Questions and Answers
What is DNA?
Nucleic acid polymer produced from covalent bonding of nucleotide monomers that contain the sugar deoxyribose; the genetic material of nearly all organisms.
Which of the following statements about nucleotides is true?
Chargaff's rules state that the number of purines equals the number of pyrimidines.
True
Who prepared an X-ray diffraction photograph of DNA?
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What is the shape of DNA?
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What term describes the process of synthesizing a new DNA double helix?
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The term for DNA replication where one old strand and one new strand are conserved is called __________.
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What is the role of RNA polymerase during transcription?
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What are the three steps involved in protein synthesis?
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What is the significance of a codon in mRNA?
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Intron sequences are retained in mature mRNA after processing.
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Study Notes
DNA Structure and Function
- DNA (deoxyribonucleic acid) is a nucleic acid polymer made of nucleotide monomers with deoxyribose sugar; serves as the genetic material for most organisms.
- Each nucleotide consists of a phosphate group, deoxyribose sugar, and one of four nitrogenous bases: purines (adenine A, guanine G) and pyrimidines (cytosine C, thymine T).
- Chargaff's rules state that in DNA, the number of purines equals the number of pyrimidines (A = T and G = C).
- Rosalind Franklin's X-ray diffraction revealed that DNA has a double helix structure with a consistent diameter and regularly stacked bases.
- Complementary base pairing occurs through hydrogen bonds between A and T, and G and C, essential for DNA structure stability.
DNA Replication
- DNA replication is the process of synthesizing a new double helix before cell division (mitosis/meiosis).
- This process is semi-conservative, producing two helices each containing one old and one new strand.
- DNA helicase unwinds the double helix, while DNA polymerase joins complementary nucleotides to form new strands.
- Antiparallel configuration of DNA strands means synthesis occurs in opposite directions; leading strand is synthesized continuously, while the lagging strand forms short segments called Okazaki fragments.
- DNA ligase connects Okazaki fragments and seals breaks in the sugar-phosphate backbone.
Gene Expression
- Gene expression involves the transcription of DNA to mRNA followed by translation into a polypeptide.
- Transcription, the first stage, uses one DNA strand as a template for mRNA synthesis, catalyzed by RNA polymerase at the promoter region.
- During mRNA processing, a 5' cap and a poly-A tail are added, and introns are removed, leaving only exons to form mature mRNA.
- Translation involves ribosomes using mRNA codons to synthesize polypeptides, requiring tRNA and rRNA.
Codons and Transfer RNA (tRNA)
- Codons are three-base sequences in mRNA that specify individual amino acids during translation.
- tRNA transfers specific amino acids to the ribosome; each tRNA molecule has an anticodon complementary to the mRNA codon.
- Polyribosomes allow multiple ribosomes to translate a single mRNA strand simultaneously, increasing protein production efficiency.
Stages of Translation
- Translation has three stages: initiation, elongation, and termination.
- Initiation begins when the ribosome assembles around the mRNA start codon.
- Elongation involves sequential addition of amino acids, facilitated by tRNA, forming a growing polypeptide chain.
- Termination occurs when a ribosome reaches a stop codon, resulting in the release of the completed protein.
Summary of Protein Synthesis
- Protein synthesis consists of transcription of DNA to mRNA followed by translation to form polypeptides.
- A gene is expressed when its corresponding protein is synthesized; this involves intricate processes of transcription, mRNA processing, and translation.
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Description
Test your knowledge on the key concepts of DNA in Biology Chapter 25. This quiz covers essential definitions and structures related to deoxyribonucleic acid, the genetic material of organisms. Perfect for reinforcing your understanding of genetics.
