{"id":198588,"date":"2025-03-10T07:18:28","date_gmt":"2025-03-10T07:18:28","guid":{"rendered":"https:\/\/learnexams.com\/blog\/?p=198588"},"modified":"2025-03-10T07:18:30","modified_gmt":"2025-03-10T07:18:30","slug":"what-is-the-length-of-an-%ce%b1-helical-section-of-a-polypeptide-chain-of-20-residues","status":"publish","type":"post","link":"https:\/\/www.learnexams.com\/blog\/2025\/03\/10\/what-is-the-length-of-an-%ce%b1-helical-section-of-a-polypeptide-chain-of-20-residues\/","title":{"rendered":"What is the length of an \u03b1-helical section of a polypeptide chain of 20 residues"},"content":{"rendered":"\n<p>What is the length of an \u03b1-helical section of a polypeptide chain of 20 residues? How do you calculate this?<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code>    90 \u00c5\n    60 \u00c5\n    30\u00c5\n    9 \u00c5\n    3 \u00c5<\/code><\/pre>\n\n\n\n<p><mark style=\"background-color:rgba(0, 0, 0, 0)\" class=\"has-inline-color has-ast-global-color-6-color\"><strong>The correct answer and explanation is :<\/strong><\/mark><\/p>\n\n\n\n<p>The correct answer is <strong>30 \u00c5<\/strong>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Calculation:<\/strong><\/h3>\n\n\n\n<p>An <strong>\u03b1-helix<\/strong> is a common secondary structure in proteins. The structural parameters of an \u03b1-helix are:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Each residue advances the helix by <strong>1.5 \u00c5<\/strong> (rise per residue).<\/li>\n\n\n\n<li>There are <strong>3.6 residues per turn<\/strong>.<\/li>\n\n\n\n<li>The pitch (height of one complete turn) of the helix is <strong>5.4 \u00c5<\/strong>.<\/li>\n<\/ul>\n\n\n\n<p>For a polypeptide segment of <strong>20 residues<\/strong>, we calculate the length using the rise per residue:<\/p>\n\n\n\n<p>[<br>\\text{Length} = \\text{Number of residues} \\times \\text{Rise per residue}<br>]<\/p>\n\n\n\n<p>[<br>= 20 \\times 1.5 \\, \\text{\u00c5}<br>]<\/p>\n\n\n\n<p>[<br>= 30 \\, \\text{\u00c5}<br>]<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Explanation:<\/strong><\/h3>\n\n\n\n<p>The \u03b1-helix is stabilized by hydrogen bonds between the backbone carbonyl oxygen of one residue and the amide hydrogen of another, four residues away. This regular structure makes the \u03b1-helix compact and stable.<\/p>\n\n\n\n<p>Each turn of the \u03b1-helix contains <strong>3.6 residues<\/strong>, meaning that a <strong>20-residue helix<\/strong> will complete approximately:<\/p>\n\n\n\n<p>[<br>\\frac{20}{3.6} \\approx 5.56 \\text{ turns}.<br>]<\/p>\n\n\n\n<p>Since the pitch of an \u03b1-helix is <strong>5.4 \u00c5 per turn<\/strong>, the total helical length could also be calculated as:<\/p>\n\n\n\n<p>[<br>5.56 \\times 5.4 \\approx 30 \\, \\text{\u00c5}.<br>]<\/p>\n\n\n\n<p>This confirms our previous calculation.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\"><strong>Conclusion:<\/strong><\/h3>\n\n\n\n<p>For a 20-residue \u03b1-helix, the total length of the helix is <strong>30 \u00c5<\/strong>. This information is crucial in understanding protein structure and function, especially in molecular biology and bioinformatics.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<figure class=\"wp-block-image size-full\"><img decoding=\"async\" src=\"https:\/\/learnexams.com\/blog\/wp-content\/uploads\/2025\/03\/image-733.png\" alt=\"\" class=\"wp-image-198589\"\/><\/figure>\n\n\n\n<p>Here is the <strong>scientific illustration<\/strong> of an \u03b1-helix polypeptide chain with labeled dimensions, showing the helical structure, hydrogen bonding, and key measurements.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>What is the length of an \u03b1-helical section of a polypeptide chain of 20 residues? How do you calculate this? The correct answer and explanation is : The correct answer is 30 \u00c5. Calculation: An \u03b1-helix is a common secondary structure in proteins. The structural parameters of an \u03b1-helix are: For a polypeptide segment of [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"site-sidebar-layout":"default","site-content-layout":"","ast-site-content-layout":"default","site-content-style":"default","site-sidebar-style":"default","ast-global-header-display":"","ast-banner-title-visibility":"","ast-main-header-display":"","ast-hfb-above-header-display":"","ast-hfb-below-header-display":"","ast-hfb-mobile-header-display":"","site-post-title":"","ast-breadcrumbs-content":"","ast-featured-img":"","footer-sml-layout":"","ast-disable-related-posts":"","theme-transparent-header-meta":"","adv-header-id-meta":"","stick-header-meta":"","header-above-stick-meta":"","header-main-stick-meta":"","header-below-stick-meta":"","astra-migrate-meta-layouts":"default","ast-page-background-enabled":"default","ast-page-background-meta":{"desktop":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"ast-content-background-meta":{"desktop":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"tablet":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""},"mobile":{"background-color":"var(--ast-global-color-5)","background-image":"","background-repeat":"repeat","background-position":"center center","background-size":"auto","background-attachment":"scroll","background-type":"","background-media":"","overlay-type":"","overlay-color":"","overlay-opacity":"","overlay-gradient":""}},"footnotes":""},"categories":[25],"tags":[],"class_list":["post-198588","post","type-post","status-publish","format-standard","hentry","category-exams-certification"],"_links":{"self":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/198588","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/comments?post=198588"}],"version-history":[{"count":0,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/posts\/198588\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/media?parent=198588"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/categories?post=198588"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.learnexams.com\/blog\/wp-json\/wp\/v2\/tags?post=198588"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}