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Acids vs Bases: What's the Difference?

Lemon juice, vinegar, soap, bleach, your own stomach — acids and bases are everywhere, and telling them apart is one of the first big skills in chemistry. The good news: the core idea is simple. The short answer: acids release hydrogen ions (H⁺) when dissolved in water and have a pH below 7. Bases do the opposite — they accept H⁺ (or release hydroxide ions, OH⁻) and have a pH above 7. Acids and bases are chemical opposites, and when they meet they cancel each other out. Quick comparison at a glance Feature Acids Bases What they do in water Release H⁺ ions Release OH⁻ ions (or accept H⁺) pH value Below 7 Above 7 Taste (never taste in a lab!) Sour Bitter Feel — Slippery / soapy Litmus paper Turns blue litmus red Turns red litmus blue Everyday examples Lemon juice, vinegar, HCl Soap, baking soda, NaOH, ammonia Reacts with Bases (neutralization) Acids (neutralization) What is an acid? An acid is a substance that produces hydrogen ions (H⁺) when dissolved in water. This ...
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What Is the Mole? Avogadro's Number Made Simple

If the word "mole" makes you picture a small animal, you're not alone — but in chemistry it's one of the most useful ideas you'll ever learn. It's also one that trips students up, usually because it sounds more complicated than it is. The short answer: a mole is just a counting unit for very small things, like atoms and molecules. One mole always means 6.022 × 10²³ of something. That huge number is called Avogadro's number . A mole is just a "chemist's dozen" You already use counting words every day: A pair = 2 A dozen = 12 A ream of paper = 500 A mole works exactly the same way — it's a name for a specific quantity. The only difference is the size: one mole = 6.022 × 10²³ particles. We need such a giant number because atoms are unimaginably tiny, and even a pinch of any substance contains trillions upon trillions of them. Why chemists count in moles You can't count atoms one by one — but you can weigh things. The m...
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Ionic vs Covalent Bonds: What's the Difference?

If you've ever stared at a chemistry question and thought "wait, is this ionic or covalent?" — you're in the right place. It's one of the most common sticking points in high school and intro college chemistry, and once it clicks, a huge amount of the rest of the course gets easier. The short answer: an ionic bond forms when one atom transfers electrons to another (usually a metal handing electrons to a nonmetal). A covalent bond forms when two atoms share electrons (usually two nonmetals). Transfer versus share — that's the heart of it. Let's unpack what that actually means, how to tell the two apart in seconds, and look at examples you'll recognize. Quick comparison at a glance Feature Ionic bond Covalent bond How it forms Electrons are transferred Electrons are shared Typical atoms Metal + nonmetal Nonmetal + nonmetal Particles produced Ions (a cation and an anion) Molecules Electronegativity difference Large (roughly > 1.7) Small ...
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Current Limitations of CAR-T Cell Therapy I - Antigen Escape

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Antigen Escape Antigen Escape is one of the most concerning challenges during the clinical development of CAR-T cell therapy. A robust initial response is often followed by a relapse in many trials. This is often due to the downregulation or the complete loss of target antigens on the tumor cells. Introduction Antigen escape describes the development of tumor resistance to a single antigen targeting CAR construct. After the initial encounter with the CAR-T cells, the malignant cells mutate and show partial or complete loss of the target antigen expression.  In patients with ALL treated with CD19-targeted CAR-T cell therapy, a downregulation or loss of CD19 antigens was observed.  In patients with myeloma treated with BCMA-targeted CAR-T cell therapy, a downregulation or loss of BCMA expression was observed.  In patients with glioblastoma, a solid tumor treated with IL13Ra2-targeted CAR-T cell therapy, a downregulation of IL13Ra2 expression was observed.  Improve...
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The structure of Chimeric Antigen Receptor (CAR) III - Transmembrane Domains

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Transmembrane Domains Among the four components of a chimeric antigen receptor (CAR), the transmembrane domain is the least studied one. How different transmembrane domains affect and contribute to each other's functions is also not well studied. That being said, we will go through the function of a transmembrane domain of a CAR, the CD3ζ transmembrane domain, and the CD8α transmembrane domain.  Introduction of the transmembrane domain The transmembrane domain is where the transmembrane proteins are located. In a CAR, the transmembrane domain has the function to anchor the CAR to the T cell membrane. How strong the CAR is anchored to the T cell membrane affects the CAR expression level and stability.  Currently, the commonly used transmembrane domain is derived from proteins such as CD3ζ, CD4, CD8α, and CD28. The CD3ζ transmembrane domain Among the transmembrane domains mentioned, the CD3ζ transmembrane may improve CAR-mediated T cell action as the CD3ζ transmembrane medi...
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The structure of Chimeric Antigen Receptor (CAR) I - Extracellular Target Antigen Binding Domains

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Antigen Binding Domains The antigen-binding domain of a chimeric antigen receptor is like the head of a train. It determines the target antigen specificity.  The antigen-binding site is made up of a heavy chain and a light chain joined together to form a single-chain variable fragment (scFv).  Single-chain variable fragment (scFv) scFv targets extracellular surface cancer antigens, the biomarkers of the tumor cells. Classically, CD19 is presented in B cells in leukemia. Hence, CD19 is the biomarker that we want the CAR to recognize and bind with it. Once the scFv of a CAR binds with the target antigen, the immune response, major histocompatibility complex (MHC)-independent T cell activation, results. This is when a cascade of molecular signaling starts to trigger an immune response to kill the tumor cells.  MHC-dependent, T cell receptors (TCR)-mimic CARs Some may call it an improvement, but a T cell receptor (TCR)-mimic CAR functions well when it targets intracellular tu...
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The structure of Chimeric Antigen Receptor (CAR) IV - Intracellular Signaling Domains

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Intracellular Signaling Domain(s) Intracellular signaling domains get the most attention as we talk about CAR-T cell therapy because it affects how CAR constructs are generated in the T cells and initiate CAR co-stimulation.  The intracellular signaling domain is the research topic where all the cell engineering happens and gets all the attention for future improvement. What co-stimulatory domain(s) is/are presented in the CAR? What co-stimulatory domains need to be avoided to decrease the likelihood of activation-induced cell death (AICD)? These are questions that cell engineers and researchers ask as they finetune the fourth component of a chimeric antigen receptor to target tumor cells.  Since the first generation of CARs is built in the late 1990s, we now mainly have three generations of CARs as the iteration happened.  First-generation CARs The very first generation of CARs built in the late 1990s contains a CD3ζ or FcRγ signaling domain. Clinical Responses Most of t...
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