Central Dogma and DNA Replication
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Questions and Answers

What is the term used for the process of copying the genetic code into RNA?

  • Translocation
  • Translation
  • Transcription (correct)
  • Replication

Which strand of DNA serves as the template during the transcription process?

  • Antisense strand (correct)
  • Coding strand
  • Leading strand
  • Sense strand

Which enzyme is primarily responsible for synthesizing RNA during transcription?

  • RNA Polymerase III
  • RNA Polymerase I
  • RNA Polymerase II (correct)
  • DNA Polymerase

What is the function of the TATA Box in the transcription process?

<p>To facilitate the binding of RNA Polymerase II (D)</p> Signup and view all the answers

Which components assist RNA Polymerase II in binding to the TATA Box during transcription initiation?

<p>General transcription factors (C)</p> Signup and view all the answers

Which transcription factor is the first to bind to the TATA box?

<p>TFIID (A)</p> Signup and view all the answers

What role does TFIIH perform in the pre-initiation complex?

<p>Acts as a helicase to split open the promoter (D)</p> Signup and view all the answers

How does TFIIF assist in the transcription process?

<p>Facilitates the binding of RNA Polymerase II on the promoter (C)</p> Signup and view all the answers

In which direction does the pre-mRNA strand run during elongation?

<p>5’ to 3’ direction (D)</p> Signup and view all the answers

Which component of TFIIH has kinase activity?

<p>7 subunits that do not use ATP (C)</p> Signup and view all the answers

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

<p>It codes for the amino acid methionine. (B)</p> Signup and view all the answers

What does aminoacyl synthetase do in the process of translation?

<p>It binds the amino acid to the tRNA. (D)</p> Signup and view all the answers

Which process describes the transfer of the amino acid chain to water during termination?

<p>Peptidyl transfer (D)</p> Signup and view all the answers

What happens to the ribosome after it reaches a stop codon?

<p>It detaches from the mRNA and splits into subunits. (B)</p> Signup and view all the answers

During which phase does the ribosome slide towards the next codon and free the A-site?

<p>Translocation (B)</p> Signup and view all the answers

What role does the tRNA anticodon play in the translation process?

<p>It complexes with the mRNA codon. (D)</p> Signup and view all the answers

What occurs when the levels of tryptophan decrease in the tryptophan operon system?

<p>The corepressor releases the aporepressor (B)</p> Signup and view all the answers

Which of the following components is NOT involved in the termination phase of translation?

<p>Aminoacyl tRNA (D)</p> Signup and view all the answers

How does gene regulation assist eukaryotic cells in growing and developing?

<p>By helping cells manage external environmental changes (D)</p> Signup and view all the answers

Which statement about transcription factors is false?

<p>Transcription factors bind to the operator to initiate transcription (A)</p> Signup and view all the answers

What is formed when the second amino acid is bound to methionine?

<p>A peptide bond (A)</p> Signup and view all the answers

What happens to transcription factors when they are not required in the nucleus?

<p>They remain in the cytoplasm (D)</p> Signup and view all the answers

What regulates the ability of transcription factors to bind to DNA?

<p>The degree of multimerization and DNA-binding domain alterations (D)</p> Signup and view all the answers

Which of the following best describes the relationship between eukaryotic genes required for enzyme synthesis?

<p>They may be located far apart on the same DNA or in different DNAs (D)</p> Signup and view all the answers

What role does phosphorylation play in the regulation of transcription factors?

<p>It allows transcription factors to enter the nucleus (B)</p> Signup and view all the answers

Which process is NOT involved in the regulation of transcription factors in eukaryotes?

<p>Regulation of teleomerase activity (B)</p> Signup and view all the answers

What role do transcription repressors play in mRNA production?

<p>They bind to mRNA and regulate where spliceosomes cut. (A)</p> Signup and view all the answers

What is the main function of micro RNAs (miRNAs) in gene regulation?

<p>To determine the fate of untranslatable mRNAs. (C)</p> Signup and view all the answers

Which scenario leads to the inhibition of translation in a cell?

<p>Insufficient nutrients, particularly amino acids. (D)</p> Signup and view all the answers

How do miRNAs affect mRNAs with complementary sequences?

<p>They lead to the destruction of the mRNA. (A)</p> Signup and view all the answers

What does the phosphorylation of eIFs result in?

<p>Inhibition of translation. (D)</p> Signup and view all the answers

In differential mRNA splicing, what determines the combination of exons included in the final mRNA?

<p>Regulatory protein binding to the mRNA. (B)</p> Signup and view all the answers

What is one way proteins can be regulated even after translation has occurred?

<p>Through the process of phosphorylation. (A)</p> Signup and view all the answers

Which statement accurately describes the effect of partially complementary miRNAs on mRNAs?

<p>They prevent the translation of the mRNA. (B)</p> Signup and view all the answers

What role does ubiquitination play in cellular protein management?

<p>It signals proteins for degradation at the proteasome. (B)</p> Signup and view all the answers

What happens to the amino acids released from protein degradation?

<p>They are recycled for new protein translation. (D)</p> Signup and view all the answers

Under what circumstance does ubiquitination typically occur?

<p>When proteins are not utilized for an extended period. (A)</p> Signup and view all the answers

Which type of gene is always active in maintaining cellular functions?

<p>Constitutive genes (B)</p> Signup and view all the answers

What characterizes facultative genes in a cell?

<p>They can be turned on or off based on the cell's needs. (D)</p> Signup and view all the answers

What is the primary function of the proteasome in the ubiquitination process?

<p>Degrading tagged proteins. (C)</p> Signup and view all the answers

Which statement regarding protein persistence is true?

<p>Ubiquitination decreases the lifespan of proteins in the cell. (C)</p> Signup and view all the answers

Which component is involved in the recycling of amino acids during protein turnover?

<p>Proteasome (C)</p> Signup and view all the answers

Flashcards

Transcription

The process where DNA is used as a template to create a copy of a gene in the form of RNA. This involves three steps: initiation, elongation, and termination.

Sense Strand

The DNA strand that contains the genetic code for a gene. It is the strand that is not used as a template for transcription.

Antisense Strand

The DNA strand that complements the sense strand and serves as the template for transcription. It is used by RNA polymerase to create the RNA copy.

Promoter

A region of DNA located at the beginning of a gene that signals the starting point for transcription. It contains a TATA Box recognized by RNA polymerase II.

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General Transcription Factors (TFII)

Proteins that help RNA polymerase II bind to the promoter region and initiate transcription. They are essential for efficient gene expression.

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TATA Box

A specific DNA sequence (usually TATAAA) found in the promoter region of many genes. It serves as a binding site for the TFIID transcription factor, initiating the transcription process.

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TFIID

The first transcription factor to bind to the TATA box. It contains a TATA Box-binding protein (TBP) that bends the promoter, allowing other transcription factors to bind.

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Pre-Initiation Complex

The group of transcription factors (TFIID, TFIIA, TFIIB, TFIIF) assembled at the promoter, preparing the DNA for transcription.

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Open Complex

The state of the promoter after the DNA strands are separated, allowing RNA polymerase II to access the template strand and begin transcription.

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TFIIH

A transcription factor with two key functions: 1) Uses ATP to unwind the DNA (helicase activity) and 2) Phosphorylates the RNA Polymerase II tail, allowing it to start transcribing.

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Start Codon

The first codon in an mRNA sequence, always AUG, which codes for the amino acid methionine and signals the start of protein synthesis.

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tRNA Anticodon

A three-nucleotide sequence on a tRNA molecule that complements the codon on mRNA, ensuring the correct amino acid is added to the growing polypeptide chain.

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Aminoacyl Synthase

An enzyme that attaches the correct amino acid to its corresponding tRNA molecule, preparing it for delivery to the ribosome.

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A-Site

The binding site on a ribosome where the tRNA carrying the next amino acid in the polypeptide chain binds

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Transpeptidation

The process where the peptide bond is formed between the newly arrived amino acid and the growing polypeptide chain, catalyzed by peptidyl transferase.

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Translocation

The movement of the ribosome along the mRNA molecule, shifting the tRNA carrying the growing polypeptide chain from the A-site to the P-site, and freeing the A-site for a new tRNA to bind.

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E-Site

The exit site on the ribosome where the tRNA, having delivered its amino acid and without an attached amino acid, leaves the ribosome.

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Stop Codon

A three-nucleotide sequence on mRNA that signals the termination of protein synthesis. No tRNA binds to the stop codon, instead a release factor binds to signal the end.

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Tryptophan Operon Regulation

A system where the presence of tryptophan inhibits its own production by repressing gene expression.

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Aporepressor

A protein that, when bound to a corepressor like tryptophan, prevents transcription of genes involved in tryptophan synthesis.

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Corepressor

A molecule that binds to an aporepressor, activating it to repress gene expression.

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Eukaryotic Gene Regulation

The control and modulation of gene expression in eukaryotic cells, crucial for development, response to environmental cues, and cellular function.

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Transcription Factors (TFs)

Proteins that bind to DNA and regulate the initiation of transcription.

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Regulation of Nuclear Localization

Control of the movement of transcription factors between the cytoplasm and the nucleus, ensuring their presence only when needed.

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Regulation of DNA-binding

Mechanisms that control the ability of transcription factors to bind to DNA, further regulating gene expression.

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Multimerization of TFs

The formation of a complex by multiple transcription factors, necessary for their activation and binding to DNA.

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Alternative Splicing

A process where one pre-mRNA molecule can be spliced in different ways, producing multiple mRNA transcripts. These transcripts can then be translated into different protein isoforms.

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Role of Regulatory Proteins in Splicing

Regulatory proteins bind to pre-mRNA and guide spliceosomes to specific splice sites. This controls which exons are included or excluded in the final mRNA transcript.

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miRNAs: mRNA Life Span Control

microRNAs (miRNAs) are small non-coding RNAs that regulate the lifespan of mRNAs. miRNAs bind to mRNAs and either degrade them or prevent their translation.

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miRNA Binding and Degradation

Complementary binding of a miRNA to an mRNA leads to the degradation of the mRNA. The mRNA is essentially chopped up and discarded.

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miRNA Binding and Translation Inhibition

Partial complementarity between a miRNA and an mRNA prevents translation of the mRNA. The mRNA is marked for silencing and no new protein is produced.

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Translation Regulation: When the Cell Can't Afford

When resources are limited (e.g., amino acids), translation is inhibited to conserve energy. This is achieved by phosphorylating and inactivating translation initiation factors (eIFs).

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Post-Translational Regulation by Phosphorylation

Even after translation, protein function can be regulated by phosphorylation. This chemical modification can either activate or deactivate a protein depending on the specific site and protein.

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Regulation of Gene Expression: A Multi-Step Process

Gene expression is regulated at multiple levels, from transcription through translation and even after protein synthesis. This ensures that the right proteins are produced in the right amounts at the right time.

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Ubiquitination

A cellular process where ubiquitin, a small protein, attaches to target proteins, effectively marking them for degradation by the proteasome.

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Proteasome

A large protein complex responsible for breaking down tagged proteins into smaller peptides and amino acids.

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Protein Persistence

The length of time a protein remains functional within a cell. Ubiquitination regulates this.

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Facultative Genes

Genes that are turned on or off depending on the cell's needs, allowing for flexibility in gene expression.

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Constitutive Genes

Genes that are always active (expressed), ensuring the fundamental functions of the cell continue.

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Housekeeping Genes

Another name for constitutive genes. They are essential for basic cell maintenance.

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ATP Production

The process by which cells generate energy in the form of ATP, crucial for cellular functions.

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Study Notes

Central Dogma and Molecular Genetics

  • The central dogma describes the flow of genetic material in organisms.
  • DNA replicates to produce new DNA.
  • DNA undergoes transcription to create RNA.
  • RNA undergoes translation to form proteins.
  • RNA can also produce DNA via reverse transcription.

Molecular Mechanisms of DNA Replication

  • DNA replication is vital for maintaining the chromosome number in cell generations.

  • This guarantees identical genetic material in all body cells, excluding gametes.

  • The process in eukaryotes is detailed, followed by a comparison with prokaryotic replication.

  • Initiation:

    • DNA helicase unwinds the parental double helix.
    • Single-strand binding proteins stabilize the unwound DNA.
    • Topoisomerase relieves the tightening of the supercoil.

  • Elongation:

    • DNA polymerase adds complementary nucleotides in a 3' to 5' direction.
    • Leading strand synthesis is continuous (5' to 3').
    • Lagging strand synthesis is discontinuous, forming Okazaki fragments (3' to 5').
    • RNA primers are synthesized by primase and extended by DNA polymerase.
    • DNA ligase joins Okazaki fragments.

  • Termination:

    • DNA ligase joins Okazaki fragments.
    • Replication bubbles meet.
    • Replication is considered semi-conservative.

Molecular Mechanisms of Gene Expression

  • Genes hold blueprints for building organisms via protein synthesis.
  • Polypeptide chains, formed from amino acids, comprise proteins.
  • Gene expression involves transcription and translation.
  • Eukaryotic gene expression is discussed initially, followed by a comparison with prokaryotic gene expression after laboratory work.

Transcription

  • Initiation:

    • The DNA strand used for transcription is the sense strand; the complementary strand is the antisense strand.
    • Transcription factors (e.g., TFIID, TFIIA, TFIIB, TFIIE, TFIIH, TFIIF).
    • Pre-initiation complex formation involving TBP helps to bind to the TATA box.
    • Open complex formation: unwinding and RNA polymerase II binding.

  • Elongation:

    • RNA polymerase II adds RNA nucleotides to the growing RNA chain according to the DNA template.
    • New RNA is synthesized using the antisense strand as a template and in a 5’ to 3’ direction.
    • Formation of pre-mRNA transcript and the formation of 5' capping.

  • Termination

    • mRNA polymerase reaches the terminal region and interacts with proteins
    • Cleavage, stimulation factors (CstFs), cleave the pre-mRNA and separate it from RNA polymerase II.
    • Poly(A) tail is added (AAUAAA sequence)
    • RNA is processed further to form mRNA transcript.

Reverse Transcription

  • Retroviruses use reverse transcription, an RNA-driven DNA synthesis.
  • Viral RNA serves as a template.
  • A single-stranded DNA is formed.
  • Complimentary DNA strand is formed.
  • Numerous copies of viral RNA and proteins are made.

Gene Regulation (Prokaryotes)

  • Genes aren't expressed simultaneously.
  • Operon hypothesis (Jacob and Monod) describes the process.
  • Operon: a system of adjacent structural genes (cistrons).
  • Operator: controls transcription.
  • Promoter: RNA polymerase binding site.
  • Regulatory gene: codes for repressor protein.

Gene Regulation (Eukaryotes)

  • Gene expression is controlled by external cues as cells develop.
  • Environmental cues are necessary for correct development.
  • Transcription factors (TF): molecules that bind to promoters to initiate transcription.
  • Regulation occurs at several stages:
    • Nuclear localization
    • DNA-binding
    • Activator proteins: enhance transcription.
    • Repressor proteins: inhibit transcription.
    • Regulation after transcription (mRNA processing).
    • Regulation of translation (e.g., phosphorylation)

Regulation of Translation

  • The cell controls protein production if resources are insufficient.
  • ElFs are involved in translation and they are phosphorylated to be deactivated if resources are insufficient

Regulation After Translation

  • Proteins are regulated after translation, through phosphorylation and ubiquitination.
  • Enzymes associated with Phosphorylation and Ubiquitination are used to influence protein activity.

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Molecular Genetics: Central Dogma & DNA Replication Notes PDF

Description

Explore the central dogma of molecular genetics and the intricate mechanisms of DNA replication. Understand how DNA is transcribed into RNA and translated into proteins, along with the replication process in eukaryotic and prokaryotic cells. This quiz highlights key processes and enzymes involved in genetic material flow.

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