Biochem Repeats

All of the following statements about ribosomes are correct except: a. mitochondria have 80S ribosomes, and all mitochondrial proteins are synthesized on these ribosomes b. the larger subunits of all ribosomes have the enzyme peptidyl transferase which forms peptide bonds c. all ribosomes have two subunits, the large subunit approximately twice the size of the smaller subunit d. eukaryotic cells have 80S ribosomes, and protein synthesis on these ribosomes can be inhibited by cycloheximide e. prokaryotic cells have 70S ribosomes, and protein synthesis on these ribosomes can be inhibited by chloramphenicol

A

Alternative splicing: a. requires different snRNAs b. involves different proteolytic processing events to generate different proteins c. gives rise to different arrangements of genomic DNA d. results in the production of distinct proteins having a number of common properties e. results from the actions of different RNases to degrade exon sequences

A

Best describe snRNAs: a. function in a variety of nuclear processes, including the splicing of pre-mRNA b. code for proteins c. form the basic structure of ribosome d. central to protein synthesis as adaptors between mRNA and amino acids e. catalyze peptide bond synthesis in the process of protein synthesis

A

Choose 5'-terminal sequences of starters which should be used to amplify- using the PCR method- an underlined fragment of a gene (only the sequence of the coding strand is shown) CCTAG`AAATCGGCGCG ----///------ATATGGGTTTT`ACTATT a. forward: AAATCGG; reverse: AAAACCC b. forward: AAATCGG; reverse: TTTTGGG c. forward: TTTAGCC; reverse: TTTTGGG d. forward: CCTAGAA; reverse: AATAGT e. forward: AAATCGG; reverse: GGGTTTT

A

Choose the correct statement concerning glycoproteins: a. N-glycosylation begins cotranslationally in the endoplasmic reticulum and involves an oligosaccharide intermediate attached to dolichol phosphate b. in N-linked glycoproteins carbohydrate is attached to the N-terminal amino group c. most cytosolic proteins are glycosylated d. large carbohydrate component usually correlates with low water solubility of a protein e. mannose phosphate in the protein-linked carbohydrate targets this protein to secretion from the cell

A

Correct statements about DNA biosynthesis are: 1) DNA polymerase copies the DNA template strand in the 3' to 5' direction 2) the new strand grows in the 5' --> 3' direction 3) the release of pyrophosphate (PPi) and its subsequent cleavage provides the energy that drives the polymerization process a. all b. 1 and 2 c. only 3 d. none e. all except 1

A

Determine if the following statements are true or false: 1) When DNA is cut with restriction enzymes and subjected to electrophoresis on an agarose gel, the smallest pieces can be found nearest to positive electrode 2) In bacteria, separate DNA polymerase complexes synthesize the DNA on the leading and lagging strands of the replication fork: a. 1 true, 2 false b. 1 false, 2 true c. 1 false, 2 false d. 1 true, 2 true e. cannot be determined

A

Figure 2 presents a ribosome just after formation of the first peptide bond during translation. Match the numbers with description: a. 1- mRNA 5'-end; 2-tRNA in P site; 3- N terminal amino acid b. 1- mRNA 3'-end; 2-tRNA in P site; 3- C terminal amino acid c. 1- mRNA 5'-end; 2-tRNA in P site; 3- C terminal amino acid d. 1- mRNA 5'-end; 2-tRNA in A site; 3- C terminal amino acid e. 1- mRNA 3'-end; 2-tRNA in A site; 3- N terminal amino acid

A

Figure 3 represents a diagram of a human mature mRNA. Which description is false: a. A is the codon that specifies the formyl-Met b. F is the place where oligo-dT primer can bind during synthesis of cDNA c. B is the site for initial binding of small ribosomal subunit d. E is the place of binding of eukaryotic releasing factors (RF) during translation e. C is region that is translated

A

In Figure 5 sequences A, B, and C correspond to: a. A- coding strand, B- template strand, C- RNA transcript b. A- coding strand, B- template strand, C- RNA strand complementary to the coding strand c. A- coding strand, B- template strand, C- RNA strand complementary to the coding strand d. A- template strand, B- coding strand, C- RNA strand complementary to the coding strand e. A- template strand, B- coding strand, C- RNA transcript

A

In eukaryotic DNA replication: a. at least one DNA polymerase has a 3' -> 5' exonuclease activity b. helicase dissociates from DNA as soon as the initiation bubble forms c. helicase is required to initiate synthesis on the leading strands d. only one replisome forms, because there is a single origin of replication e. the process occurs throughout the cell cycle

A

Micro-RNAs: a. may inhibit translation or induce degradation of specific mRNAs b. are products of intron removal and do not play any role c. result from cleavage of 5' terminal part of pre-mRNA d. are usually several hundred nucleotides long e. may control gene expression mostly through regulation of transcription initiation

A

Small nuclear RNAs such as U1-U6 affect gene expression by: a. functioning as essential components of the spliceosome b. promoting proper transcription termination c. diminishing the rate of transcription d. functioning as self-catalytic components of rRNA e. functioning as modified bases within tRNA

A

Splicing of eukaryotic mRNa precursors involves all of the following except: a. binding of DNA ligase b. need for adenine in intron c. RNA cleavage and ligation reactions d. binding of small nuclear ribonucleoproteins (snRNPs) e. assembly of spliceosome

A

The TATA box present in human genes: a. is recognized by one of the general transcription factors b. is usually localized down-stream from the start of transcription c. it represents an enhancer sequence to which gene-specific transcription factors bind d. it is essential for starting the replication e. it represents the sequence of DNA to which eukaryotic RNA polymerase can bind directly

A

The first step in protein synthesis that distinguishes a protein to be secreted from one to be retained in the cytoplasm is: a. binding of the signal recognition particle to the signal sequence b. attachment of the ribosome to a membrane c. binding of the fmet-tRNA to the ribosome d. binding of specialized ribosomes to the mRNA e. removal of signal sequences by signal peptidase

A

The formation of tautomers of the DNA bases can be mutagenic because they can cause: a. abnormal base pairing b. deamination c. cross-linking d. strand breakage e. depurination

A

The phosphodiester bonds that link adjacent nucleotides in both RNA and DNA: a. join the 3' hydroxyl of one nucleotide to the 5' hydroxyl of the next b. are uncharged at neutral pH c. are susceptible to alkaline hydrolysis d. always link A with T and G with C e. form between the planar rings of adjacent bases

A

What does not apply to the Okazaki fragment: a. a short strand of RNA or DNA that serves as a starting point for DNA synthesis b. is an intermediate in DNA replication c. is synthesized during replication of the lagging strand d. is producing by the combined action of primase and DNA polymerase III e. a short fragment of newly synthesized DNA, attached to the 3' end of a short RNA primer

A

Which of the following enzymes is involved in extending the ends of linear chromosomal DNA: a. RNA-dependent DNA polymerase b. poly A polymerase c. DNA-dependent RNA polymerase d. RNA-dependent RNA polymerase e. DNA-dependent DNA polymerase

A

Which of the following properties is common to both DNA polymerase and RNA polymerase: 1) DNA strand is used as template 2) 3' ->5' nuclease activity 3) requirement of a primer to start synthesis of nucleic acid chain 4) 5' -> 3' polymerase activity a. 1,4 b. 2,4 c. 1,2,4 d. 1,2,3,4 e. 4

A

Which one of the following functions best describes the role of DNA polymerase I in bacterial cells: a. modifies Okazaki fragments for joining into intact strands b. synthesizes most of the cellular DNA during replication c. its main role is in DNA repairs d. joins two adjacent DNA strands together e. synthesizes RNA primers to initiate Okazaki fragments

A

Which one of the following single stranded DNA molecules contains a palindrome in the double stranded state: a. GpTpCpApTpGpApCp b. none of them c. ApTpGpCpCpGpTpAp d. ApTpGpCpTpApCp e. GpCpTpApTpGpApCp

A

Which of the following defines the role of eIF2: a. eIF2 binds Met-tRNA initiator and delivers it to the 40S ribosomal subunit b. eIF2 is the cap binding protein c. eIF2 binds Met-tRNAinitiator and delivers it to the 60S ribosomal subunit d. eIF2 mediates the formation of the 80S initiation complex e. eIF2 binds Met-tRNAinitiator and delivers it to the 40S ribosomal subunit

A, E

A nuclease is an enzyme which catalyzes: a. the hydrolysis of internucleotide linkages of a polynucleotide chain b. the hydrolysis of nucleotides to nucleosides and inorganic phosphate c. the synthesis of a polynucleotide chain from nucleotide units d. the synthesis of nucleotides from bases and sugar-phosphates e. the hydrolysis of cyclic AMP

B

A nuclease is an enzyme which catalyzes: a. the synthesis of polynucleotide chain from nucleotide units b. the hydrolysis of nucleotides to nucleosides and inorganic phosphate c. the hydrolysis of internucleotide linkages of a polynucleotide chain d. the synthesis of nucleotides from bases and sugar-phosphates e. the hydrolysis of cyclic AMP

B

Adjacent deoxyribonucleotides on one strand of a double-stranded DNA molecule are connected by which of the following types of chemical bonds: a. glycosidic b. phosphodiester c. hydrogen d. electrostatic e. van der waals

B

Choose the correct description of oligonucleotide presented in figure 1: a. arrow 5 shows thymine b. arrow 1 shows N-glycosidic bond c. it is a fragment of DNA molecule d. arrow 4 shows deoxyribose e. arrow 3 shows the place of attachment of new nucleotide during transcription

B

Contains both a 7-methylguanosine triphosphate cap and a polyadenylate pre-RNA segment: a. mRNA b. tRNA c. snRNA d. rRNA

B

In cells exposed to the diphtheria toxin, which of the following processes related to gene expression are affected (direct result of its action): a. transcriptional termination b. translational elongation c. transcriptional initiation d. transcriptional elongation e. translational initiation

B

Listed are four enzymes involved in DNA replication: 1) DNA polymerase III 2) primase 3) DNA ligase 4) DNA polymerase I The correct order of these enzymes in the synthesis of lagging strand is: a. 2, 4, 1, 3 b. 2, 1, 4, 3 c. 4, 2, 1, 3 d. 4, 1, 2, 3 e. 4, 3, 2, 1

B

One enzyme necessary for the genetic information of some RNA virus to be incorporated into the chromosome of a host eukaryotic cells: a. viral RNa polymerase b. RNA-dependent DNA polymerase c. DNA-dependent-RNA polymerase d. RNA ligase e. host cell RNA polymerase

B

One of these statements is false: a. examples of nucleosides include cytidine, uridine, adenosine, guanosine, thymidine, and inosine b. since introns are largely 'genetic junk,' they do not have to be removed precisely from the primary transcript during RNA splicing c. exon is the segment of a eukaryotic gene consisting of a sequence nucleotides that will be represented in mRNA or other functional RNAs d. eukaryotic mRNA molecules carry 3' ribosyl OH groups at their 3' end e. the consequences of errors in transcription are less severe than those of errors in DNA replication

B

RNA polymerase: a. synthesizes RNA chains in the 3' -> 5' direction b. can synthesize RNA chains de novo (without a primer) c. has a subunit which acts as a proofreading ribonuclease d. binds tightly to a region of DNA thousands of base pairs away from the sequence to be transcribed e. separates DNA strands throughout a long region of DNA (up to thousands of base pairs), then copies one of them

B

Synthetic oligonucleotides of a desired sequence are used in following techniques: 1) PCR 2) detection of genes 3) detection of specific cDNA a. only 1 b. all listed c. only 2 and 3 d. only 1 and 3 e. only 1 and 2

B

The two most widely used methods of replication of any specific DNA sequence chosen by the experimentalist are molecular cloning and PCR. The fundamental difference between them is: a. molecular cloning involves replication of the DNA within a living cell, while PCR replicates DNA in the test tube, free of living cells b. all answers are correct c. molecular cloning generally uses DNA sequences from two different organisms, while PCR amplifies an existing sequence d. molecular cloning involves formation of recombinant DNA while PCR amplifies by copying an existing sequence e. two answers are correct

B

There are six general transcription factors (GTFs) that are needed for specific promoter binding- these GTFs are assembled in a specific order starting with: a. TFIIE B. TBP (pr TFIID or TATA binding protein) c. TFIIA d. TFIIB e. TFIIF- RNA Pol II

B

Which of the following characteristics of nucleosomes is important for compacting genomic DNA into chromatin: a. the histone constitutes of nucleosomes containing a relatively high proportion of leucine and asparagine amino acids b. wrapping DNA about a nucleosome core c. multiple copies of histone H1 d. multiple posttranslational modifications present on multiple amino acids in the N-terminal regions of histones within nucleosomes e. none of the above

B

Which of the following enzymes can be used for the construction of a recombinant DNA molecule: a. reverse transcriptase + DNA polymerase b. restriction enzyme + DNA ligase c. DNA polymerase + RNA polymerase d. DNA polymerase + DNA ligase e. endonuclease + reverse transcriptase

B

Which of the following proteins may be directly involved in transcription of human genes: 1) gyrase 2) helicase 3) ligase 4) primase 5) single-stranded binding proteins a. 1,5 b. 2 c. 2,3 d. 1,4 e. 1,2,3

B

Which of the following statements about double-helical DNA is correct: 1) the DNA double helix is stabilized by base-stacking interactions among aromatic nucleobases 2) the outside of the helix is neutral 3) in B-DNA, the most common double helical structure, the double helix is right-handed with about 10 nucleotides per turn 4) given the difference in widths of the major groove and minor groove, many proteins which bind to DNA do so through the wider major groove a. only (2) is correct b. all except (2) are correct c. only (3) and (4) are correct d. only (1) and (4) are correct e. all except (1) are correct

B

Which of the following statements about eukaryotic transcription factors is false: a. an enhancer is a DNA sequence that binds gene-specific transcription factors, which facilitate the recruitment of RNA polymerase to the gene promoter region b. a leucine zipper is a structural motif present in some transcription factors, which is used for interaction with DNA; it contains several Leu residues that are involved in binding of a Zn ion to the protein c. binding of a steroid hormone to its receptor causes dimerization of the receptor, and increases the affinity for DNA d. enhancers may be located several thousand base pairs upstream or downstream from the gene, and also within introns e. the zinc-finger motif, present in some steroid hormone receptors, contains an alpha helix that interacts with bases present in DNA major groove

B

Which of the following statements are true only for eukaryotic transcription and processing of mRNA but not for prokaryotic: 1) transcription is regulated by the binding of proteins to specific DNA sequences upstream of the gene 2) the RNA is terminated at the 5' end with a cap, consisting of 7-methyguanosine connected by a triphosphate bridge 3) RNA polymerase locally melts the DNA strand and copies only the template strand 4) noncoding regions of the RNA transcript are spliced out 5) the 3'-terminus of the RNA consists of a long string of A residues (poly A) which are added posttranscriptionally a. only 1, 4 and 5 are true b. only 2, 4 and 5 are true c. only 2, 3 and 4 are true d. only 3, 4 and 5 are true e. only 1, 2 and 3 are true

B

Which of these statements about nucleic acids is false: a. mitochondria contains DNA b. the DNA sequences used in the construction of recombinant DNA molecules can originate from plant DNA or fungal DNA but never from human DNA c. the genome of many viruses in RNA d. the DNA of viruses is usually much longer than the viral particle itself

B

Which one of the following statements is true: a. translation terminates in some cases due to the action of Rho factor b. if the codon sequence is AUG the anti-codon sequence of the tRNA which recognizes AUG must be UAC c. if the base sequence at the 3' end of tRNA is altered, the amino acid-tRNA synthetase will add the wrong amino acid to the tRNA d. ribosomes can bind to mRNA in prokaryotes while the RNA is still being synthesized e. in eukaryotes most of the proteins are made in the nucleus because that is where RNA is made

B

Which statement is/are correct about compound the structure of which is presented in Figure 3: a. its phosphorylated form terminates DNA chain elongation when added to the growing 3' -end by reverse transcriptase b. three are correct c. analog of deoxytymidine d. it is first approved treatment for HIV e. two are correct

B

All of the following statements about RNA polymerase and DNA polymerase are correct except: a. both are required for replication in certain systems b. both require nucleoside triphosphates as substrates c. both require a primer d. both require a template e. both elongate in the 5' to 3' direction

C

Damaged cytosolic proteins are labeled 1)______ and then are degraded by a protein complex called 2)_______ a. 1) oligosaccharide 2) chaperone b. 1) acetyl group at specific Lys residues 2) lysosome c. 1) ubiquitin 2) proteasome d. 1) phosphate at specific Ser or Thr residues 2) lysosome e. 1) ubiquitin 2) translocon

C

During translation in bacteria the correct order of steps, depicted in Figure 4 is: a. none is correct b. 3,2,4,1 c. 3,1,4,2 d. 3,2,1,4 e. 4,1,2,3

C

Genes containing intervening sequences (or introns): a. do not code for proteins b. must undergo a DNA rearrangement before expression c. code for RNA precursors which must be spliced before translation d. are rare in eukaryotic cells e. are common in prokaryotes

C

Incorrect statement is: a. DNA denaturation leads to the increase of absorbance at 260 nm b. in B-DNA helix there are about 10 base pairs per turn c. histones acetylation increases the stability of nucleosomes- is associated with transcriptional repression d. structural gene is a segment of DNA that contains the information required for the synthesis of a functional biological product (protein or RNA) e. the haploid human genome has ~3x10^9 bp in DNA

C

Mammalian ribosomes consist of: a. 40S and 60S subunits which form a 100S ribosome b. one subunit c. 40S and 60S subunits which form an 80S ribosome d. 30S and 50S subunits which form an 80S ribosome e. two 40S subunits which form an 80S ribosome

C

Many catalytic activities occur during protein synthesis. Choose the correct feature of the peptidyl transferase: a. it catalyzes a reversible reaction b. it is involved in translocation of a polypeptide across the ER membrane c. it is a ribozyme d. ATP requirement e. its activity requires eEF-2

C

Many catalytic activities occur during protein synthesis. What is unusual about the activity of peptidyl transferase: a. it is reversible b. it requires EF-2 c. it is a ribozyme d. ATP requirement e. it is independent of the ribosome

C

Rare tautomeric forms of the DNA bases can be mutagenic because they can cause: a. base deamination b. nucleotides depurination c. abnormal base pairing d. strands cross-linking e. breaking of strands

C

Replication of the DNA in a human chromosome is similar to E.coli DNA replication in all of the following except: a. RNA is used as a primer b. replication is semiconservative c. only one origin is involved per DNA molecule d. the lagging strand is synthesized discontinuously e. multiple DNA polymerases are involved

C

Which of the following is an initiation codon: a. CCC b. UAG c. AUG d. none of the answers correct e. UUU

C

Which of the following statements concerning DNA is correct: a. in cells, similarly as in water, the DNA assumes the form of a left-handed helix b. regions rich in AT pairs have higher melting temps comparing to regions rich in GC pairs c. the complementary chains in dsDNA have the opposite, antiparallel direction d. the melting temperature (Tm) is the temp at which all the hydrogen bonds holding two strands together are broken e. denaturation of dsDNA causes lowering of absorption as 260 nm

C

Which of the following statements is true: 1) 2' hydroxyl group in RNA is responsible for its higher chemical stability at alkaline solutions 2) AT-rich regions are typical to sites involved in initiation of replication or transcription 3) positively charged amino acid residues in histones help the histone bind tightly to DNA, regardless of its nucleotide sequence: a. all b. only 2 c. only 2 and 3 d. only 3 e. only 1 and 2

C

Which one of the following is not involved in the process of nucleotide-excision repair of lesions like pyrimidine dimers: 1) DNA lesions such as pyrimidine dimers are repaired by the excision of a 12- or 13-nucleotide fragment of the defective strand; 2) The ABC exonuclease makes single-strand cuts on both sides of the defect; 3) A gap in the DNA is filled in by DNA polymerase and sealed by DNA ligase: a. Only 3 b. Only 1 c. All are involved d. Only 2 e. Only 1,2 and 3

C

Choose the correct description of post-translational modification in humans: a. proteins may be glycosylated on Ser, Thr, or Try residues b. synthesis of secreted proteins involved removal of signal peptide, which is located at C-terminus of the protein c. two of the mentioned are correct d. formation of Cys-Cys disulfide bridges is a common modification of proteins synthesized in cytosol e. N-glycosylation of proteins starts in ER by transferring a complex oligosaccharide from dolicholphosphate to some Asn residues

C (D and E are correct)

A particular tRNA molecule includes the anticodon sequence AUG. What would be the corresponding sequence in the non-coding strand of the DNA molecule that encodes the mRNA that this tRNA would pair with: a. none of the mentioned b. AUG c. TAC d. ATG e. UAC

D

Analysis shows high levels of the primary transcript that codes for a protein in the brain, muscle, liver, and pancreas. However, an antibody that recognizes the C-terminal portion of the protein indicates that the protein is present in brain, muscle, and liver, but not in the pancreas. The most likely explanation for this result is: a. the gene that codes for this protein is not transcribed in the pancreas b. there is no modification of the primary transcript in the brain, muscle and liver c. alternative splicing in the brain, muscle and liver increases the level of translation d. alternative splicing in the pancreas yields a protein that is missing the portion that the antibody recognizes e. the primary transcript in the pancreas is not processed (modified)

D

During replication of DNA in the replication fork: a. no primer is required for the synthesis of the leading strand b. DNA ligase is required only for DNA replication in bacteria c. the lagging strand is synthesized in the 3' -> 5' direction, in contrast to the leading strand that is replicated in the 5' -> 3' direction d. the leading strand and the lagging strands are replicated simultaneously at similar speed because the multienzyme complex, called replisome contains two molecules of replication DNA polymerase e. the main replication enzyme is DNA polymerase I and DNA polymerase alpha, in bacteria and humans, resepctively

D

During the elongation phase of prokaryotic translation, for each amino acid added to the growing peptide chain, _____ GTP molecules is/are hydrolyzed to GDP. The hydrolysis of one of the GTP molecules is required for ________: a. 2; peptide bond formation b. 2; assembly of the small and large ribosomal subunits c. 1; binding of CAP-binding complex to the 7-methyl-guanosine cap of mRNA d. 2; aminoacyl-tRNA delivery to A site e. 1; peptide bond formation

D

Following a day spent at the beach, which of the following types of DNA damage would most commonly be found in melanocytes within the basal layer of the epidermis: a. intrastrand cross-links b. apurinic sites caused by depurination c. nucleotide alkylation d. pyrimidine dimers e. double strand breaks

D

Helicases: 1) hydrolyze phosphodiester bonds 2) perform the same role as topoisomerases 3) require ATP 4) unwind the double helix a. all correct b. only 2 and 3 correct c. only 4 correct d. only 3 and 4 correct e. only 2, 3, 4 correct

D

Peptide bonds are formed during protein synthesis between: a. the carboxyl group on a free amino acid and the amino group on a free amino acid b. the carboxyl group on aminoacyl-tRNA and the amino group on peptidyl-tRNA c. the carboxyl group on aminoacyl-tRNA and the carboxy group on a free amino acid d. the carboxyl group on a free amino acid and the amino group on aminoacyl-tRNA

D

The length of the PCR products may be determined based on: a. binding a fluorescent dye b. UV light absorption c. hybridization with specific probes d. their migration in gel electrophoresis as compared to the standards e. melting temperature

D

Translocation in protein synthesis is best defined as: a. movement of a new aminoacyl-tRNA into the A site b. movement of the growing peptide chain from the tRNA in the P site to the tRNA in the A site c. dissociation of the tRNA in the P site from the ribosome d. movement of the peptidyl-tRNA in the A site to the P site e. scanning of a ribosome along an mRNA in search of the initiation codon

D

What is the proper order of steps 1-4 in protein synthesis: 1) aminoacyl-tRNA binds to the A site 2) unloaded tRNA is released from ribosome 3) peptide bond formation shifts the growing peptide from the P to the A site 4) the 50S subunit binds to the initiation complex of the 30S subunit and mRNA: a. 1, 2, 3, 4 b. 2, 1, 4, 3 c. 4, 1, 2, 3 d. 4, 1, 3, 2 e. 1, 3, 4, 2

D

Which of the following DNA sequences is palindromic and can be cut by a restriction endonuclease (only the sequence of one chain is shown): a. ACTTCA b. two of the shown sequences c. ACTTGA d. ACTAGT e. ACTACT

D

Which of the following gene mutations will always lead to a shortened protein: a. triplet expansion b. missense mutation c. frameshift mutation d. nonsense mutation e. deletion mutation

D

Which of the following is not involved in post-translational processing and maturation of proteins: a. proteases b. chaperone proteins c. dolichol phosphate d. proteasome e. signal peptidase

D

Which of the following statements about E.coli RNA polymerase (core enzyme) is false: a. in the absence of the sigma subunit, core polymerase has little specificity for where initiation begins b. the RNA chain grows in a 5' -> 3' direction c. the core enzyme has no polymerizing activity until the sigma subunit is bound d. the RNA product is complementary to the DNA template e. the core enzyme contains several different subunits

D

Which of the following statements is false: a. Thymine dimers, which form as a result of exposure to UV, repaired in humans by photolyase b. ethidium bromide is highly mutagenic because it can intercalate between bases within DNA c. deamination of cytosine leads to formation of uracil in DNA, which is removed using uracil DNA-glycosylase d. the mismatch repair system is dependent on the ability to recognize the half-methylated sequences that exist only for a short time after replication of DNA e. deamination of cytosine can be spontaneous or chemically induced by nitrous acids

D

Which one of the following is not involved in steroid hormone action: a. zinc fingers b. transcription activation and repression c. hormone-receptor complexes d. cell surface receptors e. specific DNA sequences (HRE- hormone response elements)

D

A strain of bacteria resistant to a specific antibiotic was isolated in a hospital laboratory. Biochemical analysis demonstrated that treatment of the sensitive strain with the antibiotic resulted in a block in bacterial RNA synthesis, whereas in the resistant strain, RNA synthesis was unaffected. The resistant strain is unaffected by which of the following drug: a. chloramphenicol b. tetracycline c. acyclovir d. amoxicillin e. rifampicin

E

Base excision repair: a. is used only for bases that have deaminated b. removes above 10-15 nucleotides c. requires the action of DNA polymerase III (e.coli) d. recognizes a bulky lesion e. uses enzymes called DNA glycosylases to generate an abasic sugar site

E

Breaking of N-glycosidic bonds in DNA will lead to: a. alkylation of bases b. breaking of DNA strand c. formation of pyrimidine dimers d. conversion of cytosine to uracil e. formation of AP sites

E

Choose the correct: a. positive ELISA test for an anti-HIV antibodies provides sufficient confirmation of the infection b. reverse transcriptase is characterized by a very low error rate c. western blot method allows to detect viral genome using specific labeled DNA probes d. one can detect anti-HIV antibodies in patient's blood much earlier than viral proteins or genome e. one can use PCR to detect proviral DNA in T-cells and RT-PCR to detect virions in a blood sample

E

Concerning the human genome: a. genes can show huge variation in size b. a very large fraction of the human genome is made up of highly repetitive noncoding DNA sequence c. protein-coding DNA sequences account for 1-2% of the genome d. two statements are correct e. three statements are correct

E

During translation the mRNA template is read in the ___ direction, while the new polypeptide is made in the ___ direction: a. 5' -> 3'; C->N b. 3' -> 5'; C ->N c. 3' -> 5'; N -> C d. none of the answers are correct e. 5' -> 3'; N -> C

E

In eukaryotes, which DNA polymerase is responsible for the replication of mitochondrial DNA a. alpha b. epsilon c. beta d. delta e. gamma

E

In the DNA B structure: a. both keto and rare enol form of T can form three hydrogen bonds with A b. phosphate groups are in the interior of the helix c. the diameter of the helix is 3.4 nm d. both strands run in the same direction (are parallel) e. certain proteins bind to DNA to alter its structure or to regulate transcription or replication- it is easier for these DNA binding proteins to interact with the bases in the major groove

E

Inhibitors of bacterial topoisomerases are used as antibiotics, while inhibitors of eukaryotic topoisomerases are used in chemotherapy of cancer. What is the role of these enzymes? a. to catalyze breaking of hydrogen bonds between complementary bases b. to move the ribosome along mRNA c. none of the answers is correct d. to change the anti-conformation of nucleotides into the syn- e. to help separate DNA strands by introducing negative supercoils

E

Many catalytic activities occur during protein synthesis. What is unusual about the activity of peptidyl transferase: a. it is activated by GTP b. its reaction is reversible c. ATP requirement d. it is independent of the ribosome e. it is a ribozyme

E

Naturally occurring reverse transcriptase can be found in _______, while restriction enzymes are produced by ______ a. retrovirus, DNA viruses b. retrovirus, plant cells c. DNA viruses, bacteria d. DNA viruses, bacteria e. retroviruses, bacteria

E

On the lagging strand, the primer on an Okazaki fragment is removed by the 5' --> 3' exonuclease activity of DNA polymerase I. What enzyme replaces the degraded primer with deoxyribonucleotides: a. DNA ligase + NAD b. primase c. DNA polymerase II d. DNA polymerase III e. DNA polymerase I

E

Proteins synthesized on endoplasmic reticulum membrane bound ribosomes can end as all of the following except: a. cytoplasmic proteins b. secreted proteins c. lysosomal proteins d. plasma membrane proteins e. cell-surface receptors

E

Reactions I and II presented in Figure 4 are catalyzed by: a. I - DNA polymerase; II - DNA ligase b. I - DNA polymerase; II - 5'→3' exonuclease activity of polymerase DNA c. I - RNA polymerase; II - 3'→5' exonuclease activity of polymerase DNA d. I - RNA polymerase; II - endonuclease activity of polymerase DNA e. I - DNA polymerase; II - 3'→5' exonuclease activity of polymerase DNA

E

Regarding the process of replication in E.coli, which of the following statements is incorrect: a. DNA replication is a semiconservative process b. there is a leading strand and a lagging strand at each replicating fork c. there is a unique site at which replication is initiated d. DNA synthesis occurs in the 5' to 3' direction e. DNA replication is unidirectional

E

Restriction enzymes are: a. DNA polymerases b. RNA polymerases c. exonucleases d. none of the mentioned e. endonucleases

E

The western blot method allows to detect specific ____, using specific _____: a. DNA sequences, dyes b. RNA sequences, oligonucleotide probes c. enzymes, inhibitors d. DNA sequences, oligonucleotide probes e. proteins, antibodies

E

Transcription of human genes that code for proteins requires all of the following except: a. DNA template strand b. binding of general and gene-specific transcription factors to gene promoter region c. ribonucleoside triphosphates d. presence of TATA box localized -25 bp upstream from the start of transcription e. RNA polymerase I

E

Which component of the system for protein synthesis actually translates the nucleotide code to an amino acid code: a. DNA polymerase b. messenger RNA c. transfer RNA d. RNA polymerase e. ribosomal RNA

E

Which of the following enzymes requires ATP for the formation of the phosphodiester bond during the joining of two DNA chains into one continuous strand: 1) eukaryotic DNA ligase 2) DNA topoisomerase type I 3) gyrase 4) bacterial DNA Pol I a. 1,2,3,4 b. 1,2,3 c. 1,2,4 d. 1 e. 1,3

E

Which of the following is true concerning the structure of tRNA: a. linear structure with no H-bonding between bases b. TwC sequence at 3' end c. -CCA sequence at 5' end d. anticodon loop near amino acid binding site e. many modified bases

E

Which two reactions are catalyzed by aminoacyl tRNA synthetases: a. amino acid decarboxylation and tRNA charging b. amino acid charging and tRNA phosphorylation c. amino acid charging and tRNA activation d. amino acid activation and aminoacyl-AMP synthesis e. amino acid activation and tRNA charging

E

eukaryotic initiation factors (eIFs) are proteins or protein complexes involved in the initiation phase of eukaryotic translation; which statement does not apply to eukaryotes: a. recruitment of the 40S ribosome to the 5' end of a eukaryotic mRNA requires the cap-binding protein (component of eIF4F) b. eIF2 is the main protein complex responsible for delivering the initiator tRNA to the P-site of the preinitiation complex, as a ternary complex containing Met-tRNA and GTP c. eIFs help stabilize the formation of ribosomal preinitiation complexes around the start codon and are an important input for post-transcription gene regulation d. eIF2 has specificity for the methionine-charged initiator tRNA, which is distinct from other methionine-charged tRNAs used for elongation of the polypeptide chain e. eIF's function is the formation of a 70S ribosome complex that places the mRNA and the formyl-Met-tRNA (Met-tRNA) in the correct position for starting the elongation process

E