Why are ribonucleotide triphosphates, rather than ribonucleotides (which have one phosphate group), the monomers required for RNA synthesis in cells?
Ribonucleotide triphosphates have high potential energy, making the polymerization reaction exergonic.
David Pribnow studied the base sequences of promoters in bacteria and bacterial viruses. He found two conserved regions in these promoters (the -10 box and the -35 box). What is the function of these two regions of the promoter?
They bind the sigma subunit that is associated with RNA polymerase.
How are RNA hairpin turns related to termination?
The turns are formed from complementary base pairing and cause separation of the RNA transcript and RNA polymerase.
Which molecule or reaction supplies the energy for polymerization of nucleotides in the process of transcription?
the phosphate bonds in the nucleotide triphosphates that serve as substrates
For any given gene, what ultimately determines which DNA strand serves as the template strand?
the base sequence of the gene's promoter
Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus?
A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA. A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA. Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes.
During RNA processing a(n) _____ is added to the 3' end of the RNA.
a long string of adenine nucleotides
Which statement is correct concerning the function(s) of the 5' cap and the 3' poly(A) tail of eukaryotic mRNAs?
Both structures serve as recognition signals for the translational machinery and extend the life span of the mRNA.
5' caps and 3' poly(A) tails of eukaryotic mRNAs _____.
protect mRNA from degradation and enhance translation
A primary transcript in the nucleus of a eukaryotic cell is _____ the functional mRNA, while a primary transcript in a prokaryotic cell is _____ the functional mRNA.
larger than; the same size as
The mRNA is smaller than the length of the DNA that codes for it because _____.
post-transcriptional modification removes the introns
Death cap mushrooms produce a substance called alpha-amanitin. Alpha-amanitin efficiently blocks synthesis of mRNA, but not of tRNA or rRNA in eukaryotic organisms. How is that possible?
Alpha-amanitin efficiently interferes with the action of RNA polymerase II, but not RNA polymerase I or III.
Codons are three-base sequences that specify the addition of a single amino acid. How do eukaryotic codons and prokaryotic codons compare?
Codons are a nearly universal language among all organisms.
Which of the following occurs in prokaryotes, but not eukaryotes?
concurrent transcription and translation
Which of the following tRNA anticodons could decode the mRNA codon CAG (recall that codons are always written in the 5'→3' direction and anticodons are written in the 3'→5' direction)?
GUU or GUC. Non-standard ("wobble") base pairs between tRNA and mRNA (including G-U) are allowed at the third position of the codon.
What is recognized by an aminoacyl tRNA synthetase?
one amino acid and the set of tRNAs that is coupled to that amino acid
Refer to the figure. What is the function of the AGU on the loop of the tRNA?
It base pairs with the codon of mRNA.
If the DNA code for a particular amino acid is AGT, then the anticodon on the tRNA would be _____.
Which of the following steps occurs last in the initiation phase of translation?
The large ribosomal subunit joins the complex.
True or false. A tRNA with an anticodon complementary to the stop codon catalyzes the reaction by which translation is terminated.
During elongation, which site in the ribosome represents the location where a codon is being read?
Which of the following is not one of the steps in initiation of translation?
formation of a polypeptide bond
What could be the consequence of a mutation that changes the sequence of nucleotides in a promoter?
a change in when the corresponding gene is transcribed
When one molecule gains an electron from another, the molecule that received the electron has been _____.
How do allosteric regulation and competitive inhibition compare?
Competitive inhibition involves binding of a regulatory molecule to the active site; in allosteric regulation a regulatory molecule binds to a different location
What molecule is produced in the citric acid cycle as a by-product of glucose oxidation and is subsequently released into the bloodstream and carried to the lungs, where it is removed from the body?
Why is ATP production during cellular respiration characterized as indirect?
ATP is not produced directly by the ETC but instead via the proton gradient generated during electron transport through the ETC.
What job does the electron transport chain accomplish in order to drive the formation of ATP?
The proteins in the electron transport chain pump protons from the matrix of the mitochondria to the intermembrane space, thus establishing an electrochemical gradient.
Which answer best explains why organisms that have an ETC as well as fermentation pathways almost never ferment pyruvate if the electron acceptor required by the ETC is available?
Fermentation is extremely inefficient in terms of the number of ATP molecules produced for each molecule of glucose metabolized.
What purpose does fermentation serve?
It regenerates NAD+ from NADH to keep glycolysis going in the absence of oxygen.
These molecules are added to glucose and fructose 6-phosphate in the beginning steps of glycolysis.
The functional element of a cytochrome that is thought to bind loosely but directly to an electron
This process occurs when an electron acceptor is not present for the electron transport chain
This non-cytochrome molecule plays a key role in transferring excited electrons in the light reactions of photosynthesis.
This molecule is transported into the lumen of the thylakoids as part of the light reactions of photosynthesis.
This was the compound that could first be detected when radtioactive CO2 was added to algea
The molecules that absorb only certain wavelengths of light energy from the Sun in order to begin the photosynthetic reactions are called _____.
During photosynthesis, the light energy from the Sun is captured and stored in the bonds of _____.
Why does a leaf appear green when a person looks at it?
The chlorophyll pigments absorb all wavelengths of light except in the green spectrum, which it reflects.
When a photon of light is absorbed by a pigment molecule, electrons in the molecule _____.
enter an excited state
When a photon of light is absorbed by a pigment molecule, electrons in the molecule _____.
In both systems, ATP is produced by chemiosmosis.
According to the Z scheme, what is the path of electrons through photosystem I (PS I) and photosystem II (PS II)?
PS II → pheophytin → plastoquinone → cytochrome complex → plastocyanin → PS I → ferredoxin
Both photosystem I and photosystem II employ the use of a(n) _____, which drives the formation of ATP and NADPH.
electron transport train
During the Calvin cycle, carbon dioxide is _____, in order to drive the formation of sugars.
Plant leaves contain openings called _____, which allow the diffusion of carbon dioxide into the leaf tissue.
The most abundant enzyme on Earth, which catalyzes the fixation of carbon dioxide in photosynthesis, is _____.
Which answer best explains why it is accurate to call the Calvin cycle a "cycle"?
It regenerates a substrate of the first reaction.
Referring to a chemical reaction that can occur spontaneously, releasing heat and/or increasing entropy, and for which the Gibbs free-energy change (DG) < 0.
What is energy coupling?
the use of energy released from an exergonic reaction to drive an endergonic reaction
Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other?
anion & cation
Which of the following statements is true of the bonds in a water molecule?
Oxygen holds electrons more tightly than hydrogen does, and the net charge is zero.
A cell has enough available ATP to meet its needs for about 30 seconds. What is likely to happen when an athlete exhausts his or her ATP supply?
Catabolic processes are activated that generate more ATP.
Two ATP molecules are expended in the energy investment phase of glycolysis. Why is this energy needed to begin the process of glucose catabolism?
Some energy must be invested to make the glucose molecule unstable and begin the process of catabolism.
Canine phosphofructokinase (PFK) deficiency afflicts springer spaniels, affecting an estimated 10% of the breed. PFK is the glycolytic enzyme that phosphorylates fructose-1-phosphate and catalyzes the committed step in glycolysis. Given its critical role in glycolysis, one implication of the genetic defect resulting in PFK deficiency in dogs is _____.
an intolerance for exercise
Substrate-level phosphorylation occurs within a metabolic pathway where sufficient energy is released by a given chemical reaction to drive the synthesis of ATP from ADP and phosphate. In which of the following metabolic pathways is substrate-level phosphorylation exhibited?
in both glycolysis and the Krebs cycle
The reactions of pyruvate processing, the citric acid cycle, and the electron transport chain occur within the _____ in the cell.
Why is the citric acid cycle a cyclic pathway rather than a linear pathway?
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.
Following glycolysis and the Krebs cycle, but before the electron transport chain and oxidative phosphorylation, the carbon skeleton of glucose has been broken down to CO2 with some net gain of ATP. Most of the energy from the original glucose molecule at that point in the process, however, is in the form of _____.
In mitochondrial electron transport, what is the direct role of O2?
to function as the final electron acceptor in the electron transport chain
How would anaerobic conditions (when no O2 is present) affect the rate of electron transport and ATP production during oxidative phosphorylation?
Both electron transport and ATP synthesis would stop.
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.
C6H12O6 (glucose) + 6 O2 → 6 CO2 + 6 H2O
Where is most of the water in this reaction produced?
in the electron transport chain
The energy of electron transport serves to move (translocate) protons to the outer mitochondrial compartment. How does this help the mitochondrion to produce energy?
The translocation of protons sets up the electrochemical gradient that drives ATP synthesis in the mitochondria.
The inner mitochondrial membrane normally _____.
is virtually impermeable to hydrogen ions (protons)
Fatty acids usually have an even number of carbons in their structures. They are catabolized by a process called beta-oxidation. The end products of the metabolic pathway are acetyl groups of acetyl CoA molecules. What is the most likely fate of the acetyl groups?
They directly enter the Krebs cycle.
True or false? The potential energy in an ATP molecule is derived mainly from its three phosphate groups.
Which process is not part of the cellular respiration pathway that produces large amounts of ATP in a cell?
Into which molecule are all the carbon atoms in glucose ultimately incorporated during cellular respiration?
Which of the following statements about the electron transport chain is true?
NADH and FADH2 donate their electrons to the chain.
True or false? The reactions that generate the largest amounts of ATP during cellular respiration take place in the mitochondria.
The proteins of the electron transport chain active in the light-dependent reactions _____.
are membrane proteins present in the thylakoid
Which of the following is a difference between chlorophyll a and chlorophyll b?
Chlorophyll a and b absorb light energy at slightly different wavelengths.
Why are there several structurally different pigments in the reaction centers of photosystems?
This setup enables the plant to absorb light energy of a variety of wavelengths.
If pigments from a particular species of plant are extracted and subjected to paper chromatography, which of the following is the most believable result?
Paper chromatography would separate the pigments from a particular plant into several bands.
The absorption spectrum of a plant shows what wavelengths of light the plant absorbs. The absorption spectrum depends on _____.
the wavelengths of light to which the plant's pigments respond
What is the process called that converts the genetic information stored in DNA to an RNA copy?
Transcription begins at a promoter. What is a promoter?
A site in DNA that recruits the RNA Polymerase