Learn Unit 3: Cell Structure and Function with Free Lessons & Tips

Here is a list of proteins commonly used as therapeutic agents, along with their applications:

1. Insulin: Used for the treatment of diabetes mellitus to regulate blood sugar levels.

2. Interferons: Used to treat viral infections such as hepatitis and certain cancers by boosting the immune system's response.

3. Growth Hormone (GH): Used to treat growth disorders in children and adults with growth hormone deficiency.

4. Erythropoietin (EPO): Used to stimulate red blood cell production and treat anemia, particularly in patients with chronic kidney disease.

5. Tissue Plasminogen Activator (tPA): Used as a thrombolytic agent to dissolve blood clots in conditions such as myocardial infarction (heart attack) and ischemic stroke.

6. Monoclonal Antibodies (e.g., Rituximab, Trastuzumab): Used in cancer therapy to target specific cancer cells or proteins and stimulate the immune system's response against tumors.

7. Enzyme Replacement Therapies (e.g., Alglucosidase alfa, Lysosomal enzymes): Used to replace deficient or defective enzymes in patients with enzyme deficiencies, such as lysosomal storage disorders.

8. Factor VIII and Factor IX: Used for the treatment of hemophilia A and hemophilia B, respectively, to replace missing clotting factors in patients with bleeding disorders.

9. Granulocyte Colony-Stimulating Factor (G-CSF): Used to stimulate the production of white blood cells and enhance immune function, particularly in patients undergoing chemotherapy or bone marrow transplantation.

10. Thrombopoietin Receptor Agonists (e.g., Romiplostim, Eltrombopag): Used to stimulate platelet production and treat thrombocytopenia (low platelet count) in patients with certain blood disorders.

Other applications of proteins include:

• Enzymes: Used in various industrial processes such as food production, pharmaceutical manufacturing, and bioremediation.

• Diagnostic Proteins: Used in diagnostic tests to detect specific biomarkers or diseases, such as pregnancy tests, enzyme-linked immunosorbent assays (ELISAs), and rapid diagnostic tests for infectious diseases.

• Biological Research: Proteins are essential tools in biological research for studying protein-protein interactions, signal transduction pathways, and gene expression regulation.

• Biotechnology: Proteins are used in the production of biopharmaceuticals, recombinant vaccines, and genetically modified crops.

• Food Industry: Proteins are used as food additives, flavor enhancers, and nutritional supplements in the food industry.

• Cosmetics: Proteins are used in skincare products, hair treatments, and cosmetics for their moisturizing, anti-aging, and conditioning properties.

These examples illustrate the diverse applications of proteins in medicine, industry, research, and everyday life.

Certainly! Triacylglycerols, also known as triglycerides, are the most common type of fat found in both animal and plant tissues. They serve as a major energy storage molecule in organisms and play essential roles in metabolism and insulation. Triacylglycerols are composed of three fatty acid molecules esterified to a glycerol molecule, resulting in the formation of a triglyceride molecule. Let's break down the composition of triglycerides:

1. Glycerol (Glycerin): Glycerol, also known as glycerin, is a three-carbon alcohol molecule. It serves as the backbone of the triglyceride molecule. Glycerol contains three hydroxyl (-OH) groups, one attached to each carbon atom. These hydroxyl groups react with the carboxyl groups of fatty acids to form ester bonds, resulting in the attachment of the fatty acid chains to the glycerol molecule.

2. Fatty Acids: Fatty acids are long hydrocarbon chains with a carboxyl group (-COOH) at one end. Each triglyceride molecule contains three fatty acid molecules, one esterified to each hydroxyl group of the glycerol backbone. The fatty acid chains can vary in length and degree of saturation, influencing the physical properties of the triglyceride. Common fatty acids found in triglycerides include saturated fatty acids (e.g., palmitic acid, stearic acid) and unsaturated fatty acids (e.g., oleic acid, linoleic acid).

3. Ester Bonds: The fatty acid molecules are covalently bonded to the glycerol molecule through ester linkages. During esterification, the hydroxyl (-OH) group of glycerol reacts with the carboxyl (-COOH) group of a fatty acid, resulting in the formation of an ester bond (-COO-) and the release of a water molecule (dehydration synthesis). This process occurs three times, one for each fatty acid, leading to the formation of a triglyceride molecule.

The composition of triglycerides can vary widely depending on the types of fatty acids esterified to the glycerol backbone. The specific combination of fatty acids determines the physical properties of the triglyceride, such as its melting point, viscosity, and nutritional characteristics. Triglycerides are stored in adipose tissue as energy reserves and are broken down into glycerol and fatty acids during metabolism to release energy for cellular processes.

(a) Synapsis: Synapsis is a process that occurs during prophase I of meiosis, specifically during the zygotene stage. It involves the pairing of homologous chromosomes, forming structures known as bivalents or tetrads. Synapsis is facilitated by the formation of a protein structure called the synaptonemal complex, which holds the homologous chromosomes together along their lengths. This pairing allows for the exchange of genetic material between homologous chromosomes during crossing over, which contributes to genetic diversity among offspring.

(b) Bivalent: A bivalent, also known as a tetrad, is a structure formed during meiosis when two homologous chromosomes come together and pair up during synapsis. Each bivalent consists of four chromatids, with two chromatids from each homologous chromosome. The paired homologous chromosomes are aligned side by side, and the chromatids are closely associated along their lengths. Bivalents are essential for the proper segregation of homologous chromosomes during meiosis and play a key role in promoting genetic diversity through crossing over.

(c) Chiasmata: Chiasmata are cross-shaped structures that form at points of genetic recombination between homologous chromosomes during prophase I of meiosis. As homologous chromosomes undergo synapsis and crossing over, segments of genetic material are exchanged between chromatids, resulting in the formation of chiasmata. Chiasmata represent physical manifestations of genetic recombination, where segments of DNA are swapped between non-sister chromatids of homologous chromosomes. These exchanges of genetic material contribute to genetic diversity by producing novel combinations of alleles on the chromatids, which are then inherited by the offspring. Chiasmata are visible under a microscope and can be observed as physical connections between homologous chromosomes during late prophase I and metaphase I of meiosis.

Cytokinesis is the process of cytoplasmic division that occurs after nuclear division (mitosis or meiosis) in the cell cycle. While the overall goal of cytokinesis is the same in both plant and animal cells, there are significant differences in how it is carried out due to the structural differences between plant and animal cells:

1. Cell Plate Formation vs. Cleavage Furrow:

   • In plant cells, cytokinesis involves the formation of a cell plate, which is a structure composed of vesicles derived from the Golgi apparatus. These vesicles fuse at the equatorial plane of the dividing cell, forming a new cell wall between the two daughter cells. The cell plate gradually expands outward until it fuses with the existing plasma membrane, separating the daughter cells.
   • In contrast, animal cells undergo cytokinesis through the formation of a cleavage furrow. During this process, a contractile ring composed of actin filaments forms just beneath the plasma membrane at the equatorial plane of the dividing cell. The contractile ring contracts, pinching the cell membrane inward and eventually dividing the cell into two daughter cells.

2. Cell Wall vs. Cell Membrane:

   • Plant cells are surrounded by a rigid cell wall composed primarily of cellulose, hemicellulose, and other polysaccharides. During cytokinesis, the cell plate is deposited within the plane of the cell wall and eventually fuses with it, forming a new cell wall between the daughter cells.
   • Animal cells lack a cell wall but are instead surrounded by a flexible plasma membrane. As the cleavage furrow contracts, it pinches the plasma membrane inward until it completely separates the cytoplasm of the parent cell, resulting in the formation of two separate daughter cells.

3. Vesicle Fusion vs. Actomyosin Contraction:

   • Plant cytokinesis relies on the fusion of Golgi-derived vesicles to form the cell plate. These vesicles contain cell wall precursors such as cellulose synthase enzymes and polysaccharides, which are deposited to form the new cell wall.
   • Animal cytokinesis involves the contraction of the contractile ring, which is composed of actin filaments and myosin motor proteins. The contractile ring generates tension on the plasma membrane, leading to its invagination and eventual cleavage.

In summary, while both plant and animal cells undergo cytokinesis to divide into two daughter cells, the process differs significantly due to the presence of a cell wall in plant cells, which requires the formation of a cell plate, and the absence of a cell wall in animal cells, which allows for the formation of a cleavage furrow through actomyosin contraction.

In meiosis, the division of the cell's genetic material results in the formation of four daughter cells called gametes. These daughter cells can vary in size depending on various factors. Here are examples where the four daughter cells from meiosis are either equal or unequal in size:

1. Equal Size:

   • Microsporogenesis in Plants: In the process of microsporogenesis, which occurs in the anthers of flowering plants, diploid microsporocyte cells undergo meiosis to produce four haploid microspores. These microspores are typically equal in size and develop into pollen grains, which are important for plant reproduction.

2. Unequal Size:

   • Oogenesis in Animals: In oogenesis, which occurs in the ovaries of female animals, diploid oogonium cells undergo meiosis to produce four daughter cells, but only one of these cells becomes a functional egg (ovum), while the other three become smaller polar bodies. The ovum receives most of the cytoplasm and organelles, making it larger than the polar bodies. This asymmetry in size ensures that the developing embryo receives sufficient nutrients and cellular machinery for early development.

   • Spermatogenesis in Animals: In spermatogenesis, which occurs in the testes of male animals, diploid spermatogonium cells undergo meiosis to produce four haploid spermatids. While spermatids initially have equal sizes, during the maturation process called spermiogenesis, one of the spermatids develops into a mature sperm cell (spermatozoon), which is much smaller than the other three residual bodies. These residual bodies are eventually reabsorbed by the body or expelled. Thus, although the initial daughter cells may be equal in size, the end products of spermatogenesis are unequal in size.