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

يتكون الحمض النووي الريبي منقوص الأكسجين ، أو الحمض النووي ، من سلسلتين عديد النوكليوتيدات.
تتكون كل سلسلة من هذه السلاسل من أربعة أنواع من الوحدات الفرعية للنيوكليوتيدات.
يتكون كل نيوكليوتيد من مجموعة فوسفات واحدة وقاعدة تحتوي على النيتروجين - الأدينين ، A ، السيتوزين ، C ، الجوانين ، G ، أو الثايمين ، T ، المتصل بمنقوص الأكسجين السكر.
يخلق هذا الترتيب العمود الفقري للسكر والفوسفات لبنية الحمض النووي.
على طول العمود الفقري لكل خيط ، تربط روابط الفوسفوديستر تساهميا ذرة الكربون الثالثة من سكر واحد بذرة الكربون الخامسة من جزيء السكر التالي في السلسلة.
في الخيوط المتقابلة المتوازية ، يتم إقران كل قاعدة بشكل فريد ، C مع G و A مع T ، بسبب الاختلافات في عدد الروابط الهيدروجينية التي تتشكل بينهما.
تضمن هذه القطبية الكيميائية التعبئة الفعالة ، ولف الخيوط حول بعضهما البعض لتشكيل حلزون مزدوج ثلاثي الأبعاد ، مع عشرة أزواج أساسية في كل منعطف كامل.

لولب الحمض النووي

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حمض نووي ريبوزي منقوص الأكسجين، أو DNA، هو المادة الوراثية المسؤولة عن نقل الصفات من جيل إلى جيل في جميع الكائنات الحية ومعظم الفيروسات. يتكون الحمض النووي من شريطين من النيوكليوتيدات التي تلتف حول بعضها البعض لتشكل بنية تشبه الزنبرك تسمى اللولب المزدوج. ومع ذلك، فإن اللولب المزدوج ليس متماثلًا تمامًا. بدلا من ذلك، هناك أخاديد تحدث بانتظام في الهيكل. ويحدث الأخدود الرئيسي حيث تكون أعمدة السكر والفوسفات متباعدة نسبيًا. يتيح هذا الفضاء الوصول إلى البروتينات المرتبطة بالحمض النووي، مثل عوامل النسخ. وعلى النقيض من ذلك، يحدث الأخدود الصغير عندما تكون أعمدة السكر والفوسفات قريبة من بعضها البعض. يرتبط عدد قليل نسبيًا من البروتينات بالحمض النووي عبر الأخدود الصغير.

اكتشاف بنية الحمض النووي: تاريخ موجز

تم اكتشاف بنية الحمض النووي بشكل تدريجي على مدار ما يقرب من قرن من الزمان، وهو ما يمثل واحدة من أشهر القصص وأكثرها إثارة في تاريخ العلم.

بدأ كل شيء في عام 1869 عندما اكتشف العالم السويسري فريدريش ميشر مادة أطلق عليها اسم "النوكلين". أثناء عملية استخلاص البروتين من خلايا الدم البيضاء، اكتشف ميشر مادة غير متوقعة تحتوي على نسبة عالية نسبيًا من الفوسفور. لم يكن يعرف ما هي، لكنه شك في أنه قد يكون مهمًا من الناحية البيولوجية. وكان ميشر على حق، لكن الأمر استغرق عقودًا من الزمن قبل أن يقدر المجتمع العلمي أفكاره بشكل كامل.

الاكتشاف المهم التالي تم بواسطة عالم الكيمياء الحيوية الروسي فويبوس ليفين. في عام 1919، اقترح ليفين أن النيوكلين، الذي كان يُعرف آنذاك بالحمض النووي، كان يتكون من سلاسل من الجزيئات أطلق عليها اسم بولينوكليوتيدات. نشأ اقتراح ليفين من بحثه عن الخميرة، حيث وجد أن النيوكليوتيدات الفردية تتكون من مجموعة فوسفات، وسكر، وقاعدة تحتوي على النيتروجين. على الرغم من أن نموذج ليفين متعدد النوكليوتيدات كان صحيحًا في كثير من النواحي، إلا أنه لم يكن من الواضح كيف تم ترتيب القواعد في جزيء الحمض النووي.

قام عالم الكيمياء الحيوية النمساوي إروين تشارجاف بتوسيع عمل ليفين. من خلال العمل في أواخر الأربعينيات من القرن العشرين، توصل تشارجاف إلى نتيجة رئيسية: كمية الأدينين في الحمض النووي دائمًا ما تكون مساوية تقريبًا لكمية الثايمين، وكمية الجوانين دائمًا مساوية تقريبًا لكمية السيتوزين. أصبح هذا النمط معروفًا باسم قاعدة تشارجاف، وكان بمثابة دليل أساسي مكّن من التوضيح النهائي لبنية الحمض النووي.

في أوائل الخمسينيات من القرن الماضي، كان عالم الأحياء الأمريكي جيمس واتسون والفيزيائي الإنجليزي فرانسيس كريك يتسابقان مع منافسهما الرئيسي، الأمريكي لينوس بولينج، لاكتشاف البنية ثلاثية الأبعاد للحمض النووي. بناءً على عمل تشارجاف، استخدموا المعرفة بالفيزياء والرياضيات والكيمياء لبناء نماذج فيزيائية للحمض النووي. لكنهم لم ينجحوا حتى حصلوا على جزء مهم من البيانات: "صورة" للأشعة السينية للحمض النووي تشير بالتفصيل الدقيق إلى بنيته اللولبية المزدوجة. كانت هذه الصورة عبارة عن بيانات غير منشورة للفيزيائية روزاليند فرانكلين وتم إعطاؤها لواتسون وكريك دون علم فرانكلين. نشر واتسون وكريك وصفهما لبنية الحمض النووي في عام 1953، وفازا مع موريس ويلكنز (أحد زملاء فرانكلين) بجائزة نوبل في الفسيولوجيا أو الطب لعام 1962 لهذا الاكتشاف. للأسف، توفي فرانكلين في عام 1958، وبالتالي لم يكن مؤهلا للحصول على جائزة نوبل.
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الحمض النووي الريبي منقوص الأكسجين ، أو الحمض النووي ، هو المادة الوراثية المسؤولة عن نقل السمات من جيل إلى جيل في جميع الكائنات الحية ومعظم الفيروسات. دنا...

Education

JoVE Core

Cell Biology

بيولوجيا الخلية

Unit 1

الوحدة الأولى

Cells, Genomes, and Evolution

الخلايا والجينومات والتطور

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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

what are cells?

Cells as the Building Blocks of Life

Cells are the basic building blocks of life. A bacterium can be a single cell, while a human is made of trillions of cells. Even with this range, cells share key features that support life. A living cell has a plasma membrane. This is a bilayer of lipids that separates the cytoplasm inside the cell from the outside environment. A cell also carries genetic information in the form of DNA. In prokaryotic cells, DNA is found in a region called the nucleoid. In eukaryotic cells, DNA is enclosed...

the tree of life - bacteria, archaea, and eukaryotes

the-tree-of-life-bacteria-archaea-and-eukaryotes

Three Domains on the Tree of Life

The tree of life shows how living things are grouped into three domains: Bacteria, Archaea, and Eukaryotes. This classification helps explain the major branches of life and how they are related. Bacteria and Archaea are both single-celled organisms, but they are not the same. Eukaryotes include organisms with more complex cells, such as plants, animals, and fungi. Together, these three domains give a broad picture of life on Earth. Understanding the tree of life helps students compare cell...

prokaryotic cells

How Prokaryotes Survive Without a Nucleus

Prokaryotes are small unicellular organisms that live without a nucleus. They include the domains Archaea and Bacteria. Bacteria include common microbes such as Salmonella and E. coli, while Archaea include extremophiles that live in harsh places like volcanic springs. Prokaryotic cells still share several basic features with eukaryotic cells. They have a plasma membrane, cytoplasm, ribosomes, and genetic material in the form of single, circular DNA. Their cell parts float freely in the...

eukaryotic compartmentalization

How Organelles Keep Cells Working

Eukaryotic cells keep their organelles separate so each part can do a specific job. Organelles such as the nucleus and mitochondria are surrounded by membranes. These membranes are selectively permeable, which means they control what enters and leaves. That control creates small internal environments with conditions suited to each organelle. These controlled spaces help organelles work more efficiently. In animal cells, lysosomes keep an acidic environment that helps their enzymes digest...

eukaryotic evolution

How Eukaryotic Cells Became Complex

Eukaryotic cells became complex through a debated evolutionary path that likely involved endosymbiosis. The most accepted model is the endosymbiont theory, which explains how organelles such as mitochondria and chloroplasts may have entered an ancestral cell. Other ideas include the nucleus-first hypothesis, the mitochondria-first hypothesis, and the eukaryote-first hypothesis. The nucleus-first hypothesis says an ancestral prokaryote first formed a membrane around its DNA, creating the...

animal and plant cell structure

Plant vs Animal Cell Division and Specialization

Plant and animal cells differ in how they divide, organize into tissues, and specialize for different jobs. Both cell types divide by mitosis in non-gametic cells and by meiosis in gametic cells, but the details are not the same. These differences help explain how each cell type supports growth and reproduction. During cell division, animal cells use centrosomes to organize spindle fibers and separate chromosomes. Plant cells do not have centrosomes. Instead, they use a microtubule-organizing...

cytoplasm

Cytoplasm and the Cell’s Internal Support

The cytoplasm is the cell’s internal space that holds organelles and the cytoskeleton. It is suspended in the cytosol, an aqueous fluid made of water, ions, salts, and many organic molecules. This fluid helps keep the cell organized and supports many cellular activities. The cytoplasm is also where protein synthesis and protein folding take place. The watery cytosol helps proteins fold correctly. In a folded protein, hydrophobic amino acid side chains tend to stay buried in the core, while...

the nucleus

Nuclear DNA, Chromatin, and Nucleoli

The nucleus is a membrane-bound organelle that stores chromosomal DNA and helps control what proteins a eukaryotic cell makes. It acts as the cell’s control center. DNA in mitochondria and chloroplasts is different because it mainly supports functions specific to those organelles. Inside the nucleus, DNA is wrapped around proteins called histones. This DNA-protein complex is called chromatin. During interphase, when the cell is not dividing, chromatin stays loosely arranged so the DNA is easy...

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

DNA to Protein: RNA’s Role

DNA to protein flow depends on RNA as the link between genetic information and the amino acids that build proteins. Early scientists knew that DNA stores the information for cell functions and that proteins carry out most of those functions. For a long time, they did not know how the code in DNA became a working protein. At first, many people thought one gene was changed directly into its protein. Two findings in eukaryotic cells challenged that idea. Protein production does not happen in the...

mutations

Mutations in DNA and Inherited Disease

Mutations are changes in the DNA sequence. They can happen on their own during DNA copying, or they can be caused by environmental factors. Scientists describe mutations in several ways, including whether they change the amino acid sequence of a protein, how much DNA they affect, and whether they occur in somatic cells or germline cells. Some mutations are point mutations. A point mutation changes a single nucleotide in DNA. Other mutations are chromosomal alterations, which change the number...

genome size and the evolution of new genes

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

Genome Size and Gene Evolution

Genome size and gene evolution are linked through changes in DNA sequence and genome structure. Some genes can arise from parts of the genome that were not coding before, while others come from changes to existing genes. These shifts help explain how new genetic material can appear over time. A genome is the full set of DNA in an organism. Its size can change as DNA is added, removed, or rearranged. The transcript highlights that genome size is not fixed, and that these changes can shape the...

gene families

Shared Origins of Gene Families

Gene families are groups of related genes that share a common origin. They form when genes are copied and then change over time. These related genes can be found within the same genome. The video also connects gene families to homologous genes and orthologous genes. Homologous genes are genes with a shared evolutionary origin. Orthologous genes are homologous genes found in different species. Gene families help show how these relationships are used to study evolution and related gene functions.

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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lipid-derived-compounds-in-the-human-body

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Nucleic Acid Structure

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ATP Energy Storage and Release

ATP and Macromolecule Synthesis

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Construct an explanation to illustrate relationships between structure and function of major macromolecules essential for life.

LS.Bio.1.1

Introduction to Enzymes

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Enzymes and Activation Energy

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Introduction to Enzyme Kinetics

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Turnover Number and Catalytic Efficiency

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Catalytically Perfect Enzymes

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introduction-to-mechanisms-of-enzyme-catalysis

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Ligand Binding and Linkage

Cooperative Allosteric Transitions

Ribozymes

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LS.Bio.1.2

What are Cells?

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Cell Size

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Eukaryotic Compartmentalization

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Prokaryotic Cells

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Cytoplasm

The cytoplasm consists of organelles and a framework of protein scaffolds called the cytoskeleton suspended in an aqueous solution, the cytosol. The ...

The Nucleus

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Endoplasmic Reticulum

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Ribosomes

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Golgi Apparatus

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Lysosomes

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Peroxisomes

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Introduction to the Cytoskeleton

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Use models to explain how the structure of organelles determines its function and supports overall cell processes.

LS.Bio.1.3

Analyze how the relationship between structure and function supports life processes within organisms.

How DNA Structure Was Discovered

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