Central Dogma of Molecular Genetics

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Questions and Answers

What is the primary role of helicase in DNA replication?

  • To remove supercoils ahead of the replication fork
  • To unwind the DNA helix (correct)
  • To synthesize RNA from the DNA template
  • To attach nucleotides to the growing DNA strand

Which of the following correctly describes the difference between prokaryotic and eukaryotic DNA replication?

  • Prokaryotes tend to have one replication bubble, whereas eukaryotes have multiple (correct)
  • Eukaryotes use fewer polymerases than prokaryotes
  • Eukaryotes have smaller, circular genomes compared to prokaryotes
  • Prokaryotes have multiple origins of replication while eukaryotes have one

During which process is RNA synthesized from a DNA template?

  • Recombination
  • Translation
  • Replication
  • Transcription (correct)

What results from the hydrolysis reaction involving nucleoside triphosphates during DNA synthesis?

<p>Release of energy for the formation of phosphodiester bonds (D)</p> Signup and view all the answers

What is the main function of topoisomerase during DNA replication?

<p>To relieve the strain of supercoiling ahead of the replication fork (C)</p> Signup and view all the answers

What happens when telomeres become too short?

<p>Cells enter a state of senescence. (A)</p> Signup and view all the answers

How does telomerase relate to cancer cells?

<p>It allows cancer cells to keep dividing indefinitely. (A)</p> Signup and view all the answers

What lifestyle factors can accelerate telomere degradation?

<p>Smoking and UV exposure. (C)</p> Signup and view all the answers

What is the 'Hayflick limit' in relation to cell division?

<p>The maximum number of times a cell can divide before dying. (C)</p> Signup and view all the answers

What structure is essential for healthy telomeres?

<p>A looped end. (D)</p> Signup and view all the answers

What is the primary function of RNA primase during DNA replication?

<p>Places RNA primers on template strands (B)</p> Signup and view all the answers

Which enzyme is responsible for filling in gaps in the lagging strand during DNA replication?

<p>DNA polymerase I (A)</p> Signup and view all the answers

What differentiates epigenetic changes from genetic changes?

<p>Epigenetic changes are reversible and do not alter the DNA sequence (C)</p> Signup and view all the answers

What is an epigenome?

<p>All modifications regulating the activity of genes (D)</p> Signup and view all the answers

What role does methylation play in gene expression?

<p>It inhibits transcription by tightly packing DNA (C)</p> Signup and view all the answers

Which enzyme is significant for forming phosphodiester bonds during DNA replication?

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

Which of the following accurately describes telomeres?

<p>They prevent coding regions from being lost during replication (B)</p> Signup and view all the answers

What type of enzyme would add biochemical groups such as methyl or acetyl?

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

Flashcards

DNA Replication

Creating a duplicate of DNA for cell reproduction.

Transcription

Using DNA to create RNA for making proteins.

Translation

Using RNA to make proteins.

Prokaryotic DNA replication

DNA replication that mostly occurs in a single origin and bubble in circular genomes, simpler.

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Eukaryotic DNA replication

DNA replication that happens in multiple origins and bubbles in linear genomes.

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DNA polymerase III

The main enzyme responsible for building new DNA strands during replication, adding nucleotides one by one.

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DNA polymerase I

Plays a role in filling gaps between Okazaki fragments on the lagging strand and proofreading the final DNA strand.

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DNA Ligase

Connects the Okazaki fragments on the lagging strand, creating a continuous strand.

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RNA Primase

Places RNA primers on the template strand to initiate DNA synthesis.

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Helicase

Unwinds the DNA double helix, separating the two strands to allow replication.

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Topoisomerase

Prevents supercoiling of DNA during replication by relieving tension.

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Epigenome

The set of chemical modifications that regulate gene activity without altering the DNA sequence.

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What are the primary differences between genetic and epigenetic changes?

Genetic changes alter the DNA sequence, while epigenetic changes modify gene expression without changing the DNA sequence. Genetic changes are permanent, while epigenetic changes can be reversible.

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Telomere

A protective cap at the end of a chromosome, made of repetitive DNA sequences.

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Telomere Shortening

The gradual loss of telomere sequence with each cell division, leading to a shorter telomere.

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Cell Senescence

The state of a cell that can no longer divide due to shortened telomeres, often leading to cell death.

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Hayflick Limit

The number of times a normal human cell can divide before reaching senescence, typically around 50 divisions.

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Telomerase

An enzyme that builds telomeres, helping maintain their length and prevent shortening, found in germ cells and cancer cells.

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Study Notes

Central Dogma of Molecular Genetics

  • DNA replication is the duplication of DNA for cell reproduction
  • Transcription is the process of copying DNA to RNA
  • Translation is the process of using RNA to make proteins

DNA Structure and Replication

  • DNA is a polymer, a polynucleotide
  • DNA is composed of 6 billion letters (A,T,C,G) in chromosomes
  • A=T & C=G
  • Replication of DNA to RNA used for mitosis

Nucleic Acid (DNA/RNA)

  • DNA and RNA are nucleic acids
  • DNA is a polymer of deoxyribonucleotides
  • RNA is a polymer of ribonucleotides
  • DNA is a polynucleotide
  • DNA has a structure of a double helix
  • RNA is a single-stranded molecule

Protein

  • Proteins are complex molecules composed of amino acids
  • Amino acids are the building blocks of protein
  • Proteins can have complex structures : primary, secondary, tertiary, and quaternary structure
  • Codons are sequences of 3 nucleotides that specify amino acids

Replication vs Transcription-

  • Replication uses DNA polymerase to create a copy of DNA
  • Transcription uses RNA polymerase to create RNA from a DNA template
  • Translation uses ribosomes to translate mRNA into proteins

Energy in Replication

  • Energy in nucleic acid replication comes from nucleoside triphosphates
  • Hydrolysis of phosphates provides energy for phosphodiester bond formation

DNA Replication (more detail)

  • Chromosomes contain DNA, the genetic material
  • DNA polymerase is essential for DNA replication
  • Replication occurs at the replication fork, creating a leading and lagging strand
  • Okazaki fragments are short DNA sequences on the lagging strand
  • Helicase unwinds the DNA double helix
  • Topoisomerase smooths out the DNA strand prior to separation
  • RNA primer is essential for initial DNA synthesis

Enzymes in DNA Replication

  • Helicase unwinds the double helix
  • Topoisomerase removes strain ahead of the replication fork
  • RNA primase synthesizes RNA primers
  • DNA polymerase III adds nucleotides to the growing DNA strand
  • DNA polymerase I removes RNA primers and replaces them with DNA
  • DNA ligase joins Okazaki fragments

Epigenetics

  • Epigenome is all the modifications to DNA that affect gene expression
  • Modifications don't change DNA sequence, only how it's expressed
  • Examples: methylation, histone modification
  • Epigenetics affects cell differentiation

Epigenetic Mechanisms

  • Methylation adds chemical group to DNA, either "switching" genes "on" or "off"
  • Histone modification changes how DNA wraps around histone proteins, affecting gene expression
  • Non-coding RNAs control gene expression by affecting coding RNA and histones

Telomeres

  • Telomeres are repetitive sequences at the ends of chromosomes
  • Telomeres protect coding regions during replication
  • Telomeres shorten with each cell division
  • Telomere shortening can lead to cell aging and death
  • Cancer cells can produce telomerase to stop telomere shortening, contributing to uncontrolled cell division

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