Anatomy 12: Nucleic Acids, DNA Replication, and Protein Synthesis

Comprehensive vocabulary flashcards covering nucleic acid structures, DNA replication mechanisms, transcription, post-transcriptional processing, and translation.

Nucleic Acids

The polymers of life present in all prokaryotic and eukaryotic cells that hold genetic information necessary for protein synthesis and coordinate the joining of amino acids.

Purines

Double-ring nitrogenous bases found in nucleic acids, specifically Adenine and Guanine.

Pyrimidines

Single-ring nitrogenous bases found in nucleic acids, specifically Cytosine and Thymine in DNA, and Cytosine and Uracil in RNA.

Chargaff's Rules

The base-pairing principle stating that nitrogen bases form hydrogen bonds in complementary pairs: Adenine pairs with Thymine ($A = T$) and Guanine pairs with Cytosine ($G \equiv C$).

mRNA (Messenger RNA)

A single-stranded RNA produced in the nucleus that copies genetic information from DNA and carries codons out through nuclear pores to the cytosol and ribosomes.

tRNA (Transfer RNA)

A type of RNA operating in the cytosol and at ribosomes that carries specific amino acids to the site of protein synthesis.

rRNA (Ribosomal RNA)

A type of RNA synthesized in the nucleolus that combines with proteins to form two ribosome subunits, providing the site for protein synthesis and coordinating the joining of amino acids.

Origin

The specific nucleotide sequence where DNA replication begins.

DNA Helicase

The enzyme that breaks hydrogen bonds between bases, causing the two strands to separate or unzip at replication forks and exposing the template bases.

DNA Primase

The enzyme that binds a short piece of RNA called a primer to the 3' end of the template strand to act as the starting point for DNA replication.

DNA Polymerase

The enzyme that positions complementary nucleotides and covalently joins sugar-phosphate groups in the 5' to 3' direction to synthesize a new daughter DNA strand.

Leading Strand

The template-directed DNA strand that is replicated continuously in the 5' to 3' direction by DNA polymerase.

Lagging Strand

The antiparallel DNA strand synthesized discontinuously during replication, resulting in short segments known as Okazaki fragments.

Okazaki Fragments

Short segments of DNA formed on the lagging strand during replication.

DNA Ligase

The enzyme that connects Okazaki fragments and seals any remaining breaks in the sugar-phosphate backbone.

Semi-Conservative Replication

The mechanism of DNA replication in which each newly produced DNA molecule retains one original parent strand and one newly formed daughter strand.

Transcription

The first phase of gene expression and protein synthesis, in which a single strand of mRNA is assembled in the nucleus by complementary base pairing with a DNA template strand.

Promoter

A specific site on DNA where RNA polymerase binds, causing the DNA molecule to open at a designated section encoding a protein.

RNA Polymerase

The enzyme that checks and covalently bonds complementary mRNA nucleotides along the DNA template strand and completes synthesis at the terminator sequence.

Exons

The sequences of nitrogen bases in pre-mRNA that code for proteins and are spliced together after intron removal to form mature mRNA.

Introns

Non-coding sections of RNA transcribed from DNA that are spliced out and removed from pre-mRNA while inside the nucleus.

Codon

A sequence of three mRNA nitrogen bases that codes for a specific amino acid.

Start Codon

The specific codon AUG that marks the beginning of each protein sequence and codes for methionine.

Terminator Codons (Stop Codons)

The codons UAA, UAG, and UGA at the end of a gene that signal a releasing factor to detach the completed polypeptide protein.

Translation

The second part of protein synthesis in which the nucleotide sequence of mRNA is converted into a specific sequence of amino acids at the ribosome.

Polyribosome (Polysome)

A structure consisting of several ribosomes simultaneously translating a single strand of mRNA.

Initiation (Translation)

The energy-requiring step of translation involving the assembly of initiation factors, mRNA, the small ribosomal subunit, initiator tRNA at the P site, and the large ribosomal subunit.

Elongation (Translation)

The stage of protein synthesis in which the polypeptide chain increases in length one amino acid at a time via peptide bond formation between amino acids at the P and A sites.

Translocation

The process during elongation in which the mRNA moves forward one codon, shifting the uncharged tRNA to the E site for exit and placing the growing polypeptide chain in the P site.

A Site (Accepter Site)

The ribosome binding site that accepts an incoming tRNA carrying a specific amino acid.

P Site (Peptide Site)

The ribosome binding site that holds the initiator tRNA during initiation or the tRNA bearing the growing polypeptide chain during elongation.

E Site (Exit Site)

The ribosome binding site from which an uncharged tRNA (without an amino acid) detaches and leaves the ribosome.

Nucleic Acids

Polymers of life present in all cells that hold genetic information necessary for protein synthesis and coordinate the joining of amino acids.

DNA (Deoxyribonucleic Acid)

A polymer of nucleotides composed of deoxyribose (a 5-carbon sugar), a phosphate group, and nitrogen bases ($\text{A}$, $\text{T}$, $\text{C}$, $\text{G}$) arranged in an antiparallel double-stranded alpha helix.

Purines

Double-ring nitrogenous bases consisting of Adenine and Guanine.

Pyrimidines

Single-ring nitrogenous bases consisting of Cytosine and Thymine in DNA, and Cytosine and Uracil in RNA.

Chargaff's Rules

The base-pairing principle stating that Adenine always hydrogen-bonds with Thymine ($\text{A}=\text{T}$) and Guanine always pairs with Cytosine ($\text{G} \equiv \text{C}$).

RNA (Ribonucleic Acid)

A single-stranded polymer of nucleotides formed by dehydration synthesis, consisting of a ribose sugar, a phosphate group, and nitrogen bases ($\text{A}$, $\text{G}$, $\text{C}$, $\text{U}$).

mRNA (Messenger RNA)

RNA produced in the nucleus that copies genetic information from DNA and travels to the cytosol and ribosomes to direct protein synthesis.

tRNA (Transfer RNA)

RNA that works in the cytosol and at ribosomes to carry specific amino acids to the site of protein synthesis.

rRNA (Ribosomal RNA)

RNA synthesized in the nucleolus that combines with proteins to form two ribosome subunits, providing the physical site and coordinating the joining of amino acids into polypeptides.

Origin

The specific nucleotide sequence where DNA replication initiates.

DNA Helicase

The enzyme that breaks hydrogen bonds between bases, causing the two DNA strands to separate or unzip at replication forks.

DNA Primase

The enzyme that synthesizes and binds a short RNA primer to the $3'$ end of the DNA template strand to act as the starting point for replication.

DNA Polymerase

The enzyme that positions complementary nucleotides and covalently links sugar-phosphate groups in the $5' \rightarrow 3'$ direction along the template strand.

Leading Strand

The new DNA strand that is synthesized continuously by DNA polymerase in the $5' \rightarrow 3'$ direction.

Lagging Strand

The DNA strand replicated discontinuously, resulting in the production of short segments called Okazaki fragments.

Okazaki Fragments

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

DNA Ligase

The enzyme that seals any breaks in the sugar-phosphate backbone and connects Okazaki fragments on the lagging strand.

Semi-Conservative Replication

The replication mechanism in which each newly formed DNA molecule retains one intact parent template strand and one newly synthesized daughter strand.

Transcription

The first phase of protein synthesis occurring in the nucleus, in which an RNA polymerase enzyme synthesizes a single complementary strand of mRNA from a DNA template.

RNA Polymerase

The enzyme that opens DNA at a promoter site, aligns and covalently bonds complementary RNA nucleotides, and terminates mRNA synthesis at a specific sequence.

Promoter

A specific site on DNA where RNA polymerase binds to open the DNA strand and initiate transcription.

Introns

Non-coding sequences of nitrogen bases in pre-mRNA that are cut out and removed while inside the nucleus.

Exons

Coding sequences of nitrogen bases in mRNA that are involved in protein synthesis and spliced together to form mature mRNA.

Cap and Poly-A Tail

Modifications added to the ends of pre-mRNA following intron removal and exon splicing to produce a mature mRNA transcript ready for export.

Codon

A triplet sequence of three mRNA bases that codes for a specific amino acid.

Start Codon

The codon $\text{AUG}$ (coding for methionine) that signals the beginning of protein translation.

Stop Codons

Terminator codons ($\text{UAA}$, $\text{UAG}$, $\text{UGA}$) located at the end of an mRNA sequence that recruit a releasing factor to detach the synthesized polypeptide.

Translation

The second phase of protein synthesis, wherein the nucleotide sequence of mRNA is decoded into an amino acid sequence at a ribosome.

Polyribosome (Polysome)

A structure formed when multiple ribosomes simultaneously translate the same strand of mRNA.

A Site (Acceptor Site)

The ribosomal binding site that receives the incoming tRNA molecule carrying the next amino acid for the polypeptide chain.

P Site (Peptide Site)

The ribosomal binding site that holds the initiator tRNA or the tRNA carrying the growing polypeptide chain.

E Site (Exit Site)

The ribosomal binding site through which an uncharged tRNA (lacking an amino acid) departs from the ribosome.

Translocation

The elongation step during translation where the ribosome advances one codon along the mRNA, shifting tRNAs into adjacent sites and clearing the A site.