Module 1_Cell

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Basic points for better understanding the structure and function.

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The Cell:

The Cell The Building Block of all life

Definition:

Definition The cell is the structural and functional unit of all living organisms. Types of Organisms: Unicellular Organism consisting of a single cell. Multicellular Organism consisting of a huge number of cellsl. P. 1

Unicellular and Multicellular:

Unicellular and Multicellular Multicellular Unicellular P. 2

Anatomy of Cells:

Anatomy of Cells There are two types of cells: Prokaryotic Eukaryotic Pro karyotic Eu karyotic Before Nucleus True Nucleus P. 3

Eukaryotes:

Eukaryotes These cells contains a “Specialized Membrane Bound Nucleus” Nulcues: A membrane-delineated compartment that houses the eukaryotic cell's DNA P. 4

Parts of Eukaryotic Cell:

Parts of Eukaryotic Cell P. 4

The Organelles:

The Organelles The organs of the Cells P. 6

Organelles:

Organelles Organelles “ Compartmentalize or Departmentalize ” functions within the cell. P. 6

Cell Membrane:

Cell Membrane P. 6

Lipid Bilayer:

Lipid Bilayer Sperates the different compartments of the cells.

Proteins:

Proteins Two types of proteins: Peripheral Proteins (Present on side of lipid bilayer) Acting as receptors for durgs, hormones and neurotransmitters etc. Integral Proteins (Passes through the lipid bilayer) Act as channels for passage of various ions, salts and other water soluble materials P. 6

Proteins:

Proteins Integral Protein Peripheral Protein P. 7

Receptor:

Receptor A receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand.

Receptor Binding:

Receptor Binding Ligand binding to a receptor is an equilibrium process. Ligands bind to an empty receptor and they dissociate from it. A measure of how well a certain molecule fits into a given receptor is the binding affinity which is measured as the dissociation constant Kd (good fit means high affinity and a low Kd). The activation of the second messenger cascade and the final biological response is achieved only when at a certain time point a significant number of receptors are activated by bound ligands.

Types:

Types Receptors exist in different types, dependent on their ligand and function: Membrane Receptors Peripheral membrane proteins Transmembrane proteins Transmembrane receptors are embedded in the lipid bilayer of cell membranes, that allow the activation of signal transduction pathways in response to the activation by the binding molecule, or ligand. Intracellular Receptors Such as those for steroid and intracrine peptide hormone receptors. These receptors often can enter the cell nucleus and modulate gene expression in response to the activation by the ligand.

Regulation of Receptors:

Regulation of Receptors Cells can increase (upregulate) or decrease (downregulate) the number of receptors to a given hormone or neurotransmitter to alter its sensitivity to this molecule. This is a locally acting feedback mechanism.

Agonists Vs. Antagonists:

Agonists Vs. Antagonists Not every ligand that binds to a receptor it also activates the receptor. The following classes of ligands exist: Agonists are able to activate the receptor and result in a maximal biological response. Most natural ligands are full agonists Partial agonists are not able to activate the receptor maximally, resulting in a partial biological response compared to a full agonist. Antagonists bind to the receptor but do not activate it. This results in a receptor blockade that inhibits the binding of agonists. Inverse agonists are antagonists that are able to further reduce the receptor activation by decreasing its basal activity.

Genetics:

Genetics Two different kinds of genetic material exist: Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA)

Nucleus:

Nucleus Chromatin : DNA and proteins Nucleolus: Chromatin and ribosomal subunits Nuclear envelope : Double membrane with pores Nucleoplasm : semifluid medium inside the nucleus

PowerPoint Presentation:

The nucleus and the nuclear envelope

Mitochondria:

Mitochondria Mitochondria are found in plant and animal cells. Mitochondria are bounded by a double membrane surrounding fluid-filled matrix. The inner membranes of mitochondria are cristae . The matrix contains enzymes that break down carbohydrates and the cristae house protein complexes that produce ATP.

The endoplasmic reticulum:

The endoplasmic reticulum The endoplasmic reticulum (ER) is a system of membranous channels and saccules. Rough ER is studded with ribosomes and is the site of protein synthesis and processing. Smooth ER lacks ribosomes and is the site of synthesis of phospholipids and the packaging of proteins into vesicles, among other functions.

Endoplasmic Reticulum:

Endoplasmic Reticulum

The Golgi apparatus:

The Golgi apparatus The Golgi apparatus consists of a stack of curved saccules. The Golgi apparatus receives protein and also lipid-filled vesicles from the ER, packages, processes, and distributes them within the cell. This organelle may also be involved in secretion.

Ribosomes:

Ribosomes Protein synthesis occurs at tiny organelles called ribosomes . Ribosomes are composed of a large subunit and a small subunit. Ribosomes can be found alone in the cytoplasm, in groups called polyribosomes , or attached to the endoplasmic reticulum.

Lysosomes and vacuoles:

Lysosomes and vacuoles Lysosomes are vesicles produced by the Golgi apparatus. Lysosomes contain hydrolytic enzymes and are involved in intracellular digestion. Vacuoles (large) and vesicles (small) are membranous sacs in the cell that store substances.

Centrioles:

Centrioles Centrioles are short cylinders with a 9 + 0 pattern of microtubule triplets. Centrioles may be involved in microtubule formation and disassembly during cell division and in the organization of cilia and flagella.

Prokaryotic Cells:

Prokaryotic Cells Prokaryotic cells include the bacteria: Bacterial cells have these constant features: Outer Boundary : Cell wall Plasma membrane Cytoplasm : Ribosomes Thylakoids (Cyanobacteria) Innumerable enzymes Nucleoid : Chromosome (DNA only)

The Cellular Physiology:

The Cellular Physiology The works that cells perform

Metabolism:

Metabolism Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions: Catabolism , in which the cell breaks down complex molecules to produce energy and reducing power. Anabolism , in which the cell uses energy and reducing power to construct complex molecules and perform other biological functions.

Metabolism Contd.:

Metabolism Contd. Complex sugars are broken down into a less chemically-complex sugar molecule called glucose. Once inside the cell, glucose is broken down to make adenosine triphosphate (ATP) Glycolysis , requires no oxygen and is referred to as anaerobic metabolism. Each reaction is designed to produce some hydrogen ions that can then be used to make energy packets Adenosine Triphosphate (ATP). In prokaryotes, glycolysis is the only method used for converting energy. Krebs cycle , or citric acid cycle, occurs inside the mitochondria and is capable of generating enough ATP to run all the cell functions. Electron Transport Chain

Glycolysis:

Glycolysis The word glycolysis is derived from Greek γλυκύς (sweet) and λύσις (rupture). It is the initial process of most carbohydrate catabolism , and it serves three principal functions: The generation of high-energy molecules (ATP and NADH) as cellular energy sources as part of anaerobic and aerobic respiration. This process in the cell can have oxygen present and sometimes may not. Production of pyruvate for the citric acid cycle as part of aerobic respiration. The production of a variety of six- and three-carbon intermediate compounds, which may be removed at various steps in the process for other cellular purposes.

Glycolysis:

Glycolysis

Citric Acid Cycle:

Citric Acid Cycle The citric acid cycle oxidizes the acetyl-CoA to carbon dioxide, and, in the process, produces reduced cofactors (three molecules of NADH and one molecule of FADH 2 ) that are a source of electrons for the electron transport chain , and a molecule of GTP (that is readily converted to an ATP).

Citric Acid Cycle:

Citric Acid Cycle

Electron Transport Chain:

Electron Transport Chain Oxygen Utilization Energy Production

Cell Division:

Cell Division Cell division involves a single cell (called a mother cell ) dividing into two daughter cells . Prokaryotic cells divide by binary fission . Eukaryotic cells usually undergo a process of nuclear division, called mitosis , followed by division of the cell, called cytokinesis . A diploid cel l may also undergo meiosis to produce haploid cells, usually four. Haploid cells serve as gametes in multicellular organisms, fusing to form new diploid cells. DNA replication , or the process of duplicating a cell's genome, is required every time a cell divides. Replication, like all cellular activities, requires specialized proteins for carrying out the job.

Cell Division:

Cell Division Protein synthesis generally consists of two major steps: Transcription Translation Transcription is the process where genetic information in DNA is used to produce a complementary RNA strand. mRNA molecules bind to protein-RNA complexes called ribosomes located in the cytosol, Where they are translated into polypeptide sequences. The ribosome mediates the formation of a polypeptide sequence based on the mRNA sequence. The mRNA sequence directly relates to the polypeptide sequence by binding to transfer RNA (tRNA) adapter molecules in binding pockets within the ribosome. The new polypeptide then folds into a functional three-dimensional protein molecule.

Protein Synthesis:

Protein Synthesis This process involves the formation of new protein molecules from amino acid building blocks based on information encoded in DNA/RNA. Protein synthesis generally consists of two major steps: Transcription Translation

Tissue:

Tissue Biological tissue is a collection of interconnected cells that perform a similar function within an organism. The study of tissue is known as histology, or, in connection with disease, histopathology.

Tissue:

Tissue Collection of Cells

Types:

Types There are four basic types of tissue in the body of all animals, including the human body and lower multicellular organisms such as insects. These compose all the organs, structures and other contents: Epithelium Connective tissue Muscle tissue Nervous tissue

Cell Junctions:

Cell Junctions A cell junction is a structure within a tissue of a multicellular organism. Cell junctions are especially abundant in epithelial tissues. They consist of protein complexes and provide contact between neighbouring cells, between a cell and the extracellular matrix, or they built up the paracellular barrier of epithelia and control the paracellular transport.

Types:

Types Adherens junctions and Desmosomes Gap junctions Tight junctions

Functions:

Functions They perform three vital functions: They hold cells together They block the movement of integral membrane proteins between the apical and basolateral surfaces of the cell, allowing the specialized functions of each surface (for example receptor-mediated endocytosis at the apical surface and exocytosis at the basolateral surface) to be preserved. This aims to preserve the transcellular transport. They prevent the passage of molecules and ions through the space between cells . So materials must actually enter the cells (by diffusion or active transport) in order to pass through the tissue. This pathway provides control over what substances are allowed through. (Tight junctions play this role in maintaining the blood-brain barrier.)

End of Module 1:

End of Module 1 The Cell

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