Cell Structure and Function PDF

BIO101/FSC111 Cell structure and function  Plasma Membrane The plasma membrane / Cell Membrane or Cytoplasmic Membrane. selectively permeable membrane of the cells composed of a lipid bilayer and proteins. present both in plant and animal cells. Based on the structure of...

BIO101/FSC111 Cell structure and function  Plasma Membrane The plasma membrane / Cell Membrane or Cytoplasmic Membrane. selectively permeable membrane of the cells composed of a lipid bilayer and proteins. present both in plant and animal cells. Based on the structure of the plasma membrane, it is regarded as the fluid mosaic model. According to the fluid mosaic model, the plasma membranes are subcellular structures, made of a lipid bilayer in which the protein molecules are embedded. Functions selectively permeable membrane - permit the entry of selective materials in and out of the cell according to the requirement. In an animal cell, the cell membrane functions by providing shape and protects the inner contents of the cell. Enzymatic proteins Defensive proteins Function: Selective acceleration of Function: Protection against disease chemical reactions Example: Antibodies inactivate and help Example: Digestive enzymes catalyze the destroy viruses and bacteria. hydrolysis of bonds in food molecules. Antibodies Enzyme Virus Bacterium Storage proteins Transport proteins Function: Storage of amino acids Function: Transport of substances Examples: Casein, the protein of milk, is Examples: Hemoglobin, the iron-containing the major source of amino acids for baby protein of vertebrate blood, transports mammals. Plants have storage proteins oxygen from the lungs to other parts of the in their seeds. Ovalbumin is the protein body. Other proteins transport molecules of egg white, used as an amino acid across cell membranes. source for the developing embryo. Transport protein Ovalbumin Amino acids for embryo Cell membrane Hormonal proteins Receptor proteins Function: Coordination of an organism’s Function: Response of cell to chemical activities stimuli Example: Insulin, a hormone secreted by Example: Receptors built into the the pancreas, causes other tissues to membrane of a nerve cell detect signaling take up glucose, thus regulating blood molecules released by other nerve cells. sugar concentration. Receptor protein Insulin Signaling molecules High secreted Normal blood sugar blood sugar Structural proteins Contractile and motor proteins Function: Support Function: Movement Examples: Keratin is the protein of hair, Examples: Motor proteins are responsible horns, feathers, and other skin appendages. for the undulations of cilia and flagella. Insects and spiders use silk fibers to make Actin and myosin proteins are their cocoons and webs, respectively. responsible for the contraction of Collagen and elastin proteins provide a muscles. fibrous framework in animal connective tissues. Actin Myosin Collagen Muscle tissue 30 m Connective tissue 60 m Transport processes  Passive Processes Simple diffusion Facilitated diffusion Osmosis Filtration  Active Processes Active transport Cell Physiology (uniport, symport and antiport) Plasma -Primary active transport membrane -Secondary active transport  Active Processes Cell Bulk (vesicular) transport Physiology Endocytosis (Pinocytosis, phagocytosis and Plasma receptor mediated endocytosis) Exocytosis (and transcytosis) membrane  Cytoplasm Present in bacteria, plant and animal cells. Jelly-like substances, found between the cell membrane and nucleus. Composed mainly of water, organic and inorganic compounds. Essential components of the cell - site for most of the chemical reactions within a cell. Embedded cell organelles control all metabolic activity taking place within the cell. Ribosomes Non membrane-bound and important cytoplasmic organelles found in close association with the endoplasmic reticulum. Composed of ribosomal RNA and ribosomal proteins Prokaryotic ribosome is 70S, eukaryotic ribosome is 80S (S - Svedberg’s Unit) Both 70S and 80S ribosomes are composed of two subunits. Ribosomes are either encompassed within the endoplasmic reticulum or are freely traced in the cell’s cytoplasm. The primary function of the ribosomes includes protein synthesis in all living cells that ensure the survival of the cell. Ribosomes assemble amino acid monomers into polypeptide chains The Endomembrane System Regulates protein traffic and performs metabolic functions in the cell Includes many different structures: Endoplasmic Reticulum (and vesicles) Golgi Apparatus (and vesicles) Lysosomes Vacuoles Endoplasmic Reticulum Function Manufactures membranes and performs many bio- synthesis functions Structure Membrane connected to nuclear envelope & extends throughout cell Accounts for 50% of membranes in eukaryotic cells Types Rough ER= has ribosomes bound to it Smooth ER=does not have ribosomes bound to it Smooth Endoplasmic Reticulum Functions Metabolic processes Synthesis and hydrolysis Enzymes of smooth ER Synthesize lipids, oils, phospholipids, steroids & sex hormones Hydrolysis of glycogen into glucose in liver Detoxify drugs and poisons (in liver) Pumps calcium ions for muscle function Rough Endoplasmic Reticulum Function Produce proteins for export out of cell Protein secreting cells Packaged into transport vesicles for export Membrane Factory Synthesize membrane phospholipids Build new membrane As ER membrane expands, bud off & transfer to other parts of cell that need membranes Synthesize membrane proteins Membrane bound proteins synthesized directly into membrane Processing to make glycoproteins Golgi Apparatus Function: Finishes, sorts & ships cell products Shipping and receiving department Extensive in cells specialized for secretion Golgi Apparatus Structure Flattened membranous sac=cisternae Look like stacks of pita bread 2 sides=2 functions Cis=receives material by fusing with vesicles=“receiving” Trans=buds off vesicles that travel to other sites=“shipping” Golgi Processing During path from cis to trans, products from ER are modified into final form Tags, sorts, & packages materials into transport vesicles Golgi=“Post Office headquarters” Transport vesicles=“Delivery trucks” Delivering packages that have been tagged with their own barcode  Lysosomes Structure Function: Membrane bounded sac of A little “stomach” hydrolytic enzymes and for the cell molecules that digests Lyso-=breaking macromolecules things apart Enzymes & membrane of -some=body lysosomes are Clean up crew of the synthesized by rough ER cell & transferred to the golgi Lysosomes are Golgi-derived vesicles containing digestive enzymes Only in animal cells Cellular digestion Autophagy Lysosomes fuse with food vacuoles Lysosome breakdown cellular organelles Polymers are digested into monomers Pass to cytosol to become nutrients of cell Lysosomal enzymes Lysosomal enzymes work best at pH 5 Organelle creates custom pH Enzymes are very pH sensitive Why evolve digestive enzymes which function at pH different from cytosol Digestive enzymes won’t function well if leak into cytosol=don’t want to digest yourself When things go wrong… What if a lysosome digestive enzyme didn’t function Don’t digest a biomolecule biomolecule collects in lysosomes Lysosomes fill up with undigested material Lysosomes grow larger & larger Eventually disrupt cell & organ function Lysosomal storage diseases are usually fatal Tay-Sachs disease Lipids build up in brain cells Child dies before age 5  Peroxisomes Other oxidative enzyme sacs In both plants and animals Breakdown fatty acids to sugars Easier to transport & use as energy source Detoxify cell Detoxifies alcohol & other poisons Produce perioxide (H2O2) Central Vacuole Functions in plants Storage Vacuoles Stockpiling proteins or inorganic ions - Storage of red/blue Large, water-filled anthocyanins, acids, salts, wastes spaces (cell sap) Can take up over 90% of Depositing metabolic byproducts cell volume Storing pigments Storing defensive compounds Surrounded by against herbivores tonoplast (a single Selective membrane (tonoplast) membrane) Control what comes in and out Maintains turgor pressure —wilting Often largest structure in plant cell Other Types of Vacuoles Food vacuoles formed by phagocytosis Contractile vacuoles Pump excess water out of protist cells  The Endomembrane System: A Review The endomembrane system is a complex and dynamic player in the cell’s compartmental organization  Flow of membrane within the cell Follow pathway of membrane flow Nucleus ER Golgi apparatus Lysosomes (and other packets of materials) Plasma membrane  Nucleus Double-membraned organelle found in all eukaryotic cells. By structure - surrounded by a nuclear envelope. Largest organelle - control centre of the cellular activities and storehouse of the cell’s DNA. It is a porous membrane (like cell membrane) and forms a wall between cytoplasm and nucleus. Within the nucleus (carries essential structure called chromosomes), there are tiny spherical bodies called nucleolus (synthesis of protein and RNA) within it. Chromosomes are thin and thread-like structures which carry another important structure called a genes, which are hereditary units in organisms Controls the characters and functions of cells in our body. The primary function of the nucleus is to monitor cellular activities including metabolism and growth by making use of DNA’s genetic information. Function of Nucleus Store genes on chromosomes Organize genes into chromosomes to allow cell division. Transport regulatory factors & gene products via nuclear pores Produce messages ( messenger Ribonucleic acid or mRNA) that code for proteins Produce ribosomes in the nucleolus Organize the uncoiling of DNA to replicate key genes NUCLEAR ENVELOPE Has two membranes ( unit membrane structure) Enclose a flattened sac, connected at the nuclear pore sites. Outermost membrane is continuous with the rough endoplasmic reticulum (RER) and has ribosomes attached The space between the outer and inner membranes is also continuous with rough endoplasmic reticulum space. The nuclear envelope is enmeshed in a network of filaments (nuclear lamina) for stability.  NUCLEAR LAMINA Consists of "intermediate filaments", 30-100 nm thick. These intermediate filaments are polymers of lamin, ranging from 60-75 Kd A-type lamins are inside, next to nucleoplasm B-type lamins are near the nuclear membrane (inner). They may bind to integral proteins inside that membrane. The lamins may be involved in the functional organization of the nucleus. They may play a role in assembly and disassembly before and after mitosis. Phosphorylation triggers the disassembly of the lamina and causes the nuclear envelope to break up into vesicles. Dephosphorylation reverses this and allows the nucleus to reform  Functions of the parts of the nucleus a.Nuclear envelope (membrane) with pores ▪ Water, ions and ATP can pass through pores ▪ Other materials are regulated by “gatekeeper” proteins in the pores b.Nucleolus ▪ Site of ribosome assembly c.Chromatin ▪ Between nucleolus and envelope ▪ DNA and protein (not in nucleolus!) ▪ Replication and transcription Mitochondria provide energy for cellular functions a.Membrane-bound (two membranes) ▪ Most concentrated in metabolically active cells (i.e. muscles) b.Break down molecules to obtain their energy ▪ Energy stored “short-term” as ATP c. Have their own DNA and ribosomes; self-replicate  Mitochondria Powerhouses of the cell - produce energy-rich molecules for the cell. The mitochondrial genome is inherited maternally in several organisms. It is a double membrane-bound, sausage-shaped organelle, found in almost all eukaryotic cells. The double membranes divide its lumen into two distinct aqueous compartments. Inner compartment is called a ‘matrix’ which is folded into cristae )uter membrane forms a continuous boundary with the cytoplasm. Vary in their size maybe either round or oval in shape. Sites of aerobic respiration in the cell - produces energy in the form of ATP and helps in the transformation of the molecules. Mitochondria have their own circular DNA, RNA molecules, ribosomes (the 70s), and a few other molecules that help in protein synthesis. Plant cells: Have all the organelles previously mentioned, and also…  Plastids Plastids are large, membrane-bound organelles which contain pigments. Based on the type of pigments, plastids are of three types: Chloroplasts Double membrane-bound organelles, which usually vary in their shape – from a disc shape to spherical, discoid, oval and ribbon. Present in mesophyll cells of leaves, which store chloroplasts and other carotenoid pigments. Trap light energy for photosynthesis. Inner membrane encloses a space called the stroma. Flattened disc-like chlorophyll-containing structures known as thylakoids are arranged in a stacked manner like a pile of coins. Each pile is called a granum (plural: grana) and the thylakoids of different grana are connected by flat membranous tubules known as stromal lamella. Just like the mitochondrial matrix, the stroma of chloroplast also contains a double- stranded circular DNA, 70S ribosomes, and enzymes which are required for the synthesis of carbohydrates and proteins. Plastids Contd. Chromoplasts – The chromoplasts include fat-soluble, carotenoid pigments like xanthophylls, carotene, etc. which provide the plants with their characteristic color – yellow, orange, red, etc. Leucoplasts – Leucoplasts are colorless plastids which store nutrients. Amyloplasts store carbohydrates (like starch in potatoes), aleuroplasts store proteins, and elaioplasts store oils and fats. Cell Wall Cell walls in plant cells, prokaryotic cells, fungi 1.Plants ▪ Cell walls of cellulose 2.Fungi ▪ Cell walls of chitin 3.Function: support, protection 4.NOTE: Animal cells do NOT have cell walls!  Cytoskeleton Network of protein fibers to which organelles and even enzymes are attached Cytoskeleton functions 1.Cell shape 2.Organization of cellular structures 3.Cell movement ▪Caused by assembly, disassembly and sliding of the filaments 4.Organelle movement ▪Ex: Endocytosis ▪Movement of membrane from ER to Golgi apparatus, etc… 5.Cell division Cilia and flagella protein microtubule extensions of the plasma membrane 1.Cilia: short and numerous Examples: within oviducts to move eggs, filter-feeding in invertebrates, movement of particles out of respiratory system 2. Flagella: longer and fewer