Name: how dna structure was discovered
Uploaded: 2023-04-30T10:29:48.000Z
Duration: 1 min 7 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms- Structures and Processes

LS.Bio.1.5

The DNA Helix

חומצה דאוקסיריבונוקלאית, או DNA, מורכבת משתי שרשראות פולינוקלאוטידים.
כל אחת משרשראות אלה מורכבת מארבעה סוגים של תת-יחידות נוקלאוטידים.
כל נוקלאוטיד מורכב מקבוצת פוספטים אחת ומבסיס המכיל חנקן – אדנין, A, ציטוזין, C, גואנין, G או תימין, T, המחובר לדאוקסיריבוז סוכר.
סידור זה יוצר את עמוד השדרה של הסוכר-פוספט של מבנה הדנ"א.
לאורך עמוד השדרה של כל גדיל, קשרי פוספודיזטר מקשרים באופן קוולנטי בין אטום הפחמן השלישי של סוכר אחד לאטום הפחמן החמישי של מולקולת הסוכר הבאה בשרשרת.
בגדילים האנטי-מקביליים המנוגדים, כל בסיס מזווג באופן ייחודי, C עם G ו-A עם T, בשל ההבדלים במספר קשרי המימן הנוצרים ביניהם.
קוטביות כימית כזו מבטיחה אריזה יעילה, פיתול שני הגדילים זה סביב זה ליצירת סליל כפול תלת-ממדי, עם עשרה זוגות בסיסים בכל סיבוב מלא.

סליל ה-dna

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חומצת גרעין דאוקסיריבונוקלאית, או DNA, היא החומר הגנטי האחראי על העברת תכונות מדור לדור בכל האורגניזמים ובמרבית הנגיפים. ה-DNA מורכב משני גדילים של נוקלאוטידים המתלפפים זה סביב זה ויוצרים מבנה דמוי קפיץ הנקרא סליל כפול. עם זאת, הסליל הכפול אינו סימטרי לחלוטין. במקום זאת, ישנן תעלות המופיעות באופן קבוע במבנה. התעלה הגדולה נוצרת במקום שבו עמודי הסוכר-פוספט רחוקים יחסית זה מזה. מרחב זה מאפשר גישה לחלבונים קושרי DNA, כמו גורמי שעתוק. לעומת זאת, התעלה הקטנה נוצרת במקום שבו עמודי הסוכר-פוספט קרובים זה לזה. יחסית מעט חלבונים נקשרים ל-DNA דרך התעלה הקטנה.

גילוי מבנה ה-DNA: היסטוריה קצרה

גילוי מבנה ה-DNA התרחש בהדרגה לאורך כמעט מאה שנה, ומהווה אחד מהסיפורים המפורסמים והמושכים ביותר בהיסטוריה של המדע.

הכול החל בשנת 1869, כאשר המדען השווייצרי פרידריך מישר גילה חומר שקרא לו "נוקלאין". בתהליך של הפקת חלבון מתאי דם לבנים, מישר מצא חומר בלתי צפוי בעל תכולת זרחן גבוהה יחסית. הוא לא ידע מהו החומר, אך חשד שהוא יכול להיות בעל חשיבות ביולוגית. מישר צדק, אך לקח עשורים עד שהקהילה המדעית העריכה את תובנותיו במלואן.

הגילוי הקריטי הבא נעשה על ידי הביוכימאי הרוסי פובוס לבן. בשנת 1919, לבן הציע כי הנוקלאין, שכבר נקרא אז חומצת גרעין, מורכב משרשרות של מולקולות שקרא להן פולינוקלאוטידים. הצעתו של לבן נבעה ממחקריו על שמרים, שבהם מצא כי הנוקלאוטידים הבודדים מורכבים מקבוצת פוספט, סוכר ובסיס חנקני. אף על פי שהמודל של לבן לפולינוקלאוטידים היה נכון במובנים רבים, עדיין לא היה ברור כיצד הבסיסים מסודרים במולקולת ה-DNA.

הביוכימאי האוסטרי ארווין צ'רגף הרחיב את עבודתו של לבן. בשנות ה-40 המאוחרות, צ'רגף גילה ממצא חשוב: כמות האדנין ב-DNA תמיד שווה בערך לכמות הטימין, וכמות הגואנין שווה בערך לכמות הציטוזין. דפוס זה נודע כחוק צ'רגף והיה חלק חשוב מהראיות שאיפשרו את הפענוח הסופי של מבנה ה-DNA.

בתחילת שנות ה-50, הביולוג האמריקאי ג'יימס ווטסון והפיזיקאי האנגלי פרנסיס קריק התחרו מול יריבם הראשי, האמריקאי לינוס פאולינג, כדי לגלות את המבנה התלת-ממדי של ה-DNA. בהתבסס על עבודתו של צ'רגף, הם השתמשו בידע בפיזיקה, מתמטיקה וכימיה לבניית מודלים פיזיים של ה-DNA. אך הם לא הצליחו עד שקיבלו נתון קריטי: צילום רנטגן של ה-DNA שהצביע בפירוט מדויק על המבנה הסלילי הכפול שלו. צילום זה היה הנתון הלא מפורסם של הפיזיקאית רוזלינד פרנקלין ונמסר לווטסון וקריק ללא ידיעתה של פרנקלין. ווטסון וקריק פרסמו את תיאור מבנה ה-DNA בשנת 1953, ובשנת 1962 זכו יחד עם מוריס וילקינס (שותפה של פרנקלין) בפרס נובל לפיזיולוגיה או לרפואה על תגלית זו. למרבה הצער, פרנקלין נפטרה בשנת 1958 ולכן לא הייתה זכאית לפרס נובל.
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סליל ה-DNA

חומצה דאוקסיריבונוקלאית, או DNA, היא החומר הגנטי האחראי להעברת תכונות מדור לדור בכל האורגניזמים וברוב הנגיפים. דנ א...

Education

JoVE Core

Cell Biology

ביולוגיה של התא

Unit 1

יחידה 1

Cells, Genomes, and Evolution

תאים, גנומים ואבולוציה

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

how dna structure was discovered

DNA is the genetic material that passes traits from one generation to the next in organisms and most viruses. It is made of two strands of nucleotides that twist into a spring-like double helix. The shape is not perfectly even. It also has repeating grooves called the major groove and the minor groove.

The major groove forms where the sugar-phosphate backbones are farther apart. This wider space gives DNA-binding proteins, including transcription factors, better access to the bases. The minor groove forms where the backbones are closer together. Relatively few proteins bind to DNA through the minor groove.

The story of DNA structure unfolded over nearly a century. It began in 1869, when Swiss scientist Friedrich Miescher found a phosphorus-rich substance in white blood cells and called it nuclein. He did not know what it was, but he suspected it had biological importance. Later work showed that his idea was right.

In 1919, Russian biochemist Phoebus Levene proposed that nucleic acid was made of chains of molecules called polynucleotides. His yeast studies showed that each nucleotide contains a phosphate group, a sugar, and a nitrogen-containing base. This model was useful, but it still did not explain how the bases were arranged in DNA. In the late 1940s, Erwin Chargaff added a key clue by showing that adenine is roughly equal to thymine and guanine is roughly equal to cytosine.

That evidence helped James Watson and Francis Crick build their DNA models in the early 1950s. They were competing with Linus Pauling and used ideas from physics, mathematics, and chemistry. They succeeded only after seeing an X-ray photograph of DNA that showed the double helix in detail. The image came from Rosalind Franklin’s unpublished data and was shared without her knowledge. Watson and Crick published their description in 1953, and with Maurice Wilkins they received the 1962 Nobel Prize in Physiology or Medicine. Franklin died in 1958, so she was not eligible for the prize.

How DNA Structure Was Discovered

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eukaryotic evolution

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cytoplasm

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the nucleus

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the dna helix

DNA is the genetic material that passes traits from one generation to the next in organisms and most viruses. It is made of two strands of nucleotides that twist into a spring-like double helix. The shape is not perfectly even. It also has repeating grooves called the major groove and the minor groove. The major groove forms where the sugar-phosphate backbones are farther apart. This wider space gives DNA-binding proteins, including transcription factors, better access to the bases. The minor...

the central dogma

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mutations

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genome-size-and-the-evolution-of-new-genes

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gene families

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gene evolution - fast or slow?

Gene Evolution Rates and Selection

Gene evolution can happen at different rates, and natural selection helps shape those changes. Some genes change slowly because important DNA changes are removed over time. Other genes can change more quickly when different mutations are kept in a population. The rate of evolution depends on how a gene is used and how strongly it is affected by selection. Genes with essential jobs often stay more similar across species. Genes under weaker pressure may show more variation and may evolve faster.<br...

types of genetic transfer between organisms

types-of-genetic-transfer-between-organisms

Vertical and Horizontal Gene Transfer

Genetic transfer between organisms happens in two main ways: vertical gene transfer and horizontal gene transfer. These two routes explain how hereditary material moves from one generation to the next or between organisms that are not parent and offspring. Vertical gene transfer passes genes from parent to offspring during reproduction. This is the usual way genetic information is inherited in living things. Horizontal gene transfer moves genetic material between organisms outside of...

key terms and concepts

Explore how scientists uncovered DNA’s double helix, from Miescher’s nuclein to Chargaff’s rule, Franklin’s X-ray image, and Watson and Crick.

How DNA Structure Was Discovered | JoVE K12

cell biology

JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

Pennsylvania State Academic Standards

Life Science

Inheritance and Variation of Traits

3.1.9-12.P

3.1.9-12.Q

Louisiana Student Standards for Science

High School

Life Sciences

From Molecules To Organisms: Structures And Processes

HS-LS1-1

heredity-inheritance-and-variation-of-traits

Heredity: Inheritance And Variation Of Traits

HS-LS3-1

Biological Evolution: Unity And Diversity

HS-LS4-1

Tennessee Academic Standards

From Molecules to Organisms: Structures and Processes

BIO1.LS1.3

Virginia  Standards of Learning

HIgh School

BIO.2

BIO.2.d

BIO.5

BIO.5.b

Minnesota Academic Standards in Science

3.1.1 9L.3.1.1.4

Florida Department of Education

SC.912.L.16

SC.912.L.16.4

SC.912.L.18

SC.912.L.18.1

Texas Essential Knowledge and Skills

BIO.7

BIO.7.A

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

B-LS1-1.

Heredity: Inheritance and Variation of Traits

B-LS3-1.

Georgia Standards of Excellence

SB6.c

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How DNA Structure Was Discovered

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