Calling all AP Biology enthusiasts! It's time to challenge yourself with our free ap biology chapter 15 quiz - designed to test your understanding of DNA replication, gene expression, and molecular genetics in chapter 15 ap biology. Whether you're cramming for finals or simply sharpening your skills, this ap bio chapter 15 practice test will highlight your strengths and pinpoint areas to review. Dive into realistic scenarios, apply key concepts, and track your progress in real time. Ready for more? After tackling these questions, explore our detailed chapter 12 review or deepen your understanding with targeted MCQ practice . Don't wait - your journey to exam success starts here! Jump in now and take the first step toward mastering AP Bio!
Which enzyme synthesizes RNA primers during DNA replication?
Helicase
DNA ligase
DNA polymerase I
DNA primase
DNA primase is responsible for synthesizing the short RNA primers that DNA polymerases need to begin DNA strand elongation. Without these primers, DNA polymerases cannot initiate replication. DNA polymerase I removes RNA primers subsequently and replaces them with DNA. For more details, see Khan Academy: DNA replication.
In which direction is new DNA synthesized during replication?
Both directions simultaneously
5' to 3'
Random directions
3' to 5'
DNA polymerases can only add nucleotides to the 3' hydroxyl end of a growing strand, hence DNA synthesis occurs in the 5' to 3' direction. The template strand is read from 3' to 5', allowing complementary strand synthesis. This unidirectional activity is fundamental to replication fork dynamics. For more, see NCBI: DNA Replication.
What term describes a region of DNA where RNA polymerase binds to initiate transcription?
Enhancer
Promoter
Operator
Terminator
A promoter is a specific DNA sequence to which RNA polymerase and transcription factors bind to initiate transcription. Promoters are located upstream of the coding region. Operators are binding sites for repressors in prokaryotic operons, while enhancers act at a distance in eukaryotes. For more, see Khan Academy: Promoters and enhancers.
Which molecule carries amino acids to the ribosome during translation?
rRNA
tRNA
snRNA
mRNA
Transfer RNA (tRNA) molecules transport specific amino acids to the ribosome, matching their anticodon with the mRNA codon. Each tRNA is charged with an amino acid by aminoacyl-tRNA synthetases. rRNA is a structural component of ribosomes, and mRNA carries the codon sequence. For more, see Khan Academy: Translation overview.
Which base is found in RNA but not in DNA?
Cytosine
Guanine
Uracil
Thymine
RNA contains the base uracil instead of thymine, which pairs with adenine during transcription. Thymine is replaced by uracil in RNA to distinguish it from DNA. This difference is key to the structural and functional roles of RNA. For more, see Khan Academy: RNA vs DNA.
In the lac operon, the lac repressor binds to which DNA sequence?
Promoter
Enhancer
Operator
Terminator
The lac repressor protein binds to the operator region of the lac operon, blocking RNA polymerase from transcribing the genes needed for lactose metabolism. When an inducer molecule like allolactose binds the repressor, it cannot bind the operator and transcription proceeds. For more detail, see Khan Academy: Lac operon.
What is the primary function of DNA ligase during replication?
Synthesizes RNA primers
Adds nucleotides to the leading strand
Joins Okazaki fragments
Unwinds the DNA helix
DNA ligase seals the nicks between Okazaki fragments on the lagging strand by catalyzing the formation of phosphodiester bonds. This action is essential for creating a continuous DNA strand. Without ligase, the lagging strand would remain fragmented. For more, see NCBI: DNA ligase.
Which process removes introns from pre-mRNA to form mature mRNA?
Editing
Splicing
Capping
Polyadenylation
Splicing is carried out by the spliceosome, which recognizes conserved sequences at intron - exon junctions and excises introns. The remaining exons are ligated to form mature mRNA. Capping and polyadenylation are other processing steps but do not remove introns. For more, see Khan Academy: RNA splicing.
Which of the following is TRUE about the leading strand during DNA replication?
It is synthesized continuously toward the replication fork
It requires multiple RNA primers
It is synthesized in the 3' to 5' direction
It forms Okazaki fragments
The leading strand is synthesized continuously in the 5' to 3' direction as the replication fork opens. It requires only one RNA primer at its origin. In contrast, the lagging strand is synthesized discontinuously as Okazaki fragments. For more, see Khan Academy: DNA replication.
During elongation in translation, which site of the ribosome holds the tRNA with the growing polypeptide chain?
D site
E site
A site
P site
The P (peptidyl) site holds the tRNA carrying the growing polypeptide chain. New aminoacyl-tRNAs enter the A (aminoacyl) site, and the E (exit) site is where deacylated tRNAs leave the ribosome. For more detail, see Khan Academy: Translation.
What does the wobble hypothesis explain in genetic translation?
Alternative start codon usage
Mispairing at the first codon position
Post-translational modification of tRNA
Flexibility in codon - anticodon pairing at the third nucleotide position
The wobble hypothesis states that the third base of a codon can form nonstandard base pairs with the corresponding base of the tRNA anticodon, allowing fewer tRNAs to recognize multiple codons. This flexibility helps explain the degeneracy of the genetic code. For more, see Khan Academy: Wobble hypothesis.
Which modification adds a poly-A tail to eukaryotic mRNA?
Splicing
Polyadenylation
5' capping
RNA editing
Polyadenylation adds a stretch of adenine nucleotides to the 3' end of eukaryotic pre-mRNA, enhancing stability and aiding in nuclear export. This process is carried out by poly(A) polymerase after cleavage of the pre-mRNA. For more, see Khan Academy: mRNA processing.
Which enzyme removes RNA primers and replaces them with DNA during replication?
DNA ligase
DNA polymerase I
DNA polymerase III
Primase
In prokaryotes, DNA polymerase I has 5'?3' exonuclease activity that removes RNA primers and polymerase activity that fills in the resulting gaps with DNA. DNA polymerase III then carries out most of the elongation. For more, see NCBI: DNA polymerases.
A mutation that changes a codon for one amino acid into a codon for a different amino acid is called a what?
Frameshift mutation
Nonsense mutation
Silent mutation
Missense mutation
A missense mutation is a point mutation in which a single nucleotide change results in a codon that codes for a different amino acid. Nonsense mutations create a stop codon, silent mutations do not change the amino acid, and frameshifts alter the reading frame. For more, see Khan Academy: Mutations.
What molecule acts as the inducer in the lac operon, causing the repressor to release from the operator?
Lactose permease
cAMP
Glucose
Allolactose
Allolactose, an isomer of lactose, binds to the lac repressor and induces a conformational change that prevents it from binding the operator. This allows RNA polymerase to transcribe the operon's genes. cAMP - CAP complex regulates activation, not induction. For more, see Khan Academy: Lac operon.
What term describes a sequence of three nucleotides in mRNA that codes for one amino acid?
Anticodon
Operon
Exon
Codon
A codon is a triplet of mRNA nucleotides that specifies a single amino acid during translation. The anticodon is found on tRNA and pairs with the codon. Exons are coding regions of DNA that remain in mature mRNA. For more, see Khan Academy: Genetic code.
Which enzyme unwinds the DNA double helix to form the replication fork?
Topoisomerase
SSB proteins
DNA primase
Helicase
Helicase breaks hydrogen bonds between base pairs, unwinding the double helix and creating replication forks. Single-strand binding proteins stabilize the unwound DNA, while topoisomerase relieves supercoils. For more, see NCBI: Helicase.
During eukaryotic transcription initiation, which general transcription factor first binds to the TATA box?
TFIIF
TFIID
TFIIB
TFIIH
TFIID contains the TATA-binding protein (TBP) subunit, which first recognizes and binds the TATA box in eukaryotic promoters. This binding facilitates the assembly of other general transcription factors and RNA polymerase II. For more, see NCBI: Eukaryotic transcription initiation.
What is the role of release factors in translation?
They aid in tRNA charging
They recognize stop codons and terminate polypeptide synthesis
They bind promoters
They assist ribosome assembly
Release factors bind to the ribosomal A site when a stop codon is present, catalyzing the release of the polypeptide chain from the tRNA in the P site. This terminates translation. For more, see Khan Academy: Translation termination.
What structure forms in mRNA during attenuation of the trp operon to terminate transcription?
Rho factor binding site
Operator - repressor complex
Enhancer loop
Terminator hairpin loop
When tryptophan levels are high, the leader peptide stalls ribosomes in a way that allows a terminator hairpin loop to form in the trp operon mRNA, causing RNA polymerase to dissociate. This attenuates transcription. For more, see Khan Academy: Trp operon.
Which DNA repair mechanism removes UV-induced thymine dimers?
Mismatch repair
Nonhomologous end joining
Nucleotide excision repair
Base excision repair
Nucleotide excision repair recognizes bulky lesions like thymine dimers, removes a short single-stranded DNA segment containing the damage, and fills the gap using DNA polymerase. Base excision repair handles smaller lesions. For more, see Khan Academy: DNA repair.
The Shine-Dalgarno sequence is found in which type of organism and what is its function?
Eukaryotes; it signals polyadenylation
Prokaryotes; it helps align the ribosome with the start codon
Prokaryotes; it terminates translation
Eukaryotes; it caps the mRNA
The Shine-Dalgarno sequence is a purine-rich region upstream of the start codon in bacterial mRNA that base-pairs with the 16S rRNA to position the ribosome for initiation. Eukaryotes use the 5' cap for ribosome recruitment instead. For more, see NCBI: Translation initiation.
What is the function of the sigma factor in prokaryotic transcription?
Directs RNA polymerase to the promoter
Joins Okazaki fragments
Synthesizes RNA primers
Unwinds DNA at the replication fork
The sigma factor binds to the RNA polymerase core enzyme to form the holoenzyme, which specifically recognizes promoter sequences and initiates transcription. It dissociates after initiation. For more, see Khan Academy: Prokaryotic transcription.
Telomerase extends chromosome ends by using which of the following?
Single-strand binding proteins
A DNA primer and DNA polymerase III
An RNA template and reverse transcriptase activity
DNA ligase and topoisomerase
Telomerase is a ribonucleoprotein that carries its own RNA template, which it uses in a reverse transcriptase reaction to extend telomeric DNA repeats at chromosome ends. This counteracts the end-replication problem. For more, see Khan Academy: Telomerase.
Alternative splicing in eukaryotes is regulated by which proteins that influence spliceosome assembly?
Rho proteins
Sigma factors
SR proteins
Release factors
SR (serine/arginine-rich) proteins bind to splicing enhancer sequences on pre-mRNA and recruit spliceosomal components, regulating alternative splicing patterns. This allows production of multiple protein isoforms from a single gene. For more, see NCBI: Alternative splicing.
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Study Outcomes
Understand DNA Replication Mechanisms -
Gain a clear grasp of the enzymatic steps and molecular players involved in DNA synthesis as outlined in chapter 15 ap biology, reinforcing core replication concepts.
Analyze Gene Expression and Regulation -
Examine operon models and transcription control to compare prokaryotic and eukaryotic regulation pathways, sharpening your skills for the ap biology chapter 15 quiz.
Apply Molecular Genetics Principles -
Use problem-solving techniques to tackle practice questions on DNA replication, transcription, and translation found in the ap biology chapter 15 practice test.
Evaluate Mutation Effects -
Interpret how different types of mutations alter genetic information and protein function, preparing you to identify mutation outcomes in quiz scenarios.
Identify Key Genetic Components -
Recognize promoters, enhancers, operators, and other regulatory elements critical to understanding ap bio chapter 15 molecular genetics.
Integrate Chapter Concepts for Exam Readiness -
Combine insights from DNA replication, gene regulation, and molecular genetics to boost confidence and accuracy in AP Biology Chapter 15 assessments.
Cheat Sheet
DNA Replication Dynamics -
One core concept in Chapter 15 AP Biology is that DNA replication proceeds bidirectionally from origins of replication, with helicase unwinding strands and primase laying RNA primers for DNA polymerase III. On the lagging strand, Okazaki fragments require DNA ligase to join fragments, illustrating the 5′→3′ synthesis direction (NCBI, MIT OCW). This ensures high-fidelity copying guided by proofreading exonuclease activity.
Lac Operon Control -
In Escherichia coli, the lac operon is an inducible system where allolactose acts as an inducer to release the LacI repressor from the operator (Cold Spring Harbor). Under lactose presence, RNA polymerase transcribes lacZYA genes to metabolize lactose. Mnemonic tip: "Lactose = loosens the lock" helps recall that lactose induces transcription.
Trp Operon Mechanism -
The trp operon in E. coli is a repressible system regulated by tryptophan acting as a corepressor, enabling the TrpR protein to bind the operator and halt transcription (Nature Reviews). This negative feedback loop shuts down biosynthesis when tryptophan levels are high. Remember "Trp = trip the switch" to recall that tryptophan trips the repressor to stop its own transcription.
Chromatin Remodeling & Epigenetics -
Histone acetylation by HAT enzymes neutralizes positive charges on histone tails, loosening DNA-histone interactions and enhancing transcription (NIH Epigenomics). In contrast, DNA methylation of CpG islands by DNA methyltransferases generally silences gene expression, as reflected in cancer epigenetics studies. A handy mnemonic is "ACE = Active Chromatin via Acetylation."
RNA Processing & Alternative Splicing -
Eukaryotic pre-mRNA undergoes 5′ capping, 3′ polyadenylation, and intron removal by the spliceosome (EMBL-EBI). Alternative splicing can produce multiple protein isoforms from a single gene; for example, the Drosophila Dscam gene generates over 38,000 variants. Keep in mind "CAP and TAIL set sail," and splice variably to boost diversity.
