Smooth Endoplasmic Reticulum (SER)

The smooth endoplasmic reticulum (SER) is a type of endoplasmic reticulum characterized by the absence of ribosomes on its surface, giving it a smooth appearance. It is a network of tubular membranes and vesicles that extends throughout the cytoplasm of eukaryotic cells. The SER plays a crucial role in various cellular processes, particularly in lipid synthesis and metabolism.

Structure of smooth endoplasmic reticulum

Functions of the Smooth Endoplasmic Reticulum

1. Lipid Synthesis:
   • The SER is primarily involved in the synthesis of lipids, including phospholipids and cholesterol, which are essential components of cellular membranes. Phospholipids are critical for forming the lipid bilayer of cell membranes, while cholesterol contributes to membrane fluidity and stability.
2. Steroid Hormone Production:
   • In specialized cells, such as those in the adrenal glands and gonads, the SER is responsible for synthesizing steroid hormones from cholesterol. This includes hormones like cortisol, aldosterone, and sex hormones (estrogen and testosterone) that regulate various physiological processes. 
3. Detoxification:
   • The smooth ER plays a significant role in detoxifying harmful metabolic byproducts and drugs. In liver cells, enzymes within the SER convert these substances into water-soluble compounds that can be easily excreted from the body. 
4. Carbohydrate Metabolism:
   • The SER is involved in carbohydrate metabolism, including the conversion of glycogen to glucose. The enzyme glucose-6-phosphatase, found in the SER, catalyzes this conversion, which is vital for maintaining blood sugar levels. 
5. Calcium Ion Storage:
   • In muscle cells, a specialized form of the SER known as the sarcoplasmic reticulum regulates calcium ion concentrations. It stores calcium ions and releases them during muscle contraction, thereby playing a critical role in muscle function. 

Mechanism of Lipid Synthesis in Smooth Endoplasmic Reticulum

The lipid synthesis process in the smooth endoplasmic reticulum involves several key steps:

1. Fatty Acid Synthesis:
   • Fatty acids are synthesized from acetyl-CoA through a series of enzymatic reactions. These fatty acids can then be further modified or elongated to form various lipid molecules.
2. Phospholipid Synthesis:
   • Phospholipids are synthesized on the cytosolic side of the SER membrane. Enzymes catalyze reactions between fatty acids and water-soluble precursors (e.g., CDP-choline) to produce phospholipids, which are then incorporated into cellular membranes. 
3. Cholesterol Synthesis:
   • Cholesterol is synthesized from acetyl-CoA through a multi-step process involving several intermediates. Enzymes located in the SER facilitate these reactions, ultimately leading to cholesterol production.
4. Transport to Other Organelles:
   • Once synthesized, lipids are transported from the smooth ER to other cellular compartments such as the Golgi apparatus or directly integrated into cellular membranes via vesicular transport mechanisms.
         The smooth endoplasmic reticulum is an essential organelle involved in lipid synthesis and metabolism, detoxification processes, carbohydrate metabolism, and calcium storage. Its functions are critical for maintaining cellular homeostasis and supporting various physiological processes within eukaryotic cells. Understanding the role of SER in lipid synthesis provides insights into how cells manage their lipid content and respond to metabolic demands.

Protein processing

Protein processing refers to the series of modifications that a newly synthesized polypeptide undergoes to become a fully functional protein. This process includes various biochemical transformations, such as folding, post-translational modifications, and proteolytic cleavage. These modifications are essential for the protein to attain its correct structure and function, enabling it to participate effectively in cellular processes.

Mechanism of Protein Processing

Translation:

The initial step involves the translation of messenger RNA (mRNA) into a polypeptide                chain at the ribosome. This process is facilitated by transfer RNA (tRNA) which brings amino acids to the ribosome in accordance with the codons on the mRNA.

 

Folding:

Once synthesized, the polypeptide begins to fold into its three-dimensional structure. This folding is guided by the sequence of amino acids and is crucial for the protein's functionality. Chaperone proteins often assist in this process to prevent misfolding and aggregation.

Post-Translational Modifications (PTMs):

After folding, proteins may undergo various PTMs that can significantly alter their activity, stability, and localization. Common modifications include:

• Glycosylation: Addition of carbohydrate groups, which can affect protein stability and cell signaling.
• Phosphorylation: Addition of phosphate groups, often regulating enzyme activity and signal transduction pathways.
• Acetylation, Methylation, and Ubiquitination: These modifications can influence protein interactions and degradation pathways.

Proteolytic Cleavage:

Many proteins are synthesized as inactive precursors (zymogens) that require cleavage to become active. This proteolysis can occur in various cellular compartments and is crucial for the activation of enzymes and hormones.

Fig. Protein cleavage: Cooper GM. and Sunderland (MA) (2000).

Quality Control:

Cells have mechanisms to ensure that only correctly folded and modified proteins are transported to their functional locations. Misfolded proteins may be targeted for degradation by proteasomes or undergo refolding attempts with the help of chaperones.

Transport:

Finally, processed proteins are transported to their functional sites within or outside the cell. This may involve packaging into vesicles for secretion or delivery to specific organelles.

Protein folding

Protein folding is the process by which a linear polypeptide chain, synthesized from a sequence of amino acids, acquires its functional three-dimensional structure. This structural conformation is essential for the protein's biological activity and is determined primarily by the sequence of amino acids in the polypeptide. The correct folding is crucial as misfolded proteins can lead to loss of function or diseases, such as neurodegenerative disorders associated with amyloid fibrils and prions.

Figure 1: Protein Folding. (Public Domain; Dr. Kjaergaard via Wikipedia)

Mechanism of Protein Folding

The mechanism of protein folding involves several key interactions and stages:

Primary Structure: The sequence of amino acids (the primary structure) dictates how the protein will fold. Each amino acid has unique side chains (R-groups) that influence interactions during folding

Secondary Structure Formation: As the polypeptide chain begins to fold, it forms secondary structures such as alpha-helices and beta-sheets through hydrogen bonding between backbone atoms. These structures contribute to the overall stability and shape of the protein

Tertiary Structure Development: The secondary structures further fold into a three-dimensional shape known as the tertiary structure. This is stabilized by various interactions, including:

Hydrophobic Interactions: Non-polar side chains tend to cluster away from water, driving the folding process.

Hydrogen Bonds: These bonds form between polar side chains and contribute to stability.

Ionic Interactions: Attraction between charged side chains helps maintain structure.

Disulfide Bridges: Covalent bonds between cysteine residues can provide additional stability to the folded protein

Role of Chaperones: In vivo, protein folding is often assisted by molecular chaperones, which help prevent misfolding and aggregation by stabilizing unfolded or partially folded intermediates. For example, Hsp70 chaperones bind to nascent polypeptides during synthesis, while Hsp60 chaperonins provide an isolated environment for proper folding

Folding Pathways: The process typically follows a funnel-like energy landscape where proteins transition from high-energy unfolded states to lower-energy folded states. This pathway includes a fast initial stage leading to a molten globule state followed by a slower transition to the native state

Quality Control Mechanisms: Cells employ various quality control mechanisms to ensure proper protein folding, including proteasomes for degrading misfolded proteins and autophagy pathways for recycling damaged proteins

Protein Glycosylation, Sorting, and Export from the Golgi Apparatus

 Protein glycosylation is a critical post-translational modification that involves the covalent attachment of carbohydrates (glycans) to proteins. This process significantly enhances the diversity of the proteome, as it influences protein folding, stability, and function. Glycosylation can occur in various forms, primarily categorized into N-linked and O-linked glycosylation. N-linked glycosylation typically occurs co-translationally in the endoplasmic reticulum (ER) where glycans are attached to asparagine residues. O-linked glycosylation, on the other hand, involves the attachment of sugars to serine or threonine residues and can occur in multiple cellular compartments including the Golgi apparatus and cytoplasm.

Mechanisms of Glycosylation

Glycosylation is an enzymatic process that involves a series of steps facilitated by specific enzymes known as glycosyltransferases. These enzymes catalyze the transfer of monosaccharides from activated sugar donors to specific acceptor sites on proteins. The complexity of this modification arises from the variety of sugars involved, the potential for branching in glycan structures, and the specific sites at which these modifications occur.

The process is non-templated, relying on cellular compartmentalization to segregate different glycosylation enzymes, particularly in the ER and Golgi apparatus.

Role of the Golgi Apparatus in Protein Sorting and Export

The Golgi apparatus plays a pivotal role in the post-translational modification and sorting of proteins. After initial synthesis and N-glycosylation in the ER, proteins are transported to the Golgi for further processing. Here, they undergo additional modifications, including trimming and further glycan additions, particularly for O-linked glycans.

The Golgi is organized into distinct compartments (cis-, medial-, and trans-Golgi), each responsible for specific modifications and sorting functions.

Sorting Mechanisms

Proteins exiting the Golgi are sorted based on their final destinations—whether they are to be secreted outside the cell, delivered to lysosomes, or integrated into the plasma membrane. This sorting is facilitated by signal sequences within the proteins themselves or by their glycan structures. For example, certain glycan modifications can serve as signals for receptor-mediated endocytosis or for targeting proteins to specific organelles.

O-Linked Glycosylation

 Definition: O-linked glycosylation refers to the attachment of monosaccharides to the hydroxyl group of serine (Ser), threonine (Thr), or tyrosine (Tyr) residues. Unlike N-linked glycosylation, O-linked glycosylation does not have a specific sequence motif guiding its attachment.

Process

Location: O-linked glycosylation occurs primarily in the Golgi apparatus after the protein has been fully translated and folded.

Structure: This type of glycosylation typically involves the sequential addition of individual sugar units, resulting in shorter chains compared to N-linked glycans. O-linked glycans generally do not extend beyond a few residues 

Function: O-linked glycans are involved in various biological processes, including cell signalling, immune response modulation, and protein stability. They can also influence how proteins interact with other molecules.

N-Linked Glycosylation

Definition: N-linked glycosylation involves the attachment of glycans to the nitrogen atom of asparagine (Asn) residues in a specific sequence motif, typically denoted as Asn-X-Ser/Thr, where X can be any amino acid except proline (Pro) or aspartic acid (Asp) 

Process

Location: This process begins in the endoplasmic reticulum (ER) and continues in the Golgi apparatus. The initial glycan structure is assembled as a lipid-linked oligosaccharide (LLO) before being transferred to the protein 

Structure: The glycan typically consists of a core structure that includes a "tree" of 14 sugar residues, which is subsequently trimmed and modified as the protein matures.

Function: N-linked glycans play crucial roles in protein folding, stability, and cellular recognition. They can also act as molecular signals for quality control mechanisms during protein synthesis.

#নামৰূপ মহাবিদ্যালয়ত স্বনিয়োজনৰ কৰ্মশাল সম্পন্ন

ভাৰত চৰকাৰৰ জৈৱ-প্ৰযুক্তি বিভাগৰ আৰ্থিক সাহাৰ্যপ্ৰাপ্ত নামৰূপ মহাবিদ্যালয়ৰ বায়’টেক হাব আৰু উদ্ভিদ বিজ্ঞান বিভাগে  যোৱা ২৪ অক্টোবৰত ২০২৪ ত স্থানীয় উদ্যোগী পুৰুষ-মহিলাসকলক স্বাৱলম্বনৰ দিশে এখোজ আগুৱাই নিয়াৰ উদ্দেশ্যে “From Orchard to Innovation: Hands-on Training for Value Added Produce” শীৰ্ষক এখন কৰ্মশালা আয়োজন কৰে।  এই কৰ্মশালা খনত সমল ব্যক্তি হিচাপে অংশ লয় যোৰহাটৰ ৰজী ফোড প্ৰচেছিং গোটৰ  (Razi’s Food Processing Unit) স্বতাধিকাৰী তথা সফল উদ্যোগী ৰজিয়া ৰহমানে। এই কৰ্মাশালাৰ যোগেদি স্থানীয়ভাৱে উপলবদ্ধ পাচলি, ফল-মূল আদিৰ পৰা কেনেকৈ বজাৰত চাহিদা থকা খাদ্য সামগ্ৰী প্ৰস্তুত কৰি লাভাম্বিত হ’ব পাৰি তাৰ বিস্তৃত প্ৰশিক্ষণ দিয়া হয়। লগতে প্ৰস্তুত কৰা সামগ্ৰীবোৰ কেনেকৈ পেকিং কৰি গ্ৰাহকৰ মাজলৈ উলিয়াই দিব পাৰি, কি দৰে বজাৰৰ মূল্য নিধাৰণ কৰা হয়, কি দৰে অনুজ্ঞা পত্ৰ পাব পাৰি আদি সকলো বিষয় সামৰি কৰ্মশালাখন সম্পন্ন কৰা হয়। লগতে বজাৰ সৰ্ম্পকীয় বহুতো তথ্য দি অংশগ্ৰহণকাৰী সকলক থলুৱাভাৱে উপলব্ধ এই ধৰণৰ কেচাঁ সামগ্ৰীৰ পৰা  ব্যৱসায় কৰিব পৰাকৈ প্ৰশিক্ষণ প্ৰদান কৰা হয়।

এদিনীয়া এই কৰ্মশালাখনৰ সুভাৰম্ভণিত উদ্ধোধনী ভাষণ প্ৰদান কৰি মহাবিদ্যালয়ৰ অধ্যক্ষ ড০ দুৰ্গা প্ৰসাদ গগৈদেৱে প্ৰশিক্ষণ গ্ৰহণ কৰি প্ৰতিগৰাকী অংশগ্ৰহণকাৰীয়ে হাতে কামে লাগি আৰ্থিকভাৱে স্বছল হ’ব পাৰিব বুলি আশা প্ৰকাশ কৰে।

বায়’টেক হাবৰ মুখ্য গৱেষক ড০ জয়ন্ত সোনোৱালে নামৰূপৰ স্থানীয়লোকৰ স্বনিয়োজনৰহেতু আয়োজন কৰা কৰ্মাশালৰ প্ৰতি ৰাইজৰ আগ্ৰহ দেখি উত্সাহিত হোৱা বুলি প্ৰকাশ কৰে। ভৱিষ্যতে কৌশল বিকাশ আৰু স্বাৱলম্বিতাৰহেতু আৰু অধিক স্বনিয়োজনৰ সুবিধা থকা কৰ্মাশাল আয়োজন কৰি স্থানীয় লোকৰ কৌশল বিকাশ কৰাৰ লগতে নামৰূপৰ আগ্ৰহী উদ্যোগী যুৱচামক স্বনিয়োজনৰ বাট দেখুৱাবলৈ আৰু আচনি ল'ব বুলি কয়।  

নামৰূপৰ ৫৭ গৰাকী মহিলা আৰু ৩ গৰাকী  পুৰুষে অংশগ্ৰহণ কৰা কৰ্মশালাখনত কৰে। অংশগ্ৰহণকাৰী লোকসকলে কৰ্মাশালাখনৰ পৰা যথেষ্ট লাভাম্বিত হোৱা বুলি বক্তব্য প্ৰদান কৰে। 

এই কৰ্মশালাখনত উদ্ভিদ বিজ্ঞান বিজ্ঞাগৰ সহকাৰী অধ্যাপিকা কাকলি বৰুৱা, ড০ উৰ্মিকা ফংচপি, পৰীক্ষাগাৰৰ সহায়ক দিগন্ত বুঢ়াগোঁহাই, তৰণ চেতিয়াই বিভিন্ন দিশত সহায়-সহযোগ আগবঢ়াই সাফল্যমণ্ডিত হোৱাত সহায় কৰে।

নামৰূপ মহাবিদ্যালয়ৰ ৰাষ্টীয় কৰ্মশালা

ভাৰত চৰকাৰৰ জৈৱ-প্ৰযুক্তি বিভাগৰ দ্বাৰা আৰ্থিক সাহাৰ্য প্ৰাপ্ত নামৰূপ মহাবিদ্যালয়ৰ বায়'টেক হাবে আভ্যন্তৰিণ গুণগত মান নিৰ্ণায়ক কোষৰ সহযোগত যোৱা ২১ আৰু ২২ অক্টোবৰ ২০২৪ ত মহাবিদ্যালয়, বিশ্ববিদ্যালয়, বিভিন্ন শিক্ষা তথা গৱেষণা প্ৰতিষ্ঠানত কৰ্মৰত শিক্ষক, গৱেষক আৰু ছাত্ৰ-ছাত্ৰীসকলক সাম্প্ৰতিক সমাজৰ সকলো ক্ষেত্ৰতে শিপাই যোৱা কৃত্ৰিম বুদ্ধিমত্ৰাৰ  ধনাত্মক আৰু ঋণাত্মক প্ৰয়োগৰ বিষয়ে পৰিচয় কৰি দিয়াৰ উদ্দেশ্যে AI Tools for Teaching and Research Efficiency শীৰ্ষক অনলাইন যোগে এক ৰাষ্ট্ৰীয়  পৰ্য্যায়ৰ দুদিনীয়া কৰ্মশালা আয়োজন কৰা হয়।  এই কৰ্মশালাত চিকিম মণিপাল বিশ্ববিদ্যালয়ৰ গৱেষক তথা ২০২২-২৩ চনত ষ্টেনফৰ্ড বিশ্ববিদ্যালয়ে তৈয়াৰ কৰা পৃথিৱীৰ শীৰ্ষ ২% বিজ্ঞানীৰ তালিকাভুক্ত বিজ্ঞানী ড০ আকাশ কুমাৰ ভয়ে দুয়োটা দিনতে সমল ব্যক্তি হিচাপে অংশগ্ৰহণ কৰি বৰ্তমান কৃত্ৰিম বুদ্ধিমত্তাই গ্ৰাস কৰি পেলোৱা উচ্চ শিক্ষা আৰু গৱেষণা ক্ষেত্ৰখনত বিভিন্ন কৃত্ৰিমবুদ্ধিমত্তাৰ প্লেটফৰ্মৰ ব্যৱহাৰিক প্ৰয়োগ আৰু ল'বলগীয়া সাবধনতাৰ সৰ্ম্পকে বিভিন্ন দিশ আলোকপাত কৰি এক বিস্তৃত ৰূপত বৰ্ণনা আৰু ব্যৱহাৰ কৰিবলৈ শিকায়। এই কৰ্মশালাই উচ্চ শিক্ষা আৰু গৱেষণাৰ সৈতে জড়িত অংশগ্ৰহণকাৰী শিক্ষক, বিজ্ঞানী আৰু ছাত্ৰ-ছাত্ৰীসকলক শিক্ষা আৰু গৱেষণাৰ দিশত আবাঢ়িযোৱাত এক নতুন পথৰ সন্ধান দিয়ে। 

নামৰূপ মহাবিদ্যালয়ৰ অধ্যক্ষ ড০ দুৰ্গা প্ৰসাদ গগৈ দেৱে উদ্ধোধনী ভাষণ প্ৰদান কৰি অংশগ্ৰহণ কৰা সকলোৱে এই কৰ্মশালাৰ পৰা লাভ কৰা জ্ঞানেৰে উচ্চ শিক্ষাত শিক্ষণ-শিকণ, গৱেষণা আৰু পেশাগত ভালেখিনি দিশত ব্যৱহাৰ কৰিব পৰাকৈ জ্ঞান অৰ্জন কৰি নিজকে সবল ৰূপত আগুৱাই নিব পাৰিব বুলি আশা প্ৰকাশ কৰে। 

মাহিবদ্যালয়ৰ বায়’টেক হাবৰ মূখ্য গৱেষক তথা উদ্ভিদ বিজ্ঞান বিভাগৰ সহকাৰী অধ্যাপক ড০ জয়ন্ত সোনোৱালে এই কৰ্মশালাৰ যোগেদি বৰ্তমান অপৰিচিত হৈ থকা কৃত্ৰমি বুদ্ধিমত্ৰাৰ বিভিন্ন আহিলা আৰু এইবোৰৰ বৈধ প্ৰয়োগেৰে কেনেকৈ শিক্ষা প্ৰদান আৰু গ্ৰহণ প্ৰক্ৰিয়াৰ লগতে গৱেষণাৰ সৈতে জড়িত শিক্ষক, গৱেষক আৰু ছাত্ৰ-ছাত্ৰীসকলক অধিক ফলপ্ৰসু কৰিব পাৰি এই কৰ্মশালাৰ দ্বাৰা তাক সঠিক ৰূপত সমাজৰ মাজলৈ লৈ যোৱাৰ এটা প্ৰয়াস বুলি মন্তব্য কৰে। 

এই কৰ্মশালাত ভাৰতৰ বিভন্ন শিক্ষা আৰু গৱেষণা প্ৰতিষ্ঠানৰ লগত কৰ্মৰত শিক্ষক, গৱেষক, ছাত্ৰ-ছাত্ৰীয়ে অংশ গ্ৰহণ কৰাৰ উপৰিও বাংলাদেশ আৰু পাকিস্তানকে ধৰি মুঠ ২৬১ গৰাকী লোকে অংশগ্ৰহণ কৰে। 

এই কৰ্মশালাখন আয়োজন কৰিবলৈ কাৰিকৰী দিশত সহায় কৰিছিল প্ৰাণী বিজ্ঞান বিভাগৰ মুৰব্বী তথা সহকাৰী অধ্যাপক চাজিদূৰ ৰহমান, কাৰ্যসূচী আত ধৰে উদ্ভিদ বিজ্ঞান বিভাগৰ সহকাৰী অধ্য়াপিকা কাকলি বৰুৱা, অনলাইন প্লেটফৰ্ম নিয়ন্ত্ৰক সমীৰণ ভূঞা আৰু স্বোৱেতা বৰ্ধনে।