Name: dna base pair rules
Uploaded: 2020-11-23T11:47:35.000Z
Duration: 2 min 27 s
Channel: JoVE

K12 Standards

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Biology

Heredity

Cellular genetics

DNA Base Pairing

דנ"א דומה לסולם מפותל. ושלבי סולם הדנ"א הם זוגות משלימים של בסיסים חנקניים. על פי כללי זיווג בסיס, אדנין, שהוא פורין, נקשר לתימין, שהוא פירימידין, עם שני קשרי מימן.וגואנין, שהוא פורין, מופיע עם ציטוזין, שהוא פירימידין, עם שלושה קשרי מימן. אך מדוע פורינים תמיד נקשרים לפירימידינים? בגלל אילוצים סטריים, שהם מגבלות מרחביות המוטלות על ידי עמוד השדרה של סוכר הפוספט של הדנ"א, רק 10.85 אנגסטרוםנחלל זמין לזוגות בסיס בסליל דנ"א כפול.לפורינים יש שני מבנה טבעתי כפול. לכן, שני פורינים יחד יהיו גדולים מכדי להיכנס למרחב זה. מצד שני, אם נחבר בין שני פירימידינים, הכוללים רק טבעת אחת, המרחק ביניהם יהיה גדול מכדי ליצור קשרי מימן, שהם באורך של כשני אנגסטרומים.יחד עם זאת, אם נקשר פורין ופירימידין, הם יתאימו באופן מושלם לתוך סליל הדנ"א ויהיו די קרובים זה לזה כדי ליצור קשרי מימן. קשרי מימן יכולים להיווצר כשאטום מימן הוא במרחק של כשני אנסטגרומים מאטום בעל אלקטרושליליות כגון חמצן או חנקן. לאדנין יש אטום מימן אחד הקרוב לחמצן ולתימין.ולתימין יש מימן אחד קרוב לחנקן ולאדנין. זה מוביל להיווצרות שני קשרי מימן. אדנין לא יכול ליצור קשרי מימן עם ציטוזין מפני שלציטוזין יש אטום מימן במקום שבו יימצאו החמצן והתימין.ואטום המימן הנמצא בתימין נעדר מציטוזין. תופעה דומה מתרחשת בזוג הבסיסים גואנין וציטוזין, שבו החמצן בגואנין וחמצן וחנקן בציטוזין ממוקמים כל אחד מול מימן, מה שמוביל להיווצרות של שלושה קשרי מימן, מה שלא קורה בזיווג בסיסים של גואנין ותימין. הספציפיות הגבוהה של זיווג בסיסים, וכן העזרה של אנזימי שכפול דנ"א, הם הסיבה לכך שאדנין נקשר תמיד לתימין וגואנין נקשר תמיד לציטוזין.

זיווג בסיס dna

<div style="direction:rtl">הכללים של ארווין צ'רגף על שקילות DNA סללו את הדרך לגילוי של זיווג בסיסים ב-DNA. הכללים של צ'רגף קובעים שבמולקולת DNA דו-גדילית, <ol style="padding-right: 35px; margin: 0;"> <li style="text-align: right;">כמות האדנין (A) שווה לכמות הטימין (T);</li> <li style="text-align: right;">כמות הגואנין (G) שווה לכמות הציטוזין (C); ו</li> <li style="text-align: right;">סכום הפורינים, A ו-G, שווה לסכום הפירימידינים, C ו-T (כלומר, A+G = C+T).</li> </ol> עבודה מאוחרת יותר של ווטסון וקריק גילתה שב-DNA דו-גדילי, A תמיד יוצר שני קשרי מימן עם T, ו-G תמיד יוצר שלושה קשרי מימן עם C. זיווג בסיסים זה שומר על רוחב קבוע של הסליל הכפול של DNA, כמו גם A-T וגם זוגות C-G הם באורך 10.85Å ומשתלבים בצורה מסודרת בין שני עמודי השדרה של הסוכר-פוספט. זיווגי בסיסים גורמים לבסיסים החנקניים להיות בלתי נגישים למולקולות אחרות עד שקשרי המימן נפרדים. עם זאת, אנזימים ספציפיים יכולים לשבור בקלות את קשרי המימן הללו כדי לבצע תהליכים נחוצים בתא, כגון שכפול ותעתוק DNA. מכיוון שלזוג G-C יש יותר קשרי מימן מאשר זוג A-T, DNA עם אחוז גבוה של זוגות G-C יזדקק לאנרגיה הגבוהה יותר להפרדה של שני גדילי DNA מאשר אחד עם אחוז דומה של זוגות A-T. אנלוגים בסיס כרפואה זיווג בסיסים נכון חיוני לשכפול הנאמן של ה-DNA. אנלוג בסיס הם מולקולות שיכולות להחליף את בסיסי ה-DNA הסטנדרטיים במהלך שכפול ה-DNA. אנלוגים אלה הם אנטי-ויראליים ואנטי-סרטניים יעילים נגד מחלות כמו הפטיטיס, הרפס ולוקמיה. אציקלוביר, הידוע גם בשם אציקלוגואנוזין, הוא אנלוג בסיס של גואנין והוא נפוץ בטיפול בנגיף ההרפס סימפלקס. חלק הגואנוזין של אציקלוביר מזדווג עם אדנין כרגיל במהלך שכפול ה-DNA; עם זאת, מכיוון שאין לו קצה 3' של הנוקלאוטיד, DNA פולימראז לא יכול להמשיך ליצור זוגות בסיסים, והשכפול מסתיים.</div>

זיווג בסיס DNA

חוקי שקילות הדנ"א של ארווין צ'רגאף סללו את הדרך לגילוי זיווג בסיסים בדנ"א. הכללים של Chargaff קובעים כי ב ...

Education

JoVE Core

Molecular Biology

ביולוגיה מולקולרית

Unit 1

יחידה 1

DNA Replication

שכפול DNA

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

dna base pair rules

DNA base pairing follows specific rules that help DNA carry genetic information. In DNA, the bases pair in a regular way, with adenine matching thymine and cytosine matching guanine. These pairs fit together because of their chemical shapes and bonding patterns.

These base pairs also support accurate DNA replication. When DNA copies itself, each strand can guide the formation of a new partner strand using the pairing rules. Understanding base pairing helps explain how DNA stays organized and how genetic information is passed on.

DNA Base Pair Rules

replication in prokaryotes

Prokaryotic DNA Replication Steps

Prokaryotic DNA replication copies the chromosome before a cell divides. In bacteria, this process starts at a specific DNA site called the origin of replication. From there, the cell builds new DNA strands using enzymes that match each base with its partner. The DNA double helix first opens so replication can begin. As the strands separate, each original strand serves as a template. New nucleotides are added in a set order, which helps the cell make an accurate copy of its genetic material. <br...

replication in eukaryotes

Eukaryotic DNA Replication Steps

Eukaryotic DNA replication copies the genome before a cell divides. In eukaryotes, this process happens in a controlled sequence so each new cell can receive genetic information. Replication begins at specific sites on the DNA called origins. The DNA is opened, and each original strand serves as a template, meaning it guides the building of a new complementary strand. This sets up two DNA molecules from one original molecule. The process then continues as enzymes add matching nucleotides to...

dna base pairing

DNA base pairing follows specific rules that help DNA carry genetic information. In DNA, the bases pair in a regular way, with adenine matching thymine and cytosine matching guanine. These pairs fit together because of their chemical shapes and bonding patterns. These base pairs also support accurate DNA replication. When DNA copies itself, each strand can guide the formation of a new partner strand using the pairing rules. Understanding base pairing helps explain how DNA stays organized and...

the dna replication fork

DNA Replication Stress and Fork Stalling

DNA replication stress and fork stalling can disrupt the copying of a cell’s genome. The replication fork is the Y-shaped site where DNA strands separate and new complementary strands are made at the same time. This linked unwinding and synthesis helps cells duplicate DNA efficiently and with fewer errors. In organisms with small circular DNA, such as E. coli, replication often begins at a single origin. That setup creates two replication forks that move in opposite directions from the opening...

proofreading

Proofreading in DNA Replication

Proofreading in DNA replication helps keep DNA copying accurate. It is a built-in check that reduces mistakes as new DNA is made. DNA polymerase is the enzyme that carries out this checking during replication. When it adds a wrong nucleotide, it can remove the error and replace it with the correct one. This correction step helps maintain the correct DNA sequence. Proofreading is an important part of DNA replication because it supports genetic accuracy. By catching mistakes as they happen, the...

dna helicases

Helicase Motor Proteins in DNA Unwinding

Helicase motor proteins help unwind DNA during key cell processes. They use energy from ATP hydrolysis, which is the breakdown of ATP to release usable energy. This movement lets helicases separate DNA strands when the cell needs access to the genetic code. These enzymes are involved in DNA replication, repair, recombination, and transcription. Helicases are found in all living organisms, but their structure, function, and movement can differ. In prokaryotes, the DnaB helicase moves along the...

the replisome

DNA Replication Teams in the Replisome

DNA replication depends on the replisome, a coordinated complex of proteins that copies DNA with high accuracy. This DNA replication machinery brings many parts together so the leading and lagging strands can be made at the same time. A key idea in this process is the trombone model, proposed by Bruce Alberts in 1980. In this model, a loop forms on the lagging strand when a primer is made. The loop grows as an Okazaki fragment is synthesized, then falls apart when that fragment is finished.

lagging strand synthesis

Okazaki Fragments in DNA Replication

DNA replication uses a leading strand and a lagging strand, and they are made at different rates. The leading strand starts first. The lagging strand starts later, moves more slowly, and is made in pieces. The two strands also differ in direction and starting steps. Leading strand synthesis follows the opening replication fork. Lagging strand synthesis goes in the opposite direction. The leading strand needs one RNA primer, while the lagging strand needs multiple RNA primers. After priming,...

mismatch repair

Fixing DNA Copying Errors

Mismatch repair helps fix DNA copying errors after replication. When DNA is copied, small mistakes can slip through. This repair system finds those mismatches and corrects them before they become permanent changes. The process depends on a group of mutator proteins. These proteins work together to detect the error, remove the incorrect section, and help replace it with the proper DNA sequence. In this way, mismatch repair supports the accuracy of genetic information. If the repair system does...

dna topoisomerases

How Topoisomerases Untwist DNA

DNA topoisomerases are enzymes that untwist DNA when it becomes overcoiled during cell processes such as DNA replication and transcription. They help regulate positive and negative DNA supercoiling without changing the nucleotide sequence. Clockwise overwinding creates positively supercoiled DNA, while counterclockwise underwinding produces negatively supercoiled DNA. Topoisomerases are grouped into two main types. Type I topoisomerases act on one strand of double-stranded DNA, and they...

telomeres and telomerase

How Telomerase Protects Chromosome Ends

Telomerase helps protect chromosome ends during eukaryotic DNA replication. When the final primer is removed, a single-stranded DNA fragment can remain at the end of the chromosome. That piece cannot be copied in the same way as the rest of the strand because there is no 3' end for new DNA to attach to. If this end piece is not replaced, chromosomal DNA is gradually lost each time a cell divides. The exposed single-stranded DNA can also trigger a DNA damage response from enzymes that detect it.

non-nuclear inheritance

Cytoplasmic Inheritance in Cells

Cytoplasmic inheritance explains how some traits are passed through cell structures outside the nucleus. These traits come from organelles such as mitochondria and chloroplasts. They do not follow the usual nuclear pattern of inheritance. Mitochondria and chloroplasts each contain their own DNA. Because of this, they can carry genetic information that affects cell function and certain visible traits. In high school biology, this topic helps explain why not all inherited traits come from...

animal mitochondrial genetics

Animal Mitochondrial DNA and Inheritance

Animal mitochondrial DNA has its own genome, separate from nuclear DNA. It is a double-stranded, closed circular molecule with about 20,000 base pairs. One strand is the heavy, or H-strand, because it is rich in guanine. The other is the light, or L-strand, because it is rich in cytosine. Compared with nuclear DNA, mitochondrial DNA has very little non-coding sequence. It also has no introns. Its genes are packed closely together, and some even overlap. The D-loop is the main non-coding...

comparing mitochondrial, chloroplast, and prokaryotic genomes

comparing-mitochondrial-chloroplast-and-prokaryotic-genomes

How Organelle Genomes Resemble Bacteria

Mitochondrial and chloroplast genomes still keep several traits from their bacterial ancestors. They also show changes that happened after these organelles evolved inside eukaryotic cells. Eukaryotic cells are cells with a nucleus, while prokaryotes are cells without one. Like prokaryotic genomes, mitochondrial and chloroplast genomes do not bind with histone-like proteins. They also do not show the complex chromosome-like packaging seen in eukaryotes. Mitochondria and chloroplasts divide by...

export of mitochondrial and chloroplast genes

export-of-mitochondrial-and-chloroplast-genes

How Organelles Pass Genes to the Nucleus

Eukaryotic cells can carry three genetic systems: nuclear, mitochondrial, and chloroplast. Over time, many genes from mitochondria and chloroplasts have moved into the nucleus. In some plant species, this gene transfer is still happening. This movement has affected large parts of the genome in some organisms. About 18% of the Arabidopsis thaliana nuclear genome is thought to come from the chloroplast's cyanobacterial ancestor. In yeast, around 75% of the genome is derived from the...

single-strand dna binding proteins

How SSB Proteins Protect DNA Strands

Single-strand DNA-binding proteins, or SSB proteins, help protect DNA during replication. When double-stranded DNA is unwound, the two strands separate. SSB proteins bind to the exposed single strands and keep them stable. These proteins bind in a sequence-independent manner. That means the order of the nitrogenous bases does not have to follow a specific pattern for SSB proteins to attach. Their binding straightens single-stranded DNA and makes it more rigid. This support may help DNA...

key terms and concepts

Learn how DNA bases pair in regular patterns and how those rules help DNA copy itself and preserve genetic information in high school biology.

DNA Base Pair Rules | JoVE K12

molecular biology

JoVE Core Molecular Biology showcases the molecular processes of the cell through clear and concise animated video lessons. Additionally, in scientist-in-action videos, these concepts' application is demonstrated through real experiments in modern laboratories.

Alabama Course of Study Science

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

From Molecules to Organisms: Structures and Processes

9-12.B.1.3

Genomic DNA in Prokaryotes

The genome of most prokaryotic organisms consists of double-stranded DNA organized into one circular chromosome in a region of cytoplasm called the ...

Genomic DNA in Eukaryotes

Eukaryotes have large genomes compared to prokaryotes. To fit their genomes into a cell, eukaryotic DNA is packaged extraordinarily tightly inside the ...

The DNA Helix

Overview

Deoxyribonucleic acid, or DNA, is the genetic material responsible for passing traits from generation to generation in all organisms and most ...

DNA Packaging

Overview

Eukaryotes have large genomes compared to prokaryotes. In order to fit their genomes into a cell, eukaryotes must pack their DNA tightly inside ...

Organization of Genes

Overview

The genomes of eukaryotes can be structured in several functional categories. A strand of DNA is comprised of genes and intergenic regions. ...

The Central Dogma

The central dogma explains the flow of genetic information from DNA nucleotides to the amino acid sequence of proteins.
RNA is the Missing Link Between ...

Replication in Prokaryotes

Overview

DNA replication has three main steps: initiation, elongation, and termination. Replication in prokaryotes begins when initiator proteins bind to ...

Replication in Eukaryotes

What is the Cell Cycle?

Interphase

Mitosis and Cytokinesis

What is Meiosis?

Meiosis vs. Mitosis

Cell division is necessary for growth and reproduction in organisms. Mitosis aids cell growth and development by dividing somatic cells. In contrast, ...

Cellular genetics

Content elaboration: Life is specified by genomes. Each organism has a genome that contains all the biological information needed to develop and maintain that organism. The biological information contained in a genome is encoded in its deoxyribonucleic acid (DNA) and is divided into discrete units called genes. Genes code for proteins. Different parts of the genetic instructions are used in different types of cells, influenced by the cell's environment and history. The many body cells in an individual can be very different from one another, even though they are all descended from a single cell and thus have essentially identical genetic instructions.

Punnett Squares

Monohybrid Crosses

Dihybrid Crosses

Trihybrid Crosses

Trihybrid Crosses
Some of Mendel&#8217;s crosses examined three pairs of contrasting characteristics. Such a cross is called a trihybrid cross. A ...

Law of Independent Assortment

Base-pairing and DNA Repair

Homologous Recombination

The basic reaction of homologous recombination (HR) involves two chromatids that contain DNA sequences sharing a significant stretch of identity. One of ...

Restarting Stalled Replication Forks

DNA replication is initiated at sites containing predefined DNA sequences known as origins of replication. DNA is unwound at these sites by the ...

Gene Conversion

Other than maintaining genome stability via DNA repair, homologous recombination plays an important role in diversifying the genome. In fact, the ...

overview-of-transposition-and-recombination

Overview of Transposition and Recombination

Transposons make up a significant part of genomes of various organisms. Therefore, it is believed that transposition played a major evolutionary role in ...

Meiosis I

Meiosis is the division of a diploid cell into haploid cells forming sperm and eggs in animals through differentiation. Meiosis I is the first stage of ...

Meiosis II

Meiosis II entails cell division and segregation of the sister chromatids, resulting in the production of four unique haploid gametes. The steps for ...

Crossing over

Nondisjunction

Spermatogenesis

Spermatogenesis is the process by which haploid sperm cells are produced in the male testes. It starts with stem cells located close to the outer rim of ...

Oogenesis

In human women, oogenesis produces one mature egg cell or ovum for every precursor cell that enters meiosis. This process differs in two unique ways from ...

Fertilization

During fertilization, an egg and sperm cell fuse to create a new diploid structure. In humans, the process occurs once the egg has been released from the ...

Structure and function of DNA in cells

Content elaboration: Mendel's laws of inheritance (introduced in grade 8) are interwoven with current knowledge of DNA and chromosome structure and function to build toward basic knowledge of modern genetics. Genes are segments of DNA molecules. The sequence of DNA bases in a chromosome determines the sequence of amino acids in a protein. Inserting, deleting or substituting segments of DNA molecules can alter genes. Sorting and recombination of genes in sexual reproduction and meiosis specifically result in a variance in traits of the offspring of any two parents. This content can be explicitly connected to evolution.

Structure and function of DNA in cells

Chi-square Analysis

The chi-square test is a statistical hypothesis test. It is used to check whether there is a significant difference between an expected value and an ...

Pedigree Analysis

Multiple Allele Traits

Incomplete Dominance

Gregor Mendel&#39;s work (1822 - 1884) was primarily focused on pea plants. Through his initial experiments, he determined that every gene in a diploid ...

Lethal Alleles

Agouti: A Lethal Allele
Lucien Cu&#233;not discovered lethal alleles in 1905 while studying the inheritance of coat color in mice. The agouti gene is ...

Polygenic Traits

background-and-environment-affect-phenotype

Background and Environment Affect Phenotype

Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as ...

X and Y Chromosomes

Among mammals, the gender of an organism is determined by the sex chromosomes. Humans have two sex chromosomes, X and Y. Every human diploid cell has 22 ...

The Y Chromosome Determines Maleness

The Y chromosome is a sex chromosome&#160;found in several vertebrates and mammals, including humans. In addition to 22 pairs of autosomes, the human ...

The Ratio of X Chromosome to Autosomes

In most organisms, sex is determined by the ratio of X and Y chromosomes. However, in some organisms, such as Drosophila and C.elegans, sex is determined ...

X-linked Traits

Sex Linked Disorders

Dosage Compensation

In animals, gender is determined by the number and type of sex chromosome. For example, human females have two X chromosomes, and males have one X and one ...

X-inactivation

Genetic mechanisms and inheritance

Content elaboration: Genetic variation in traits among offspring is a result of the movement of chromosomes crossing over, independent assortment, and recombination during gamete formation. Gene interactions described in middle school were limited primarily to dominant and codominant traits. In high school, genetic mechanisms, both classical and modern, including incomplete dominance, sex-linked traits, and dihybrid crosses, are investigated through real-world examples. Statistics and probability allow us to compare observations made in the real world with predicted outcomes. Dihybrid crosses can be used to explore linkage groups, gene interactions and phenotypic variations. Chromosome maps reveal linkage groups.

Genetic mechanisms and inheritance

Mutations

Mutations are changes in the sequence of DNA. These changes can occur spontaneously or they can be induced by exposure to environmental factors. Mutations ...

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

Genome Size and the Evolution of New Genes

Gene Families

Gene Evolution - Fast or Slow?

types-of-genetic-transfer-between-organisms

Types of Genetic Transfer Between Organisms

Mutations

Content elaboration: Genes can be altered by insertion, deletion, or substitution of a segment of DNA molecules. An altered gene is a mutation and will be passed on to every cell that develops from it. The resulting features may help, harm or have little or no effect on the offspring's success in its environments. Gene mutations in gametes are passed on to offspring.

Modern genetics

Content elaboration: Technological developments that lead to the current knowledge of heredity are introduced for study. The development of the model for DNA structure was the result of experimentation, hypothesis, testing, statistical analysis and technology as well as the studies and ideas of many scientists. James Watson and Francis Crick developed the current model based on the work of Rosalind Franklin and others. Scientists continue to extend the model and use it to devise technologies to further our understanding and application of genetics. [cite: 143, 149] The emphasis is not on the memorization of specific steps of gene technologies, but rather on the interpretation and application of the results.

Modern genetics

DNA Base Pair Rules

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