Name: the genetic code and codons
Uploaded: 2020-09-24T15:06:53.000Z
Duration: 3 min 6 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

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

From Molecules To Organisms: Structures And Processes

HS-LS1-1

From DNA to Protein

דנ"א כולל גנים, רצפי נוקלאוטידים, שחלקם הם הוראות המקדדות את סדרת חומצות האמינו בחלבון. זרימת המידע הגנטי מדנ"א לרנ"א של חלבון היא תהליך הנקרא הדוגמה הראשית"השלב הראשון בתהליך זה הוא תעתוק, שבמהלכו אנזים פולימראז הרנ"א מיצר עותק רנ"א מבוסס או תעתיק של הגן. הדנ"א משמש כתבנית שבה כל בסיס רנ"א חדש שנוסף לתעתיק משלים את גדיל הדנ"א המקורי.חלק מהתעתיקים, המכונים רנ"א שליח או mRNA, משמשים כקוד לחלבון, בעוד שתעתיקים שאינם קוד משתתפים בתהליכים אחרים בתאים. לדוגמה, rRNA ריבוזומלי ו-tRNA מעביר משתתפים ביצירת חלבון. השלב הבא הוא התרגום, שבמהלכו ה-mRNA מפוענח כדי ליצר שרשרת של חומצות אמינו.מערכת הוראות הנקראת הקוד הגנטי משמשת לקריאת mRNA. רוב האורגניזמים משתמשים באותו קוד אוניברסלי, המורכב משלוש קבוצות נוקלאוטידיות הנקראות קודון"המתורגמות לחומצות אמינו מסוימות. יש 64 שלישיית נוקלאוטידים, אך רק עשרים חומצות אמינו סטנדרטיות שגורמות לקוד להתנוון, כלומר, סטים מרובים של קבוצות קודון יכולים לתת את אותן הוראות.שישים ואחד סטים של קודים לחומצות אמינו ושלושה אותות להפסקת התרגום. תרגום מתרחש בריבוזום, קומפלקס גדול של rRNAs וחלבונים, בעזרת tRNA. ל-tRNA יש שלושה מבנים של לולאות סיכה.לולאה אחת כוללת רצף הנקרא האנטי-קודון, שהוא בעל בסיסים משלימים לקודון. חומצת אמינו התואמת לרצף הזה מחוברת לקצה ה-tRNA, המעביר אותה לריבוזום. חלבונים המכונים גורמי אתחול מחברים את יחידת הריבוזום הקטנה, tRNA אתחול, וה-mRNA.לאחר הרכבת הקומפלקס, הריבוזום מחליק לאורך ה-mRNA בחיפוש אחר אתר תחילת התרגום. כאן אנטי-קודון האתחול tRNA נקשר לקודון המשלים;יחידת הריבוזום הגדולה נקשרת למכלול ומתחילה התרגום. כשה-tRNA הבא נכנס, חומצת האמינו מהמאתחל מתנתקת ומועברת לחומצת האמינו השכנה, והתוצאה היא שרשרת פוליפפטיד מתארכת.התוספת של חומצות אמינו ממשיכה עד שקודון סיום מאובחן ב-mRNA. לאחר מכן הריבוזום משחרר את השרשרת כך שהיא יכולה להתקפל לכדי חלבון מתפקד.

מ-dna לחלבון

<div style="direction:rtl">זרימת המידע הגנטי בתאים מ-DNA ל-mRNA לחלבון מתוארת על ידי הדוגמה המרכזית, הקובעת שגנים מציינים את רצף ה-mRNA, שבתורם מציינים את רצף חומצות האמינו המרכיבות את כל החלבונים. הפענוח של מולקולה אחת לאחרת מתבצע על ידי חלבונים ו-RNA ספציפיים. מכיוון שהמידע המאוחסן ב-DNA כל כך מרכזי בתפקוד הסלולרי, הגיוני אינטואיטיבי שהתא יוצר עותקי mRNA של מידע זה לסינתזת חלבון תוך שמירה על ה-DNA עצמו שלם ומוגן. ההעתקה של DNA ל-RNA היא פשוטה יחסית, כאשר נוקלאוטיד אחד מתווסף לגדיל ה-mRNA עבור כל נוקלאוטיד שנקרא בגדיל ה-DNA. התרגום לחלבון הוא קצת יותר מורכב מכיוון ששלושה נוקלאוטידים mRNA תואמים לחומצת אמינו אחת ברצף הפוליפפטידים. עם זאת, התרגום לחלבון הוא עדיין שיטתי וקולינארי, כך שנוקלאוטידים 1 עד 3 תואמים לחומצה אמינית 1, נוקלאוטידים 4 עד 6 תואמים לחומצת אמינו 2, וכן הלאה. הקוד הגנטי הוא מנוון ואוניברסלי כל חומצת אמינו מוגדרת על ידי רצף בן שלושה נוקלאוטידים הנקרא קודון המשולש. בהתחשב במספרים השונים של "אותיות" ב"אלפבית" של mRNA וחלבונים, מדענים שיערו כי חומצות אמינו בודדות חייבות להיות מיוצגות על ידי שילובים של נוקלאוטידים. כפילות נוקלאוטידים לא יספיקו כדי לציין כל חומצת אמינו מכיוון שיש רק 16 שילובים אפשריים של שני נוקלאוטידים (42). לעומת זאת, יש 64 שלישיות נוקלאוטידים אפשריות (43), שזה הרבה יותר ממספר חומצות האמינו. מדענים גרסו כי חומצות אמינו מקודדות על ידי שלישיות נוקלאוטידים וכי הקוד הגנטי "מנוון". במילים אחרות, חומצת אמינו נתונה יכולה להיות מקודדת על ידי יותר משלישיית נוקלאוטידים אחת. זה אושר מאוחר יותר בניסוי: פרנסיס קריק וסידני ברנר השתמשו במוטגן הכימי פרופלאבין כדי להחדיר נוקלאוטיד אחד, שניים או שלושה לגן של וירוס. כאשר הוכנסו נוקלאוטיד אחד או שניים, החלבונים הנורמליים לא נוצרו. כאשר הוכנסו שלושה נוקלאוטידים, החלבון היה מסונתז ופעל. זה הוכיח שחומצות האמינו חייבות להיות מוגדרות על ידי קבוצות של שלושה נוקלאוטידים. שלישיות נוקלאוטידים אלו נקראות קודונים. החדרה של נוקלאוטיד אחד או שניים שינתה לחלוטין את מסגרת הקריאה של הטריפלט, ובכך שינתה את המסר לכל חומצת אמינו שלאחר מכן. למרות שהחדרה של שלושה נוקלאוטידים גרמה להחדרת חומצת אמינו נוספת במהלך התרגום, שלמות שאר החלבון נשמרה. בנוסף לקודונים המורים על הוספת חומצת אמינו ספציפית לשרשרת פוליפפטיד, שלושה מתוך 64 הקודונים מפסיקים את סינתזת החלבון ומשחררים את הפוליפפטיד ממנגנון התרגום. שלישיות אלו נקראות קודוני שטות או קודונים-סיום. לקודון נוסף, AUG, יש גם פונקציה מיוחדת. בנוסף לציון חומצת האמינו מתיונין, הוא משמש גם כקודון ההתחלה לתחילת התרגום. מסגרת הקריאה לתרגום נקבעת על ידי קודון ההתחלה של AUG ליד קצה 5' של ה-mRNA. לאחר קודון ההתחלה, ה-mRNA נקרא בקבוצות של שלושה עד שנתקל בקודון-סיום. המפרט של חומצת אמינו בודדת על ידי מספר קודונים דומים נקרא "ניוון". מאמינים כי ניוון הוא מנגנון תאי להפחתת ההשפעה השלילית של מוטציות אקראיות. קודונים המציינים את אותה חומצת אמינו נבדלים בדרך כלל רק על ידי נוקלאוטיד אחד. בנוסף, חומצות אמינו עם שרשראות צד דומות מבחינה כימית מקודדות על ידי קודונים דומים. לדוגמה, אספרטאט (Asp) וגלוטמט (Glu), אשר תופסים את בלוק GA*, שניהם טעונים שלילי. ניואנס זה של הקוד הגנטי מבטיח שמוטציה של החלפת נוקלאוטידים בודדת עשויה לציין את אותה חומצת אמינו אך ללא השפעה או לציין חומצת אמינו דומה, ומונעת מהחלבון להפוך ללא תפקודי לחלוטין. הקוד הגנטי הוא כמעט אוניברסלי. למעט כמה חריגים קטנים, כמעט כל המינים משתמשים באותו קוד גנטי לסינתזת חלבון. שימור קודונים פירושו שניתן להעביר mRNA מטוהר המקודד לחלבון הגלובין בסוסים לתא צבעוני, והצבע יסנתז את גלובין הסוס. העובדה שיש רק קוד גנטי אחד היא עדות חזקה לכך שכל החיים על פני כדור הארץ חולקים מקור משותף, במיוחד בהתחשב בכך שיש כ-1084 שילובים אפשריים של 20 חומצות אמינו ו-64 קודונים משולשים. 
טקסט זה מותאם מv<a href="https://openstax.org/books/biology-2e/pages/15-1-the-genetic-code">Openstax, Biology 2e, Chapter 15.1: </a><a href="https://openstax.org/books/biology-2e/pages/15-1-the-genetic-code">The Genetic Code</a>.
</div>

מ-DNA לחלבון

זרימת המידע הגנטי בתאים מ- DNA ל- mRNA לחלבון מתוארת על ידי הדוגמה המרכזית, הקובעת כי גנים מציינים את רצף ...

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מונחים ומושגים מרכזיים

the genetic code and codons

The genetic code and codons explain how cells turn DNA information into proteins. Genes first direct the sequence of mRNA, and mRNA then directs the sequence of amino acids that make up proteins. Specific proteins and RNAs carry out this decoding. Cells copy DNA into mRNA so the original DNA stays protected while the cell uses the message for protein synthesis.

Copying DNA to RNA is relatively simple. One nucleotide is added to the mRNA strand for every nucleotide read on the DNA strand. Translating mRNA into protein is more complex because three mRNA nucleotides correspond to one amino acid. Even so, the process is orderly and stays collinear. Nucleotides 1 to 3 specify amino acid 1, nucleotides 4 to 6 specify amino acid 2, and the pattern continues in the same way.

Each amino acid is defined by a three-nucleotide codon, also called a triplet codon. Scientists proposed this idea because the mRNA and protein alphabets are different sizes. Two-nucleotide combinations would not be enough, since there are only 16 possible doublets. Three-nucleotide combinations provide 64 possible triplets, which is far more than the number of amino acids. This led to the idea that the code is degenerate, meaning one amino acid can be encoded by more than one codon.

Francis Crick and Sydney Brenner tested this idea with the chemical mutagen proflavin. They inserted one, two, or three nucleotides into a virus gene. Inserting one or two nucleotides prevented normal proteins from being made. Inserting three nucleotides still allowed a functional protein to be synthesized. This showed that amino acids are read in groups of three. One- or two-nucleotide insertions shift the reading frame and change every later amino acid, while a three-nucleotide insertion adds one amino acid but preserves the rest of the protein.

Some codons do not add amino acids. Three of the 64 codons are stop codons, also called nonsense codons, and they end protein synthesis. Another codon, AUG, has two roles. It codes for methionine and also acts as the start codon that begins translation. The AUG start codon near the 5' end of the mRNA sets the reading frame. After that, the mRNA is read in groups of three until a stop codon appears.

Degeneracy may help reduce the effects of random mutations. Codons that specify the same amino acid usually differ by only one nucleotide. Amino acids with similar side chains are also often encoded by similar codons. For example, aspartate and glutamate are both negatively charged and fall in the GA* codon block. This means a single-nucleotide substitution may have no effect, or it may lead to a similar amino acid instead of a harmful change.

The genetic code is nearly universal. With a few minor exceptions, most species use the same code to make proteins. This shared code means a purified mRNA for horse globin could be placed in a tulip cell, and the tulip would make horse globin. The near-universal code is also strong evidence that life on Earth shares a common origin, especially since there are about 10^84 possible combinations of 20 amino acids and 64 triplet codons.

The Genetic Code and Codons

functional groups

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dna base pairing

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Carbohydrates are important energy sources in human and animal diets. Grains, fruits, and vegetables are natural sources of carbohydrates. They help provide energy to the body, especially through glucose, a simple sugar found in starch and many staple foods. Carbohydrates are identified by the stoichiometric formula (CH2O)n, where n is the number of carbons in the molecule. This means the ratio of carbon to hydrogen to oxygen is usually 1:2:1. The name carbohydrate comes from this pattern,...

protein and protein structure

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amino acids

Amino Acids and Protein Building

Amino acids are the building blocks of proteins. Each amino acid has the same basic structure. A central carbon atom, called the alpha carbon, is bonded to an amino group, a carboxyl group, and a hydrogen atom. Each amino acid also has an R group, or side chain, attached to the central carbon. The R group is different for every amino acid. It helps determine whether an amino acid is acidic, basic, polar, or nonpolar. Scientists call these molecules amino acids because they contain both amino...

peptide bonds

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nucleic acids

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dna replication

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from dna to protein

The genetic code and codons explain how cells turn DNA information into proteins. Genes first direct the sequence of mRNA, and mRNA then directs the sequence of amino acids that make up proteins. Specific proteins and RNAs carry out this decoding. Cells copy DNA into mRNA so the original DNA stays protected while the cell uses the message for protein synthesis. Copying DNA to RNA is relatively simple. One nucleotide is added to the mRNA strand for every nucleotide read on the DNA strand.

polymers

Polymer Chains and How They Form

Polymers are long chains of molecules made from repeating units called monomers. The word polymer comes from the Greek words "poly," meaning many, and "mer," meaning parts. Polymers can be found in nature, such as DNA and proteins, or made synthetically, such as plastics. A polymer’s shape helps define its properties. Some polymers form linear chains, while others are branched or arranged in complex networks. Functional groups on a polymer also affect how it behaves. The repeating units in a...

key terms and concepts

Learn how codons, stop signals, and the AUG start codon guide protein synthesis, and why the genetic code is nearly universal across species.

The Genetic Code and Codons | JoVE K12

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Structure and Function

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Nucleic Acids and Nucleotides

Nucleic acids are the most important macromolecules for the continuity of life. They carry the cell&#39;s genetic blueprint and have instructions for its ...

Nucleic Acid Structure

The pentose sugar in DNA is deoxyribose, while in RNA the pentose sugar is ribose. The difference between the sugars is the presence of the hydroxyl group ...

DNA Base Pairing

Erwin Chargaff&#x2019;s rules on DNA equivalence paved the way for the discovery of base pairing in DNA. Chargaff&#x2019;s rules state that in a ...

The flow of genetic information in cells from DNA to mRNA to protein is described by the central dogma, which states that genes specify the sequence of ...

The DNA Helix

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

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 ...

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 ...

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 ...

RNA Structure

Overview
The basic structure of RNA consists of a five-carbon sugar and one of four nitrogenous bases. Although most RNA is single-stranded, it can form ...

RNA Stability

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pre-mRNA Processing

In eukaryotic cells, transcripts made by RNA polymerase are modified and processed before exiting the nucleus. Unprocessed RNA is called precursor mRNA or ...

Types of RNA

Overview
Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs ...

DNA as a Genetic Template

What is Gene Expression?

A gene is a stretch of DNA that serves as the blueprint for functional RNAs and proteins. Since DNA is comprised&#160; of nucleotides and proteins are ...

Transcription

Transcription is the synthesis of RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene sequence. ...

Translation

Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following transcription, it constitutes ...

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that ...

tRNA Activation

Initiation of Translation

Termination of Translation

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Cell Diversity

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Cells of the Epidermis

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Bone Cells and Tissue

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Gross Anatomy of Skeletal Muscles

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Structure of Cardiac Muscles

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Structure and Organization of Smooth Muscles

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Chromosome Replication

Before a cell can divide, it must accurately replicate all of its chromosomes, including the DNA and its associated histone and non-histone ...

Neurons: The Cell Body and the Dendrites

A typical nerve cell comprises three main components: the cell body, dendrites, and the axon. The cell body, also known as the soma or perikaryon, serves ...

Lampbrush Chromosomes

In 1882, Flemming observed lampbrush chromosomes (LBC) in salamander eggs. Later in 1892, R&#252;ckert observed LBCs in shark egg cells and coined the ...

Neurons: The Axon

The axon is a long, thin extended portion of the neuron that carries impulses from its cell body toward the effector cell.
Axoplasm, the axon&#39;s ...

Polytene Chromosomes

Polytene chromosomes are giant interphase chromosomes with several DNA strands placed side by side. They were discovered in the year 1881 by Balbiani in ...

Nervous Tissue: Neuron Types

Neurons, the fundamental units of the nervous system, can be classified based on both their structural and functional characteristics.
Structurally, ...

Euchromatin

The extent of chromatin compaction can be studied by staining chromatin using specific DNA binding dyes. Under the microscope, the dense-compacted regions ...

Nervous Tissue: Glial Cells

Glial cells or neuroglia are non-neuronal cells in the nervous system that outnumber neurons. These include astrocytes, oligodendrocytes, microglia, and ...

Heterochromatin

Lymphoid Cells and Tissues

Lymphoid cells and lymphoid tissues are the two major components of lymphoid organs.
Lymphoid cells consist of immune system cells such as B and T ...

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Chromatin Position Affects Gene Expression

Chromatin is the massive complex of DNA and proteins packaged inside the nucleus. The complexity of chromatin folding and how it is packaged inside the ...

Two structural features of the DNA molecule provide a basis for the mechanisms of heredity: the four nucleotide bases and its double-stranded nature. The ...

Organization of Genes

Chromosome Structure

A functional eukaryotic chromosome must contain three elements: a centromere, telomeres, and numerous origins of replication.
The centromere is a DNA ...

Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells. Emphasis is on the conceptual understanding that DNA sequences determine the amino acid sequence and thus protein structure. Students can produce scientific writing, or presentations, and/or physical models that communicate constructed explanations.

Characteristics of Life

Biology is a natural science that studies life and living organisms, including their structure, function, development, interactions, evolution, ...

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Levels of Organization

Biological organization is the classification of biological structures, ranging from atoms at the bottom of the hierarchy to the Earth&#x27;s biosphere. ...

The Scientific Method

The scientific method is a detailed, empirical problem-solving process used by biologists and other scientists. This iterative approach involves ...

Taxonomy

Taxonomy is the science of defining and naming groups of biological organisms based on shared characteristics. It uses a hierarchy of increasingly ...

Phylogeny

Phylogeny is concerned with the evolutionary diversification of organisms or groups of organisms. A group of organisms with a name is called a taxon ...

Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, or organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.

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Overview of Metabolism

Living cells constantly carry out various chemical reactions which are necessary for their proper functioning. These reactions are interlinked to one ...

Regulation of Metabolism

Cellular needs and conditions vary from cell to cell and change within individual cells over time. For example, the required enzymes and energetic demands ...

Positive and Negative Feedback Loops

Animal organs and organ systems constantly adjust to internal and external changes through a process called homeostasis (&#34;steady state&#34;). Examples ...

Functions of Life

Human life is characterized by a variety of functions that are essential for survival and well-being. These functions include metabolism, movement, ...

Requirements for Human Life

The Earth and its atmosphere have provided humans with air, water, and food, but these are not the only requirements for survival. Humans also require a ...

What is Homeostasis?

Maintaining homeostasis requires that the body continuously maintain its internal conditions. Each physiological condition has a particular set point, ...

Negative and Positive Feedback

Homeostatic Imbalance

Homeostasis is the maintenance of a stable internal environment within the body, which is crucial for the proper functioning of cells, tissues, organs, ...

pH Homeostasis

Acid-base homeostasis is essential for maintaining normal physiological activities in humans. The pH of various body fluids is strictly regulated because ...

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Homeostatic Imbalances in Body Temperature

Hyperthermia is an umbrella term for elevated body temperature that occurs when heat production exceeds the body&#39;s ability to dissipate it.
...

Regulation of Food Intake

The hypothalamus releases peptides influencing feeding behavior.
Two hypothalamic neuronal groups participate in this process.
Neuropeptide Y (NPY) and ...

Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis in living organisms. Examples of investigations could include heart rate responses to exercise, stomate responses to moisture and temperature, root development in response to water levels, or cell response to hypertonic and hypotonic environments.

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What is the Cell Cycle?

The cell cycle refers to the sequence of events occurring throughout a typical cell&#8217;s life. In eukaryotic cells, the somatic cell cycle has two ...

Interphase

The cell cycle occurs over approximately 24 hours (in a typical human cell) and in two distinct stages: interphase, which includes three phases of the ...

The Cell Cycle Control System

Positive Regulator Molecules

Inhibition of CDK Activity

S-Cdk Initiates DNA Replication

M-Cdk Drives Transition Into Mitosis

Mitogens and the Cell Cycle

Replicative Cell Senescence

Abnormal Proliferation

Use a model to illustrate the role of the cell cycle and differentiation in producing and maintaining complex organisms. Emphasis is on conceptual understanding that mitosis passes on genetically identical materials via replication, not on the details of each phase in mitosis.

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The Genetic Code and Codons

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