Name: nucleolus and ribosome assembly
Uploaded: 2023-04-30T18:28:44.000Z
Duration: 2 min 55 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

NC K-12 Science Standard Course of Study

9-12

Biology

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms- Structures and Processes

LS.Bio.1.5

The Nucleolus

Within the nucleus are several organelles with specialized functions. Of these organelles, the nucleolus is one of the most prominent.&#160;
A nucleolus is the site of ribosomal RNA, or rRNA, transcription and processing and ribosome assembly. Hence it is also referred to as a &#8216;ribosome producing factory.&#8217;
A membraneless organelle, the nucleolus is an aggregate of rRNA genes and the various proteins and RNAs that are required for rRNA transcription and ribosome assembly. These include small nucleolar ribonucleoproteins, or snoRNPs, rRNA-processing enzymes, assembly factors, and partially assembled ribosomes.&#160;
In eukaryotes, three rRNA genes, 18S, 5.8S, and 28S, are encoded by a single transcription unit. This transcription unit is tandemly repeated in the form of arrays in one to several chromosomes.&#160;
The chromosomal regions which contain these rRNA gene clusters are known as &#8216;nucleolar organizer regions&#8217;, or N-O-Rs, and these are the regions around which the organization of nucleolus takes place.&#160;
As a cell transits between the two major cell cycle stages, interphase and mitosis or M-phase, its requirement of protein synthesis changes drastically.&#160;
It is high during interphase, becomes

the nucleolus

The nucleolus is the most prominent substructure of the nucleus. When it was first discovered, it was considered to be an isolated organelle that forms fibrils and granules. In 1931, the relationship between the nucleolus and chromosomes was first described by Heitz. He observed that the appearance and size of nucleolus varies depending on the stage of the cell cycle. He also noticed constricted regions on different chromosomes clustered together at definite cell cycle stages. These regions, now called nucleolar organizer regions or NORs, are known to contain the genes encoding ribosomal RNA (rRNA).
The structure and number of nucleoli vary depending on the requirement for ribosomal RNA synthesis. Thus, the specific state of differentiation of a cell can be identified from its nucleoli. In aggressive breast cancer cells, the nucleolus becomes 30% larger during tumor progression, which demands heightened ribosomal production. Transversely, in lymphocytes, ribosome synthesis is terminated at the final stage of cell differentiation. Consequently, the nucleoli reduce in size to become tiny fibrillar structures.
The nucleolus consists of three distinct structural regions: the fibrillar center, dense fibrillar component, and granular component. The different regions correspond to the sites of rRNA transcription, processing, and ribosomal assembly, at different stages. The fibrillar centers contain rRNA genes that are transcribed at the boundary separating them from the dense fibrillar component. Processing of precursor rRNAs starts in the dense fibrillar component and extends in the granular component, where the processed rRNAs are assembled with ribosomal proteins. The newly formed pre-ribosomal subunits are then exported to the cytoplasm for further processing into mature ribosomes.

The nucleolus is the most prominent substructure of the nucleus. When it was first discovered, it was considered to be an isolated organelle that forms ...

Education

JoVE Core

Cell Biology

Unit 1

Transcription: DNA to RNA

KEY TERMS AND CONCEPTS

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 helps prepare the parts that later become fully functional ribosomes. That makes the nucleolus an important part of cell activity.

Nucleolus and Ribosome Assembly

what is gene expression?

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 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 the nucleolus as the site where ribosome assembly begins, including rRNA production and nucleolar organizer regions in the nucleus.

Nucleolus and Ribosome Assembly | JoVE K12

cell biology

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.

Virginia  Standards of Learning

HIgh School

BIO.2

BIO.2.d

Minnesota Academic Standards in Science

Life Science

3.2.1 9L.3.2.1.1

Alabama Course of Study Science

From Molecules to Organisms: Structures and Processes

9-12.B.1.2

Florida Department of Education

High School

SC.912.L.16

SC.912.L.16.5

SC.912.L.16.6

south-carolina-college-and-career-ready-science-standards

South Carolina College and Career Ready Science Standards

B-LS1-1.

Compounds Essential to Human Function

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lipid-derived-compounds-in-the-human-body

Lipid-derived Compounds in the Human Body

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Globular Proteins

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Role of Proteins in the Human Body

Proteins are the building block of life. They are also&#160; the most abundant macromolecules with as many diverse roles in the body. They are part of ...

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Nucleic acids are the most important macromolecules for the continuity of life. They carry the cell&#39;s genetic blueprint and have instructions for its ...

Nucleic Acid Structure

The pentose sugar in DNA is deoxyribose, while in RNA the pentose sugar is ribose. The difference between the sugars is the presence of the hydroxyl group ...

ATP Energy Storage and Release

ATP and Macromolecule Synthesis

Biological macromolecules are organic compounds, predominantly composed of carbon atoms. The carbon atoms are covalently bonded with hydrogen, oxygen, ...

Construct an explanation to illustrate relationships between structure and function of major macromolecules essential for life.

LS.Bio.1.1

Introduction to Enzymes

The use of enzymes by humans dates to 7000 BCE. Humans first used enzymes to ferment sugars and produce alcohol without knowing that this was an ...

Enzymes and Activation Energy

The activation energy (or free energy of activation), abbreviated as Ea, is the small amount of energy input necessary for all chemical reactions to ...

Introduction to Enzyme Kinetics

Enzyme kinetics studies the rates of biochemical reactions. Scientists monitor the reaction rates for a particular enzymatic reaction at various substrate ...

Turnover Number and Catalytic Efficiency

The turnover number of an enzyme is the maximum number of substrate molecules it can transform per unit time. Turnover numbers for most enzymes range from ...

Catalytically Perfect Enzymes

The theory of catalytically perfect enzymes was first proposed by W.J. Albery and J. R. Knowles in 1976. These enzymes catalyze biochemical reactions at ...

introduction-to-mechanisms-of-enzyme-catalysis

Introduction to Mechanisms of Enzyme Catalysis

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Ligand Binding and Linkage

Cooperative Allosteric Transitions

Ribozymes

Carry out investigations to illustrate how enzymes act as catalysts for biochemical reactions and how environmental factors affect enzyme activity.

LS.Bio.1.2

What are Cells?

Cells are the smallest and basic units of life, whether it is a single cell that forms the entire organism, e.g., in a bacterium or trillions of them, ...

Cell Size

Cell sizes vary widely among and within organisms. Bacterial cells range between 1-10 micrometers (&#x3BC;m)and are considerably smaller than most ...

Eukaryotic Compartmentalization

One of the distinguishing features of eukaryotic cells is that they contain membrane-bound organelles, such as the nucleus and mitochondria, that carry ...

Prokaryotic Cells

Prokaryotes are small unicellular organisms that include the domains&#x2014;Archaea and Bacteria. Bacteria include many common organisms, such as ...

Cytoplasm

The cytoplasm consists of organelles and a framework of protein scaffolds called the cytoskeleton suspended in an aqueous solution, the cytosol. The ...

The Nucleus

The nucleus is a membrane-bound organelle that acts as a control center in a eukaryotic cell. It contains chromosomal DNA, which controls gene expression ...

Endoplasmic Reticulum

Endoplasmic ReticulumThe endoplasmic reticulum (ER) is an extensive network of membranous sacs and tubules in eukaryotic cells, continuous with the outer ...

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that ...

Golgi Apparatus

As they leave the Endoplasmic Reticulum (ER), properly folded and assembled proteins are selectively packaged into vesicles. These vesicles are ...

Lysosomes

Lysosomes are membrane-enclosed spherical sacs derived from the Golgi apparatus. The most important function of the lysosome is degrading macromolecules ...

Peroxisomes

Peroxisomes and mitochondria are two important oxygen-utilizing organelles in eukaryotic cells. Mitochondria carry out cellular respiration&#x2014;the ...

Introduction to the Cytoskeleton

Overview of the Cytoskeleton
The cytoskeleton is a network of protein filaments present within the cell, having three distinct filaments ...

Introduction to Actin

Actin is a highly conserved cytoskeletal protein found abundantly in eukaryotic cells. It constitutes 10% weight of the total cellular protein in muscle ...

Cell Structure

Background
Cells represent the most basic biological units of all organisms, whether it be simple, single-celled organisms like bacteria, or large, ...

overview-of-myosin-structure-and-function

Overview of Myosin Structure and Function

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Visualizing Onion and Cheek Cells
ExpandImmediately before the experiment, wash and peel onion bulbs for the class.
Remove the entire brown outer skin and ...

Microtubules

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The Structure of Intermediate Filaments

The intermediate filaments are one of three widely studied cytoskeletal filaments. They are so named as their diameter (10 nm) is in between that of ...

Types of Intermediate Filaments

The intermediate filaments are an essential component of the cytoskeleton. Presently six types of intermediate filament have been identified. Type I and ...

Gap Junctions

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The Extracellular Matrix

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Tissues

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Plant Cell Wall

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Use models to explain how the structure of organelles determines its function and supports overall cell processes.

LS.Bio.1.3

Analyze how the relationship between structure and function supports life processes within organisms.

Nucleolus and Ribosome Assembly

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