Bonus Questions
What is the gene that can lead to cancer if mutated? What causes a cell to become cancerous? What gene encodes proteins to inhibit cell division? What is a growth factor?
1. A normal gene that, if mutated, can lead to cancer is called a proto-oncogene. 2. A gene that causes a cell to become cancerous is called a(n) ocogene 3. A(n) tumor-suppressor gene is a gene that encodes proteins that inhibit cell division. Such proteins normally help prevent cells from becoming cancerous. 4. A(n) growth factor is a protein that promotes cell division. In excess, such a protein may lead to cancer.
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1. An enzyme is denatured when it loses its native conformation and its biological activity. 2. An enzyme is considered a catalyst because it speeds up chemical reactions without being used molecule. 3. An enzyme is specific because of its ability to recognize the shape of a particular complex. 4.A cofactor, such as a vitamin, binds to an enzyme and plays a role in catalysis. 5. When properly aligned, the enzyme and substrate form an enzyme-substrate (ES) 6. A substrate binds to an enzyme at the active site, where the reaction occurs. 7. In a catalyzed reaction a reactant is often called a substrate
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1. When a compound donates (loses) electrons, that compound becomes oxidized. Such a compound is often referred to as an electron donor. 2. When a compound accepts (gains) electrons, that compound becomes reduced. Such a compound is often referred to as an electron acceptor. 3. In glycolysis, the carbon-containing compound that functions as the electron donor is glucose 4. Once the electron donor in glycolysis gives up its electrons, it is oxidized to a compound called pyruvate 5. NAD+ is the compound that functions as the electron acceptor in glycolysis. 6. The reduced form of the electron acceptor in glycolysis is NADH . V Correct In the net reaction for glycolysis, glucose (the electron donor) is oxidized to pyruvate. The electrons removed from glucose are transferred to the electron acceptor, NAD+, creating NADH.
Which equation summarizes photosynthesis?
6 CO2 + 6 H20 + (energy) --> C6H12O6 + 6 O2
After transcription begins, several steps must be completed before the fully processed mRNA is ready to be used as a template for protein synthesis on the ribosomes. Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus? (3)
A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA. Correct Once RNA polymerase II is bound to the promoter region of a gene, transcription of the template strand begins. As transcription proceeds, three key steps occur on the RNA transcript: • Early in transcription, when the growing transcript is about 20 to 40 nucleotides long, a modified guanine nucleotide is added to the 5' end of the transcript, creating a 5' cap. • Introns are spliced out of the RNA transcript by spliceosomes, and the exons are joined together, producing a continuous coding region. • A poly-A tail (between 50 and 250 adenine nucleotides) is added to the 3' end of the RNA transcript. Only after all these steps have taken place is the mRNA complete and capable of exiting the nucleus. Once in the cytoplasm, the mRNA can participate in translation.
The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water is an example of what?
A catabolic pathway
What is a molecule that specifically binds to another molecule (often a larger one)?
A ligand
What is the process of RNA _____?
A modified guanine Segments of the RNA Segments of the RNA Extra adenine The completed nucleotide is added to strand that do not that do code for the nucleotides are added messenger RNA the beginning of the actually code for the protein are to the end of the RNA (mRNA) leaves the RNA strand as a cap. protein are removed. reconnected. strand, forming a tail. nucleus.
What happens during transcription?
A molecule of RNA is formed based on the sequence of nucleotides in DNA. Correct During transcription, RNA nucleotides line up with their complementary DNA partners, transcribing the information in DNA into RNA.
Suppose that a cell's demand for ATP suddenly exceeds its supply of ATP from cellular respiration. Which statement correctly describes how this increased demand would lead to an increased rate of ATP production?
ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production. Correct An increased demand for ATP by a cell will cause an initial decrease in the level of cellular ATP. Lower ATP decreases the inhibition of the PFK enzyme, thus increasing the rate of glycolysis, cellular respiration, and ATP production. It is the initial decrease in ATP levels that leads to an increase in ATP production.
What enters the citric acid cycle?
Acetyl CoA Correct Acetyl CoA is a reactant in the citric acid cycle
What is NOT a product of the citric acid cycle?
Acetyl CoA Correct, Acetyl CoA ENTERS the citric acid cycle
Which of the following enzymes converts ATP to cAMP?
Adenylyl cyclase Correct Adenylyl cyclase converts ATP to cAMP, which helps CAP bind and facilitates binding of RNA polymerase to the lac promoter.
What is the role of the three different RNAs?
All attempts used; correct answer displayed. Cells contain many ribosomes; therefore, the most abundant type of RNA is the RNA that makes up the ribosomes. The cell uses three different types of RNAs to build proteins. rRNA is part of the ribosome, which is the site of protein synthesis. mRNA carries the genetic information from the DNA; the information specifies the sequence of amino acids in the new protein. tRNA interprets the information from the mRNA and brings the appropriate amino acids to the ribosome.
Which noncoding RNAs are correctly matched with their function?
All of the above. Dicer protein acts as an enzyme that works during RNA interference. Piwi-associated RNAs (piRNAs) reestablish appropriate methylation patterns in the genome during gamete formation. MicroRNAs (miRNAs) bind to complementary sequences in mRNA and block its translation. Small interfering RNAs (siRNAs) bind to complementary sequences in mRNA and block its translation. All of the above
What are polypeptides assembled from?
Amino acids Correct Proteins are composed of amino acid monomers
A protein kinase activating many other protein kinases is an example of what?
Amplification Correct By activating many other molecules the initial signal is amplified
If a mutated DNA sequence produces a protein that differs in one central amino acid from the normal protein, which of the following kinds of mutations could have occurred?
An addition mutation and a deletion mutation. Correct If the mutations occur within the same codon, only that codon (amino acid) will be altered.
Which of the following statements about mutations is false?
An addition mutation results in an added base in the DNA sequence. A knock-out mutation results in a total absence of the mutated protein. Addition and deletion mutations disrupt the primary structure of proteins. A deletion mutation results in the loss of a base in the DNA sequence. Correct A knock-out mutation refers to the loss of a protein's function but not necessarily to its complete absence.
Which of the following statements best defines the term operon?
An operon is a region of DNA that codes for a series of functionally related genes under the control of the same promoter. Correct This arrangement of genes is common in bacteria. For example, genes involved in lactose metabolism are clustered in the lac operon of E. coli, and genes involved in tryptophan metabolism are in the trp operon.
What type of DNA mutations is likely to be damaging to the protein it specifies?
Base-pair deletion
Which of the following is the first event to take place in translation in eukaryotes?
Binding of the larger ribosomal subunit to smaller ribosomal subunits
How would anaerobic conditions (when no 02 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation? (Note that you should not consider the effect on ATP synthesis in glycolysis or the citric acid cycle.)
Both electron transport and ATP synthesis would stop. Correct Oxygen plays an essential role in cellular respiration because it is the final electron acceptor for the entire process. Without 02, mitochondria are unable to oxidize the NADH and FADH2 produced in the first three steps of cellular respiration, and thus cannot make any ATP via oxidative phosphorylation. In addition, without 02 the mitochondria cannot oxidize the NADH and FADH2 back to NAD+ and FAD, which are needed as inputs to the first three stages of cellular respiration.
What role does a transcription factor play in a signal transduction pathway?
By binding to DNA it triggers the transcription of a specific gene A signal transduction pathway is initiated when a signal molecule binds to a receptor The binding of a signal molecule to a receptor initiates a signal transduction pathway
Where are calcium ions stored?
Calcium ions that act as second messengers are stored in the endoplasmic reticula
What is the term for metabolic pathways that release stored energy by breaking down complex molecules?
Catabolic pathways
Catabolism is to anabolism as ____ is to _____?
Catabolism is to anabolism as exergonic is to endergonic
What is Apoptosis?
Controlled cell suicide
A signal molecule is also known as what?
Correct A ligand is a signal molecule.
Where does a substrate bind?
Correct A substrate binds at an enzyme's active site; the enzyme typically recognizes the specific shape of its substrate. A cofactor, such as an inorganic ion or vitamin, may bind to the enzyme and assist in catalyzing the reaction. The reaction environment must be appropriate for catalysis to proceed. An enzyme will denature, or change its shape and lose its biological activity, at too high a temperature or at a pH outside the enzyme's optimal range.
The light reactions of photosynthesis use water and produce NADP+
Correct NADPH is a reactant in the Calvin Cycle
What does nearly every mRNA gene coding for a protein begin with?
Correct Nearly every mRNA gene that codes for a protein begins with the start codon, AUG, and thus begins with a methionine. Nearly every protein-coding sequence ends with one of the three stop codons (UAA, UAG, and UGA), which do not code for amino acids but signal the end of translation.
A signal transduction pathway is initiated when what?.
Correct The binding of a signal molecule to a receptor initiates a signal transduction pathway.
Are animal and yeast cells similar?
Correct Yeast and mammal cells, for example, are very distantly related yet share many similarities in cell signalling.
What molecule can act as a second messenger?
Cyclic AMP can act as second messengers
Which one of the following does not play a role in translation?
DNA Correct DNA contains the instructions for making proteins, but these instructions are transcribed to RNA before translation occurs
The flow of information in a cell proceeds in what sequence?
DNA to RNA to protein
If a DNA sequence is altered from TAGCTGA to TAGTGA, what kind of mutation has occurred?
Deletion Correct The original sequence has lost the base C
Why are there often so many steps between the original signal event and the cell's response?
Each step in a cascade produces a large number of activated products, causing singal amplification as the cascade progresses Correct this amplification permits the signalling molecule to have a widespread effect throughout the cell
Which one of the following is true of tRNAs?
Each tRNA binds a particular amino acid Correct Aminoacyl-tRNA synthetase joins a specific amino acid to a tRNA, a single strand of RNA about 80 nucleotides long.
What is the process of how food molecules reaches the body's cells and fuel cellular respiration?
Eating food provides fuel and building blocks for your body After food is broken down in the digestive system, it is transported to cells via the circulatory system Fuel molecules are broken down further in glycolysis and the critic acid cycle (Also called the Krebs cycle) ATP is produced with the help of the electron transport chain
What does the citric acid cycle transfer?
Electrons to NADH and FADH2
True or false? A codon is a group of three bases that can specify more than one amino acid?
False Correct A codon is a group of three bases that can specify only one amino acid
True or false? The mechanism by which glucose inhibits expression of the lac structural genes is known as catabolite stimulation, whereas the mechanism by which lactose stimulates expression of the lac structural genes is known as allosteric regulation.
False Correct The process by which lactose binds to the lac repressor and inactivates it by causing it to change shape is known as allosteric regulation. However, the process by which glucose causes cAMP levels in the cell to drop, thereby preventing CAP from stimulating expression of the lac structural genes, is known as catabolite repression.
NADH and FADH2 are both electron carriers that donate their electrons to the electron transport chain. The electrons ultimately reduce 02 to water in the final step of electron transport. However, the amount of ATP made by electrons from an NADH molecule is greater than the amount made by electrons from an FADH2 molecule. Which statement best explains why more ATP is made per molecule of NADH than per molecule of FADH2?
Fewer protons are pumped across the inner mitochondria] membrane when FADH2 is the electron donor than when NADH is the electron donor. Correct Electrons derived from the oxidation of FADH2 enter the electron transport chain at Complex II, farther down the chain than electrons from NADH (which enter at Complex I). This results in fewer H+ ions being pumped across the membrane for FADH2 compared to NADH, as this diagram shows. Thus, more ATP can be produced per NADH than FADH2.
In the combined processes of glycolysis and cellular respiration, what is consumed and what is produced?
Glucose is consumed, and carbon dioxide is produced. Correct The carbon in glucose is oxidized to carbon dioxide during cellular respiration.
During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell's demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions. What would happen to the cell's rate of glucose utilization?
Glucose utilization would increase a lot. Correct ATP made during fermentation comes from glycolysis, which produces a net of only 2 ATP per glucose molecule. In contrast, aerobic cellular respiration produces about 30 ATP per glucose molecule. To meet the same ATP demand under anaerobic conditions as under aerobic conditions, a cell's rate of glycolysis and glucose utilization must increase about 15-fold.
Which metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule?
Glycolysis
What is allosteric regulation?
In allosteric regulation, a small molecule binds to a large protein and causes it to change its shape and activity. Correct Allosteric regulation is an important mechanism for changing enzyme activity, as well as for changing the function of some gene repressors and activators.
Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. Which of these statements is the correct explanation for this observation?
In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration. Correct NAD+ couples oxidative phosphorylation to acetyl CoA formation. The NAD+ needed to oxidize pyruvate to acetyl CoA is produced during electron transport. Without 02, electron transport stops, and the oxidation of pyruvate to acetyl CoA also stops because of the lack of NAD+.
Enzymes are described as catalysts, which means that the what?
Increase the rate of a reaction without being consumed by the reaction This permits enzyme molecules to be used repeatedly
Lipid-soluble signalling molecules, such as testosterone, cross the membranes of all cells but affect only target cells because why?
Intracellular receptors are present only in target cells
What is the effect of a nonsense mutation in a gene?
It introduces a premature stop codon into the mRNA
In the oxidation of pyruvate to acetyl CoA, one carbon atom is released as CO2. However, the oxidation of the remaining two carbon atoms—in acetate—to CO2 requires a complex, eight-step pathway—the citric acid cycle. Consider Correct sible explanations for why the last two carbons in acetate are converted to CO2 in a complex cyclic pathway rather than through a simple, linear reaction. Use your knowledge of the first three stages of cellular respiration to determine which explanation is correct.
It is easier to remove electrons and produce CO2 from compounds with three or more carbon atoms than from a two-carbon compound such as acetyl CoA. Correct Although it is possible to oxidize the two-carbon acetyl group of acetyl CoA to two molecules of CO2, it is much more difficult than adding the acetyl group to a four-carbon acid to form a six-carbon acid (citrate). Citrate can then be oxidized sequentially to release two molecules of CO2.
Which of the following describes the process of glycolysis?
It represents the first stage in the chemical oxidation of glucose by a cell. Correct Catabolism of glucose begins with glycolysis.
What is the function of RNA polymerase?
It unwinds the double helix and adds nucleotides to a growing strand of RNA. Correct RNA polymerase has several functions in transcription, including unwinding the DNA double helix and adding RNA nucleotides.
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Keep in mind that steroid receptors are usually found in the cytoplasm. Does cortisol bind to a receptor on the outside of the cell? Cortisol is a small, hydrophobic steroid hormone that can pass through the plasma membrane of cells. In target cells, cortisol binds to the intracellular receptor protein in the cytoplasm, forming a hormone-receptor complex. The hormone-receptor complex then moves into the nucleus and acts as a transcription factor, binding to specific genes and activating their transcription into mRNA. The mRNA that is produced is eventually translated into specific proteins. Proteins produced in response to the cortisol signal function in the stress response. For example, some of these proteins aid in elevating glucose levels in the blood, helping an animal to meet the demands of starvation or intense physical activity. Both G protein-coupled receptors and receptor tyrosine kinases are transmembrane receptors that have a binding domain located on the extracellular side of the plasma membrane. The binding of a signaling molecule to these receptors is the first step in a signaling pathway. However, what happens after a signaling molecule binds is different for each receptor. An activated G protein-coupled receptor activates a G protein inside the cell, which involves the release of GDP and the binding of GTP. The activated G protein then activates an associated enzyme, leading to a cellular response. Receptor tyrosine kinases form dimers after binding signaling molecules. The tyrosines are then phosphorylated, fully activating the receptor. Each phosphorylated tyrosine can bind a relay protein, each of which can trigger a transduction pathway. In this way, a single signaling-molecule binding event can trigger multiple signal transduction pathways and thus multiple cellular responses. Keep in mind that the binding site of a G protein-coupled receptor is located outside the cell. When histamine encounters a target cell, it binds extracellularly to the H1 receptor, causing a change in the shape of the receptor. This change in shape allows the G protein to bind to the H1 receptor, causing a GTP molecule to displace a GDP molecule and activating the G protein. The active G protein dissociates from the H1 receptor and binds to the enzyme phospholipase C, activating it. The active phospholipase C triggers a cellular response. The G protein then functions as a GTPase and hydrolyzes the GTP to GDP. The G protein dissociates from the enzyme and is inactive again and ready for reuse. Receptor proteins (located in the plasma membrane or inside the cell) bind signaling molecules. The reception of the signal causes a shape change in the receptor molecule, to which other molecules inside the cell respond. The message is then relayed through signal transduction, which may involve a phosphorylation cascade or second messengers such as cAMP, Ca2+, or IP3. Possible responses to the signal may include synthesis of a particular protein or regulation of a particular enzyme. After the reception of the histamine signaling molecule, the active G protein activates the enzyme phospholipase C. Phospholipase C cleaves PIP2 into DAG and IP3. IP3 diffuses through the cytosol and binds to an IP3-gated calcium channel in the ER membrane, causing it to open. As a result, Ca2+ ions flow out of the ER and into the cytosol. The increase in the calcium ion concentration in the cytosol helps activate the cellular response. Signal transduction pathways that involve phosphorylation cascades or multiple second messengers, such as histamine's signal transduction pathway, enable a signal to be amplified and regulated at different points. Similarly, multistep pathways can facilitate the coordination of cellular responses to multiple signals. When histamine binds to a histamine receptor, the specific cellular response that results is determined by the following factors: • the type of histamine receptor • the type of cell in which the receptor is located • the enzyme that is activated by the G protein associated with the receptor • the types of second messengers involved in the signal transduction pathway • the proteins activated by the second messengers Signaling molecules can trigger a multitude of cellular responses, which may ultimately affect the transcription of genes, the activity of proteins, or cell growth and division.
What are scaffolding proteins?
Large molecules to which several relay proteins attach to facilitate cascade effects
Which set of reaction uses water and produces oxygen?
Light-dependent reactions Correct The light-dependent reactions uses water and produce oxygen
Apoptosis involves all but which of the following?
Lysis of the cell
What is the overall function of the Calvin cycle?
Making sugar Correct Using the ATP and NADPH made during the light reactions, carbon is reduced in the Calvin cycle and sugar is made
During translation, nucleotide base triplets (codons) in mRNA are read in sequence in the 5' —* 3' direction along the mRNA. Amino acids are specified by the string of codons. What amino acid sequence does the following mRNA nucleotide sequence specify? 5' — AUGGCAAGAAAA — 3' Express the sequence of amino acids using the three-letter abbreviations, separated by hyphens
Met-Ala-Arg-Lys Correct An amino acid sequence is determined by strings of three-letter codons on the mRNA, each of which codes for a specific amino acid or a stop signal. The mRNA is translated in a 5' —* 3' direction.
What amino acid sequence does the following DNA nucleotide sequence specify? 3' - TACAGAACGGTA - 5' Express the sequence of amino acids using the three-letter abbreviations, separated by hyphens (e.g., Met-Ser-His-Lys-Gly).
Met-Ser-Cys-His correct answer displayed Before mRNA can be translated into an amino acid sequence, the mRNA must first be synthesized from DNA through transcription. Base pairing in mRNA synthesis follows slightly different rules than in DNA synthesis: uracil (U) replaces thymine (T) in pairing with adenine (A). The codons specified by the mRNA are then translated into a string of amino acids.
Which of the following is true of metabolism in its entirety in all organisms?
Metabolism consists of all the energy transformation reactions in an organism.
IN addition to ATP, what are the end products of glycolysis?
NADH and pyruvate
Which of the following molecules is the primary product of photosystem I?
NADPH Correct The NADPH produced by photosystem I is used to supply energy for the production of sugars during photosynthesis.
Under which conditions are the lac structural genes expressed most efficiently?
No glucose, high lactose Correct When glucose is absent and lactose levels are high, the lac structural genes are expressed the most efficiently. Without glucose, cAMP is produced and CAP can stimulate transcription of the structural genes. In the presence of lactose, the repressor does not bind to the operator and therefore does not block transcription.
Which mutation(s) would not change the remainder of the reading frame of a gene sequence that follows the mutation(s)?
One addition and one deletion mutation. Correct This combination results in no net change in the number of bases, so the reading frame would eventually be restored.
What occurs during the breakdown of glucose?
One of the substrates is a molecule derived from the breakdown of glucose. A bond must be broken between an organic molecule and phosphate before ATP can form. An enzyme is required in order for the reaction to occur
What is the final electron acceptor of cellular respiration?
Oxygen
Which of the following statements is most likely to be true in the case of the feedback-regulated enzymatic pathway shown?
P4 binds E1 and deactivates it Correct Many enzymatic pathways are regulated by the feedback inhibition model described here. In fact, it is so common that another name for it is end-product inhibition.
What does Phospholipase C do?
Phospholipase C catalyzes the production of IP3, which then opens an ion channel that release Ca2+ into the cell's cytoplasm Correct Phospholipase C Cleaves IP3 from a membrane protein, and IP3 then binds to a calcium channel on the ER
What process produces oxygen? Photosynthesis or cellular respiration?
Photosynthesis Correct Oxygen is a by-product of the photosynthetic process
Why is the Calvin cycle important for plants?
Plants are autotrophs, and the Calvin cycle produces a simple sugar. Correct Plants are autotrophs: they create their own organic molecule, such as sugars. The Calvin cycle produces a simple sugar that the plant cell can use either to produce ATP, or to build larger storage polysaccharides for later use.
Enzyme complexes that break down protein are called what?
Proteasomes Correct Proteasomes are enzyme complexes that break down proteins
Protein-phosphorylating enzymes' role in the regulation of gene expression involves what?
Protein activation Correct Proteins are often activated by phosphorylation.
Proto-oncogenes can change into oncogenes that cause cancer. Which of the following best explains the presence of these potential time bombs in eukaryotic cells?
Proto-oncogenes normally help regulate cell division.
Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?
Pyruvate, ATP and NADH Correct ATP is the main product of cellular respiration that contains energy that can be used by other cellular processes. Some ATP is made in glycolysis. In addition, the NADH and pyruvate produced in glycolysis are used in subsequent steps of cellular respiration to make even more ATP.
What happens during the process of transcription?
RNA is synthesized
What molecule binds to promoters in bacteria and transcribes the coding regions of the genes?
RNA polymerase Correct RNA polymerase is the enzyme that binds to promoters and transcribes the coding regions of genes into RNA.
What is the function of a spliceosome?
RNA processing
What name is given to the process in which pre-mRNA is edited into mRNA?
RNA processing Correct RNA processing edits the RNA transcript that has bene assembled along a DNA template
What is an example of post-transcriptional control of gene expression?
Removal of introns and alternative splicing of exons
The site of translation is where?
Ribosomes in the cell cytoplasm
Which molecule is regenerated in the regeneration phase of the Calvin cycle? Without regeneration of this molecule, the Calvin cycle would stop.
RuBP Correct the regeneration of RuBP ensures that the Calvin cycle can proceed indefinitely, since RuBP fixes carbon dioxide into an organic molecule that is used to produce sugar
Transcription in eukaryotes requires which of the following in addition to RNA polymerase?
Several transcription factors (TFs)
What has to happen before transcription can begin in Eukaryotic cells?
Several transcription factors have to be bound to the promoter
In the citric acid cycle, ATP molecules are produced by what?
Substrate-level phosphorylation A phosphate group is transferred from GTP to ADP
What is the primary function of the Calvin cycle?
Synthesize simple sugars from CO2
When fan the Calvin cycle take place?
The Calvin cycle can take place in darkness, as ATP and NADPH produced during light reactions drive the Calvin cycle. Correct During light reactions, the obtained energy from photons is captured into two energy currency molecules, ATP and NADPH. Then ATP and NADPH are used in the Calvin cycle to produce a simple sugar. The Calvin cycle does not require photons from sunlight, but requires ATP and NADPH.
In cellular respiration, a series of molecules forming an electron transport chain alternately accepts and then donates electrons. What is the advantage of such an electron transport chain?
The advantage of an electron transport chain is that a small amount of energy is released with the transfer of an electron between each pair of intermediates. Correct As the electrons "fall" down the electron transport chain, the energy released is used to actively transport protons into the inner-membrane space. This way the energy is used effectively, and not lost in the process.
What initiates a signal transduction pathway?
The attachment of a signal molecule to a plasma membrane receptor initiates a signal transduction pathway
The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Increasing the substrate concentration reduces the inhibitory effects of this compound. Which of the following could account for this observation?
The compound is a competitive inhibitor. Correct A competitive inhibitor slows down the enzyme by competing with the substrate for binding at the active site. Increasing substrate concentrations will reduce the effectiveness of a competitive inhibitor.
Which of the following statements about ATP (adenosine triphosphate) is correct?
The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways. Correct Catabolic pathways provide the energy needed to make ATP from ADP and Pi. The hydrolysis of ATP to ADP + Pi releases the same amount of energy.
Where does glycolysis occur?
The cytosol
Where does glycolysis take place in eukaryotic cells?
The cytosol
Which of the following statements about the role of ATP in cell metabolism is true?
The energy from the hydrolysis of ATP may be directly coupled to endergonic processes by the transfer of the phosphate group to another molecule. Correct A key feature in the way cells manage their energy resources to do work is energy coupling, the use of an exergonic process to drive an endergonic one. Often the phosphate group released is bound to another molecule in phosphorylation during energy coupling.
Which of the following statements best describes the relationship between the light-dependent and light-independent reactions of photosynthesis?
The light-dependent reactions produce ATP and NADPH, which are then used by the light-independent reactions. Correct Light energy drives the formation of ATP and NADPH during the light-dependent reactions; these energy molecules are then used during the light-independent reactions to form sugars.
What is the importance of the light-independent reactions in terms of carbon flow in the biosphere?
The light-independent reactions turn CO2, a gas, into usable carbon in the form of sugars. Correct CO2 is unusable until plants have "fixed" this carbon into sugar.
What accomplishes the main coupling among the stages of cellular respiration?
The main coupling among the stages of cellular respiration is accomplished by NAD+ and NADH. In the first three stages, NAD+ accepts electrons from the oxidation of glucose, pyruvate, and acetyl CoA. The NADH produced in these redox reactions then gets oxidized during oxidative phosphorylation, regenerating the NAD+ needed for the earlier stages.
Which of the following provides molecular evidence that signal transduction pathways evolved early in the history of life?
The molecular details of cell signalling are quite similar in organisms whose last common ancestor was a billion years ago.
How is translation initiated?
The small ribosomal subunit binds to the mRNA. The tRNA bearing methionine binds to the start codon. The large ribosomal subunit binds to the small one. The start codon signals the start of translation. All of the above. Correct All of these processes occur at the initiation of translation.
Why can a signalling molecule cause different responses in different cells?
The transduction process is unique to each cell type; to respond to a signal, different cells require only a similar membrane receptor. Correct The signal simply initiates a process by activating a membrane receptor. How transduction proceeds can be quite different for different cells.
What are the key principles in predicting the sequence of the mRNA chain?
There are three principles to keep in mind when predicting the sequence of the mRNA produced by transcription of a particular DNA sequence. 1. The RNA polymerase reads the sequence of DNA bases from only one of the two strands of DNA: the template strand. 2. The RNA polymerase reads the code from the template strand in the 3' to 5' direction and thus produces the mRNA strand in the 5' to 3' direction. 3. In RNA, the base uracil (U) replaces the DNA base thymine (T). Thus the base-pairing rules in transcription are A—U, T - A, C—G, and G—C, where the first base is the coding base in the template strand of the DNA and the second base is the base that is added to the growing mRNA strand.
What happens to the expression of the lacl gene if lactose is not available in the cell?
There is no change—the lacl gene is constitutively expressed. Correct The lacl gene is expressed regardless of the presence of lactose. Only the structural genes of the lac operon are affected by the presence or absence of lactose.
What is the biological significance of the light-independent reactions of photosynthesis?
They convert carbon dioxide to sugar. Correct All organisms use the sugars produced by photosynthesis to generate energy.
What name is given to the process in which a strand of DNA is used as a template for the manufacture of a strand of pre-mRNA?
Transcription Correct Transcription is the process by which a DNA template is used for the manufacture of several different types of RNA
Which of these is the second of the three stages of cell signaling?
Transduction is the second of the three stages of cell signaling
What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?
Translation Correct Translation is the process by which information encoded in RNA is used to manufacture a polypeptide
True or False? The light-dependent reactions of photosynthesis use water and produce oxygen?
True Correct The water molecules are split to replenish electrons in photosystem II, leaving behind protons, which are used to generate a proton gradient for the formation of ATP, and oxygen, which is released as a by-product
If the sequence ATGCATGTCAATTGA were mutated such that a base were inserted after the first G and the third T were deleted, how many amino acids would be changed in the mutant protein?
Two Correct The second and third codons in the new sequence are different from the original codons.
Why is the lac operon said to be an inducible operon?
When allolactose is present, it induces the inactivation of the lac repressor. The lac repressor keeps the production of lactose-digesting enzymes turned off. When allolactose is present, the lac repressor is inactivated, allowing the expression of lactose-digesting enzymes.
Which of the following would be most likely to lead to cancer?
amplification of a proto-oncogene and inactivation of a tumour-suppressor gene Correct Excess copies of the proto-oncogene could stimulate cell division abnormally, and the inactivation of a tumour-suppressor gene would eliminate a brake on cell division.
To what does the term "ligand" refer in cell biology?
any small molecule that can bind in a specific manner to a larger one Correct Ligands are the small signalling molecules that bind specifically to corresponding protein-receptor molecules.
miRNAs can control gene expression by what action?
binding to mRNAs and degrading them or blocking their translation Correct miRNAs can effectively "silence" genes by binding to mRNA transcripts. The mRNAs are either broken down by enzymes or are unable to physically interact with the ribosomes to complete translation.
What would occur if the repressor of an inducible operon were mutated so it could not bind the operator?
continuous transcription of the operon's genes
Which of the following mutations would likely be most dangerous to a cell?
deletion of one nucleotide Correct Deletion of one nucleotide would shift the reading frame, altering the coding for all subsequent amino acids. In most cases, this would destroy the function of the protein produced from this gene.
What is the function of tyrosine kinase receptors?
enzymatic phosphorylation of tyrosine in the receptor protein Correct Phosphorylated tyrosine kinase receptors then interact with relay proteins within the cell.
Apoptosis involves all but which of the following?
lysis of the cell digestion of cellular contents by scavenger cells fragmentation of the DNA cell-signalling pathways
RNA processing converts the RNA transcript into what?
mRNA Correct the editing of the RNA transcript produces mRNA
Which of the following does not occur during RNA processing?
mRNA attaches to the small subunit of a ribosome. Correct mRNA attaches to the small subunit of a ribosome at the beginning of translation.
Where does mRNA move from?
mRNA moves from the nucleus to the cytoplasm following RNA processing. Correct mRNA undergoes RNA processing in the nucleus and then moves to the cytoplasm for translation.
What three reactions occur during the light reactions in photosynthesis?
oxidation of water, reduction of NADP+, formation of ATP Correct The three components of the light reaction are oxidation of water, reduction of NADP+, and the synthesis of ATP from ADP and phosphate.
Photosynthesis is a redox reaction. This means that H2O is what during the light reactions and CO2 is what during the Calvin cycle.
oxidized...reduced Correct During the light reactions of photosynthesis, water is oxidized, and during the Calvin cycle, carbon is reduced.
The nuclear membrane's role in the regulation of gene expression involves what?
regulating the transport of mRNA to the cytoplasm
Where does the Calvin cycle occur?
stroma
For any given gene, what ultimately determines which DNA strand serves as the template strand?
the base sequence of the gene's promoter Correct In eukaryotes, binding of RNA polymerase II to DNA involves several other proteins known as transcription factors. Many of these transcription factors bind to the DNA in the promoter region (shown below in green), located at the 3' end of the sequence on the template strand. Although some transcription factors bind to both strands of the DNA, others bind specifically to only one of the strands. Transcription factors do not bind randomly to the DNA. Information about where each transcription factor binds originates in the base sequence to which each transcription factor binds. The positioning of the transcription factors in the promoter region determines how the RNA polymerase II binds to the DNA and in which direction transcription will occur.
Where do apoptic signals come from?
the nucleus, the ER, Ligand binding, Mitochondrial protein leakage, all of the above
In mitochondrial electron transport, what is the direct role of 02?
to function as the final electron acceptor in the electron transport chain Correct The only place that 02 participates in cellular respiration is at the end of the electron transport chain, as the final electron acceptor. Oxygen's high affinity for electrons ensures its success in this role. Its contributions to driving electron transport, forming a proton gradient, and synthesizing ATP are all indirect effects of its role as the terminal electron acceptor.
The functioning of enhancers is an example of what?
transcriptional control of gene expression.
Rank these by reaction rate, as measured by the rate of product formation per unit time, from lowest reaction rate to highest reaction rate. To rank items as equivalent, overlap them.
uncatalyzed reaction reaction catalyzed by enzyme A reaction catalyzed by enzyme B Correct Enzymes lower the activation energy of a chemical reaction. This means that a catalyzed reaction is more likely to proceed than an uncatalyzed reaction, and it forms products more rapidly than an uncatalyzed reaction.
Which part of the adenosine triphosphate molecule is released when it is hydrolyzed to provide energy for biological reactions?
y-phosphate (the terminal phosphate) Correct The y-phosphate is the primary phosphate group on the ATP molecule that is hydrolyzed when energy is needed to drive anabolic reactions. Located the farthest from the ribose sugar, it has a higher energy than either the alpha or beta-phosphate.
Stage of cellular respiration - Location Glycolysis, Acetly CoA formation, Citric Acid Cycle, Oxidative phosphorylation
- Glycolysis - cytosol - Acetyl CoA formation - mitochondrial matrix - Citric acid cycle - mitochondrial matrix - Oxidative phosphorylation - inner mitochondrial membrane All attempts used; correct answer displayed You labeled 2 of 4 targets incorrectly. Remember that acetyl CoA is formed from pyruvate, which is actively transported from the cytosol into the mitochondrion. The enzymes that carry out the conversion of pyruvate to acetyl CoA are located in the mitochondrial matrix. Cellular respiration begins with glycolysis in the cytosol. Pyruvate, the product of glycolysis, then enters the mitochondrial matrix, crossing both the outer and inner membranes. Both acetyl CoA formation and the citric acid cycle take place in the matrix. The NADH and FADH2 produced during the first three stages release their electrons to the electron transport chain of oxidative phosphorylation at the inner mitochondrial membrane. The inner membrane provides the barrier that creates an H+ gradient during electron transport, which is used for ATP synthesis.
Drag each compound to the appropriate bin. If the compound is not involved in Citric Acid Cycle, drag it to the "not input or output" bin.
- Net input o ADP, Acetyl CoA, NAD+ - Net output o NADH, CO2, Coenzyme A, ATP - Neither o Oxygen (O2), Glucose, Pyruvate
Drag each compound to the appropriate bin. If the compound is not involved in glycolysis, drag it to the "not input or output" bin.
- Net input o Glucose, ADP, NAD+ - Net output o Pyruvate, ATP, NADH - Neither o Oxygen, CO2, Acetyl CoA, Coenzyme A All attempts used; correct answer displayed You sorted 4 out of 10 items incorrectly. In cellular respiration, all of the carbon that enters in glucose is eventually oxidized to CO2. However, in glycolysis, the six-carbon sugar glucose is converted to two molecules of pyruvate, a three-carbon acid. Is there any production of CO2 in glycolysis? In glycolysis, the six-carbon sugar glucose is converted to two molecules of pyruvate (three carbons each), with the net production of 2 ATP and 2 NADH per glucose molecule. There is no 02 uptake or CO2 release in glycolysis.
Drag each compound to the appropriate bin. If a compound is not involved in oxidative phosphorylation, drag it to the "not input or output" bin.
- Net input o NADH, ADP, Oxygen - Net output o ATP, NAD+, H20 - Neither o Glucose, pyruvate, CO2, Acetyl CoA, Coenzyme A Correct In oxidative phosphorylation, the NADH and FADH2 produced by the first three stages of cellular respiration are oxidized in the electron transport chain, reducing 02 to water and recycling NAD+ and FAD back to the first three stages of cellular respiration. The electron transport reactions supply the energy to drive most of a cell's ATP production.
Drag each compound to the appropriate bin. If the compound is not involved in Acetyl CoA formation, drag it to the "not input or output" bin.
- Net input o Pyruvate, Coenzyme A, NAD+ - Net output o NADH, CO2, Acetyl CoA - Neither o Oxygen (O2), ATP, ADP, Glucose
What is ATP role?
- This molecule fuels many different endergonic (energy-requiring) enzymatic processes in biological organisms. ATP molecules diffuse or are transported to the place where the energy is needed and deliver chemical energy from the breaking of their phosphate bonds. Adenosine triphosphate (ATP) is the high-energy form of adenosine because it contains the most phosphate groups (three).
