Molecular Genetics Basics

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Questions and Answers

What is a primary function of genes at the molecular level?

  • To regulate metabolic processes
  • To facilitate cellular transport mechanisms
  • To direct the synthesis of polypeptides (correct)
  • To store energy for cellular functions

What is the consequence if DNA mutations escape repair?

  • They have no impact on genetic expression
  • They can lead to the development of new traits (correct)
  • They always result in immediate disease
  • They always result in harmful effects

Which aspect of gene regulation involves determining when and where a gene is activated?

  • Nucleotide sequencing
  • Gene expression (correct)
  • Transcription initiation
  • Protein synthesis

What is an essential requirement for DNA replication to prevent mutations?

<p>It must be exact and include error correction mechanisms (C)</p> Signup and view all the answers

How does DNA primarily transmit genetic information to the next generation?

<p>By replicating accurately (A)</p> Signup and view all the answers

What role does RNA polymerase play during transcription?

<p>It synthesizes mRNA by adding nucleotide bases. (A)</p> Signup and view all the answers

Which component is essential for the initiation of transcription?

<p>The TATA box within the promoter. (D)</p> Signup and view all the answers

During elongation, RNA polymerase adds nucleotides to which end of the growing mRNA strand?

<p>3’ end. (A)</p> Signup and view all the answers

What happens at the termination stage of transcription?

<p>The RNA transcript is released from the DNA template. (D)</p> Signup and view all the answers

What base is used in RNA instead of thymine found in DNA?

<p>Uracil. (D)</p> Signup and view all the answers

Which sequence in the DNA indicates where RNA polymerase should start transcribing?

<p>The promoter. (B)</p> Signup and view all the answers

What is the function of transcription factors in eukaryotic transcription?

<p>They assist in the recognition of the TATA box. (D)</p> Signup and view all the answers

How does RNA polymerase ensure that the newly synthesized mRNA strand is complementary to the DNA template?

<p>By pairing adenine with uracil and guanine with cytosine. (A)</p> Signup and view all the answers

What is the primary role of RNA in the process of gene expression?

<p>Translating the genetic code into amino acids (B)</p> Signup and view all the answers

What role does RNA polymerase play during transcription?

<p>It creates the mRNA transcript from the DNA template (C)</p> Signup and view all the answers

Which statement accurately describes the template and non-template strands of DNA?

<p>The non-template strand is used to create the mRNA transcript. (D)</p> Signup and view all the answers

How does the genetic code demonstrate universality across life forms?

<p>It utilizes the same 20 amino acids for building proteins. (D)</p> Signup and view all the answers

What is necessary for the accurate reading of the genetic code during translation?

<p>Maintaining the correct reading frame of codons (D)</p> Signup and view all the answers

What signifies the starting point of transcription in a gene?

<p>The promoter region is recognized by transcription factors (B)</p> Signup and view all the answers

What is the consequence of reading the genetic code in the wrong frame?

<p>The synthesis of non-functional proteins (B)</p> Signup and view all the answers

What best describes the flow of information in the central dogma of molecular biology?

<p>DNA -&gt; RNA -&gt; Polypeptide (D)</p> Signup and view all the answers

What is the role of the 5' cap added to pre-mRNA in eukaryotic cells?

<p>It helps export mRNA from the nucleus. (A)</p> Signup and view all the answers

What distinguishes eukaryotic genes from prokaryotic genes concerning promoters?

<p>Each eukaryotic gene has its own promoter. (A)</p> Signup and view all the answers

What is the significance of splicing in mRNA processing?

<p>It removes introns and joins exons together. (D)</p> Signup and view all the answers

During transcription in prokaryotes, what is the fate of mRNA once it is synthesized?

<p>It is immediately translated. (C)</p> Signup and view all the answers

Which of the following modifications is NOT performed on mRNA in eukaryotic cells?

<p>Translation to a polypeptide. (A)</p> Signup and view all the answers

How do prokaryotic genomes differ from eukaryotic genomes regarding introns?

<p>Prokaryotic genomes do not contain introns. (D)</p> Signup and view all the answers

What are the two major components required for the translation process?

<p>tRNA and mRNA. (C)</p> Signup and view all the answers

What occurs immediately after the termination of transcription in eukaryotic cells?

<p>The pre-mRNA undergoes splicing. (B)</p> Signup and view all the answers

What is the primary difference in gene structure between prokaryotes and eukaryotes?

<p>Prokaryotes lack introns in their gene structure. (A)</p> Signup and view all the answers

During translation termination, which component binds to the ribosomal complex?

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

Where does transcription occur in eukaryotic cells?

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

Which of the following modifications occurs in eukaryotic mRNA but not in prokaryotic mRNA?

<p>Addition of a 5' cap (D)</p> Signup and view all the answers

What initiates the process of transcription in both prokaryotes and eukaryotes?

<p>Promoter sequence (D)</p> Signup and view all the answers

What is a critical signal for termination during transcription?

<p>Terminator sequence in DNA (C)</p> Signup and view all the answers

How do prokaryotes generally differ from eukaryotes in the process of gene expression?

<p>Transcription and translation occur simultaneously in prokaryotes. (B)</p> Signup and view all the answers

What type of mutation could potentially occur during the splicing of mRNA in eukaryotes?

<p>Deletion of exons in the final mRNA (D)</p> Signup and view all the answers

What component of the ribosome is primarily involved in the process of translation?

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

What is the primary function of tRNA in the translation process?

<p>To link mRNA codons to specific amino acids (B)</p> Signup and view all the answers

During which phase of translation does the codon-anticodon pairing occur?

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

How many different codon combinations can be formed from the genetic code?

<p>64 (B)</p> Signup and view all the answers

What role does the large ribosomal subunit play in translation?

<p>It binds to tRNA and facilitates peptide bond formation (B)</p> Signup and view all the answers

What happens to the free tRNA after it has delivered its amino acid?

<p>It is moved to the E site and released (C)</p> Signup and view all the answers

What is the significance of the reading frame in translation?

<p>It groups codons into groups of three for interpretation (B)</p> Signup and view all the answers

Which amino acid is coded by the start codon AUG?

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

Flashcards

Gene Expression

The process by which a gene's information is used to create a functional product, usually a protein.

Gene Regulation

The process that controls when and where a gene is turned 'on' or expressed.

Mutation

A change in the DNA sequence that can have no effect, be harmful, or beneficial.

DNA Replication

The process of creating an exact copy of a DNA molecule; essential for cell division and inheritance.

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Polypeptide Synthesis

The process by which information encoded in a gene is used to create a protein.

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Gene Expression

DNA directing protein (or RNA) synthesis

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Transcription vs. Translation

DNA to RNA to protein; RNA creates protein

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DNA role

Genetic material, instructions for proteins

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RNA role

Protein synthesis and gene regulation

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Central Dogma

DNA to RNA to protein; flow of info

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Genetic Code

Codons (mRNA triplets) code for amino acids

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Template strand

DNA strand used to create mRNA; non-coding

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Genetic Code Significance

Universal code for all life forms; 64 codons

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Transcription Unit

A segment of DNA that contains the instructions for making a protein or RNA molecule.

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RNA Polymerase

An enzyme that builds an mRNA molecule from a DNA template.

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Promoter

A DNA sequence that tells RNA polymerase where to begin transcribing.

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Transcription Initiation

The first step in transcription, where RNA polymerase attaches to the promoter sequence.

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Transcription Elongation

The process of adding nucleotides to the growing RNA molecule.

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Transcription Termination

The final step of transcription, where RNA polymerase detaches from the DNA.

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mRNA

A messenger RNA molecule that carries the genetic code from DNA to ribosomes.

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TATA box (eukaryotes)

A DNA sequence in the promoter region of a eukaryotic gene, crucial for initiation.

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Ribosome function

Site of protein synthesis (translation).

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tRNA role

Transfers amino acids to ribosomes based on mRNA codons.

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tRNA anticodon

Pairs with a complementary mRNA codon.

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Ribosome structure

Made of rRNA and proteins, created in the nucleolus.

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mRNA codon

Three-base sequence that codes for an amino acid.

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Genetic Code

Set of rules that determines how codons are translated into amino acids.

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Reading frame

Groups of three mRNA bases, read sequentially.

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Genetic Code Universality

Same genetic code used by all living organisms.

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mRNA Processing (Eukaryotes)

Modifying pre-mRNA to create mature mRNA, including capping, polyadenylation, and splicing to remove introns.

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Prokaryotic vs. Eukaryotic Gene Expression

Prokaryotes transcribe and translate simultaneously; eukaryotes process mRNA before translation in the nucleus.

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Introns

Non-coding DNA sequences removed during mRNA processing in eukaryotes.

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Exons

Coding DNA sequences that remain in the mature mRNA to be used in protein synthesis.

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RNA Splicing

The process of removing introns and joining exons in pre-mRNA to create mature mRNA.

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5' Cap and 3' Poly-A Tail

Added to pre-mRNA in eukaryotes and protect mRNA from degradation and promote translation.

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Transcription Termination

The process of stopping transcription by transcribing a termination sequence in DNA, resulting in mRNA and polymerase detaching.

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Components of Translation (Simplified)

mRNA (message), tRNA (interpreter), ribosomes required for protein assembly.

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Translation Termination

The final step of protein synthesis, where a stop codon signals the release of the polypeptide chain.

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Prokaryotic Gene Expression

Transcription and translation occur simultaneously in the cytoplasm.

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Eukaryotic Gene Expression

Transcription occurs in the nucleus, and translation occurs in the cytoplasm.

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Transcription Initiation (general)

RNA polymerase binds to a DNA sequence (promoter) to start mRNA production.

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Translation Initiation signal

The AUG start codon in mRNA signals the beginning of protein synthesis.

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Transcription vs. Translation location

Transcription: Nucleus; Translation: Cytoplasm

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Eukaryotic gene structure

Includes introns (non-coding regions) and exons (coding regions).

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Types of Mutations (General)

Changes in the DNA sequence that can have various effects.

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Study Notes

Chapter 17: Transcription, RNA Processing, and Translation

  • This chapter examines how genetic information in genes directs the synthesis of RNA and proteins.
  • It explores how DNA is transcribed into RNA, how eukaryotes process RNA, and how messenger RNA is translated into proteins.
  • It also looks at the structure and function of transfer RNA and ribosomes.

Learning Objectives

  • Describe the steps of transcription.
  • Describe how primary transcripts are processed.
  • Describe the roles of ribosomes, mRNA, and tRNAs in translation.
  • Analyze the structure and function of transfer RNA.
  • Explain the events of translation initiation, elongation, termination, and post-translational modification.

Part I: Transcription

  • Transcription utilizes RNA polymerase to synthesize RNA from a DNA template.
  • RNA polymerase moves along the DNA template strand in the 3' to 5' direction, synthesizing the RNA transcript in the 5' to 3' direction.
  • The RNA transcript is complementary to the template and identical to the nontemplate (coding) DNA strand, with uracil (U) replacing thymine (T).

Review: Differences between DNA and RNA

  • DNA is a double helix while RNA is a single stranded molecule.
  • DNA contains the sugar deoxyribose and bases Adenine, Guanine, Cytosine and Thymine.
  • RNA contains the sugar ribose and bases Adenine, Guanine, Cytosine and Uracil.

Review: What are DNA's functions?

  • DNA stores genetic information in the form of genes, which can come in different versions.
  • DNA regulates when and where genes are expressed.
  • DNA transmits genetic information to the next generation through replication.
  • Replication must be exact, but errors may occur, leading to mutations which can have varying impacts.

Transcription versus Translation

  • Transcription converts DNA information into RNA.
  • Translation converts RNA information into proteins.

Functions of DNA and RNA

  • DNA is genetic material passed from parents to offspring and contains instructions for making proteins.
  • RNA is essential for protein synthesis and plays a role in gene expression regulation.

Central Dogma of Molecular Biology

  • Information flows from DNA to RNA to polypeptide (protein).
  • Transcription converts DNA to RNA.
  • Translation converts RNA to protein.
  • Ribosomes are the site of translation.

The Genetic Code

  • A sequence of three nucleotides (codon) codes for a specific amino acid.
  • Multiple codons can code for the same amino acid.
  • The genetic code is read in groups of three nucleotides (codons) in the correct reading frame.
  • The genetic code is universal, meaning it is the same for all life forms.

What do we need for Transcription?

  • DNA template strand, RNA polymerase, transcription factors.

RNA Polymerase

  • Separates DNA strands and synthesizes mRNA in the 5′ to 3′ direction.
  • RNA polymerase travels along the DNA, reads the nontemplate strand and builds the complementary mRNA strand.

Eukaryotic Transcription Initiation

  • Eukaryotic cells utilize TATA boxes within promoters for transcription factor recognition and subsequent RNA polymerase binding.

Elongation

  • RNA polymerase continues adding bases to the growing mRNA strand in a complementary fashion to the template strand.

Termination

  • RNA polymerase transcribes a terminator sequence in the DNA, then mRNA and polymerase detach.
  • Prokaryotic cells = mRNA is ready for use after transcription.
  • Eukaryotic cells require further processing of mRNA called pre-mRNA which occurs after transcription.

mRNA processing in eukaryotes

  • Pre-mRNA has introns (noncoding regions) and exons (coding regions).
  • Introns are removed and exons are joined together via splicing to form mRNA.
  • A 5' cap and 3' poly-A tail are added to the mRNA transcript.
  • Modification enhances mRNA stability, the export of mRNA from the nucleus, and proper binding to ribosomes.
    • 5' cap = modified guanine.
    • 3' poly-A tail = 50-520 adenine molecules.

RNA Splicing

  • Introns are removed and exons are spliced together to form the mature transcript in a process called splicing.
  • This results in a smaller, more compact, mature mRNA molecule ready to be transported from the nucleus.

Translation

  • mRNA, tRNA, and ribosomes are required for protein synthesis.
  • Ribosome = site of translation.
  • tRNA carries amino acids to the ribosomes.
  • mRNA codes for amino acids which tRNA translates to proteins.
  • mRNA carries a sequence of codons that code for amino acids for forming polypeptide chains.
  • tRNA contains an anticodon which is complementary to the mRNA codon and carries a specific amino acid.

tRNA Role

  • Specific to each amino acid.
  • Transfers amino acids to ribosomes.
  • Contains an anticodon that pairs with the complementary mRNA codon.

Ribosome Components

  • Ribosomes have an EPA site for tRNA binding, where codon-anticodon interactions occur to bring the correct amino acid into the growing polypeptide chain.

Translation Steps

  • Initiation, elongation, termination.

Initiation

  • The small ribosomal subunit binds to the mRNA's recognition sequence.
  • A Met (methionine) tRNA binds to the AUG start codon.
  • The large ribosomal subunit completes the initiation complex.

Elongation

  • An incoming tRNA carries an amino acid and binds to the next codon in the A site.
  • A peptide bond forms between the amino acids in the P and A sites.
  • The ribosome moves one codon along the mRNA, moving the tRNA to the E site, where it then disassociates from the ribosome, freeing the tRNA to carry a new amino acid.

Termination

  • When the ribosome encounters a stop codon, a release factor enters the A site.
  • The polypeptide chain is released. The mRNA and ribosomal subunits separate.

Signals that start Initiation and Termination in Transcription and Translation

  • Transcription signals:
    • Initiation: promoter
    • Termination: terminator.
  • Translation signals:
    • Initiation: start codon
    • Termination: stop codon.

Compare gene expression in prokaryotes vs. eukaryotes

  • Prokaryotes: transcription and translation occur in the cytoplasm. Genes lack introns, and no mRNA modification occurs.
  • Eukaryotes: transcription occurs in the nucleus and translation in the cytoplasm. Genes contain introns, and mRNA must be processed before leaving the nucleus.

Possible effects of mutations on gene expression

  • Mutations are changes in DNA sequence.
  • Mutations can cause silent mutations (no change in amino acid sequence), missense mutations (change in amino acid sequence), or nonsense mutations (early stop codon).
  • Frame shift mutations (insertion or deletion of a nucleotide) cause alterations in subsequent amino acids.

Missense Mutation causes Sickle-Cell Anemia

  • A nucleotide substitution changes the amino acid, from glutamic acid to valine, causing abnormal polypeptide structure, and thus abnormal hemoglobin function in red blood cells.

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