Molecular Genetics Lecture Flashcards

65 Question & Answer flashcards covering DNA & RNA basics, replication, transcription, translation, mutations, and bacterial genetics.

Which four nucleotides make up DNA?

Adenine (A), Thymine (T), Guanine (G), Cytosine (C)

What structural feature describes DNA’s two complementary strands?

They are antiparallel and form a double helix.

Which four nucleotides make up RNA?

Adenine (A), Uracil (U), Guanine (G), Cytosine (C)

What is the primary role of mRNA?

It serves as the single-stranded template for protein synthesis.

What is the function of tRNA?

It transports a specific amino acid to its corresponding mRNA codon.

What does rRNA contribute to in the cell?

It forms part of the ribosome and helps catalyze protein synthesis.

How is the leading strand synthesized during DNA replication?

Continuously in the 5′→3′ direction.

How is the lagging strand synthesized?

Discontinuously, producing Okazaki fragments.

What are Okazaki fragments?

Short DNA segments formed on the lagging strand during replication.

What enzyme lays down the RNA primer in replication?

Primase

Which enzyme synthesizes most of the new DNA on the leading and lagging strands?

DNA Polymerase III

Which enzyme removes RNA primers and replaces them with DNA?

DNA Polymerase I

What enzyme seals the gaps between Okazaki fragments?

DNA Ligase

What is a telomere?

A protective DNA segment added to chromosome ends to prevent loss of coding DNA.

What does telomerase do?

It adds telomere sequences to the ends of chromosomes.

Where does DNA replication begin on a chromosome?

At the origin of replication.

What is the role of helicase in replication?

It unwinds and separates the DNA double helix.

How does topoisomerase aid replication?

It relieves supercoiling stress by cutting and rejoining DNA strands.

What do single-strand binding proteins do?

They stabilize separated DNA strands, preventing re-annealing.

In which direction are new DNA strands synthesized?

5′ to 3′, adding nucleotides to the 3′ end.

Why do linear chromosomes gradually shorten, and how is this mitigated?

The lagging strand cannot fully replicate the ends; telomeres buffer the loss.

How does transcription differ from DNA replication in scope?

Transcription copies a specific gene; replication copies the entire genome.

What is the function of transcription factors?

They bind promoter or regulatory sequences to control gene transcription.

Define the promoter region.

A DNA sequence where RNA polymerase binds to initiate transcription.

What is the most effective way to stop a gene’s expression experimentally?

Delete or mutate its promoter region.

Why are a 5′ cap and poly-A tail added to eukaryotic mRNA?

To increase mRNA stability and aid translation initiation/export.

What is RNA splicing?

Removal of introns and joining of exons in pre-mRNA.

What are exons?

Protein-coding regions retained in mature mRNA.

What are introns?

Non-coding regions removed from pre-mRNA.

What does alternative splicing accomplish?

It generates different proteins from one gene by varying exon combinations.

During transcription initiation, what first binds the promoter?

RNA Polymerase (with transcription factors in eukaryotes).

What happens during transcription elongation?

RNA polymerase adds RNA nucleotides complementary to the DNA template.

How is transcription terminated?

RNA polymerase reaches a termination sequence and detaches from DNA.

What occurs during translation initiation?

Small ribosomal subunit and Met-tRNA bind AUG on mRNA; large subunit joins.

In what order do tRNA-bound sites on the ribosome participate during elongation?

A site → P site → E site

What causes translation termination?

Stop codons (UAA, UAG, UGA) recruit release factors, freeing the polypeptide.

What is a point mutation?

A single nucleotide change by substitution, insertion, or deletion.

Define a silent mutation.

A base change that does not alter the encoded amino acid.

What is a missense mutation?

A base change that substitutes one amino acid for another.

What is a nonsense mutation?

A base change that converts a codon into a premature stop codon.

What is a frameshift mutation?

Insertion or deletion shifting the mRNA reading frame, altering downstream amino acids.

What is a forward mutation?

A change from wild-type allele to mutant allele.

What is a backward (reversion) mutation?

A mutation that converts a mutant allele back to wild type.

How does bacterial DNA replication initiate and proceed?

From a single origin, proceeding bidirectionally around the circular chromosome.

What is binary fission?

Bacterial asexual reproduction where DNA duplicates and the cell divides into two.

Why don’t bacteria form a mitotic spindle?

Replication and chromosome segregation occur simultaneously without spindle apparatus.

What is a plasmid?

A small, circular, independently replicating DNA molecule in bacteria carrying non-essential genes.

List the three basic parts of an operon.

Promoter, operator, and structural genes.

What is the promoter’s role in an operon?

It is the binding site for RNA polymerase to start transcription.

What is the operator’s function?

It can bind a repressor to block RNA polymerase movement.

What do structural genes code for in an operon?

Proteins needed for a specific metabolic pathway.

What are regulatory genes?

Genes encoding products (e.g., repressors) that control other genes’ expression.

How does a repressor protein regulate transcription?

By binding the operator to decrease transcription of downstream genes.

What is an activator in prokaryotic gene regulation?

A protein that binds DNA to enhance RNA polymerase attachment and increase transcription.

What induces the lac operon?

The presence of lactose, which inactivates the lac repressor to allow transcription.

When is the trp operon repressed?

When tryptophan is abundant and binds the repressor, enabling it to block transcription.

Describe bacterial conjugation.

Direct DNA transfer from donor to recipient via a pilus bridge.

What is bacterial transformation?

Uptake of free environmental DNA by a competent bacterium.

Define transduction in bacteria.

DNA transfer between bacteria mediated by a bacteriophage.

What is the genome of an organism?

Its complete set of genetic information, largely non-coding in humans.

What is the transcriptome?

All RNA molecules that a cell can produce.

Define proteome.

The full set of proteins expressed by an organism or cell.

What special plasmid is transferred during conjugation to form a pilus?

The F (fertility) plasmid.

Why are plasmid genes considered advantageous but non-essential?

They provide benefits (e.g., antibiotic resistance) but are not required for basic survival.

In which direction does bacterial DNA replication proceed around the chromosome?

In both directions (bidirectionally) from the single origin.