Bio Exam 4- Mastering Bio

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Which of these extracellular signal molecules could diffuse through a plasma membrane and bind to an intracellular receptor?

Estrogen, Nonpolar molecules can diffuse through the plasma membrane and bind to intracellular receptors.

A(n) _____ is an example of a signal molecule that can bind to an intracellular receptor and thereby cause a gene to be turned on or off.

Steroid, Steroids bind to intracellular receptors, which can then bind to, and regulate, the expression of genes.

What role does a transcription factor play in a signal transduction pathway?

By binding to DNA it triggers the transcription of a specific gene.

Which of these, when activated by a signal transduction pathway, moved from the cytoplasm to the nucleus of a cell?

transcription factor, Activated transcription factors trigger transcription.

Which of these acts as a second messenger?

cyclic AMP, Cyclic AMP can act as second messengers

Calcium ions that act as second messengers are stored in _____.

endoplasmic reticula, The ER stores calcium ions.

_____ catalyzes the production of _____, which then opens an ion channel that releases _____ into the cell’s cytoplasm.

Phospholipase C … IP3 …. Ca2+, Phospholipase C cleaves IP3 from a membrane protein, and IP3 then binds to a calcium channel on the ER

A protein kinase activating many other protein kinases is an example of _____.

Amplification, By activating many other molecules the initial signal is amplified.

Which of these is a logical signal transduction pathway?

A G-protein-linked receptor activates G protein, which activates phospholipase C, which cleaves a membrane protein to form IP3, which binds to a calcium channel on the ER, which opens to release calcium ions into the cytoplasm, which bind to an intracellular enzyme that carries out a response.

The cleavage of glycogen by glycogen phosphorylase releases _____.

glucose-1-phosphate, Glycogen is a polysaccharide composed of glucose monomers.

Epinephrine acts as a signal molecule that attaches to _____ proteins.

G-protein-linked receptor, Epinephrine acts via G-protein-linked receptors.

Which of these is a receptor for calcium ions?

Calmodulin, Calmodulin is a calcium ion receptor.

Which of these is NOT correct?

Cyclic AMP binds to calmodulin., Calcium binds to calmodulin.

A toxin that inhibits the production of GTP would interfere with the function of a signal transduction pathway that is initiated by the binding of a signal molecule to _____ receptors.

G-protein-linked, GTP activates G proteins.

What is the process called that converts the genetic information stored in DNA to an RNA copy?

Transcription, DNA is transcribed to give an RNA copy.

DNA does not store the information to synthesize which of the following?

Organelles, Synthesis of organelles is not directly coded in the DNA.

Transcription begins at a promoter. What is a promoter?

A site in DNA that recruits the RNA Polymerase, This is the site where the RNA polymerase must bind to initiate transcription.

Which of the following statements best describes the promoter of a protein-coding gene?

The promoter is a nontranscribed region of a gene, The promoter is the regulatory region of a protein-coding gene at which RNA polymerase must bind to initiate transcription—it is not transcribed into the RNA.

What determines which base is to be added to an RNA strand during transcription?

Base pairing between the DNA template strand and the RNA nucleotides, Transcription involves the formation of an RNA strand that is complementary to the DNA template strand.

Which of the following terms best describes the relationship between the newly synthesized RNA molecule and the DNA template strand?

Complementary, Because the template strand determines the nucleotides to be added to the RNA strand, using the same complementarity rules of the DNA, they will be complementary to each other.

What happens to RNA polymerase II after it has completed transcription of a gene?

It is free to bind to another promoter and begin transcription, The enzyme is free to transcribe other genes in the cell.

During RNA processing a(n) _____ is added to the 5′ end of the RNA?

a long string of adenine nucleotides, A poly-A tail is added to the 3′ end of the RNA.

Spliceosomes are composed of _____

snRNPs and other proteins, These are the component of spliceosomes.

The RNA segments joined to one another by spliceosomes are _____.

Exons, Exons are expressed regions.

Translation occurs in the _____.

Cytoplasm, Ribosomes, the sites of translation, are found in the cytoplasm.

Which of these correctly illustrates the pairing of DNA and RNA nucleotides?

GTTACG CAAUGC, In RNA, uracil takes the place of thymine.

The direction of synthesis of an RNA transcript is _____.

5′ —> 3′, Nucleotides are added to the 3′ end of RNA.

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, Transcription is the process by which a DNA template is used for the manufacture of several different types of RNA.

What name is given to the process in which the information encoded in a strand of mRNA is used to construct a protein?

Translation, Translation is the process by which information encoded in RNA is used to manufacture a polypeptide.

What name is given to the process in which pre-mRNA is edited into mRNA?

RNA processing, RNA processing edits the RNA transcript that has been assembled along a DNA template.

Polypeptides are assembled from _____.

amino acids, Proteins are composed of amino acid monomers.

RNA processing converts the RNA transcript into _____.

mRNA, The editing of the RNA transcript produces mRNA.

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, 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 molecule binds to promoters in bacteria and transcribes the coding regions of the genes?

RNA polymerase, RNA polymerase is the enzyme that binds to promoters and transcribes the coding regions of genes into RNA.

What is allosteric regulation?

In allosteric regulation, a small molecule binds to a large protein and causes it to change its shape and activity, Allosteric regulation is an important mechanism for changing enzyme activity, as well as for changing the function of some gene repressors and activators.

Under which conditions are the lac structural genes expressed most efficiently?

No glucose, high lactose, 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.

What happens to the expression of the lacI gene if lactose is not available in the cell?

There is no change—the lacI gene is constitutively expressed, The lacI 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 function of the lacZ gene?

This gene encodes an enzyme, b-galactosidase, which cleaves lactose into glucose and galactose, The lacZ gene encodes b-galactosidase, a key enzyme in lactose metabolism. When lactose is present in the cell, the cell expresses lacZ and metabolizes lactose.

Which of the following enzymes converts ATP to cAMP?

Adenylyl cyclase, Adenylyl cyclase converts ATP to cAMP, which helps CAP bind and facilitates binding of RNA polymerase to the lac promoter.

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, 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.

The operon model of the regulation of gene expression in bacteria was proposed by _____.

Jacob and Monod, In 1961 Jacob and Monod proposed the operon model of gene regulation.

Which of these is NOT a component of the lac operon?

regulatory gene only, The regulatory gene, while not a part of the operon, plays a role in regulating the expression of the genes of the operon.

Regulatory proteins bind to _____.

the operator, Transcription is inhibited when a regulatory protein binds to the lac operon operator.

In the presence of a regulatory protein the lac operon is _____.

not transcribed, The regulatory protein of the lac operon is a repressor.

Enzyme complexes that break down protein are called _____.

Proteasomes, Proteasomes are enzyme complexes that break down proteins.

The nuclear membrane’s role in the regulation of gene expression involves _____.

regulating the transport of mRNA to the cytoplasm

What is the function of a spliceosome?

RNA processing

Protein-phosphorylating enzymes’ role in the regulation of gene expression involves _____.

protein activation, Proteins are often activated by phosphorylation.

Which of the following terms describes the DNA-protein complexes that look like beads on a string?

Nucleosome, The "beads on a string" appearance of nucleosomes comes from the wrapping of DNA around a core of eight histone proteins.

Which of the following regulatory elements is not composed of DNA sequences?

Activators, Activators are proteins that are involved in transcription initiation

True or false? Regulatory and basal transcription factors regulate transcription by binding to the promoter.

False, Basal transcription factors do indeed bind to the promoter, but regulatory transcription factors bind to promoter-proximal elements and enhancers.

Which of the following regulatory DNA sequences might be located thousands of nucleotides away from the transcription start site of a gene?

Enhancer, Enhancers can function thousands of nucleotides away from the promoter and transcription start site.

Which of the following events in transcription initiation likely occurs last?

RNA polymerase binds to the promoter of the gene, RNA polymerase is recruited only when other transcription factors, including TBP, are assembled at the promoter.

True or false? One possible way to alter chromatin structure such that genes could be transcribed would be to make histone proteins more positively charged.

False, The positive charge on histone proteins allows them to interact tightly with negatively charged DNA, thus inhibiting transcription. To disrupt this interaction, the histone proteins would have to be made more negatively charged.

Which of these is NOT a carcinogen?

Testosterone, fat, UV light, cigarette smoke all can cause carcinogens

_____ is a carcinogen that promotes colon cancer.

Fat, A diet high in fat increases the risk of both colon and breast cancer.

Which of the following is a function of the S phase in the cell cycle?

The synthesis of sister chromatids, DNA replication occurs during S phase and results in two sister chromatids for each original chromosome.

The copying of chromosomes occurs during which of the following phases of the cell cycle?

S phase, Chromosomes must undergo replication before mitosis can occur- this copying occurs during the S phase.

For the first several divisions of early frog embryos, cells proceed directly from the M phase to the S phase and back to M without gaps. Which of the following is likely to be true about dividing cells in early frog embryos?

The cells get smaller with each generation, Without gap phases, the cells have no opportunity to grow.

True or false? The M phase is characterized by the replication and division of a cell’s chromosomes.

False, Correct: Cells replicate their chromosomes during the S phase and divide partition their chromosomes during the M phase.

If an organism normally has 34 chromosomes, how many molecules of DNA should there be in the G1 phase of the cell cycle?

34, There is one DNA molecule per chromosome.

Which of the following events would cause the cell cycle to arrest?

Poor nutrient conditions, Poor nutrient conditions would arrest the cell cycle at the G1 checkpoint.

Which of the following factors does not affect membrane permeability?

The polarity of membrane phospholipids, Phospholipids contain both a polar head and a nonpolar hydrocarbon tail, both of which are necessary for their ability to form membrane bilayers.

How can a lipid be distinguished from a sugar?

Lipids are mostly nonpolar, Lipids are nonpolar molecules, whereas sugars are polar.

True or false? Osmosis is a type of diffusion.

True, Osmosis is the diffusion of water across a selectively permeable membrane.

What property of dishwashing liquid (detergent) makes it useful to wash grease from pans?

Amphipathic nature, Detergents form micelles around the grease, which are then washed away because the polar head groups facing outward on the micelle are water-soluble.

Which of the following particles could diffuse easily through a cell membrane?

Oxygen (O2), Small nonpolar molecules such as oxygen can diffuse across cell membranes.

True or false? The water-soluble portion of a phospholipid is the polar head, which generally consists of a glycerol molecule linked to a phosphate group.

True, The hydrophilic, or water-loving, portion of a phospholipid is the polar head, whereas the hydrophobic portion is the nonpolar tail.

If a red blood cell is placed in a salt solution and bursts, what is the tonicity of the solution relative to the interior of the cell?

Hypotonic, The salt concentration in the solution is lower than it is in the cell, so water enters the cell, causing it to burst.

What name is given to the process by which water crosses a selectively permeable membrane?

Osmosis, Osmosis is the passive transport of water.

What distinguishes facilitated diffusion from simple diffusion?

Membrane proteins help move molecules across the membrane, Membrane proteins facilitate the movement of molecules across the membrane.

Which of the following transporters does not use passive transport to move molecules across a membrane?

Sodium-potassium pump, This pump uses the energy provided by ATP hydrolysis to transport sodium and potassium ions across the membrane.

True or false? Active transport differs from passive transport in that active transport does not require an input of energy.

False, Active transport requires the input of energy, whereas passive transport is primarily driven by the gradient. Active transport requires energy, whereas passive transport does not

Which membrane protein would be used to move glucose across a membrane from a region of higher concentration to a region of lower concentration?

Transporter, The GLUT-1 transporter assists the diffusion of glucose through the membrane.

Which of the following statements is true about the net movement of an ion across a membrane by passive diffusion through a membrane channel?

The charge on the other side of the membrane is generally the opposite of the ion’s charge., Ions tend to move toward regions of unlike charge.

True or false? During active transport through the sodium-potassium pump, ATP hydrolysis provides the energy to pump three sodium ions into the cell for every two potassium ions pumped out of the cell.

False, The sodium-potassium pump maintains a state in which the concentration of sodium is low inside the cell relative to the outside and the concentration of potassium is high inside the cell relative to the outside, thus, three sodium ions are pumped out of the cell and two potassium ions are pumped into the cell against the electrochemical gradient.

Lactose transport by membrane proteins occurs under conditions in which the concentration of lactose inside the cell is higher than the concentration outside the cell. What type of transport is used to move lactose into the cell?

Active transport, Under these conditions, lactose moves against its concentration gradient, so its transport will require energy.

Endocytosis moves materials _____ a cell via _____.

into … membranous vesicles, The prefix "endo-" means "inward."

A white blood cell engulfing a bacterium is an example of _____.

Phagocytosis, Phagocytosis occurs when a cell engulfs a large particle.

A phospholipid has a head" made up of glycerol molecule attached to a single ______, which is attached to another small molecule.

phosphate group

Phospholipids vary in the small molecules attached to the phosphate group. The phospholipid shown in the figure has a _________ attached to phosphate.

choline group

Because the phosphate group and its attachments are either charged or polar, the phospholipid head is________, which means it has an affinity for water.


A phospholipid also has two "tails" made up of two _________ molecules, which consist of a carboxyl group with a long hydrocarbon chain attached.

Fatty acid

Because the C-H bonds in the fatty acit tails are relatively nonpolar, the phsophplipid tails are _________. Which means they are excluded from water.


A(n)________ is a specific small molecule that binds to a bacteria regulatory protein and changes its shape so that it cannot bind to an operator, thus switching an operon on.


operon is not transcribed

lac operon: lactose absent, Trp operon: tryptphan present

operon is transcribed, but not sped up through positive control

trp operon: tryptophan absent Lac operon: lactose present, glucose present

operon is transcribed quickly through positive control

lac operon: lactose present, glucose absent

trp operon is regulated through _______control only. When typtophan is present, the operon genes are not transcribed.


The lac operon is regulated through both _______control and ______ control.

negative, positive

trp & lac operons regulations during negative control

when lactos is absent, the repressor protein is active & transcription is turned off When lactoctose is present, the repressor protein is inactivated, and transcription is turned on.

trp & lac operons regulations during postive control

When glucose is absent, another regulatory protein (CAP) binds to the promoter of the lac operon, increasing the rate of transcription if lactose is present.

A(n) ________ is a stretch of DNA consisting of an operator, a promoter & genes for a related set of protein, usually making up an entire metabolic pathway.


The ________is/are arranged sequentially after the promoter.

genes of an operon

A(n) _________ is a specific nucleotide sequence in DNA that binds RNA polymerase, positioning it to start transcribing RNA at the appropriate place.


A(n) ________ codes for a protein, such as a repressor, that controls the transcription of another gene or group of genes

regulatory gene

Regulatory proteins bind to the _______to control expression of the operon.


A(n) _______is a protein that inhibits gene transcription. In prokaryotes, this protein binds to the DNA in or near the promoter.


Facilitated Diffusion via channels and carrier proteins

provide a hydrophilic path across the membrane, Transport solutes down a concentration or electrochemical gradient, Are integral membrane protains

Facilitated Diffusion via channels only

provide a continuous path across the membrane, Allow water molecules and small ions to flow quickly across the membrane

Facilitated Diffusion via carrier proteins only

transport primarily small polar organic molecules, Undergo a change in shape to transport solutes across the membrane


increases the surface area of the plasma membrane, Requires fusion of vesicles with the plasma membrane Secretes large molecules out of the cell, requires cellular energy, Transported substances never physically corss the plasma membrane


decreases the surface area of the plasma membrane, Forms vesicles from inward folding of the plasma membrane, requires cellular energy, Transported substances never physically corss the plasma membrane

exocytosis & endocytosis

requires cellular energy, Transported substances never physically corss the plasma membrane

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