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Questions and Answers
What is the primary purpose of genetic engineering?
What are the components of a nucleotide in DNA?
Which of the following pairs of nitrogenous bases follow the base-pairing rules in DNA?
What structural form does DNA take?
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Why do nucleotides always pair in a specific way?
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What is the role of the upstream regulatory region in gene expression?
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What is an open reading frame (ORF)?
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What is true regarding the molecular size measurements of DNA and RNA?
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How is the number of amino acids derived from the number of gene's codons?
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If the molecular weight of a protein is given as 390 KD, what is the estimated molecular size of its corresponding gene in base pairs?
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What is the structure of B-type DNA?
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Which type of DNA has a zigzag pattern and is left-handed?
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What do structural genes primarily encode?
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What is the primary function of regulatory genes?
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What type of bond connects the phosphate of one nucleotide to the hydroxyl group of another nucleotide in DNA?
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How is a gene defined in terms of its coding structure?
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Who were awarded the Nobel Prize in 1962 for the discovery of the DNA double helix structure?
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What are pseudogenes?
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Which of the following statements about the structure of DNA is true?
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What does the term base pair (bp) refer to?
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What do cytosine and guanine connect through?
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What is the significance of DNA being described as anti-parallel?
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What primarily causes the formation of A-DNA?
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Which of the following processes is primarily enhanced by the phosphodiester bond arrangement in DNA strands?
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What is the relationship defined by Chargaff’s rules?
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What misnomer describes the type of DNA that has a left-handed double helix configuration?
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Study Notes
Genetic Engineering
- Genetic engineering is the intentional manipulation of genetic material (mainly DNA) to modify, repair, or enhance form, function, or introduce new traits.
- Traditionally, humans indirectly manipulated genomes by controlling and selecting offspring with desired traits.
- Most often, a gene from a different species is introduced into the host to transfer the desired phenotype.
DNA Structure
- DNA consists of two molecules arranged in a ladder-like structure called a double helix.
- A DNA molecule is made up of millions of tiny subunits called nucleotides.
- Each nucleotide consists of a phosphate group, a pentose sugar, and a nitrogenous base.
- The nitrogenous bases are the only difference between the four nucleotides.
- Nucleotides always pair in the same way: A pairs with T, and C pairs with G.
- The consistent pairing of a pyrimidine (single ring) with a purine (double ring) results in a uniform width of the helix.
DNA Bonds
- Hydrogen bonds: Between complementary nitrogenous bases on opposite strands.
- Phosphodiester bonds: Covalent linkage between the phosphate of one nucleotide and the hydroxyl (OH) group on the 3′ carbon of the deoxyribose sugar in an adjacent nucleotide, forming the “sugar-phosphate backbone” of DNA.
- Glycoside bonds: Exist between the pentose sugar molecule and nitrogenous base.
DNA Structure Discovery
- Watson and Crick determined the three-dimensional structure of DNA through model building.
- They discovered DNA is a double helix with a sugar-phosphate backbone on the outside and bases on the inside.
- Their discovery won them the Nobel Prize in Physiology or Medicine in 1962.
- Their work was based on Rosalind Franklin’s x-ray images suggesting DNA was a double helix of even width and Erwin Chargaff’s rules stating A=T and C=G.
DNA Double Helix Properties
- Most DNA double helices are right-handed.
- Only Z-DNA is left-handed.
- The DNA double helix is anti-parallel, with the 5' end of one strand paired with the 3' end of its complementary strand (and vice versa).
Importance Of Antiparallel DNA Double Helix Structure
- The antiparallel structure enables hydrogen bonding between complementary nitrogenous base pairs.
- The phosphodiester bonds in one strand run from a 3' carbon to a 5' carbon of adjacent nucleotides, while those in the complementary strand run vice versa, maximizing base-pair packing efficiency.
DNA Configurations
- A-DNA: Right-handed DNA with a double helix structure. Occurs under conditions like desiccation.
- B-DNA: Right-handed DNA with a double helix structure. Most common form under normal physiological conditions.
- Z-DNA: Left-handed DNA with a double helix structure and a zigzag pattern to the left.
Genes
- A gene is the basic unit of heredity passed from parents to offspring.
- Genes contain information that specifies physical and biological traits.
- Most genes code for specific proteins or segments of proteins, performing different functions within the body.
- Humans have approximately 20,000 protein-coding genes.
Gene Types
- Structural genes: Encode amino acids.
- Regulatory genes: Located upstream (promoter), control the expression of one or more structural genes by regulating the production of regulatory proteins.
- Housekeeping genes: Consistently expressed across tissues, playing crucial roles in cellular maintenance.
- Pseudogenes: Nonfunctional segments of DNA that resemble functional genes, including start and stop codons.
Gene Structure
- A gene is a sequence of DNA starting with a start codon (ATG) and ending with a stop codon (TAG, TGA, or TAA) from 5' to 3' direction.
- Gene size is measured in base pairs (bp).
- If there are two start (or stop) codons within a gene, the first one is typically chosen.
- The start codon ATG encodes for Methionine.
Molecular Weight & Calculations
- The molecular weight of DNA and RNA is measured in Daltons.
- 1 base pair (bp) = 650 Daltons.
- In prokaryotes, the molecular size of DNA (bp) = molecular size of RNA (bases).
- To calculate the number of base pairs in a gene encoded to a protein, divide the protein's molecular weight by 650.
- The number of bases in the RNA template is equal to the number of base pairs in the gene.
- The number of amino acids in a protein is equal to the number of codons in the gene, minus one.
- The number of peptide bonds in a protein is equal to the number of amino acids, minus one.
Protein Molecular Weight Estimation
- If the molecular weight of a protein is known, the molecular size of the corresponding gene (DNA) can be estimated:
- Divide the protein’s molecular weight by 1000 to get the molecular weight in Daltons.
- Divide that result by 650 to get the molecular size of the gene in base pairs (bp).
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Description
This quiz explores the fundamentals of genetic engineering and the structure of DNA. Dive into the processes of manipulating genetic material and learn about the double helix formation and nucleotide pairing. Perfect for students and enthusiasts eager to understand molecular biology concepts.
