Cell Online Quiz

Front 1

What did stanley miller's experiments show about the formation of organic molecules?

Back 1

That organic molecules, including several amino acids, can be formed spontaneously from a mixture of reducing gases.

Front 2

What kind of macromolecule is capable of directing its own replication?

Back 2

RNA is uniquely capable of both serving as a template and catalyzing the chemical reactions required for its own replication.

Front 3

Discuss the evidence that mitochondria and chloroplasts originated from bacteria that were engulfed by the precursor of eukaryotic cells.

Back 3

They contain their own DNA and ribosomes, are similar in size to bacteria, and divide like bacteria. Their ribosomal proteins and RNA are more like bacteria than eukaryotic nuclear genomes.

Front 4

Why is the evolution of photosynthesis thought to have favored the subsequent evolution of oxidative metabolism?

Back 4

Because O2 became abundant in Earth's atmosphere as a result of photosynthesis.

Front 5

What model organism provides the simplest system for studying eukaryotic DNA replication?

Back 5

Yeast

Front 6

You are studying a gene involved in mammalian embryonic development. Which model organism would be best suited for your studies?

Back 6

Mice

Front 7

Although gylcogen and cellulose are both composed of glucose monomers, they are chemically distinct. Why?

Back 7

Glycogen is a polymer of glucose residues connected by alpha(1-4) glycosidic bonds, and some alpha(1-6) bonds that produce branches.
Cellulose is straight, unbranched with beta(1-4) bonds between glucose residues.

Front 8

What are the major functions of fats and phospholipids in cells?

Back 8

Fats accumulate in fat droplets of cells and are an efficient form of energy storage. Phospholipids function as the major components of cell membranes.

Front 9

In addition to serving as the building blocks for nucleic acids, what other important functions do nucleotides have in cells?

Back 9

Nucleotides function as carriers of chemical energy (ATP) and as intracellular signaling molecules (cAMP)

Front 10

If you removed all the bases from an mRNA molecule, could it still function as an information-carrying molecule?

Back 10

No. The information in nucleic acids is conveyed by the sequence of its bases. If the bases were removed, we would be left with a linear sugar phosphate chain with little informational content.

Front 11

What was the experimental evidence that demonstrated that the information necessary for the folding of proteins is contained in the sequence of their amino acids?

Back 11

Christian Anfisen and his colleagues showed that denatured ribonuclease can spontaneously refold into the active enzyme in the absence of other cellular constituents.

Front 12

How does the side chain of cysteine help in the folding of certain proteins?

Back 12

The side chain of cysteine contains a sulfhydryl group that can form covalent disulfide bonds with another cysteine residue, stabilizing the structure of cell surface and secreted proteins.

Front 13

What are the biological roles of cholesterol?

Back 13

Cholesterol can be incorporated into membranes where it can regulate membrane fluidity. also used to synthesize steroid hormones.

Front 14

Why are membrane spanning regions of transmembrane proteins frequently alpha helical? What other protein structure is capable of spanning membranes?

Back 14

The alpha helical membrane spanning structure allows the CO and NH groups of peptide bonds t form hydrogen bonds with each other, neutralizing their polar character. Beta barrels are also capable of transversing lipid bilayers.

Front 15

Which amino acids are most likely to be found in a membrane spanning alpha helix?

Back 15

Amino acids with hydrophobic side chains capable of interacting with the fatty acids of membrane lipids. Alanine.

Front 16

Many eukaryotic organisms have genome sizes that are much larger than their complexity would seem to require. Explain this paradox.

Back 16

Organisms with larger genomes than their complexity have larger amounts of noncoding DNA

Front 17

How do intron sequences in the human genome increase the diversity of proteins expressed from the limited number of 20,000-25,000 genes?

Back 17

Through alternative splicing more than one protein can be synthesized from the same gene, thereby increasing the diversity of proteins expressed from a limited number of genes.

Front 18

What is the average distance between genes in the human genome?

Back 18

100kb

Front 19

How was the approach used by Celera Genomics to sequence the human genome different from that used by the International Human Genome Sequencing Consortium?

Back 19

The IHGSC sequenced BAC clones that had already been mapped to distinct regions of human chromosomes. Celera used whole genome shotgun approach in which DNA frags were sequenced at random and overlaps between fragments were then used to reassemble a complete genome sequence

Front 20

Why is it more difficult to identify regulatory sequences than it is to identify protein coding sequences? What are the different approaches used to identify functional regulatory sequences?

Back 20

unlike protein coding sequence, regulatory sequences are short, poorly defined sequences that occur frequently by chance in large genomes, making it difficult to identify functional regulatory sequences. approaches used to identify functional regulatory sequences include looking for clusters of regulatory elements, for sequences that are conserved in evolution, and for sequences that are present in coordinately regulated genes.

Front 21

How does footprinting identify a protein-binding site on DNA

Back 21

The DNA sequence is radiolabeled at one end. it is then incubated with the protein and subjected to partial digestion with DNAase. The site at which the protein binds will be protected from digestion, so no labeled pieces of that length will be seen after electrophoresis of the digested DNA.

Front 22

What is the role of sigma factors in bacterial RNA synthesis?

Back 22

Sigma factors bind to sequences upstream of the transcription start site, bringing RNA polymerase specifically to the promotor region to initiate transcription.

Front 23

How do enhancers differ from promoters as cis-acting regulatory sequences in eukaryotes?

Back 23

The activity of enhancers depends neither on their distance nor their orientation with respect to the transcription start site. Promotors are defined as being near the transcription start site.

Front 24

You are studying the enhancer of a gene that normally is expressed only in neurons. Constructs in which this enhancer is linked to a reporter gene are expressed in neuronal cells but not in fibroblasts. however, if you mutate a specific sequence element within the enhancer, you find expression in both fibroblasts and neuronal cells. What type of regulatory protein do you expect binds the sequence element?

Back 24

The sequence element would be a potential binding site for a tissue-specific repressor.

Front 25

What are the functions of insulators?

Back 25

They divide chromosomes into individual domains of chromatin structure that can be euchromatin or heterochromatin but cannot spread beyond and insulator. Also, they prevent an enhancer in one domain from acting on a promotor in the next domain.

Front 26

What property of Sp1 was exploited for its purification by DNA affinity chromography? How would you determine that the purified protein is indeed sp1?

Back 26

The specific high-affinity binding of sp1 to the GC box DNA sequence is exploited for its biochemical purification by DNA-affinity chromatogrpahy. To demonstrate that the purified protein is Sp1, you could carry out in vitro transcription assays.

Front 27

How can noncoding RNA's regulate the concentration of a specific mRNA within a cell

Back 27

Noncoding RNAs can repress the transcription of a target gene via RITS complex and they can induce the degredation of a target mRNA via the RISC complex. Thus noncoding RNAs can regulate both the synthesis and degradation of target transcripts.

Front 28

E. Coli Contain 64 different codons in their mRNAs, 61 of which code for amino acids. How can they synthesize proteins when they have only 40 different tRNAs?

Back 28

many tRNAs are able to recognize more than one codon because the third base of their anticodon can "Wobble" or form hydrogen bonds in nonstandard ways with bases other than the usual complementary pairs.

Front 29

You wish to express a cloned eukaryotic cDNA in bacteria. What type of sequence must you add in order for the mRNA to be translated on prokaryotic ribosomes?

Back 29

A shine-dalgarno sequence is needed.

Front 30

Discuss the evidence that ribosomal RNA is the major catalytic component of the ribosome.

Back 30

ribosomes depleted of most of their proteins can still synthesize polypeptides, whereas treatment with RNase completely abolishes translational activity. In addition, high-resolution structural analysis of the 50S ribosomal subunit showed that the site at which the peptidyl transferase reaction occurs is composed of rRNA, not ribosomal protein.

Front 31

What are chaperones? Why is it beneficial for the synthesis of heat-shcok proteins to be induced by exposure of cells to elevated temperatures?

Back 31

Chaperones are proteins that aid in proper folding of other proteins. elevated temp can denature proteins. heat-shock proteins are chaperones that aid in the refolding of these denatured proteins, restoring protein function.

Front 32

You are interested in studying a protein expressed on the surface of liver cells. How could treatment of these cells with a phospholipase enable you to determine whether you protein is a transmembrane protein or one that is attached to the cell surface by a GPI anchor?

Back 32

phospholipase treatment would release a GPI-anchored protein but not a transmembrane protein from the cell surface.

Front 33

How do miRNAs regulate the translation of specific mRNAs?

Back 33

miRNAs can target specific mRNAs via the RISC complex, leading to either mRNA degradation or inhibition of translation

Front 34

What is the function of 3' UTR's in mRNAs?

Back 34

Sequences in the 3' UTRs can regulate mRNA stabiliity, localizaion, and translation by serving as binding sites for regulatory factors and miRNAs

Front 35

Why did noller and colleagues use ribosomes of T. aquaticus for their studies?

Back 35

since T. aquaticus grows at high temperatures its rRNA is more stable than e. coli rRNA and better able to withstand the vigorous protein extraction procedures used in Noller's experiments

Front 36

Why is regulated proteolytic cleavage important for the activity of certain proteins?

Back 36

Signal sequences that target proteins to a specific cellular compartments are often removed by the action of signal peptidases. additionally, many proteins are synthesized as larger precursor proteins and are proteolyticlaly processed to yeild the mature proteinn

Front 37

You are studying a pathway responsible for the secretion of ribonuclease (RNase) in cultured pancreatic cells, by assaying the activity of secreted RNase in cultured medium. how would the expression of siRNA targeted against protein disulfide isomerase (PDI) affect the amount of RNase you detect in your experiments?

Back 37

PDI allows rapid exchanges between paired disulfides, yielding a pattern of disulfide bonds that is compatible with the stably folded conformation of a protein. inhibiting PDI with the siRNA will interfer with the correct folding of RNase, so you will detect much lower RNase activity in the medium of cells expressing the siRNA.

Front 38

What is miRNA

Back 38

short, double stranded RNAs that can regulate gene expression at both the transcriptional and translational levels.

Front 39

What does protein disulfide isomerase (PDI) do?

Back 39

PDI promotes rapid exchanges between paired disulfides, allowing the protein to attain the pattern of disulfide bonds that is comparable to stably folded conformation. STABILIZES PROTEIN STRUCTURE

Front 40

Describe the following post-translational modifications of proteins, 1.) Cleavage and 2.) Glycosylation (N-linked and O-linked)

Back 40

Cleavage: secreted proteins and proteins incorporated into most eukaryotic organelles are targeted to their destinations by amino terminal sequences that are removed by protolytic cleavages as the polypeptide chain crosses the membrane.
Many eukaryotic proteins, especially secreted and membrane proteins, are modified by the addition of carbohydrates in the endoplasmic reticulum and golgi aparatus.

Front 41

What role does the attachment of lipids have in protein processing?

Back 41

Covalently attached lipids frequently target and anchor proteins to the plasma membrane.

Front 42

How does cholesterol extend the functional temperature range of a lipid bilayer?

Back 42

At high temp cholesterols ring structure inhibits movement of phospholipids in the bilayer. at low temps it interfers with fatty acid chain interactions and maintains fluidity

Front 43

How are peripheral membrane proteins distinguished form integral membrane proteins?

Back 43

Peripheral membrane proteins can be reomoved from a membrane by a high-salt wash or by solutions of extreme pH that do not disrupt the phospholipid bilayer. Integral membrane proteins can only be extracted from membranes by detergents that disrupt the bilayer

Front 44

How did the cell fusion experiments of Frye and Edidin support the fluid mosaic model? What results would they have obtained if they incubated fused cells at 2 C?

Back 44

Fused mouse and human cells and looked at distribution of membrane proteins after staining with fluorescent dyes. Proteins intermixed, showing lateral membrane fluidity. 2 is too cold.

Front 45

What are the main functions of the glycocalyx?

Back 45

The glycocalyx protects the cell surface and is involved in cell-cell interactions

Front 46

How does the selectivity filter of K+ channels differentiate between K+ and Na+ ions?

Back 46

The K+ channel is lined with carbonyl oxygen atoms. K+ becomes dehydrated when it associates with the carbonyl oxygens and is able to fit through. The Na+ are too small to interact with the carbonyl oxygen and remain associated with water molecules and can't fit through the channel.

Front 47

How can glucose be transported against its concentration gradient without the direct expenditure of ATP in intestinal epithelial cells?

Back 47

The uptake of glucose against its concentration gradient is coupled to the transport of Na+ ions in the energetically favorable direction

Front 48

How does mdr gene confer drug resistance upon cancer cells?

Back 48

The mdr gene encodes an ABC transporter that is frequently overexpressed in cancer cells. the transporter can recognize a variety of drugs and pump them out of the cell, conferring resistance to chemotheraputic drugs

Front 49

What was the original experimental evidence for the secretory pathway from rough ER-->Golgi apparatus --> Secretory vesicles-->secreted protein?

Back 49

Palade and coworkers labeled pancreatic acinar cells with a pulse of radioactive amino acids. Autoradiography showed that the labeled proteins had moved to the golgi apparatus and after longer periods, the labeled proteins were found in secretory vesicles and then outside of cells. PULSE CHASE

Front 50

Compare and contrast cotranslational and posttranslational translocation of polypeptide chains into the ER

Back 50

Cotranslational involves binding of nascent polypeptide to the signal recognition particle and translocation through a translocon driven by protein synthesis. Posttranslational targets a polypeptide to the ER after synthesis is complete and does not require SRP. a Sec 62/63 complex recognizes a polypeptide to be incorporated and inserts it into a translocon. The polypeptide is pulled through into the ER lumen by the chaperone BiP