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SAQ 1 Fill in the blanks   a) ............. discovered plasma membrane. Answer: Karl Nageli and C. Cramer b) The phospholipid contains .................. charged phosphate group in the hydrophilic part of head. Answer: Negatively c) ................... proposed Sandwich (lipid-protein) model of cell membrane. Answer: Danielli and Davson d) The protein layer present in cell membrane model proposed by Robertson is .................. thick. Answer: 20 A° e) The proteins are aligned properly with the help of ....................... within the lipid bilayer in membrane. Answer: Transmembrane segments SAQ 2 i) Answer in one word: a) Complex integral proteins transmit signals via plasma membrane. Answer: Receptors b) The cellular processes such as movement, growth, division etc. are regulated by this property of membrane. Answer: Fluidity c) No energy is required for transter of substances from high concentration zone to low concentration zone in this proces. Answer: Passive d) Cer...

SAQ 1 i) The resting membrane potential is created due to: a) Buildup of the negative ions in the cytosol along the inside of the membrane. b) The separation of positive and negative electrical charges along both sides of the plasma membrane. c) Difference in charge across the membrane of the cell. d) All of the above. Answer: d) All of the above ii) Which of the following factor/s contribute to the resting membrane potential of the cell? a) Unequal distribution of ions in the ECF and cytosol b) Activity of Na⁺/K⁺ ATPases c) Most anions cannot leave the cell d) all of the above Answer: d) All of the above iii) The extracellular fluid (ECF) has high concentration of positively charged sodium ions and negatively charge chloride ions. a) True b) False Answer: a) True iv) Intracellular fluid (ECF) in contact with the cell membrane is positively charged with high concentration of potassium ions, phosphate ions and anionic proteins. a) True b) False Answer: a) True v) Usually, sodium ion...

SAQ 1  Fill in the blanks:  a) The fibrous and rope-like structures refer to .................... . Answers:  Intermediate filaments b) A protein that provides the mechanical strength and integrity to skin and hair is called ..................... . Answers:   Keratin  c) How many types of polypeptides are present in intermediate filaments? Intermediate filaments (IFs) are a key component of the cytoskeleton in eukaryotic cells, providing essential structural support and maintaining the shape and stability of cells. These filaments are composed of polypeptides, which are long chains of amino acids that fold into a functional structure. The polypeptides in intermediate filaments polymerize to form filamentous structures that help to anchor organelles, support cell shape and provide mechanical strength. Each type of intermediate filament is made from a specific group of polypeptides that are tissue-specific and vary in their amino acid composition and function. Th...

Actin and myosin are two primary filamentous proteins that play a direct and central role in muscle contraction. These proteins are located inside the sarcomere, which is the basic contractile unit of striated muscle fibers. Their interaction is responsible for producing the force and movement necessary for muscle contraction, based on the  Sliding Filament Theory  proposed independently by Huxley and Niedergerke, and Huxley and Hanson in 1954. Role of Actin Actin forms the  thin filaments  of the sarcomere. It is a polymer of globular actin (G-actin), which forms a helical structure called  filamentous actin (F-actin).  Each actin filament contains binding sites for the heads of myosin. These sites are normally blocked by a regulatory protein called  tropomyosin,  which is held in place by a calcium-sensitive complex known as  troponin.  When a nerve impulse stimulates the muscle, calcium ions are released from the sarcoplasmic reticulu...

The targeting of soluble lysosomal proteins, such as hydrolytic enzymes, to endosomes and lysosomes is a well-organised and highly regulated process. This mechanism ensures that such enzymes reach the lysosomes accurately, where they are needed for intracellular digestion, and are not secreted outside the cell. This entire process takes place through a series of interconnected steps, involving specific molecular signals, vesicle formation and organelle targeting, which begins in the rough endoplasmic reticulum (RER) and ends in the lysosome. Step 1: Synthesis in the Rough Endoplasmic Reticulum (RER) Soluble lysosomal enzymes are synthesised by ribosomes attached to the rough ER. As the mRNA is translated, the growing polypeptide is inserted into the ER lumen. Inside the ER, these proteins are properly folded and undergo N-linked glycosylation, which prepares them for further modifications in the Golgi. Step 2: Transfer to the Golgi Apparatus From the ER, the glycosylated proteins are t...

The fluid mosaic model is one of the most widely accepted and foundational concepts that explains the structural organization of the plasma membrane in living cells. It was first proposed by  S.J. Singer and Garth L. Nicolson in 1972  and remains relevant today, though slightly refined with modern findings. Before we move into the components and structure, it is important to understand that this model helps explain how the membrane remains flexible, selectively permeable, and functionally active for processes like transport, cell signaling and communication. Basic Concept of the Fluid Mosaic Model According to the fluid mosaic model, the plasma membrane is viewed as a dynamic, semi-fluid bilayer of lipids with proteins embedded in it, much like boats floating in a sea. The word  "fluid"  refers to the lateral movement of lipids and some proteins within the membrane, while  "mosaic"  refers to the patchwork arrangement of various proteins that float freely o...

The cortical cytoskeleton is a specialized and dynamic part of the cell's cytoskeleton located just beneath the plasma membrane. It is primarily composed of  actin filaments  (microfilaments) along with associated proteins like spectrin, ankyrin, filamin and ERM (ezrin, radixin, moesin) proteins. This region forms a dense network of filamentous proteins that help maintain the cell's shape, provide mechanical support and regulate interactions with the external environment. The cortical cytoskeleton plays a key role in cellular processes like endocytosis, cell motility, signal transduction and adhesion, especially in animal cells. Structure of the Cortical Cytoskeleton The main structural element of the cortical cytoskeleton is  F-actin,  which forms a thin, mesh-like layer closely attached to the inner surface of the plasma membrane. This layer is cross-linked by actin-binding proteins such as filamin and is anchored to membrane proteins via adaptor proteins like spec...

SAQ Fill in the blanks:  a) The basic unit of microtubules is …………… . Answer: α β tubulin heterodimers b) α tubulin occurs at ............. end, and β tubulin is at .............. of microtubules. Answer: plus, minus c) GTP-GTP tubulin cap stabilises and promotes the .................. . Answer: polymerisation of microtubules d) The plus end-directed motor protein of microtubules is …………. . Answer: kinesin e) The hydrolysis of GTP from β-tubulin causes …………. of microtubules. Answer: Depolymerisation f) The cellular function of γ-tubulins is. ………..... . Answer: nucleate the growth of MTs  g) Colchicine binds to ………… . Answer: free tubulin SAQ 2 a) Classify the microtubules involved in mitosis. Microtubules play a central role during mitosis by forming the mitotic spindle, which ensures the correct segregation of chromosomes into daughter cells. These microtubules are dynamically reorganized during cell division and can be classified into three main types, based on their...

When GABA is inhibited in the brain, it leads to a neurological condition called  epilepsy.  This happens because GABA normally controls brain activity by stopping too much nerve signalling. When GABA is not working properly, the brain loses its balance and nerve cells start becoming overactive. This overactivity can lead to  seizures,  which is the main feature of  epilepsy. Seizures  are sudden, uncontrolled electrical disturbances in the brain that can cause changes in behavior, movements, feelings, or consciousness. They may last from a few seconds to minutes and can be caused by epilepsy, fever, head injury, or other neurological conditions. Seizures vary in type and severity. Step-by-Step Explanation: How GABA Inhibition Leads to Epilepsy To understand how epilepsy is caused by inhibiting GABA, we can break the process into simple steps. These steps explain what GABA normally does, what changes happen when it is blocked and how those changes result in...

The brain is not only the central organ of the nervous system but also contains two major secretory glands that are directly involved in endocrine functions. These are: Pituitary gland (Hypophysis) Pineal gland (Epiphysis cerebri) These glands are part of the neuroendocrine system, which links the brain and hormonal regulation. They help in maintaining homeostasis, regulating growth, metabolism, stress response, sleep cycle, reproduction and many other vital processes. 1. Pituitary Gland: The Master Gland The pituitary gland is called the  "master gland"  because it controls the activity of almost all other endocrine glands in the body. It is located at the base of the brain, in a bony cavity called the sella turcica of the sphenoid bone. It is connected to the  hypothalamus  by a stalk called the  infundibulum,  which carries signals from the brain to control hormone secretion. The pituitary gland has two main lobes: i. Anterior Pituitary (Adenohypophysis)...