What is gene therapy and how does it work to treat genetic disorders?

Gene therapy is an advanced medical approach designed to treat or potentially cure genetic disorders by modifying or replacing faulty genes within a patient's cells. Genetic disorders arise due to mutations or defects in DNA, leading to the production of abnormal, insufficient or missing proteins necessary for normal bodily functions. Unlike conventional treatments that manage symptoms, gene therapy targets the root cause of genetic diseases, making it a highly promising and potentially curative strategy. It is particularly effective for monogenic disorders (caused by mutations in a single gene), but ongoing research is exploring its application in more complex, polygenic conditions.

The foundation of gene therapy was laid by William French Anderson, Michael Blaese and Kenneth Culver, who conducted the first successful gene therapy trial in 1990 to treat severe combined immunodeficiency (SCID) caused by ADA deficiency. Another key contributor, Richard Mulligan, significantly advanced retroviral vector technology, enhancing the efficiency and safety of gene delivery. Additionally, Emmanuelle Charpentier and Jennifer Doudna revolutionized gene editing with their discovery of CRISPR-Cas9, a powerful tool that enables precise correction of genetic mutations and holds great potential for future gene therapy applications.

To achieve its therapeutic effects, gene therapy relies on specialized delivery systems called vectors, which transport the therapeutic gene into the patient's cells. The most commonly used vectors are viral vectors, such as modified adenoviruses, lentiviruses and adeno-associated viruses (AAVs), which can efficiently introduce new genetic material into target cells. Non-viral methods, such as liposomes, nanoparticles and electroporation, provide alternative delivery approaches that avoid potential immune system reactions. These vectors ensure that the corrected gene reaches the appropriate cells, allowing them to function normally.

Gene therapy is being explored as a potential treatment for a wide range of genetic disorders, including SCID, cystic fibrosis, hemophilia, muscular dystrophy, sickle cell anemia and certain inherited retinal diseases. As research continues, scientists aim to refine gene therapy techniques to improve their safety, effectiveness and accessibility.

Gene therapy can be classified based on two major criteria, which define how the therapy works and its impact on the individual and future generations:

1. Based on Target Cells

This classification focuses on whether the genetic modification affects only the individual being treated or can be inherited by future generations. It includes:
    1. Somatic Gene Therapy (modifies body cells, non-inheritable)
    2. Germline Gene Therapy (modifies reproductive cells, inheritable)

2. Based on Mechanism of Action

This classification explains the specific way gene therapy corrects or alters genetic material. It includes:
  1. Gene Replacement Therapy (Restoring Missing or Defective Genes)
  2. Gene Silencing Therapy (Suppressing Harmful Gene Activity)
  3. Gene Editing Therapy (Correcting Genetic Mutations )

Mechanisms of Gene Therapy in Treating Genetic Disorders

Gene therapy works by directly modifying the genetic material of a person's cells to restore normal function and correct the underlying cause of a genetic disorder. This can be achieved in different ways depending on the nature of the disease and the specific genetic defect involved. The three primary mechanisms through which gene therapy treats genetic disorders are:
  1. Gene Replacement Therapy (Restoring Missing or Defective Genes)
  2. Gene Silencing Therapy (Suppressing Harmful Gene Activity)
  3. Gene Editing Therapy (Correcting Genetic Mutations )

1. Gene Replacement Therapy (Restoring Missing or Defective Genes)

Gene replacement therapy works by introducing a normal, functional copy of a gene into a patient's cells to compensate for a defective or missing gene. This method is particularly effective for diseases caused by loss-of-function mutations, where the affected gene either fails to produce a necessary protein or produces a non-functional version. By supplying the correct gene, this therapy restores protein function and helps alleviate disease symptoms.

This mechanism is particularly effective for monogenic disorders like spinal muscular atrophy (SMA), severe combined immunodeficiency (SCID) and Leber congenital amaurosis (LCA), where a single missing or defective gene is responsible for the disease. In such cases, gene replacement therapy can offer long-term relief or even a potential cure.

How Gene Replacement Works

Gene replacement therapy works by introducing a fully functional copy of a gene into the patient's cells to compensate for a defective or missing gene. This process restores the ability of the affected cells to produce the essential protein required for normal function, thereby alleviating or even completely reversing the disease symptoms.

Gene replacement involves four main steps: identification of the target gene, preparation of the replacement gene, delivery into the cells and integration with the genome. Each step is essential for ensuring that the new gene functions properly and produces the desired effect.
  1. Identification of the Target Gene
    • The first step in gene replacement is identifying the gene that needs to be replaced. This is done using various genetic analysis techniques such as genome sequencing, polymerase chain reaction (PCR),and bioinformatics tools. Scientists analyze the gene sequence and locate mutations or defects responsible for a disease or undesirable trait. Understanding the gene's location, structure and function is crucial for designing a suitable replacement.
  2. Preparation of the Replacement Gene
    • Once the faulty gene is identified, a functional copy of the gene is prepared. The replacement gene is synthesized in the laboratory using recombinant DNA technology, ensuring it has the correct sequence and regulatory elements required for proper expression. If necessary, the gene is modified to enhance its stability, efficiency or compatibility with the target organism's genome. The replacement gene is usually inserted into a vector, such as a plasmid, viral vector, or bacterial artificial chromosome (BAC), to facilitate its delivery into cells.
  3. Delivery into the Cells
    • The replacement gene must be delivered into the target cells using an efficient method. The choice of delivery method depends on the organism, cell type and specific requirements of the replacement process. The most commonly used methods include:
      • Viral Vectors: Viruses like lentiviruses, adenoviruses, or adeno-associated viruses (AAV) are engineered to carry the replacement gene and infect target cells, delivering the gene into their genome.
      • Microinjection: The replacement gene is directly injected into the nucleus of a cell using a fine needle, ensuring precise placement.
      • Electroporation: Electrical pulses create temporary pores in the cell membrane, allowing the replacement gene to enter the cells.
      • Liposome-Mediated Delivery: Artificial lipid vesicles (liposomes) carry the replacement gene and merge with the cell membrane to introduce the gene inside.
  4. Integration with the Genome
    • Once inside the cell, the replacement gene must integrate with the genome to ensure stable expression. The integration can occur through different mechanisms:
      • Homologous Recombination: The replacement gene is designed with sequences matching the flanking regions of the defective gene, allowing precise replacement at the target site. This method ensures accurate gene correction but occurs at a lower frequency.
      • Non-Homologous End Joining (NHEJ): The new gene randomly integrates into the genome, which is less precise but more efficient in certain cases.
      • CRISPR-Cas9 Mediated Integration: The CRISPR-Cas9 system introduces a specific cut in the genome and the cell's repair machinery incorporates the replacement gene at the correct location. This method is highly efficient and widely used in gene editing.
    • If successful, the new gene starts producing functional proteins, restoring normal cellular function. In therapeutic applications, this can lead to the correction of genetic disorders such as cystic fibrosis, sickle cell anemia and muscular dystrophy.

Types of Vectors Used in Gene Replacement Therapy

Gene therapy relies on vectors to deliver therapeutic genes into cells efficiently. The most commonly used vectors include:
  1. Viral Vectors:
    1. Adeno-associated viruses (AAVs): Non-pathogenic viruses that can deliver therapeutic genes to long-lived cells with minimal immune response.
    2. Lentiviruses: Capable of integrating the functional gene into the patient's genome, making it suitable for long-term effects.
    3. Retroviruses: Insert the gene into the host genome but have risks of insertional mutations.
  2. Non-viral Vectors:
    1. Liposomes: Fat-based particles that encapsulate DNA and deliver it into cells.
    2. Plasmid DNA: Circular DNA molecules that enter cells to express therapeutic proteins but do not integrate into the genome.

Examples of Gene Replacement Therapy

Gene replacement therapy has shown success in treating monogenic disorders where a single defective gene is responsible for the disease. Some examples include:
  • Spinal Muscular Atrophy (SMA): A disorder caused by mutations in the SMN1 gene, leading to motor neuron degeneration. Gene therapy (e.g., Zolgensma) delivers a functional SMN1 gene using AAVs to restore protein function.
  • Severe Combined Immunodeficiency (SCID): Known as "bubble boy syndrome," this disorder results from a lack of immune function due to mutations in genes like ADA or IL2RG. Gene therapy introduces functional copies of these genes to restore immune response.
  • Leber Congenital Amaurosis (LCA): An inherited blindness disorder caused by mutations in the RPE65 gene. Gene therapy delivers a normal RPE65 gene to retinal cells, restoring vision.

2. Gene Silencing Therapy (Suppressing Harmful Gene Activity)

Gene silencing, also known as gene inhibition therapy, is used to reduce or stop the expression of a faulty or overactive gene. This approach is beneficial in conditions where a gain-of-function mutation causes excessive production of a harmful protein. Instead of replacing the gene, this therapy prevents it from being expressed, thus blocking the disease-causing effects.

How Gene Silencing Works

Gene silencing therapy functions by blocking or reducing the expression of a faulty gene that produces harmful or excessive proteins, which cause disease. Instead of replacing a defective gene, this approach prevents it from being translated into a protein, thereby stopping its harmful effects.

Gene silencing involves four main steps: identification of the target gene, selection of a silencing method, delivery into the cells and suppression of gene expression. Each step is crucial for ensuring the effective inhibition of the target gene.
  1. Identification of the Target Gene
    • The first step in gene silencing is identifying the gene that needs to be suppressed. This is done using genetic analysis techniques such as genome sequencing, polymerase chain reaction (PCR) and bioinformatics tools. Scientists analyze the gene sequence and its role in cellular functions or diseases. Understanding the gene's location, expression pattern and function helps in selecting the most effective silencing strategy.
  2. Selection of a Silencing Method
    • Once the target gene is identified, an appropriate silencing method is chosen. There are three major types of gene silencing:
      1. RNA Interference (RNAi): This method uses small RNA molecules to degrade the gene's messenger RNA (mRNA) before it can produce a protein. It includes two types:
        1. Small Interfering RNA (siRNA): Short double-stranded RNA molecules that bind to complementary mRNA sequences and trigger degradation by the RNA-induced silencing complex (RISC).
        2. MicroRNA (miRNA): Naturally occurring small RNA molecules that partially bind to mRNA, blocking translation or causing degradation.
      2. Antisense Oligonucleotides (ASOs): Short synthetic DNA or RNA sequences that bind to the target mRNA, preventing it from being translated into protein or marking it for degradation.
      3. CRISPR-Cas9 Mediated Silencing: The CRISPR-Cas9 system can be used to permanently silence a gene by introducing targeted mutations that disrupt its function. This is done using a guide RNA (gRNA) to direct Cas9 to the gene's DNA, where it creates a break, leading to loss of function.
  3. Delivery into the Cells
    • The selected silencing molecules (siRNA, miRNA, ASOs, or CRISPR components) must be delivered into the target cells efficiently. The efficiency of delivery depends on the method used, the cell type and the stability of the silencing molecules. The most commonly used delivery methods include:
      • Viral Vectors: Engineered viruses such as lentiviruses and adenoviruses can deliver gene-silencing molecules into cells.
      • Liposome-Mediated Delivery: Lipid-based nanoparticles carry the silencing molecules and fuse with cell membranes to release their contents.
      • Electroporation: Electrical pulses create temporary pores in the cell membrane, allowing gene-silencing molecules to enter.
      • Direct Injection: In some cases, silencing molecules are directly injected into tissues or the bloodstream for systemic effects.
  4. Suppression of Gene Expression
    • Once inside the cell, the gene-silencing molecules act to suppress gene expression through different mechanisms:
      • mRNA Degradation: In RNAi-based silencing, siRNA or miRNA binds to complementary mRNA sequences, marking them for destruction by the RISC complex. This prevents translation into proteins.
      • Translation Inhibition: In cases where miRNA does not completely degrade the mRNA, it still blocks the ribosomes from translating it into protein, reducing gene activity.
      • DNA Modification: In CRISPR-based silencing, mutations introduced into the gene prevent it from being transcribed into mRNA, leading to permanent loss of function.
      • Epigenetic Changes: Some gene-silencing techniques use DNA methylation or histone modifications to prevent a gene from being transcribed, leading to long-term or permanent suppression.
    • If successful, gene silencing reduces or eliminates the production of the target protein, which can help in treating diseases, modifying traits, or studying gene functions.

Types of Vectors Used in Gene Silencing

  1. Viral Vectors
    1. Adeno-associated viruses (AAVs): Used in RNAi-based therapies due to their ability to deliver siRNA into cells with minimal immune response.
    2. Lentiviruses: Can integrate siRNA or ASOs into the genome for stable and long-term gene silencing.
  2. Non-Viral Vectors
    1. Lipid Nanoparticles (LNPs): These are widely used in siRNA therapies, including FDA-approved RNAi drugs, as they protect RNA molecules from degradation.
    2. Polymeric Nanoparticles: Biodegradable polymers that enhance siRNA delivery into target cells.

Examples of Gene Silencing Therapy

  • Huntington's Disease (HD): A neurodegenerative disorder caused by excessive production of mutated huntingtin protein. ASOs can reduce protein production and slow disease progression.
  • Amyotrophic Lateral Sclerosis (ALS): Some forms of ALS are caused by toxic protein accumulation. Gene silencing therapy can help reduce these proteins and delay nerve degeneration.

3. Gene Editing Therapy (Correcting Genetic Mutations )

Gene editing therapy permanently modifies the patient's genome to correct genetic defects at the DNA level. Unlike gene replacement, which introduces an additional copy of a gene, gene editing directly repairs mutations in the existing DNA sequence, offering a permanent cure.

How Gene Editing Works

Gene editing involves four main steps: identification of the target gene, selection of an editing method, delivery into the cells, and modification of the genome. Each step is essential to ensure precise and effective genetic changes.
  1. Identification of the Target Gene
    • The first step in gene editing is identifying the gene that needs to be modified. This is done using various genetic analysis techniques such as genome sequencing, polymerase chain reaction (PCR) and bioinformatics tools. Scientists analyze the gene's sequence, function and role in biological processes or diseases. Identifying the exact location of the gene within the genome is crucial for designing a precise editing strategy.
  2. Selection of an Editing Method
    • Once the target gene is identified, an appropriate gene-editing method is chosen. There are three major types of gene editing 
      1. CRISPR-Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats): This is the most widely used gene-editing tool. It consists of a guide RNA (gRNA) that directs the Cas9 enzyme to a specific DNA sequence, where it creates a precise cut. The cell's repair mechanisms then introduce the desired modification. CRISPR is highly specific, efficient, and relatively easy to use.
      2. Zinc Finger Nucleases (ZFNs): These are engineered proteins that bind to specific DNA sequences and introduce cuts. ZFNs were among the first gene-editing tools developed, but they are more complex to design than CRISPR.
      3. TALENs (Transcription Activator-Like Effector Nucleases): These function similarly to ZFNs but use a different DNA-binding domain. TALENs offer high specificity but are more labor-intensive to develop than CRISPR.
    • The choice of editing method depends on factors such as target sequence specificity, efficiency and the type of genetic modification required.
  3. Delivery into the Cells
    • The gene-editing components (CRISPR-Cas9, ZFNs, or TALENs) must be delivered into the target cells efficiently. The success of gene editing depends on the efficiency of delivery, stability of the editing molecules and the ability to reach the target cells. The most commonly used delivery methods include:
      • Viral Vectors: Engineered viruses such as lentiviruses and adenoviruses can carry gene-editing components into cells.
      • Liposome-Mediated Delivery: Lipid-based nanoparticles encapsulate the gene-editing molecules and help them enter the cells.
      • Electroporation: Electrical pulses create temporary pores in the cell membrane, allowing the editing molecules to enter.
      • Microinjection: A fine needle injects the editing components directly into cells, ensuring precise delivery.
  4. Modification of the Genome
    • Once inside the cell, the gene-editing tool modifies the genome through different mechanisms:
      • Gene Knockout (Deletion): The editing tool creates a double-strand break in the DNA and the cell's repair system removes the targeted gene segment, leading to loss of function.
      • Gene Insertion (Addition): A new DNA sequence is inserted at the cut site to introduce a functional gene or correct a mutation.
      • Gene Correction (Base Editing): Instead of cutting the DNA completely, a single nucleotide (A, T, G, or C) is directly modified to correct a mutation without causing double-strand breaks.
      • Epigenetic Editing: Modifications are introduced to alter gene expression without changing the DNA sequence, such as adding chemical markers to activate or silence a gene.
    • If successful, the edited gene produces the desired effect, which can restore normal function in disease conditions, enhance crop traits, or help scientists understand gene functions.

Types of Vectors Used in Gene Editing Therapy

  1. Viral Vectors
    1. Adeno-associated viruses (AAVs): Commonly used in CRISPR-based gene editing due to their ability to deliver guide RNA and Cas9 into cells with high efficiency while causing minimal immune response. They are non-integrating, making them safer for therapeutic applications.
    2. Lentiviruses: Used for delivering gene-editing components like CRISPR-Cas9 or TALENs into dividing and non-dividing cells. They integrate into the genome, allowing for stable and long-term gene correction but require careful safety considerations.
  2. Non-Viral Vectors
    1. Lipid Nanoparticles (LNPs): These are widely used for delivering CRISPR-based gene-editing tools, such as mRNA encoding Cas9 and guide RNA, ensuring effective gene correction while preventing immune activation. LNPs were also used in mRNA-based COVID-19 vaccines, highlighting their safety and efficacy.
    2. Polymeric Nanoparticles: Biodegradable polymers that enhance the delivery of gene-editing components like plasmid DNA or CRISPR ribonucleoproteins (RNPs) into target cells, improving stability and reducing off-target effects.

Examples of Gene Editing Therapy

  • Sickle Cell Disease: CRISPR is used to correct the mutation in the β-globin gene, restoring normal hemoglobin function.
  • β-Thalassemia: A blood disorder caused by mutations in the HBB gene. Gene editing repairs this defect, enabling proper red blood cell function.
  • Duchenne Muscular Dystrophy (DMD): A fatal muscle disorder caused by mutations in the dystrophin gene. CRISPR can restore dystrophin production.



Also Read:


Comments

Post a Comment

Popular posts from this blog

What is the purpose of the G2 checkpoint?

The G2 checkpoint is often referred to as the  G2-M checkpoint  because it is located at the boundary between the G2 phase and the M phase (mitosis) of the cell cycle. This checkpoint plays a key role in deciding whether the cell is ready to move from G2 phase into mitosis. The name "G2-M" itself reflects its position and function, it lies at the end of the G2 phase but directly regulates the cell's entry into the M phase. During the G2 phase, the cell completes the synthesis of proteins and prepares all necessary components for mitosis. However, before entering mitosis, the cell must ensure that the DNA, which was replicated during the S phase, is completely and correctly duplicated and that there is no DNA damage. At this critical point, the  G2-M checkpoint becomes active.  It functions like a gatekeeper or quality control system. It checks: Whether DNA  replication has been completed without any errors Whether the DNA is  free of any damage Whether the ...
Read more

What is the significance of the G2 phase in the cell cycle?

Image
The G2 phase (also known as Gap 2 phase) is the third and final phase of  interphase  in the cell cycle. It occurs after DNA replication in the S phase and before the cell enters mitosis (M phase). While the G2 phase may seem like a resting phase, it is actually a highly active period during which the cell prepares for division. The G2 phase ensures that the cell has successfully completed DNA replication and is ready to divide. It also serves as a  checkpoint  for the cell to correct any errors that may have occurred during DNA replication, ensuring that only healthy, complete genetic material is passed on to daughter cells. 1. DNA Damage Check and Repair through the G2-M Checkpoint One of the major significances of the G2 phase is to check for DNA damage that may have occurred during the  S phase , where DNA replication takes place. If there is any damage in the DNA, the cell does not immediately move into mitosis. Instead, a special control system known as th...
Read more

UNIT 14 – Signal Transduction (Q&A) | MZO-001 MSCZOO | IGNOU

SAQ 1 Mark the correct option: a) The cellular response to a particular signaling molecule depends on the number of     i) receptor     ii) ligand     iii) receptor-ligand complexes Answer: iii) receptor-ligand complexes b) The binding of receptor to ligand binding is mediated through weak     i) non-covalent forces     ii) covalent forces Answer: i) non-covalent forces c) Different receptors of the same class that bind different ligands often induce the     i) same cellular responses in a cell     ii) different cellular responses in a cell Answer: i) same cellular responses in a cell d) Many signaling molecules bind to multiple types of receptors, each of which can activate different intracellular signaling pathways and thus induce     i) same cellular responses     ii) different cellular responses Answer: ii) different cellular responses SAQ 2 Fill in the blanks: a) The binding of ligands to many...
Read more

Why is the dynamic regulation of cyclins important?

Cyclins are essential regulatory proteins that control the progression of the cell cycle. Their activity is highly regulated in a dynamic manner to ensure the cell cycle proceeds at the appropriate time and under the right conditions. This regulation involves the synthesis, activation and degradation of cyclins at specific points during the cycle. The precise control of cyclin levels and activity is crucial for maintaining normal cell function and preventing diseases like cancer. The dynamic regulation of cyclins helps coordinate various processes such as DNA replication, cell division and checkpoint control, ensuring the cell divides only when it is ready and the conditions are appropriate. Importance of Dynamic Regulation of Cyclins: 1. Controlled Progression through the Cell Cycle: Cyclins regulate the transition of cells from one phase of the cell cycle to the next by activating Cyclin-Dependent Kinases (CDKs). The dynamic regulation of cyclins ensures that the cell proceeds from o...
Read more

What are cyclins?

Cyclins are a special group of regulatory proteins that control the proper timing and order of the cell cycle. They are called  "cyclins"  because their concentration inside the cell rises and falls in a  cyclical pattern  during different phases of the cell cycle. They are not enzymes by themselves but become functional when they bind with another group of proteins called  cyclin-dependent kinases (CDKs).  These CDKs are enzymes that phosphorylate target proteins and this phosphorylation triggers specific events in the cell cycle like DNA replication or mitosis. Cyclins are essential because they ensure that the cell cycle progresses in the correct sequence. Without them, cells would not know when to grow, when to copy DNA, or when to divide. Cyclins are produced at specific times during the cell cycle and once their function is complete, they are broken down by a system called the  ubiquitin-proteasome pathway.  This degradation prevents the cel...
Read more

How are cyclins named?

Cyclins are named based on their  cyclical pattern  of appearance and disappearance during the cell cycle and the specific phases in which they are active. The term "cyclin" was first introduced by  Tim Hunt,  a British scientist, who discovered a protein in  1982  in sea urchin embryos that increased and decreased in regular cycles during cell division. Because of this repeating pattern, he casually named the protein "cyclin" to reflect its cyclic behaviour. His research was officially published in  1983  and later he was awarded the Nobel Prize in Physiology or Medicine in 2001, along with  Paul Nurse  and  Leland Hartwell,  for their work on cell cycle regulation. After this discovery, more cyclins were identified in other organisms. As a result, they were systematically named using letters like Cyclin A, B, C, D, and E. This naming usually depends on either the order in which they were discovered or the cell cycle phase in ...
Read more

Which proteins regulate the progression from G1 to S phase?

In eukaryotic cells, the transition from G1 to S phase of the cell cycle is one of the most important and carefully regulated steps. This phase decides whether a cell will proceed toward DNA replication or stay in a resting state (G₀ Phase) or even go for repair. Cells make this decision based on internal and external signals, and this entire decision making process is controlled by specific regulatory proteins. There are five main types of protein regulators that play a central role in G1 to S phase transition. These proteins work in coordination and any disturbance in their function can lead to abnormal cell division or diseases like cancer. 1. Cyclins (Cyclin D and Cyclin E) Cyclins are regulatory proteins that appear and disappear during different phases of the cell cycle. During the early G1 phase,  Cyclin D  is produced in response to external signals like growth hormones or mitogens. It binds to  CDK4  and  CDK6,  forming active complexes that start ...
Read more

UNIT 15 – Cell Surface Receptors (Q&A) | MZO-001 MSCZOO | IGNOU

Image
SAQ 1 a) What would happen if there were substances that could bind to Ga subunits just like GTP does, but could not be hydrolysed by the intrinsic GTPase? If substances were present that could bind to the Gα subunits just like GTP does, but could not be hydrolyzed by the intrinsic GTPase activity, it would lead to a persistent activation of the G-protein signaling pathway. This is because the normal process of signal termination in G-protein signaling involves GTP hydrolysis by the intrinsic GTPase activity of the Gα subunit. When GTP is hydrolyzed to GDP, the Gα subunit becomes inactive, effectively terminating the signaling cascade. However, if a substance mimics GTP binding but does not undergo hydrolysis, the Gα subunit would remain in its active GTP-bound form indefinitely. This leads to prolonged activation of downstream signaling pathways, such as the activation of second messengers like cAMP, DAG and IP3, and the continuous activation of effector proteins. Such persistent sig...
Read more

What is the role of cyclins in the cell cycle?

Cyclins are  regulatory proteins  that play a very important role in the regulation of the cell cycle. They are a special group of regulatory proteins that control the proper timing and order of different phases of the cell cycle, such as G1, S, G2 and M phase. Cyclins do not work alone. They bind with specific enzymes called  Cyclin-Dependent Kinases (CDKs)  to form an active  cyclin-CDK complex.  This complex helps in starting and controlling various steps of the cell cycle. The levels of cyclins are not constant. They rise and fall at specific times during the cycle. This timely appearance and disappearance of cyclins ensure that the cell cycle proceeds in a proper sequence. Cyclins Have the Following Roles in the Cell Cycle: 1. Regulation of Phase Transitions: Cyclins regulate the transition of the cell from one phase to another. Each cyclin activates a specific CDK complex that is required for the progression to the next phase. For example,  Cycli...
Read more

UNIT 16 – Cell Death and Renewal (Q&A) | MZO-001 MSCZOO | IGNOU

Image
SAQ i) Match the items in column I with column II: Answer: a) → iv;    b) → iii;    c) → vii;    d) → viii;    e) → vi;    f) → i;    g) → ii;    h) → x;    i) → v;    j) → xi;    k) → ix ii) Fill in the blanks: a) Autophagy includes the formation of three different vesicles including ....................., which circularizes to form ......................, which then fuses with a lysosome to form the ..................... . Answer: phagophore, autophagosome, autolysosome b) Apoptosis can be mediated by two modes or pathways, ....................... or ....................... . Answer: intrinsic, extrinsic c) Pharmacological inhibitors such as ....................... block the lysosomal proton transport and thus autophagy. Answer: Bafilomycin A1 d) ...................... is released from the mitochondria upon MOMP and binds to the adapter protein Apaf1 to form the complex known as ..........
Read more