DNA Replication Process
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Questions and Answers

What is a characteristic of DNA replication?

  • It is spontaneous, meaning that it occurs without the need for enzymes
  • It is unidirectional, meaning that replication occurs in one direction only
  • It is semiconservative, meaning that each new DNA molecule contains one original strand and one new strand (correct)
  • It is conservative, meaning that the original DNA molecule is preserved

    • What is the function of specific proteins in initiation of DNA replication?

  • To recognize and bind to the origin of replication (correct)
  • To proofread the newly synthesized DNA
  • To unwind the double helix
  • To synthesize new DNA strands

    • What is the term for the point at which the replication process is occurring?

  • Replication origin
  • Replication molecule
  • Replication fork (correct)
  • Replication enzyme

    • What is the result of DNA replication?

    <p>Two DNA molecules with one original strand and one new strand</p> Signup and view all the answers

    What is the direction of DNA replication in bacteria?

    <p>Bidirectional, occurring in both directions from the origin of replication</p> Signup and view all the answers

    What is the function of the origin of replication?

    <p>To initiate DNA replication</p> Signup and view all the answers

    What is the composition of each new DNA molecule after replication?

    <p>One original strand and one new strand</p> Signup and view all the answers

    What is the name of the process by which DNA replication occurs?

    <p>Semi-conservative replication</p> Signup and view all the answers

    What is necessary before DNA synthesis can begin on the lagging strand?

    <p>RNA primer</p> Signup and view all the answers

    Why are Okazaki fragments formed during DNA replication?

    <p>Because the lagging strand is synthesized in short fragments</p> Signup and view all the answers

    What is the role of DNA polymerase in Okazaki fragment synthesis?

    <p>Removing RNA primer nucleotides and replacing them with deoxynucleotides</p> Signup and view all the answers

    What is the function of DNA ligase during DNA replication?

    <p>Sealing gaps between nucleotides</p> Signup and view all the answers

    What is the result of the replication of a circular bacterial chromosome?

    <p>Two complete DNA molecules</p> Signup and view all the answers

    What is the time it takes for the replication of the E. coli chromosome?

    <p>40 minutes</p> Signup and view all the answers

    What event occurs when the two replication forks meet during DNA replication?

    <p>The formation of two complete DNA molecules</p> Signup and view all the answers

    Which enzyme is responsible for reinitiating synthesis on the lagging strand?

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

    What is the primary function of ribosomes?

    <p>To translate mRNA into a polypeptide</p> Signup and view all the answers

    What type of bond is formed between two amino acids during protein synthesis?

    <p>Peptide bond</p> Signup and view all the answers

    What do ribosomes locate on the mRNA molecule?

    <p>Key punctuation sequences</p> Signup and view all the answers

    What is the result of protein synthesis in ribosomes?

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

    Where do ribosomes bind to the mRNA molecule?

    <p>At the ribosome binding site</p> Signup and view all the answers

    What is the role of the start codon in protein synthesis?

    <p>To initiate protein synthesis</p> Signup and view all the answers

    What is the role of mRNA?

    <p>To carry encoded instructions for protein synthesis</p> Signup and view all the answers

    What happens when RNA polymerase encounters a terminator?

    <p>It falls off the DNA template and releases the newly synthesized RNA</p> Signup and view all the answers

    What is the function of the genetic code?

    <p>To translate mRNA sequences into amino acid sequences</p> Signup and view all the answers

    What is the number of different codons possible in the genetic code?

    <p>64</p> Signup and view all the answers

    What is translation?

    <p>The process of decoding mRNA to synthesize proteins</p> Signup and view all the answers

    What is the result of a single gene being transcribed repeatedly?

    <p>The rapid synthesis of multiple copies of the same protein</p> Signup and view all the answers

    What is the composition of proteins?

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

    What is the term for a sequence of three nucleotides?

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

    What is the primary function of a tRNA molecule?

    <p>To carry an amino acid to the ribosome</p> Signup and view all the answers

    What is the role of the anticodon in a tRNA molecule?

    <p>To recognize and bind to the mRNA codon</p> Signup and view all the answers

    What is the result of the interaction between a tRNA and the mRNA codon?

    <p>The amino acid is transferred to the growing polypeptide chain</p> Signup and view all the answers

    What is the function of the P-site in the ribosome?

    <p>To bind the initiating tRNA</p> Signup and view all the answers

    What is the function of the rRNA in the ribosome?

    <p>To create a peptide bond between amino acids</p> Signup and view all the answers

    What determines the sequence of amino acids in a protein?

    <p>The sequence of codons in the mRNA</p> Signup and view all the answers

    What is the role of the AUG codon in translation?

    <p>It initiates translation only when preceded by a ribosome-binding site</p> Signup and view all the answers

    What is the result of peptide bond formation between two amino acids?

    <p>The polypeptide chain is elongated</p> Signup and view all the answers

    What is the direction of RNA synthesis during transcription?

    <p>From 5' to 3'</p> Signup and view all the answers

    What is the role of sigma factor during transcription?

    <p>To initiate transcription</p> Signup and view all the answers

    What happens to the sigma factor during elongation?

    <p>It dissociates from RNA polymerase</p> Signup and view all the answers

    What is the region of DNA where RNA polymerase binds?

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

    What is the result of RNA polymerase binding to the promoter?

    <p>Melting of a short stretch of DNA</p> Signup and view all the answers

    What is the function of RNA polymerase during transcription?

    <p>To synthesize RNA</p> Signup and view all the answers

    What is the template strand during transcription?

    <p>The 3' strand of DNA</p> Signup and view all the answers

    What is the purpose of the promoter region during transcription?

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

    In which direction is RNA synthesized?

    <p>5' to 3'</p> Signup and view all the answers

    What happens to RNA polymerase when it encounters a terminator?

    <p>It falls off the template and releases the newly synthesized RNA</p> Signup and view all the answers

    What is the location of the promoter in relation to the RNA?

    <p>Before the RNA synthesis starts</p> Signup and view all the answers

    What is the role of RNA polymerase in RNA synthesis?

    <p>To add nucleotides to the 3' end of the growing chain</p> Signup and view all the answers

    What is the sequence of events during RNA synthesis?

    <p>Promoter recognition, RNA synthesis, termination</p> Signup and view all the answers

    What is the function of the 5' end of the RNA?

    <p>To initiate RNA synthesis</p> Signup and view all the answers

    What happens to the RNA polymerase after RNA synthesis is complete?

    <p>It dissociates from the template</p> Signup and view all the answers

    What is the role of the 3' end of the RNA during synthesis?

    <p>To add nucleotides to the growing chain</p> Signup and view all the answers

    Which component of the bacterial RNA polymerase recognizes the promoter?

    <p>Sigma factor</p> Signup and view all the answers

    What is the role of transcription factors in eukaryotic cells and archaea?

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

    What is the function of the sigma subunit in bacterial RNA polymerase?

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

    Which of the following is NOT a characteristic of RNA polymerase in eukaryotic cells and archaea?

    <p>Has a sigma subunit</p> Signup and view all the answers

    What is the direction of nucleotide addition during RNA synthesis?

    <p>Only at the 3' end</p> Signup and view all the answers

    What is the energy source for RNA synthesis?

    <p>High-energy phosphate bonds</p> Signup and view all the answers

    What type of immune response involves the generation of antibodies reactive with a particular antigen?

    <p>Adaptive humoral response</p> Signup and view all the answers

    What is the role of B cells in the immune response?

    <p>To produce antibodies reactive with a particular antigen</p> Signup and view all the answers

    What is the developmental pathway of B cells dependent on?

    <p>Bone marrow</p> Signup and view all the answers

    What is the role of dendritic cells in the immune response?

    <p>To recognize general pathogen features</p> Signup and view all the answers

    What is the result of the effector phase of the immune response?

    <p>The antigen is eliminated</p> Signup and view all the answers

    What is the characteristic of cellular immune responses?

    <p>Are dependent on an intact thymus</p> Signup and view all the answers

    What is the result of immunodeficiency?

    <p>The immune system fails</p> Signup and view all the answers

    What is the term for the lymphocytes responsible for cellular immune responses?

    <p>T cells</p> Signup and view all the answers

    Which IgM molecule feature is critical for activation of the classical pathway?

    <p>The pentameric structure with critically spaced binding sites</p> Signup and view all the answers

    What is the final result of the lytic pathway of the complement system?

    <p>Lysis of the target cell</p> Signup and view all the answers

    Which immune cells are capable of antibody-dependent cellular cytotoxicity (ADCC)?

    <p>NK cells, monocytes, and neutrophils</p> Signup and view all the answers

    What is required to trigger low-affinity FcγRIII receptors?

    <p>Multiple IgG molecules clustered together</p> Signup and view all the answers

    Which immunoglobulin isoforms do not activate the classical pathway?

    <p>IgA, IgD, and IgE</p> Signup and view all the answers

    What is the role of C1q in the classical pathway?

    <p>To bind to IgM and activate the classical pathway</p> Signup and view all the answers

    What is the result of the convergence of all pathways in the complement system?

    <p>The lysis of target cells</p> Signup and view all the answers

    What is the common feature of the Fc regions of IgM molecules that allows for efficient activation of C1q?

    <p>Critical spacing</p> Signup and view all the answers

    Where are natural killer cells thought to develop?

    <p>Both thymus and bone marrow</p> Signup and view all the answers

    What type of molecules carry messages between cells in the immune response?

    <p>Soluble mediators, including interleukins, cytokines, and chemokines</p> Signup and view all the answers

    What type of receptors recognize conserved microbial structures directly?

    <p>Pattern recognition receptors</p> Signup and view all the answers

    What is the result of high doses of antigen on the immune response?

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

    What is the route of entry for an antigen that leads to a response in the spleen?

    <p>Intravenous (IV)</p> Signup and view all the answers

    What type of molecules are recognized by the innate immune system?

    <p>Pathogen-associated molecular patterns (PAMPs)</p> Signup and view all the answers

    What is the function of toll-like receptors?

    <p>To recognize conserved microbial structures</p> Signup and view all the answers

    What is the result of moderate doses of antigen on the immune response?

    <p>Large amounts of antibody with mixed affinity and broad specificity</p> Signup and view all the answers

    Study Notes

    DNA Replication

    • DNA replication is semiconservative, meaning each new molecule contains one original strand paired with a newly synthesized strand.
    • Replication forks are formed at the origin of replication, and the process is bidirectional.

    Initiation of DNA Replication

    • Specific proteins recognize and bind to the origin of replication to initiate DNA synthesis.
    • An RNA primer is made first, and then DNA polymerase adds nucleotides to the end of the primer.
    • The result is a series of small fragments called Okazaki fragments, each with a short stretch of RNA at one end.

    Synthesis of the Lagging Strand

    • Discontinuous synthesis generates Okazaki fragments.
    • DNA polymerase adds nucleotides to the end of one Okazaki fragment, eventually reaching the end of another.
    • Another DNA polymerase then removes the RNA primer nucleotides and replaces them with deoxynucleotides.
    • The enzyme DNA ligase seals the gaps between fragments by forming a covalent bond.

    Termination of Transcription

    • Transcription is terminated when RNA polymerase encounters a sequence called a terminator.
    • The enzyme falls off the DNA template and releases the newly synthesized RNA.

    Translation

    • Translation is the process of decoding the information carried in mRNA to synthesize a protein.
    • Ribosomes serve as translation "machines" that string amino acids together to make a polypeptide.
    • tRNAs carry an amino acid to be used in translation and recognize specific codons in the mRNA.

    The Role of mRNA

    • mRNA is a temporary copy of the information in DNA, carrying encoded instructions for synthesis of a specific protein.
    • The information in mRNA must be decoded into amino acids using the genetic code.

    The Genetic Code

    • The genetic code correlates a series of three nucleotides, a codon, with one amino acid.
    • There are 64 different codons, and three are stop codons.
    • The genetic code is practically universal, meaning it is used by all living things with a few minor changes.

    The Role of Ribosomes

    • Ribosomes locate key punctuation sequences on the mRNA molecule, such as the points at which protein synthesis should begin.
    • Ribosomes have two sites, the P-site and the A-site, where amino acid-carrying tRNAs can bind.

    Elongation of the Polypeptide Chain

    • At the start of translation, the initiating tRNA carrying the f-Met occupies the P-site.
    • A tRNA that recognizes the next codon on the mRNA then fills the unoccupied A-site.
    • Once both sites are filled, an rRNA creates a peptide bond between the two amino acids carried by the tRNAs.

    RNA Synthesis Process

    • RNA polymerase binds to the promoter and melts a short stretch of DNA, and the template strand is used to synthesize a single-stranded RNA molecule.
    • Sigma factor dissociates from RNA polymerase during elongation, leaving the core enzyme to complete transcription.

    RNA Polymerase Structure and Function

    • RNA polymerase has a loosely attached subunit called sigma (s) factor that recognizes the promoter.
    • Cells can produce various types of s factors, each recognizing different promoters.
    • Controlling which s factors are made allows cells to transcribe specialized sets of genes as needed.

    Eukaryotic and Archaeal RNA Polymerases

    • RNA polymerases of eukaryotic cells and archaea use proteins called transcription factors to recognize promoters.

    Transcription Process

    • RNA is synthesized in the 5' to 3' direction as the enzyme adds nucleotides to the 3' end of the growing chain.
    • Nucleotides are added only to the 3' end, and the reaction is fueled by hydrolyzing a high-energy phosphate bond of the incoming nucleotide.

    Initiation

    • RNA polymerase binds to the promoter and melts a short stretch of DNA during initiation.

    Elongation

    • RNA polymerase denatures a new stretch of DNA and allows the previous portion to renature during elongation.
    • This exposes a new region of the template so elongation can continue.

    Termination

    • When RNA polymerase encounters a terminator, it falls off the template and releases the newly synthesized RNA.
    • RNA polymerase dissociates from the template after termination.

    Humoral and Cellular Immune Responses

    • Humoral responses result in the generation of antibodies reactive with a particular antigen
    • Antibodies are proteins with similar structures, known collectively as immunoglobulins (Ig)
    • Adaptive humoral responses can be transferred passively to another individual by injection of serum
    • Cellular immune responses are dependent on an intact thymus, and the lymphocytes responsible are known as thymus-dependent (T) cells

    B Cells and T Cells

    • Antibody-producing lymphocytes, dependent on the bone marrow, are known as B cells
    • In response to antigen stimulation, B cells will mature to antibody-secreting plasma cells
    • T cells are responsible for cellular immune responses and are dependent on an intact thymus

    Recognition Phase

    • The recognition phase is common to both adaptive and innate immunity
    • It involves professional cells, known as classical dendritic cells, that recognize general pathogen features or specific antigenic molecules
    • Dendritic cells process antigens and present antigen fragments to other cells of the immune system

    Effector Phase

    • In the effector phase, neutrophils and macrophages (innate immunity) and antibodies and effector T lymphocytes (adaptive immunity) eliminate the antigen

    Immune System Diseases

    • The immune system may fail (immunodeficiency), become malignant (lymphoid malignancies), or produce aberrant responses (such as in autoimmunity or allergy)

    Effector Mechanisms

    • Effector mechanisms are often dependent on messages from initiating or regulating cells
    • Soluble mediators, which carry messages between cells, are known as interleukins, cytokines, and chemokines

    Molecules Recognized by Immune Systems

    • Foreign substances are recognized by both the innate and adaptive systems, but in different ways, using different receptors
    • The innate system is activated by ‘danger signals’, due to pattern recognition receptors (PRRs) on dendritic cells recognizing conserved microbial structures directly

    Factors Influencing the Immune Response

    • The nature of the molecule (protein content, size, solubility) influences the immune response
    • The dose of the antigen influences the immune response, with low doses provoking small amounts of antibody with high affinity and restricted specificity
    • The route of entry of the antigen influences the immune response, with different routes leading to different immune responses

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    Description

    Understand the semiconservative process of DNA replication, where each new molecule contains one original strand paired with a new one.

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