DNA, RNA, and Genetic Information Flow: Key Concepts and Techniques

What is the central dogma of molecular biology?

The central dogma describes the flow of genetic information from DNA to RNA to proteins.

What are the four types of bases found in nucleic acids?

Adenine, guanine, cytosine, and thymine (in DNA); uracil replaces thymine in RNA.

What sugar is found in RNA?

Ribose.

What sugar is found in DNA?

Deoxyribose.

What type of linkage connects nucleotides in a nucleic acid?

Beta-Glycosidic linkage.

What is the significance of the base-pairing rules?

Adenine pairs with thymine, and guanine pairs with cytosine, ensuring accurate DNA replication.

What percentage of adenine is present if a DNA molecule contains 20% guanine?

30% adenine.

What is B-DNA?

B-DNA is the most common form of DNA, characterized by a right-handed double helix.

What is Z-DNA?

Z-DNA is a left-handed double helix with a zigzag backbone, occurring under certain conditions.

What is the Meselson-Stahl experiment known for?

It demonstrated that DNA replication is semiconservative.

What is hypochromism in the context of DNA?

Hypochromism refers to the increased absorbance of single-stranded DNA compared to double-stranded DNA.

What enzyme catalyzes DNA replication?

DNA polymerase.

What is the role of reverse transcriptase in retroviruses?

It converts RNA genomes into DNA.

What are the key roles of RNA in gene expression?

RNA serves as a template for protein synthesis and plays roles in transcription and translation.

What is the function of RNA polymerase?

RNA polymerase synthesizes RNA from a DNA template and does not require a primer.

What is a promoter site?

A region of DNA where RNA polymerase binds to initiate transcription.

What is the significance of the Shine-Dalgarno sequence?

It helps ribosomes recognize the start of translation in prokaryotic mRNA.

Introns and exons

__________non-coding regions of a gene, while______ are coding regions that are expressed.

What is alternative splicing?

A process that allows a single gene to produce multiple protein variants by including or excluding certain exons.

What is the role of tRNA in protein synthesis?

tRNA transports amino acids to the ribosome and matches them to the mRNA codons.

What is a codon?

A sequence of three nucleotides in mRNA that specifies a particular amino acid.

How does the reading frame affect protein synthesis?

The reading frame determines how codons are grouped and read during translation, affecting the resulting protein.

What is the function of the poly(A) tail in mRNA?

The poly(A) tail protects mRNA from degradation and aids in the export of mRNA from the nucleus.

What is the structure of an aminoacyl-tRNA?

It consists of an amino acid attached to the 3' end of tRNA and an anticodon for template recognition.

What is the role of the hairpin structure in mRNA?

The hairpin structure can signal termination of transcription in prokaryotes.

What is the significance of the 5' cap in eukaryotic mRNA?

The 5' cap aids in mRNA stability and recognition by ribosomes during translation.

What are the key tools used in the exploration of genes?

Restriction-enzyme analysis, blotting techniques, DNA sequencing, solid-phase synthesis of nucleic acids, and polymerase chain reaction (PCR).

What is a characteristic feature of restriction enzyme cleavage sites?

They almost always possess twofold rotational symmetry and are palindromic sequences.

What is the Sanger method used for?

DNA sequencing by controlled termination of replication.

What are the three steps in a polymerase chain reaction (PCR) cycle?

Denaturation (separation of DNA strands), annealing (hybridization of primers), and elongation (extension of primers by DNA synthesis).

What are the two classes of plasmids used in DNA cloning?

Cloning vectors for insertion and replication of DNA fragments, and expression vectors for production of large amounts of protein.

What is the role of lambda phage in DNA cloning?

Lambda phage can integrate into the host genome or multiply within a host, making it an ideal vector for cloning.

What are bacterial artificial chromosomes (BACs) and yeast artificial chromosomes (YACs) used for?

To propagate larger pieces of DNA, with BACs accommodating up to 300 kb and YACs up to 1000 kb.

How is complementary DNA (cDNA) prepared from mRNA?

By using reverse transcriptase to synthesize a cDNA strand, digesting the original RNA strand, and synthesizing a complementary DNA strand.

What is site-directed mutagenesis?

A method used to create specific, targeted changes in the DNA sequence.

What are next-generation sequencing (NGS) methods?

Techniques that enable rapid determination of complete genome sequences, including reversible terminator sequencing, pyrosequencing, and ion semiconductor sequencing.

What is the significance of comparative genomics?

It provides insights into evolutionary events by comparing genomes of different species.

What is the purpose of gene-expression analysis with DNA microarrays?

To simultaneously analyze the expression levels of thousands of genes.

Why can many eukaryotic genes only be expressed correctly in eukaryotic host cells?

Because bacteria lack the necessary enzymes for posttranslational modifications.

What is microinjection in the context of gene expression?

A method where cloned plasmid DNA is injected into the male pro-nucleus of a fertilized egg.

What are the methods used for gene disruption and genome editing?

Homologous recombination for gene knockout, RNA interference (siRNA) for gene knockdown, and genome editing by site-specific nucleases.

What is the recognition sequence for the restriction enzyme TaqI?

T|CGA.

What is the role of PCR in medical diagnostics?

PCR is used to amplify DNA for analysis, such as in forensic investigations.

What is the significance of the palindromic nature of restriction enzyme recognition sites?

It allows for the symmetrical cleavage of DNA, facilitating cloning and analysis.

What challenges are associated with preparing eukaryotic DNA libraries?

The need to remove intronic sequences to focus on protein-coding regions.

What is the purpose of using ethidium bromide in gel electrophoresis?

To stain DNA fragments for visualization under UV light.

How can DNA probes be synthesized?

By automated solid-phase methods.

What is the function of a polylinker in plasmid vectors?

To facilitate the insertion of foreign DNA sequences.

What is the role of terminal transferase in cDNA synthesis?

To add several G bases to the DNA after RNA digestion.

What is the importance of amplifying DNA isolated from forensic samples?

It allows for comparison with DNA from potential suspects to identify matches.

What is the outcome of using gel electrophoresis in DNA analysis?

It separates DNA fragments based on size for further analysis.

What is the significance of the polymerase chain reaction (PCR) in molecular evolution studies?

PCR allows for the amplification of specific DNA sequences, facilitating evolutionary analysis.

Alkaline hydrolysis susceptibility of RNA

Vulnerability to base-catalyzed degradation driven by the presence of the $2'\text{-OH}$ group on ribose, which acts as an intramolecular nucleophile to cleave the phosphodiester backbone.

Base stacking interactions

Hydrophobic interactions and van der Waals forces between adjacent, parallel base pairs that provide primary thermodynamic stability to the nucleic acid duplex.

Melting temperature ($T_m$)

The temperature at which half of the helical structure of duplex DNA is denatured into random coils, monitored at an absorbance of $260\text{ nm}$.

Hyperchromic effect

The substantial increase in optical absorbance at $260\text{ nm}$ observed when double-stranded DNA melts into separate single strands.

Sugar pucker conformation in B-DNA

$\text{C-2' endo}$, an arrangement that spaces adjacent phosphate groups farther apart along the helical axis.

Sugar pucker conformation in A-DNA

$\text{C-3' endo}$, producing a shorter, broader helix with a smaller rise per base pair.

Glycosidic bond conformations in Z-DNA

Alternating anti and syn conformations along the repeating purine-pyrimidine dinucleotide units of the left-handed helix.

Prokaryotic promoter consensus sequences

Conserved hexameric elements centered at $-10$ (the Pribnow box) and $-35$ upstream of the transcription initiation site.

Eukaryotic core promoter elements

Conserved regulatory sequences including the TATA box (Hogness box) near $-25$ and the CAAT box near $-75$.

Initiator amino acid in bacterial translation

$N\text{-formylmethionine}$ ($\text{fMet}$).

Exon shuffling

A recombination process that rearranges distinct protein-coding exons between genes to create novel proteins with mosaic domain architectures.

DNA ligase

An enzyme that seals nicks and joins recombinant fragments by catalyzing the formation of phosphodiester bonds between adjacent nucleotides.

Cohesive (sticky) ends

Short, complementary single-stranded extensions generated by staggered, asymmetric cleavage of restriction endonucleases.

Blunt ends

Fully base-paired termini generated when restriction endonucleases cleave both strands symmetrically at the identical phosphodiester position.

Cassette mutagenesis

A technique that replaces a defined target region flanked by restriction cleavage sites with a synthetic double-stranded oligonucleotide carrying desired mutations.

Southern blotting

A technique for identifying specific DNA restriction fragments immobilized on a nitrocellulose membrane using a labeled, complementary probe.

Northern blotting

An analytical method used to resolve, transfer, and identify specific target RNA molecules using hybridization probes.

Reporter function of the lacZ gene in plasmid pUC18

Encodes $\beta\text{-galactosidase}$, enabling colorimetric blue-white screening where recombinant insertion disrupts the coding region and produces white colonies.

Chemical identity of the eukaryotic mRNA 5' cap

A $7\text{-methylguanylate}$ residue joined to the terminal transcript via an uncommon $5'\text{ to }5'$ triphosphate bridge.

Next-generation sequencing (NGS)

High-throughput sequencing technologies, including reversible terminator and pyrosequencing platforms, that allow rapid, massively parallel genome sequencing.

Structural difference between dATP and ATP

$\text{dATP}$ contains a $2'\text{-H}$ on its deoxyribose ring, whereas $\text{ATP}$ possesses a $2'\text{-OH}$ group on its ribose ring.

Substrates and cofactors required for DNA replication elongation

DNA polymerase, a primed template strand, $\text{Mg}^{2+}$ ions, and four deoxynucleoside triphosphates ($\text{dATP}$, $\text{dTTP}$, $\text{dCTP}$, and $\text{dGTP}$).

Base composition of a DNA genome containing 21% G residues

$21\%$ cytosine, $29\%$ adenine, and $29\%$ thymine, according to Chargaff rules.

Structural ring composition of purines

A fused bicyclic aromatic heterocyclic system composed of a six-membered pyrimidine ring joined to a five-membered imidazole ring.

Structural ring composition of pyrimidines

A monocyclic six-membered aromatic ring containing two nitrogen atoms at positions 1 and 3.

Ribonucleosides corresponding to adenine and guanine

Adenosine and guanosine.

Ribonucleosides corresponding to cytosine and uracil

Cytidine and uridine.

Deoxyribonucleosides corresponding to thymine and cytosine

Thymidine and deoxycytidine.

Chemical composition of adenylate (AMP)

An adenine base linked to a ribose sugar esterified to a single $5'\text{-phosphate}$ group.

Phosphodiester linkage orientation in nucleic acids

Bridges the $3'\text{-hydroxyl}$ group of one pentose sugar to the $5'\text{-hydroxyl}$ group of the adjacent sugar via a phosphate group.

Glycosidic bond linkage site in purine nucleotides

Name of the bond connecting the $N\text{-9}$ atom of the purine base to the $C\text{-1'}$ carbon of the pentose sugar.

Glycosidic bond linkage site in pyrimidine nucleotides

A $\beta\text{-glycosidic}$ bond connecting the $N\text{-1}$ atom of the pyrimidine base to the $C\text{-1'}$ carbon of the pentose sugar.

Hydrogen bond count in an A-T base pair

Two hydrogen bonds.

Hydrogen bond count in a G-C base pair

Three hydrogen bonds.

Dominant thermodynamic contributor to double helix stability

Hydrophobic base-stacking interactions and van der Waals forces between adjacent, parallel base pairs.

Rise per base pair in B-DNA

$3.4\,\text{\AA}$ ($0.34\,\text{nm}$).

Pitch per turn of the B-DNA helix

$35.4\,\text{\AA}$ ($3.54\,\text{nm}$).

Helix diameter of B-DNA

Approximately $23.7\,\text{\AA}$ ($2.0\,\text{nm}$).

Base pairs per helical turn in B-DNA

$10.4$ base pairs ($10\text{ to }10.5$ base pairs).

Groove dimensions of B-DNA

A wide, deep major groove and a narrow, relatively shallow minor groove.

Physicochemical conditions promoting A-DNA formation

Low humidity, dehydrated environments, or high salt concentrations.

Rise per base pair in A-DNA

$2.3\,\text{\AA}$ ($0.29\,\text{nm}$).

Pitch per turn of the A-DNA helix

$25.3\,\text{\AA}$ ($3.2\,\text{nm}$).

Helix diameter of A-DNA

$25.5\,\text{\AA}$ ($2.6\,\text{nm}$), representing the broadest of the canonical DNA duplex forms.

Base pairs per helical turn in A-DNA

$11$ base pairs.

Groove dimensions of A-DNA

A narrow, deep major groove and a broad, shallow minor groove.

Base pair tilt in A-DNA

Approximately $19^\circ\text{ to }20^\circ$ relative to the perpendicular helical axis.

Repeating sequence motif associated with Z-DNA

Alternating purine-pyrimidine dinucleotide repeats, such as poly$\text{d(GC)}$ sequences.