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Questions and Answers
What is the main characteristic of the B-DNA form?
What is the main characteristic of the B-DNA form?
What links the nucleotide monomers within the DNA structure?
What links the nucleotide monomers within the DNA structure?
Which variation of DNA is characterized by a left-handed helix?
Which variation of DNA is characterized by a left-handed helix?
What is the effect of very high salt concentrations on DNA?
What is the effect of very high salt concentrations on DNA?
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In DNA, what term describes the orientation of the two strands?
In DNA, what term describes the orientation of the two strands?
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What are the components of a nucleotide?
What are the components of a nucleotide?
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Which of the following statements about nucleosides is correct?
Which of the following statements about nucleosides is correct?
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Which purine bases are commonly found in nucleotides?
Which purine bases are commonly found in nucleotides?
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What distinguishes RNA from DNA?
What distinguishes RNA from DNA?
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Which of the following is NOT a type of nucleotide?
Which of the following is NOT a type of nucleotide?
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Which statement about the roles of nucleotides is incorrect?
Which statement about the roles of nucleotides is incorrect?
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What is the correct way to name purine nucleosides?
What is the correct way to name purine nucleosides?
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Where is DNA primarily found in a cell?
Where is DNA primarily found in a cell?
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What is the role of tRNA with the anticodon CAU during translation?
What is the role of tRNA with the anticodon CAU during translation?
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Which step of translation follows the initiation phase?
Which step of translation follows the initiation phase?
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What happens if the mRNA message is read incorrectly starting at the wrong nucleotide?
What happens if the mRNA message is read incorrectly starting at the wrong nucleotide?
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What is the significance of the stop codons UAA, UAG, and UGA in translation?
What is the significance of the stop codons UAA, UAG, and UGA in translation?
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What happens to the initiator tRNA after it has completed its function?
What happens to the initiator tRNA after it has completed its function?
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Which of the following is NOT a main step in the translation process?
Which of the following is NOT a main step in the translation process?
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How does energy play a role during the elongation phase of translation?
How does energy play a role during the elongation phase of translation?
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What specifies the insertion of a particular amino acid during translation?
What specifies the insertion of a particular amino acid during translation?
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What can be diagnosed by detecting the genome using the polymerase chain reaction (PCR)?
What can be diagnosed by detecting the genome using the polymerase chain reaction (PCR)?
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Which genetic condition is primarily associated with a single base mutation affecting protein function?
Which genetic condition is primarily associated with a single base mutation affecting protein function?
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Which of the following is produced by genetically modified plants?
Which of the following is produced by genetically modified plants?
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What is the purpose of genetically modified crops like Bt corn?
What is the purpose of genetically modified crops like Bt corn?
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Which illness can be diagnosed by analyzing the genetic area for protein production?
Which illness can be diagnosed by analyzing the genetic area for protein production?
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Which of these is an example of a genetically modified organism primarily for food use?
Which of these is an example of a genetically modified organism primarily for food use?
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Which of the following is NOT a genetic condition listed for genetic diagnosis?
Which of the following is NOT a genetic condition listed for genetic diagnosis?
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By what mechanism do genetically modified plants like corn typically gain herbicide resistance?
By what mechanism do genetically modified plants like corn typically gain herbicide resistance?
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What is the direction of the strand that acts as a template during the synthesis of mRNA?
What is the direction of the strand that acts as a template during the synthesis of mRNA?
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What role does DNA polymerase play during DNA replication?
What role does DNA polymerase play during DNA replication?
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What does the term 'semi-conservative' refer to in DNA replication?
What does the term 'semi-conservative' refer to in DNA replication?
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During transcription, which enzyme catalyzes the formation of mRNA?
During transcription, which enzyme catalyzes the formation of mRNA?
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What is the first step in the process of translation?
What is the first step in the process of translation?
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What is the function of the anticodon on tRNA?
What is the function of the anticodon on tRNA?
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What role do proteins play during DNA replication?
What role do proteins play during DNA replication?
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What is the end product of the transcription process?
What is the end product of the transcription process?
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Which of the following accurately describes codons?
Which of the following accurately describes codons?
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What happens if DNA polymerase's proofreading active site fails to correct an error?
What happens if DNA polymerase's proofreading active site fails to correct an error?
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What indicates the directionality of the DNA strands?
What indicates the directionality of the DNA strands?
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Which nitrogenous base pairs with adenine in RNA?
Which nitrogenous base pairs with adenine in RNA?
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What is the primary structural difference between DNA and RNA?
What is the primary structural difference between DNA and RNA?
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Which type of RNA is mainly involved in protein synthesis?
Which type of RNA is mainly involved in protein synthesis?
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What type of bond holds guanine and cytosine pairs together?
What type of bond holds guanine and cytosine pairs together?
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What is true regarding the GC content in ribosomal RNA?
What is true regarding the GC content in ribosomal RNA?
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What structural feature does transfer RNA (tRNA) possess?
What structural feature does transfer RNA (tRNA) possess?
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How does base pairing in RNA differ from that in DNA?
How does base pairing in RNA differ from that in DNA?
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What is the primary role of messenger RNA (mRNA)?
What is the primary role of messenger RNA (mRNA)?
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What process allows RNA to be formed from DNA?
What process allows RNA to be formed from DNA?
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Study Notes
Nucleic Acids
- Nucleic acids are the energy-rich compounds that are the monomers of nucleic acids.
- They provide energy for metabolic processes.
- They are part of enzyme cofactors, such as NAD (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide).
- They act as secondary chemical messengers in response to hormones.
- A nucleotide consists of three portions: a nitrogenous base, a sugar (deoxyribose or ribose), and one or more phosphate groups.
Nucleotides
- Common purine bases are adenine and guanine.
- Common pyrimidine bases are cytosine, uracil, and thymine.
- Some common nucleotides include ATP (adenosine triphosphate), ADP (adenosine diphosphate), AMP (adenosine monophosphate), GTP (guanosine triphosphate), UTP (uridine triphosphate), and CTP (cytidine triphosphate).
Nucleosides
- A nucleoside consists of a nitrogenous base covalently attached to a sugar (ribose or deoxyribose) but without the phosphate group.
- When a nucleoside is phosphorylated, a nucleotide is formed.
- Purine nucleosides end in "-sine" (e.g., adenosine, guanosine).
- Pyrimidine nucleosides end in "-dine" (e.g., cytidine, uridine, deoxythymidine).
Nucleic Acids - DNA
- DNA is found in the chromatin of the cell's nucleus and also in mitochondria and chloroplasts.
- It contains genetic information in segments called genes.
- It provides information for constructing other cell components.
- DNA is made of nucleotide monomers and has a double helix structure.
- The double helix is also called B-form DNA or B-DNA and is very stable.
- DNA exists in other variations such as A-DNA and Z-DNA which are converted into B-DNA at normal physiological conditions.
- The backbone of DNA is comprised of deoxyribose sugar linked by phosphodiester bridges.
- The 3' hydroxyl group of one sugar is linked to the 5' hydroxyl group of another sugar by a phosphodiester bond
- The strands run antiparallel to each other (one strand runs 3' to 5', and the other runs 5' to 3').
- The nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G).
- Adenine pairs with thymine (A=T) via two hydrogen bonds.
- Guanine pairs with cytosine (G≡C) via three hydrogen bonds.
- The GC pair is held together more strongly than the AT pair due to the stronger triple bonds.
- The pairing of bases is called complementary base pairing and the sequences are complementary but not identical.
- The DNA helix can be bent or supercoiled due to flexibility. This allows the DNA to be wrapped around proteins, compacting DNA into smaller volumes.
Nucleic Acids - RNA
- RNA is found in the cell's cytoplasm and nucleolus.
- It is formed from DNA by a process called transcription.
- RNA consists of a phosphate group, a nitrogenous base (adenine (A), uracil (U), cytosine (C), and guanine (G)), and a sugar (ribose).
- RNA is similar to DNA, the nitrogenous bases carry genetic information and the sugar-phosphate serves to maintain the structure.
- RNA structure is single stranded and runs in the 5' to 3' direction.
- Base pairing can occur, thus the molecule can fold on itself in the form of a hairpin structure which does not require equal amounts of complementary base pairs.
Types of RNA
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Ribosomal RNA (rRNA) makes up 80% of RNA in cells and is the most abundant and stable form.
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rRNA has a higher GC content than AU content.
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In the cytoplasm, rRNA combines with proteins to form ribosomes.
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Transfer RNA (tRNA) occupies 15% of the total RNA in the cell and is the smallest polymeric form.
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tRNA functions as a carrier of activated amino acids to a growing polypeptide chain in protein synthesis.
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tRNA binds to specific amino acids and has a three-fold clover leaf configuration.
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The 3' end of tRNA contains the CCA sequence. Amino acids bind to this end via esterification.
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The anticodon region base pairs to the corresponding codon region on the mRNA molecule. Each tRNA molecule has a specific anticodon triplet.
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Messenger RNA (mRNA) comprises 5% of RNA in the cell and is otherwise called template RNA.
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It is synthesized on the surface of the DNA template and carries genetic information from nuclear DNA to the cytosol.
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mRNA is used as a template for protein synthesis.
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monocistronic mRNA carries the code for a single protein.
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polycistronic mRNA carries the code for more than one kind of protein.
Genetic Code
- The sequence of bases that encodes a functional protein is called a gene
- The relationship between the base sequence and the amino acid sequence of a particular protein is called the genetic code
- A codon consists of 3 nucleotides.
- There is a table of these codons and their corresponding amino acids.
Consequences of Altering the Nucleotide Sequence
- Silent mutation: A change in the nucleotide sequence that doesn't alter the amino acid or protein function.
- Nonsense mutation: A change in an mRNA codon that encodes a STOP codon, thus prematurely stopping the protein translation process.
- Missense mutation: A change in an mRNA codon that results in substituting one amino acid for another in the polypeptide chain.
DNA Replication
- DNA replication is the duplication of genetic material.
- During replication the hydrogen bonds between nitrogenous bases are broken separating the strands.
- Each separated strand serves as a template for the synthesis of a new strand that is complementary to the parent strand.
- The enzyme DNA polymerase moves along each template strand and reads the nucleotide.
- The enzyme ligase joins the complementary nucleotide in the new strand.
- DNA polymerase moves in the 3' to 5' direction.
- Other proteins are needed for unwinding the helix, separating the strands, and joining segments into a continuous strand.
- DNA replication is semi-conservative, meaning each new DNA molecule contains one original strand and one new strand.
DNA Replication
- DNA polymerase is a remarkable enzyme that minimizes mistakes during base pairing.
- It contains two active sites: one for polymerization and one for proofreading.
- If a wrong nucleotide is inserted, the proofreading site recognizes the error and removes it.
- If not recognized, the change results in a permanent alteration; a genetic mutation.
Transcription
- This is the process by which RNA is formed from DNA.
- The information in the DNA molecule is carried by the mRNA molecule.
- During transcription, the double helix of the DNA temporarily separates.
- A complementary strand of mRNA (anti-sense strand) assembles on one DNA strand.
- The process is catalyzed by RNA polymerase in a 5' to 3' direction.
- mRNA then leaves the DNA template and carries the information to the ribosomes for polypeptide synthesis.
Translation
- In translation every three consecutive nucleotides on the mRNA is called a codon.
- Each codon codes for a particular amino acid.
- mRNA determines the sequence of amino acids in a protein, which occurs in the translation process.
- Translation is the process that requires numerous enzymes, ribosomes, amino acids, mRNA, tRNA, and energy (ATP and GTP).
- One of the tRNA folds has a specific triplet codon to which an amino acid is attached.
- The amino acid binds covalently to this region, and at least one kind of tRNA is present for each of the 20 amino acids.
- Some amino acids have more than one tRNA molecule.
- There is a triplet codon called an anticodon located at another folded end of the tRNA molecule.
- The anticodon is the complementary code for the attached amino acid.
- When an amino acid is linked to the tRNA molecule, base pairing can occur between the anticodon region of the tRNA and the mRNA molecule.
- Translation involves three major steps (initiation, elongation, and termination).
Translation- Initiation
- During initiation, the small subunit of the ribosome binds at the start codon (AUG) near the 5' end of the mRNA strand.
- The large subunit of the ribosome joins with a special initiator tRNA molecule (which codes for methionine).
- If the reading is at the wrong nucleotide, the remaining triplets will be incorrectly read.
- Incorrect amino acids will be inserted producing a useless polypeptide.
Translation- Elongation
- A tRNA with the amino acid, bonded to it, then base pairs with the mRNA molecule.
- This process requires energy.
- The preceding amino acid is linked to the incoming amino acid by a peptide bond.
- The initiator tRNA to which methionine was attached is then released.
Translation- Termination
- Translation ends when the ribosome reaches a stop codon (UAA, UAG, or UGA).
- No tRNA molecules have anticodons to stop codons, so no amino acids are assigned to these codons.
- Release factors recognize stop codons and release the polypeptide chain from the ribosome.
- The process needs energy.
- The ribosome then splits into subunits and can be reassembled for another round of protein synthesis.
- Many mRNA molecules can be translated simultaneously.
Biotechnology
- Biotechnology encompasses fields like forensic science, DNA profiling, genetically modified foods, and various applications.
- Applications include genetically modified plants, micro-propagation, bio-fertilizers/bio-pesticides for agriculture; stem cells, monoclonal antibodies, and vaccines for health care; industrial enzymes for fermentation processes; biofuels and in bioinformatics/bio-mining.
Genetic Diagnosis
- Methods like PCR (polymerase chain reaction) are used to detect genetic variations related to diseases such as haemophilia, HIV, cystic fibrosis, sickle-cell anemia, phenylketonuria, multiple sclerosis, Tay-Sachs disease, and Alzheimer's disease, along with metabolic diseases like lactose intolerance.
Genetic Diseases
- A small change in the genetic code can lead to significant differences in the resulting protein, impacting the protein's function, which may cause major malfunction or disease.
Other Applications
- Proteins made by genes in bacteria, such as insulin or tissue plasminogen activator (TPA) to dissolve blood clots.
- Genetically modified crops like soybeans, maize, tomatoes, rice, and sweet potatoes.
Genetically Modified Foods
- Genetically modified organisms (GMOs) are primarily used for food production.
- Examples include soybean, corn and canola that are herbicide-resistant.
- Bt corn and cotton provide resistance to insect pests.
- Also papaya resistant to a virus, and rice/sugar cane improvements.
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Description
Test your knowledge on the structural characteristics of DNA and RNA, including nucleotide composition, variations, and roles in cellular processes. This quiz covers key concepts such as helical forms, base pairing, and translation mechanisms.
