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Transcription

Transcription

Description:

This lesson will examine the process of transcription as the first step in protein synthesis. It will also identify the three types of RNA.

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Tutorial

What's Covered

This lesson will cover the process of transcription and its role in protein synthesis by looking at:

  1. Transcription
  2. Types of RNA
  3. Codons

1. Transcription

The path from genes to proteins involves two steps:

  • Transcription
  • Translation

Transcription is the first step in protein synthesis. In transcription, a single strand of RNA is assembled using the  DNA as a template. It pairs using the base pair rules except adenine will pair with uracil since RNA does not contain thymine. This process occurs in the nucleus of the cell. Certain proteins, called regulatory proteins, can stop or speed up transcription.

Terms to Know

  • Protein Synthesis
  • The formation of proteins by using information stored in DNA to form proteins.
  • Transcription
  • The process of converting DNA into RNA.
  • Regulatory Proteins
  • Proteins that can stop or speed up transcription.

Think About It

If RNA builds off of a DNA template, what makes RNA and DNA different?

  • While there are similarities, there are also many differences:
  • RNA stands for ribonucleic acid, and DNA stands for deoxyribonucleic acid
  • RNA is also single stranded, while DNA is double stranded
  • RNA has ribose sugar in its nucleotide, and DNA has a deoxyribose sugar in its nucleotide
  • Their nitrogen bases are different: RNA has uracil instead of thymine. (The rest are the same)

Most importantly, both of these types of molecules contain genetic information, but the information RNA contains is specific to protein building.

Term to Know

  • Genetic Code
  • Information stored in the nucleotide sequence of DNA that forms our genes.


2. Types of RNA


There are three different types of RNA:

  • Messenger RNA or mRNA-carries protein-building instructions and is the type of RNA that's actually transcribed into a protein
  • Transfer RNA or tRNA- picks up amino acids and pairs with mRNA to build polypeptide chains.
  • Ribosomal RNA or rRNA -combines with proteins to form a ribosome, which plays a role in protein synthesis.

Terms to Know

  • rRNA
  • Ribosomal RNA is used to produce the structure of ribosomes.
  • mRNA
  • Messenger RNA that is used to convert RNA code into protein.
  • tRNA
  • Transfer RNA that is used to bind ribosomes to the start codon of a nucleotide chain in order for translation to occur.

Ribosomes are composed of a large subunit and a small subunit. These subunits are made in the nucleolus and then sent out into the cytoplasm. Here they join together and help produce proteins during translation, the second step of protein synthesis.

Subunit.png

Messenger RNA is the RNA that plays a role in transcription.


3. Codons

There are specific gene regions on a strand of DNA that code for certain types of proteins. RNA will combine with DNA in a process similar to DNA replication. RNA polymerase will unwind the DNA, and this will allow messenger RNA to form using the strand of DNA as a template.

transcription (2).png

RNA polymerases will just move down this gene region as that messenger RNA is built. When it's finished, the DNA will wind back up into what we started with up here.

Term to Know

  • RNA Polymerases
  • An enzyme used to form a single strand of RNA from a DNA strand.

Codons are sets of three nucleotides in messenger RNA that are used to build proteins; they code for amino acids. There are a total of 64 different codons that make up the genetic code and provide these protein making instructions.

Term to Know

  • Codons
  • Sections of 3 nucleotides that code for an amino acid.

Start codons mark the first amino acid of a polypeptide chain.

ExampleAUG is an example of a start code. This is adenine, uracil, guanine together in this chunk of three nucleotides. It would signal the start of a polypeptide chain.

A stop codon marks the end of a polypeptide chain. Stop codons are UAA, UAG, and UGA. It marks the end of a polypeptide chain, and that when that polypeptide chain would be finished being made.

transcription (3).png

Terms to Know

  • Start Codon
  • A codon used to signal the start of an amino acid sequence on a strand of mRNA.
  • Stop Codon
  • A codon used to signal the stop of an amino acid sequence on a strand of mRNA.

In between, we have these other codons that code for specific amino acids. As those amino acids are being built, they are linked together and form polypeptide chains.

At this point, the mRNA is not completely finished. Introns are parts of the mRNA that don't code for proteins, and exons are the parts of the mRNA that do code for proteins. The introns get snipped out from the mRNA, and the exons are spliced together. After this, the mRNA can head into the cytoplasm for the next stage of protein synthesis, which is translation.

Term to Know

  • Exons
  • Sections of RNA that code for proteins.

Summary

Transcription is the first step in the process of using genes to build proteins. DNA is used as a template for RNA to be built. There are three types of RNA : mRNA, tRNA, an rRNA. The RNA that plays a role in transcription is mRNA. Depending on the nucleotides that line up in this mRNA, it forms which then code for specific amino acids. The amino acids then form polypeptide chains. Once the nucleotides are joined, the mRNA is released from the DNA, and the DNA rewinds back together. Codons are sections of three nucleotides that code for amino acids. The start codon marks the first amino acid of a polypeptide chain, and the stop codon indicates the end of the chain.

Source: This work is adapted from Sophia Author Amanda Soderlind

TERMS TO KNOW
  • Protein Synthesis

    The formation of proteins by using information stored in DNA to form proteins.

  • Transcription

    The process of converting DNA into RNA.

  • rRNA

    Ribosomal RNA is used to produce the structure of ribosomes.

  • mRNA

    Messenger RNA that is used to convert RNA code into protein.

  • tRNA

    Transfer RNA that is used to bind ribosomes to the start codon of a nucleotide chain in order for translation to occur.

  • Exons

    Sections of RNA that code for proteins.

  • Regulatory Proteins

    Proteins that can stop or speed up transcription.

  • RNA Polymerases

    An enzyme used to form a single strand of RNA from a DNA strand.

  • Codons

    Sections of 3 nucleotides that code for an amino acid.

  • Genetic Code

    Information stored in the nucleotide sequence of DNA that forms our genes.

  • Start Codon

    A codon used to signal the start of an amino acid sequence on a strand of mRNA.

  • Stop Codon

    A codon used to signal the stop of an amino acid sequence on a strand of mRNA.