Genetics: DNA and Cell Division
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What is the primary function of plasmids in bacteria and archaea?

  • They carry the entire genetic information of the organism.
  • They are essential for all cell functions.
  • They can confer advantages under specific conditions. (correct)
  • They are responsible for cellular respiration.

    • Which statement is true about R plasmids?

  • They are essential for conjugation.
  • They are involved in nitrogen fixation.
  • They range in size from 100 bp to 10 kbp.
  • They confer resistance to antibiotics and other inhibitors. (correct)

    • What can be a consequence of carrying multiple antibiotic resistance genes on a single R plasmid?

  • Enhanced ability to survive under selective pressures. (correct)
  • Decrease in plasmid replication.
  • Reduction in metabolic efficiency.
  • Increased sensitivity to antibiotics.

    • What is one essential role of plasmids in the process of conjugation?

    <p>To facilitate the transfer of genetic material between cells.</p> Signup and view all the answers

    What is the size range of plasmids?

    <p>1 kbp to more than 1 mbp</p> Signup and view all the answers

    How do transposons relate to antibiotic resistance?

    <p>They can carry antibiotic-resistance genes.</p> Signup and view all the answers

    What is a characteristic of the genetic information encoded on plasmids?

    <p>It varies in importance depending on environmental conditions.</p> Signup and view all the answers

    Which of the following is NOT a function associated with plasmids?

    <p>Regulating metabolic processes for cellular respiration.</p> Signup and view all the answers

    What is the primary function of DNA Polymerase III during DNA replication?

    <p>Synthesizing the majority of the DNA sequence</p> Signup and view all the answers

    Which enzyme is responsible for unwinding the DNA double helix?

    <p>DNA Helicase</p> Signup and view all the answers

    In which direction does DNA replication proceed during synthesis?

    <p>5’ to 3’</p> Signup and view all the answers

    What is the role of the single-stranded binding protein (Ssbp) during DNA replication?

    <p>To stabilize the unwound single-stranded DNA</p> Signup and view all the answers

    Which part of the DNA is created by primase during DNA synthesis?

    <p>RNA primer</p> Signup and view all the answers

    What is the function of DNA Ligase in the DNA replication process?

    <p>Sealing gaps in DNA after primer removal</p> Signup and view all the answers

    How does DNA synthesis differ between the leading and lagging strands?

    <p>Leading strand is synthesized more quickly than the lagging strand</p> Signup and view all the answers

    What initiates DNA replication at the origin of replication in prokaryotes?

    <p>Helicase binding</p> Signup and view all the answers

    What ensures the accurate replication of DNA to maintain fidelity?

    <p>Enzymatic proofreading by polymerases</p> Signup and view all the answers

    What happens to supercoiled DNA during replication?

    <p>It gets relaxed</p> Signup and view all the answers

    What role does DNA Polymerase I serve in the replication process?

    <p>Removes RNA primers and replaces them with DNA</p> Signup and view all the answers

    What do hydrogen bonds connect in the DNA structure?

    <p>Nucleotides across complementary strands</p> Signup and view all the answers

    What characterizes the leading strand during DNA synthesis?

    <p>It is synthesized continuously</p> Signup and view all the answers

    Which statement about the replication fork is true?

    <p>It is a zone of unwound DNA where replication occurs.</p> Signup and view all the answers

    What is the primary method that bacteria use to package their DNA?

    <p>Supercoiling</p> Signup and view all the answers

    Which type of supercoiling is typically harder to unwind during DNA replication?

    <p>Positive supercoiling</p> Signup and view all the answers

    What are sister chromatids?

    <p>Identical copies of a chromosome attached at the centromere</p> Signup and view all the answers

    How is the structure of eukaryotic chromosomes primarily organized?

    <p>Around histone proteins</p> Signup and view all the answers

    Which of the following is true about trisomy?

    <p>Usually results in miscarriage</p> Signup and view all the answers

    What type of chromosomes are autosomes?

    <p>Chromosomes not involved in determining sex</p> Signup and view all the answers

    What is the characteristic of a diploid cell?

    <p>Contains two copies of each chromosome</p> Signup and view all the answers

    Which structure in a chromosome is responsible for holding sister chromatids together?

    <p>Centromere</p> Signup and view all the answers

    What describes the genome size in relation to an organism's complexity?

    <p>Larger genomes usually reflect greater complexity</p> Signup and view all the answers

    What distinguishes sex chromosomes from autosomes?

    <p>Sex chromosomes determine the genetic sex of an individual</p> Signup and view all the answers

    What indicates positive supercoiling in DNA?

    <p>Higher stress and tighter twisting of the helix</p> Signup and view all the answers

    In eukaryotic cells, how is DNA organized when preparing for cell division?

    <p>The DNA is duplicated and then organized into sister chromatids</p> Signup and view all the answers

    Which type of chromosomes are typically referred to as the 'last pair' in humans?

    <p>Sex chromosomes</p> Signup and view all the answers

    What is the total time in minutes for DNA polymerase to complete replication of a 4.6mbp DNA strand?

    <p>76 minutes</p> Signup and view all the answers

    Which enzyme is responsible for connecting DNA fragments on the lagging strand during replication?

    <p>DNA Ligase</p> Signup and view all the answers

    During DNA replication in prokaryotes, what type of replication occurs?

    <p>Bidirectional replication</p> Signup and view all the answers

    What are the precursors needed to synthesize RNA?

    <p>NTPs</p> Signup and view all the answers

    What is the first step of the transcription process in bacteria?

    <p>Initiation</p> Signup and view all the answers

    What triggers the termination of RNA transcription?

    <p>Reaching a specific sequence</p> Signup and view all the answers

    How many different types of rRNA are produced in bacteria?

    <p>3 types</p> Signup and view all the answers

    What initiates the binding of RNA polymerase to the DNA during transcription?

    <p>Pribnow box</p> Signup and view all the answers

    In what direction does RNA synthesis occur during transcription?

    <p>5' to 3'</p> Signup and view all the answers

    What is the role of the sigma factor during transcription?

    <p>To identify the promoter region</p> Signup and view all the answers

    Which of the following statements is true about the transcription process in bacteria?

    <p>Terminator sequences are essential.</p> Signup and view all the answers

    Before translation, what must happen to the primary transcript?

    <p>It must be spliced.</p> Signup and view all the answers

    In archaea, how many subunits does RNA polymerase have?

    <p>13 subunits</p> Signup and view all the answers

    What happens if both strands of the template are used in transcription?

    <p>The amino acid sequence will differ.</p> Signup and view all the answers

    What is the outcome when a nucleus from Organism A’s egg cell is replaced by a nucleus from Organism B?

    <p>The egg cell produces a clone of Organism B.</p> Signup and view all the answers

    What is the primary benefit of using plasmids in bacteria?

    <p>They can carry antibiotic resistance genes.</p> Signup and view all the answers

    Which of the following describes the role of bacteriocins encoded by plasmids?

    <p>They combat closely related bacterial species.</p> Signup and view all the answers

    What are the two main informational macromolecules involved in encoding the phenotype of an organism?

    <p>Proteins and nucleic acids</p> Signup and view all the answers

    What process is responsible for the conversion of DNA to RNA?

    <p>Transcription</p> Signup and view all the answers

    Which enzyme is responsible for translating RNA into proteins?

    <p>Ribosomes</p> Signup and view all the answers

    In partial cloning, which type of cells are primarily utilized to synthesize organs?

    <p>Somatic stem cells</p> Signup and view all the answers

    How do plasmids contribute to the spread of antibiotic resistance among bacteria?

    <p>Through horizontal gene transfer.</p> Signup and view all the answers

    What significant role do proteins play in an organism?

    <p>They catalyze biochemical processes.</p> Signup and view all the answers

    Which of the following is NOT a step in the flow of genetic information?

    <p>Diversity</p> Signup and view all the answers

    Which statement best describes the Central Dogma?

    <p>It describes the flow of genetic information to protein synthesis.</p> Signup and view all the answers

    Which of the following is a misconception about plasmids?

    <p>They are essential for aerobic respiration.</p> Signup and view all the answers

    What limits the effectiveness of penicillin in certain bacterial strains?

    <p>Alteration of penicillin-binding proteins.</p> Signup and view all the answers

    Partial cloning is primarily accepted for which purpose?

    <p>Synthesize organs and tissues.</p> Signup and view all the answers

    Study Notes

    DNA Structure

    • E. coli has a genome of ~5 million base pairs
    • Histones are found in eukaryotes and archaea
    • Bacteria do not have histones
    • DNA consists of two strands twisted into a double helix
    • DNA molecules and proteins are organized into chromosomes
    • DNA can coil in two directions: positive and negative
    • Positive supercoiling is more "stressful" and happens in most archaea
    • Negative supercoiling is more relaxed and allows for easier unwinding of the molecule, this occurs in the majority of prokaryotes and bacteria

    Cell Division and Chromosomes

    • During cell division, the entire chromosome is duplicated, forming sister chromatids
    • Daughter cells receive identical copies of the chromosomes
    • Each eukaryotic cell has a characteristic number of chromosomes
    • Diploid cells have two pairs of each type of chromosome
    • Humans have 46 chromosomes
    • Trisomy is a condition where an individual has an extra chromosome, most cases are fatal, trisomy 21 is Down syndrome
    • Chromosomes are organized into autosomes (non-sex chromosomes) and sex chromosomes
    • Sex chromosomes differ between males and females, the last pair

    Karyotyping

    • Karyotyping reveals the characteristics of an individual's chromosomes
    • It is a visual representation of the chromosomes
    • Genome size shows the complexity of an organism, larger genomes are more complex

    Genetic Elements

    • Plasmids are found in many bacteria and archaea
    • Plasmids contain genetic information that is not essential for cell function, but it might give an advantage to the cell
    • Plasmids can confer a selective growth advantage
    • Plasmids range in size from 1kbp to more than 1mbp
    • R plasmids are resistance plasmids that confer antibiotic resistance
    • R plasmids contain many antibiotic resistance genes

    Cloning

    • Dolly the sheep was the first successfully cloned mammal
    • Dolly was cloned by removing the nucleus from an egg cell and implanting the nucleus from a donor cell
    • In humans, partial cloning is more accepted, it is used to synthesize organs and uses somatic stem cells

    Antibiotic Resistance

    • Penicillin and other beta-lactam antibiotics inhibit penicillin-binding proteins
    • Resistance to penicillin occurs due to modified cross-linking enzymes
    • Antibiotic resistance can mis-spread via plasmids, which can transfer from one bacteria to another via horizontal gene transfer

    The Central Dogma

    • The flow of genetic information includes replication, transcription, and translation
    • This flow is known as the central dogma
    • The central dogma describes how genetic information is turned into proteins

    Transcription

    • Transcription is the process of DNA to RNA
    • RNA polymerase is the main enzyme involved

    Translation

    • Translation is the process of RNA to protein
    • Ribosomes are the main enzyme involved
    • Viruses are also involved in replication, transcription, and translation, but they can violate the central dogma

    DNA Replication

    • There are 5 DNA polymerases involved in DNA replication
    • DNA Polymerase I: plays a lesser role in DNA replication
    • DNA Polymerase II: repairs DNA damage
    • DNA Polymerase III: primary enzyme for replication of chromosomal DNA
    • DNA Polymerase IV: repairs DNA damage
    • DNA Polymerase V: repairs DNA damage
    • Replication occurs ONLY from the 5' end to the 3' end of the DNA strand
    • DNA replication requires extraordinary fidelity to prevent gene mutations
    • Gene mutations can cause irregularities in an organism
    • Gene mutations can also render genes useless or different
    • The origin of replication in prokaryotes is a specific DNA sequence where replication begins
    • Replisomes move to the origin of replication and initiate replication
    • Replisomes contain the enzymes necessary to replicate DNA
    • Helicase unwinds the DNA double helix to create the replication fork
    • Single-strand binding proteins (Ssbp) help to stabilize the unwound DNA strand, preventing it from rewinding
    • The replication fork is the point on the DNA where replication occurs
    • DNA polymerase III adds nucleotides at a rate of 1000 per second
    • Primase creates a short RNA primer to initiate DNA synthesis.
    • DNA polymerase III synthesizes the majority of the new DNA sequence
    • DNA polymerase I removes the RNA primer and replaces it with DNA
    • DNA ligase seals the gaps left by the removal of the RNA primer
    • DNA replication is antiparallel, with one strand running from 5’ to 3’ and the other from 3’ to 5’
    • The leading strand is synthesized continuously in a 5’ to 3’ direction
    • The lagging strand is synthesized discontinuously in a 5’ to 3’ direction
    • Synthesis of the lagging strand requires the creation of Okazaki fragments
    • Okazaki fragments are short segments of DNA that are ligated together to form the complete lagging strand
    • DNA is supercoiled to maximize space inside the cell and allow for compacting into a small space
    • Supercoiling is relaxed during replication to allow for proper unwinding and replication
    • Replication is done on BOTH STRANDS of DNA

    Applications

    • Understanding DNA replication helps to develop new treatments for diseases caused by gene mutations
    • Replication errors are a major cause of cancer initiation and progression
    • DNA polymerase inhibitors are commonly used in chemotherapy to prevent cancer cell replication.

    DNA Replication

    • DNA polymerase adds 1000 nucleotides per second.
    • It takes 76 minutes to complete replication of a 4.6mbp coli genome.
    • Leading and lagging strands are replicated simultaneously during DNA replication.
    • Replication is bidirectional in prokaryotes due to their circular chromosome structure.
    • The replisome is a complex of proteins involved in replication, including enzymes that move as one.
    • DNA ligase seals the nicks in DNA fragments on the lagging strand.

    Transcription

    • Transcription is the process of synthesizing RNA from a DNA template strand.
    • RNA polymerase is the primary enzyme responsible for transcribing DNA to mRNA.
    • The sigma factor identifies the promoter region and determines the direction of transcription.
    • The sigma factor attaches RNA polymerase to the promoter region and is then released allowing transcription to start.
    • Transcription occurs from 5' to 3', similar to DNA replication, with the template strand oriented in the 3' to 5' direction.
    • RNA polymerase does not require a primer to initiate transcription.
    • Transcription uses ribonucleotides (NTPs) instead of deoxyribonucleotides (dNTPs).
    • RNA polymerase can transcribe both strands of DNA, resulting in different amino acid sequences, hence the need for a single strand template.

    Transcription Initiation

    • The sigma factor recognizes the promoter region on DNA, including the Pribnow box (-10 region) and TTGACA (-35 region).
    • The Pribnow box (-10 region) is located 10 bases before the start of transcription and is also known as a TATA box.
    • The TTGACA (-35 region) is located 35 bases before the start of transcription.
    • Different sigma factors recognize different promoter sequences.

    Transcription Elongation

    • RNA polymerase makes copies of DNA using RNA.
    • The RNA polymerase employs A-U and G-C base pairing, as opposed to DNA's A-T and G-C pairing.

    Transcription Termination

    • Transcription terminates when RNA polymerase reaches a specific sequence that signals the end of the process.
    • The RNA transcript is released, and the process allows for translation.

    Transcription in Bacteria

    • Bacteria transcribe genes into operons (DNA segments transcribed into one RNA molecule bounded by initiation and termination sites).
    • Operons ensure efficient expression of genes needed for a specific function.
    • Most genes encode proteins, but some genes produce non-protein-coding RNAs like rRNA and tRNA, which are involved in protein synthesis.
    • The process of transcription involves the production of a primary transcript containing intervening sequences that need to be removed before translation.
    • These intervening sequences do not code for proteins, are known as jumping genes, and are removed from the sequence.
    • The final RNA product corresponds to the RNAs involved in the translation process.

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    Description

    This quiz covers key concepts in genetics related to DNA structure and the processes of cell division. Understand the differences in chromosome organization between prokaryotes and eukaryotes, as well as the implications of genetic conditions like trisomy. Test your knowledge of these fundamental biological principles.

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