chapter 7 (bio test #3) (AI)

According to the Central Dogma, what is the primary function of genetic information in DNA?

Directing the synthesis of proteins.

What specific component of DNA encodes genetic information?

The sequence of nucleotides.

The process by which one strand of DNA is used as a template to synthesize a complementary strand of RNA is called _____.

Transcription

In some genes, what is the final functional product instead of a protein?

RNA

Which process uses the sequence of nucleotides in RNA to direct the synthesis of a protein?

Translation

What sugar is found in the backbone of RNA, distinguishing it from DNA?

Ribose

What sugar is found in the backbone of DNA?

Deoxyribose

Which nucleotide base does RNA use in place of Thymine (T)?

Uracil (U)

How does the typical strandedness of RNA in cells differ from DNA?

RNA exists as single-stranded molecules, whereas DNA is double-stranded.

How can a single-stranded RNA molecule form double-stranded regions?

By folding in a configuration that forms base pairs between different regions of the same strand.

True or False: Base pairing rules are more strict in RNA than they are in DNA.

FALSE

Which DNA strand is used to guide the synthesis of an RNA molecule?

The template strand.

Why is the top strand of DNA in a transcription example called the 'coding strand'?

Its sequence is equivalent to the RNA product, with $T$ replaced by $U$.

RNA Polymerase

The enzyme responsible for transcribing DNA into RNA.

In which direction does RNA polymerase 'read' the DNA template?

$3'$ to $5'$ direction.

In which direction is the RNA molecule synthesized?

$5'$ to $3'$ direction.

Can multiple RNA polymerase molecules transcribe the same gene simultaneously?

Yes

What is the primary function of Messenger RNAs (mRNAs)?

To encode proteins.

What is the structural role of Ribosomal RNAs (rRNAs)?

They serve as components of ribosomes.

Which type of RNA serves as an adapter between mRNA and amino acids during protein synthesis?

Transfer RNAs (tRNAs)

What specific DNA sequence indicates where RNA polymerase should start and stop transcription?

A gene promoter.

In bacteria, which protein subunit of RNA polymerase is responsible for recognizing the promoter sequence?

Sigma factor

What happens to the sigma factor once transcription has begun in bacteria?

It is released from the RNA polymerase.

What sequence at the end of a bacterial gene triggers the release of the DNA template and RNA transcript?

The terminator sequence.

In eukaryotes, which specific enzyme is responsible for synthesizing mRNAs?

RNA polymerase II

What group of proteins must assemble at the promoter for RNA polymerase II to initiate transcription?

General transcription factors.

The specific site within a eukaryotic promoter where general transcription factors typically begin assembly is the _____.

TATA box

What is the function of the general transcription factor TFIIH?

It phosphorylates RNA polymerase II, causing it to release the general transcription factors.

How does the DNA double helix behave as RNA polymerase moves along it?

The helix opens in front of the polymerase and closes immediately behind it.

Which proteins associate with RNA polymerase to help it transcribe through DNA wrapped around histones?

Elongation factors

Nucleosome

A structural unit of eukaryotic chromatin consisting of DNA wrapped around histones.

Where must eukaryotic mRNAs be processed before they are exported for translation?

In the nucleus.

What modification is added to the $5'$ end of a eukaryotic mRNA during processing?

A methylguanosine cap.

Polyadenylation

The addition of a few hundred adenines to the $3'$ end of an mRNA molecule.

In the context of RNA processing, what are 'exons'?

The sequences of an mRNA that encode amino acids.

What term refers to the non-amino acid encoding sequences in eukaryotic mRNAs that must be removed?

Introns

What is the primary benefit of alternative RNA splicing?

It allows a single gene to produce different mRNA transcripts (and thus different proteins).

The export of fully processed mRNA from the nucleus depends on proteins that bind to which two structures?

The $5'$ cap and the poly-A tail.

Why can translation begin before transcription is complete in prokaryotes?

Prokaryotes lack internal compartments (like a nucleus) to separate the two processes.

A sequence of three nucleotides in mRNA that encodes one amino acid is called a(n) _____.

Codon

Given four different nucleotides, how many possible codons exist in the genetic code?

$64$ (calculated as $4 \times 4 \times 4$)

How many codons in the genetic code function as 'stop' signals rather than encoding amino acids?

Three

Which specific codon serves as the 'start' signal for translation?

AUG

Which amino acid is encoded by the start codon AUG?

Methionine

What molecular complex, composed of proteins and RNA, performs protein synthesis?

The ribosome.

The sequence on a tRNA that is complementary to an mRNA codon is called the _____.

Anticodon

On which end of the tRNA molecule is the amino acid linked?

The $3'$ end.

What class of enzymes is responsible for attaching the correct amino acid to its corresponding tRNA?

Aminoacyl-tRNA synthetases

What term is used to describe the process of an aminoacyl-tRNA synthetase attaching an amino acid to a tRNA?

Charging

How many different aminoacyl-tRNA synthetase enzymes typically exist in a cell?

One for each codon (or amino acid).

Which subunit of the ribosome contains the binding site for mRNA?

The small subunit.

List the three tRNA binding sites formed by the assembly of ribosomal subunits.

A, P, and E sites.

During eukaryotic translation initiation, which structure on the mRNA does the small ribosomal subunit complex first bind to?

The $5'$ cap.

What is the 'scanning' process in eukaryotic translation initiation?

The small ribosomal subunit moving in the $3'$ direction to find the AUG start codon.

What event triggers the dissociation of translation initiation factors in eukaryotes?

The matching of the initiator tRNA anticodon with the mRNA start codon.

In which ribosomal site is the initiator tRNA positioned when the large subunit joins the complex?

The P site.

In prokaryotes, where does the ribosome bind to initiate translation since there is no $5'$ cap?

Ribosome binding sites (specific nucleotide sequences).

What is the consequence of a tRNA entering the A site with an anticodon that does not match the mRNA codon?

The tRNA will leave the A site without any reaction taking place.

During elongation, the ribosome catalyzes a bond between the amino acid in the P site and the one in the A site. What is this bond called?

A peptide bond.

When the ribosome translocates during elongation, how many nucleotides does it move?

Three nucleotides.

In which ribosomal site does a tRNA reside immediately before it exits the ribosome?

The E site.

What type of molecule binds to the A site when the ribosome reaches a stop codon?

A protein release factor.

What are the two final results of a release factor binding to the ribosome?

Disassembly of the ribosome and release of the completed protein.

Polyribosome

A structure where several ribosomes simultaneously translate a single mRNA molecule.

Does a ribosome have to complete translation before another can begin on the same mRNA?

No

Aside from the rate of synthesis, what determines the total amount of a particular protein in a cell?

The rate of degradation.

What small protein is used to tag other proteins for degradation?

Ubiquitin

What is the name of the protein complex that breaks down ubiquitin-tagged proteins?

The proteosome.

Identify one example of a 'post-translational modification' that can regulate protein activity.

Phosphorylation

List three stages of the gene-to-protein pathway that the cell can target for regulation.

Transcription, mRNA processing, and Translation (or Protein folding/degradation).

What unique capability of RNA supports the theory that the earliest forms of life were RNA-based?

The ability to act as a catalyst for biochemical reactions.

In modern life, what are the primary catalysts of biochemical reactions?

Proteins

In modern life, which molecule is primarily responsible for storing genetic information?

DNA

What happens to the double helix once RNA polymerase has passed a specific stretch of DNA?

It closes back up.

Which ribosomal site receives the incoming aminoacyl-tRNA during the elongation cycle?

The A site.