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?

Two DNA molecules with one original strand and one new strand Signup and view all the answers

What is the direction of DNA replication in bacteria?

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

What is the function of the origin of replication?

To initiate DNA replication Signup and view all the answers

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

One original strand and one new strand Signup and view all the answers

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

Semi-conservative replication Signup and view all the answers

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

RNA primer Signup and view all the answers

Why are Okazaki fragments formed during DNA replication?

Because the lagging strand is synthesized in short fragments Signup and view all the answers

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

Removing RNA primer nucleotides and replacing them with deoxynucleotides Signup and view all the answers

What is the function of DNA ligase during DNA replication?

Sealing gaps between nucleotides Signup and view all the answers

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

Two complete DNA molecules Signup and view all the answers

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

40 minutes Signup and view all the answers

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

The formation of two complete DNA molecules Signup and view all the answers

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

Primase Signup and view all the answers

What is the primary function of ribosomes?

To translate mRNA into a polypeptide Signup and view all the answers

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

Peptide bond Signup and view all the answers

What do ribosomes locate on the mRNA molecule?

Key punctuation sequences Signup and view all the answers

What is the result of protein synthesis in ribosomes?

A polypeptide chain Signup and view all the answers

Where do ribosomes bind to the mRNA molecule?

At the ribosome binding site Signup and view all the answers

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

To initiate protein synthesis Signup and view all the answers

What is the role of mRNA?

To carry encoded instructions for protein synthesis Signup and view all the answers

What happens when RNA polymerase encounters a terminator?

It falls off the DNA template and releases the newly synthesized RNA Signup and view all the answers

What is the function of the genetic code?

To translate mRNA sequences into amino acid sequences Signup and view all the answers

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

64 Signup and view all the answers

What is translation?

The process of decoding mRNA to synthesize proteins Signup and view all the answers

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

The rapid synthesis of multiple copies of the same protein Signup and view all the answers

What is the composition of proteins?

Amino acids Signup and view all the answers

What is the term for a sequence of three nucleotides?

Codon Signup and view all the answers

What is the primary function of a tRNA molecule?

To carry an amino acid to the ribosome Signup and view all the answers

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

To recognize and bind to the mRNA codon Signup and view all the answers

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

The amino acid is transferred to the growing polypeptide chain Signup and view all the answers

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

To bind the initiating tRNA Signup and view all the answers

What is the function of the rRNA in the ribosome?

To create a peptide bond between amino acids Signup and view all the answers

What determines the sequence of amino acids in a protein?

The sequence of codons in the mRNA Signup and view all the answers

What is the role of the AUG codon in translation?

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

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

The polypeptide chain is elongated Signup and view all the answers

What is the direction of RNA synthesis during transcription?

From 5' to 3' Signup and view all the answers

What is the role of sigma factor during transcription?

To initiate transcription Signup and view all the answers

What happens to the sigma factor during elongation?

It dissociates from RNA polymerase Signup and view all the answers

What is the region of DNA where RNA polymerase binds?

Promoter Signup and view all the answers

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

Melting of a short stretch of DNA Signup and view all the answers

What is the function of RNA polymerase during transcription?

To synthesize RNA Signup and view all the answers

What is the template strand during transcription?

The 3' strand of DNA Signup and view all the answers

What is the purpose of the promoter region during transcription?

To bind RNA polymerase Signup and view all the answers

In which direction is RNA synthesized?

5' to 3' Signup and view all the answers

What happens to RNA polymerase when it encounters a terminator?

It falls off the template and releases the newly synthesized RNA Signup and view all the answers

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

Before the RNA synthesis starts Signup and view all the answers

What is the role of RNA polymerase in RNA synthesis?

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

What is the sequence of events during RNA synthesis?

Promoter recognition, RNA synthesis, termination Signup and view all the answers

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

To initiate RNA synthesis Signup and view all the answers

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

It dissociates from the template Signup and view all the answers

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

To add nucleotides to the growing chain Signup and view all the answers

Which component of the bacterial RNA polymerase recognizes the promoter?

Sigma factor Signup and view all the answers

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

To recognize the promoter Signup and view all the answers

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

To recognize the promoter Signup and view all the answers

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

Has a sigma subunit Signup and view all the answers

What is the direction of nucleotide addition during RNA synthesis?

Only at the 3' end Signup and view all the answers

What is the energy source for RNA synthesis?

High-energy phosphate bonds Signup and view all the answers

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

Adaptive humoral response Signup and view all the answers

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

To produce antibodies reactive with a particular antigen Signup and view all the answers

What is the developmental pathway of B cells dependent on?

Bone marrow Signup and view all the answers

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

To recognize general pathogen features Signup and view all the answers

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

The antigen is eliminated Signup and view all the answers

What is the characteristic of cellular immune responses?

Are dependent on an intact thymus Signup and view all the answers

What is the result of immunodeficiency?

The immune system fails Signup and view all the answers

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

T cells Signup and view all the answers

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

The pentameric structure with critically spaced binding sites Signup and view all the answers

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

Lysis of the target cell Signup and view all the answers

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

NK cells, monocytes, and neutrophils Signup and view all the answers

What is required to trigger low-affinity FcγRIII receptors?

Multiple IgG molecules clustered together Signup and view all the answers

Which immunoglobulin isoforms do not activate the classical pathway?

IgA, IgD, and IgE Signup and view all the answers

What is the role of C1q in the classical pathway?

To bind to IgM and activate the classical pathway Signup and view all the answers

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

The lysis of target cells 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?

Critical spacing Signup and view all the answers

Where are natural killer cells thought to develop?

Both thymus and bone marrow Signup and view all the answers

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

Soluble mediators, including interleukins, cytokines, and chemokines Signup and view all the answers

What type of receptors recognize conserved microbial structures directly?

Pattern recognition receptors Signup and view all the answers

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

Tolerance Signup and view all the answers

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

Intravenous (IV) Signup and view all the answers

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

Pathogen-associated molecular patterns (PAMPs) Signup and view all the answers

What is the function of toll-like receptors?

To recognize conserved microbial structures Signup and view all the answers

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

Large amounts of antibody with mixed affinity and broad specificity 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.