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WorksheetsDe Bio Exam 4
Total questions: 89
Worksheet time: 45mins
Which observation from Griffith’s experiment best supports the idea of transformation in bacteria?
Live R mixed with heat-killed S kills mice
Heat-killed S strain is nonpathogenic in mice
R strain alone remains harmless in lung tissue
Live S strain causes disease in healthy mice
During the Hershey–Chase experiment, which labeled element was found inside infected bacteria, indicating the genetic material?
Radioactive phosphorus labeling viral DNA
Radioactive sulfur labeling viral proteins
Radioactive phosphorus labeling viral proteins
Radioactive sulfur labeling viral DNA
Which set correctly lists the components of a DNA nucleotide?
Ribose sugar, phosphate group, nitrogenous base
Deoxyribose sugar, phosphate group, nitrogenous base
Deoxyribose sugar, phospholipid group, nitrogenous base
Deoxyribose sugar, peptide group, nitrogenous base
Which statement accurately reflects Chargaff’s rules for double-stranded DNA?
Ratios of A:T:G:C identical in all species
A equals T; G equals C within a genome
Purines equal pyrimidines only in RNA
A equals G; T equals C across species
Select all features of the Watson–Crick DNA model supported by experimental evidence.
Covalent bonds between paired bases at the helix core
Double helix with base-paired strands
Two antiparallel sugar–phosphate backbones
Hydrogen bonds between complementary bases inside
Uniform pairing of purines with purines
Why does pairing one purine with one pyrimidine contribute to DNA’s structural stability?
It allows bases to attach to the sugar’s 3′ carbon
It increases phosphodiester bond formation rate
It keeps constant helix diameter across the length
It maximizes hydrogen bond numbers per base
Which description correctly distinguishes the 5′ and 3′ ends of a DNA strand?
Both ends have free phosphate groups only
Both ends have free hydroxyl groups only
5′ has a free hydroxyl; 3′ has a free phosphate
5′ has a free phosphate; 3′ has a free hydroxyl
Which combination of labels correctly matches base pairing and strand orientation in a DNA molecule?
Complementary strands run antiparallel 5′→3′ and 3′→5′
Strands run parallel 5′→3′ in the same direction
G pairs with C via hydrogen bonds
A pairs with T via hydrogen bonds
Base pairing occurs on the outside of the helix
Which observation from the Meselson–Stahl experiment most directly supports semiconservative replication?
Immediately, all DNA showed medium density
After one round, DNA showed medium density
After two rounds, all DNA showed light density
After one round, all DNA showed heavy density
In semiconservative replication, what happens to parental DNA strands during replication?
One strand serves as template for both daughters
Parental strands join to form a new helix
Each parental strand serves as template for one daughter
Both strands are degraded and replaced
Which component is required by DNA polymerase to begin synthesis on a new DNA strand?
A free 3′ hydroxyl primer end
A free 5′ phosphate primer end
A nicked template backbone
A single-stranded circular template
Which statement correctly describes DNA polymerase directionality during synthesis?
Reads 5′ to 3′, builds 3′ to 5′
Reads 3′ to 5′, builds 5′ to 3′
Reads 5′ to 3′, builds 5′ to 3′
Reads 3′ to 5′, builds 3′ to 5′
In E. coli, which DNA polymerase is primarily responsible for bulk DNA synthesis at the replication fork?
DNA polymerase I
DNA polymerase II
DNA polymerase III
DNA primase
What is the role of DNA primase during replication?
Extends Okazaki fragments with DNA
Builds short RNA primers for initiation
Removes RNA primers from lagging strand
Seals nicks between DNA fragments
Which enzyme unwinds the DNA helix and requires energy?
Helicase
DNA gyrase
SSB protein
DNA ligase
What is the primary function of single-strand binding (SSB) proteins during replication?
Add nucleotides to the 3′ end
Coat exposed single strands to stabilize them
Form RNA primers near the fork
Prevent supercoiling by cutting DNA
Which best distinguishes leading and lagging strand synthesis?
Leading uses RNA; lagging uses DNA
Leading continuous; lagging discontinuous fragments
Leading needs primer; lagging does not
Leading 3′ to 5′; lagging 5′ to 3′
Okazaki fragments are joined into a continuous lagging strand by which enzyme?
DNA polymerase I
DNA gyrase
DNA ligase
DNA polymerase III
Which statement best explains why linear eukaryotic chromosomes need telomerase?
Primase fails to add primers on lagging ends
Helicase overextends strands during replication
Ligase removes nucleotides from chromosome tips
DNA polymerase shortens 3' ends every cycle
Which combination correctly matches a DNA repair mechanism to its primary function?
Proofreading repair: re-synthesizes via undamaged strand
Photo repair: repairs UV-induced thymine dimers
Mismatch repair: replaces incorrect base pairs
Excision repair: removes damaged DNA nonspecifically
Telomerase activity typically shows which trend in normal human aging?
Activity decreases with age
Activity increases steadily
Activity oscillates annually
Activity remains constant
In the one gene–one polypeptide hypothesis, what is the key implication for gene function?
Each gene specifies a single polypeptide
Each gene makes multiple unrelated enzymes
Each gene directly produces mature proteins
Each gene codes entire metabolic pathways
Select all accurate statements about the central dogma.
DNA to RNA is transcription
DNA to protein is replication
RNA to DNA is telomere synthesis
RNA to protein is translation
Which statement best describes transcription in cells?
RNA polymerase copies the coding strand into tRNA
RNA polymerase synthesizes mRNA using the template strand
Ribosomes read mRNA to assemble amino acids into proteins
Reverse transcriptase converts proteins back into RNA
Which RNA directly interacts with both amino acids and mRNA during translation?
rRNA catalyzes peptide bond formation in ribosomes
tRNA pairs anticodons and delivers specific amino acids
mRNA carries codon sequences to the ribosome
snRNA processes pre-mRNA in the nucleus
Which set correctly identifies features of the genetic code?
Includes stop codons UAA, UAG, UGA
Is completely unique to each species
Has start codon AUG for methionine
Read in triplets called codons
During prokaryotic transcription initiation, what event occurs first at the promoter?
DNA ligase seals nicks in the coding strand
Ribosomes bind to the start site of the gene
RNA polymerase binds the promoter to begin transcription
Reverse transcriptase forms RNA-DNA hybrids
Which statements about transcription termination in prokaryotes are correct?
Occurs at defined terminator sequences
Always needs ribosomes to dissociate mRNA
Can involve formation of a hairpin structure
Requires the start codon AUG to appear
Which eukaryotic RNA polymerase primarily transcribes protein-coding genes (mRNA)?
RNA polymerase I
RNA polymerase II
RNA polymerase III
Mitochondrial RNA polymerase
Which feature is characteristic of a typical RNA polymerase II promoter in eukaryotes?
Shine–Dalgarno site
Pribnow box motif
TATA sequence element
Operator sequence region
Which modification is added to the 5′ end of eukaryotic mRNA during processing?
5′ methyl G cap
3′ poly-A tail
3′ CCA addition
5′ intron excision
Which statement correctly describes polyadenylation of eukaryotic mRNA?
Initiates transcription of rRNA genes
Removes exons from the transcript
Adds a 3′ tail of many A residues
Adds a 5′ protective cap
Which components catalyze intron removal from pre-mRNA in eukaryotes?
Aminoacyl‑tRNA synthetase
Ribozymes within rRNA
Spliceosome with snRNA
DNA ligase complex
Which outcome can result from alternative splicing of a single gene?
Multiple mRNAs producing protein variants
Identical proteins from all transcripts
Elimination of the 5′ cap addition
Loss of the poly-A tail on mRNA
Which pair correctly matches a tRNA structural feature with its function?
Variable loop—houses the poly-A sequence
Acceptor end—carries attached amino acid
Anticodon loop—base-pairs with mRNA codon
D loop—binds the ribosomal E site
Which statement about ribosome functional sites is accurate?
P site holds the peptidyl‑tRNA
E site forms peptide bonds
E site binds the charged tRNA
A site binds the exiting tRNA
During translation initiation in eukaryotes, which event occurs earliest to position the start codon for protein synthesis?
Peptidyl transferase forms first bond
Small subunit with factors scans mRNA
Release factors recognize AUG codon
Large subunit binds to mRNA
Which statement best describes the A, P, and E sites during elongation in the ribosome?
A releases tRNA, P forms chain, E accepts new tRNA
A accepts tRNA, P holds chain, E releases tRNA
A forms peptide, P exits tRNA, E holds chain
A holds growing chain, P accepts new tRNA, E exits
Translocation in elongation refers to which coordinated movement?
Large subunit detaches from small subunit
Ribosome shifts one codon on mRNA
Release factors move into the P site
tRNA anticodon mutates to match codon
Which factor triggers termination of translation?
Initiator tRNA leaves the ribosome
Wobble pairing occurs at E site
Stop codon enters the A site
Start codon appears in P site
Which option correctly matches mutation type with its typical effect on coding sequence?
Triplet repeat expansion shortens protein coding
Frameshift insertion alters downstream reading frame
Nonsense substitution creates a stop codon
Missense substitution changes the amino acid
Silent substitution leaves amino acid unchanged
Small insertions or deletions collectively termed indels most often cause which consequence in an open reading frame?
Increase copy number across the genome
Change start codon to different codon
Introduce early stop by nonsense
Cause frameshift when not in multiples of three
Copy number variation (CNV) includes which structural changes?
Gene duplications increasing copies
Balanced inversions preserving copy count
Translocations reducing copy number
Point substitutions altering bases
Gene deletions removing segments
Proteins destined for secretion are targeted to which cellular destination during or after translation?
Mitochondrial outer membrane via Tat
Lysosome via COPI vesicles
Endoplasmic reticulum via SRP
Nuclear pore via Ran-GTP
Which level of gene expression control is most commonly targeted to regulate phenotype conversion from genotype?
DNA replication fidelity
Post-translational modification
Translation elongation control
Transcription initiation control
Regulatory proteins influence transcription by binding specific DNA sequences. What are the two general outcomes of this binding?
Blocking RNA polymerase binding
Facilitating RNA polymerase binding
Increasing ribosome binding
Changing DNA replication origin firing
Altering mRNA splicing patterns
DNA-binding domains of regulatory proteins commonly interact with which structural feature of the double helix?
Major groove of DNA
Minor groove of DNA
Phosphate backbone only
Histone cores exclusively
Negative control of transcription relies on repressors. Which statement best describes their action at the operator?
Repressors open chromatin to silence genes
Repressors degrade mRNA to reduce expression
Repressors bind the promoter to recruit polymerase
Repressors bind the operator to block transcription
Positive control involves activators. What is their primary role at promoters?
Increase mutation rate of genes
Terminate transcription early
Remove repressors from operators
Help RNA polymerase bind DNA
In prokaryotes, operons coordinate genes for pathways. Which pairing correctly matches condition and regulatory effect?
Lactose absent induces the lac operon
Tryptophan present represses the trp operon
Tryptophan absent represses the trp operon
Lactose present represses the lac operon
Lactose present induces the lac operon
In the lac operon, what is the direct effect when allolactose binds the lac repressor?
RNA polymerase detaches from promoter
cAMP levels immediately increase
Repressor cannot bind the operator
Repressor binds operator more tightly
Select all statements that correctly describe glucose repression of the lac operon.
Activator needs cAMP to bind DNA
Cells prefer glucose over lactose
cAMP rises when glucose is abundant
Glucose import limits lactose transport
Which feature distinguishes eukaryotic transcription regulation from prokaryotes?
Single promoter without enhancers
Specific activators bind distant enhancers
RNA polymerase binds operator sequences
cAMP-CRP controls most transcription
Choose the correct statements about transcription factors in eukaryotes.
Specific factors act in particular tissues or times
Activators are a type of specific transcription factor
General factors form initiation complex at promoter
Mediators block RNA polymerase II binding
Which chromatin modification most commonly correlates with transcriptional activation in eukaryotes?
Histone phosphorylation on centromeres
Histone acetylation on lysine tails
DNA methylation at CpG promoters
miRNA loading onto RISC complex
High levels of DNA methylation at a gene promoter typically lead to which outcome?
Chromatin compaction and silencing
Increased mRNA export efficiency
Recruitment of RNA polymerase II
Enhanced transcription initiation
X-chromosome inactivation in female mammals primarily serves what biological purpose?
Enhance transcription of autosomes
Dosage compensation between sexes
Generate extra copies of X-linked genes
Promote meiotic recombination on X
Which statements about histone modifications are correct? Select all that apply.
Effect depends on modification position
Modifications only inhibit gene expression
Acetylation generally increases transcription
Multiple histones can be chemically modified
miRNAs typically regulate gene expression by which mechanism?
Editing bases in mature mRNA
Enhancing ribosome recruitment
Translational repression via RISC
Promoter demethylation in the nucleus
Which description best distinguishes siRNA from miRNA pathways?
miRNA targets DNA for cleavage
siRNA binds mRNA to direct degradation
siRNA promotes ribosome assembly
miRNA always increases translation
Alternative splicing of a single gene can result in which outcome?
Identical proteins in all tissues
Loss of 5′ cap structures
Multiple protein isoforms per gene
Immediate mRNA degradation
Which posttranscriptional controls can regulate translation initiation in eukaryotes? Select all that apply.
Nuclear pore exclusion of mRNA
RISC complex blocking ribosomes
Presence of a poly(A) tail
Repressor proteins binding the 5′ cap
Which statement best describes the role of ubiquitin in eukaryotic cells?
Acts as a protease that cleaves damaged proteins
Directly unfolds misfolded proteins into active form
Signals proteins for proteasome-mediated degradation
Marks mRNA transcripts for rapid cytoplasmic decay
What does the proteasome primarily degrade after tagging?
Phospholipid membranes
Ribosomal RNA
Double-stranded DNA
Polyubiquitinated proteins
Which pair correctly matches a tool with its function in recombinant DNA work?
DNA ligase—separates DNA fragments by size
Restriction endonuclease—cuts DNA at specific sequences
Gel electrophoresis—joins DNA fragments into plasmids
Ubiquitin—creates sticky ends for cloning
Restriction enzymes often recognize palindromic sequences. What does palindromic mean in this context?
Forms a hairpin loop upon cutting
Has variable length depending on enzyme
Contains only purines in the motif
Reads the same 5′ to 3′ on both strands
Cutting between the G and A in GAATTC by EcoRI produces which feature useful for cloning?
Blunt ends lacking overhangs
Sticky ends with complementary overhangs
Single-stranded breaks without overhangs
Covalently closed circular DNA
Which statements are true about gel electrophoresis of DNA fragments?
DNA migrates toward the positive pole
Agarose gels separate fragments by size
Larger fragments move faster than smaller ones
Fluorescent dyes enable visualization
After electrophoresis, how can DNA fragments be used to construct recombinant molecules?
Purify bands and join fragments using DNA ligase
Expose gel to proteasomes for fragment fusion
Neutralize charges to halt migration permanently
Tag fragments with ubiquitin to enhance joining
What reaction is catalyzed by DNA ligase during cloning?
Hydrolysis of palindromic sequences into mononucleotides
Creation of sticky ends by asymmetric cleavage
Formation of a phosphodiester bond between adjacent nucleotides
Denaturation of DNA into single strands
Which statement best explains why reverse transcriptase is crucial for creating cDNA libraries from eukaryotic cells?
It converts mRNA into complementary DNA lacking introns
It copies genomic DNA including introns into plasmids
It synthesizes RNA primers for DNA polymerase
It ligates DNA fragments into bacterial chromosomes
A researcher wants only protein-coding sequences from brain tissue. Which approach should be used to build the library?
Genomic DNA library from whole-cell extracts
cDNA library generated using reverse transcriptase
Mitochondrial DNA library from isolated organelles
Whole-transcriptome sequencing of all RNAs
Which pair correctly matches a cloning vector type with a typical example used in labs?
Eukaryotic chromosome — yeast centromere plasmid
Plasmid vector — small circular DNA molecule
Viral vector — linear bacterial chromosome fragment
Artificial chromosome — mitochondrial RNA template
During PCR, what happens in the denaturation step?
DNA strands separate at high temperature
Primers bind to template at low temperature
RNA is converted to DNA by reverse transcriptase
DNA polymerase extends primers at mid temperature
Why is Taq polymerase suitable for PCR?
It synthesizes RNA primers for cDNA cloning
It remains active at high temperatures without denaturing
It denatures primers during high heat cycles
It proofreads mismatches at cold temperatures
Select all statements that accurately describe PCR primer use in diagnostic testing for pathogens.
Primers enable amplification of nucleic acids from infectious agents
Primers anneal during the denaturation step of PCR
Only pathogen-specific primers are required for detection
Primers must flank a region unique to the pathogen
Which scenario correctly distinguishes RT‑PCR from standard PCR when detecting RNA viruses?
RT‑PCR replaces DNA polymerase with ligase during synthesis
RT‑PCR adds a reverse transcriptase step to copy RNA into cDNA
RT‑PCR omits primers to avoid RNA degradation issues
RT‑PCR uses lower denaturation temperatures than DNA PCR
Bacteria cannot process introns. What consequence does this have for expressing a human gene in E. coli?
Genomic DNA must be cloned to include regulatory introns
cDNA derived from mature mRNA should be cloned
Precursor mRNA is directly translated by ribosomes
Introns are spliced by bacterial RNA polymerase
Which combination of steps correctly orders a basic PCR cycle?
Denaturation, annealing, synthesis
Synthesis, denaturation, annealing
Denaturation, synthesis, annealing
Annealing, synthesis, denaturation
Which feature makes short tandem repeats useful for DNA fingerprinting in forensics?
They occur only in mitochondrial DNA
They encode essential protein sequences
They vary in repeat number among individuals
They are identical across all individuals
In CRISPR/Cas9 editing, what determines the specific genomic target of Cas9?
A guide RNA complementary to the target
Short tandem repeat variability
PCR primers flanking the locus
Random binding of Cas9 nuclease
Which step follows Cas9-mediated DNA cutting during gene editing?
Protein degradation by proteasomes
Methylation of promoter regions
RNA splicing of the target gene
DNA repair that can replace sequences
Which statement best distinguishes knockout mice from knockin mice?
Knockouts inactivate a gene; knockins replace with altered allele
Knockouts remove a gene entirely; knockins insert a plasmid
Knockouts change promoters; knockins use viral vectors
Knockouts edit RNA; knockins modify epigenetic marks
During creation of knockout mice, why are embryonic stem cells grown with neomycin?
To increase STR repeat instability
To induce meiotic recombination events
To trigger Cas9 expression in embryos
To select cells carrying the interrupted gene
Which applications directly rely on DNA fingerprinting using STRs? Select all that apply.
Pinpointing a gene’s chromosomal location
Determining paternity relationships
Quantifying mRNA expression of a gene
Identifying an individual from bodily fluids
What is a transgene in the context of transgenic organisms?
A mutated endogenous allele
A gene introduced from another species
An epigenetic modification marker
A noncoding regulatory sequence
Why does the universality of the genetic code enable transgenesis across species?
DNA repair pathways are universal
Proteins fold identically in all organisms
Ribosomes read the same codons to amino acids
Promoters are conserved across all genomes
Which statement describes a capability of CRISPR/Cas9 beyond cutting DNA?
It can translate mRNA into protein
It can amplify DNA via thermostable polymerase
It can activate or repress gene expression
It can sequence genomes rapidly
When using PCR primers to analyze STRs in forensics, which principle is essential?
Primers must encode neomycin resistance genes
Primers flank regions known to contain STRs
Primers bind uniquely to mitochondrial DNA
Primers target guide RNA sequences for Cas9
