Nucleic Acids II
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Questions and Answers

What is the purpose of the start codon AUG in protein synthesis?

  • It codes for Glycine
  • It initiates the translation of all proteins
  • It terminates protein synthesis
  • It codes for Methionine (correct)

    • The genetic code is nonoverlapping, meaning that codons overlap with one another.

    False

    How many codons are responsible for terminating protein synthesis?

    3

    In eukaryotic ribosomes, the two subunits are ____ and ____.

    <p>60S and 40S</p> Signup and view all the answers

    Match the components required for protein synthesis with their roles:

    <p>Amino acids = Building blocks of proteins tRNA = Transfers specific amino acids to the ribosome mRNA = Carries genetic information from DNA Ribosomes = Sites of protein synthesis</p> Signup and view all the answers

    Which of the following codons are termination codons recognized by releasing factors?

    <p>UGA</p> Signup and view all the answers

    Antibiotics can only affect eukaryotic ribosomes due to their size.

    <p>False</p> Signup and view all the answers

    What is the function of releasing factors in protein synthesis?

    <p>To promote the hydrolysis of the bond between peptide and tRNA.</p> Signup and view all the answers

    The structure that consists of one mRNA and multiple ribosomes is called a __________.

    <p>polysome</p> Signup and view all the answers

    Match each antibiotic with its corresponding action:

    <p>Streptomycin = Distorts ribosome structure Tetracycline = Prevents tRNA recognition of codons Chloramphenicol = Inhibits peptidyl transferase Puromycin = Incorporates into growing peptide chain</p> Signup and view all the answers

    What is the role of the P site in protein synthesis?

    <p>Carry the growing polypeptide chain</p> Signup and view all the answers

    The A site is responsible for the assembly of components before peptide bond formation.

    <p>False</p> Signup and view all the answers

    What is the significance of the initiator tRNA?

    <p>It carries methionine and recognizes the start codon AUG.</p> Signup and view all the answers

    Protein synthesis translates the codons on mRNA into _____ that constitute the protein.

    <p>amino acids</p> Signup and view all the answers

    Match the following steps of protein synthesis with their descriptions:

    <p>Initiation = Assembly of components before peptide bond formation Elongation = Addition of amino acids to the growing polypeptide chain Termination = Final step when a termination codon is reached Translocation = Movement of ribosomes along the mRNA</p> Signup and view all the answers

    During which step of protein synthesis does peptidyl transferase enzyme act?

    <p>Elongation</p> Signup and view all the answers

    The ribosomes move three bases toward the 5’ end of mRNA during translocation.

    <p>False</p> Signup and view all the answers

    What happens during the termination step of protein synthesis?

    <p>The ribosome encounters a termination codon in the A site and stops translation.</p> Signup and view all the answers

    What is released when a new nucleotide is added to the growing RNA chain?

    <p>Pyrophosphate (PPi)</p> Signup and view all the answers

    The presence of palindromes in the termination region on DNA is irrelevant for RNA polymerase.

    <p>False</p> Signup and view all the answers

    What is the role of the 7-methylguanosine triphosphate in mRNA processing?

    <p>It facilitates the initiation of translation and protects the 5' end from exonucleases.</p> Signup and view all the answers

    The process of adding a chain of 40-250 adenine nucleotides to the 3' end of mRNA is known as __________.

    <p>polyadenylation</p> Signup and view all the answers

    Match the following steps of mRNA post-transcriptional modifications with their descriptions:

    <p>5' Capping = Addition of 7-methylguanosine to the 5' end Poly-A tail = Addition of a chain of adenine nucleotides to the 3' end Splicing = Removal of introns and ligation of exons</p> Signup and view all the answers

    What is the function of the Rho factor in RNA termination?

    <p>To bind with RNA polymerase and cause termination</p> Signup and view all the answers

    Codons are the sequences of 4 nucleotide bases on mRNA.

    <p>False</p> Signup and view all the answers

    What is the genetic code?

    <p>The dictionary that relates the sequence of bases in DNA and mRNA to a sequence of amino acids in a protein.</p> Signup and view all the answers

    What is the primary role of mRNA in a cell?

    <p>To carry genetic information from DNA to the cytosol for protein synthesis</p> Signup and view all the answers

    Ribosomal RNA (rRNA) makes up 15% of the total RNA in the cell.

    <p>False</p> Signup and view all the answers

    What are the three main steps of transcription?

    <p>Initiation, Elongation, Termination</p> Signup and view all the answers

    The ___________ region in prokaryotic cells is recognized by the RNA polymerase during initiation.

    <p>promoter</p> Signup and view all the answers

    Match the following RNA types with their primary functions:

    <p>mRNA = Carries genetic information for protein synthesis tRNA = Transfers specific amino acids to the ribosome rRNA = Makes up the structural framework of ribosomes small RNA = Performs regulatory functions in the cell</p> Signup and view all the answers

    Which RNA polymerase in eukaryotic cells is responsible for synthesizing mRNA?

    <p>RNA polymerase II</p> Signup and view all the answers

    All types of RNA in prokaryotes are synthesized by multiple RNA polymerases.

    <p>False</p> Signup and view all the answers

    How many base pairs are found between the Pribnow box and the second nucleotide sequence in prokaryotic promoters?

    <p>19</p> Signup and view all the answers

    The building blocks of RNA are ribonucleotides, which consist of a nitrogenous base, sugar __________, and phosphate.

    <p>ribose</p> Signup and view all the answers

    Which of the following statements regarding the anticodon region of tRNA is correct?

    <p>It is complementary to the codons on mRNA.</p> Signup and view all the answers

    Study Notes

    Nucleic Acids II

    • Nucleic acids are single-stranded polynucleotides.
    • The central dogma describes the flow of genetic information from DNA to RNA to protein.
    • DNA is the master plan, containing the genetic information of an organism.
    • mRNA is the working copy of DNA, expressing the master plan.
    • Transcription is the process of copying DNA to create mRNA.
    • Translation is the process of converting mRNA into protein.
    • RNA types include mRNA, tRNA, rRNA, and small RNA molecules.
    • mRNA carries genetic information from DNA to the cytoplasm for protein synthesis.
    • mRNA makes up about 5% of the total RNA in a cell.
    • Each three consecutive nucleotides in mRNA form a codon, which codes for a specific amino acid.
    • tRNA is an adaptor molecule carrying amino acids.
    • tRNA makes up about 15% of the total RNA.
    • tRNA has three loops and two free ends.
    • tRNA has an anticodon region that is complementary to codons on mRNA.
    • rRNA is found in association with proteins in ribosomes, serving as sites for protein synthesis.
    • rRNA makes up about 80% of the total RNA.
    • Prokaryotic ribosomes are 70S with subunits 50S and 30S.
    • Eukaryotic ribosomes are 80S with subunits 60S and 40S, differences in ribosomal subunit composition.
    • RNA consists of a nucleotide compound with nitrogenous bases, a ribose sugar, and a phosphate group.
    • RNA's nucleotides are linked by phosphodiester bonds.
    • RNA exists as single strands capable of complex folding.
    • The most common nitrogenous bases in RNA include adenine, guanine, cytosine, and uracil (instead of thymine).

    RNA Structure

    • RNA is a polynucleotide, building blocks of nucleotides.
    • A nucleotide is composed of a nitrogenous base, ribose sugar, and monophosphate.
    • Nucleotides are connected via phosphodiester bonds.
    • RNA exists as single strands that can fold into complex structures.

    Messenger RNA (mRNA)

    • mRNA is the working copy of the DNA.
    • It carries genetic information from DNA to the cytosol for protein synthesis.
    • It comprises about 5% of total RNA.
    • mRNA codons specify particular amino acids.

    Transfer RNA (tRNA)

    • tRNA is a molecule that carries amino acids.
    • tRNA comprises about 15% of total RNA in a cell.
    • tRNA has three loops and two free ends and an anticodon.
    • tRNA's anticodon sequence matches corresponding mRNA codons.

    Ribosomal RNA (rRNA)

    • rRNA is found in ribosomes and is essential for protein synthesis.
    • rRNA makes up the majority (about 80%) of total RNA in a cell.
    • Prokaryotic rRNA has three types (5S, 23S, and 16S)
    • Eukaryotic rRNA has four types (5S, 5.8S, 28S, and 18S)
    • S refers to Svedberg units, a measure of sedimentation rate.

    RNA Transcription

    • mRNA synthesis is known as RNA transcription.
    • Transcription requires a DNA template, ribonucleotides (phosphates A, G, C, U) and RNA polymerase.
    • DNA template consists of a promoter region, a transcription unit, and a termination unit.
    • Promoter region initiates transcription.
    • Transcription unit is the transcribed region.
    • Termination unit ends transcription.

    Promoter Region

    • Prokaryotic promoters have a Pribnow box (-10 region) and a -35 region.
    • Eukaryotic promoters have a TATA box and a CAAT box.

    Prokaryotic RNA Polymerase

    • One type of RNA polymerase synthesizes all types of RNA molecules.
    • RNA polymerase enzyme responsible for synthesis of RNA molecules.

    Eukaryotic RNA Polymerases

    • Eukaryotes have three types of RNA polymerases: I, II, and III.
    • RNA polymerase I synthesizes rRNA.
    • RNA polymerase II synthesizes mRNA and has a promoter region.
    • RNA polymerase III synthesizes tRNA and small RNA.

    Steps of Transcription

    • Initiation, elongation, and termination.

    Steps of protein synthesis

    • Initiation, elongation, and termination.

    Initiation

    • Ribosomes, mRNA, aminoacyl-tRNA specified by the first codon (AUG for methionine), and initiation factors are involved.
    • The initiator tRNA (carrying methionine) enters the P site. First codon recognized by a special initiator tRNA.

    Elongation

    • Amino acids are added to the growing polypeptide chain.
    • The aminoacyl-tRNA whose codon appears next on mRNA will be delivered to the A-site.
    • The carboxyl group of aminoacyl-tRNA in the P site is transferred to the amino group of the new aminoacyl-tRNA in the A site.
    • Ribosomes move three bases along the mRNA.
    • The uncharged tRNA leaves the ribosome.

    Termination

    • The ribosome reaches a termination codon (UAA, UAG, or UGA).
    • Release factors recognize termination codons.
    • The bond between peptide and tRNA is hydrolyzed.
    • The polypeptide is released.
    • Ribosome subunits dissociate.

    Polysomes

    • Multiple ribosomes can translate the same mRNA simultaneously.
    • This complex of mRNA and ribosomes is called a polysome.

    Inhibition of Protein Synthesis

    • Antibiotics target bacterial ribosomes (70S), which are different from eukaryotic ribosomes (80S).

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    Lecture 9 Nucleic Acids II PDF

    Description

    This quiz covers essential concepts related to nucleic acids, including the structure and function of mRNA, tRNA, and rRNA. You will explore the central dogma of molecular biology, which describes the transfer of genetic information from DNA to RNA to protein. Test your understanding of processes like transcription and translation, as well as the roles of various RNA types.

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