The nucleotide monomers in a nucleic acid polymer are connected by phosphodiester bonds. And you can see these here in our diagrams of DNA and RNA. Here is a phosphodiester bond in DNA and here is a phosphodiester bond in RNA. Now, the individual strands of DNA are actually said to be antiparallel to each other. And the way I like to think of this is if you look at a strand of DNA and generally speaking, we read the code of DNA in the 5' to 3' direction. So if you look at a strand of DNA, you notice that at one end, we have the 5' end and the 5' end is going to have a phosphate group on it. And at the other end, we have a 3' end and that's going to have a hydroxyl group on it. So if you notice, on the other side, the 3' end and the 5' end are actually flipped from the other strand. So if you think about this as an arrow, an arrow that points from 5' to 3'. You can see if I draw my arrows on the two sides of DNA, they are going in directions. They are parallel to each other but they are pointing in opposite directions and that's what we mean when we say antiparallel. That's basically the definition of the term. So, two parallel lines pointing in opposite directions, just like we have here in DNA. If you think of the 3' and 5' ends as different ends of an arrow. Again, it's important to remember that your 5' end is going to be the one with the phosphate group because the phosphate group is attached to the 5' carbon of your pentose sugar. Likewise, your 3' end is going to be the one with the hydroxyl group because that hydroxyl group is attached to the 3' carbon. So, that's where these ends in this naming convention are coming from. It's just coming from the carbon numbers. Now, RNA is actually less stable than DNA and that's because at high pH, this 2' hydroxyl group is reactive and it can actually react with the phosphate group next door, basically, and what you'll wind up with is some kind of structure that looks like this. You know, I'm kind of half drawing my sugar here, but it'll basically react with itself and of course, that's bad. It can cause the strand to break in half or whatever. So, because of this, DNA has been favored as the genetic information on the 3' on the 2' carbon. So, there are some It's thought that very early life forms would have used RNA as their genetic storage. But over the course of evolution, DNA has been, like vastly favored by comparison to RNA. Because basically, all life uses DNA. You know, some viruses use RNA, as their genetic information storage. But that begs the question of are viruses even alive and, you know, that's a whole other tangent. So the main point is DNA much more stable and it's all because of, the absence of that 2' hydroxyl group. Now, nucleotides and nucleic acids, it's important to remember they have this property where they absorb light, they absorb the maximum amount of light at 260 nanometers. The wavelength, 260 nanometers. This is important because proteins absorb light maximally at 280 nanometers. Nanometers. And you might remember it's actually the amino acids, tryptophan, and tyrosine that are doing the most absorption of light at that frequency or at that wavelength. So, this is important because it allows biochemists a really easy way to test for, the presence or absence of DNA versus protein. So if you're trying to isolate something from a cell for example, you're trying to isolate its DNA, you can go through you know the various steps and then test your sample by running it through a spectrophotometer and seeing what lengths it absorbs. If it's only absorbing at 260 and it's not absorbing at 280, then you know you probably got rid of the proteins and you just have your nucleic acids there. So, a small property but an important fact to know. Now, the two strands of DNA are said to be complementary. And basically, that means that the code on one strand complements the code on the other strand and this is due to the specificity of base pairing. And basically, what that means is there are specific rules that guide base pairing and those rules more or less are what we see, below here. So we have in on the left here, we have an adenine that is binding to thymine. And on the right, you can see that we have a guanine and I'm just going to take myself out of the image so you can see this better. We have a guanine binding to cytosine. Now, a couple of things to note here. First, adenine and thymine are forming 2 H bonds. Whereas, guanine and cytosine are forming 3 H bonds. Now, this is important because it's going to result in strands of DNA with higher GC composition having a higher melting temperature or just generally being harder to separate and it literally comes from the fact that they're going to have more hydrogen bonds holding the strands of DNA together making them stick together stronger. Another important thing to note is while while RNA is generally you know in in the areas we're going to be exploring, is generally going to be single stranded. Its bases, it can be double stranded first of all but its bases will also form these bonds with DNA during gene expression and during the transcription process. So, what I'm getting to here is that when that happens, adenine will actually be binding with uracil just like we see it, with thymine here and let me like put this in parenthesis. That's not what we are that's not what this image is but, that's what is the presence of this methyl group there. But yeah. So the basic story is because there are these specific base pairing rules, if you have one strand of DNA or just a single strand piece of RNA, you can very easily determine what the complementary strand is. In fact, that's how genetic information is transmitted in the cell. So, a little thought experiment here. What percentage of DNA is going to be made up of purines and what percentage is going to be made up of pyrimidines? Well, let's think about this for a second. Adenine always pairs with thymine, right? And guanine always pairs with cytosine. Now, adenine and guanine are both purines and thymine and cytosine are both pyrimidines. So, that means that we're always going to have a purine bind to a pyrimidine meaning that DNA is going to be 50% purines 50% pyrimidines. This is actually very important because it means that the width of the double stranded DNA is going to be consistent. It's always going to have the same width and you can see that, that's determined by the fact that we have the 2 ring structure and the 1 ring structure always binding to each other and that's the width will be the same regardless if it's a GC pair or an AT pair. So always going to be 50% purines, 50% pyrimidines. Now, let's do another little thought experiment here. If a piece of double-stranded DNA has 35% adenine and 15% cytosine, how much thymine and guanine is it going to have? Sort of in a similar line of thinking to the last problem, if there's 35 percent adenine, then that means there has to be 35% thymine, right? Because adenine is always going to be bound to thymine. Likewise, if there's 15% cytosine, then there's going to have to be 15% guanine because cytosine always binds to guanine. So, you're going to find those in equal amounts. Now, let's flip the page and talk a little bit more about these ideas we've just explored.
- 1. Introduction to Biochemistry4h 34m
- What is Biochemistry?5m
- Characteristics of Life12m
- Abiogenesis13m
- Nucleic Acids16m
- Proteins12m
- Carbohydrates8m
- Lipids10m
- Taxonomy10m
- Cell Organelles12m
- Endosymbiotic Theory11m
- Central Dogma22m
- Functional Groups15m
- Chemical Bonds13m
- Organic Chemistry31m
- Entropy17m
- Second Law of Thermodynamics11m
- Equilibrium Constant10m
- Gibbs Free Energy37m
- 2. Water3h 23m
- 3. Amino Acids8h 10m
- Amino Acid Groups8m
- Amino Acid Three Letter Code13m
- Amino Acid One Letter Code37m
- Amino Acid Configuration20m
- Essential Amino Acids14m
- Nonpolar Amino Acids21m
- Aromatic Amino Acids14m
- Polar Amino Acids16m
- Charged Amino Acids40m
- How to Memorize Amino Acids1h 7m
- Zwitterion33m
- Non-Ionizable Vs. Ionizable R-Groups11m
- Isoelectric Point10m
- Isoelectric Point of Amino Acids with Ionizable R-Groups51m
- Titrations of Amino Acids with Non-Ionizable R-Groups44m
- Titrations of Amino Acids with Ionizable R-Groups38m
- Amino Acids and Henderson-Hasselbalch44m
- 4. Protein Structure10h 4m
- Peptide Bond18m
- Primary Structure of Protein31m
- Altering Primary Protein Structure15m
- Drawing a Peptide44m
- Determining Net Charge of a Peptide42m
- Isoelectric Point of a Peptide37m
- Approximating Protein Mass7m
- Peptide Group22m
- Ramachandran Plot26m
- Atypical Ramachandran Plots12m
- Alpha Helix15m
- Alpha Helix Pitch and Rise20m
- Alpha Helix Hydrogen Bonding24m
- Alpha Helix Disruption23m
- Beta Strand12m
- Beta Sheet12m
- Antiparallel and Parallel Beta Sheets39m
- Beta Turns26m
- Tertiary Structure of Protein16m
- Protein Motifs and Domains23m
- Denaturation14m
- Anfinsen Experiment20m
- Protein Folding34m
- Chaperone Proteins19m
- Prions4m
- Quaternary Structure15m
- Simple Vs. Conjugated Proteins10m
- Fibrous and Globular Proteins11m
- 5. Protein Techniques14h 5m
- Protein Purification7m
- Protein Extraction5m
- Differential Centrifugation15m
- Salting Out18m
- Dialysis9m
- Column Chromatography11m
- Ion-Exchange Chromatography35m
- Anion-Exchange Chromatography38m
- Size Exclusion Chromatography28m
- Affinity Chromatography16m
- Specific Activity16m
- HPLC29m
- Spectrophotometry51m
- Native Gel Electrophoresis23m
- SDS-PAGE34m
- SDS-PAGE Strategies16m
- Isoelectric Focusing17m
- 2D-Electrophoresis23m
- Diagonal Electrophoresis29m
- Mass Spectrometry12m
- Mass Spectrum47m
- Tandem Mass Spectrometry16m
- Peptide Mass Fingerprinting16m
- Overview of Direct Protein Sequencing30m
- Amino Acid Hydrolysis10m
- FDNB26m
- Chemical Cleavage of Bonds29m
- Peptidases1h 6m
- Edman Degradation30m
- Edman Degradation Sequenator and Sequencing Data Analysis4m
- Edman Degradation Reaction Efficiency20m
- Ordering Cleaved Fragments21m
- Strategy for Ordering Cleaved Fragments58m
- Indirect Protein Sequencing Via Geneomic Analyses24m
- 6. Enzymes and Enzyme Kinetics13h 38m
- Enzymes24m
- Enzyme-Substrate Complex17m
- Lock and Key Vs. Induced Fit Models23m
- Optimal Enzyme Conditions9m
- Activation Energy24m
- Types of Enzymes41m
- Cofactor15m
- Catalysis19m
- Electrostatic and Metal Ion Catalysis11m
- Covalent Catalysis18m
- Reaction Rate10m
- Enzyme Kinetics24m
- Rate Constants and Rate Law35m
- Reaction Orders52m
- Rate Constant Units11m
- Initial Velocity31m
- Vmax Enzyme27m
- Km Enzyme42m
- Steady-State Conditions25m
- Michaelis-Menten Assumptions18m
- Michaelis-Menten Equation52m
- Lineweaver-Burk Plot43m
- Michaelis-Menten vs. Lineweaver-Burk Plots20m
- Shifting Lineweaver-Burk Plots37m
- Calculating Vmax40m
- Calculating Km31m
- Kcat46m
- Specificity Constant1h 1m
- 7. Enzyme Inhibition and Regulation 8h 42m
- Enzyme Inhibition13m
- Irreversible Inhibition12m
- Reversible Inhibition9m
- Inhibition Constant26m
- Degree of Inhibition15m
- Apparent Km and Vmax29m
- Inhibition Effects on Reaction Rate10m
- Competitive Inhibition52m
- Uncompetitive Inhibition33m
- Mixed Inhibition40m
- Noncompetitive Inhibition26m
- Recap of Reversible Inhibition37m
- Allosteric Regulation7m
- Allosteric Kinetics17m
- Allosteric Enzyme Conformations33m
- Allosteric Effectors18m
- Concerted (MWC) Model25m
- Sequential (KNF) Model20m
- Negative Feedback13m
- Positive Feedback15m
- Post Translational Modification14m
- Ubiquitination19m
- Phosphorylation16m
- Zymogens13m
- 8. Protein Function 9h 41m
- Introduction to Protein-Ligand Interactions15m
- Protein-Ligand Equilibrium Constants22m
- Protein-Ligand Fractional Saturation32m
- Myoglobin vs. Hemoglobin27m
- Heme Prosthetic Group31m
- Hemoglobin Cooperativity23m
- Hill Equation21m
- Hill Plot42m
- Hemoglobin Binding in Tissues & Lungs31m
- Hemoglobin Carbonation & Protonation19m
- Bohr Effect23m
- BPG Regulation of Hemoglobin24m
- Fetal Hemoglobin6m
- Sickle Cell Anemia24m
- Chymotrypsin18m
- Chymotrypsin's Catalytic Mechanism38m
- Glycogen Phosphorylase21m
- Liver vs Muscle Glycogen Phosphorylase21m
- Antibody35m
- ELISA15m
- Motor Proteins14m
- Skeletal Muscle Anatomy22m
- Skeletal Muscle Contraction45m
- 9. Carbohydrates7h 49m
- Carbohydrates19m
- Monosaccharides15m
- Stereochemistry of Monosaccharides33m
- Monosaccharide Configurations32m
- Cyclic Monosaccharides20m
- Hemiacetal vs. Hemiketal19m
- Anomer14m
- Mutarotation13m
- Pyranose Conformations23m
- Common Monosaccharides33m
- Derivatives of Monosaccharides21m
- Reducing Sugars21m
- Reducing Sugars Tests19m
- Glycosidic Bond48m
- Disaccharides40m
- Glycoconjugates12m
- Polysaccharide7m
- Cellulose7m
- Chitin8m
- Peptidoglycan12m
- Starch13m
- Glycogen14m
- Lectins16m
- 10. Lipids5h 49m
- Lipids15m
- Fatty Acids30m
- Fatty Acid Nomenclature11m
- Omega-3 Fatty Acids12m
- Triacylglycerols11m
- Glycerophospholipids24m
- Sphingolipids13m
- Sphingophospholipids8m
- Sphingoglycolipids12m
- Sphingolipid Recap22m
- Waxes5m
- Eicosanoids19m
- Isoprenoids9m
- Steroids14m
- Steroid Hormones11m
- Lipid Vitamins19m
- Comprehensive Final Lipid Map13m
- Biological Membranes16m
- Physical Properties of Biological Membranes18m
- Types of Membrane Proteins8m
- Integral Membrane Proteins16m
- Peripheral Membrane Proteins12m
- Lipid-Linked Membrane Proteins21m
- 11. Biological Membranes and Transport 6h 37m
- Biological Membrane Transport21m
- Passive vs. Active Transport18m
- Passive Membrane Transport21m
- Facilitated Diffusion8m
- Erythrocyte Facilitated Transporter Models30m
- Membrane Transport of Ions29m
- Primary Active Membrane Transport15m
- Sodium-Potassium Ion Pump20m
- SERCA: Calcium Ion Pump10m
- ABC Transporters12m
- Secondary Active Membrane Transport12m
- Glucose Active Symporter Model19m
- Endocytosis & Exocytosis18m
- Neurotransmitter Release23m
- Summary of Membrane Transport21m
- Thermodynamics of Membrane Diffusion: Uncharged Molecule51m
- Thermodynamics of Membrane Diffusion: Charged Ion1h 1m
- 12. Biosignaling9h 45m
- Introduction to Biosignaling44m
- G protein-Coupled Receptors32m
- Stimulatory Adenylate Cyclase GPCR Signaling42m
- cAMP & PKA28m
- Inhibitory Adenylate Cyclase GPCR Signaling29m
- Drugs & Toxins Affecting GPCR Signaling20m
- Recap of Adenylate Cyclase GPCR Signaling5m
- Phosphoinositide GPCR Signaling58m
- PSP Secondary Messengers & PKC27m
- Recap of Phosphoinositide Signaling7m
- Receptor Tyrosine Kinases26m
- Insulin28m
- Insulin Receptor23m
- Insulin Signaling on Glucose Metabolism57m
- Recap Of Insulin Signaling in Glucose Metabolism6m
- Insulin Signaling as a Growth Factor1h 1m
- Recap of Insulin Signaling As A Growth Factor9m
- Recap of Insulin Signaling1m
- Jak-Stat Signaling25m
- Lipid Hormone Signaling15m
- Summary of Biosignaling13m
- Signaling Defects & Cancer20m
- Review 1: Nucleic Acids, Lipids, & Membranes2h 47m
- Nucleic Acids 19m
- Nucleic Acids 211m
- Nucleic Acids 34m
- Nucleic Acids 44m
- DNA Sequencing 19m
- DNA Sequencing 211m
- Lipids 111m
- Lipids 24m
- Membrane Structure 110m
- Membrane Structure 29m
- Membrane Transport 18m
- Membrane Transport 24m
- Membrane Transport 36m
- Practice - Nucleic Acids 111m
- Practice - Nucleic Acids 23m
- Practice - Nucleic Acids 39m
- Lipids11m
- Practice - Membrane Structure 17m
- Practice - Membrane Structure 25m
- Practice - Membrane Transport 16m
- Practice - Membrane Transport 26m
- Review 2: Biosignaling, Glycolysis, Gluconeogenesis, & PP-Pathway3h 12m
- Biosignaling 19m
- Biosignaling 219m
- Biosignaling 311m
- Biosignaling 49m
- Glycolysis 17m
- Glycolysis 27m
- Glycolysis 38m
- Glycolysis 410m
- Fermentation6m
- Gluconeogenesis 18m
- Gluconeogenesis 27m
- Pentose Phosphate Pathway15m
- Practice - Biosignaling13m
- Practice - Bioenergetics 110m
- Practice - Bioenergetics 216m
- Practice - Glycolysis 111m
- Practice - Glycolysis 27m
- Practice - Gluconeogenesis5m
- Practice - Pentose Phosphate Path6m
- Review 3: Pyruvate & Fatty Acid Oxidation, Citric Acid Cycle, & Glycogen Metabolism2h 26m
- Pyruvate Oxidation9m
- Citric Acid Cycle 114m
- Citric Acid Cycle 27m
- Citric Acid Cycle 37m
- Citric Acid Cycle 411m
- Metabolic Regulation 18m
- Metabolic Regulation 213m
- Glycogen Metabolism 16m
- Glycogen Metabolism 28m
- Fatty Acid Oxidation 111m
- Fatty Acid Oxidation 28m
- Citric Acid Cycle Practice 17m
- Citric Acid Cycle Practice 26m
- Citric Acid Cycle Practice 32m
- Glucose and Glycogen Regulation Practice 14m
- Glucose and Glycogen Regulation Practice 26m
- Fatty Acid Oxidation Practice 14m
- Fatty Acid Oxidation Practice 27m
- Review 4: Amino Acid Oxidation, Oxidative Phosphorylation, & Photophosphorylation1h 48m
- Amino Acid Oxidation 15m
- Amino Acid Oxidation 211m
- Oxidative Phosphorylation 18m
- Oxidative Phosphorylation 210m
- Oxidative Phosphorylation 310m
- Oxidative Phosphorylation 47m
- Photophosphorylation 15m
- Photophosphorylation 29m
- Photophosphorylation 310m
- Practice: Amino Acid Oxidation 12m
- Practice: Amino Acid Oxidation 22m
- Practice: Oxidative Phosphorylation 15m
- Practice: Oxidative Phosphorylation 24m
- Practice: Oxidative Phosphorylation 35m
- Practice: Photophosphorylation 15m
- Practice: Photophosphorylation 21m
Nucleic Acids 2 - Online Tutor, Practice Problems & Exam Prep
Nucleic acids, such as DNA and RNA, are polymers of nucleotides linked by phosphodiester bonds. DNA strands are anti-parallel, with a 5' phosphate end and a 3' hydroxyl end. DNA is more stable than RNA due to the absence of a reactive 2' hydroxyl group. Base pairing rules dictate that adenine pairs with thymine (2 H bonds) and guanine pairs with cytosine (3 H bonds), leading to consistent DNA width. This complementary nature ensures that DNA is 50% purines and 50% pyrimidines, crucial for genetic information transmission.
Nucleic Acids 2
Video transcript
Here’s what students ask on this topic:
What are phosphodiester bonds and how do they function in nucleic acids?
Phosphodiester bonds are the linkages between nucleotide monomers in nucleic acid polymers like DNA and RNA. These bonds form between the 3' hydroxyl group of one nucleotide and the 5' phosphate group of the next nucleotide. This creates a sugar-phosphate backbone that is essential for the structure of nucleic acids. In DNA, these bonds contribute to the stability and integrity of the double helix, while in RNA, they are part of the single-stranded structure. The formation of phosphodiester bonds is catalyzed by enzymes like DNA polymerase during DNA replication and RNA polymerase during transcription.
Why are DNA strands described as anti-parallel?
DNA strands are described as anti-parallel because they run in opposite directions. One strand runs from the 5' to 3' direction, while the complementary strand runs from 3' to 5'. This orientation is crucial for the proper base pairing and the overall stability of the DNA double helix. The 5' end of a DNA strand has a phosphate group attached to the 5' carbon of the sugar, while the 3' end has a hydroxyl group attached to the 3' carbon. This anti-parallel arrangement allows for the complementary base pairing of adenine with thymine and guanine with cytosine.
How does the stability of DNA compare to RNA, and why?
DNA is more stable than RNA primarily due to the absence of a 2' hydroxyl group in its sugar component. In RNA, the presence of the 2' hydroxyl group makes it more reactive and susceptible to hydrolysis, especially under alkaline conditions. This increased reactivity can lead to strand breakage. DNA's stability is further enhanced by its double-stranded structure, which provides additional protection against chemical and enzymatic degradation. This stability is one reason why DNA is the preferred molecule for long-term genetic information storage in most organisms.
What is the significance of base pairing rules in DNA?
Base pairing rules in DNA are crucial for maintaining the structure and function of the molecule. Adenine (A) pairs with thymine (T) via two hydrogen bonds, and guanine (G) pairs with cytosine (C) via three hydrogen bonds. These specific pairings ensure that the DNA double helix has a consistent width and that genetic information can be accurately copied during DNA replication. The complementary nature of base pairing also allows for the accurate transcription of DNA into RNA, which is essential for protein synthesis. These rules are fundamental to the fidelity of genetic information transmission.
How can you determine the presence of DNA versus protein using spectrophotometry?
To determine the presence of DNA versus protein using spectrophotometry, you measure the absorbance of your sample at specific wavelengths. DNA absorbs light maximally at 260 nm, while proteins absorb maximally at 280 nm, primarily due to the amino acids tryptophan and tyrosine. By running your sample through a spectrophotometer and observing the absorbance peaks, you can distinguish between DNA and protein. If the sample shows a peak at 260 nm and not at 280 nm, it indicates the presence of DNA with minimal protein contamination. This method is widely used in molecular biology for nucleic acid purification and quantification.