Introduction to Molecular Biology (2)

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Questions and Answers

What is the primary function of messenger RNA (mRNA)?

  • To transport amino acids during protein synthesis
  • To regulate gene expression through RNA interference
  • To serve as a structural component of ribosomes
  • To carry information from DNA to ribosomes for protein synthesis (correct)

Which type of RNA makes up the largest portion of total RNA in a cell?

  • Messenger RNA (mRNA)
  • Transfer RNA (tRNA)
  • Ribosomal RNA (rRNA) (correct)
  • Non-coding RNA (ncRNA)

What characterizes transfer RNA (tRNA) among the different types of RNA?

  • It has the longest nucleotide sequence.
  • It is primarily involved in the transcription process.
  • It is essential for linking amino acids during protein synthesis. (correct)
  • It constitutes the majority of RNA in the cell.

How do ribosomal RNA (rRNA) molecules function within ribosomes?

<p>They form structural elements and catalyze peptide bond formation. (A)</p> Signup and view all the answers

Which statement about non-coding RNAs (ncRNA) is true?

<p>They can have various roles including gene regulation and RNA processing. (C)</p> Signup and view all the answers

What is a major structural difference between RNA and DNA?

<p>RNA is single-stranded while DNA is typically double-stranded. (C)</p> Signup and view all the answers

Which of the following best describes a function of non-coding RNAs?

<p>They are involved in regulating gene expression. (C)</p> Signup and view all the answers

What type of chromatin is primarily associated with gene silencing?

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

How are nucleosomes organized within chromatin?

<p>DNA wraps around histone proteins to form nucleosomes. (D)</p> Signup and view all the answers

Which statement accurately reflects gene expression regulation?

<p>Environmental factors can influence gene expression. (A)</p> Signup and view all the answers

What is the estimated percentage of the human genome that consists of coding DNA?

<p>2% (C)</p> Signup and view all the answers

What defines genetic polymorphism in the context of DNA?

<p>The occurrence of two or more variant forms of a specific DNA sequence. (C)</p> Signup and view all the answers

What role do centromeres play in cellular division?

<p>They direct the assembly of microtubules for chromosome segregation. (B)</p> Signup and view all the answers

What is the primary function of the linker histone H1 in relation to nucleosomes?

<p>It stabilizes the 30-nm fiber and higher-order chromatin structures. (B)</p> Signup and view all the answers

Which characteristic distinguishes euchromatin from heterochromatin?

<p>Euchromatin is enriched in genes and often active in transcription. (A)</p> Signup and view all the answers

What can be concluded about the role of different H1 histone subtypes in gene expression?

<p>Some H1 subtypes can attenuate or accentuate position effects in gene expression. (D)</p> Signup and view all the answers

Which statement accurately describes the composition of heterochromatin?

<p>It denotes regions that are more compact and darkly stained. (D)</p> Signup and view all the answers

What is the role of the arrangement of linker histones on chromatin fiber?

<p>It influences higher-order chromatin structure and gene expression levels. (D)</p> Signup and view all the answers

Which of the following describes a significant feature of chromosomes?

<p>They represent the highest level of DNA organization and are formed from condensed chromatin fibers. (A)</p> Signup and view all the answers

Which of the following statements reflects a similarity between euchromatin and heterochromatin?

<p>Both consist of polynucleotide chains of DNA. (C)</p> Signup and view all the answers

In the context of gene regulation, what is the importance of histone H1 subtypes?

<p>They play differential roles in the regulation of gene expression. (D)</p> Signup and view all the answers

Flashcards

Linker histone H1

A histone protein that binds to DNA entry/exit sites of nucleosomes, stabilizing them and higher-order chromatin structures.

Nucleosome

A structural unit of DNA wrapped around histone proteins.

Chromatin

DNA and protein complex that condenses to form chromosomes.

Euchromatin

Less condensed form of chromatin, often containing active genes.

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Heterochromatin

More condensed form of chromatin, often containing inactive genes.

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Chromosome

The tightly packed structure of DNA and proteins.

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H1 subtypes

Different variations of linker histone H1.

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Position effect

Changes in gene expression due to its location on a chromosome.

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What is mRNA?

Messenger RNA (mRNA) carries genetic information from DNA in the nucleus to ribosomes in the cytoplasm, where proteins are synthesized.

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What is tRNA?

Transfer RNA (tRNA) is a small RNA molecule that carries specific amino acids to ribosomes during protein synthesis.

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What is rRNA?

Ribosomal RNA (rRNA) is a major component of ribosomes, the cellular machinery that synthesizes proteins.

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Types of RNA

The three main types of RNA are mRNA, tRNA, and rRNA. They play crucial roles in protein synthesis and other cellular processes.

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Non-coding RNA

Non-coding RNA (ncRNA) does not produce proteins but performs various functions in gene regulation, RNA processing, and other cellular processes.

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Centromere Function

Centromeres are essential for equal chromosome segregation during cell division. They act as attachment points for microtubules, pulling sister chromatids apart.

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Centromere Location

Centromeres are typically found in gene-poor regions of chromosomes, though they may contain genes and are often transcribed at low levels.

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Human Genome: What is it?

It's the complete set of genetic instructions for humans, encoded in DNA. It includes both genes that code for proteins and non-coding DNA.

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Nuclear Genome Size

The human nuclear genome consists of about 3.2 billion nucleotides of DNA, organized into 46 linear molecules called chromosomes.

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Gene Count in Humans

The Human Genome Project estimated that humans have between 20,000 and 25,000 genes.

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Junk DNA

Regions of DNA that do not code for proteins, often referred to as 'junk DNA.'

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Human Genome Project

A large-scale international project launched in 1990 to determine the sequence of the human genome and identify its genes.

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Genetic Polymorphism

The presence of two or more variant forms of a specific DNA sequence among individuals or populations.

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Study Notes

Introduction to Molecular Biology (2)

  • Course module: Cell biology and molecular biology
  • Academic year: 2022-2023
  • Instructor: Pr. Raouf Alami
  • Course material covers: RNA and DNA, eukaryotic chromosomes organization, human genome, genetic polymorphisms, and relevant methods/tests

Course Contents

  • Ribonucleic acid (RNA):

    • RNA and DNA structure comparison
    • RNA size variation
    • RNA backbone components (phosphate and ribose)
    • RNA structures (primary, secondary, and tertiary)
    • RNA functions (coding, decoding, regulating, expressing genes, carrying out biochemical reactions, and serving as enzymes)
    • RNA integrity assessment methods (denaturing agarose gel with ethidium bromide)
    • Types of RNA (mRNA, rRNA, tRNA, non-coding RNAs, microRNA and ncRNA)
    • Relative abundance of each RNA type in a human cell (rRNA ~ 80%, tRNA~15%, mRNA ~ 5%)

  • Organization of eukaryotic chromosomes:

    • Chromatin structure (nucleosome, 30nm chromatin fiber, and higher-level structures)
    • Nucleosome makeup (histone octamer and DNA wrapping)
    • Telomeres (repeated DNA sequences at chromosome ends)
    • Telomere sequence (TTAGGG)
    • Telomere function (protecting chromosome ends)
    • Eukaryotic nucleus size ranges from 5-10 µm
    • Euchromatin vs heterochromatin (structural and functional differences)
    • Euchromatin (less compact, rich in genes, actively transcribed)
    • Heterochromatin (more compact, less active transcription)

  • Human Genome:

    • Genome definition (complete set of nucleic acid sequences)
    • Chromosome number (23 pairs in humans)
    • DNA molecule regions (coding and non-coding)
    • Human Genome Project (HGP) overview (goal was to determine the sequence of 3 billion base pairs, including identifying genes)
    • Estimated gene number (20,000 – 25,000)
    • Gene redundancy (two copies of each gene, one from each parent)
    • Non-coding DNA function (genetic regulation and other roles)

  • Genetic Polymorphism:

    • Definition (variation in DNA sequences among individuals/populations)
    • Types (single nucleotide polymorphisms (SNPs), short tandem repeats (STRs))
    • Application in forensic investigations (comparing DNA profiles to identify suspects)
    • Paternity testing approach (comparing DNA profiles for biological father determination)

  • Quiz Questions:

    • Number of chromatins per chromosome (1)
    • Number of DNA molecules per chromosome (1)
    • Three major differences between RNA and DNA
    • RNA backbone components (phosphate and ribose)
    • Method for assessing RNA integrity (run an aliquot of RNA on a denaturing agarose gel)
    • mRNA first description (1961 by Jacob and Monod)
    • tRNA function (essential component of translation)
    • Non-coding RNA examples (tRNA, rRNA, hammerhead ribozyme)
    • Chromatin first description (1880 by Fleming)
    • Base pairs per nucleosome (~ 147)
    • Proteins per nucleosome (8)
    • DNA compaction ratio for a chromosome (10,000-20,000 fold)
    • H1 histone function (linker histones for DNA entry/exit and stabilize the 30nm chromatin fiber)
    • Similarities between euchromatin and heterochromatin (both made up of nucleotides, visible more distinctly in interphase & interact with histones)
    • Differences between euchromatin and heterochromatin
    • Heterochromatin presence in prokaryotes (yes)
    • Role of chromosomes (protecting DNA from tangling & damage)
    • Definition of karyotype (lab produced image of chromosomes)
    • Human telomere sequence (TTAGGG)
    • Telomere repeated times (~ 3,000 to 15,000)
    • Role of centromeres (linking pair of sister chromatids during cell division)

  • Number of DNA molecules in a human cell. (46)

  • Definition of "junk DNA" (regions of DNA that don't code for proteins in genetics)

  • Date of the human genome gold standard release (2003)

  • SNP meaning (single nucleotide polymorphism)

  • Tandem repeat application (genetic markers and DNA fingerprinting)

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