Questions and Answers
What is a pyrimidine?
What is a purine?
How are nucleotides joined together?
Condensation
What does mRNA do?
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What does tRNA do?
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What does rRNA do?
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What is feedback inhibition?
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What are exonucleases?
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What are endonucleases?
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What is DNA polymerase III?
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What are ORI sites?
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What is the function of helicase?
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What does ligase do?
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What are telomeres?
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What is the role of RNA polymerase?
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What do spliceosomes do?
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What is the function of enhancers?
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What is a Poly-A tail?
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What is the purpose of the 5' cap?
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What is aminoacyl tRNA?
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What is the function of ribosomes?
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What is the path of a tRNA in a ribosome?
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How is translation initiated?
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How is translation terminated?
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What is reverse transcriptase?
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What is pleiotropy?
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Study Notes
Nucleotides and Nitrogenous Bases
- Pyrimidines consist of a single carbon ring and include Cytosine, Thymine, and Uracil.
- Purines are characterized by two carbon rings and include Adenine and Guanine.
- Nucleotides are joined together through condensation reactions.
RNA Function and Types
- mRNA (messenger RNA) carries genetic code from DNA to ribosomes for protein synthesis; marks the transition from transcription to translation.
- tRNA (transfer RNA) decodes mRNA and matches amino acids to the corresponding mRNA code, crucial for protein synthesis.
- rRNA (ribosomal RNA) forms part of the ribosome's structure, is the most abundant RNA, and facilitates the coupling of tRNA to mRNA codons.
Enzymes and Inhibition
- Feedback Inhibition occurs when the end product of a metabolic pathway acts as a noncompetitive inhibitor, binding to an allosteric site.
- Exonucleases degrade nucleic acids by removing nucleotides one at a time from the ends by cleaving phosphodiester bonds.
- Endonucleases cleave phosphodiester bonds within a nucleic acid chain, often at palindromic recognition sites and creating sticky ends.
DNA Replication Mechanism
- DNA polymerase III synthesizes new DNA strands by reading existing ones and always adds nucleotides to the 3' end; it cannot initiate a strand independently.
- ORI (origin of replication) sites trigger the replication process on chromosomes.
- Gyrase (a type of topoisomerase) unwinds DNA ahead of the replication fork to relieve tension.
- Helicase breaks hydrogen bonds in the double helix to separate strands for replication.
- Primase synthesizes RNA primers, providing starting points for DNA polymerase III.
Strands and Fragments
- Single-strand DNA-binding proteins (SSBPs) stabilize unwound DNA during replication.
- Okazaki fragments are short DNA segments synthesized on the lagging strand, later joined by DNA ligase.
- DNA ligase forms covalent bonds between nucleotides, sealing gaps during replication.
Processes in DNA Replication
- Steps of DNA replication include initiation, elongation, and termination.
- Telomeres protect the ends of chromosomes during replication to maintain genetic integrity.
Transcription Elements
- The -10 box (TATA box) is a promoter region located 10 bases upstream of the transcription start site, facilitating RNA polymerase binding.
- The -35 box, TTGACA, is another promoter element located 35 bases upstream of the start site.
RNA Polymerase Activity
- RNA polymerase opens the DNA double helix and synthesizes RNA in the 3' to 5' direction, forming covalent bonds between nucleotides.
Post-Transcriptional Modifications
- Spliceosomes, comprised of small nuclear RNAs (snRNPs), remove introns and join exons during RNA processing.
- Enhancers are regulatory elements located far from promoters that influence tissue-specific or cell-specific gene expression.
- The Poly-A tail, a series of 100-250 adenine nucleotides, protects mRNA from degradation in the cytoplasm.
- The 5' cap is added to the mRNA's 5' end, signaling readiness for translation and providing a binding site for ribosomes.
Translation Mechanics
- Aminoacyl tRNA refers to tRNAs that carry specific amino acids.
- Ribosomes consist of large and small subunits that facilitate the interaction between mRNA and tRNAs, catalyzing peptide bond formation.
- The tRNA moves through the ribosome in the order A (aminoacyl site) → P (peptidyl site) → E (exit site).
Initiation and Termination of Translation
- Translation initiation occurs when the small ribosomal subunit binds to the mRNA's ribosomal binding site, followed by the large subunit joining the complex.
- Termination happens when a stop codon is encountered, with a release factor binding to the ribosome, leading to the release of the newly synthesized polypeptide.
Reverse Transcription
- Reverse transcriptase is an enzyme that converts RNA into DNA, following the path mRNA → ssDNA → cDNA → dsDNA.
Genetic Concepts
- Pleiotropy refers to the phenomenon where a single gene influences multiple phenotypic traits.
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Prepare for the ASCP Molecular Biology Exam with this comprehensive quiz focusing on key concepts such as nucleotides and their functions. Each flashcard includes definitions and detailed explanations to enhance your understanding of molecular biology. Perfect for students and professionals alike!