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Questions and Answers
What is the primary function of RNA polymerase II?
Which of the following represents a difference between RNA and DNA?
What is the role of the poly(A) tail during post-transcriptional modification?
What is the structure of RNA compared to DNA?
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How many main classes of RNA are predominantly synthesized by RNA polymerase?
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Which of the following describes transcription?
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What are the genetic words that code for amino acids called?
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Which process occurs on ribosomes and is directed by mRNA?
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What are the two types of nucleic acids?
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What holds the two strands of DNA together in a double helix?
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Which RNA type accounts for the majority of total RNA in the cell?
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What is the main function of mRNA?
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Which of the following statements about DNA structure is TRUE?
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What type of bond connects deoxyribonucleotides in a DNA strand?
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How many hydrogen bonds are formed between adenine and thymine in DNA?
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Which of the following roles does transfer RNA (tRNA) perform?
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Study Notes
Nucleic Acids
- Nucleic acids store and express genetic information.
- There are two types of nucleic acids: deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
DNA Structure
- DNA’s structure was first described by James Watson and Francis Crick in 1953.
- DNA is a double helix, consisting of two complementary strands of deoxyribonucleotides (dAMP, dGMP, dCMP, dTMP) connected by phosphodiester bonds.
- The phosphodiester bonds are formed between the 3’-OH group of the deoxyribose sugar on one nucleotide and the 5’ phosphate group on the adjacent one.
- The phosphate and sugar form the DNA strand's backbone.
- The nitrogenous bases project inwards.
- The two complementary strands of DNA run antiparallel, meaning the 5’ end of one strand is base-paired with the 3’ end of the other.
- Hydrogen bonds hold together the two strands of DNA within the double helical structure.
- Adenine forms two hydrogen bonds with thymine, while guanine and cytosine are connected by three.
- This base pairing stabilizes the interior of the double-stranded DNA.
RNA Structure
- There are three main types of RNA involved in protein synthesis: rRNA, tRNA, and mRNA.
- These are unbranched polymeric molecules composed of nucleoside monophosphates joined by 3'→5'-phosphodiester bonds.
- They differ in size, function, and structural modifications.
Ribosomal RNA (rRNA)
- rRNA accounts for approximately 80% of total RNA in the cell.
- Ribosomes are responsible for protein synthesis and contain peptidyl transferase activity, which is catalyzed by ribozymes.
Transfer RNA (tRNA)
- tRNA is the smallest of the three RNAs.
- It carries amino acids during protein synthesis.
Messenger RNA (mRNA)
- mRNA carries genetic information from DNA to the cytosol for translation.
DNA Replication
- The process of producing two identical copies from one original DNA molecule is called DNA replication.
- Important enzymes involved in replication are DNA polymerases.
Transcription
- The synthesis of RNA from a DNA template is called transcription.
- Genes are transcribed by enzymes called RNA polymerases.
- Eukaryotic cells have several distinct RNA polymerases, each responsible for a major class of RNA:
- RNA polymerase I: synthesizes most rRNA.
- RNA polymerase II: synthesizes mainly mRNA.
- RNA polymerase III: synthesizes mainly tRNA.
Post-Transcriptional Modification of RNA
- This includes:
- Capping of mRNA
- Addition of a poly(A) tail
- Splicing
Translation
- The process of producing proteins occurs on ribosomes and is directed by mRNA.
- The genetic message encoded in DNA is first transcribed into mRNA, and the nucleotide sequence in the coding region of the mRNA is then translated into the amino acid sequence of the protein.
- Codons are the genetic words used in this process. Each codon consists of three successive nitrogenous bases.
Post-Translational Modifications
- These include:
- Trimming
- Covalent modifications
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Description
This quiz explores the fundamental concepts of nucleic acids, specifically focusing on DNA structure as defined by Watson and Crick. You will learn about the components, bonding, and configurations that make DNA the blueprint of life.
