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Questions and Answers
What distinguishes the semi-conservative nature of DNA replication?
What distinguishes the semi-conservative nature of DNA replication?
Which protein is responsible for unwinding the DNA strands during replication?
Which protein is responsible for unwinding the DNA strands during replication?
What type of DNA sequences are referred to as replication origins?
What type of DNA sequences are referred to as replication origins?
During the initiation of DNA replication in eukaryotes, which complex includes the inactive helicase?
During the initiation of DNA replication in eukaryotes, which complex includes the inactive helicase?
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What is formed when a sugar is joined to a nitrogenous base?
What is formed when a sugar is joined to a nitrogenous base?
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What is the function of single-strand binding proteins during DNA replication?
What is the function of single-strand binding proteins during DNA replication?
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Which statement about DNA polymerase is true?
Which statement about DNA polymerase is true?
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At which carbon of ribose or deoxyribose is a phosphate group attached to form a nucleotide?
At which carbon of ribose or deoxyribose is a phosphate group attached to form a nucleotide?
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Which experiment demonstrated the semi-conservative nature of DNA replication?
Which experiment demonstrated the semi-conservative nature of DNA replication?
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How are mononucleotides linked together in a polynucleotide chain?
How are mononucleotides linked together in a polynucleotide chain?
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Which of the following names a common nucleoside?
Which of the following names a common nucleoside?
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What is formed at the sites where double-stranded DNA becomes single-stranded during replication?
What is formed at the sites where double-stranded DNA becomes single-stranded during replication?
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In what sequence is a polynucleotide typically written?
In what sequence is a polynucleotide typically written?
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Why are phosphate groups negatively charged at cellular pH?
Why are phosphate groups negatively charged at cellular pH?
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What term is used for a nucleotide with two phosphate groups?
What term is used for a nucleotide with two phosphate groups?
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What structure do DNA strands usually form in cells?
What structure do DNA strands usually form in cells?
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What is one main function of RNA in living systems?
What is one main function of RNA in living systems?
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Which of the following correctly distinguishes DNA from RNA?
Which of the following correctly distinguishes DNA from RNA?
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Which of the following is not a purine?
Which of the following is not a purine?
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What is the role of nucleosomes in eukaryotic cells?
What is the role of nucleosomes in eukaryotic cells?
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Which statement about the nitrogenous bases in nucleic acids is true?
Which statement about the nitrogenous bases in nucleic acids is true?
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Which structure forms the backbone of nucleic acid polymers?
Which structure forms the backbone of nucleic acid polymers?
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What effect do changes in sequence or conditions have on the melting temperature of a DNA double helix?
What effect do changes in sequence or conditions have on the melting temperature of a DNA double helix?
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Which of the following correctly pairs each type of RNA with its main function?
Which of the following correctly pairs each type of RNA with its main function?
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What is the primary purpose of cDNA in molecular biology?
What is the primary purpose of cDNA in molecular biology?
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What is the function of reverse transcriptase in the synthesis of cDNA?
What is the function of reverse transcriptase in the synthesis of cDNA?
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What does the presence of introns in genomic DNA imply for cDNA preparation?
What does the presence of introns in genomic DNA imply for cDNA preparation?
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What is the role of DNA polymerase in PCR?
What is the role of DNA polymerase in PCR?
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Which step in PCR requires a decrease in temperature?
Which step in PCR requires a decrease in temperature?
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Why was the discovery of thermostable polymerases significant for PCR?
Why was the discovery of thermostable polymerases significant for PCR?
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What is the approximate temperature to denature DNA during PCR?
What is the approximate temperature to denature DNA during PCR?
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How many times are the PCR steps usually repeated?
How many times are the PCR steps usually repeated?
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What are the consensus sequences for the -10 and -35 elements in bacterial promoters?
What are the consensus sequences for the -10 and -35 elements in bacterial promoters?
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Which factor does NOT contribute to the differential regulation of transcription in bacterial promoters?
Which factor does NOT contribute to the differential regulation of transcription in bacterial promoters?
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What occurs when lactose binds to the Lac repressor in E. coli?
What occurs when lactose binds to the Lac repressor in E. coli?
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Which protein acts as a repressor for the Lac operon?
Which protein acts as a repressor for the Lac operon?
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How do activator proteins, like CAP, enhance transcription?
How do activator proteins, like CAP, enhance transcription?
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In the context of the Lac operon, what is the primary carbon source preferred by E. coli?
In the context of the Lac operon, what is the primary carbon source preferred by E. coli?
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Why do some bacterial promoters have different activity levels?
Why do some bacterial promoters have different activity levels?
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What represents positive control in the regulation of the Lac operon?
What represents positive control in the regulation of the Lac operon?
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What is the main reason that DNA synthesis on the lagging strand occurs discontinuously?
What is the main reason that DNA synthesis on the lagging strand occurs discontinuously?
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How long are Okazaki fragments in E. coli compared to humans?
How long are Okazaki fragments in E. coli compared to humans?
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What does the trombone model illustrate about DNA replication?
What does the trombone model illustrate about DNA replication?
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Why does DNA synthesis on the lagging strand require more primers than on the leading strand?
Why does DNA synthesis on the lagging strand require more primers than on the leading strand?
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What role does proofreading play in DNA synthesis?
What role does proofreading play in DNA synthesis?
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Recent studies suggest that during lagging strand synthesis, what might happen more frequently than previously thought?
Recent studies suggest that during lagging strand synthesis, what might happen more frequently than previously thought?
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What advantage might the presence of a third DNA polymerase provide in the replisome?
What advantage might the presence of a third DNA polymerase provide in the replisome?
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What is a common error that DNA polymerases can make during replication?
What is a common error that DNA polymerases can make during replication?
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Study Notes
Nucleic Acid Structure
- Nucleic acids are polymers of nucleotides
- DNA and RNA are the two major types
- DNA stores genetic information
- RNA has various functions, including protein synthesis and gene regulation
- Nucleotides consist of a monosaccharide, a nitrogenous base, and a phosphate group
- Ribose is the sugar in RNA; deoxyribose is the sugar in DNA
- Nitrogenous bases: purines (adenine, guanine) and pyrimidines (cytosine, thymine, uracil)
- Purines and pyrimidines are attached to the anomeric carbon of the sugar. A sugar joined to a nitrogenous base is called a nucleoside
- Nucleotides are formed when a phosphate group is attached at the 5' position of the sugar.
- The names of nucleotides are usually abbreviated using the nitrogenous base followed by an indication of the number of phosphates present (e.g., ADP for adenosine diphosphate).
- Phosphates are negatively charged
- DNA forms a double helix, stabilized by base stacking and base pairing
- RNA can form various secondary structures
- DNA and RNA have different structural organizations in eukaryotic cells, the nucleosome is an important example
DNA Replication
- DNA replication is semi-conservative, each new DNA molecule contains one original strand
- Replication starts at replication origins, which are rich in A-T base pairs
- Initiator proteins bind to replication origins
- Helicase unwinds the DNA, forming a replication bubble
- Single-strand binding proteins prevent the separated strands from re-annealing
- Primase synthesizes RNA primers
- DNA polymerase III synthesizes DNA in the 5' to 3' direction, extending from the 3' end of RNA primers
- There are leading and lagging strands
- Okazaki fragments are synthesized on the lagging strand
- DNA polymerase I removes RNA primers and fills in the gaps
- DNA ligase connects Okazaki fragments
- DNA polymerase proofreads - the ability to remove incorrect bases, increasing the accuracy of replication to about 1 error in 10^6 or 10^7 bases
DNA Repair
- DNA polymerase makes mistakes during replication
- Depurination: loss of a purine base
- Deamination: conversion of a base to a different base
- Pyrimidine dimers: formation of covalent links between adjacent pyrimidines, e.g., thymine dimers, usually from UV light
- Other base modifications: damage from ionizing radiation
- Strand breaks: single-strand or double-strand breaks
- DNA repair mechanisms include: proofreading, mismatch repair, base excision repair, nucleotide excision repair
Cancer
- Cancer is a disease characterized by rapid proliferation of abnormal cells
- Cancer cells do not respond to signals that normally control cell division
- Cancer cells are not sensitive to normal pathways of cellular differentiation or programmed cell death (apoptosis)
- Cancer cells can escape their normal environment and proliferate at foreign sites (metastasize)
- Cancer is a genetic disease, resulting from multiple mutations in genes
Bacterial Transcription
- Genes are transcribed into RNA using RNA polymerase
- Transcription starts at the promoter, and stops at the terminator sequence
- Promoters consist of consensus sequences (-10 and -35) that are recognized by RNA polymerase
- Bacterial genes are often organized in operons; a single promoter controls expression of multiple genes
- Genes transcription can be regulated by proteins that bind to specific regulatory regions of DNA
- Transcription factors can act as activators to enhance transcription, and repressors to block it
Eukaryotic Transcription
- Eukaryotes have three different RNA polymerases
- Transcription initiation in eukaryotes is more complex due to chromatin structure and presence of several transcription factors
- Transcription factors bind to the promoter, and other regulatory regions
- Genes in eukaryotes are typically transcribed into single units, not operons
- Eukaryotic genes contain introns that are removed by splicing before translation
RNA Processing
- Primary transcript in eukaryotes must be processed to mature mrRNA. This process includes
- Capping of 5' end: crucial for RNA stability and translation
- Polyadenylation (addition of the poly A tail) at the 3' end: enhances stability and translation
- Splicing: removal of introns - non-coding regions between coding regions, exons.
Translation
- Decoding mRNA sequences to produce proteins occurs in ribosomes
- tRNAs carry amino acids to the ribosome, matching to the mRNA codons using their anticodons
- Aminoacyl-tRNA synthetases (aaRS): enzymes that link the correct amino acid to tRNA
- Ribosomes synthesize proteins in the 5' to 3' direction, based on the mRNA codon sequence
Recombinant DNA Technology
- Recombinant DNA technology is used to manipulate genes and create new organisms, such as cloning genes, over-expressing proteins, and creating transgenic organisms
- Techniques like PCR, restriction enzymes, DNA ligation, plasmids, cloning
- DNA sequencing is used to determine precise order of nucleotides
- Methods for creating genomic libraries (e.g shotgun method)
Genome Sequencing
- DNA sequencing is the process of determining the order of nucleotides in a DNA molecule
- Shotgun sequencing: a method to create random fragments of the genome that are cloned an sequenced, then assembled into contigs, and ultimately into the full genome sequence
- Genomic Annotation: process of identifying genes, regulatory elements, and other important regions of a sequenced genome. A process following genome sequencing
- Methods to identify DNA or RNA sequences based on their known sequence
- Tools for gene cloning: PCR, restriction enzymes, DNA ligase and plasmids
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Description
Explore the fundamental components and functions of nucleic acids, including DNA and RNA. This quiz covers the structures of nucleotides, the roles of purines and pyrimidines, and the overall significance of these molecules in genetic information storage and protein synthesis.
