Take the amino acid proline, for example. Proline is coded for by four codons: CCU, CCC, CCA, and CCG. Let's say that the codon is CCU; if there's a point mutation at the third base, no matter which of the remaining three bases is substituted for the uracil, the net product will still be proline. So a point mutation is the type of mutation least likely to affect their productivity. Thus, choice A is correct.Choice B, frameshift mutation, is a mutation causing genetic material to be inserted or deleted during DNA replication or transcription. This produces a shift in the reading frame of the mRNA strand being translated, usually leading to the formation of nonsense polypetides. Changes in protein synthesis would most likely be dangerous for the mitochondria and the cell itself; therefore, choice B is incorrect. Lethal mutations, choice C, are those that would cause the mitochondria to become nonfunctional, so choice C is incorrect. Choice D is incorrect because nondisjunction is the failure of homologous chromosomes to separate during meiosis. First of all, mitochondria have one circular chromosome there aren't any homologous chromosomes. Second, mitochrondria do not undergo meiosis only specialized eukaryotic cells in sexually reproducing organisms undergo meiosis. So, choice D cannot even be a consideration.
Aerobic respiration is the major process used by oxygen- requiring organisms to generate energy. During respiration, glucose is metabolized to generate chemical energy in the form of ATP:C6H12O6 + 6O2 6CO2 + 6H2O + 36ATPThe biochemical machinery necessary for cellular respiration is found in the mitochondria, small organelles scattered throughout the cytoplasm of most eukaryotic cells. The number of mitochondria per cell varies by tissue type and cell function.Mitochondria are unusual in that they have their own genetic systems that are entirely separate from the cell's genetic material. However, mitochondrial replication is still dependent upon the cell's nuclear DNA to encode essential proteins required for replication. Despite this fact, mitochondria seem to replicate randomly, out of phase with both the cell cycle and other mitochondria.The nature of the mitochondrial genome and protein synthesizing machinery has led many researchers to postulate that mitochondria may have arisen as the result of the ingestion of a bacterium by a primitive cell millions of years ago. It is postulated that the two may have entered into a symbiotic relationship and eventually became dependent on each another; the cell sustained the bacterium, while the bacterium provided energy for the cell. Gradually, the two evolved into the present-day eukaryotic cell, with the mitochondrion retaining some of its own DNA. This is known as the endosymbiotic hypothesis. Because mitochondrial DNA is inherited in a non-Mendelian fashion (mitochondria are inherited from the maternal parent, who supplies most of the cytoplasm to the fertilized egg), it has been used to look at evolutionary relationships among different organisms.Which of the following mitochondrial genome characteristics differs most from the characteristics of the nuclear genome?
To answer this question, you are supposed to pick the characteristic of the mitochondrial genome that differs most from characteristics of the nuclear genome. Now since you probably don't know a lot of information about the mitochondrial genome, and there is little information about it in the passage, let's approach this problem from a slightly different perspective. You do know a lot about the characteristics of the nuclear genome from your introductory biology class. So let's look over the answer choices and find the one that is not a characteristic of the nuclear genome; and this will be our right answer. The nuclear genome is comprised of double-helical DNA that codes for mRNA, tRNA, and rRNA. Therefore, choices A and B are characteristics of the nuclear genome and are therefore incorrect. If a mutation occurred in the nuclear genome that rendered an essential gene non-functional, such as an enzyme involved in glycolysis, the organism would die. Thus, choice C is also a characteristic of the nuclear genome and an incorrect choice. Although the nuclear genome encodes many products, most of the bases of DNA are NON-CODING. That is, they are involved in the regulation of gene expression and do not themselves code for any product. Therefore, choice D is not consistent with the nuclear genome, so choice D is the correct answer. The mitochondrial genome is so small, compared to that of the nucleus, that almost every nitrogen base has to code for a product, the mitochondrial genome doesn't have any DNA to waste!
Aerobic respiration is the major process used by oxygen- requiring organisms to generate energy. During respiration, glucose is metabolized to generate chemical energy in the form of ATP:C6H12O6 + 6O2 6CO2 + 6H2O + 36ATPThe biochemical machinery necessary for cellular respiration is found in the mitochondria, small organelles scattered throughout the cytoplasm of most eukaryotic cells. The number of mitochondria per cell varies by tissue type and cell function.Mitochondria are unusual in that they have their own genetic systems that are entirely separate from the cell's genetic material. However, mitochondrial replication is still dependent upon the cell's nuclear DNA to encode essential proteins required for replication. Despite this fact, mitochondria seem to replicate randomly, out of phase with both the cell cycle and other mitochondria.The nature of the mitochondrial genome and protein synthesizing machinery has led many researchers to postulate that mitochondria may have arisen as the result of the ingestion of a bacterium by a primitive cell millions of years ago. It is postulated that the two may have entered into a symbiotic relationship and eventually became dependent on each another; the cell sustained the bacterium, while the bacterium provided energy for the cell. Gradually, the two evolved into the present-day eukaryotic cell, with the mitochondrion retaining some of its own DNA. This is known as the endosymbiotic hypothesis. Because mitochondrial DNA is inherited in a non-Mendelian fashion (mitochondria are inherited from the maternal parent, who supplies most of the cytoplasm to the fertilized egg), it has been used to look at evolutionary relationships among different organisms.What is the net number of ATP molecules synthesized by an obligate anaerobe per molecule of glucose?
Again, this is one of those straight knowledge questions that doesn't really have anything to do with the passage per se. Yes, it's a related topic, but you won't find out the answer by reading the passage. To answer this question, you must know how many ATP are formed from the catabolism of one molecule of glucose by an obligate anaerobe. An obligate anaerobe is an organism that must live WITHOUT oxygen in order to survive.Obligate anaerobes produce ATP via fermentation, which includes both glycolysis and the reactions necessary to regenerate the NAD+ necessary for glycolysis to continue. Fermentation leads to a net production of 2 ATP; this ATP is generated during glycolysis. Therefore, an obligate anaerobe will produce 2 ATP per molecule of glucose. Aerobic organisms produce a net of 36 ATP, choice D, per molecule of glucose, as shown in the equation provided in the passage. So, choice D is wrong
Aerobic respiration is the major process used by oxygen- requiring organisms to generate energy. During respiration, glucose is metabolized to generate chemical energy in the form of ATP:C6H12O6 + 6O2 6CO2 + 6H2O + 36ATPThe biochemical machinery necessary for cellular respiration is found in the mitochondria, small organelles scattered throughout the cytoplasm of most eukaryotic cells. The number of mitochondria per cell varies by tissue type and cell function.Mitochondria are unusual in that they have their own genetic systems that are entirely separate from the cell's genetic material. However, mitochondrial replication is still dependent upon the cell's nuclear DNA to encode essential proteins required for replication. Despite this fact, mitochondria seem to replicate randomly, out of phase with both the cell cycle and other mitochondria.The nature of the mitochondrial genome and protein synthesizing machinery has led many researchers to postulate that mitochondria may have arisen as the result of the ingestion of a bacterium by a primitive cell millions of years ago. It is postulated that the two may have entered into a symbiotic relationship and eventually became dependent on each another; the cell sustained the bacterium, while the bacterium provided energy for the cell. Gradually, the two evolved into the present-day eukaryotic cell, with the mitochondrion retaining some of its own DNA. This is known as the endosymbiotic hypothesis. Because mitochondrial DNA is inherited in a non-Mendelian fashion (mitochondria are inherited from the maternal parent, who supplies most of the cytoplasm to the fertilized egg), it has been used to look at evolutionary relationships among different organisms.A mating type of a wild-type strain of the algae C. reinhardii is crossed with the opposite mating type of a mutant strain of the algae, which has lost all mitochondrial functions due to deletions in their mitochondrial genome. All of the offspring from this cross also lack mitochondrial functions. Based on information in the passage, this can best be explained by the:
Answer(s): B
In this question you are presented with a cross between two strains of the algae C. reinhardiI). You do not need to know anything about this species of algae to answer the question. From the question stem you know that the mating type of a wild-type strain, which has normal mitochondrial DNA, is crossed with the opposite mating type of a strain that lacks functional mitochondria due to deletions in the mitochondrial genome. This whole thing about "mating types" is another way of saying male and female in species that do not technically have opposite genders, such as algae and yeast. In addition, you're told that the offspring of this cross do not have functional mito- chondria either. What does this mean? Somehow the offspring have the same deleted mitochondrial genome as the mutant strain. Now all you have to do is find the choice that best accounts for this occurrence.Choice A is incorrect because the endosymbiotic theory attempts to explain the derivation of mitochondria in eukaryotic cells, not the inheritance of mitochondriA. Choice B is correct. Since you're told that the offspring lack mitochondrial functions, this implies that they inherited their mitochondria from the mutant strain mating type. In other words, the mutant strain was the organelle-donating parent the female in this cross.Therefore, the non-Mendelian inheritance pattern of mitochondria, as explained in the passage, best accounts for these experimental observations. If the mating type of the wild-type strain had been the organelle-donating parent, then all of the offspring would have normal mitochondrial function. Choice C is wrong because the word recombination implies the formation of new gene combinations due to crossing over events that occur during reproduction. If recombinations did occur, you would expect some of the offspring to regain mitochondrial functions since wild-type mitochondrial DNA would replace the deleted segments of DNA in some offspring.Although choice D is a true statement, it does not explain the inheritance patterns observed in this cross, thus choice D is incorrect.
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