biochemistry chapter 7: rna and the genetic code

What is the central dogma of molecular biology?

DNA is transcribed to RNA, which is translated to protein.

What does a degenerate code allow?

Multiple codons to encode for the same amino acid.

What is the start codon?

AUG

What are the stop codons?

UAA, UGA, UAG

How does redundancy and wobble affect mutations?

Allows mutations to occur without effects in the protein.

What are the types of point mutations?

Silent mutations: no effect on protein synthesis. Nonsense mutations: produce a premature stop codon. Missense mutations: code for a different amino acid.

What do frameshift mutations result from?

Nucleotide addition or deletion that changes the reading frame.

How does RNA differ structurally from DNA?

Substitution of ribose sugar for deoxyribose. Substitution of uracil for thymine. It is single-stranded instead of double-stranded.

What are the three types of RNA?

Messenger RNA (mRNA), Transfer RNA (tRNA), Ribosomal RNA (rRNA)

What does messenger RNA (mRNA) do?

Carries the message from DNA in the nucleus to the cytoplasm for translation.

What is the role of transfer RNA (tRNA)?

Brings in amino acids and recognizes the codon on the mRNA using its anticodon.

What does ribosomal RNA (rRNA) contribute to?

Makes up the ribosome and is enzymatically active.

What is the role of helicase in transcription?

Unwinds the DNA double helix.

Where does RNA polymerase II bind during transcription?

To the TATA box within the promoter region, 25 base pairs upstream.

What is produced from the DNA template strand during transcription?

hnRNA (heterogeneous nuclear RNA)

How is RNA synthesized from DNA?

By using the antisense strand as a template.

What cap is added to the 5' end of RNA during posttranscriptional modifications?

A 7-methylguanylate triphosphate cap.

What is added to the 3' end of RNA during posttranscriptional modifications?

A polyadenosyl (poly-A) tail.

What processes are performed by snRNA and snRNPs in the spliceosome?

They remove introns and ligate exons together.

How do prokaryotic cells increase variability in gene products?

Through polycistronic genes.

What allows eukaryotic cells to achieve variability in gene products?

Through alternative splicing.

What does tRNA do during translation?

It translates the codon into the correct amino acid.

In which cellular structure does translation occur?

Ribosomes.

What are the three stages of translation?

Initiation, elongation, and termination.

What happens during initiation in prokaryotes?

The 30S ribosome attaches to the Shine-Dalgarno sequence.

In eukaryotes, how does initiation occur?

The 40S ribosome attaches to the 5' cap and scans for a start codon.

What occurs during elongation in translation?

A new aminoacyl-tRNA enters the A site.

What triggers termination in translation?

A stop codon in the A site.

What role do release factors play during translation?

They place a water molecule on the polypeptide chain to release the protein.

What are some posttranslational modifications?

Folding by chaperones, Formation of quaternary structure, Covalent addition of biomolecules

How do transcription factors function in eukaryotes?

They search for promoter and enhancer regions in DNA.

Where are promoters located relative to the transcription start site?

Within 25 base pairs of the start site.

Where are enhancers located relative to the transcription start site?

More than 25 base pairs away from the start site.

What effect does histone acetylation have on transcription?

It increases accessibility of DNA.

What does DNA methylation do to transcription accessibility?

It decreases accessibility.

What is the Jacob Monod model about?

It explains how operons work with repressors and activators.

What is an inducible system in gene expression?

A system like the lac operon that can be turned on by an inducer.

What is removed during posttranscriptional splicing?

Introns are removed from the transcript.

What structure do exons form after splicing?

They are ligated together to form the final transcript.

What role do chaperones play in protein synthesis?

They assist in the folding of proteins.

What is the result of covalent modifications like phosphorylation?

They alter the function of proteins by attaching other biomolecules.

What initiates the first step of protein synthesis in prokaryotes?

The recruitment of the 30S ribosome.

What amino acid is laid down by the 40S ribosome in eukaryotic initiation?

Methionine.

How prolonged is the pause of the uncharged tRNA in the E site?

It's a brief pause before exiting the ribosome.

During termination, what does the release factor activate?

It activates the addition of a water molecule to the polypeptide chain.

What is the function of a corepressor in repressible systems?

It binds to the repressor to turn off transcription.

Can operons be classified? If so, how?

They can be inducible or repressible.

What happens to exons during the process of splicing?

They are joined together after introns are removed.

How does DNA methylation influence gene expression?

It generally silences genes by decreasing accessibility.

In what manner do transcription factors affect transcription efficiency?

They modify chromatin structure, enhancing or inhibiting transcription factor access.

What model explains the function of operons?

The Jacob-Monod model of repressors and activators.

What are operons?

Clusters of genes transcribed as a single mRNA that are either inducible or repressible.

How do inducible systems like the lac operon function?

They are bonded to a repressor under normal conditions and can be turned on by an inducer.

What triggers the activation of an inducible operon?

An inducer pulls the repressor from the operator site.

What do repressible systems like the trp operon do?

They are transcribed under normal conditions but can be turned off by a corepressor.

How does a corepressor affect a repressible operon?

It couples with the repressor and binds the complex to the operator site.

What role do transcription factors play in gene expression?

They search for promoter and enhancer regions in the DNA.

Where are promoters located?

Within 25 base pairs of the transcription start site.

What are enhancers in gene regulation?

Regions that are more than 25 base pairs away from the transcription start site.

How does chromatin structure modification affect gene expression?

It affects transcriptional enzymes' access to DNA.

What effect does histone acetylation have on gene expression?

It increases accessibility to the DNA.

What does DNA methylation do?

Decreases accessibility to the DNA.