Lecture #6: Fundamental Molecular Genetic Mechanisms

A set of practice flashcards covering DNA structure, transcription, RNA processing, RNA roles in translation, tRNA and ribosome function, codons and the genetic code, and eukaryotic vs. prokaryotic gene regulation from Lecture 6 notes.

What is the role of DNA as a stable information molecule?

DNA stores genetic information in its base sequence and is used to build all cellular proteins and RNAs.

Name the four basic molecular genetic processes.

Transcription, RNA processing, Translation, and DNA replication.

What happens during transcription?

The DNA code is copied into precursor mRNA (pre-mRNA) by RNA polymerase.

What is RNA processing?

Removal of noncoding sequences and other modifications to pre-mRNA to make mature mRNA for export.

What happens during translation?

Ribosomes read mRNA codons with tRNAs to assemble amino acids into a polypeptide.

What occurs during DNA replication?

DNA is duplicated to yield two identical copies, one for each daughter cell, using dNTPs.

In what direction is RNA synthesized?

5′ to 3′ direction, opposite to the template DNA strand.

Which DNA strand serves as the template during transcription?

The template strand; the non-template strand is its complement and RNA sequence matches it (with U instead of T).

What is capping?

Addition of a 5′ cap (7-methylguanosine) to the transcript, facilitating export, stability, translation, and splicing.

What is polyadenylation?

Addition of a poly(A) tail (about 150–200 adenines) at the 3′ end; stabilizes mRNA and promotes translation.

What is splicing?

Removal of introns and joining of exons; donor sites (5′) and acceptor sites (3′) define intron boundaries; UTRs are retained.

What are the three RNA types involved in protein synthesis?

mRNA, tRNA, and rRNA.

What is the role of tRNA?

Each tRNA carries a specific amino acid and has an anticodon that base-pairs with the mRNA codon to place the amino acid in the ribosome.

What is wobble base pairing?

Some anticodons can pair with more than one codon, reducing the number of tRNAs needed.

Where is the anticodon located in tRNA and what does it do?

Located in the anticodon loop; base-pairs with the mRNA codon to specify the amino acid delivered to the ribosome.

What are aminoacyl-tRNA synthetases?

Enzymes that charge tRNAs with the correct amino acid; about 20 distinct synthetases (one per amino acid).

What is the acceptor stem of tRNA?

The 3′ end containing the CCA sequence where the amino acid is covalently attached.

What domains exist within aminoacyl-tRNA synthetases?

A docking site for tRNA, a recognition site for the anticodon, and a catalytic site that transfers the amino acid to the tRNA (ATP-dependent).

What are ribosomes composed of?

Ribosomes contain rRNA and proteins; LSU and SSU; rRNA provides catalytic function in the LSU.

What are the roles of the A, P, and E sites on the ribosome?

A site accepts the new aminoacyl-tRNA; P site holds the growing polypeptide; E site is the exit for deacylated tRNA.

How is translation initiated in eukaryotes?

initiation factors and initiator tRNA with Met bind the small subunit, attach to the 5′ cap, and scan to the start codon (usually AUG); the large subunit then joins.

What is unique about the initiator tRNA in eukaryotes?

The initiator tRNA delivers methionine as the first amino acid; it is distinct from other Met-tRNAs.

What triggers termination of translation?

Stop codons (UAA, UAG, UGA) are recognized by release factors, which lead to peptide release and ribosome dissociation.

What is circularization of mRNA and why is it important?

mRNA circularization via the interaction of poly(A)-binding protein (PABP), eIF4E, and eIF4G bridges the 5′ cap and 3′ poly(A) tail, increasing translation efficiency; polysomes involve multiple ribosomes translating the same mRNA.

What is the genetic code?

The set of rules translating mRNA codons into amino acids; 64 codons; codons are triplets; codons are degenerate but not ambiguous; start and stop codons exist.

What is a reading frame?

One of three possible ways to divide an mRNA sequence into codons; only one frame yields the correct protein; others can produce nonfunctional products.

How does codon-anticodon recognition work in decoding?

tRNA anticodon base-pairs with mRNA codon; the first nucleotide of the anticodon pairs with the third nucleotide of the codon; wobble allows some flexibility.

How many tRNA genes do humans have and how many distinct tRNAs?

About 500 tRNA genes encoding roughly 48 distinct tRNA species (I = inosine can pair with multiple codons).

What is the role of donor and acceptor sites in RNA splicing?

Donor site is the 5′ end of intron; acceptor site is the 3′ end of intron; conserved sequences define boundaries for intron removal.

What is alternative splicing?

Generation of multiple protein isoforms from a single gene by varying exon inclusion; can be cell-type specific or developmentally regulated.

What is a polyribosome?

A structure with multiple ribosomes translating a single mRNA concurrently, increasing translation efficiency.

How do promoters and enhancers regulate transcription?

Promoters recruit RNA polymerase; enhancers are DNA motifs bound by activators/repressors to modulate transcription; can be distant from the promoter and act via looping; mediator helps assemble the initiation complex.

What is prokaryotic operon organization?

In bacteria, operons are contiguous gene clusters transcribed from a single promoter into one polycistronic mRNA, with multiple start sites translating into several proteins.

How does eukaryotic gene organization differ from prokaryotic?

Eukaryotic genes typically have their own promoters and are transcribed into monocistronic mRNA for a single protein per gene, with greater regulatory complexity.