## The Building Blocks: 20 Amino Acids [4ccd854b9baf] 1. Proteins are made up of smaller units called **amino acids**, of which there are **20 standard types** encoded by the genetic code. 2. Each amino acid has a unique side chain, known as an **R-group**, which gives it specific properties, such as being **polar**, **non-polar**, **acidic**, or **basic**. 3. These chemical differences allow proteins to perform a vast array of functions. [{"_key":"block_6","_type":"block","asset":null,"children":[{"_key":"51572bb10d17","_type":"span","markDefs":[],"marks":[],"text":"Although there are 20 standard amino acids, some organisms can chemically modify these after synthesis, adding even more diversity to their proteins."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] ## Infinite Combinations: How Sequence Determines Variety [39668e33ea48] 1. The **ribosome** assembles polypeptides by linking amino acids in a specific sequence dictated by the **genetic code**. 2. This sequence, known as the **primary structure**, determines the protein's final shape and function. 3. **Exponential Growth of Combinations:** 1. **Dipeptide (2 amino acids):** 202=400202=400 possible combinations. 2. **Tripeptide (3 amino acids):** 203=8,000203=8,000 possible combinations. 3. **Polypeptide (100 amino acids):** 2010020100 possible combinations, a number so large it's effectively **infinite**. [{"_key":"fef7f609d453","_type":"block","asset":null,"children":[{"_key":"63f7ef16b74e","_type":"span","marks":[],"text":"The "},{"_key":"1c6140abf234","_type":"span","marks":["strong"],"text":"order"},{"_key":"5e64c4dc1d19","_type":"span","marks":[],"text":" of amino acids in a polypeptide is crucial for determining the protein's structure and function."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] [{"_key":"block_15","_type":"block","asset":null,"children":[{"_key":"ccf977cc02b4","_type":"span","markDefs":[],"marks":[],"text":"Imagine a short peptide made of four amino acids: glycine (G), alanine (A), valine (V), and serine (S). "}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"c1ccd7b3e5b4","_type":"block","asset":null,"children":[{"_key":"66b9bd65b28e","_type":"span","markDefs":[],"marks":[],"text":"Possible sequences include GAVS, AGVS, VASG, and many more. "}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"6618ffedbf28","_type":"block","asset":null,"children":[{"_key":"a8ac1163d862","_type":"span","markDefs":[],"marks":[],"text":"Now, extend this to 20 amino acids—each additional position exponentially increases the number of possible combinations."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] [{"_key":"block_17","_type":"block","asset":null,"children":[{"_key":"d1848c934b40","_type":"span","markDefs":[],"marks":[],"text":"To calculate the number of possible sequences for a polypeptide of length $n$, use the formula $20^n$, where 20 represents the number of amino acids."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] ## The Role of Sequence in Protein Function [9205ae3b2248] 1. The sequence of amino acids in a polypeptide determines how the chain **folds** into its **three-dimensional structure**, which in turn dictates its **function**. 2. Even a single change in the sequence can drastically alter the protein's properties. [{"_key":"4b2386e5a108","_type":"block","asset":null,"children":[{"_key":"95e89a695b13","_type":"span","marks":["strong"],"text":"Hemoglobin:"}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"3e2c08c2e9a9","_type":"block","asset":null,"children":[{"_key":"ea501c6e2eee","_type":"span","marks":["strong"],"text":"Function:"},{"_key":"13f13e799ff5","_type":"span","marks":[],"text":" Oxygen-carrying protein in red blood cells."}],"level":2,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"2f651095c09f","_type":"block","asset":null,"children":[{"_key":"04bb1f06a0f1","_type":"span","marks":["strong"],"text":"Mutation Impact:"},{"_key":"3aeffa283adc","_type":"span","marks":[],"text":" A single amino acid substitution can cause "},{"_key":"20611eac1813","_type":"span","marks":["strong"],"text":"sickle cell anemia"},{"_key":"b359eb64d013","_type":"span","marks":[],"text":", where red blood cells deform and cannot transport oxygen efficiently."}],"level":2,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"c726d803b66c","_type":"block","asset":null,"children":[{"_key":"aeb3d2e0dad9","_type":"span","marks":["strong"],"text":"Enzymes:"}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"881cd06b07f8","_type":"block","asset":null,"children":[{"_key":"f327ef768728","_type":"span","marks":["strong"],"text":"Function:"},{"_key":"5130dbc46502","_type":"span","marks":[],"text":" Biological catalysts that facilitate biochemical reactions."}],"level":2,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"7e2954aab761","_type":"block","asset":null,"children":[{"_key":"b601f04ae819","_type":"span","marks":["strong"],"text":"Mutation Impact:"},{"_key":"ace79d81dc49","_type":"span","marks":[],"text":" Any alteration in the amino acid sequence can disrupt the "},{"_key":"3084f2b6e91b","_type":"span","marks":["strong"],"text":"active site"},{"_key":"63c94b6f77b9","_type":"span","marks":[],"text":", rendering the enzyme "},{"_key":"a2f5378c78e3","_type":"span","marks":["strong"],"text":"non-functional"},{"_key":"8974076a58fb","_type":"span","marks":[],"text":"."}],"level":2,"listItem":"bullet","markDefs":[],"style":"normal"}] [{"_key":"75e2a0371e6b","_type":"block","asset":null,"children":[{"_key":"26f034756ccf","_type":"span","marks":[],"text":"Understanding mutations in amino acid sequences helps explain certain genetic diseases and enzyme malfunctions."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] [{"_key":"block_24","_type":"block","asset":null,"children":[{"_key":"a20a6f4878b9","_type":"span","markDefs":[],"marks":[],"text":"Do not confuse the sequence of amino acids ("},{"_key":"da139fc63dd4","_type":"span","markDefs":[],"marks":["strong"],"text":"primary"},{"_key":"73aaed7cbf84","_type":"span","markDefs":[],"marks":[],"text":" structure) with the three-dimensional folding of the protein (tertiary structure). "}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"4c11a391af29","_type":"block","asset":null,"children":[{"_key":"479f441417e9","_type":"span","markDefs":[],"marks":[],"text":"The sequence determines the folding, but they are distinct concepts."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] ## Examples of Polypeptides [2c92f6cf3d75] To appreciate the diversity of polypeptides, consider these examples: 1. **Beta-Endorphin** 1. **Function:** Natural painkiller produced by the pituitary gland. 2. **Structure:** Consists of **31 amino acids**. 2. **Insulin** 1. **Function:** Hormone that regulates blood sugar levels. 2. **Structure:** Made of **two polypeptide chains, **one with **21 amino acids** and the other with **30**. 3. **Alpha-Amylase** 1. **Function:** Enzyme in saliva that breaks down starch. 2. **Structure:** Composed of a **single polypeptide chain** with **496 amino acids**. 4. **Titin** 1. **Function:** Largest known polypeptide, found in muscle tissue. 2. **Structure:** Consists of **34,350 amino acids** in humans. [{"_key":"f59df2b2e39e","_type":"block","asset":null,"children":[{"_key":"b7a39a2067c8","_type":"span","marks":[],"text":"Familiarize yourself with key proteins and their structures to understand their functions in the body."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] ![](https://cdn.sanity.io/images/w7j7fz60/production/09b21d7053dfe3488b82c736b8fe419541c16517-1200x800.png) [{"_key":"block_34","_type":"block","asset":null,"children":[{"_key":"VCt5InIJjuFfZERcwZ1dyd","_type":"span","markDefs":[],"marks":[],"text":"Although organisms can theoretically produce an astronomical number of different polypeptides, their actual repertoire is constrained by the genetic instructions encoded in their DNA. "}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"3e282ae0a94a","_type":"block","asset":null,"children":[{"_key":"c55c7ce80ae9","_type":"span","markDefs":[],"marks":[],"text":"This unique set of proteins is called the "},{"_key":"32a4466ed27b","_type":"span","markDefs":[],"marks":["strong"],"text":"proteome"},{"_key":"1f023ef9bed7","_type":"span","markDefs":[],"marks":[],"text":"."}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] ## Why Infinite Variety Matters [465d7fe81608] 1. The nearly **infinite variety** of peptide chains is crucial for life because it enables the production of proteins with highly specialized functions. For example: 1. **Structural Proteins: Collagen **provides strength and support to tissues. 2. **Transport Proteins: Hemoglobin** carries essential molecules such as oxygen. 3. **Enzymes: **Catalyze biochemical reactions with remarkable specificity and efficiency. 4. **Signaling Proteins: Insulin **regulates physiological processes. 2. This diversity also allows organisms to **adapt** to different environments. 3. For example, 1. **Extremophiles **produce proteins that remain functional under **high temperatures** or in **highly acidic environments**. Organisms that thrive in extreme conditions. [{"_key":"5688838bd367","_type":"block","asset":null,"children":[{"_key":"15545e805b9a","_type":"span","marks":[],"text":"The diversity of proteins underpins the complexity and adaptability of life, enabling organisms to perform a wide range of biological functions."}],"markDefs":[],"style":"normal"}] [{"_key":"block_44","_type":"block","asset":null,"children":[{"_key":"VCt5InIJjuFfZERcwZ1dzE","_type":"span","markDefs":[],"marks":[],"text":"How does the concept of infinite peptide variety challenge our understanding of life's origins? "}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"1b898904f1df","_type":"block","asset":null,"children":[{"_key":"f5776d624141","_type":"span","markDefs":[],"marks":[],"text":"Consider the Theory of Knowledge question: \"How do we know what we cannot observe?\""}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}] [{"_key":"block_49","_type":"block","asset":null,"children":[{"_key":"VCt5InIJjuFfZERcwZ1dzp","_type":"span","markDefs":[],"marks":[],"text":"How many different polypeptides can be formed from a chain of 5 amino acids?"}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"block_50","_type":"block","asset":null,"children":[{"_key":"VCt5InIJjuFfZERcwZ1e0Q","_type":"span","markDefs":[],"marks":[],"text":"Why is the sequence of amino acids important for protein function?"}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"},{"_key":"block_51","_type":"block","asset":null,"children":[{"_key":"VCt5InIJjuFfZERcwZ1e11","_type":"span","markDefs":[],"marks":[],"text":"Can you name a protein and describe its function and structure?"}],"level":1,"listItem":"bullet","markDefs":[],"style":"normal"}]