Lecture 26 Flashcards
Which of the following describes the central dogma of biology described by Francis crick in 1956
1-DNA is a nucleic acid in a double helix
2- proteins are constructed from one or more polypeptides
3- there is a flow of information from DNA to RNA to protein
4- eukaryotes usually have more genes that prokaryotes
3
The ____ alphabet for genetic code consists of the 4 letters A,U,G, AND C
RNA
DNA
POLYPEPTIDE
ANINO ACID
RNA
Which of the following about genetic code is TRUE?
1- of the 64 codons on functions as a start codon and 3 as stop codons
2- genetic code contains many synonyms in specifying amino acids (degeneracy)
3- genetic code is universal, specifying the same amino acids in all organisms with minor exceptions
4- all of the above
The correct answer is: 4 – all of the above
Here’s why each statement is true:
1. “Of the 64 codons, one functions as a start codon and 3 as stop codons” – True. AUG is the start codon (also codes for methionine), and UAA, UAG, and UGA are stop codons.
2. “Genetic code contains many synonyms in specifying amino acids (degeneracy)” – True. Multiple codons can code for the same amino acid, which is called degeneracy or redundancy of the code.
3. “Genetic code is universal, specifying the same amino acids in all organisms with minor exceptions” – True. Almost all organisms use the same genetic code, with very few exceptions like in some mitochondria or rare organisms.
Which of the following statements about RNA polymerases in transcription is true?
1- RNA polymerases require both DNA nucleotide strands as templates
2- RNA polymerases create mRNA with double polynucleotide chains
3- RNA polymerases require no primer
4- RNA polymerases create RNA in the 3’ -> 5’ direction
The correct answer is: 3 – RNA polymerases require no primer
Here’s why the other options are incorrect:
1. False – RNA polymerase uses only one of the DNA strands (the template strand) to synthesize RNA.
2. False – mRNA is single-stranded, not double.
3. True – Unlike DNA polymerase, RNA polymerase does not require a primer to begin transcription.
4. False – RNA is synthesized in the 5’ → 3’ direction, not 3’ → 5’.
What is the role of a promoter in transcription?
1- a promoter specifies where the transcription of the DNA begins
2- promoters are key to the production of larger amounts of protein
3- a promoter signals the termination of RNA synthesis
4- most promoters work to make more copies of specific genes in the DNA
The correct answer is: 1 – a promoter specifies where the transcription of the DNA begins
Explanation:
• A promoter is a specific DNA sequence located upstream of a gene.
• It serves as the binding site for RNA polymerase, signaling where transcription should start.
The other options are incorrect because:
• 2: Promoters don’t directly control protein amount; gene regulation does that.
• 3: Promoters are involved in starting, not ending transcription.
• 4: Promoters don’t make more copies of genes; they regulate when transcription starts.
Which of the following statements is true?
1- transcription is not found in prokaryotes because there is no nucleus
2- both prokaryotic and eukaryotic mRNAs contain regions that code for proteins and no coding regions
3- prokaryotic mRNAs are double-stranded polynucleotides that allow for faster information processing
4- eukaryotic transcription usually takes place outside of the nucleus
The correct answer is:
2 – both prokaryotic and eukaryotic mRNAs contain regions that code for proteins and non-coding regions
Explanation:
• 1 – False: Transcription does occur in prokaryotes; it just happens in the cytoplasm because they lack a nucleus.
• 2 – True: mRNAs in both prokaryotes and eukaryotes have coding regions (exons/coding sequences) and non-coding regions (like untranslated regions or introns in eukaryotes).
• 3 – False: mRNA is single-stranded, not double-stranded, in both types of organisms.
• 4 – False: In eukaryotes, transcription occurs inside the nucleus, not outside.
So the correct and true statement is option 2.
The transcription unit of a eukaryotic protein-coding gene contains non-protein-coding sequences called _____ that interrupt the protein coding sequence
1- ribosomes
2- exons
3-introns
4- poly(A) tails
The correct answer is: 3 – introns
Explanation:
• Introns are non-protein-coding sequences within a gene that interrupt the coding regions (exons).
• During RNA processing, introns are removed and exons are spliced together to form mature mRNA.
The other options are:
• 1 – Ribosomes: Not part of the gene; they are involved in translation.
• 2 – Exons: These are the coding sequences that remain in the final mRNA.
• 4 – Poly(A) tails: These are added to the 3’ end of eukaryotic mRNA for stability, not part of the interrupting sequence.
Which process is necessary to remove introns from eukaryotic pre-mRNAs and join exons together before translation?
1-mRNA splicing
2-translation
3- insertion of introns
4- all of the above
The correct answer is: 1 – mRNA splicing
Explanation:
• mRNA splicing is the process that removes introns from pre-mRNA and joins exons together to form mature mRNA that can be translated into protein.
The other options are incorrect:
• 2 – Translation: This is the process of making protein from mRNA, which happens after splicing.
• 3 – Insertion of introns: Introns are part of the original gene; they aren’t inserted during processing.
• 4 – All of the above: Incorrect because only splicing is directly involved in removing introns and joining exons.
Which of the following statements about translation is false
1- in translation, mRNA associates with a ribosome
2- translation in eukaryotes takes place mostly in the cytoplasm
3- the sequence of amino acids in the polypeptide chain is determined by the sequence of codons in the mRNA
4- tRNA molecules are captured by mRNAs and become part of the new polypeptide chain at the ribosome
The correct answer is: 4 – tRNA molecules are captured by mRNAs and become part of the new polypeptide chain at the ribosome
Explanation:
• This statement is false because tRNA molecules do not become part of the polypeptide chain. Instead, they deliver the correct amino acids to the ribosome based on codon-anticodon matching, and then exit the ribosome to be reused.
The other statements are true:
• 1: mRNA does associate with a ribosome during translation.
• 2: In eukaryotes, translation happens mostly in the cytoplasm.
• 3: The codon sequence in mRNA determines the amino acid sequence of the polypeptide.
How does a tRNA “know” which amino acid to bring to a ribosome during translation?
1- because any tRNA can carry any amino acid, they can respond to a signal from the ribosome
2- the codon on each end of a tRNA is identical to an mRNA codon
3- each tRNA has an anticodon at one end that pairs with a complementary codon in mRNAs
4- exon shuffling creates tRNAs specific to each mRNA
The correct answer is: 3 – each tRNA has an anticodon at one end that pairs with a complementary codon in mRNAs
Explanation:
• During translation, each tRNA molecule has an anticodon that is complementary to an mRNA codon.
• This anticodon-codon pairing ensures that the correct amino acid is brought to the ribosome and added to the growing polypeptide chain.
The other options are incorrect:
• 1: tRNAs are specific to particular amino acids; not any tRNA can carry any amino acid.
• 2: The anticodon, not a codon, is what’s on the tRNA.
• 4: Exon shuffling is a process in gene evolution, not related to tRNA specificity.
The process of adding an amino acid to a tRNA is called ____.
1- initiation
2- aminoacylation
3- shuffling
4- automation
The correct answer is: 2 – aminoacylation
Explanation:
• Aminoacylation (also called tRNA charging) is the process where an amino acid is attached to its corresponding tRNA by an enzyme called aminoacyl-tRNA synthetase.
• This charged tRNA can then deliver the correct amino acid during translation.
The other options are unrelated:
• 1 – Initiation: Refers to the start of translation or transcription.
• 3 – Shuffling: Not related to tRNA; exon shuffling refers to gene rearrangement.
• 4 – Automation: Not a biological term in this context.
Which of the following statements best describes ribosomes
1- a ribsome is a short polypeptide
2- ribosomes are ribonucleoprotein particles
3- prokaryotic ribosomes are significantly larger than eukaryotic ribosomes
4- ribosomes carry key sections of nuclear DNA to direct protein synthesis
The correct answer is: 2 – ribosomes are ribonucleoprotein particles
Explanation:
• Ribosomes are made of ribosomal RNA (rRNA) and proteins, making them ribonucleoprotein particles.
• They are responsible for assembling amino acids into proteins during translation.
The other options are incorrect:
• 1: A ribosome is not a polypeptide; it makes polypeptides.
• 3: Prokaryotic ribosomes are smaller, not larger, than eukaryotic ones.
• 4: Ribosomes do not carry DNA; they read mRNA to direct protein synthesis.
How does a ribosome “know” where on an mRNA molecule to begin translation?
1- the first nucleotide of the mENA is recognized as the beginning of information to be translated
2- there is an enzyme at the 3’ end of the mRNA that catalyzes translation
3- the signal of the mRNA molecule is indicated by a long string of RNA nucleotides
4- the first aminoacyl- tRNA of the new polypeptide chain binds to the AUG start codon on the mRNA molecule
The correct answer is: 4 – the first aminoacyl-tRNA of the new polypeptide chain binds to the AUG start codon on the mRNA molecule
Explanation:
• Translation begins at the start codon, which is AUG, coding for methionine.
• The initiator tRNA, carrying methionine, recognizes and binds to this start codon with the help of the ribosome and initiation factors.
The other options are incorrect:
• 1: Translation doesn’t start at the very first nucleotide—it starts at the start codon (AUG).
• 2: No such enzyme exists at the 3’ end of mRNA to start translation.
• 3: A long string of RNA nucleotides doesn’t indicate the start; AUG does.
The central reactions of translation take place in the ____ stage
1- elongation
2- hydrolytic
3- initiation
4- binding
The correct answer is: 1 – elongation
Explanation:
• The elongation stage of translation is where the central reactions occur:
• Amino acids are added one by one to the growing polypeptide chain.
• The ribosome moves along the mRNA, reading codons and forming peptide bonds between amino acids.
The other options are incorrect:
• 2 – Hydrolytic: Not a stage of translation.
• 3 – Initiation: This is the setup phase where the ribosome assembles and binds to the start codon.
• 4 – Binding: Not a distinct stage of translation; binding happens during initiation and elongation.
What is the result of a nonsense mutation in a base-pair change in DNA?
1- any proteins produced by this altered gene will have a different amino acid sequence than those produced by the original gene
2- a codon will be altered from an amino acid coding codon to a termination codon in the mRNA, resulting in a shorter polypeptide
3- the changes codon still specifies the same amino acid as the original codon
4- the reading frame of the resulting mRNA is altered
The correct answer is:
2 – a codon will be altered from an amino acid coding codon to a termination codon in the mRNA, resulting in a shorter polypeptide
Explanation:
• A nonsense mutation changes a codon that normally codes for an amino acid into a stop codon (like UAG, UAA, or UGA).
• This causes translation to stop prematurely, resulting in a truncated (shortened) and usually nonfunctional protein.
Here’s why the other options are incorrect:
• 1: This describes a missense mutation, not a nonsense mutation.
• 3: This describes a silent mutation, where the amino acid doesn’t change.
• 4: This describes a frameshift mutation, caused by insertions or deletions.
