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6.3 Transcription and RNA Processing

7 min readjanuary 17, 2023

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Meet the RNA

Going back to the big idea relationship between structure and function, the sequence of the bases, together with the structure of the molecule, determines function!

mRNA: Messenger RNA

mRNA molecules, also known as messenger , are transcribed from DNA and carry genetic information from the DNA to the ribosome, where the information is translated into a primary peptide sequence. 💬

The sequence of bases in the mRNA molecule codes for the specific amino acid sequence of a protein. The structure of the mRNA molecule, including its secondary and tertiary structure, also plays a role in determining its function.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-nfOC2l5k3D6W.avif?alt=media&token=7ec3f49b-adea-4e75-b798-b8ed10afbf0b

Source: The Conversation

tRNA: Transfer RNA

tRNA molecules, also known as transfer , are small molecules that function in protein synthesis. They have specific binding sites for specific amino acids, as well as an anticodon sequence that base pairs with the codon sequence of the mRNA.

During translation, tRNA molecules are recruited to the ribosome, where they bring the correct amino acid to be incorporated into the growing peptide chain based on the mRNA sequence. The structure of tRNA molecules also plays a role in their function, including the L-shaped conformation that allows them to bind both amino acids and the ribosome. 🚜

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-FVfHRnFV7Mjr.jpg?alt=media&token=1ba41cc1-3030-4792-9c6d-7019a6064cec

Source: National Human Genome Research Institute

rRNA: Ribosomal RNA

rRNA molecules, also known as ribosomal , are the most abundant type of in cells and are the functional building blocks of ribosomes. Ribosomes are the cellular structures that carry out protein synthesis, and rRNA molecules form the structural backbone of the ribosome.

They also interact with the mRNA and tRNA molecules during the translation process, helping to position the tRNA molecules and catalyze the peptide bond formation. The sequence and structure of rRNA molecules are also important for their function, as mutations in these regions can affect the efficiency and accuracy of protein synthesis. ⚙️

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-jZtnoLbJcC6y.png?alt=media&token=0800f8e7-8dc5-4692-aef0-d4ce5b66be46

Source: Miami Bio

To summarize the three types of :

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-02%20at%208.28.22%20PM.png?alt=media&token=cf0c9e38-4fce-4e7e-9b6e-159688677987

The Central Dogma: DNA to RNA to Protein

Genetic information flows from DNA to protein through a process known as the central dogma of molecular biology. This process begins with the transcription of DNA into , specifically messenger (mRNA) molecules. During transcription, a specific portion of the DNA double helix, known as a gene, is copied into a complementary molecule. 🐕

This process is catalyzed by an enzyme called , which reads the DNA sequence and synthesizes a complementary strand. The sequence of nucleotides in the DNA is used as a template to determine the sequence of bases in the mRNA molecule.

The sequence of bases in the mRNA molecule, known as the codon, carries the genetic information that codes for the specific amino acid sequence of a protein. This genetic information is translated into a protein through the process of translation. Translation, which we'll explore further in the next section, occurs on the ribosome, a large complex of and protein molecules.

This process of transcription and translation results in the formation of a protein, with a specific sequence of amino acids determined by the sequence of nucleotides in the DNA. This protein can then perform a wide range of functions, including catalyzing metabolic reactions, replicating DNA, responding to stimuli, and transporting molecules across cell membranes.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FPSL_DNAtoProtein.en-NenYg2wmDxx1.png?alt=media&token=8e90e19d-e31b-4e7f-9f8d-7a0a80e7153a

Source: Labster Theory

RNA Polymerase, the Ace of Transcription

Again, transcription is the process by which a specific portion of DNA, known as a gene, is copied into a complementary molecule. This process is catalyzed by an enzyme called , which reads the DNA sequence and synthesizes a complementary strand. 🪡

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-WU1kHAACJL7I.jpg?alt=media&token=b0fab54d-8059-419f-8105-40b5e5315b0e

Source: Biology LibreTexts

The binds to a specific region of the DNA called the , which signals the start of the gene. The enzyme then moves along the of DNA, reading the sequence of nucleotides and adding complementary nucleotides to the growing strand. The process of transcription results in the formation of a , which can then undergo further processing to generate a mature molecule.

During transcription, the uses a single strand of DNA, known as the template strand, as a guide to determine the sequence of bases in the newly formed molecule. This process is known as template-directed synthesis, and it results in the formation of an molecule that is complementary to the of DNA. The other strand of DNA, known as the coding strand, has the same sequence as the , except that thymine is replaced by uracil.

Template Strand

The DNA strand that serves as the template strand during transcription is also referred to as the , minus strand, or antisense strand. This is because the sequence of the is not directly translated into a protein, unlike the which has the same sequence as the mRNA, except that thymine is replaced by uracil. The selection of which DNA strand serves as the during transcription depends on the gene being transcribed.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-sLwNqmhfwd1G.jpg?alt=media&token=bf90c09e-5d3b-4496-b37a-e33e977ee13f

Source: Samford University

Not included in the AP Bio curriculum but interesting to compare and contrast: In prokaryotic cells, transcription usually occurs on the that runs in the opposite direction as the , also known as the antisense strand. This is known as divergent transcription, where the coding and non-coding strands are oriented in opposite directions from one another.

In eukaryotic cells, which are cells with a defined nucleus, the majority of transcription occurs on the that runs in the same direction as the , also known as the sense strand. This is known as convergent transcription, where the coding and non-coding strands are oriented in the same direction. However, there are also examples of divergent transcription in eukaryotic cells too.

The selection of the can also be determined by certain regions of the DNA called regulatory elements, such as enhancers and promoters. These regions can bind to , which are proteins that help to control the transcription process. The binding of these factors can determine which strand will be used as the , and can also affect the rate and efficiency of transcription. 🚗💨

Processing the mRNA Transcript

In eukaryotic cells, the undergoes a series of enzyme-regulated modifications to generate a mature mRNA molecule that is ready for translation. These modifications include: 🔧

a. Addition of a : The addition of a string of adenine nucleotides, known as a , to the 3' end of the transcript. This process is catalyzed by an enzyme called and it helps to protect the mRNA from degradation and also helps in the transport of mRNA out of the nucleus.

b. Addition of a : The addition of a modified nucleotide, known as a , to the 5' end of the transcript. This process is catalyzed by an enzyme called (no need to remember for the AP exam). The cap helps to protect the mRNA from degradation, and also helps in the recognition of the mRNA by the translation machinery.

c. Excision of introns and splicing and retention of exons: The contains both coding regions (exons) and non-coding regions (introns) . The introns are removed by a process called splicing. This process is catalyzed by a complex of enzymes called the . The exons are then joined together to form a mature mRNA molecule that contains only the coding regions.

d. Excision of introns and splicing and retention of exons can generate different versions of the resulting mRNA molecule; this is known as . This occurs when different combinations of exons are joined together to form different mRNA molecules, each coding for a different protein or a different version of a protein. This process allows a single gene to produce multiple proteins and can increase the diversity of the protein products of a gene.

is a major mechanism of gene regulation in eukaryotic cells and it plays a key role in the complexity and diversity of eukaryotic organisms.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-Tfm1YXilTces.jpg?alt=media&token=c55a166c-df3b-4998-9264-b8927f3d3154

Source: Medbullets

Key Terms to Review (20)

Alternative Splicing

: Alternative splicing is a regulated process during gene expression that results in a single gene coding for multiple proteins. In this process, certain exons of a gene may be included within or excluded from the final processed messenger RNA (mRNA) produced from that gene.

Central Dogma: DNA to RNA to Protein

: The Central Dogma describes the flow of genetic information in cells from DNA to messenger RNA (mRNA) to protein.

Coding Strand

: The coding strand is the DNA strand whose base sequence corresponds to the RNA sequence that is produced during transcription. It's also known as the sense strand.

GTP Cap

: A modified guanine nucleotide added to the 5' end of pre-mRNAs during transcription. This cap protects mRNA from degradation and assists in ribosome binding during translation.

Guanylyltransferase

: Guanylyltransferase is an enzyme that catalyzes the transfer of a guanine nucleotide to the 5' end of a messenger RNA molecule during the capping process.

Introns and Exons

: Introns are non-coding sequences within genes that are removed during RNA processing, while exons are coding sequences that remain in the mature mRNA and code for proteins.

mRNA (Messenger RNA)

: mRNA is a type of RNA that carries instructions from DNA for controlling the synthesis of proteins.

Noncoding Strand

: The noncoding strand, also known as the template strand, is the DNA strand that serves as a template for RNA synthesis. It does not code for proteins directly but provides the sequence from which mRNA is synthesized.

Poly-A Tail

: The Poly-A tail is a string of adenine nucleotides added to the 3' end of a pre-mRNA molecule during RNA processing.

Polyadenylate Polymerase

: An enzyme that adds adenine residues to the 3' end of pre-mRNA molecules forming the poly-A tail.

Primary RNA Transcript

: The primary RNA transcript is an initial product resulting from transcription before any modifications occur. It's essentially an unedited copy of one strand of DNA sequence.

Promoter

: A promoter is a region of DNA that initiates transcription of a particular gene. It's where RNA polymerase binds to start the transcription process.

Regulatory Elements

: Regulatory elements are regions of DNA that can bind regulatory proteins to control gene expression, essentially turning genes on or off.

RNA

: RNA (Ribonucleic Acid) is a molecule similar to DNA that plays a crucial role in protein synthesis and other chemical activities of the cell.

RNA Polymerase

: RNA polymerase is an enzyme that synthesizes RNA from DNA during transcription.

rRNA: Ribosomal RNA

: rRNA is a type of RNA that combines with proteins to form ribosomes, the structures where protein synthesis occurs.

Spliceosome

: A spliceosome is a complex assembly of RNA and protein molecules that removes introns from pre-mRNA during splicing.

Template Strand

: The template strand is the DNA strand that serves as a guide for synthesizing an RNA molecule during transcription.

Transcription Factors

: Transcription factors are proteins involved in the process of converting, or transcribing, DNA into RNA. They help regulate gene expression by binding to specific sites on DNA and controlling how often genes get transcribed into mRNA molecules.

tRNA (Transfer RNA)

: tRNA is a type of RNA that transports specific amino acids to ribosomes during protein synthesis based on coding sequences present on mRNA.

6.3 Transcription and RNA Processing

7 min readjanuary 17, 2023

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Samantha Himegarner

Samantha Himegarner

Jed Quiaoit

Jed Quiaoit

Meet the RNA

Going back to the big idea relationship between structure and function, the sequence of the bases, together with the structure of the molecule, determines function!

mRNA: Messenger RNA

mRNA molecules, also known as messenger , are transcribed from DNA and carry genetic information from the DNA to the ribosome, where the information is translated into a primary peptide sequence. 💬

The sequence of bases in the mRNA molecule codes for the specific amino acid sequence of a protein. The structure of the mRNA molecule, including its secondary and tertiary structure, also plays a role in determining its function.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-nfOC2l5k3D6W.avif?alt=media&token=7ec3f49b-adea-4e75-b798-b8ed10afbf0b

Source: The Conversation

tRNA: Transfer RNA

tRNA molecules, also known as transfer , are small molecules that function in protein synthesis. They have specific binding sites for specific amino acids, as well as an anticodon sequence that base pairs with the codon sequence of the mRNA.

During translation, tRNA molecules are recruited to the ribosome, where they bring the correct amino acid to be incorporated into the growing peptide chain based on the mRNA sequence. The structure of tRNA molecules also plays a role in their function, including the L-shaped conformation that allows them to bind both amino acids and the ribosome. 🚜

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-FVfHRnFV7Mjr.jpg?alt=media&token=1ba41cc1-3030-4792-9c6d-7019a6064cec

Source: National Human Genome Research Institute

rRNA: Ribosomal RNA

rRNA molecules, also known as ribosomal , are the most abundant type of in cells and are the functional building blocks of ribosomes. Ribosomes are the cellular structures that carry out protein synthesis, and rRNA molecules form the structural backbone of the ribosome.

They also interact with the mRNA and tRNA molecules during the translation process, helping to position the tRNA molecules and catalyze the peptide bond formation. The sequence and structure of rRNA molecules are also important for their function, as mutations in these regions can affect the efficiency and accuracy of protein synthesis. ⚙️

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-jZtnoLbJcC6y.png?alt=media&token=0800f8e7-8dc5-4692-aef0-d4ce5b66be46

Source: Miami Bio

To summarize the three types of :

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-04-02%20at%208.28.22%20PM.png?alt=media&token=cf0c9e38-4fce-4e7e-9b6e-159688677987

The Central Dogma: DNA to RNA to Protein

Genetic information flows from DNA to protein through a process known as the central dogma of molecular biology. This process begins with the transcription of DNA into , specifically messenger (mRNA) molecules. During transcription, a specific portion of the DNA double helix, known as a gene, is copied into a complementary molecule. 🐕

This process is catalyzed by an enzyme called , which reads the DNA sequence and synthesizes a complementary strand. The sequence of nucleotides in the DNA is used as a template to determine the sequence of bases in the mRNA molecule.

The sequence of bases in the mRNA molecule, known as the codon, carries the genetic information that codes for the specific amino acid sequence of a protein. This genetic information is translated into a protein through the process of translation. Translation, which we'll explore further in the next section, occurs on the ribosome, a large complex of and protein molecules.

This process of transcription and translation results in the formation of a protein, with a specific sequence of amino acids determined by the sequence of nucleotides in the DNA. This protein can then perform a wide range of functions, including catalyzing metabolic reactions, replicating DNA, responding to stimuli, and transporting molecules across cell membranes.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FPSL_DNAtoProtein.en-NenYg2wmDxx1.png?alt=media&token=8e90e19d-e31b-4e7f-9f8d-7a0a80e7153a

Source: Labster Theory

RNA Polymerase, the Ace of Transcription

Again, transcription is the process by which a specific portion of DNA, known as a gene, is copied into a complementary molecule. This process is catalyzed by an enzyme called , which reads the DNA sequence and synthesizes a complementary strand. 🪡

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-WU1kHAACJL7I.jpg?alt=media&token=b0fab54d-8059-419f-8105-40b5e5315b0e

Source: Biology LibreTexts

The binds to a specific region of the DNA called the , which signals the start of the gene. The enzyme then moves along the of DNA, reading the sequence of nucleotides and adding complementary nucleotides to the growing strand. The process of transcription results in the formation of a , which can then undergo further processing to generate a mature molecule.

During transcription, the uses a single strand of DNA, known as the template strand, as a guide to determine the sequence of bases in the newly formed molecule. This process is known as template-directed synthesis, and it results in the formation of an molecule that is complementary to the of DNA. The other strand of DNA, known as the coding strand, has the same sequence as the , except that thymine is replaced by uracil.

Template Strand

The DNA strand that serves as the template strand during transcription is also referred to as the , minus strand, or antisense strand. This is because the sequence of the is not directly translated into a protein, unlike the which has the same sequence as the mRNA, except that thymine is replaced by uracil. The selection of which DNA strand serves as the during transcription depends on the gene being transcribed.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-sLwNqmhfwd1G.jpg?alt=media&token=bf90c09e-5d3b-4496-b37a-e33e977ee13f

Source: Samford University

Not included in the AP Bio curriculum but interesting to compare and contrast: In prokaryotic cells, transcription usually occurs on the that runs in the opposite direction as the , also known as the antisense strand. This is known as divergent transcription, where the coding and non-coding strands are oriented in opposite directions from one another.

In eukaryotic cells, which are cells with a defined nucleus, the majority of transcription occurs on the that runs in the same direction as the , also known as the sense strand. This is known as convergent transcription, where the coding and non-coding strands are oriented in the same direction. However, there are also examples of divergent transcription in eukaryotic cells too.

The selection of the can also be determined by certain regions of the DNA called regulatory elements, such as enhancers and promoters. These regions can bind to , which are proteins that help to control the transcription process. The binding of these factors can determine which strand will be used as the , and can also affect the rate and efficiency of transcription. 🚗💨

Processing the mRNA Transcript

In eukaryotic cells, the undergoes a series of enzyme-regulated modifications to generate a mature mRNA molecule that is ready for translation. These modifications include: 🔧

a. Addition of a : The addition of a string of adenine nucleotides, known as a , to the 3' end of the transcript. This process is catalyzed by an enzyme called and it helps to protect the mRNA from degradation and also helps in the transport of mRNA out of the nucleus.

b. Addition of a : The addition of a modified nucleotide, known as a , to the 5' end of the transcript. This process is catalyzed by an enzyme called (no need to remember for the AP exam). The cap helps to protect the mRNA from degradation, and also helps in the recognition of the mRNA by the translation machinery.

c. Excision of introns and splicing and retention of exons: The contains both coding regions (exons) and non-coding regions (introns) . The introns are removed by a process called splicing. This process is catalyzed by a complex of enzymes called the . The exons are then joined together to form a mature mRNA molecule that contains only the coding regions.

d. Excision of introns and splicing and retention of exons can generate different versions of the resulting mRNA molecule; this is known as . This occurs when different combinations of exons are joined together to form different mRNA molecules, each coding for a different protein or a different version of a protein. This process allows a single gene to produce multiple proteins and can increase the diversity of the protein products of a gene.

is a major mechanism of gene regulation in eukaryotic cells and it plays a key role in the complexity and diversity of eukaryotic organisms.

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2F-Tfm1YXilTces.jpg?alt=media&token=c55a166c-df3b-4998-9264-b8927f3d3154

Source: Medbullets

Key Terms to Review (20)

Alternative Splicing

: Alternative splicing is a regulated process during gene expression that results in a single gene coding for multiple proteins. In this process, certain exons of a gene may be included within or excluded from the final processed messenger RNA (mRNA) produced from that gene.

Central Dogma: DNA to RNA to Protein

: The Central Dogma describes the flow of genetic information in cells from DNA to messenger RNA (mRNA) to protein.

Coding Strand

: The coding strand is the DNA strand whose base sequence corresponds to the RNA sequence that is produced during transcription. It's also known as the sense strand.

GTP Cap

: A modified guanine nucleotide added to the 5' end of pre-mRNAs during transcription. This cap protects mRNA from degradation and assists in ribosome binding during translation.

Guanylyltransferase

: Guanylyltransferase is an enzyme that catalyzes the transfer of a guanine nucleotide to the 5' end of a messenger RNA molecule during the capping process.

Introns and Exons

: Introns are non-coding sequences within genes that are removed during RNA processing, while exons are coding sequences that remain in the mature mRNA and code for proteins.

mRNA (Messenger RNA)

: mRNA is a type of RNA that carries instructions from DNA for controlling the synthesis of proteins.

Noncoding Strand

: The noncoding strand, also known as the template strand, is the DNA strand that serves as a template for RNA synthesis. It does not code for proteins directly but provides the sequence from which mRNA is synthesized.

Poly-A Tail

: The Poly-A tail is a string of adenine nucleotides added to the 3' end of a pre-mRNA molecule during RNA processing.

Polyadenylate Polymerase

: An enzyme that adds adenine residues to the 3' end of pre-mRNA molecules forming the poly-A tail.

Primary RNA Transcript

: The primary RNA transcript is an initial product resulting from transcription before any modifications occur. It's essentially an unedited copy of one strand of DNA sequence.

Promoter

: A promoter is a region of DNA that initiates transcription of a particular gene. It's where RNA polymerase binds to start the transcription process.

Regulatory Elements

: Regulatory elements are regions of DNA that can bind regulatory proteins to control gene expression, essentially turning genes on or off.

RNA

: RNA (Ribonucleic Acid) is a molecule similar to DNA that plays a crucial role in protein synthesis and other chemical activities of the cell.

RNA Polymerase

: RNA polymerase is an enzyme that synthesizes RNA from DNA during transcription.

rRNA: Ribosomal RNA

: rRNA is a type of RNA that combines with proteins to form ribosomes, the structures where protein synthesis occurs.

Spliceosome

: A spliceosome is a complex assembly of RNA and protein molecules that removes introns from pre-mRNA during splicing.

Template Strand

: The template strand is the DNA strand that serves as a guide for synthesizing an RNA molecule during transcription.

Transcription Factors

: Transcription factors are proteins involved in the process of converting, or transcribing, DNA into RNA. They help regulate gene expression by binding to specific sites on DNA and controlling how often genes get transcribed into mRNA molecules.

tRNA (Transfer RNA)

: tRNA is a type of RNA that transports specific amino acids to ribosomes during protein synthesis based on coding sequences present on mRNA.


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AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.


© 2024 Fiveable Inc. All rights reserved.

AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.