Plant Cell Structure and Function PDF

Plant Cell :Structure and Function PLANT CELL Importance: ◦ defines the boundary of the cell ◦ controls the passage of materials into and out of the cell ◦ govern the interaction of the cell with other cells fluid mosaic model ◦ two layered phospholipid membrane (phospholipid bilayer) w...

Plant Cell :Structure and Function PLANT CELL Importance: ◦ defines the boundary of the cell ◦ controls the passage of materials into and out of the cell ◦ govern the interaction of the cell with other cells fluid mosaic model ◦ two layered phospholipid membrane (phospholipid bilayer) with anchored proteins  A. Membrane Lipids B. Membrane Proteins Phospholipids ◦ constitute 75% of the membrane lipids; ◦ occur as two layers (phospholipid bilayer) ◦ Composition: 🞄Head - glycerol and phosphate unit 🞄hydrophilic; faces the fluid part of the cell 🞄Tail - two fatty acid chains 🞄hydrophobic; oriented away from the fluid environment Cholesterol – constitute 20% of the membrane lipids - it gives fluidity to the cell membrane Glycolipids - constitute 5% of the membrane lipids - 2 fatty acids + short carbohydrate chains Two kinds: a. Integral proteins –pass all the way through the cell membrane b. Peripheral proteins –adhere to the surface of the cell membrane 🞄 glycoproteins  proteins + short carbohydrate chains Receptors ◦ bind to chemical messengers such as hormones ◦ binding to receptor results to a physiological change in the cell ◦ important for cell communication Enzymes –act as catalyst for chemical reaction to take place  Anchor proteins - physically link intracellular structures with extracellular structures Transport proteins ◦ 3 kinds: 🞄Channel proteins –allow the passage of water and solutes to enter or exit the cell 🞄Carrier proteins 🞄 transport substances into and out of the cell 🞄the membrane protein changes shape in transporting substances 🞄Protein pumps 🞄 transport substances against its concentration gradient  (protein pumps) (Channel/carrier proteins) Functions of membrane proteins: Integral protein Fluidity of membranes ◦ permits movement of membrane pieces ◦ allow for vesicle formation and fusion ◦ important for 🞄1. transport of materials by: 🞄exocytosis – release materials to the outside (secretion) 🞄endocytosis – materials are taken inside the cell 🞄phagocytosis – solid substances 🞄pinocytosis – liquid substances ◦ 2. compartmentalization 🞄Each compartment is specialized for a particular process producing a particular substance 🞄 Ex. Cellular organelles Permeability of the membrane ◦ Selectively permeable 🞄hydrophobic substances, smaller molecules (ex. water) – may diffuse easily through the phospholipid bilayer 🞄large hydrophilic substances (ex. amino acid, glucose) and ions - pass through membrane proteins by facilitated diffusion or active transport Protoplasm - all substance inside the cell membrane except the vacuole - includes the nucleus and the cytoplasm the part between the cell membrane, nucleus, and or the vacuole ◦ divided into two components: 🞄Cytosol 🞄fluid portion containing water and dissolved solutes and suspended particles 🞄Organelles 🞄subcellular structure each having a characteristic shape and specific function in cellular growth, maintenance and reproduction Membranous organelles ◦ surrounded by one or two bilayer lipid membrane ◦ includes the endomembrane system 🞄 set of membranes that form a single functional unit, either being connected directly, or exchanging material through vesicle transport. 🞄 works together to modify, package, and transport lipids and proteins. Nonmembranous organelles ◦ lack membranes and directly in contact with the cytosol Endomembrane Nucleus System Endoplasmic Reticulum Golgi apparatus (Dictyosomes) Microbodies Central vacuole Mitochondria Plastids Spherical structure with double layered membrane ◦ Outer membrane continuous with the rough endoplasmic reticulum ◦ with nuclear pores for the passage of substances between the nucleus and the cytoplasm ◦ contain the following: 🞄Nucleoli(us) - involved in the synthesis and assembly of ribosomes 🞄Chromatin – tightly coiled DNA and histone proteins 🞄Nucleoplasm - fluid substance containing water, enzymes, RNA - Extensive membranous network continuous with the nuclear membrane Two kinds: 🞄Rough ER 🞄with ribosomes 🞄synthesize proteins for secretions 🞄Smooth ER 🞄lacks ribosomes 🞄synthesize membrane lipids Consist of flattened membrane sacs which receive protein from ER or lipids from SER ◦ Form vesicles that process, sort and package proteins/lipids for transport to different parts of the cell (vacuole, lysosome, etc) or for secretion ◦ Parts: 🞄 cis face - “entry" side of dictyosome 🞄 trans face - “exit" side of dictyosome Formation of cell plate ◦ Fused vesicles at the equator during telophase ◦ Cell plate forms the middle lamella after cytokinesis Secretion of carbohydrates in nectaries, cell wall material and mucilages spherical shaped organelle surrounded by a single membrane contain enzymes that participate in the biochemical reactions in the cell ◦Glyoxysomes Involved in converting stored fats into 🞄 sugars 🞄Important during germination of fat-rich, oily seeds 🞄 ex. peanut, sunflower and coconut contain enzymes that degrade fatty acids and amino acids detoxify harmful substances in the cell ◦ ex. Hydrogen peroxide (H2O2) H2O2 catalase H2O + Oxygen Compose of a single membrane called tonoplast functions : ◦ Digestive - break down of macromolecules ◦ Storage - ions, sugars, amino acids, toxic waste ◦ Maintain cell turgidity - high ionic concentration generates high water potential ◦ Cell growth – as it expands, it forces the cell to grow rapidly Site of aerobic cell respiration ◦ C6H12O6 + O2 - - > CO2 + H2O+ Energy (ATP) the process that breaks down organic compounds in the presence of oxygen to yield energy (as ATP) - Energy is used for synthesis of new compounds or for cell metabolism  with DNA and ribosomes distinct from those of the cell o Capable of reproduction Smooth outer membrane ◦ give shape and rigidity ◦ freely permeable Inner membrane ◦ arranged into folds called crista(e) ◦ site of energy generation (ATP) during cell respiration ◦ selectively permeable ◦ with abundance of enzymes for ATP production 🞄Matrix - fluid inner portion of the mitochondria 3 4 5 6 7 8 associated with pigments and storage products with outer and inner membrane with distinct ribosomes and circular DNA ◦ Capable of reproduction Types: 1. Proplastid 5. Leucoplast: 2. Chloroplast - Amyloplast 3. Etioplast - Proteinoplast 4. Chromoplast - Elaioplast Proplastids ◦ small undifferentiated plastids ◦ in young developing cells ◦ may develop into chloroplast when exposed to light Chloroplast ◦ site of photosynthesis 🞄conversion of solar energy to chemical energy in the form sugars sunlight ◦ CO2 + H2O ----------> C6H12O6 + O2 Outer membrane Inner membrane Thylakoid is a third internal membrane system 🞄contain membrane-bound photosynthetic pigments (chlorophyll molecules) 🞄site of light reaction of photosynthesis (the conversion of light energy to ATP) 🞄site of O2 generation in photosynthesis Stroma - fluid portion of chloroplast 🞄site of CO2 fixation of photosynthesis (Calvin cycle) 🞄site of sugar synthesis (carbon metabolism) Chromoplast ◦ store pigments (ex. carotennoids) found in flowers and fruits ◦ lipids are present as droplets (plastoglobuli) ◦ transformed from chloroplast during fruit ripening or leaf senescence Etioplasts - chloroplasts that have not been exposed to light - plants grown in the dark for several days, cause the chloroplasts to convert to etioplasts - stimulation of chlorophyll synthesis by the hormone cytokinin soon after exposure to light converts etioplast to chloroplasts Kinds: ◦ Amyloplast 🞄for long term storage of starch 🞄in plant tissues that do not photosynthesize (roots, bark and wood) 🞄layers of starch are deposited around the hilum 🞄 may transform into chloroplast in the presence of light Statoliths ◦ Special type of amyloplast in root cap and nodes of shoots ◦ Involved in sensing gravity Elaioplast ◦ store large amounts of oil Proteinoplast (aleuroplast) ◦ store proteins ◦ forms the aleurone layer in the seed  Ribosome Cytoskeleton consist of RNA and proteins important for protein synthesis with two structural parts: ◦ large subunit and small subunit Two forms: Free ribosomes - free in the cytosol Bound ribosomes - attached to endoplasmic reticulum network of different kinds of protein filaments that extend throughout the cytosol ◦ maintains cell shape and provide support ◦ anchors organelles & enzymes to specific regions of the cell ◦ contractility and movement (amoeboid movement) ◦ intracellular transport – provide tracks for vesicle and organelle movement microfilaments ◦ thinnest protein filaments; compose of protein actin ◦ Important for cytoplasmic streaming (cyclosis) intermediate filaments ◦ thicker than microfilaments but thinner than microtubules ◦ help anchor organelles and counter mechanical stress microtubules ◦ largest of the cytoskeleton ◦ compose of tubulin proteins ◦ participate in the migration of chromosomes during cell division ◦ forms the flagella for cell movement Cytoplasmic streaming (cyclosis) - moving currents of cytoplasm - facilitate the transport of nutrients, enzymes, and other substances between the cell and its surroundings, and within the cell itself Compose of cellulose, hemicellulose, pectin substances, lignin and proteins (structural or enzymatic) Three layers: 1. Middle lamella/intercellular layer - consist primarily of pectin - cement like substance that bind individual cells to form tissues 2. Primary cell wall - first true cell wall - Compose of cellulose bound by hemicellulose - develops on newly formed cells 3. Secondary cell wall - formed on the inner surface of the primary wall - much thicker - impregnated with lignin – increase strength, waterproof, resistant to pathogens - develop in mature functional cells Plasmodesmata - channels through cell walls that connects the cytoplasms of adjacent cells