Name: how cells control gene expression
Uploaded: 2023-04-30T10:42:14.000Z
Duration: 1 min 36 s
Channel: JoVE

K12 Standards

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NC K-12 Science Standard Course of Study

9-12

Biology

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From Molecules to Organisms- Structures and Processes

LS.Bio.1.5

What is Gene Expression?

Almost every cell in the body contains the entire genome. However, only some genes are expressed into proteins, and these differ between cells. For instance, neurons and muscle cells express different genes, allowing them to have specialized functions.
The process of gene expression starts with transcription, when DNA acts as a template for RNA synthesis.
The RNA transcript then undergoes splicing, the removal of non-coding intron sequences, leaving the coding exons. The final result is messenger RNA, mRNA, that then travels to the cytoplasm for translation. Here, the ribosome and transfer RNA, tRNA, together translate the three nucleotide codons in the mRNA, into a sequence of amino acids.
Usually, the resulting polypeptide chain of amino acids then undergoes further processing to become a functional protein.
Gene expression can be regulated at any point in this process. For example, epigenetic modifications that alter the structure of the DNA molecule, without changing its sequence, can inhibit or promote transcription of certain genes.
Also, once a gene is transcribed, translation can be inhibited, for instance, by small regulatory RNAs, stopping the gene from being expressed in

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 comprised of amino acids, a mediator is required to convert the information encoded in DNA into proteins. This mediator is the messenger RNA (mRNA). mRNA copies the blueprint from DNA by a process called transcription. In eukaryotes, transcription occurs in the nucleus by complementary base-pairing with the DNA template. The mRNA is then processed and transported into the cytoplasm, serving as a template for protein synthesis during translation. In prokaryotes, which lack a nucleus, the processes of transcription and translation occur at the same location and almost simultaneously since the newly-formed mRNA is susceptible to rapid degradation.
Gene Expression Can Be Regulated at Any Stage during Transcription
Every cell of an organism contains the same DNA and, consequently, the same set of genes. However, not all genes in a cell are &#34;turned on&#34;&#160;or used to synthesize proteins. A gene is said to be expressed when the protein it encodes is produced by the cell. Gene expression is regulated to ensure the proper generation of proteins in specific cells at specific times. Various intrinsic and extrinsic mechanisms regulate gene expression before and during transcription.
The structure of chromatin&#8212;compacted DNA and its associated histone proteins&#8212;can be chemically modified to be open or closed. Such modifications allow or restrict access to the DNA by the transcriptional machinery. Chromatin modification is an intrinsic mechanism employed during development to form different cell types (e.g., neuron versus muscle cell) from the same genome.
DNA-binding proteins, called transcription factors, regulate transcription by binding to specific DNA sequences near or within the coding regions of genes. Transcription factors that promote the initiation of transcription are called activators. Proteins that prevent the transcription machinery from binding to the transcription initiation site are called repressors. Transcriptional activators or repressors respond to external stimuli such as signaling molecules, nutritional deficiencies, temperature, and oxygen.
Gene Expression Can Be Post-transcriptionally and Post-translationally Regulated
Gene expression can be regulated by post-transcriptional mRNA processing. In eukaryotes, transcribed mRNA undergoes splicing and other modifications that protect the ends of the RNA strand from degradation. Splicing removes introns&#8212;segments that do not encode proteins&#8212;and joins the protein-coding regions called exons. Alternative splicing allows for the expression of functionally diverse proteins from the same gene. Regulation of gene expression by alternative splicing plays an important role in organ development, cell survival and proliferation, and adaptation to environmental factors.
Gene expression can also be altered by regulating the translation of mRNA into proteins. Translation can be regulated by microRNAs&#8212;small, non-coding RNAs&#8212;that bind to a specific mRNA sequence and block the initiation of translation or degrade the transcribed mRNA. In addition, proteins called translational repressors can bind to RNA and interfere with translation initiation.
Translated polypeptides undergo processing to form functional proteins. The addition or removal of chemical groups can alter the activity, stability, and localization. For instance, adding or removing phosphate groups can activate or inactivate proteins. Similarly, the addition of ubiquitin groups causes protein degradation. Thus, post-translational protein modifications are the final stage of gene regulation.

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 ...

Education

JoVE Core

Cell Biology

Unit 1

Transcription: DNA to RNA

KEY TERMS AND CONCEPTS

how cells control gene expression

Cells control gene expression to decide when a gene makes a protein. A gene is a stretch of DNA that holds the instructions for functional RNAs and proteins. Because DNA is built from nucleotides and proteins are built from amino acids, messenger RNA (mRNA) acts as the link between them.

The first step is transcription. During transcription, mRNA copies the DNA blueprint. In eukaryotes, this happens in the nucleus through complementary base-pairing with the DNA template. The mRNA is then processed and moved into the cytoplasm, where it becomes the template for protein synthesis during translation. In prokaryotes, which do not have a nucleus, transcription and translation happen in the same place and almost at the same time. This matters because newly made mRNA can break down quickly.

Gene expression is also controlled before and during transcription. Every cell in an organism has the same DNA and the same set of genes, but not every gene is turned on in every cell. A gene is considered expressed when the cell produces the protein it encodes. Gene expression must be regulated so the right proteins are made in the right cells at the right times.

One way cells regulate gene expression is through chromatin, the compacted DNA and histone proteins around it. Chromatin can be chemically modified to become more open or more closed. These changes can allow or block access to the DNA for the transcription machinery. This type of control helps cells form different cell types from the same genome during development, such as neurons and muscle cells. DNA-binding proteins called transcription factors also help control transcription by attaching to specific DNA sequences near or within genes. Activators promote transcription start, while repressors prevent the machinery from binding at the initiation site. These factors can respond to external signals such as signaling molecules, nutritional deficiencies, temperature, and oxygen.

Gene expression can also be controlled after transcription. In eukaryotes, the new mRNA is spliced and further modified to protect its ends from degradation. Splicing removes introns, which do not code for proteins, and joins exons, which do. Alternative splicing lets one gene produce different functional proteins. This process is important for organ development, cell survival and proliferation, and responses to environmental factors.

Control can continue at the translation stage. MicroRNAs are small non-coding RNAs that bind to a specific mRNA sequence. They can block translation from starting or cause the mRNA to be degraded. Translational repressors can also bind RNA and interfere with translation initiation. After translation, polypeptides are processed into functional proteins. Chemical groups can be added or removed to change a protein’s activity, stability, or location. For example, phosphate groups can turn proteins on or off, and ubiquitin groups can mark proteins for degradation. These post-translational changes are the final stage of gene regulation.

How Cells Control Gene Expression

Cells control gene expression to decide when a gene makes a protein. A gene is a stretch of DNA that holds the instructions for functional RNAs and proteins. Because DNA is built from nucleotides and proteins are built from amino acids, messenger RNA (mRNA) acts as the link between them. The first step is transcription. During transcription, mRNA copies the DNA blueprint. In eukaryotes, this happens in the nucleus through complementary base-pairing with the DNA template. The mRNA is then...

rna structure

RNA Shapes and Protein Synthesis

RNA shapes and protein synthesis are linked through the molecule’s single-stranded structure. RNA is made of ribonucleotides joined by phosphodiester bonds, and it can fold into secondary and tertiary shapes that help control transcription and translation. These shapes are important in both regulation and protein production. Messenger RNA, transfer RNA, and ribosomal RNA are the three main RNA types used in protein synthesis. They all share the same basic build: a single strand of nucleotides.

types of rna

RNA Roles in Protein Synthesis

RNA plays key roles in protein synthesis, and its main forms work together to make proteins in the cell. Messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA) each have a specific job. RNA can also be grouped as protein-coding or non-coding RNA. mRNA is the protein-coding RNA. It carries codons, which are sets of three nucleotides that specify an amino acid. tRNA and rRNA are non-coding RNAs. tRNA acts as an adaptor that reads the mRNA sequence and brings amino acids into the...

transcription

RNA Synthesis and Gene Control

Transcription is the process that makes RNA from a DNA sequence. RNA polymerase carries out this synthesis. It is the first step in turning a gene into a protein, and several other proteins and control sequences help make messenger RNA, or mRNA, correctly. In eukaryotes, DNA is first copied into pre-mRNA. This RNA can then be processed into mature mRNA, which serves as the template for protein synthesis. In prokaryotes, translation into a polypeptide can start before transcription has finished.

bacterial rna polymerase

Bacterial RNA Polymerase and Sigma Factor

Bacterial RNA polymerase carries out transcription, the process of copying DNA into RNA. It is the enzyme that starts RNA synthesis in bacteria and helps control which genes are used. The core enzyme works with a sigma factor, which is a protein that helps the polymerase find the right place to begin. Together, they form the holoenzyme. The sigma factor is important for promoter recognition, so the enzyme can bind near the start of a gene. Once transcription begins, RNA polymerase separates...

eukaryotic rna polymerases

Three Eukaryotic RNA Polymerases

Eukaryotic RNA polymerases are the enzymes that make RNA from DNA in cells with a nucleus. In eukaryotes, this work is divided among three main RNA polymerases. Each enzyme has a specific role in transcription, the process of copying genetic information into RNA. RNA polymerase I makes most ribosomal RNA, or rRNA. RNA polymerase II produces messenger RNA, or mRNA, which carries the instructions for making proteins. RNA polymerase III makes transfer RNA, or tRNA, and also some small RNAs used...

general transcription factors

Tissue-Specific Transcription Factors in Gene Control

Tissue-specific transcription factors help control which genes turn on in different mammal cells. These proteins bind to promoter sequences and can direct a gene to be expressed in one tissue but not another. This selective control helps cells carry out very different jobs in the body. A clear example is the beta globin gene, which makes part of hemoglobin. The gene is present in all body cells, but it is expressed only in red blood cells. That happens because the transcription factors needed...

rna polymerase ii accessory proteins

RNA Polymerase II Helper Proteins

RNA polymerase II helper proteins support the transcription process in eukaryotic cells. They work with RNA polymerase II, the enzyme that makes RNA from a DNA template. These proteins help the enzyme start, move, and finish transcription in the right way. Some helper proteins act as accessory factors. They can assist RNA polymerase II at different stages of gene expression. Their roles are important because transcription must be controlled accurately for cells to make the correct RNA...

transcription elongation factors

RNA Polymerase Pausing and Elongation

RNA polymerase pausing and elongation factors help control how RNA is made from DNA. During transcription, RNA polymerase moves along the gene and builds an RNA strand. Elongation factors support this process by helping the enzyme continue after it pauses. These factors are part of the elongation stage of transcription. They are not the same as the proteins used to start transcription. Their role is to keep RNA polymerase moving so RNA can be copied efficiently. In high school biology, this...

pre-mrna processing: modification of pre-mrna ends

pre-mrna-processing-modification-of-pre-mrna-ends

How Pre-mRNA Becomes Mature mRNA

Pre-mRNA becomes mature mRNA through a series of processing steps in eukaryotic cells. RNA polymerase first makes the transcript, and the RNA is modified before it leaves the nucleus. The unprocessed form is called precursor mRNA, or pre-mRNA, to separate it from mature mRNA. After about 20 to 40 ribonucleotides have been added, enzymes place a cap on the 5' end of the growing RNA. This cap replaces the 5' phosphate with modified guanosine, which carries a methyl group called 7-methyl...

pre-mrna processing: rna splicing

Pre-mRNA Splicing and Intron Removal

Pre-mRNA splicing removes introns from a pre-mRNA molecule and joins the remaining exons together. This step is part of pre-mRNA processing, which helps turn the first RNA copy into a mature message that can be used later in gene expression. Splicing is carried out by the spliceosome, a large RNA-protein complex. The spliceosome recognizes the intron boundaries and cuts out the intron. It then links the exons together in the correct order. A key feature of splicing is the lariat, a looped RNA...

chromatin structure and rna splicing

Chromatin and RNA Splicing Control

Chromatin and RNA splicing work together to shape how genes are used in a cell. Chromatin is the DNA-protein material that packages genetic information, and RNA splicing is a step in which introns are removed from a pre-mRNA transcript. The video explains how chromatin structure can influence this RNA processing step. A compact chromatin structure can make a gene less accessible, while a more open structure can make it easier for the cell to use that gene. This change in access can affect how...

alternative rna splicing

RNA Splicing in Gene Expression

RNA splicing in gene expression helps cells turn one gene into different RNA messages. During RNA processing, introns are removed and exons are joined together. This editing step changes which parts of the RNA stay in the final message. Alternative splicing gives cells a way to make more than one protein from the same gene. By including or skipping different exons, a cell can produce different RNA versions from one starting transcript. This process adds flexibility to gene expression without...

nuclear export of mrna

How mRNA Leaves the Nucleus

Messenger RNA, or mRNA, must move from the nucleus to the cytoplasm before it can be used to make protein. This step is called nuclear export of mRNA. It connects gene expression in the nucleus with protein production in the cytoplasm. During export, the cell selects mRNA molecules that are ready to leave the nucleus. These molecules pass through nuclear pores, which are openings in the nuclear envelope. The process helps keep mRNA transport organized and controlled. Once mRNA reaches the...

transfer rna synthesis

tRNA Genes and RNA Processing

Transfer RNA synthesis begins with transcription of tRNA genes into a primary RNA copy. That first copy is not yet ready to function in protein building. It must be processed before it can become mature transfer RNA. During processing, the cell trims the ends of the RNA and removes extra segments when needed. The transcript also shows that some transfer RNAs carry modified bases. These changes help create the final tRNA structure. Mature transfer RNA folds into a shape that can work in...

ribosomal rna synthesis

Ribosomal RNA and Ribosome Formation

Ribosomal RNA synthesis is part of how cells build ribosomes. Ribosomes are the structures that help make proteins. In this process, cells produce ribosomal RNA, or rRNA, which becomes a key part of the ribosome. The transcript focuses on the making of rRNA and its role in ribosome formation. Ribosomal RNA is not just a message like messenger RNA. It is a structural and functional part of the ribosome itself. Because of that, rRNA synthesis is closely tied to the assembly of ribosomes. This...

the nucleolus

Nucleolus and Ribosome Assembly

The nucleolus is a small structure inside the nucleus. It is the site where ribosome assembly begins. Ribosomes are the cell structures that help make proteins. The nucleolus forms around nucleolar organizer regions, or NORs. These regions contain the genes used to make ribosomal RNA, also called rRNA. Inside the nucleolus, rRNA is produced and combined with proteins to start building ribosomes. Because of this role, the nucleolus is closely tied to protein production in the cell. Its work...

additional subnuclear structures

Subnuclear Bodies and Their Roles

Subnuclear structures are specialized bodies inside the nucleus. They help organize nuclear activity and appear as distinct regions under the microscope. The nucleolus is one of the best-known subnuclear structures. It is the site where ribosomes begin to assemble. Cajal bodies are another nuclear structure. They are linked to the processing and assembly of RNA-related particles. These additional subnuclear structures show that the nucleus is not a uniform space. Instead, it contains...

key terms and concepts

Explore how cells control gene expression through transcription, RNA processing, translation, and protein modification. Built for high school biology students.

How Cells Control Gene Expression | JoVE K12

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JoVE Core Cell Biology illustrates complex cellular processes in easy-to-understand yet comprehensive animated video lessons. This collection focuses on the essential components and functions of cells, including organelles and membranes, cellular transport, and cell energetics. It is complemented by scientist-in-action videos that demonstrate the application of cell biology in real-world research experiments.

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How Cells Control Gene Expression

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