Bio Midterm Two
How do "reducing agents" work?
"Reducing agents" act by donating electrons to another substance, causing the charge on that substance to be reduced.
What is the first part the process of the most common pathway for the large amount of ATP that is made during aerobic respiration of food?
1. During glycolysis and the citric acid cycle most of the energy from food that is not used to produce heat is used to make NADH (and FADH2).
What is the second part the process of the most common pathway for the large amount of ATP that is made during aerobic respiration of food?
2. During the electron transport part of oxidative phosphorylation, energy from NADH (and FADH2) is used to generate proton gradient across the inner membrane of the mitochondria (in eukaryotic cells).
How many different amino acids could be specified if codons were four nucleotides in length?
256 codons could be formed (4 x 4 x 4 x 4).
What is the third part the process of the most common pathway for the large amount of ATP that is made during aerobic respiration of food?
3. During the chemiosmotic part of oxidative phosphorylation energy from the proton gradient is used to combine ADP and inorganic phosphate to form ATP.
How many different codons can be formed?
64 codons can be formed.
What kind of cells are very likely to become cancerous?
A cell with a mutation that causes increased expression of a proto-oncogene and mutations in several tumor-suppressor genes that cause decreased expression of those genes.
The group of three nucleotides that specifies an amino acid is a what?
A codon.
What does accurate translation require?
A correct match between a tRNA and an amino acid by an aminoacyl tRNA synthetase AND a correct match between the tRNA anticodon and the mRNA codon.
What shape are double-stranded DNA molecules in the shape of?
A double helix.
What is meant by regulation gene expression?
A gene that is producing its product (protein or non-coding RNA) in a functional form is said to be "expressed", and so is a gene that produces high levels of its product (protein or non-coding RNA) in a functional form - genes may be regulated (controlled) so that they are more or less highly expressed.
What would not be considered a gene that is being expressed?
A gene that is producing mRNA, but no protein. Due to the fact that the final product of a gene that encodes an mRNA is a protein, a gene that is producing mRNA but no protein is not considered to be expressed.
Which of the following shows the correct base pairing of deoxyribonucleotides that occurs in nature?
A is paired with T.
A lack of which molecule would result in the cell's inability to "turn off" genes?
A lack of the corepressor.
What is the way that aerobic cellular respiration generates a small amount of ATP?
A little ATP is made relatively directly by a phosphate group being transferred from a phosphorylated pathway intermediate to ADP during glycolysis and the citric acid cycle.
What type of mutation, resulting in an error in the mRNA just after the AUG start of translation, is likely to have the most serious effect on the polypeptide product?
A mutation that includes the deletion of two nucleotides.
What happens in the process known as "substrate-level phosphorylation"?
A phosphate group is transferred from a substrate molecule to ADP.
During photosynthesis, what is energy from light first captured by?
A pigment molecule in a light harvesting complex.
What could be a possible result of a mutation that inactivated the regulatory (repressor) gene of a repressible operon in an E. coli cell?
A possible result is continuous transcription of the structural gene controlled by that regulator.
What is a promoter in an operon?
A promoter is the DNA sequence to which RNA polymerase binds to begin transcription of the transcribed part of the gene.
Why are most cancers more frequent among older people?
A single mutation is usually not sufficient for cancer to develop. Cancer cells typically have at least one oncogene and several mutated tumor-suppressor genes. Because mutations are acquired slowly over time, the cells of younger people are less likely to have acquired enough mutations for their cells to become cancerous.
What occurs during initiation of translation?
A small ribosomal subunit binds with mRNA and a special initiator tRNA (which has the amino acid methionine attached to it). The small subunit moves along the mRNA molecule until it reaches the start codon, the large ribosomal subunit becomes part of the complex and binding of the initiator and the tRNA takes place so that the initiator tRNA is in the P site of the large ribosomal unit. The anticodon of the initiator tRNA hydrogen bonds with the start codon of the mRNA.
What is formed during the citric acid cycle?
A steep proton gradient forms during the electron transport phase of oxidative phosphorylation.
What are nucleotides composed of?
A sugar, a phosphate group, and a nitrogenous base.
The light reactions of photosynthesis supply the Calvin cycle with what?
ATP and NADPH.
Which nitrogenous bases are considered complementary of each other?
Adenine and Thymine (or Uracil for RNA) and Guanine and Cytosine.
What happens when proteins recognize the specific DNA sequences (at the very beginning of DNA replication).
After recognizing the specific DNA sequences the proteins bind to the origins of replication, causing the DNA strands to separate and form replication "bubbles" in the double-stranded DNA molecule - some proteins unwind the DNA double helix and others bind the stretches. As part of the double-stranded DNA is unwound it causes the rest of the DNA molecule to be wound even tighter, straining the DNA molecule. (particular proteins partially unwind the DNA strands by breaking them, and then rejoining the ends of the broken strand).
What happens after carbon fixation?
After the carbon fixation process the fixed carbon is then reduced by the addition of electrons from NADPH formed during the light reactions and energy to drive the process is provided by ATP that was formed during the light reactions.
What happens when the primases bind to single-stranded DNA near a replication fork?
After this happens a primase takes a ribonucleotide and helps it hydrogen bond to one of the deoxyribonucleotides in the single stranded DNA to which the primase is bound.
High levels of citric acid inhibit the enzyme phosphofructokinase, a key enzyme in glycolysis. Citric acid binds to the enzyme at a different location from the active site. What is this an example of?
Allosteric regulation.
A single gene is known to code for three different, but related, proteins. What could cause this?
Alternative RNA splicing.
What occurs during the elongation phase of translation?
Amino acids are added, one by one, to the preceding amino acid.
Most repressor proteins are allosteric. What binds with the repressor to alter its conformation?
An inducer binds with the repressor.
Flies with mutant bicoid genes develop posterior structures at both ends. The bicoid gene product is normally localized to the anterior end of the embryo. If large amounts of the product were injected into the posterior end of a normal (i.e. unmutated) fly embryo, which of the following would occur?
Anterior structures would form in both sides of the embryo.
Where does DNA replication begin?
At special sites on the parental double-stranded DNA molecule, known as origins of replication, that have specific DNA sequences.
During translation, where do the charged tRNAs enter the ribosome?
At the A (amino acyl) site.
Why is photosynthesis so important?
Because most life on earth is dependent on photosynthesis. Photosynthesis also converts solar (light) energy into chemical energy.
Which of the following shows the correct base pairing of deoxyribonucleotides that occurs in nature?
C with G.
Which of the protein complexes labeled with Roman numerals will transfer electrons to O2?
Complex IV.
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 would occur.
What are three very important aspects of regulating gene expression?
Controlling the rate at which primary mRNAs are modified, controlling the rate at which mRNAs leave the nucleus, and controlling protein stability.
Is DNA a polymer or monomer?
DNA is a polymer, and nucleotides are the monomers that are linked together by covalent bonds to form a DNA polymer.
What are some possible chromatin modifications?
DNA may be modified to make nearby DNA less accessible to the transcription machinery, histones may be modified to make nearby DNA less accessible to the transcription machinery, and histones may be modified to make nearby DNA more accessible to the transcription machinery.
Which of the following enzymes removes the RNA nucleotides from the primer and adds equivalent DNA nucleotides to the 3' end of DNA fragments resulting from DNA replication of one of the two DNA strands?
DNA polymerase I.
What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?
DNA polymerase can join new nucleotides only to the 3' end of a growing strand.
What is the structure of DNA?
DNA strands are composed of deoxyribonucleotides that are covalently linked by phosphodiester bonds.
Which component is not directly involved in translation?
DNA.
What are DNA's nucleotides called?
Deoxyribonucleotides.
How do different subsets of genes come to be expressed in different cell types?
Different cell types express different combinations of transcriptional activators, which turn on expression of different combinations of genes.
What occurs during the process of photosynthesis (In regards to the percentage of energy from the sunlight the process uses)?
During photosynthesis, less than 100% of the energy captured from sunlight is transformed into potential energy in the form of a hydrogen ion gradient and then into potential energy in the form of covalent bonds.
The energy from an excited electron can be passed from one pigment molecule to another during which process?
During resonance energy transfer.
According to the "semi-conservative" model of DNA replication, after a double-stranded DNA molecule is replicated what happens?
Each of the two resulting double-stranded DNA molecules will consist of one "daughter" and one "parental" DNA strand.
In photosynthesis, how do electrons get to higher energy states?
Energy from photons moves electrons of pigment molecules to higher energy (excited) states.
Is the following statement about proton gradients true or false? Proton gradients cannot be used to do work.
False.
What do reactions in fermentation regenerate?
Fermentation consists of glycolysis plus reactions that regenerate NAD+, so it can be re-used in glycolysis.
What are ribosomes made from?
From proteins and RNA or rRNA.
Tumor-suppressor genes may encode polypeptides that do what?
Function in DNA repair, function in cell adhesion, and decrease the rate of cell division.
In colorectal cancer, several genes must be mutated in order to make a cell a cancer cell. Which of the following kinds of genes would you expect to be mutated?
Genes involve in the control of the cell cycle.
In aerobic metabolism, most of the ATP produced by the oxidation of glucose to carbon dioxide is produced by which process?
Glycolysis.
What occurs during translation?
Groups of three ribonucleotides of an mRNA molecule (codons) are read by the translation machinery in the 5' to 3' direction (which is the opposite of the DNA polymerase and RNA polymerase because they go in the 3' to 5' direction) - each codon specifies which of the 20 amino acids should be placed at the corresponding position along a polypeptide.
During certain types of cell division in Drosophila, studies have shown that there is phosphorylation of an amino acid in the tails of histones of gametes. A mutation in flies that interferes with this process results in sterility. Which of the following is the most likely hypothesis?
Histone tail phosphorylation prohibits chromosome condensation.
In a nucleosome, what is the DNA wrapped around?
Histones.
Will the chromosomes you pass onto your children be shorter than your chromosomes? And why or why not?
Hopefully not, because telomerase will restore the telomeres in your germline cells (the cells that produce egg or sperm cells) to approximately their original length.
The "universal" genetic code is now known to have exceptions. Evidence for this can be found if which of the following is true?
If UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only).
What if an organism uses the "conservative" model of DNA replication, rather than the normal "semi-conservative" model of DNA replication?
If this is the case, after DNA replication occurs, one of the two double-stranded DNA molecules will consist of two "daughter" DNA strands and the other will consist of two "parental" DNA strands.
Where dos glycolysis occur?
In the cytosol.
When does a DNA molecule wrap around multiple groups of histone proteins to form structures known as nucleosomes?
In the first level of chromatin packing.
Where does the citric acid cycle occur?
In the matrix of the mitochondria.
Where are the proteins of the electron transport chain located?
In the mitochondrial inner membrane.
In prokaryotes, where is the respiratory electron transport located?
In the plasma membrane.
What happens if there is insufficient oxygen during the cellular respiration process?
In the presence of insufficient oxygen, cells can generate ATP via anaerobic respiration or fermentation.
In a plant cell, where are the ATP synthase complexes located?
In the thylakoid membrane and inner mitochondrial membrane.
How does translation of mRNA almost always begin?
It almost always begins at an AUG codon, which specifies methionine.
When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, what happens to the molecule?
It becomes oxidized.
What could happen if you were to alter the expression of a single transcriptional activator?
It can have a huge effect on organism development and could even cause one body part to develop in the place of another.
How may photosynthesis be carried out?
It can only be carried out by certain eukaryotes and certain prokaryotes.
There is a mutation in the lac repressor gene that results in production of an altered lac repressor protein known as a "super-repressor" because it represses the lac operon permanently. Which of these would characterize such a mutant?
It cannot bind to the inducer.
What is the release factor in termination and what does it do?
It causes the addition of a water molecule, instead of an amino acid, to the polypeptide chain - this reaction releases the polypeptide, and the translation assembly then comes apart.
What does photosynthesis combine in order to produce?
It combines CO2 and H2O to produce glucose and O2.
What does a chromosome consist of?
It consists of a single, long, DNA molecule that is complexed together with proteins to form chromatin.
What processes does fermentation NOT have?
It does not have the citric acid cycle, an electron transport train, or chemiosmosis.
What model does DNA replication follow?
It follows the semi-conservative model.
What is the normal function of a tumor-suppressor gene?
It functions to decrease the rates of cell division and/or growth, or to function in DNA repair or cell adhesion.
What kind of arrangement does an Okazaki fragment have?
It has 5' RNA nucleotides and DNA nucleotides 3'.
What does the chemiosmotic process in chloroplasts involve?
It involves the establishment of a proton gradient across the thylakoid membrane.
A particular triplet of bases in the coding strand of a gene is GGG. If an mRNA is made from this gene, what is the anticodon on the tRNA that will bind the codon on the mRNA?
It is CCC.
What is alternative RNA splicing?
It is a mechanism that is commonly used by eukaryotes to allow their genes to produce multiple, related, proteins.
Define Exergonic Reaction
It is a reaction that releases energy.
What is a charged tRNA?
It is a tRNA with a covalently attached amino acid.
What is a characteristic of the product of the p53 gene?
It is a transcriptional activator for other genes.
What does the enzyme "telomerase" do?
It is able to partially or fully restore the lengths of telomeres. It is believed by many scientists that increasing the activity of telomerase could slow down the shortening of chromosomes that contributes to aging.
What is the transfer of electrons from the primary electron acceptor of photosystem II to the P700+ chlorophyll a molecules of photosystem I?
It is an exergonic reaction, as the P700+ chlorophyll a molecule is more electronegative than the primary electron acceptor.
Receiving electrons from the thylakoid membrane electron transport chain is directly associated with which photosystem?
It is directly associated with photosystem I.
Absence of bicoid mRNA from a Drosophila egg leads to the absence of anterior (e.g. head) larval body parts and mirror-image duplication of posterior parts. What is this evidence of?
It is evidence that the product of the bicoid gene normally leads to formation of head structures.
What is an oncogene formed by?
It is formed by a mutation in a proto-oncogene that causes increased expression of the proto-oncogene.
What is respiration in the presence of oxygen known as?
It is known as aerobic respiration.
What is the direct product of the reaction catalyzed by ribulose bisphosphate carboxylase oxygenase, or "Rubisco"?
It is not a sugar molecule and must be reduced using electrons from NADPH to form sugar molecules.
In aerobic metabolism, most of the ATP produced by the oxidation of glucose to carbon dioxide is produced by what?
It is produced by oxidative phosphorylation.
Define Endergonic Reaction
It is reaction that absorbs energy.
Carbon dioxide (CO2) is released during which of the following stages of cellular respiration?
It is released during oxidation of pyruvate to acetyl CoA and the citric acid cycle.
What is the enzyme that attaches CO2 to a 5-carbon long sugar to form a 6-carbon long molecule?
It is ribulose bisphosphate carboxylase oxygenase, or "Rubisco".
What is RNA splicing carried out by?
It is sometimes carried out by protein/RNA complexes known as spliceosomes.
What is the operator in an operon?
It is the DNA sequence to which an active repressor protein can bind, preventing transcript
What is the transcription initiation complex?
It is the complex of RNA polymerase and transcription factors.
What is a primary RNA?
It is the initial transcript produced by a eukaryote and they are modified in the nucleus before being transported through a nuclear pore to the cytoplasm.
What is carbon fixation?
It is the process in which CO2 is added to a small organic molecule to form a larger, more complex organic molecule.
What is true about the DNA in one of your brain cells?
It is the same as the DNA in one of your heart cells.
What is a codon?
It is three nucleotides that specify an amino acid sequence.
How is the energy from excited electrons transferred between pigment molecules?
It is transferred between the pigment molecules via resonance energy transfer.
Is the following statement true or false? When lac repressor protein binds allolactose, it is stabilized in its inactive shape, allowing transcription of the genes of the lac operon to proceed.
It is true.
In the light reactions what is the energy from the sunlight used for?
It is used to drive the transfer of electrons from water to NADP+, which leads to the formation of NADPH.
What is the proton gradient that's formed during the citric acid cycle used for?
It is used to power ATP synthase, so that many molecules of ATP are formed during the chemiosmotic phase of oxidative phosphorylation.
What is photophosphorylation?
It is when energy from the sunlight is used to generate ATP using chemiosmosis.
What can protein degradation be mediated by?
It may be mediated by ubiquitin binding a protein and targeting it for degradation by a proteasome.
A particular small interfering RNA (siRNA) will most likely do what?
It may help target a specific mRNA for degradation.
What does the genetic code is almost universal mean?
It means that a gene from one organism may be moved to another organism, where that gene will still specify production of a polypeptide of the same amino acid sequence as the original organism.
What does the genetic code is redundant but not ambiguous mean?
It means that some amino acids are specified by more tha one codon but that each codon specifies only one amino acid, so the code is not ambiguous.
The two strands of DNA in a double-stranded DNA molecule are oriented in what is known as an antiparallel arrangement. What does this mean?
It means that the 5' end of one DNA strand is base paired with the 3' end of the other DNA strand.
In photosynthetic cells, when does synthesis of ATP by the chemiosmotic mechanism occur?
It occurs during both photosynthesis and respiration.
When does termination occur?
It occurs when a stop codon on the mRNA reaches the A site of the ribosome, the A site accepts a protein called a release factor.
What is "wobble" in regards to anticodons and base pairing?
It refers to the flexibility in base pairing between some anticodons on tRNAs and codons on mRNAs.
What does RNA splicing do?
It removes the introns and joins the exons from a mRNA molecule, leading to the formation of an mRNA molecule with a continuous coding sequence.
Transcription in eukaryotes requires what in addition to RNA polymerase?
It requires several transcription factors.
What does cellular respiration result in?
It results in carbohydrates, proteins and lipids being broken down and combined with oxygen to form primarily CO2 and H2O.
What is the function of chemiosmosis?
It serves to generate ATP in both photosynthesis and respiration, but NADPH is produced by chemiosmosis during photosynthesis whereas NADH is used up by chemiosmosis during respiration.
Where does translation take place?
It takes place at ribosomes.
If stretched out, how long would the DNA in a single human chromosome be?
It would be about 4 cm long.
What would happen if you removed an operon?
It would result in the genes of that operon being off permanently.
What is the DNA molecule in a chromosome complexed together with?
It's complexed together with proteins to form "chromatin".
What process is photosynthesis the reverse of?
Its the reverse of cellular respiration.
You briefly expose bacteria undergoing DNA replication to radioactively labeled nucleotides. When you centrifuge the DNA isolated from the bacteria, the DNA separates into two classes. One class of labeled DNA includes very large molecules (thousands or even millions of nucleotides long), and the other includes short stretches of DNA (several hundred to a few thousand nucleotides in length). What do these two classes of DNA probably represent?
Leading strands and Okazaki fragments.
What attached the Ozaki fragments together?
Ligase.
What are the two processes in photosynthesis?
Light reactions and the Calvin cycle (also known as dark reactions).
Which of the following statements comparing mRNAs produced by prokaryotes versus eukaryotes is true?
Mature prokaryotic mRNAs often code for multiple polypeptides whereas mature eukaryotic mRNAs typically code for only one polypeptide.
The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mol and the free energy for the reduction of NAD+ to NADH is +53 kcal/mol. What is the main reason that only two molecules of NADH formed during glycolysis when it appears that as many as a dozen could be formed?
Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis.
Describe NAD+.
NAD+ is reduced to NADH during glycolysis, pyruvate oxidation, and the citric acid cycle.
What is formed during glycolysis?
NADH AND FADH2 are formed during this process.
What is used up during oxidative phosphorylation in mitochondria?
NADH is used up.
When is NADPH generated?
NADPH is generated during the light reactions of photosynthesis.
What is the final electron acceptor for the electron transport chain in aerobic respiration?
O2 is the final electron acceptor for the electron transport chain.
What are the components of an operon?
Operons have promoters, which are DNA sequences where RNA polymerase binds; operators, which are DNA sequences where transcriptional repressors bind; and structural genes that typically code for proteins that function together in a particular process.
What is an enzyme that synthesizes short segments of RNA?
Primase.
A mutant bacterial cell has a defective aminoacyl synthetase that attaches a lysine to tRNAs with the anticodon AAA instead of the normal phenylalanine. What could be the consequence of this for the cell?
Proteins in the cell will include lysine instead of phenylalanine at amino acid positions specified by the codon UUU.
What happens in the first level of chromatin packing?
Proteins known as histones join together to form complexes, a double-stranded DNA molecule wraps twice around each histone complex to form what are known as nucleosomes (now the DNA molecule with the nucleosomes resembles beads on a string).
What occurs during transcription?
RNA polymerase moves along the DNA, separating the two DNA strands and catalyzing the addition of RNA nucleotides to the growing RNA chain.
What occurs during termination of transcription in eukaryotes?
RNA polymerase transcribes a DNA sequence known as a polyadenylation signal sequence - proteins end up cutting the RNA transcript free of the RNA polymerase.
What are replication forks in regards to DNA replication?
Replication forks are at the ends of the replication bubbles and DNA replication proceeds in both directions from these forks.
In short, what does the process of cellular respiration do?
Respiration sugars (or other organic molecules)and O2 are converted to CO2 and H2O.
What are RNA's nucleotides called?
Ribonucleotides.
Why might different cells may have different combinations of transcriptional activators?
Some cells may produce chemicals that turn off expression of transcriptional activators in nearby cells, during cell division cytoplasmic determinants may not be evenly distributed to the two daughter cells, and cytoplasmic determinants may not be equally distributed within egg cells.
What happens to the Ozaki fragments as the DNA replication process proceeds?
Specific RNA polymerases remove the RNA primers at the beginning of each Ozaki fragment and fill in the resulting gaps with deoxyribonucleotides.
What do the ends of a pre-RNA get?
The 5' end receives a 5 cap and the 3 end gets a poly-a-tail. These modifications may facilitate export of the mRNA from the nucleus, protect the mRNA from degradation, and help ribosomes attach to the 5' end of the mRNA.
What product is reduced during photosynthesis?
The CO2 is reduced which helps to form sugar molecules.
Reactions that require CO2 take place where?
The Calvin cycle alone.
Where do reactions that require CO2 take place?
The Calvin cycle alone.
What happens when the RNA primer is removed from the 5' end of a daughter DNA strand?
The DNA molecules get a little shorter each time they are replicated as cells in a growing organism.
What is the leading strand?
The DNA strand that can be synthesized using only one primer at the DNA fork.
What is the lagging strand?
The DNA strand that is synthesized using multiple RNA primers.
What is the order in which chromatin packing occurs?
The DNA wraps around histones, forming nucleosomes; the histones within each nucleosome interact with adjacent nucleosomes and with the DNA between nucleosomes to form a 30-nm fiber; the chromatin forms loops by attaching to scaffold proteins, forming a 300-nm fiber.
What occurs during termination of transcription in bacteria?
The RNA polymerase transcribes through a terminator sequence DNA. The transcribed terminator sequence on the RNA then causes the RNA polymerase to detach from the RNA and DNA molecules.
A particular triplet of bases in the template strand of DNA is TTT. The anticodon on the tRNA that binds the mRNA codon is what?
The answer is UUU.
A part of an mRNA molecule with the following sequence is being read by a ribosome: 5' CCG-ACG 3' (mRNA). The anticodon loop of the first tRNA that will complement this mRNA is what?
The anticodon is 3' GGC 5'.
A particular triplet of bases in the template strand of DNA is GGG. What is the anticodon on the tRNA that binds the mRNA codon?
The anticodon is GGG.
What is the nitrogenous base that is found in ATP, RNA, and DNA?
The base is Adenine.
Accuracy in the translation of mRNA into the primary structure of a polypeptide depends on specificity in what process?
The bonding of the anticodon to the codon and the attachment of amino acids to tRNAs.
What happens in the third level of chromatin packing?
The chromatin forms loop by attaching to a scaffold made up of proteins and these interactions make the chromatin into an even thicker and shorter form - during metaphase the looped domains of the chromatin coil and fold.
A flask containing photosynthetic green algae and a control flask containing water with no algae are both placed under a bank of lights, which are set to cycle between 12 hours of light and 12 hours of dark. The dissolved oxygen concentrations in both flasks are monitored. Predict what the relative dissolved oxygen concentrations will be in the flask with algae compared to the control flask.
The dissolved oxygen in the flask with algae will be higher in the light, but lower in the dark.
What is one of the most important differences between aerobic and anaerobic respiration?
The electron transport chain used in aerobic respiration uses O2 as the final electron acceptor whereas the electron transport chain used in anaerobic respiration uses something other than O2 as the final electron acceptor.
What does cellular respiration do with much of the energy from food?
The energy from the food is used to generate heat or being stored in the form of ATP.
Eukaryotic telomeres replicate differently than the rest of the chromosome. What is this a consequence of?
The fact that DNA polymerases can only add deoxyribonucleotides to the 3' end of an existing nucleotide chain.
What is base pairing?
The formation of hydrogen bonds between the nitrogenous bases of complementary nucleotides.
Where is ATP synthase located in the mitochondrion?
The inner membrane.
If a researcher moves the lac operator to a position upstream from the promoter for the lac operon, what would occur?
The lac operon will be expressed continuously.
How do the leading and lagging strands differ?
The leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction.
During cellular respiration, acetyl CoA accumulates in which location?
The mitochondrial matrix.
What happens to mRNA molecules after they have been modified?
The molecules leave the nucleus trough nuclear pores.
A mutation in yeast makes it unable to convert pyruvate to ethanol. How will this mutation affect these yeast cells?
The mutant yeast will be unable to grow anaerobically.
What can happen to mutations that increase the expression of a proto-oncogene?
The mutation can turn into an oncogene that tends to promote excessive rates of cell division and/or growth and that increases the chances of a cell becoming cancerous.
The nucleotide sequence of the coding strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' TTTAAGG 3'
The nucleotide sequence will be 5' UUUAAGG 3'.
What are three ways a complex of polypeptides and a micro RNA (miRNA) or a small interfering RNA (siRNA) reduce expression of specific genes?
The nucleotides of the miRNA can base pair with complementary nucleotides on the mRNA, the miRNA-protein complex can then block translation of the mRNA molecule by ribosomes, the nucleotides of the siRNA can base pair with complementary nucleotides on the mRNA. Polypeptide(s) in the siRNA-protein complex can then degrade the mRNA molecule, and the nucleotides of the miRNA can base pair with complementary nucleotides on the mRNA. Polypeptide(s) in the miRNA-protein complex can then degrade the mRNA molecule.
The pH of the inner thylakoid space and of the stroma have been measured. What kind of relationship, if any, would you expect to find?
The pH within the inner thylakoid space is less than that of the stroma.
What is the primary difference between aerobic and anaerobic respiration?
The primary difference is that the electron transport chain used in anaerobic respiration uses something other than O2 as the final electron acceptor.
It is possible to prepare vesicles from portions of the inner mitochondrial membrane. What process could still be carried out by this isolated inner membrane?
The process known as oxidative phosphorylation.
In the absence of oxygen, yeast cells can obtain energy by fermentation which results in the production of what?
The production of ATP, CO2, and ethanol (ethyl alcohol).
Within a cell, the amount of protein made using a given mature mRNA molecule partly depends on what?
The rate at which the mRNA is degraded.
What is the function of the release factor?
The release factor binds to the stop codon in the A site in place of a tRNA.
What is the direct result of hydrogen ions being pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space?
The result is the creation of a proton-motive force.
What is the result of anaerobic respiration for having a different final electron acceptor?
The result of not using O2 (the other acceptor used is less electronegative) is that less energy is released per oxidized molecule and so less ATP is produced.
What do ribosomes facilitate in regards to tRNA and mRNA and protein synthesis?
The ribosomes facilitate coupling of tRNA anticodons and mRNA codons during protein synthesis.
A particular triplet of bases in the template strand of DNA is 5' GGT 3'. The corresponding codon for the mRNA transcribed is what?
The sequence is 3' CCA 5'.
A particular triplet of bases in the template strand of DNA is 5' AAT 3'. The corresponding codon for the mRNA would be transcribed as what?
The sequence is 3' UUA 5'.
If the template strand of the DNA molecule is TTT, the mRNA will have the sequence AAA, but what is the anticodon that binds AAA on the mRNA? The sequence of the anticodon that binds to AAA on the mRNA will thus be UUU.
The sequence of the anticodon that binds to AAA on the mRNA will thus be UUU.
The nucleotide sequence of the coding strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' AATTCGGG 3'
The sequence would be 5' AAUUCGGG 3'.
The nucleotide sequence of the coding strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' ATGCGTA 3'
The sequence would be 5' AUGCGUA 3'.
The nucleotide sequence of the template strand of a DNA molecule is shown below. What will be the nucleotide sequence of the RNA molecule made from this segment of DNA? 5' TTTAAGG 3'
The sequence would be 5' CCUUAAA 3'.
What would be the sequence of the DNA molecule made by replication of the DNA molecule shown below? 5' TTCCGGA 3'
The sequence would be 5' TCCGGAA 3'.
An experimenter moves the operator for the lactose operon to the far end of the operon (past all of the structural genes in the lactose operon). Which of the following would likely occur when the cell is exposed to lactose?
The structural genes will be transcribed continuously.
What is the order of sites before the tRNA exits the ribosome?
The tRNA is either in the P or the A site. If it is in the P site before the ribosome shifts it then goes to the E site, and if it is in the A site before the ribosome shifts it goes to the P site.
The sequence of an RNA molecule will be complementary to the sequence of the what?
The template strand from which that RNA molecule was made
What is the template strand of a DNA molecule?
The template strand of a DNA molecule is the strand that is hydrogen bonded to complementary ribonucleotides during the formation of an RNA molecule. The sequence of the RNA molecule will be complementary to the sequence of the DNA template strand.
The HXK gene is transcribed, resulting in production of HXK mRNA molecules. The total number of HXK mRNA molecules that are present in a cell at any given moment depends on what?
The total number is equally dependent on the rate at which the HXK mRNA molecules are made (transcribed) and the rate at which they are broken down.
What percentage of living organisms are dependent, directly or indirectly, on food molecules produced via photosynthesis?
The vast majority.
How many codons are there that specify an amino acid?
There are 61 codons that specify an amino acid but only about 45 varieties of tRNAs are made.
What is the end result of DNA replication?
There will now bw two identical double-stranded DNA molecules, each of which has one DNA strand from the original "parental" DNA molecule and one new "daughter" DNA strand.
What are the three special base triplets involved with termination?
They are UAA, UAG, UGA - they do not code for amino acids but instead act as stop codons.
What are the three stop codons?
They are UAA, UAG,and UGA.
How are nucleotides added to a growing nucleotide chain?
They are added by forming a phosphodiester bond between the hydroxyl group on the #3 carbon of the nucleotide at the end of the chain and the phosphate group of the new nucleotide.
What are 3 metabolic process that include glycolysis?
They are aerobic respiration, anaerobic respiration, and fermentation.
What is the name of the genes that encode polypeptides that decrease the rate of cell division?
They are called tumor-suppressor genes.
What are operons?
They are clusters of genes that are under the control of a single regulatory sequence
What are the three steps of elongation?
They are codon recognition, peptide bond formation, and translocation.
The reactions of the Calvin Cycle are what?
They are endergonic and require a source of free energy to occur.
What are amino acyltRNA synthetases?
They are enzymes that catalyze the formation of a covalent bond between an amino acid and an appropriate tRNA molecule (there are 20 different amino acyl tRNA syntheses, one for each of the amino acids).
What are the three metabolic stages that cellular respiration is divided into?
They are glycolysis, the citric acid cycle, and oxidative phosphorylation.
What are the three stages of transcription?
They are initiation, elongation, and termination.
What are the three stages of translation?
They are initiation, elongation, and termination.
How are nucleotides joined?
They are joined by a condensation reaction (specifically a dehydration reaction) to form nucleotide polymers.
What are the enzymes called that carry out the main work of synthesizing new DNA chains?
They are known as DNA polymerases.
The pairs of nucleotides that interact to join together two DNA strands are known as what?
They are known as complementary nucleotides.
What are the noncoding regions in eukaryotic genes and the RNA molecules made from these genes that lie between coding regions?
They are known as intervening sequences or introns - the regions are called EXONS because they are eventually expressed.
Some genes that encode polypeptides that function in DNA repair are known as what?
They are known as tumor-suppressor genes.
What are bacterial (prokaryotic) genes often organized in?
They are often organized in operons. Operons consist of a promoter and an operator.
What are histones?
They are part of nucleosomes.
What are the covalent linkages joining together nucleotides in a DNA molecule?
They are phosphodiester linkages.
What are transcription factors in transcription initiation?
They are proteins that help RNA polymerase bind the DNA and initiate transcription.
What are transfer RNA molecules?
They are small RNA molecules that are not translated to form proteins.
What are promoters in transcription initiation?
They are special nucleotide sequences at the 5' ends of genes tat signal the RNA synthesis.
What are the daughter DNA strands?
They are the DNA strands that are made by copying the parental DNA strands.
What are telomeres?
They are the ends of linear DNA molecules and they get shorter each time the DNA molecule is replicated.
What are Ozaki fragments?
They are the short DNA fragments that are formed during synthesis of the lagging strand.
What are the parental DNA strands?
They are the strands in the original double-stranded DNA molecule.
What do microRNAs (miRNAs) do?
They bind specific mRNA molecules, blocking translation of the mRNA or causing it to be chopped up.
What can redox reactions result in?
They can result in a transfer of electrons and can also result in a change in electron sharing in covalent bonds.
What can several RNA polymerases do during trasnscription?
They can simultaneously transcribe the same gene.
What can DNA polymerases not do?
They can't initiate the synthesis of a new deoxyribonucleotide chain but can only add to an existing nucleotide chain.
What do primases do?
They catalyze the synthesis of RNA primers. They use the DNA strand they are helping to copy as a template, to catalyze formation of the RNA primer.
What do RNA molecules contain in place of U?
They contain T (Thymine).
How do the nucleotides used to make RNA molecules differ from those used to make DNA molecules?
They differ because the nucleotides used to make RNA molecules have ribose instead of deoxyribose as their sugar and uracil instead of thymine as one of their nitrogenous bases.
What is the main reason muscle cells differ from nerve cells?
They express different genes.
When scientists analyzed the transcripts produced from a couple of human chromosomes what did they find?
They found that about 10x more DNA is transcribed than what would be predicted by the percentage of DNA sequences that code for polypeptides.
What is the normal function of pro to-oncogenes?
They function to produce polypeptides that increase the rate of cell division and/or growth.
What is the function of the corepressor?
They help repress transcription of the genes in the operon.
What do eukaryotic transcriptional activators do?
They increase (or activate) transcription of the genes they regulate.
In eukaryotes, what is it that transcriptional activators may do in regards to binding specific DNA sequences?
They may bind specific DNA sequences associated with genes and increase the affinity of RNA polymerase for the promoters for those genes.
Ribosomes in regards to translation
They play a critical role in the translation of mRNAs to form polypeptides.
What do the exergonic redox reactions in mitochondria do?
They provide the energy that establishes the proton gradient.
Besides CO2 and H2O, to produce sugars through the reactions of the Calvin cycle what else do cells require?
They require ATP as an energy source to "drive" the otherwise endergonic reaction and NADPH as a reducing agent.
In prokaryotes, where do mRNA transcription and translation take place?
They take place in the same part of the cell but are immediately translated without being processed.
What do mitochondria use energy from food to form?
They use energy from food to form a proton gradient.
What do chloroplasts use energy from light to form?
They use the energy from light to form a proton gradient.
What are three things that will happen to your chromosomes as you become older?
They will become shorter.
What are the two DNA strands in double stranded DNA molecules held together by?
They're held together by hydrogen bonds between G and C and A and T deoxyribonucleotides.
How are two DNA strands held together?
They're held together by hydrogen bonds between the nitrogenous bases of complementary nucleotides to form a double stranded DNA molecule.
During the light reactions of photosynthesis, where are electrons transferred from?
They're transferred from special chlorophyll a molecules to primary electron acceptors.
Which photosystem does the following statement describe? "The electron vacancies in P680+ are filled by electrons derived from water."
This describes photosystem II.
Why is less ATP produced by anaerobic respiration than by aerobic respiration? (There are three reasons).
This happens because anaerobic respiration uses a final electron acceptor that is less electronegative than O2, which is used as the final electron acceptor in aerobic respiration, anaerobic respiration does not make use of the citric acid cycle, and because anaerobic respiration does not make use of an electron transport chain.
Why are different genes expressed in different cells of our bodies?
This happens because different cells have different combinations of activators.
Why does the oxidation of organic compounds by molecular oxygen to produce CO2 and water release free energy?
This happens because electrons are being moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O).
Why does a new DNA strand elongates only in the 5' to 3' direction?
This is because DNA polymerase can only add nucleotides to the free 3' end.
Is the following statement true or false? NADPH is the reducing agent for CO2
This is true.
Is the following statement true or false? P680+ is part of photosystem II and is such a strong oxidizing agent it can strip an electron from water.
This is true.
What is meant by the statement that "the genetic code is redundant"?
This means that most amino acids are specified by more than one codon.
Why do chromosomes become shorter as we age?
This occurs because DNA polymerases can only add nucleotides to an existing nucleotide chain and an RNA primer is used to initiate DNA synthesis. Once that RNA primer is removed from the end of a linear chromosome, there is no mechanism to completely fill in the missing nucleotides at the end of a linear chromosome.
The P Site (peptidyl tRNA)
This site holds the tRNA that carries the growing polypeptide chain.
The A Site (amino acyl)
This site holds the tRNA that carries the next amino acid to be added to the polypeptide chain.
The E Site (exit)
This site is the exit site, where discharged tRNAs leave the ribosome.
Is this statement regarding the transcriptional activators true or false? Most genes are regulated by several different transcriptional activators.
This statement is true.
Which base does DNA have that RNA does not have?
Thymine.
During translation, what is the role of release factors?
To bind the mRNA stop codon in the A site of the ribosome, causing release of the completed polypeptide.
What is transcription?
Transcription is the synthesis of RNA under the direction of DNA (using DNA as the template) - Transcription produces a number of different types of RNA, including mRNA.
Where do transcription and translation take place in eukaryotes?
Transcription takes place in the nucleus and translation takes place in the cytoplasm - the mRNA transcripts can be modified before leaving the nucleus and being translated.
What is translation?.
Translation is the synthesis of a polypeptide, using an mRNA as a template.
Is the following statement true or false? When the trp repressor protein binds tryptophan, it is stabilized in its active shape, preventing transcription of the genes of the trp operon from occurring.
True.
What are two common types of fermentation?
Two common types of fermentation are alcohol fermentation and lactic acid fermentation.
Which base does RNA have that DNA does not have?
Uracil.
If your muscles used alcohol fermentation instead of lactic acid fermentation, which of the following might occur?
You might become drunk during an intense workout.
A colleague of yours is asked to develop a strain of mutant mice that will be extremely likely to develop cancer so that these mice can be used to study cancer treatments. Your colleague causes a mutation in a mouse that causes the mouse to express a proto-oncogene at greatly increased levels. However, your colleague is disappointed to find the mouse does not have cancer and asks your advice on what he should do next. What should you tell him?
You remind him that a mutation that increases the expression of a single proto-oncogene is generally not sufficient to cause cells to become cancerous. He should also cause some mutations in the mouse's DNA that cause decreased expression of some of the mouse's tumor-suppressor genes.
What would you expect of a eukaryote lacking telomerase?
You would expect a reduction in chromosome length in gametes.
What are not found in operons?
miRNAs.
Why do some scientists feel that telomerase might be used to slow the aging process?
some scientists believe this because telomere extension in mice and worms has reversed some signs of aging.
What is an anticodon?
tRNA molecules have them at the other end of the molecule from where it can carry an amino acid. The anticodon consists of three adjacent nucleotides and they are able to base pair with codons that have appropriate sequences.
What happens in the second level of chromatin packing?
tThe histone proteins in each nucleosome interact with adjacent nucleosomes and with the DNA between nucleosomes. These interactions cause the chromatin to coil or fold to a thicker, shorter form (often found in this form during interphase).
Approximately what percentage of human genes that have more than on exon undergo alternative splicing?
~95%.