Week 27 / Nucleic Acid Biochemistry Flashcards
Q: What is the process of copying DNA into RNA called?
A: Transcription
Q: What is the process of converting RNA into a protein called?
A: Translation
Q: What is the final product of translation?
A: A protein
Q: What is DNA?
A: DNA (Deoxyribonucleic Acid) is the genetic material of the cell that carries instructions for growth, development, and function.
Q: How is genetic information organized in DNA?
A: DNA is arranged into functional units called genes, which encode proteins or regulatory elements.
Q: What is the structural arrangement of DNA strands?
A: DNA is a duplex of two anti-parallel strands, meaning they run in opposite directions.
Q: What is the three-dimensional shape of DNA?
[what is the shape of DNA?,
how is it stabilised?[2]]
A: DNA forms a double-helix conformation, stabilized by hydrogen bonds and base stacking.
Q: How do the two strands of DNA stay together?
A: Through complementary base pairing:
Adenine (A) pairs with Thymine (T)
Cytosine (C) pairs with Guanine (G)
Q: How does DNA serve as a template for replication?
A: Each strand acts as a template during replication, ensuring that new DNA molecules are identical to the original.
Q: What does DNA stand for?
A: DNA stands for Deoxyribonucleic Acid.
Q: What is the primary function of DNA?
A: DNA serves as the information store of life, containing genetic instructions for cellular functions and heredity.
Q: Is DNA a complex or simple molecule chemically?
[what is DNA made up of?]
A: Chemically, DNA is a relatively simple molecule, composed of nucleotides (sugar, phosphate, and nitrogenous bases).
Q: What is unique about DNA replication?
A: DNA can direct its own replication, ensuring genetic continuity across generations.
Q: What does RNA stand for?
A: RNA stands for Ribonucleic Acid.
Q: Why is the DNA double helix considered stable? [2]
A: The DNA double helix is remarkably stable, due to
hydrogen bonding between complementary bases
and stacking interactions between base pairs.
Q: Does RNA have a single function?
A: No, RNA has multiple functions, including protein synthesis, gene regulation, and catalysis.
Q: Is RNA chemically complex or simple?
A: Chemically, RNA is relatively simple, consisting of ribose sugar, phosphate, and nitrogenous bases.
Q: Can RNA form stable structures?
A: Yes, RNA forms a range of stable structures, such as hairpins and loops, which contribute to its function.
Q: Can RNA act as a catalyst?
A: Yes, some RNA molecules, called ribozymes, can perform catalytic functions, similar to enzymes.
Q: How is RNA involved in gene regulation?
A: RNA plays a crucial role in regulating gene expression, through mechanisms like microRNAs (miRNAs) and RNA interference (RNAi).
Q: What are the three components of a nucleotide?
A: A nucleotide consists of:
Nitrogenous base
Sugar (deoxyribose in DNA, ribose in RNA)
Phosphate group
Q: What are DNA and RNA made of?
A: Both are polymers made up of repeating monomer units called nucleotides.
Q: What is a nucleoside?
A: A nucleoside consists of:
A nitrogenous base
A sugar (without the phosphate group)
Q: What is a nucleotide?
A: A nucleotide is a nucleoside with an added phosphate group.
Q: How do DNA and RNA differ in sugar composition?
A: - DNA contains deoxyribose (lacking an oxygen at the 2’ carbon).
RNA contains ribose (with an OH group at the 2’ carbon).
Q: What are the nitrogenous bases in DNA and RNA?
A: - DNA: Adenine (A), Thymine (T), Cytosine (C), Guanine (G)
RNA: Adenine (A), Uracil (U), Cytosine (C), Guanine (G)
Q: What type of chemical structures do DNA and RNA bases have?
A: They are heterocyclic aromatic rings containing carbon and nitrogen with various substituents.
Q: What are the two categories of nitrogenous bases?
A: Purines (bicyclic, two fused rings) and Pyrimidines (monocyclic, one ring).
Q: Which bases are purines?
Q: Which bases are pyrimidines?
A: Adenine (A) and Guanine (G).
A: Cytosine (C), Thymine (T), and Uracil (U).
Q: Which base is found in RNA instead of thymine?
Q: What is thymine also known as?
A: Uracil (U) replaces Thymine (T) in RNA.
A: 5-Methyluracil, because it is chemically similar to uracil with an added methyl (-CH₃) group.
Q: What is tautomerism?
A: Tautomerism is a reaction involving the intramolecular transfer of a proton, resulting in two isomers that readily interconvert.
Q: What catalyzes tautomerization?
A: Tautomerization can be catalyzed by both acid and base.
Q: What sugar is present in RNA nucleosides?
Q: What sugar is present in DNA nucleosides?
A: Ribose, where the R group = OH at the 2’-position.
A: 2’-Deoxyribose, where the R group = H at the 2’-position.
Q: What is a nucleoside?
A: A nucleoside is a nitrogenous base covalently attached to the 1’-position of a pentose sugar, without a phosphate group.
Q: At which position do pyrimidines attach to the sugar?
Q: At which position do purines attach to the sugar?
A: At the 1-position (N-1) of the pyrimidine base.
A: At the 9-position (N-9) of the purine base.
Q: What type of bond connects the nitrogenous base to the sugar?
A: A glycosidic (or glycosylic) bond.
Q: What is a nucleotide?
A: A nucleotide is a nucleoside with one or more phosphate groups covalently attached.
Q: At which positions can the phosphate group attach in nucleotides?
A: Phosphate groups can be attached to the 3’-position, 5’-position, or (in ribonucleotides only) the 2’-position.
Q: What are deoxynucleotides?
A: Nucleotides with a deoxyribose sugar (instead of ribose) are called deoxynucleotides.
Q: How do nucleotides differ from nucleosides?
A: Nucleotides have one or more phosphate groups, while nucleosides lack a phosphate group.
Q: How does the 2’OH group contribute to RNA’s catalytic functions?
A: The 2’OH group is crucial for many of RNA’s catalytic functions, including the activity of ribozymes, which rely on this group for their catalytic properties.
Q: Why is RNA more chemically reactive than DNA?
A: RNA is more reactive because the 2’OH group makes it prone to spontaneous cleavage in solution, whereas DNA lacks this hydroxyl group.
Q: How does the 2’OH group affect the function of RNA and DNA?
A: The presence of the 2’OH group in RNA (missing in DNA) is a key factor in RNA’s chemical reactivity and its ability to perform catalytic functions.
Q: How does the 2’OH group in RNA impact its stability?
A: The 2’OH group in RNA makes it less stable than DNA, as it makes RNA more susceptible to hydrolysis and degradation.
What is polymerisation?
Linking the nucleotides together
Q: How are nucleotides linked in DNA or RNA?
A: Nucleotides are linked by a phosphodiester bond, where a phosphate group connects the 5’-hydroxyl of one nucleotide’s sugar to the 3’-hydroxyl of the next nucleotide’s sugar.
Q: Why is it called a phosphodiester bond?
A: It is called a phosphodiester bond because the phosphate group forms a diester linkage between the two sugars of adjacent nucleotides.
Q: What direction does a nucleic acid chain have?
A: A nucleic acid chain has a direction, with a free 5’-end (which may or may not have attached phosphate groups) and a free 3’-end (which usually has a free hydroxyl group).
Q: How can a nucleic acid chain be described?
A: A nucleic acid chain is a string of nucleotides connected by phosphodiester bonds, forming a linear polymer with directionality.
Q: Do all nucleic acid chains have a free 5’-end and 3’-end?
A: Yes, all nucleic acid chains (except circular ones) have a free 5’-end and a free 3’-end.
Q: What charge does each phosphate group in a nucleic acid have?
Q: What kind of ions are nucleic acids?
Q: How are nucleic acids charged?
A: Each phosphate group carries a single negative charge, making it acidic.
A: Nucleic acids are anions of strong acids due to the negatively charged phosphate groups.
A: Nucleic acids are highly charged polymers because of the negative charges on the phosphate groups in the phosphodiester bonds.
Q: What is the most common structure of DNA?
Q: How are the DNA strands arranged in the double helix?
[what type of double helix]
Q: What is the most common helical form of DNA?
Q: How many phosphates are present per turn in the B-form of DNA?
A: DNA most commonly occurs in nature as the double helix.
A: The DNA strands are two separate chains that are wound around each other, following a helical path, forming a right-handed double helix.
A: The most common helical form of DNA is the B-form.
A: In the B-form, there are 10 phosphates per turn, corresponding to a 360° turn.
Q: Where are the sugar-phosphate backbones located in the DNA double helix?
Q: Where are the bases located in the DNA structure?
A: The sugar-phosphate backbones are on the outside of the DNA helix.
A: The planar bases are stacked on the inside of the helix, protected from the outside environment.
Q: What structures are formed between the two backbone strands in the DNA double helix?
A: The major and minor grooves run between the two backbone strands, following the helical path.
Q: How are the two strands of DNA held together?
A: The strands are held together by non-covalent hydrogen bonding between complementary base pairs.
Q: What is the role of base pairs in DNA?
A: Base pairs form through hydrogen bonds between complementary bases, helping to stabilize the double helix structure.
Q: How are the two DNA strands oriented relative to each other?
Q: What makes the two strands of DNA complementary?
Q: Why do purine-pyrimidine base pairs form in DNA?
Q: How do the bases on opposite strands of DNA bond together?
A: The two DNA strands are oriented antiparallel, meaning one strand runs 5’ to 3’ and the other runs 3’ to 5’.
A: The two strands are complementary in terms of sequence because base pairing follows specific rules, where purines (A, G) pair with pyrimidines (T, C).
A: The structures of the bases and the constraints of the DNA backbone dictate that purine-pyrimidine pairs have similar geometry and dimensions, allowing for stable hydrogen bonding.
A: The bases on opposite strands are joined non-covalently by hydrogen bonds to form complementary base pairs.
Q: Why is DNA a double-stranded molecule?
A: DNA is double-stranded to provide two complementary strands that can act as templates for the copying and repair of genetic information.
Q: How does the second strand of DNA help with repair?
A: The second strand of DNA can serve as a template for repairing a damaged strand, ensuring the accuracy of genetic information.
Q: What role does the double-helix structure play in genetic information storage?
A: The double-helix structure provides a chemically stable environment in which to securely store genetic information, protecting it from external damage.
Q: What is the nucleoid?
A: The nucleoid is an area in prokaryotic cells where the DNA is concentrated, though it is not surrounded by a membrane.
Q: How do complementary strands contribute to genetic fidelity?
A: The complementary strands ensure that genetic information is accurately copied and maintained through replication and repair mechanisms.
Q: How much DNA is in a eukaryotic cell compared to a prokaryotic cell?
A: Eukaryotic cells have thousands of times more DNA than prokaryotic cells, organized into discrete structures called chromosomes. In humans, there are 46 chromosomes.
Q: How is eukaryotic DNA packaged into the nucleus?
A: Eukaryotic DNA must be packaged into the nucleus, which has a volume similar to that of a bacterial cell, resulting in a high DNA concentration of about 200 mg/ml.
Q: What is the composition of chromatin?
A: Chromatin is made up of more than 50% protein, along with DNA.
Q: What is the structure that packages DNA in eukaryotes?
A: DNA is packaged into a nucleoprotein complex called chromatin, which is a highly organized complex of DNA and protein.
Q: How does the level of chromatin condensation change throughout the cell cycle?
A: Chromosomes change their level of condensation, being highly condensed during metaphase (just before cell division) and more diffuse during interphase.
Q: What does the change in chromatin condensation indicate?
A: The change in condensation suggests the existence of different levels of chromatin organization, which help regulate DNA accessibility during the cell cycle.
Q: What is the most common protein in eukaryotic chromatin?
A: Most of the protein in eukaryotic chromatin consists of histones.
Q: What is the charge of histone proteins?
A: Histone proteins have a large positive charge, as 20–30% of their amino acid sequences consist of the basic amino acids lysine and arginine.
Q: How do histones interact with DNA?
A: The positive charge of histones allows them to bind very strongly to the negatively charged DNA, helping to form chromatin.
Q: How are histones organized in chromatin?
A: Histones are assembled into octamers, consisting of 8 subunits, around which the DNA is wrapped.
Q: Why is chromosomal DNA in a highly compact state during mitosis?
A: Chromosomal DNA is highly compact during mitosis to prevent shearing by the forces generated as the daughter chromosomes are pulled apart by the mitotic spindle.
Q: What does the X-structure of a chromosome illustrate?
A: The X-structure represents two identical sister chromatids, which are the products of replication of a single chromosome, joined at their centromeres.
A: The X-structure represents two identical sister chromatids, which are the products of replication of a single chromosome, joined at their centromeres.
Q: What are the tips of chromosomes called?
A: The tips of chromosomes are called telomeres, and they are also the ends of the DNA molecule.
Q: What is the function of telomeres?
A: Telomeres are specialized DNA sequences that form the ends of linear DNA molecules and protect the chromosome ends from degradation and loss of genetic material.
Q: What is the structure of telomeres?
A: Telomeres consist of hundreds of copies of a short repeated sequence (e.g., 5’-TTAGGG-3’ in humans).
Q: Where is the centromere located on a chromosome?
A: The centromere is the constricted region where the two sister chromatids are joined in the metaphase chromosome.
Q: What is a gene?
A: A gene is a functional unit of heredity, containing the information necessary to produce an RNA molecule.
Q: What does a gene sequence encode?
A: A gene sequence encodes the information to make an RNA molecule, which may then be used to synthesize a protein.
Why does DNA run from 5’ to 3’?
DNA goes from 5’ to 3’ because DNA polymerase can only add nucleotides to the 3’ end during synthesis.
