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Questions and Answers
Which of the following traits is NOT controlled by DNA in microbes?
Which of the following traits is NOT controlled by DNA in microbes?
What is the correct sequence in the central dogma of molecular biology?
What is the correct sequence in the central dogma of molecular biology?
What does genotype refer to in an organism?
What does genotype refer to in an organism?
Which of the following processes involves the synthesis of an RNA molecule from a DNA template?
Which of the following processes involves the synthesis of an RNA molecule from a DNA template?
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Which step in the central dogma follows DNA replication?
Which step in the central dogma follows DNA replication?
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What is the role of transfer RNA (tRNA) in the translation process?
What is the role of transfer RNA (tRNA) in the translation process?
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Virulence factors in microbes are primarily encoded by which type of genes?
Virulence factors in microbes are primarily encoded by which type of genes?
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Which statement about DNA replication is true?
Which statement about DNA replication is true?
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What is the primary function of rRNA?
What is the primary function of rRNA?
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Where is rRNA synthesized in prokaryotic cells?
Where is rRNA synthesized in prokaryotic cells?
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Which of the following best describes mRNA?
Which of the following best describes mRNA?
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What is the role of tRNA during translation?
What is the role of tRNA during translation?
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What does the promoter do?
What does the promoter do?
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Which step is NOT part of the RNA processing in eukaryotes?
Which step is NOT part of the RNA processing in eukaryotes?
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During transcription, in which direction is the RNA strand synthesized?
During transcription, in which direction is the RNA strand synthesized?
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What occurs during the elongation phase of transcription?
What occurs during the elongation phase of transcription?
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What are exons?
What are exons?
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Which type of RNA polymerase is found in eukaryotic cells?
Which type of RNA polymerase is found in eukaryotic cells?
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What is the purpose of adding a poly-A tail during RNA processing?
What is the purpose of adding a poly-A tail during RNA processing?
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In prokaryotes, what can terminate transcription?
In prokaryotes, what can terminate transcription?
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What is a key difference in RNA processing between prokaryotes and eukaryotes?
What is a key difference in RNA processing between prokaryotes and eukaryotes?
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What is the function of the 5' cap in mature mRNA?
What is the function of the 5' cap in mature mRNA?
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How are peptide bonds formed between amino acids?
How are peptide bonds formed between amino acids?
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What is the role of nonsense codons?
What is the role of nonsense codons?
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How many possible codons exist in the genetic code?
How many possible codons exist in the genetic code?
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What does the redundancy in the genetic code imply?
What does the redundancy in the genetic code imply?
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What is the start codon and what amino acid does it encode for?
What is the start codon and what amino acid does it encode for?
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Which of the following modifications is made to eukaryotic mRNA?
Which of the following modifications is made to eukaryotic mRNA?
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What distinguishes the chemical properties of amino acids?
What distinguishes the chemical properties of amino acids?
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Which codons are considered stop codons?
Which codons are considered stop codons?
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What do sense codons do?
What do sense codons do?
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What is the role of the 3' poly-A tail in mRNA?
What is the role of the 3' poly-A tail in mRNA?
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What enzyme is responsible for unwinding the double helix during DNA replication?
What enzyme is responsible for unwinding the double helix during DNA replication?
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Which of the following is a difference between transcription in prokaryotes and eukaryotes?
Which of the following is a difference between transcription in prokaryotes and eukaryotes?
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What is the primary result of gene expression?
What is the primary result of gene expression?
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Where does DNA replication occur in eukaryotic cells?
Where does DNA replication occur in eukaryotic cells?
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Which bond connects the sugar of one nucleotide to the phosphate group of another nucleotide?
Which bond connects the sugar of one nucleotide to the phosphate group of another nucleotide?
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What defines the 5' end of a DNA strand?
What defines the 5' end of a DNA strand?
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What type of bond forms between adenine and thymine in DNA?
What type of bond forms between adenine and thymine in DNA?
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Why are DNA strands described as antiparallel?
Why are DNA strands described as antiparallel?
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In which cellular location does translation occur in eukaryotic cells?
In which cellular location does translation occur in eukaryotic cells?
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During which stage of the cell cycle does DNA replication occur?
During which stage of the cell cycle does DNA replication occur?
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Which of the following describes recombination?
Which of the following describes recombination?
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What are the components of a nucleotide?
What are the components of a nucleotide?
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What distinguishes ribose from deoxyribose in nucleotides?
What distinguishes ribose from deoxyribose in nucleotides?
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What type of nitrogenous base are adenine and guanine classified as?
What type of nitrogenous base are adenine and guanine classified as?
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What is the role of ribosomes during translation?
What is the role of ribosomes during translation?
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In which direction is mRNA read during translation?
In which direction is mRNA read during translation?
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What is the function of the A site in a ribosome?
What is the function of the A site in a ribosome?
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What is a stop codon?
What is a stop codon?
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What are anticodons?
What are anticodons?
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What is meant by spontaneous mutation?
What is meant by spontaneous mutation?
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What is the primary role of mutagens?
What is the primary role of mutagens?
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Which process occurs simultaneously in prokaryotic cells?
Which process occurs simultaneously in prokaryotic cells?
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What is the purpose of the E site in a ribosome?
What is the purpose of the E site in a ribosome?
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What is a base substitution mutation?
What is a base substitution mutation?
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What is the initial event during the initiation phase of translation?
What is the initial event during the initiation phase of translation?
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What are the components involved in translation?
What are the components involved in translation?
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What is the primary function of topoisomerase during DNA replication?
What is the primary function of topoisomerase during DNA replication?
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How does DNA polymerase I contribute to DNA replication?
How does DNA polymerase I contribute to DNA replication?
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What distinguishes vertical gene transfer from horizontal gene transfer?
What distinguishes vertical gene transfer from horizontal gene transfer?
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What happens during the uptake phase of transformation in bacteria?
What happens during the uptake phase of transformation in bacteria?
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What is a key characteristic of conjugation in bacteria?
What is a key characteristic of conjugation in bacteria?
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What role does RNA polymerase play in transcription?
What role does RNA polymerase play in transcription?
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What is one of the main functions of ribosomal RNA (rRNA)?
What is one of the main functions of ribosomal RNA (rRNA)?
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What distinguishes bidirectional replication from unidirectional replication?
What distinguishes bidirectional replication from unidirectional replication?
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Which component is responsible for joining adjacent Okazaki fragments?
Which component is responsible for joining adjacent Okazaki fragments?
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What is the main structural difference between DNA and RNA?
What is the main structural difference between DNA and RNA?
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What characteristic of ribosomal RNA contributes to its function?
What characteristic of ribosomal RNA contributes to its function?
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Which process requires a bacterium to be in a 'competent' state?
Which process requires a bacterium to be in a 'competent' state?
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What is typically the starting point for DNA replication in prokaryotes?
What is typically the starting point for DNA replication in prokaryotes?
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During what process is naked DNA taken up from the environment by bacteria?
During what process is naked DNA taken up from the environment by bacteria?
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In RNA, which base replaces thymine found in DNA?
In RNA, which base replaces thymine found in DNA?
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What is the role of a repressor protein in gene regulation?
What is the role of a repressor protein in gene regulation?
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Which process refers to the molecular mechanisms after mRNA has been synthesized?
Which process refers to the molecular mechanisms after mRNA has been synthesized?
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What type of mutation is characterized by the introduction of a stop codon?
What type of mutation is characterized by the introduction of a stop codon?
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How do mutagens primarily affect mutation rates?
How do mutagens primarily affect mutation rates?
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What is a plasmid?
What is a plasmid?
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What happens during nucleotide excision repair?
What happens during nucleotide excision repair?
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Which type of mutation involves a change in the reading frame?
Which type of mutation involves a change in the reading frame?
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Which molecules can induce transcription by inactivating repressor proteins?
Which molecules can induce transcription by inactivating repressor proteins?
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What distinguishes transposons from plasmids?
What distinguishes transposons from plasmids?
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What is the function of an activator protein in transcription?
What is the function of an activator protein in transcription?
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What distinguishes the leading strand from the lagging strand during DNA replication?
What distinguishes the leading strand from the lagging strand during DNA replication?
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In which direction is the template strand read during DNA replication?
In which direction is the template strand read during DNA replication?
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What are Okazaki fragments?
What are Okazaki fragments?
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Which enzyme is responsible for unwinding the DNA double helix at the replication fork?
Which enzyme is responsible for unwinding the DNA double helix at the replication fork?
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What role do RNA primers play in DNA replication?
What role do RNA primers play in DNA replication?
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What is the function of DNA ligase during DNA replication?
What is the function of DNA ligase during DNA replication?
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Which statement about the lagging strand is true?
Which statement about the lagging strand is true?
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What happens to RNA primers after they have served their purpose in DNA replication?
What happens to RNA primers after they have served their purpose in DNA replication?
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What enzyme is responsible for synthesizing RNA primers during DNA replication?
What enzyme is responsible for synthesizing RNA primers during DNA replication?
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What is the role of single-strand binding proteins (SSBs) during DNA replication?
What is the role of single-strand binding proteins (SSBs) during DNA replication?
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What is the direction of synthesis for both the leading and lagging strands?
What is the direction of synthesis for both the leading and lagging strands?
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Which of the following statements about the replication fork is correct?
Which of the following statements about the replication fork is correct?
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The enzyme topoisomerase is primarily responsible for:
The enzyme topoisomerase is primarily responsible for:
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What characteristic of DNA polymerase limits its function during replication?
What characteristic of DNA polymerase limits its function during replication?
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What is a characteristic feature of a missense mutation?
What is a characteristic feature of a missense mutation?
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What is the result of a nonsense mutation?
What is the result of a nonsense mutation?
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What defines a frameshift mutation?
What defines a frameshift mutation?
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What is one potential benefit of mutations?
What is one potential benefit of mutations?
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Which of the following defines genomics?
Which of the following defines genomics?
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Which statement accurately describes DNA's role as genetic information?
Which statement accurately describes DNA's role as genetic information?
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What are the steps of transcription?
What are the steps of transcription?
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How do prokaryotes differ from eukaryotes in protein synthesis?
How do prokaryotes differ from eukaryotes in protein synthesis?
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What is the function of operons in prokaryotic cells?
What is the function of operons in prokaryotic cells?
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What is an example of a structural component of a gene?
What is an example of a structural component of a gene?
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What characterizes an organism's phenotype?
What characterizes an organism's phenotype?
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How does the genetic code relate to protein synthesis?
How does the genetic code relate to protein synthesis?
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In what way do introns differ from exons in eukaryotic genes?
In what way do introns differ from exons in eukaryotic genes?
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Study Notes
Microbial Genetics
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DNA controls nearly all microbial traits, encoding proteins and RNA for various functions: metabolism (enzymes), structure (cell components), reproduction, virulence (disease factors), and antibiotic resistance.
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Genotype is the organism's genetic makeup (DNA sequence). Phenotype is the observable traits (resulting from expressed genes).
Central Dogma
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The central dogma describes the flow of genetic information: DNA → RNA → Protein.
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DNA Replication: copies DNA for cell division.
- Involves Helicase, Primase, DNA Polymerase, and Ligase.
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Transcription: converts DNA to RNA (mRNA).
- RNA Polymerase binds to the promoter, synthesizes mRNA from the DNA template, and post-transcriptional processing (in eukaryotes) removes introns and joins exons.
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Translation: converts mRNA to protein at the ribosome.
- Ribosomes translate mRNA codons into amino acid sequences using tRNA, which brings specific amino acids.
Replication, Transcription, & Translation Locations
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Prokaryotes: DNA replication and transcription occur in the cytoplasm, with translation often simultaneous and cytoplasmic
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Eukaryotes: DNA replication occurs in the nucleus; transcription occurs within the nucleus (where mRNA is processed before exiting); and translation happens in the cytoplasm using cytoplasmic ribosomes.
Gene Expression, Recombination, & Replication
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Gene Expression: Processes that use DNA to produce proteins/RNA leading to observable traits.
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Recombination: Rearranging genetic material (sexual reproduction or horizontal transfer), increasing diversity.
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DNA Replication: Copying DNA for cell division.
Nucleotides
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Nucleotides consist of: Phosphate group, sugar (deoxyribose in DNA, ribose in RNA), and a nitrogenous base (adenine, guanine, cytosine, thymine, or uracil).
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1' carbon attached to the base; 2' carbon with -OH (ribose) or -H (deoxyribose); 3' carbon forms phosphodiester bonds, 4' and 5' form part of the ribose/deoxyribose ring and is bound to the phosphate group.
Nucleotide Bonds
- Phosphodiester bonds link nucleotides: formed between the 3' hydroxyl of one sugar and the 5' phosphate of another, creating the backbone.
DNA Strands: Antiparallel
- DNA strands run anti-parallel (5' to 3' and 3' to 5') which enables enzymes to work efficiently in a directional manner as DNA is synthesized in one direction only
Base Pairing Rules
- Adenine (A) pairs with Thymine (T). Cytosine (C) pairs with Guanine (G). (In RNA, Uracil (U) replaces Thymine.)
DNA Strand Ends
- 5' end: phosphate group attached to the 5' carbon.
- 3' end: hydroxyl group attached to the 3' carbon. DNA strands are synthesized in a 5' to 3' direction.
DNA Replication: Semi-Discontinuous
- Leading strand: Synthesized continuously.
- Lagging strand: Synthesized discontinuously as Okazaki fragments(needs RNA primers).
DNA Replication Template & Synthesis Direction
- Template read: 3' to 5'
- New strand made: 5' to 3'
Replication Fork
- Y-shaped region where DNA double helix is unwound during replication. Involves various enzymes (Helicase, SSBs, Topoisomerase, Primase, etc.).
Leading vs. Lagging Strand Synthesis
- Leading strand: Continuous synthesis.
- Lagging strand: Discontinuous synthesis in Okazaki fragments, needing many RNA primers
Okazaki Fragments
- Short DNA fragments synthesized on the lagging strand during replication, later joined with DNA ligase into a continuous strand. Okazaki fragments need RNA primers, to start synthesis
Primers
- Short RNA sequences that initiate DNA synthesis.
- Needed because DNA polymerase can only add nucleotides to an existing strand.
DNA Replication Fork Events
- Helicase unwinds, SSBs stabilize, Topoisomerase relieves strain, Primase makes RNA primers, DNA polymerase extends primers, DNA polymerase I removes RNA, DNA ligase joins fragments.
Enzymes in DNA Replication
- DNA replication involves: Helicase, SSBs, Topoisomerase, Primase, DNA Polymerase III, DNA Polymerase I, and DNA Ligase. (Each has a specific function).
Origin of Replication
- Specific site on DNA where replication begins (multiple origins in eukaryotes; one in prokaryotes).
Bidirectional Replication
- Replication occurs in two directions from a single origin, forming two replication forks.
Gene Transfer
- Vertical: Inheritance from parent to offspring.
- Horizontal: Transfer between organisms without reproduction, using a variety of methods in bacteria like transformation, conjugation, and transduction.
Transformation
- Bacteria take up foreign DNA and incorporate it into their genome.
Conjugation
- Transfer of genetic material between bacterial cells through a physical connection.
Transcription Template
- One DNA strand (non-template/coding strand) acts as the template to create the mRNA.
RNA vs. DNA
- DNA: Double-stranded, deoxyribose sugar, A-T, C-G, stable, stores genetic information.
- RNA: Single-stranded, ribose sugar, A-U, C-G, less stable, involved in protein synthesis.
Ribosomal RNA (rRNA)
- Component of ribosomes, essential for protein synthesis, responsible for binding mRNA, tRNA, and catalyzing peptide bond formation during translation.
Messenger RNA (mRNA)
- Carries genetic information from DNA to the ribosomes for protein synthesis (pre-mRNA is processed in eukaryotes).
Transfer RNA (tRNA)
- Brings amino acids to ribosome, matches mRNA codons, an adapter molecule that attaches the corresponding amino acid.
RNA Polymerase
- Enzyme that synthesizes RNA from a DNA template during transcription.
Promoter
- DNA sequence where RNA polymerase attaches and initiates transcription (upstream from the gene).
Terminator
- DNA sequence that signals the end of transcription, causing RNA polymerase to detach.
Transcription Stages
- Initiation: RNA polymerase binds to the promoter.
- Elongation: RNA polymerase moves along DNA, synthesizing mRNA.
- Termination: RNA polymerase reaches the terminator, stopping.
Transcription Direction
- DNA template read: 3' to 5'
- RNA synthesized: 5' to 3'
RNA Processing
- Modifications of pre-mRNA in eukaryotes before it leaves the nucleus (5' capping, splicing, polyadenylation).
Exons
- Coding sequences of a gene that are expressed in the protein.
Introns
- Non-coding sequences of a gene that are removed before translation.
5' Cap and 3' Poly-A Tail
- 5' cap: Protects mRNA, aids in ribosome binding.
- 3' poly-A tail: Stabilizes mRNA, aids in translation initiation.
Amino Acids
- Building blocks of proteins, each with a central carbon, hydrogen, carboxyl group, amino group, and variable side chain (R group).
Peptide Bonds
- Covalent bonds linking amino acids in a protein.
Codons
- Three-nucleotide sequences in mRNA that specify amino acids. Found in mRNA.
Sense vs. Nonsense Codons
- Sense: Code for amino acids.
- Nonsense/Stop: Signal the end of translation (UAA, UAG, UGA).
Number of Codons
- 64 possible codons (4 bases * 3 positions); 61 sense, 3 stop.
Codon Redundancy
- Some amino acids have multiple codons (degeneracy).
Start Codon
- AUG codes for methionine (initiator amino acid).
Ribosomes in Translation
- Molecular machines composed of rRNA and proteins that carry out protein synthesis.
Anticodons
- Three-nucleotide sequences on tRNA molecules that are complementary to mRNA codons.
mRNA Reading Direction during Translation
- mRNA read: 5' to 3'.
Ribosome Sites (A, P, E)
- A site: Incoming aminoacyl-tRNA binds.
- P site: Holds tRNA with growing polypeptide chain; peptide bond formation occurs.
- E site: Exit site for empty tRNA.
Translation Stages
- Initiation: Ribosome assembles at start codon.
- Elongation: Amino acids added to polypeptide chain.
- Termination: Release factor binds to stop codon, releasing the polypeptide.
Transcription & Translation Coupling
- Prokaryotes typically couple transcription and translation, occurring in the cytoplasm simultaneously.
Mutation Types
- Base Substitutions: Silent, missense, or nonsense mutations.
- Frameshift Mutations: Insertion or deletion of nucleotides that alter the reading frame (affects many amino acids).
Mutagens & Spontaneous Mutations
- Mutagens: Increase mutation rate.
- Spontaneous: Occur naturally.
DNA Repair Mechanisms
- Mismatch repair: Correct errors in DNA replication.
- Nucleotide excision repair: Repairs damaged DNA (like from UV light).
Mutagens & Mutation Rate
- Mutagens increase the mutation rate.
Plasmids & Transposons
- Plasmids: Small, circular DNA molecules that can replicate independently and carry genes.
- Transposons: "Jumping genes," DNA sequences that can move within a genome.
Functions of Plasmids and Transposons
- Plasmids: Often contain traits like antibiotic resistance and virulence; can be transferred between cells.
- Transposons: Can move within genomes, disrupting genes and causing mutations.
Protein synthesis comparison in prokaryotes and eukaryotes
- Prokaryotes: Transcription and translation happen simultaneously.
- Eukaryotes: Transcription in nucleus; translation in cytoplasm.
Operons
- Clusters of functionally related genes in prokaryotes; regulated together.
Pre-transcriptional Regulation
- Mechanisms that control transcription before mRNA synthesis (e.g., repressors, inducers, activators).
Post-transcriptional Regulation
- Mechanisms that control gene expression after mRNA transcription (e.g., RNA splicing, RNA stability, RNA interference).
Mutation Classifications
- Various types of mutations (discussed above).
Effects of Mutagens
- Increase mutation rate by altering DNA structure (discussed above).
Definitions (genetics terms)
- Definitions of terms listed above.
DNA as Genetic Information
- DNA encodes instructions for all life processes.
Protein Synthesis Summary
- Summary of both transcription and translation, and their steps. Note the differences between prokaryotes and eukaryotes.
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Description
Test your understanding of key concepts in microbiology genetics. This quiz covers the central dogma of molecular biology, the role of various RNA types, and the nature of genotype in organisms. Perfect for students looking to solidify their knowledge on microbial traits and DNA processes.