Introduction to Genetic Code

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Questions and Answers

Which of the following cannot pass through the filter?

Free charged tRNA

mRNA

Ribosomes (correct)

Charged tRNA

What happens when the ribosome translocates to a stop codon?

There is no tRNA with an anticodon that can pair with the codon in the A site.

What are the release factors involved in the termination of translation?

RF-1 and RF-3 (correct)

GTP and GDP

tRNA and mRNA

IF-1 and IF-2

The ribosome consists of two subunits: the large subunit () and the small subunit ().

50S, 30S Signup and view all the answers

What sequence binds to the small subunit of the ribosome during initiation?

Shine-Dalgarno sequence Signup and view all the answers

The first tRNA attaches to the initiation codon.

True Signup and view all the answers

What is formed when a tRNA charged with N-formylmethionine binds during initiation?

30S initiation complex Signup and view all the answers

What does GTP bind to during initiation of translation?

Initiation factors Signup and view all the answers

Match the amino acids with their corresponding codons:

Leucine = GAU Arginine = CGU Isoleucine = AUC Glycine = GGC Signup and view all the answers

What do the letters A, G, T, and C correspond to in DNA?

Nucleotides Signup and view all the answers

How many codons are there in total?

64 Signup and view all the answers

What is the triplet code?

Each codon consists of three bases. Signup and view all the answers

Which of the following statements about the genetic code is true?

The genetic code is universal. Signup and view all the answers

The genetic code is degenerate, meaning that some amino acids are coded by more than one codon.

True Signup and view all the answers

What is the start codon for protein synthesis?

AUG Signup and view all the answers

The three nonsense codons are ___, _, and ___

UAA, UAG, UGA Signup and view all the answers

What is the significance of the Wobble Hypothesis in genetics?

It explains how tRNA can recognize multiple codons for the same amino acid. Signup and view all the answers

Which of the following is NOT a characteristic of the genetic code?

Overlapping Signup and view all the answers

Who conducted experiments that helped decipher the genetic code?

Marshall Nirenberg and Heinrich Matthaei Signup and view all the answers

What amino acid does the codon UUU specify?

Phenylalanine Signup and view all the answers

What does the term 'non ambiguous' refer to in the context of the genetic code?

Each codon codes for only one amino acid. Signup and view all the answers

Study Notes

Introduction - Genetic Code

The genetic code is a set of rules that determines how the nucleotide sequence of a gene is translated into the amino acid sequence of a protein.
DNA is composed of four nucleotides: Adenine (A), Guanine (G), Thymine (T), and Cytosine (C).
These nucleotides are organized into triplets called codons.
There are 64 possible codons (4 x 4 x 4).
61 codons code for the 20 amino acids found in proteins.
Three codons are stop codons, signaling the end of protein synthesis.

Genetic Code

The genetic code is universal, meaning that the same codons code for the same amino acids in all organisms.
The genetic code is non-ambiguous, meaning that each codon codes for only one amino acid.
The genetic code is commaless, meaning that there are no punctuation marks between codons.
The genetic code is degenerate, meaning that some amino acids are coded for by more than one codon.
The genetic code is non-overlapping, meaning that each nucleotide is part of only one codon.

Translation

Translation is the process of protein synthesis.
The genetic code is used to translate the nucleotide sequence of mRNA into the amino acid sequence of a protein.

Important Features of the Genetic Code

The genetic code is a triplet code, meaning that each codon consists of three nucleotides.
The genetic code contains one start codon (AUG), which codes for methionine.
The genetic code contains three stop codons (UAA, UAG, and UGA), which signal the end of translation.

The Wobble Hypothesis

Some tRNAs can recognize more than one codon.
The wobble hypothesis explains how this is possible.
The third base in a codon can pair with more than one base in the anticodon of a tRNA.
This is because the third base in a codon is not as important as the first two bases.

Universal

The genetic code is nearly universal, meaning that the same codons code for the same amino acids in all organisms.
There are some exceptions to this rule, particularly in mitochondrial DNA.

Terminator Codons

There are three codons that do not code for any amino acid.
These codons are called termination codons or stop codons.
They signal the end of protein synthesis.

Initiator Codon

AUG is the initiation codon.
It signals the start of protein synthesis.

Genetic Code - Universal

The genetic code is universal, meaning that the same codons code for the same amino acids in all organisms.
There are a few exceptions to this rule, found in mitochondrial DNA.
The universality of the genetic code provides strong evidence that all living things share a common evolutionary heritage.

Marshall Nirenberg and Heinrich Matthaei experiments

Nirenberg and Matthaei conducted experiments that helped to decipher the genetic code.
They used synthetic mRNAs to determine which codons coded for which amino acids.

Genetic Code Cracking Phase 1 - Nirenberg & Matthaei

Nirenberg and Matthaei used a cell-free translation system to study the genetic code.
They added synthetic mRNAs to the system and measured the amount of protein produced.
They discovered that the codon UUU coded for the amino acid phenylalanine.

Experiment

Nirenberg and Leder developed a technique using ribosome-bound tRNAs to provide additional information about the genetic code.

Filter

This method involved passing a mixture of ribosomes, mRNA, and tRNAs through a nitrocellulose filter.
Only ribosomes bound to mRNA would stick to the filter.
The tRNAs bound to the ribosomes could then be analyzed to determine which amino acid they carried.

Thank You

Termination of Translation

The ribosome moves along the mRNA, reading codons and adding amino acids to a growing polypeptide chain.
When the ribosome reaches a stop codon, translation terminates.
This process involves release factors, which bind to the stop codon and cause the polypeptide to be released from the ribosome.

Initiation of Translation

The process of translation begins with the initiation of a 70S initiation complex.
This complex consists of the small ribosomal subunit, the mRNA, and the initiator tRNA.
The initiation factors (IF-1, IF-2, and IF-3) play a role in the assembly of the initiation complex.

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Description

Explore the fundamental concepts of the genetic code, including its structure and significance in translating nucleotide sequences into proteins. This quiz covers codons, amino acids, and the unique characteristics that define the genetic code across all organisms.