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Semester 1: Cytology, Genetics and Infectious Diseases
Structure and Function of Cell Organelles I: Plasma membrane, cell-cell interaction, endomembrane system
Structure and Function of Cell Organelles
Plasma Membrane
The plasma membrane is a selectively permeable barrier that surrounds the cell, composed of a phospholipid bilayer with embedded proteins. It regulates the entry and exit of substances, facilitating communication and signaling between cells. The fluid mosaic model describes the dynamic arrangement of lipids and proteins in this membrane.
Cell-Cell Interaction
Cell-cell interactions are crucial for maintaining tissue structure and function. These interactions are mediated by various cell adhesion molecules, such as cadherins and integrins. They play roles in processes like signaling, immune responses, and developmental biology. Gap junctions enable direct communication between adjacent cells.
Endomembrane System
The endomembrane system consists of several membrane-bound organelles including the endoplasmic reticulum (ER), Golgi apparatus, lysosomes, and vesicles. The rough ER is involved in protein synthesis, while the smooth ER is involved in lipid synthesis and detoxification. The Golgi apparatus modifies, sorts, and packages proteins for secretion or delivery to other organelles. Lysosomes contain enzymes for breaking down waste materials and cellular debris.
Structure and Function of Cell Organelles II: Cytoskeleton, mitochondria, peroxisome and ribosome
Structure and Function of Cell Organelles II: Cytoskeleton, Mitochondria, Peroxisome and Ribosome
Cytoskeleton
The cytoskeleton is a complex network of fibers that provides structural support to the cell. It is primarily composed of three types of filaments: microfilaments, intermediate filaments, and microtubules. Microfilaments, made of actin, are involved in cell movement and shape. Intermediate filaments provide mechanical support and stability. Microtubules, made of tubulin, are essential for cell division, intracellular transport, and maintaining cell shape.
Mitochondria
Mitochondria are known as the powerhouses of the cell, generating adenosine triphosphate (ATP) through oxidative phosphorylation. Each mitochondrion has a double membrane; the inner membrane is folded into cristae to increase surface area for ATP production. Mitochondria also play a role in regulating apoptosis and serve as sites for metabolic pathways, such as the citric acid cycle.
Peroxisome
Peroxisomes are small, membrane-bound organelles that contain enzymes for oxidative reactions. They play a key role in lipid metabolism, including the breakdown of fatty acids via beta-oxidation. Peroxisomes also detoxify harmful substances, including hydrogen peroxide, using the enzyme catalase. They are important for maintaining cellular health and metabolism.
Ribosome
Ribosomes are the molecular machines responsible for protein synthesis. They can be found freely floating in the cytoplasm or attached to the endoplasmic reticulum, forming rough ER. Ribosomes consist of ribosomal RNA and proteins, and they translate messenger RNA into polypeptide chains. Their function is critical for cellular functions and growth.
Nucleus and Chromatin Structure: nucleus, DNA and RNA structure, chromatin organization, chromosomes
Nucleus and Chromatin Structure
Nucleus
The nucleus is a membrane-bound organelle found in eukaryotic cells. It contains the cell's genetic material and is surrounded by a double membrane called the nuclear envelope. The nuclear envelope contains pores that regulate the passage of substances in and out of the nucleus. Inside, the nucleoplasm contains chromatin and nucleolus, the latter being involved in ribosomal RNA synthesis.
DNA Structure
DNA, or deoxyribonucleic acid, is composed of two strands forming a double helix. Each strand consists of nucleotides, which include a phosphate group, a sugar (deoxyribose), and a nitrogenous base (adenine, thymine, cytosine, guanine). The complementary base pairing (A-T and C-G) enables the formation of the helical structure and the stability of genetic information.
RNA Structure
RNA, or ribonucleic acid, is typically single-stranded and consists of nucleotides that include a phosphate group, a sugar (ribose), and one of four nitrogenous bases (adenine, uracil, cytosine, guanine). RNA plays crucial roles in various biological processes, including protein synthesis, as messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA).
Chromatin Organization
Chromatin is DNA wrapped around histone proteins, forming a complex that helps to package DNA into a compact structure. There are two types: euchromatin, which is loosely packed and transcriptionally active, and heterochromatin, which is tightly packed and transcriptionally inactive. Chromatin structure changes during the cell cycle, affecting gene expression.
Chromosomes
Chromosomes are structures that become visible during cell division, formed from condensed chromatin. Humans typically have 46 chromosomes, organized into 23 pairs. Each chromosome contains many genes, which are segments of DNA that code for proteins. The arrangement and number of chromosomes are critical for genetic stability and inheritance.
Cell cycle, Cell Division and Cell Signalling: mitosis, meiosis, cell cycle regulation, apoptosis, signal transduction
Cell Cycle, Cell Division and Cell Signalling
Cell Cycle
The cell cycle is a series of phases that cells undergo to grow and divide. It consists of interphase (G1, S, G2) and the mitotic phase (M). During interphase, the cell grows and duplicates its DNA, while in the mitotic phase, the cell divides into two daughter cells.
Mitosis
Mitosis is a form of cell division that produces two genetically identical daughter cells. It has several stages: prophase, metaphase, anaphase, and telophase. Mitosis is important for growth, repair, and asexual reproduction.
Meiosis
Meiosis is a specialized type of cell division that occurs in the formation of gametes. It consists of two rounds of division (meiosis I and meiosis II) resulting in four non-identical daughter cells, each with half the chromosome number of the parent cell. This process introduces genetic diversity through recombination and independent assortment.
Cell Cycle Regulation
The cell cycle is tightly regulated by various checkpoints and proteins, including cyclins and cyclin-dependent kinases (CDKs). These mechanisms ensure that the cell only proceeds to the next phase when it is ready, preventing uncontrolled cell division.
Apoptosis
Apoptosis is a programmed cell death process that eliminates damaged or unneeded cells. It plays a crucial role in development and homeostasis, and its dysregulation can lead to diseases such as cancer.
Signal Transduction
Signal transduction refers to the process by which cells respond to external signals. This involves receptor activation, signal relay through pathways, and subsequent cellular responses such as division, differentiation, or apoptosis. It is essential for communication and coordination within and between cells.
Mendelism and Sex Determination: Mendel's laws, dominance types, sex determination, sex-linked characteristics
Mendelism and Sex Determination
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Each individual has two alleles for each gene, which segregate during gamete formation, ensuring each gamete carries only one allele.
Alleles of different genes assort independently of one another during gamete formation, leading to genetic variation.
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In a heterozygote, the dominant allele completely masks the effect of the recessive allele.
The phenotype of heterozygotes is intermediate between those of the two homozygotes.
Both alleles in a heterozygote are fully expressed, resulting in a phenotype that displays characteristics of both.
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In many animals, including humans, sex is determined by the presence of X and Y chromosomes; females typically have two X chromosomes and males have one X and one Y.
In some insects, such as grasshoppers, the presence of a single X chromosome determines male sex; females are XX and males are X0.
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Traits that are associated with genes located on sex chromosomes, specifically the X chromosome in many organisms.
Color blindness and hemophilia are examples of sex-linked inherited disorders found mainly in males due to the presence of one X chromosome.
Extensions of Mendelism, Genes and Environment: Multiple alleles, gene interaction, genomic imprinting, gene-environment interaction
Extensions of Mendelism, Genes and Environment
Multiple Alleles
Multiple alleles refer to the presence of more than two alleles at a locus in a population. This situation leads to a greater variety of phenotypes compared to simple dominance and recessive traits. An example is the ABO blood group system in humans, which is determined by three alleles: I^A, I^B, and i. The expression of these alleles results in four possible blood types: A, B, AB, and O.
Gene Interaction
Gene interaction occurs when two or more genes influence the same trait and their alleles interact. This can result in various phenotypes due to epistasis, where one gene can mask or modify the effect of another gene. An example is the color inheritance in sweet peas, where two genes interact to produce a range of flower colors.
Genomic Imprinting
Genomic imprinting is an epigenetic phenomenon where certain genes are expressed in a parent-of-origin-specific manner. This means that only one allele of a gene is active, while the allele from the other parent is inactive. Disorders such as Prader-Willi syndrome and Angelman syndrome are examples of conditions that arise from abnormalities in genomic imprinting.
Gene-Environment Interaction
Gene-environment interaction occurs when the effect of a gene on a phenotype is influenced by the environment. This means that the same genotype can lead to different phenotypes based on environmental factors. An example is the impact of diet on the expression of genes related to obesity and metabolic disorders.
Human Chromosomes and Patterns of Inheritance: human karyotype, chromosomal anomalies, pedigree analysis, inheritance patterns
Human Chromosomes and Patterns of Inheritance
Human Karyotype
The human karyotype consists of 23 pairs of chromosomes, totaling 46. Of these, 22 pairs are autosomes and 1 pair is sex chromosomes (XX or XY). Karyotyping involves the visualization of the chromosome structure, number, and arrangement, aiding in the diagnosis of genetic disorders.
Chromosomal Anomalies
Chromosomal anomalies are variations from the normal karyotype that can lead to genetic disorders. They include numerical abnormalities, like aneuploidy (e.g., Down syndrome, caused by an extra chromosome 21), and structural abnormalities, such as deletions, duplications, inversions, and translocations.
Pedigree Analysis
Pedigree analysis is a method of tracking inheritance patterns across generations through family trees. Symbols are used to represent individuals and their relationships. This analysis helps identify carriers, affected individuals, and the mode of inheritance (autosomal dominant, autosomal recessive, X-linked, etc.) of genetic traits.
Inheritance Patterns
Inheritance patterns explain how traits and disorders are passed down through generations. Common patterns include: 1. Autosomal Dominant: Requires only one copy of the mutated gene for phenotypic expression. 2. Autosomal Recessive: Requires two copies of the mutated gene. 3. X-linked Dominant/Recessive: Linked to sex chromosomes, affecting males and females differently.
Infectious Diseases: pathogenic organisms, parasites like Trypanosoma, Giardia, Wuchereria and related diseases
Infectious Diseases: Pathogenic Organisms and Parasites
Introduction to Infectious Diseases
Infectious diseases are caused by pathogenic organisms such as bacteria, viruses, fungi, and parasites. Understanding the biology and life cycle of these organisms is crucial for effective prevention and treatment.
Pathogenic Organisms
Pathogenic organisms are capable of causing disease in hosts. The mechanisms of infection, including entry, colonization, and production of toxins, play a critical role in the pathogenesis of infectious diseases.
Trypanosoma and Related Diseases
Trypanosoma is a genus of parasitic protozoa that causes diseases such as African sleeping sickness and Chagas disease. These diseases are transmitted by tsetse flies and triatomine bugs, respectively.
Giardia and Its Impact on Human Health
Giardia is a protozoan parasite that causes giardiasis, an intestinal infection leading to diarrhea and malabsorption. Transmission occurs via contaminated water and food.
Wuchereria and Lymphatic Filariasis
Wuchereria bancrofti is a filarial worm responsible for lymphatic filariasis, leading to conditions such as elephantiasis. It is transmitted by mosquitoes.
Prevention and Control Measures
Preventive measures for infectious diseases include sanitation, vaccination, and vector control. Awareness and education play a significant role in reducing transmission.
Current Research and Developments
Research on vaccines, medications, and genetic studies of pathogens is ongoing. Innovations aim to improve diagnosis, treatment, and prevention of infectious diseases.
