Name: protein recycling by the proteasome
Uploaded: 2023-04-30T18:28:45.000Z
Duration: 2 min 18 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 Proteasome

Due to errors in transcription, RNA splicing, and translation, some proteins never fold correctly and need to be degraded.&#160;
In eukaryotes, the major pathway for selective protein degradation is the ubiquitin-proteasome pathway.&#160;
A ubiquitin ligase can differentiate between a normal protein and a target protein by recognizing certain degradation signals on their surface.&#160;
It then catalyses the transfer of several ubiquitin molecules to a specific amino acid on the target proteins to mark them for degradation.&#160;
These polyubiquitinated proteins are degraded by an ATP-dependent protease complex called the proteasome.
Each proteasome consists of a central hollow cylinder or the core, and large ring-shaped protein complexes called the caps at one or both ends of the core.
The core is formed by multiple protein subunits that assemble as a stack of rings. The proteolytic active sites of the core lie in its hollow inner chamber.
The caps at the end of the proteasome core act as the gatekeepers and only allow proteins marked by ubiquitin for entry into the core.&#160;
The cap contains a deubiquitinase that cleaves ubiquitin from the substrate protein so that the released ubiquitin can be recycled

the proteasome

Eukaryotic cells can degrade proteins through several pathways. One of the most important amongst these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. A series of enzymes carry out the ubiquitination of the target proteins - E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3 (ubiquitin ligase). The synergy of all these three enzymes helps to attach ubiquitin molecules to the target proteins covalently.
The proteasome, a large multi-subunit protease, can hence differentiate between a healthy protein and target protein by recognizing the ubiquitin chain on the target protein. Once the proteasome recognizes the ubiquitin chain, it unfolds the target protein and ultimately degrades it. The leftover peptides of the substrate protein are then released into the cytosol for further processing.
Targeted destruction of proteins is critical to the well-being of the cell, and any alterations in the ubiquitin-proteasome pathway can lead to disease. For example, if misfolded proteins are not degraded, they form protein aggregates in the cytoplasm. Such protein aggregates can lead to prominent neurodegenerative disorders such as Parkinson, Huntington, and Alzheimer&#39;s.
On the contrary, excess quality control by the ubiquitin-proteasome pathway may also lead to disease. For example, the destruction of misfolded but partially functional chloride ion-channels leads to cystic fibrosis, a life-threatening disorder in humans.

Eukaryotic cells can degrade proteins through several pathways. One of the most important amongst these is the ubiquitin-proteasome pathway. It helps the ...

Education

JoVE Core

Cell Biology

Unit 1

Translation: RNA to Protein

KEY TERMS AND CONCEPTS

protein recycling by the proteasome

The proteasome breaks down proteins inside cells. It helps control which proteins stay active and which are removed. This process is an important part of protein recycling.

Proteins can be tagged for destruction before they enter the proteasome. The cell uses this system to remove proteins that are no longer needed or that must be cleared away. The proteasome then cuts them into smaller pieces.

This protein breakdown helps the cell stay organized and function properly. By clearing selected proteins, the proteasome supports normal cell activity and keeps protein levels under control.

Protein Recycling by the Proteasome

translation

How Cells Build Proteins from mRNA

Translation is the cell process that builds proteins from messenger RNA, or mRNA. It comes after transcription and is the final step in gene expression. Ribosomes, which are made of protein and specialized RNA, carry out this process with help from transfer RNA, or tRNA, and other proteins. The result is a chain of amino acids called a polypeptide. Proteins are called the building blocks of life because they make up much of an organism, from muscle fibers and hair to parts of the immune system.

ribosomes

Ribosomes in Protein Synthesis

Ribosomes build proteins by reading messenger RNA, or mRNA, and turning that genetic code into an amino acid chain. Both prokaryotic and eukaryotic cells have ribosomes. Cells that make large amounts of protein, such as secretory cells in the human pancreas, can contain millions of them. Ribosomes are made of ribosomal RNA, or rRNA, and proteins. In eukaryotes, rRNA is transcribed from genes in the nucleolus, a region of the nucleus that specializes in making ribosomes. There, rRNA joins with...

trna activation

Charging tRNA for Protein Synthesis

tRNA charging is the step that prepares transfer RNA for protein synthesis. In this process, an amino acid is attached to its matching tRNA by an enzyme called aminoacyl-tRNA synthetase. The charged tRNA can then deliver that amino acid during translation. tRNA charging is a key part of how cells build proteins from genetic information. The transcript focuses on the activation of tRNA and the role of aminoacyl-tRNA synthetases in this process. These enzymes help ensure that the correct amino...

initiation of translation

Translation Begins with Ribosome Assembly

Translation begins when a ribosome assembles on an mRNA molecule and starts reading its code. During this first stage of protein synthesis, the cell prepares the machinery needed to build a protein from amino acids. The small ribosomal subunit binds to the mRNA first. It helps position the message so the ribosome can find the correct start site. Then the initiator tRNA, which carries the first amino acid, pairs with the start codon on the mRNA. After the start codon is matched, the large...

termination of translation

How Protein Synthesis Ends

Protein synthesis ends when translation reaches a stop signal on the mRNA. At this stage, the ribosome no longer adds amino acids to the growing polypeptide chain. Instead, the process shifts to releasing the completed protein.

improving translational accuracy

Boosting Protein Translation Fidelity

Protein translation fidelity helps cells build the right protein from an mRNA message. The ribosome must read each codon correctly and add the matching amino acid in order. Even small errors can change the final protein. The transcript explains how accuracy can be improved during translation. It focuses on the steps that help the ribosome choose the correct tRNA and keep the growing peptide chain on track. These controls reduce mistakes while the protein is being made. This topic is important...

nonsense-mediated mrna decay

Nonsense-Mediated mRNA Decay and UPF Proteins

Nonsense-mediated mRNA decay is a cell quality-control process that removes faulty mRNA before it can make a shortened protein. It helps protect cells from errors during gene expression. The pathway depends on UPF proteins, which help identify and trigger the breakdown of the problem message. This process matters when an mRNA contains a premature stop signal, also called a nonsense codon. Instead of allowing translation to continue, the cell recognizes the defective message and targets it for...

molecular chaperones and protein folding

Chaperones Guide Protein Folding

Molecular chaperones help proteins fold into the correct shape. Protein folding is a key step after a protein is made, because shape affects function. If a protein does not fold properly, it may not work as it should. Chaperones do not become part of the final protein. Instead, they assist the folding process and help proteins avoid harmful misfolding. They are especially important when newly made proteins are still fragile and need support as they take on their proper structure. This topic...

The proteasome breaks down proteins inside cells. It helps control which proteins stay active and which are removed. This process is an important part of protein recycling. Proteins can be tagged for destruction before they enter the proteasome. The cell uses this system to remove proteins that are no longer needed or that must be cleared away. The proteasome then cuts them into smaller pieces. This protein breakdown helps the cell stay organized and function properly. By clearing selected...

regulated protein degradation

How Cells Remove Unneeded Proteins

Cells remove unneeded proteins through regulated protein degradation. This process helps control which proteins stay active and which proteins are broken down. Protein degradation is not random. The cell uses signals to mark proteins for removal at the right time. This regulation lets the cell respond to changing needs and keep protein levels balanced. Regulated protein degradation is an important part of molecular biology. It shows how cells maintain control over their internal processes by...

proteins: from genes to degradation

Protein Synthesis and Breakdown

Proteins are made from genes and later broken down when they are no longer needed. This page follows that path from gene information to protein degradation, or protein breakdown. It shows how cells build proteins and how they remove them at the right time. The process begins with genes, which carry the instructions for making proteins. Those instructions are used to produce proteins with specific jobs in the cell. After a protein has done its work, the cell can degrade it instead of keeping it...

key terms and concepts

Learn how the proteasome breaks down tagged proteins inside cells and helps control protein recycling, removal, and normal cell function.

Protein Recycling by the Proteasome | 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

Alabama Course of Study Science

From Molecules to Organisms: Structures and Processes

9-12.B.1.2

Florida Department of Education

High School

Life Science

SC.912.L.16

SC.912.L.16.5

Compounds Essential to Human Function

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Macromolecules

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

Lipid-derived Compounds in the Human Body

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Protein Organization

Globular Proteins

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Nucleic Acids and Nucleotides

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Nucleic Acid Structure

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ATP Energy Storage and Release

ATP and Macromolecule Synthesis

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LS.Bio.1.1

Introduction to Enzymes

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Introduction to Enzyme Kinetics

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Turnover Number and Catalytic Efficiency

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Catalytically Perfect Enzymes

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introduction-to-mechanisms-of-enzyme-catalysis

Introduction to Mechanisms of Enzyme Catalysis

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Ligand Binding and Linkage

Cooperative Allosteric Transitions

Ribozymes

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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

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Eukaryotic Compartmentalization

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Prokaryotic Cells

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Cytoplasm

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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

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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

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Peroxisomes

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Introduction to the Cytoskeleton

Overview of the Cytoskeleton
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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

Myosins are a family of molecular motor proteins, first identified in the skeletal muscles, where they are responsible for muscle contraction. Along with ...

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

Microtubules are the thickest cytoskeletal filaments with a diameter of 25 nm. In prokaryotic organisms, microtubules are commonly found in locomotory ...

The Structure of Intermediate Filaments

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Types of Intermediate Filaments

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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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Plasmodesmata

The organs in a multicellular organism&#x2019;s body are made up of tissues formed by cells. To work together cohesively, cells must communicate. One way ...

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

LS.Bio.1.3

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, ...

the-tree-of-life-bacteria-archaea-and-eukaryotes

The Tree of Life - Bacteria, Archaea, and Eukaryotes

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Prokaryotic vs. Eukaryotic Cells

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Construct explanations to compare prokaryotic and eukaryotic cells in terms of structures and degree of complexity.

LS.Bio.1.4

The DNA Helix

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RNA is the Missing Link Between ...

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RNA Structure

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Types of RNA

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Transcription

Transcription is the synthesis of RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene sequence. ...

Bacterial RNA Polymerase

Eukaryotic RNA Polymerases

General Transcription Factors

Tissue-specific transcription factors contribute to diverse cellular functions in mammals. For example, the gene for beta globin, a major component of ...

Construct an explanation to summarize how DNA and RNA direct the synthesis of proteins.

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

Protein Recycling by the Proteasome

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