Cell Structures and Their Functions PDF

Cell Structures and Their Functions __________ Ms. Daisy R. Sucaldito CASE – Biology Department  Topic Learning Outcomes Identify the structure of the cell and its various functions. Explain the important processes that happen inside the cell. Discuss the relati...

Cell Structures and Their Functions __________ Ms. Daisy R. Sucaldito CASE – Biology Department  Topic Learning Outcomes Identify the structure of the cell and its various functions. Explain the important processes that happen inside the cell. Discuss the relationship between cell function and aging.  Cell Structure Organelles Specialized structures in cells that perform specific functions. Example: nucleus, mitochondria, golgi apparatus Cytoplasm A jelly-like substance that holds organelles. Cell membrane Also termed the plasma membrane. A structure that encloses the cytoplasm. Generalized Cell  Functions of the Cell Smallest units of life. Cell metabolism and energy use. Synthesis of molecules. Communication. Reproduction and inheritance.  Cell Membrane The cell membrane is the outermost component of a cell. It forms a boundary between material in inside the cell and the outside. Materials inside the cell are intracellular and those outside are extracellular. It acts as a selective barrier.  Cell Membrane Structure The fluid-mosaic model is the model used to describe the cell membrane structure. The membrane contains phospholipids, cholesterol, proteins, and carbohydrates. Phospholipids form a bilayer. Phospholipids contain 2 regions: polar and nonpolar.  Phospholipid Structure A phospholipid molecule has a polar head region that is hydrophilic and a nonpolar tail region that is hydrophobic. The polar region is exposed to water around the membrane. The nonpolar region is facing the interior of the membrane. The Cell Membrane Movement through the Cell Membrane The cell membrane has selective permeability, which allows only certain substances to pass in and out of the cell. Substances such as enzymes, glycogen, and potassium are found in higher concentrations inside the cell. Substances such as sodium, calcium, and chloride are found in higher concentrations outside the cell.  Cell Membrane Passage Some substances, like O2 and CO2, can pass directly through the cell membrane’s phospholipid bilayer. Some substances must pass through transmembrane protein channels, such as Na+ through its channels. The route of transport through the membrane depends on the size, shape, and charge of the substance.  Cell Membrane Passage Some substances require carrier molecules to transport them across the cell membrane, such as glucose. Some substances require a vesicular transport across the membrane. The vesicle must fuse with the cell membrane for transport. Active Transport and Passive Transport Passive membrane transport does not require the cell to expend energy. Active membrane transport does require the cell to expend energy, usually in the form of ATP. Active Transport and Passive Transport Passive membrane transport mechanisms include diffusion, osmosis, and facilitated diffusion. Active membrane transport mechanisms include active transport, secondary active transport, endocytosis, and exocytosis.  Diffusion Diffusion generally involves movement of substances in a solution down a concentration gradient. A solution is generally composed of two major parts, solutes and the solvent. Solutes are substances dissolved in a predominant liquid or gas, which is called the solvent. Solutes, such as ions or molecules, tend to move from an area of higher concentration of a solute to an area of lower concentration of that same solute in solution. This movement from high concentration to a low concentration is diffusion.  Concentration Gradient A concentration gradient is the difference in the concentration of a solute in a solvent between two points divided by the distance between the two points. The concentration gradient is said to be steeper when the concentration difference is large and/or the distance is small. Diffusion  Leak and Gated Channels Lipid soluble substances can diffuse directly through the phospholipid bilayer. Water-soluble substances, such as ions, can diffuse across the cell membrane only by passing through cell membrane channels. Diffusion through the Cell Membrane  Leak and Gated Channels 2 Two classes of cell membrane channels include leak channels and gated channels. Leak channels constantly allow ions to pass through. Gated channels limit the movement of ions across the membrane by opening and closing. Leak and Gated Membrane Channels  Osmosis Osmosis is the diffusion of water (a solvent) across a selectively permeable membrane from a region of higher water concentration to one of lower water concentration. Osmosis exerts a pressure, termed osmotic pressure, which is the force required to prevent movement of water across cell membrane.  Osmotic Pressure and the Cell Osmotic pressure depends on the difference of solution concentrations inside a cell relative to outside the cell. A cell may be placed in solutions that are either hypotonic, isotonic, or hypertonic compared to the cell cytoplasm.  Hypotonic A hypotonic solution has a lower concentration of solutes and a higher concentration of water relative to the cytoplasm of the cell. Water moves by osmosis into the cell, causing it to swell. If the cell swells enough, it can rupture, a process called lysis.  Isotonic A cell immersed in an isotonic solution has the same solute concentrations inside and outside the cell. The cell will neither shrink nor swell.  Hypertonic The hypertonic solution usually has a higher solute concentration of solutes and a lower concentration of water than the cytoplasm of the cell. Water moves by osmosis from the cell into the hypertonic solution, resulting in cell shrinkage, or crenation. Red Blood Cell Changes in Differing Solutions ©David M. Phillips/Science Source  Carrier-Mediated Transport Some water-soluble, electrically charged or large sized particles cannot enter or leave through the cell membrane by diffusion. These substances include amino acids, glucose, and some polar molecules produced by the cell. Carrier molecules are proteins within the cell membrane involved in carrier-mediated transport.  Carrier-Mediated Transport Carrier-mediated transport mechanisms include facilitated diffusion and active transport. Facilitated diffusion does not require ATP for energy. Active transport does require ATP for transport.  Facilitated Diffusion Facilitated diffusion is a carrier-mediated transport process that moves substances across the cell membrane from an area of higher concentration to an area of lower concentration of that substance. Because movement is with the concentration gradient, metabolic energy in the form of ATP is not required. Facilitated Diffusion  Active Transport Active transport is a carrier-mediated process, requiring ATP, that moves substances across the cell membrane from regions of lower concentration to those of higher concentration against a concentration gradient. A major example of active transport is the action of the sodium-potassium pump present in cell membranes.  Sodium-Potassium Pump The sodium-potassium pump moves Na+ out of cells and K+ into cells. The result is a higher concentration of Na+ outside cells and a higher concentration of K+ inside cells.  Secondary Active Transport Secondary active transport uses the energy provided by a concentration gradient established by the active transport of one substance, such as Na+ to transport other substances. No additional energy is required above the energy provided by the initial active transport pump.  Secondary Active Transport In cotransport, the diffusing substance moves in the same direction as the initial active transported substance. In countertransport, the diffusing substance moves in a direction opposite to that of the initial active transported substance. Secondary Active Transport  Endocytosis Endocytosis is a process that that brings materials into cell using vesicles. Receptor-mediated endocytosis occurs when a specific substance binds to the receptor molecule and is transported into the cell. Phagocytosis is often used for endocytosis when solid particles are ingested. Pinocytosis has much smaller vesicles formed, and they contain liquid rather than solid particles. Receptor-Mediated Endocytosis  Exocytosis Exocytosis involves the use of membrane- bound sacs called secretory vesicles that accumulate materials for release from the cell. The vesicles move to the cell membrane and fuse, ultimately releasing the material by exocytosis. Examples of exocytosis are the secretion of digestive enzymes. Exocytosis (b) ©Dr. Birgit H. Satir  General Cell Structure The interior of a cell is composed of the cytoplasm, which a jelly-like fluid that surrounds the organelles. Organelles are specialized structures that perform certain functions. Organelles include the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria, cytoskeleton, centrioles, cilia, flagella, and microvilli. Generalized Cell Cell Nucleus (b,c) ©Don W. Fawcett/Science Source  Cell Nucleus Usually located near the center of the cell. The nucleus is bounded by a nuclear envelope, which consists of outer and inner membranes. The nuclear membrane contains nuclear pores, through which materials can pass into or out of the nucleus.  Cell Nucleus Within the nucleus are nucleoli, which are diffuse bodies with no surrounding membrane. There are usually one to several nucleoli within the nucleus. The subunits of ribosomes, a type of cytoplasmic organelle, are formed within a nucleolus. These ribosomal components exit the nucleus through nuclear pores.  Cell Nucleus The nuclei of human cells contain 23 pairs of chromosomes which consist of DNA and proteins. During most of a cell’s life, the chromosomes are loosely coiled and collectively called chromatin. When a cell prepares to divide, the chromosomes become tightly coiled and are visible when viewed with a microscope. Chromosome Structure  Ribosomes Ribosome components are produced in the nucleolus. Ribosomes are the organelles where proteins are produced. Ribosomes may be attached to other organelles, such as the endoplasmic reticulum. Ribosomes that are not attached to any other organelle are called free ribosomes. Ribosome Production  Endoplasmic Reticulum The endoplasmic reticulum (ER) is a series of membranes forming sacs and tubules that extends from the outer nuclear membrane into the cytoplasm. The rough ER is involved in protein synthesis and is rough due to attached ribosomes. The smooth ER has no attached ribosomes and is a site for lipid synthesis, cellular detoxification, and it stores calcium ions in skeletal muscle cells. Endoplasmic Reticulum  Golgi Apparatus The Golgi apparatus, also called the Golgi complex, consists of closely packed stacks of curved, membrane-bound sacs. It collects, modifies, packages, and distributes proteins and lipids manufactured by the ER. The Golgi apparatus forms vesicles, some of which are secretory vesicles, lysosomes, and other vesicles. Golgi Apparatus (b) ©Biophoto Associates/Science Source  Lysosomes Lysosomes are membrane-bound vesicles formed from the Golgi apparatus. They contain a variety of enzymes that function as intracellular digestive systems. Vesicles formed by endocytosis may fuse with lysosomes in order to breakdown materials in the endocytotic vesicles. One example is white blood cells phagocytizing bacteria. Lysosome Action  Peroxisomes Peroxisomes are small, membrane-bound vesicles containing enzymes that break down fatty acids, amino acids, and hydrogen peroxide (H2O2). Hydrogen peroxide is a by-product of fatty acid and amino acid breakdown and can be toxic to a cell. The enzymes in peroxisomes break down hydrogen.  Mitochondria Mitochondria (singular mitochondrion) are small organelles responsible for producing considerable amounts of ATP by aerobic (with O2) metabolism. They have inner and outer membranes separated by a space. The outer membranes have a smooth contour, but the inner membranes have numerous folds, called cristae, which project into the interior of the mitochondria.  Mitochondria The material within the inner membrane is the mitochondrial matrix and contains enzymes and mitochondrial DNA (mtDNA). Cells with a large energy requirement have more mitochondria than cells that require less energy. Mitochondrion (b) ©EM Research Services, Newcastle University RF  The Cytoskeleton The cytoskeleton gives internal framework to the cell. It consists of protein structures that support the cell, hold organelles in place, and enable the cell to change shape. These protein structures are microtubules, microfilaments, and intermediate filaments.  Microtubules Microfilaments Intermediate Filaments Microtubules are hollow Microfilaments are small Intermediate filaments are structures formed from fibrils formed from protein fibrils formed from protein protein subunits. subunits that structurally subunits that are smaller in support the cytoplasm, diameter than determining cell shape. microtubules but larger in The microtubules perform diameter than a variety of roles, including microfilaments. helping to support the Microfilaments in muscle cytoplasm of cells, cells enable the cells to assisting in cell division, shorten, or contract. They provide mechanical and forming essential support to the cell. components of certain organelles, such as cilia and flagella. A specific type of intermediate filament is keratin, a protein associated with skin cells. The Cytoskeleton (b) ©Don Fawcett/Science Source  Centrioles The centrosome is a specialized area of cytoplasm close to the nucleus where microtubule formation occurs. It contains two centrioles, which are normally oriented perpendicular to each other. Each centriole is a small, cylindrical organelle composed of microtubules. The centriole is involved in the process of mitosis.  Whole Cell Activity A cell’s characteristics are determined by the type of proteins produced. The proteins produced are in turn determined by the genetic information in the nucleus. Information in DNA provides the cell with a code for its cellular processes.  DNA DNA contains the information that directs protein synthesis; a process called gene expression. A DNA molecule consists of nucleotides joined together to form two nucleotide strands. The two strands are connected and resemble a ladder that is twisted around its long axis. Each consists of a 5-carbon sugar, a phosphate group, and a nitrogenous base.  DNA Each nucleotide on one DNA strand has a specific bonding pattern to another nucleotide on the opposite strand. A gene is a sequence of nucleotides that provides a chemical set of instructions for making a specific protein.  Gene Expression Gene expression, which is protein synthesis, involves transcription and translation. Transcription involves copying DNA into messenger RNA. Translation involves messenger RNA being used to produce a protein.  Transcription Transcription takes place in the nucleus of the cell. DNA (template) determines the structure of mRNA through transcription. During transcription, the double strands of a DNA segment separate, and DNA nucleotides of the gene pair with RNA nucleotides that form the mRNA. www.bing.com  Transcription DNA contains one of the following nucleobases : thymine, adenine, cytosine, or guanine. Messenger RNA (mRNA) contains uracil, adenine, cytosine, or guanine.  Transcription DNA nucleotides pair only with specific RNA nucleotides. DNA’s thymine pairs with RNA’s adenine. DNA’s adenine pairs with RNA’s uracil. DNA’s cytosine pairs with RNA’s guanine DNA’s guanine pairs with RNA’s cytosine. Transcription  Translation Translation occurs in the cell cytoplasm after mRNA has exited the nucleus through the nuclear pores. The mRNA attaches to a ribosome. Codons (3 nucleotide bases which code for specific amino acids) on the mRNA are read by anticodons (3 nucleotide bases) on transfer RNA (tRNA). A series of 3 nucleotides of each tRNA molecule (the anticodon), pairs with the codon of the mRNA.  Translation Transfer RNA transports specific amino acids from the cytoplasm to the ribosome-mRNA complex and initiates formation of the polypeptide chain. The process continues until the entire polypeptide is completely formed. Note: Some codons do not code for amino acids (AA) but perform other functions such as the stop codon. A stop codon codes for no AA, this also acts as a signal for stopping the addition of AA to a protein.  Translation of mRNA in Protein Synthesis Overview of Gene Expression  The Cell Cycle During growth and development, cell division occurs to increase the number of cells or replace damaged or dying ones. This cell division involves a cell cycle. The cell cycle includes two major phases: a nondividing phase, called interphase, and a cell dividing phase, termed mitosis.  The Cell Cycle A cell spends most of its life cycle in interphase performing its normal functions. During interphase, the DNA (located in chromosomes in the cell’s nucleus) is replicated. The two strands of DNA separate from each other, and each strand serves as a template to produce a new strand of DNA.  The Cell Cycle Nucleotides in the DNA of each template strand pair with new nucleotides that are subsequently joined by enzymes to form a new strand of DNA. The sequence of nucleotides in the DNA template determines the sequence of nucleotides in the new strand of DNA. Replication of DNA gives two identical chromatids joined at a centromere; both form one chromosome.  DNA Replication  Cell Genetic Content Each human cell (except for the gamete/sex cells) contains 23 pairs of chromosomes, a total of 46 (diploid). The sperm and egg (gamete/sex cells) contain 23 chromosomes (haploid) total. One pair of chromosomes are the sex chromosomes, which consist of two X chromosomes if the person is a female or an X and Y chromosome if the person is a male.  Mitosis Mitosis involves formation of 2 daughter cells from a single parent cell. Mitosis is divided into four phases: prophase, metaphase, anaphase, and telophase.  Prophase During prophase the chromatin condenses to form visible chromosomes. Microtubules, termed spindle fibers, form to assist in breaking the centromere between the chromatids and move the chromosomes to opposite sides of the cell. The nuclear membrane dissolves.  Metaphase During metaphase, the chromosomes align near the center of the cell. The movement of the chromosomes is regulated by the attached spindle fibers.  Anaphase At the beginning of anaphase, the chromatids separate, and each chromatid is called a chromosome. Each of the two sets of 46 chromosomes is moved by the spindle fibers toward the centriole at one of the poles of the cell. At the end of anaphase, each set of chromosomes has reached an opposite pole of the cell, and the cytoplasm begins to divide.  Telophase During telophase, the chromosomes in each of the daughter cells become organized to form two separate nuclei, one in each newly formed daughter cell. The chromosomes begin to unravel and resemble the genetic material during interphase. Following telophase, cytoplasm division is completed, and two separate daughter cells are produced. The Cell Cycle ©Ed Reschke/Photolibrary/Getty Images  Differentiation A sperm cell and an oocyte unite to form a single cell, then a great number of mitotic divisions occur to give the trillions of cells of the body. The process by which cells develop with specialized structures and functions is called differentiation. During differentiation of a cell, some portions of DNA are active, but others are inactive. Diversity of Cell Types  Apoptosis Apoptosis, termed programmed cell death, is a normal process by which cell numbers within various tissues are adjusted and controlled. In the developing fetus, apoptosis removes extra tissue, such as cells between the developing fingers and toes. In some adult tissues, apoptosis eliminates excess cells to maintain a constant number of cells within the tissue.  Cellular Aspects of Aging There are various causes for cellular aging. Existence of a cellular clock Presence of death genes DNA damage Formation of free radicals Mitochondrial damage  Tumors Tumors are abnormal proliferations of cells. They are due to problems occurring in the cell cycle. Some tumors are benign, and some are malignant (cancer). Malignant tumors can spread by a process, termed metastasis. QUESTIONS? THANK YOU!