Cell Life Cycle, Nucleic Acids, and DNA Biotechnology - Comprehensive Notes
Learning outcomes (from Page 2):
Understand cell structure and the function and features of cell parts that enable those functions.
Describe organelles of a typical cell and the specific functions of each.
Understand the cell cytoskeleton.
Understand tissue structure and the functions and structural features of major tissue types.
Gain an an understanding of mitosis and the phases of the cell life cycle.
Understand the role of mitosis in renewing/expanding somatic cell populations.
Know fundamental concepts of nucleic acids and analytical tools for qualitative and quantitative measurements of nucleic acids.
Recognize bioengineering applications of nucleic acids.
Cell life cycle overview (Page 3):
Most of a cell’s life is spent in a nondividing state (interphase), during which the cell grows, replicates its DNA, and prepares for division.
Somatic cells, which are all body cells except for gametes, divide through a precisely regulated process involving three main stages:
DNA replication: The process by which the entire genetic material, DNA, is duplicated precisely to ensure that each daughter cell receives a complete and identical set of chromosomes. This occurs during the S phase of interphase.
Mitosis: A form of nuclear division that ensures the accurate segregation of duplicated chromosomes into two identical sets. The genetic material is divided into two equal sets of chromosomes, leading to two genetically identical nuclei.
Cytokinesis: The cytoplasmic division that follows mitosis, resulting in the physical separation of the parent cell into two distinct daughter cells. This process divides the cytoplasm and all cellular organelles.
Interphase details (Page 4):
Interphase is a period of cell growth and DNA replication, preparing the cell for division. It consists of three main phases, and sometimes a quiescent G0 phase:
G0 (G-zero) phase: A resting state where cells are not actively preparing to divide. Cells in G0 typically perform specialized cell functions only (e.g., mature neurons, muscle cells). Cells can enter G0 from G1 and may re-enter the cell cycle under specific conditions or stimuli.
G1 phase (First Gap): The primary growth phase where the cell increases in size, synthesizes proteins and RNA, and duplicates its organelles (such as mitochondria and ribosomes) to prepare for DNA synthesis. Checkpoints within G1 ensure the cell is ready to proceed.
S phase (Synthesis): The crucial phase where DNA replication occurs. Each chromosome is duplicated to form two identical sister chromatids. Histone proteins, essential for packaging DNA into chromatin, are also synthesized during this phase.
G2 phase (Second Gap): A period of further cell growth and preparation for mitosis. The cell synthesizes proteins necessary for cell division, such as microtubules for the spindle apparatus. Centriole replication is completed if the cell is an animal cell. There are also checkpoints here to ensure DNA replication is complete and damage-free before entering mitosis.
Mitosis overview (Page 5):
Mitosis is the process of nuclear division where the duplicated DNA is precisely divided into two sister chromatids.
Prior to mitosis, during prophase, the long, thin DNA molecules, which exist as chromatin, coil tightly and condense extensively to form compact, visible chromatids.
Each duplicated chromosome consists of two identical sister chromatids, which are exact copies of each other.
These sister chromatids remain connected at a constricted region called the centromere. The centromere is vital for chromosome segregation.
A specialized protein complex called the kinetochore forms around each centromere. Kinetochores serve as attachment sites for spindle microtubules, which are responsible for pulling the sister chromatids apart during anaphase.
General cell cycle visuals (Page 6):
During Interphase, the DNA is loosely coiled as chromatin within the nucleus, and individual chromosomes are not visible under a light microscope. The nucleus is clearly present and intact.
Mitosis then follows interphase, characterized by the formation of an organized spindle apparatus (composed of microtubules) that orchestrates chromosome movement and segregation.
Mitosis phases (Pages 7–8):
Mitosis is a continuous process, but it is typically divided into four distinct phases for better understanding:
Prophase:
The chromatin condenses into visible chromosomes, each consisting of two sister chromatids joined at the centromere.
The nucleoli, which are involved in ribosome synthesis, disappear.
In animal cells, the two centriole pairs, which duplicated during interphase, begin to migrate toward opposite poles of the cell, forming the mitotic spindle.
Spindle fibers (microtubules) begin to extend from the centrosomes.
Late prophase (sometimes called prometaphase): The nuclear envelope (nuclear membrane) breaks down into small vesicles. Spindle fibers, now called kinetochore microtubules, attach to the kinetochores on each sister chromatid. Non-kinetochore microtubules overlap at the metaphase plate.
Metaphase:
Chromosomes are maximally condensed and align precisely along the metaphase plate, an imaginary equatorial plane equidistant from the two spindle poles. This alignment ensures that each daughter cell receives one copy of each chromosome.
The kinetochore microtubules are now fully attached to the kinetochores, and the chromosomes are held under tension.
Anaphase:
This is the shortest but most critical phase. Sister chromatids abruptly separate, becoming individual daughter chromosomes.
Microtubules shorten, pulling the daughter chromosomes apart toward opposite poles of the cell, guided by the mitotic spindle.
Simultaneously, the cell elongates as non-kinetochore microtubules push against each other.
Telophase:
The separated daughter chromosomes arrive at the opposite poles of the cell and begin to decondense and uncoil, returning to their chromatin state.
New nuclear membranes (nuclear envelopes) reform around each set of chromosomes at the poles, creating two distinct nuclei.
The nucleoli reappear within each new nucleus.
The mitotic spindle apparatus disassembles.
Cytokinesis:
Typically overlaps with telophase. It is the division of the cytoplasm and organelles, leading to the formation of two distinct, genetically identical daughter cells.
In animal cells, a cleavage furrow forms as a contractile ring of actin and myosin filaments pinches the cell membrane inward.
In plant cells, a cell plate forms in the middle of the cell, eventually developing into a new cell wall separating the two daughter cells.
Meiosis (Pages 9–12):
Meiosis is a specialized form of cell division essential for sexual reproduction. It reduces the chromosome number by half to produce gametes (sex cells: spermatozoa in males, oocytes in females).
Germ cells (precursor cells in gonads) undergo meiosis to give rise to haploid gametes.
Each gamete contains exactly 23 chromosomes (haploid, denoted as ), representing one set of chromosomes.
The fusion of a male gamete (sperm) and a female gamete (egg) during fertilization yields a zygote with 46 chromosomes (diploid, denoted as ). This restores the full set of chromosomes characteristic of the species.
Unlike mitosis, meiosis is not a repeatable cycle for gametes themselves. Once gametes are formed, they contain half the normal number of chromosomes and are specialized for fertilization; they cannot undergo further meiotic divisions.
Meiosis introduces significant genetic diversity through two main mechanisms during Meiosis I:
Reduction division: Meiosis involves two successive divisions (Meiosis I and Meiosis II) that result in a reduction of the chromosome number from diploid () to haploid ().
Recombination (Crossing Over): Exchange of genetic material between homologous chromosomes during Prophase I. This shuffles alleles and creates new combinations of genes on chromosomes.
Independent Assortment: Random alignment of homologous chromosome pairs at the metaphase plate during Metaphase I, leading to various combinations of chromosomes in the resulting gametes.
Key chromosome terms revisited:
Chromatid: A single copy of a duplicated chromosome, joined to its identical sister chromatid at the centromere.
Centromere: The constricted region on a chromosome that links sister chromatids.
Sister chromatids: Two identical copies of a chromosome produced by DNA replication, joined at the centromere.
Chromosome: A structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. Before replication, a chromosome consists of one chromatid; after replication, it consists of two sister chromatids.
Chromosome counts in humans relevant to the cell cycle:
Pre-DNA replication (G1 phase): A somatic cell has chromosomes, each consisting of a single chromatid. So, chromosomes with chromatids.
Post-DNA replication (G2/prophase of mitosis or meiosis I): A somatic cell (or germ cell before meiosis I) still has chromosomes, but each chromosome now consists of two sister chromatids. So, chromosomes with chromatids.
After Meiosis I: Two cells, each with chromosomes, where each chromosome still consists of two chromatids. So, chromosomes with chromatids per cell.
After Meiosis II: Four haploid gametes, each with chromosomes, and each chromosome consists of a single chromatid. So, chromosomes with chromatids per gamete.
Biopolymers and cellular composition (Pages 13–16):
Cells are complex systems composed of various biopolymers, which are large molecules essential for life, along with water, ions, and metabolites.
Cytosolic and nuclear localization of biopolymers: Most biopolymers are found in the cytoplasm (cytosol), while nucleic acids (DNA) are primarily localized within the nucleus (in eukaryotes).
Substance weight composition of a typical cell (approximate percentages):
Water: A solvent, accounting for the largest percentage, crucial for all cellular reactions .
Proteins: Function as enzymes, structural components, transporters, signals; highly diverse .
Nucleic Acids (DNA and RNA): Store and transmit genetic information, involved in protein synthesis .
Carbohydrates: Primary energy source, structural components (e.g., cell walls in plants) .
Lipids: Form cell membranes, energy storage, signaling molecules .
Metabolic intermediates, cofactors, inorganic ions, and trace elements: Involved in various metabolic pathways and cellular functions .
Major polymers ("Polymers of life"):
Nucleic acids (DNA, RNA)
Proteins
Lipids (can form large complexes but are technically not polymers in the same chain-like sense as proteins/nucleic acids)
Carbohydrates (polysaccharides)
Monomers that form these biopolymers:
Nucleotides (for nucleic acids)
Amino acids (for proteins)
Sugars/monosaccharides (for carbohydrates)
Fatty acids and glycerol (for lipids)
Nucleic acids as polymers (Pages 18–19):
Nucleic acids are essential biopolymers responsible for the storage and transmission of genetic information.
Roles and properties:
They are the primary molecules responsible for information storage, dictating the hereditary characteristics of an organism and guiding protein synthesis.
Each nucleic acid monomer, a nucleotide, contains three main components: a phosphate group, a five-carbon sugar (either deoxyribose in DNA or ribose in RNA), and one of four nitrogenous bases.
Two primary types:
Deoxyribonucleic acid (DNA): The genetic material in most organisms, forming a double helix.
Ribonucleic acid (RNA): Plays various roles in gene expression, acting as a messenger, a carrier of amino acids, and a structural component of ribosomes.
DNA structure and base pairing (Pages 20–27):
Double helix structure: The iconic structure of DNA, first described by Watson and Crick, resembling a twisted ladder.
The "rails" or "sides" of the ladder are composed of a repeating sugar–phosphate backbone, formed by alternating deoxyribose sugar molecules and phosphate groups. This backbone provides structural integrity.
The "steps" or "rungs" of the ladder are formed by pairs of nitrogenous bases, which are held together by hydrogen bonds.
The sugar–phosphate backbone is oriented in a direction. This refers to the carbon atoms in the deoxyribose sugar. The carbon (which has a phosphate group attached) and the carbon (which has a hydroxyl group attached) are crucial for forming phosphodiester bonds.
Nucleotide components: Each nucleotide building block of DNA consists of:
A phosphate group (attached to the carbon of the sugar).
A five-carbon sugar: deoxyribose in DNA. It is a monosaccharide that crucially lacks a hydroxyl (-OH) group at its -position (hence "deoxy"). This absence makes DNA more stable and less reactive than RNA.
A nitrogenous base: One of four types: Adenine (A), Thymine (T), Guanine (G), or Cytosine (C).
Polynucleotide formation and backbone connectivity:
Individual nucleotides are linked together to form a polynucleotide strand via phosphodiester bonds. These are strong covalent bonds that connect the -hydroxyl group of one nucleotide's sugar to the -phosphate group of the next nucleotide's sugar, creating the sugar-phosphate backbone.
The sugar-base linkage is a beta-N-glycosidic linkage.
Base pairing rules (Chargaff's Rules): The nitrogenous bases pair specifically across the two strands, forming the "steps" of the ladder:
Adenine (A) always pairs with Thymine (T) via hydrogen bonds.
Guanine (G) always pairs with Cytosine (C) via hydrogen bonds.
The difference in the number of hydrogen bonds ( for A-T, for G-C) contributes to varying stability and melting temperatures of DNA regions.
Complementary strands and antiparallel orientation:
The two polynucleotide chains in a DNA double helix are complementary (the sequence of one strand dictates the sequence of the other based on base pairing rules).
They also run in opposite directions, meaning they are antiparallel (one strand runs , while the other runs ). This antiparallel arrangement is essential for DNA replication and transcription.
DNA base chemistry (Purines vs. Pyrimidines):
Purines: Larger, double-ring nitrogenous bases. These include Adenine (A) and Guanine (G).
Pyrimidines: Smaller, single-ring nitrogenous bases. These include Thymine (T) and Cytosine (C) (and Uracil (U) in RNA).
A purine always pairs with a pyrimidine, ensuring a consistent diameter for the double helix.
RNA structure and properties (Pages 28–31):
RNA is a crucial biopolymer involved in various aspects of gene expression.
RNA as a genetic messenger (mRNA): One of its primary roles is to carry genetic information from DNA in the nucleus to the ribosomes in the cytoplasm, where it serves as a template for protein synthesis.
Structure: Unlike DNA's double helix, RNA is generally single-stranded. However, it can fold into complex three-dimensional shapes due to intramolecular base pairing, which is critical for its function and stability (e.g., tRNA, rRNA).
Nucleotide components: Each RNA nucleotide consists of:
A ribose sugar (a five-carbon sugar that, unlike deoxyribose, possesses a hydroxyl group at the -position). This -OH makes RNA more reactive and less stable than DNA.
A phosphate group.
A nitrogenous base: Adenine (A), Guanine (G), Cytosine (C), or Uracil (U). Uracil replaces Thymine found in DNA.
Directionality: RNA synthesis and readout occur in the direction, meaning new nucleotides are added to the end of the growing RNA strand.
Central dogma and gene expression (Page 32):
The central dogma of molecular biology describes the flow of genetic information within a biological system, typically from DNA to RNA to protein.
DNA replication: The process by which DNA is duplicated, ensuring that genetic material is faithfully copied before cell division (DNA -> DNA). This is essential for heredity.
Transcription: The process of synthesizing an RNA molecule (specifically messenger RNA, mRNA) from a DNA template. This occurs in the nucleus of eukaryotic cells, catalyzed by RNA polymerase. The newly synthesized RNA is then transported to the cytoplasm.
Translation: The process of protein synthesis, where the genetic code carried by mRNA is decoded to produce a specific sequence of amino acids, forming a polypeptide chain (protein). This occurs at ribosomes in the cytoplasm. Transfer RNA (tRNA) molecules act as adaptors, carrying specific amino acids to the ribosome according to the codons on the mRNA. Ribosomal RNA (rRNA) is a key structural and catalytic component of ribosomes themselves.
DNA replication (Page 33):
DNA replication is a semi-conservative process, meaning each new DNA double helix consists of one old (template) strand and one newly synthesized strand.
Key players:
DNA helicase: An enzyme responsible for unwinding and unzipping the DNA double helix by breaking the hydrogen bonds between base pairs. This creates a replication fork, a Y-shaped structure where replication synthesis occurs.
DNA polymerase: The primary enzyme that synthesizes new DNA strands. It adds deoxyribonucleotides complementary to the template strand in a direction. DNA polymerase also has proofreading capabilities to ensure accuracy.
The process occurs bidirectionally from origins of replication, with continuous synthesis on the leading strand and discontinuous synthesis (in Okazaki fragments) on the lagging strand, both proceeding in the direction relative to the new strand.
Transcription (Page 34):
Transcription is the process where the genetic information from DNA is copied into an RNA molecule.
RNA polymerase is the enzyme that unwinds a portion of the DNA double helix and synthesizes an RNA strand using one of the DNA strands as a template.
RNA synthesis proceeds in the direction, meaning RNA polymerase reads the DNA template strand in the direction and adds nucleotides to the end of the growing RNA molecule.
Non-template (coding/sense) strand: This DNA strand has a sequence identical to the newly synthesized RNA molecule (except for T in DNA being U in RNA). It is called "coding" because its sequence directly represents the genetic code for the protein.
Template (antisense/non-coding) strand: This DNA strand is used by RNA polymerase as the blueprint for RNA synthesis. Its sequence is complementary to the RNA molecule.
In eukaryotes, RNA is transcribed in the nucleus, undergoes processing (splicing, capping, polyadenylation), and then the mature mRNA is transported to the cytoplasm for translation.
Types of RNA (Page 35):
Messenger RNA (mRNA): Carries the genetic message from DNA in the nucleus to the ribosomes in the cytoplasm. Its sequence of codons determines the amino acid sequence of a protein.
Transfer RNA (tRNA): A small RNA molecule that acts as an adaptor. It carries a specific amino acid to the ribosome and recognizes the corresponding mRNA codon through its anticodon loop.
Ribosomal RNA (rRNA): A major structural and catalytic component of ribosomes, the cellular machinery responsible for protein synthesis (translation). rRNA forms the core of the ribosome, facilitating peptide bond formation.
DNA analysis and gel electrophoresis (Pages 36–41):
Gel electrophoresis is a widely used molecular biology technique that separates DNA (or RNA or protein) fragments based on their size and charge. It involves applying an electric field to a nucleic acid sample loaded into a porous gel matrix.
Applications:
Verify amplification by sequencing reactions: Confirming the presence and approximate size of DNA fragments after PCR or other amplification techniques before proceeding to sequencing.
Assess quality and quantity of genomic DNA after extraction: Checking for degradation (smearing) and estimating concentration of purified DNA samples.
Separate DNA fragments for cloning: Isolating a specific DNA band of interest from a mixture for further molecular cloning or manipulation.
Forensic analysis (DNA fingerprinting), paternity testing, disease diagnosis (e.g., detecting mutations).
Agarose gel specifics (Page 38):
Agarose is a linear polysaccharide polymer derived from red seaweed. It forms a porous matrix when gelled, through which nucleic acids can migrate. Different concentrations of agarose create gels with different pore sizes, affecting the migration rate of DNA fragments of varying sizes.
Procedure overview (Page 39):
Make the gel: Agarose powder is dissolved in a buffer, heated, and poured into a mold with a comb to create wells.
Load samples: DNA samples (mixed with a loading dye for visualization and density) are carefully pipetted into the wells of the solidified gel.
Cover with buffer: The gel is submerged in a running buffer (e.g., TAE or TBE) that conducts electricity and maintains pH.
Apply power: An electric current is passed through the gel, causing DNA fragments to migrate.
Principles (Page 40):
Charge-based migration: DNA molecules possess a net negative charge due to their phosphate backbone. Therefore, when placed in an electric field, they migrate from the negatively charged cathode toward the positively charged anode.
Size-based separation: The agarose gel acts as a molecular sieve. Smaller DNA fragments can pass more easily through the pores of the gel matrix and thus migrate further and faster than larger fragments.
Migration dependencies: The rate of DNA migration also depends on the electric field strength (higher voltage = faster migration), the type and concentration of the running buffer (influences conductivity and pH), and the density/concentration of the agarose gel (higher concentration = smaller pores = slower migration, better separation of smaller fragments).
Visualization (Page 41):
DNA is typically invisible in the gel. After electrophoresis, DNA bands are observed by applying DNA-binding dyes (e.g., Ethidium Bromide, SYBR Green) that intercalate into the DNA double helix and fluoresce under UV light.
Alternatively, autoradiography can be used if the DNA has been radioactively labeled (e.g., with ), where emitted radiation exposes X-ray film, producing an image of the bands.
Applications of nucleic acids in biomedical engineering (Pages 42–47):
The unique properties of nucleic acids, particularly DNA, make them highly valuable in fields like biomedical engineering and nanotechnology.
Molecular recognition: DNA's exquisite ability for sequence-specific base pairing (A-T, G-C) allows for the design of precise nanoscale structures and devices. This self-assembly property can be programmed for various biomedical applications such as biosensing, targeted drug delivery, and diagnostic tools.
DNA as a generic material: Beyond its biological role as genetic information, DNA is proving to be a versatile and robust engineering material.
Mechanically robust: DNA strands are relatively stable and can withstand certain physical manipulations.
Programmable and engineerable: Its sequence can be precisely designed and synthesized, allowing for the creation of intricate and predictable shapes at the nanoscale. This offers a level of precise manipulation difficult to achieve with most other synthetic polymers.
Efficient processing: DNA can be synthesized, cut, joined, and amplified using well-established molecular biology techniques.
DNA origami (2D and 3D nanostructures) (Page 45):
A revolutionary technique in DNA nanotechnology where a long scaffold strand (usually from a virus like M13 bacteriophage) is folded into predefined two- or three-dimensional shapes using hundreds of short, synthetic staple strands. The staple strands bind to specific regions of the scaffold, holding it in the desired conformation.
2D origami: Typically forms planar, lattice-like geometries, often used for creating patterns or guiding molecular assembly on surfaces.
3D origami: Can form more complex, wireframe, or helical assemblies. These structures have potential for precisely positioning molecules (e.g., enzymes, drugs) or serving as molecular robots.
Example scales related to DNA structure are critical for design:
Diameter of DNA double helix: approximately .
Base-pair spacing: approximately per base pair along the helix.
Helical turn: complete turn of the B-DNA helix contains about base pairs and measures approximately in length.
These dimensions are fundamental for designing precise nanoscale features and spacing in DNA origami structures.
Gene delivery and tissue engineering scaffolds (Page 46):
Nucleic acids (particularly DNA for gene therapy) are delivered to cells to produce therapeutic proteins or modify cell behavior. They can be integrated into tissue engineering scaffolds for controlled release strategies.
Polymeric release: Encapsulating therapeutic DNA/RNA within biodegradable polymer matrices. This allows for controlled and sustained release of the genetic material into the local environment of tissues, which is beneficial for long-term therapeutic effects or tissue regeneration.
Substrate-mediated delivery: Immobilizing DNA directly onto the surface of tissue engineering scaffolds (e.g., biomaterial implants). This approach facilitates localized and targeted delivery of genetic material to cells interacting with the scaffold, promoting desired cellular responses (e.g., cell differentiation, tissue growth).
Takeaway (Page 47): DNA is not merely the carrier of genetic information but also a highly versatile, programmable material that can be engineered at the nanoscale to create novel structures and devices with significant practical implications in diagnostics, therapeutics, and regenerative medicine. This field is known as nucleic acid engineering.
Practical and ethical considerations (implicit across content):
The discussion of powerful capabilities in DNA nanotechnology and gene delivery inherently raises important real-world implications. These include:
Biosafety: Ensuring DNA-based technologies are safe for human health and the environment (e.g., preventing unintended immune responses, off-target effects, environmental spread of modified organisms).
Ethical considerations: Issues surrounding germline editing, gene editing in humans, equitable access to advanced therapies, and potential dual-use concerns (misuse of technology). These topics are crucial for responsible development and application of nucleic acid-based bioengineering.
References (Page 48):
Key sources include Nature Scitable, current opinions in colloids and interface science, Nature Communications, and foundational biochemistry texts.
Connections to foundational principles
Central dogma: Provides a unifying framework for understanding how genetic information flows from DNA to RNA to protein. This interconnected process (DNA replication, transcription (DNA -> RNA), translation (RNA -> protein)) is fundamental to all life.
Cell cycle control: The precise regulation of interphase (G1, S, G2) and mitotic phases (M) ensures accurate cell division, which is critical for tissue growth, repair, and renewal in multicellular organisms. Meiosis specifically ensures the production of genetically diverse gametes for sexual reproduction. Checkpoints throughout the cell cycle prevent uncontrolled proliferation and ensure genetic integrity.
Structure–function relationship: This principle is evident at multiple levels:
The physical structure of DNA (reiterated double helix, antiparallel strands, specific base pairing via hydrogen bonds) is directly responsible for its ability to replicate faithfully, serve as a template for transcription, and maintain genetic fidelity.
The higher-order organization of chromosomes (e.g., condensation into chromatids, the role of the centromere as an attachment point, and the function of the kinetochore in connecting to spindle fibers) explicitly drives the mechanical process of chromosome segregation during mitosis and meiosis.
Biopolymer diversity and function: Cells are complex biochemical factories. Their fundamental composition of water and major biopolymers (nucleic acids, proteins, carbohydrates, and lipids), each present in specific weight percentages, underpins all cellular processes. Each type of polymer has unique structural, catalytic, energy storage, or signaling roles essential for life.
Technology and ethics note: The dual nature of nucleic acids, serving as both carriers of biological information and programmable engineered materials, opens vast opportunities in biomedical engineering but also necessitates careful consideration of associated ethical issues, biosafety protocols, and governance frameworks to ensure responsible innovation.
Important formulas and identifiers (LaTeX)
Hydrogen bonding in base pairs:
Directionality of nucleic acids synthesis/reading:
DNA haploid/diploid chromosome counts in humans:
Haploid gametes: chromosomes
Diploid somatic cells: chromosomes
Composition by weight of a typical cell (approximate values):
Water:
Proteins:
Nucleic Acids:
Carbohydrates:
Lipids:
Metabolic intermediates and cofactors:
Key structural dimensions mentioned in DNA origami figures (approximate for B-DNA):
Diameter of DNA double helix: approximately
Base-pair spacing (rise per base pair): approximately per base pair
Helical turn length and pitch: (meaning per turn based on pitch per bp)
These precise dimensions are fundamental for engineering nanoscale structures using DNA.
Some terms to recall for exams
Centromere: The constricted region on a chromosome that links sister chromatids and serves as the attachment point for spindle fibers.
Kinetochore: A protein complex assembled on the centromere, providing the attachment site for microtubules of the mitotic spindle.
Chromatid: One of two identical copies of a chromosome produced during DNA replication, still joined to its sister chromatid.
Sister chromatids: Two identical chromatids joined together at the centromere, representing a duplicated chromosome.
Metaphase plate: An imaginary plane in the cell's equator where chromosomes align during metaphase of mitosis and meiosis.
Phosphodiester bond: The covalent bond that links nucleotides together in a nucleic acid chain, forming the sugar-phosphate backbone (between the -OH of one sugar and the -phosphate of the next).
Beta-N-glycosidic linkage: The covalent bond connecting a nitrogenous base to the carbon of the sugar in a nucleotide.
Antiparallel strands: Refers to the opposite orientation of the two complementary strands in a DNA double helix (one , the other ).
Complementary base pairing: The specific pairing of purine bases with pyrimidine bases (A with T/U, G with C) via hydrogen bonds, fundamental to DNA structure and function.
Types of RNA:
mRNA (Messenger RNA): Carries genetic code from DNA to ribosomes.
tRNA (Transfer RNA): Carries specific amino acids to the ribosome during translation.
rRNA (Ribosomal RNA): A component of ribosomes, essential for protein synthesis.
Gel electrophoresis principles: A technique that separates DNA fragments based on size and charge using an electric field and a porous gel matrix. Key concepts include DNA's negative charge, migration toward the positive electrode, and smaller fragments migrating faster/further.
DNA origami concept: A nanotechnology technique using a long scaffold DNA strand and numerous short staple strands to fold DNA into precisely designed 2D and 3D nanostructures.
Gene delivery concepts: Methods for introducing genetic material into cells, including encapsulation in polymeric scaffolds (polymeric release) or immobilization on substrate surfaces (substrate-mediated delivery) for controlled and localized therapeutic effects.