Chapter 6: DNA and Protein Synthesis

Vocabulary flashcards covering DNA structure, replication, RNA types, transcription, translation, and gene regulation concepts from Chapter 6.

Hershey-Chase Experiment

Experiments conducted by Alfred Hershey and Martha Chase in the 1950s using viruses and bacteria labeled with radioactive $^{32}\text{P}$ (DNA) and $^{35}\text{S}$ (protein coat), confirming that DNA is the genetic material.

Chargaff's Rules

Rules stating that in DNA, Adenine equals Thymine, Guanine equals Cytosine, and purines equal pyrimidines (Rule 1); and that the ratio of A+T to G+C varies between different species but remains identical across tissues of the same organism (Rule 2).

Rosalind Franklin

The scientist who used X-ray diffraction to investigate DNA's structure, providing key contributions to discovering the double helix.

Watson and Crick

James Watson and Francis Crick, the scientists credited with discovering that DNA has a double-helix shape.

Deoxyribonucleic Acid (DNA)

The nucleic acid stored in the nucleus and mitochondria that contains genes, replicates to transmit genetic information, and undergoes mutations to provide genetic variability.

Nucleotide

The building block subunit of nucleic acids, consisting of a phosphate group, a pentose sugar (deoxyribose or ribose), and a nitrogen-containing base.

Purines

Nitrogenous bases containing a double-ring structure, specifically Adenine and Guanine.

Pyrimidines

Nitrogenous bases containing a single-ring structure, specifically Cytosine and Thymine in DNA, or Uracil in RNA.

Complementary Base Pairing Rules

The pairing pattern in DNA where Adenine forms two hydrogen bonds with Thymine, and Guanine forms three hydrogen bonds with Cytosine.

Antiparallel Strands

The opposite orientation of the two strands in a DNA double helix, where one strand runs in the $5'$ to $3'$ direction and the other runs in the $3'$ to $5'$ direction.

Semiconservative Replication

The process of DNA replication in which each newly formed double helix consists of one original parental strand and one newly synthesized strand.

DNA Helicase

The enzyme responsible for unwinding and unzipping the DNA double helix by breaking hydrogen bonds between nitrogenous bases.

DNA Polymerase

The enzyme that synthesizes new DNA strands by joining nucleotides complementary to the original template strand.

Okazaki Fragments

Short segments of DNA synthesized discontinuously along the lagging strand during DNA replication.

DNA Ligase

An enzyme that seals breaks in the sugar-phosphate backbone during DNA replication.

Mutation

An uncorrected error in DNA replication that alters the sequence of bases in the new strand, creating new alleles and phenotype variations.

Messenger RNA (mRNA)

RNA produced in the nucleus that carries genetic instructions from DNA to ribosomes in the cytoplasm for protein assembly.

Ribosomal RNA (rRNA)

RNA produced in the nucleolus that joins with proteins to form the large and small subunits of ribosomes.

Transfer RNA (tRNA)

RNA that carries specific amino acids to ribosomes during translation, matching its anticodon to mRNA codons.

Small Nuclear RNAs (snRNAs)

A class of small RNAs involved in splicing pre-mRNA before it leaves the nucleus.

MicroRNAs (miRNAs)

Small RNAs in the cytoplasm that attach to mRNAs to block unnecessary translation.

Small Interfering RNAs (siRNAs)

Small RNAs that bind to mRNAs in the cytoplasm and mark them for degradation by nucleases.

Transcription

The first phase of gene expression in which a segment of DNA serves as a template to produce a complementary RNA molecule inside the nucleus.

Translation

The second phase of gene expression in which the nucleotide sequence of an mRNA molecule is decoded into a sequence of amino acids in the cytoplasm.

Codon

A three-base sequence in mRNA that specifies a particular amino acid, start signal ($\text{AUG}$), or stop signal ($\text{UAA}$, $\text{UAG}$, $\text{UGA}$).

Promoter

A non-coding region of a gene where RNA polymerase binds to initiate transcription.

Introns

Non-coding nucleotide segments of DNA/pre-mRNA that interrupt genes and are removed during RNA processing.

Exons

Coding portions of a gene that remain in mature mRNA and are expressed into a protein product.

Spliceosome

A complex composed of RNA and protein that carries out mRNA splicing by removing introns and joining exons.

Alternative mRNA Splicing

A processing mechanism where cells select different combinations of exons from pre-mRNA, enabling a single gene to encode multiple distinct proteins.

Anticodon

A three-base sequence on a tRNA molecule that pairs complementarily with a specific codon on mRNA.

A Site (Aminoacyl Site)

The ribosomal binding site where an incoming tRNA carrying a new amino acid enters and pairs with mRNA.

P Site (Peptidyl Site)

The ribosomal binding site occupied by the tRNA carrying the growing polypeptide chain.

E Site (Exit Site)

The ribosomal binding site from which an uncharged, empty tRNA exits the ribosome during elongation.

Release Factor

A protein that binds to a stop codon in the ribosomal A site, hydrolyzing the bond between the polypeptide and the last tRNA to terminate translation.