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

DNA, bazıları bir proteindeki amino asit serilerini kodlayan talimatlar olan genler ve nükleotid dizileri içerir. DNA'dan RNA'ya ve proteine genetik bilginin akışı, Merkezi Dogma olarak bilinen bir süreçtir. Bu sürecin ilk adımı, bir RNA polimeraz enziminin genin RNA bazlı bir kopyasını veya transkriptini sentezlediği transkripsiyondur.DNA, transkripte eklenen her yeni RNA bazının orijinal DNA zincirine tamamlayıcı olduğu bir şablon olarak kullanılır. Messenger veya mRNA adı verilen bazı transkriptler proteinleri kodlarken, kodlamayanlar diğer hücresel işlemlere katılır. Örneğin ribozomal rRNA ve transfer tRNA, protein sentezine katılır.Bir sonraki adım, bir amino asit zincirini sentezlemek için mRNA'nın kodunun çözüldüğü çeviridir. mRNA'yı okumak için genetik kod olarak bilinen bir dizi talimat kullanılır. Çoğu organizma, spesifik amino asitlere çevrilen kodonlar adı verilen üç nükleotid grubundan oluşan bu aynı evrensel kodu kullanır.64 farklı nükleotid üçlüsü vardır ancak proteinlerde kodu dejenere yapan sadece 20 standart amino asit vardır, yani çoklu kodon setleri aynı talimatı verebilir. Altmış bir set amino asit kodunu belirler ve üçü translasyonun stop sinyalidir. Translasyon, büyük bir rRNA ve protein kompleksi olan ribozomda tRNA'nın yardımıyla gerçekleşir.tRNA, üç firkete ilmek yapısına sahiptir. Bir döngü, kodona tamamlayıcı bazlara sahip olan antikodon adı verilen bir dizi içerir. Bu diziye karşılık gelen bir amino asit, onu ribozoma taşıyan tRNA'nın ucuna eklenir.Başlatma faktörleri adı verilen proteinler, küçük ribozom birimini, küçük ribozom birimini, bir başlatıcı tRNA'yı ve mRNA'yı bir araya getirir. Kompleksin birleştirilmesinden sonra ribozom, çeviri başlangıç bölgesini aramak için mRNA boyunca kayar. Burada, başlatıcı tRNA antikodonu, tamamlayıcı kodona bağlanır;büyük ribozom birimi montaja bağlanır ve translasyon başlatılır.Bir sonraki tRNA geldiğinde, başlatıcıdan gelen amino asit ayrılır ve komşu amino aside aktarılır, bu da büyüyen bir polipeptit zinciri ile sonuçlanır. Amino asitlerin eklenmesi, mRNA'da bir durdurma kodonu saptanana kadar devam eder. Ribozom daha sonra zinciri, işlevsel bir proteine katlanabilmesi için serbest bırakır.

dna'dan proteine

Hücrelerdeki genetik bilginin DNA'dan mRNA'ya ve proteine akışı, genlerin mRNA'ların sırasını belirlediğini ve bunun da tüm proteinleri oluşturan amino asitlerin sırasını belirlediğini belirten merkezi dogma tarafından tanımlanır. Bir molekülün, diğer bir molekülün kodunu deşifre etmesi, spesifik proteinler ve RNA'lar tarafından gerçekleştirilir. DNA'da depolanan bilgi, hücresel fonksiyon için çok merkezi olması nedeniyle, DNA'nın kendisini sağlam ve korumalı tutmasına karşın, hücrenin protein sentezi için bu bilginin mRNA kopyalarını üretmesi sezgisel olarak mantıklıdır. DNA'nın RNA'ya kopyalanması, DNA zincirinde okunan her nükleotit için mRNA zincirine bir nükleotit eklenmesiyle nispeten basitleştirilir. Protein translasyonu, biraz daha karmaşıktır çünkü üç mRNA nükleotidi, polipeptit dizisindeki bir amino aside karşılık gelir. Bununla birlikte, protein translasyonu sistematik ve doğrusaldır, öyle ki nükleotit 1 ila 3, amino asit 1'e karşılık gelir, nükleotit 4 ila 6, amino asit 2'ye karşılık gelir vb.
 
 Genetik Kod Dejenere ve Evrenseldir
 
 Her amino asit, üçlü kodon adı verilen üç nükleotit dizisi ile tanımlanır. mRNA farklı numaradaki “harfler” ve protein “alfabeleri” göz önüne alındığında bilim adamları, tek amino asitlerin nükleotit kombinasyonları ile temsil edilmesi gerektiğini teorileştirdiler. Nükleotit çiftleri, her amino asidi belirtmek için yeterli olmayacaktır çünkü yalnızca 16 olası iki nükleotit kombinasyonu (42) vardır. Buna karşılık, amino asit sayısından çok daha fazla olan 64 olası nükleotit üçlüsü (43) vardır. Bilim adamları, amino asitlerin nükleotit üçlüleri tarafından kodlandığını ve genetik kodun “dejenere” olduğunu teorileştirdiler. Başka bir deyişle, belirli bir amino asit, birden fazla nükleotid üçlüsü tarafından kodlanabilir. Bu daha sonra deneysel olarak doğrulanmıştır: Francis Crick ve Sydney Brenner, bir virüsün genine bir, iki veya üç nükleotit eklemek için kimyasal mutajen proflavin'i kullandılar. Bir veya iki nükleotit yerleştirildiğinde normal proteinler üretilmemiştir. Üç nükleotit eklendiğinde, protein sentezlenmiş ve işlevsel olmuştur. Bu, amino asitlerin üç nükleotitlik gruplar tarafından nitelendirilmesi gerektiğini göstermiştir. Bu nükleotit üçlülerine kodon denir. Bir veya iki nükleotidin eklenmesi, üçlü okuma çerçevesini tamamen değiştirmiştir, böylece sonraki her amino asit için mesajı değiştirmiştir. Üç nükleotidin eklenmesi, translasyon sırasında fazladan bir amino asidin eklenmesine neden olsa da, proteinin geri kalanının bütünlüğü korunmuştur.
 
 Bir polipeptit zincirine spesifik bir amino asidin eklenmesi talimatını veren kodonlara ek olarak, 64 kodonun üçü, protein sentezini sonlandırır ve polipeptidi translasyon mekanizmasından serbest bırakır. Bu üçlülere anlamsız kodonlar veya durdurma kodonları denir. Başka bir kodon olan AUG'nin de özel bir işlevi vardır. Amino asit metiyonini belirtmeye ek olarak, translasyonu başlatmak için başlangıç kodonu olarak da hizmet eder. Translasyon için okuma çerçevesi, mRNA'nın 5' ucuna yakın AUG başlangıç kodonu tarafından ayarlanır. Başlatma kodonunu takiben mRNA, bir durdurma kodonu ile karşılaşılıncaya kadar üçlü gruplar halinde okunur.
 
 Tek bir amino asidin birden çok benzer kodon tarafından spesifikasyonuna "dejenerasyon" denir. Dejenerasyonun, rastgele mutasyonların olumsuz etkisini azaltmak için hücresel bir mekanizma olduğuna inanılmaktadır. Aynı amino asidi niteleyen kodonlar, tipik olarak sadece bir nükleotit kadar farklılık gösterir. Ek olarak, kimyasal olarak benzer yan zincirlere sahip amino asitler, benzer kodonlar tarafından kodlanır. Örneğin, GA* bloğunu işgal eden aspartat (Asp) ve glutamat (Glu) negatif yüklüdür. Genetik kodun bu nüansı, bir tek nükleotit ikame mutasyonunun aynı amino asidi belirtebilmesini ancak hiçbir etkisinin olmamasını veya benzer bir amino asidi belirtmesini sağlayarak proteinin tamamen işlevsiz hale gelmesini engeller.
 
 Genetik kod neredeyse evrenseldir. Birkaç küçük istisna dışında, neredeyse tüm türler protein sentezi için aynı genetik kodu kullanır. Kodonların korunması, atlarda globin proteinini kodlayan saflaştırılmış bir mRNA'nın bir lale hücresine aktarılabileceği ve lalenin at globinini sentezleyeceği anlamına gelir. Tek bir genetik kodun olması, özellikle 20 amino asit ve 64 üçlü kodonun yaklaşık 1084 olası kombinasyonu olduğu düşünüldüğünde, Dünya'daki tüm yaşamın ortak bir kökeni paylaştığına dair güçlü bir kanıttır.
 
 Bu metin bu kaynaktan uyarlanmıştır: <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>.

DNA'dan Proteine

Hücrelerdeki genetik bilginin DNA'dan mRNA'ya ve proteine akışı, genlerin dizisini belirlediğini belirten merkezi dogma tarafından tanımlanır ...

Education

JoVE Core

Chemistry

Kimya

Biochemistry

Biyokimya

KEY TERMS AND CONCEPTS

TEMEL TERİMLER VE KAVRAMLAR

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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amino acids

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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.

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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

chemistry

JoVE Core Kimya, özlü ve kolay anlaşılır animasyon video derslerini kullanarak genel kimya kavramlarına hayat veriyor. Ek olarak, bilim insanı uygulama videolarımız ile klasik ve orijinal araştırma deneylerini dünya çapında günümüz laboratuvarlarında görselleştiriyoruz.

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New York State Science Learning Standards

Life Science

Structure and Function

HS-LS1-1.

matter-and-energy-in-organisms-and-ecosystems

Matter and Energy in Organisms and Ecosystems

HS-LS1-6.

Nucleic Acids and Nucleotides

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Nucleic Acid Structure

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DNA Base Pairing

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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

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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

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Genomic DNA in Eukaryotes

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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
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RNA Stability

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pre-mRNA Processing

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Types of RNA

Overview
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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

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tRNA Activation

Initiation of Translation

Termination of Translation

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Cell Diversity

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Euchromatin

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Heterochromatin

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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.

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Levels of Organization

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The Scientific Method

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Taxonomy

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Phylogeny

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HS-LS1-2

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Regulation of Metabolism

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Positive and Negative Feedback Loops

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Functions of Life

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Requirements for Human Life

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What is Homeostasis?

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Negative and Positive Feedback

Homeostatic Imbalance

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pH Homeostasis

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Homeostatic Imbalances in Body Temperature

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HS-LS1-3

What is the Cell Cycle?

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Interphase

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The Cell Cycle Control System

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Inhibition of CDK Activity

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Mitogens and the Cell Cycle

Replicative Cell Senescence

Abnormal Proliferation

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Cells Coordinate Growth and 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.

HS-LS1-4

The Genetic Code and Codons

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