Cell Structure and Function

Cells Smallest living unit (plants and animals are composed of cells) Most are microscopic

Discovery of Cells Robert Hooke (mid-1600s) –Observed sliver of cork –Saw “row of empty boxes” –Coined the term cell

Cell theory (1839)Theodor Schwann & Matthias Schleiden “ all living things are made of cells” (50 yrs. Later) Louis Pasteur “all cells come from cells”

Principles of Cell Theory All living things are made of cells The smallest living unit of structure and function of all organisms is the cell Cells carry out the functions needed to support life. All cells arise from preexisting cells (this principle discarded the idea of spontaneous generation)

Why study cells? Cells  Tissues  Organs  Bodies –bodies are made up of cells –cells do all the work of life!

The Work of Life What jobs do cells have to do for an organism to live… –“breathe” gas exchange: O 2 in vs. CO 2 out –eat take in & digest food –make energy ATP –build molecules proteins, carbohydrates, fats, nucleic acids –remove wastes –control internal conditions homeostasis –respond to external environment –build more cells growth, repair, reproduction & development ATP

Cells provide structure and form to the body. They appear in a variety of shapes; round, concave, rectangular, tapered, spherical, and other. Cell shape seems to be related to specialized function.

Cell Size (Varies)

Cells are: Unit of Function: Each cell is a living unit. A cell performs many metabolic functions to sustain life. Each cell is a biochemical factory using food molecules for energy; repair of tissues, growth and ultimately reproduction.

Unit of Growth: Each living organism begins as a single cell. Some organisms such as a protist, remain unicellular. For a multicellular organism, as the number of cells increases in the body of a plant or animal, so too does its size.

Unit of heredity: New cells only arise from preexisting cells. A cell grows to optimum size and then divides, producing either two cells identical to itself OR four cells not identical. Cells carry hereditary information from one generation to the next. This information is coded in molecules of DNA (deoxyribonucleic acid).

Characteristics of All Cells Have a surrounding membrane Cytoplasm – cell contents in thick fluid Organelles – structures for cell function Control center with DNA

Cell Types Prokaryotic Eukaryotic

Two Types of Cells Prokaryotes First cells to evolve No nucleus Hereditary info is contained within cytoplasm Ex. Bacteria Eukaryotes Evolved from Prokaryotes Have a nucleus Hereditary Info is contained within the nucleus Ex. Plants, Animals, Fungi

Prokaryotic Cells First cell type on earth Cell type of Bacteria and Archaea

Prokaryotic Cells No membrane bound nucleus Nucleoid = region of DNA concentration Organelles not bound by membranes

Bacterium Shapes

Eukaryotic Cells Nucleus bound by membrane Include fungi, protists, plant, and animal cells Possess many organelles Protozoan

Representative Animal Cell

Representative Plant Cell

Organelles Cellular machinery

Cell Walls Found in plants, fungi, & many protists Surrounds plasma membrane Made of cellulose Is rigid Provides support and protection for the cell

Cell Wall Differences Plants – mostly cellulose Fungi – contain chitin

Cell membrane Surrounds all cells In a plant cell, it lies beneath the cell wall – In animal cells, it is the outer boundary (made of cholesterol) Lipid bilayer with embedded proteins Provides cell with – Protection Isolates the cell’s contents from external environment Regulates the flow of materials into and out of the cell (i.e. selectively permeable ) Allows interaction among cells Support

Cytoplasm Viscous fluid containing organelles components of cytoplasm –Interconnected filaments & fibers –Fluid = cytosol Found in both plant and animal cells Located beneath cell membrane Supports and protects cell organelles

Organelles Functional components within cytoplasm

Nucleus Function –control center of cell –protects DNA instructions for building proteins Structure –nuclear membrane –nucleolus ribosome factory –chromosomes DNA

Hereditary material Chromosomes

Nucleic Acid Deoxyribonucleic acid (DNA) has two functions: DNA controls protein synthesis in the cell DNA is replicated and passed on to progeny cells during reproduction

Nucleolus Most cells have 2 or more Directs synthesis of RNA Forms ribosomes

Endoplasmic Reticulum Helps move substances within cells Network of interconnected tubes Two types –Rough endoplasmic reticulum –Smooth endoplasmic reticulum

Rough Endoplasmic Reticulum Ribosomes attached to surface –Manufacture proteins –Not all ribosomes attached to rough ER

Smooth Endoplasmic Reticulum No attached ribosomes Has enzymes that help build molecules –Carbohydrates –Lipids

Endo-membrane System

transport vesicles vesicles carrying proteins Golgi Apparatus Function –finishes, sorts, labels & ships proteins like UPS headquarters –shipping & receiving department –ships proteins in vesicles “UPS trucks” Structure –membrane sacs

Lysosomes Found only in animal cells Contain digestive enzymes Functions –Aid in cell renewal –Break down old cell parts –Digests invaders

Lysosome

Peroxisome Similar to lysosome Membrane-bound vesicle that contains enzymes Enzymes are used to breakdown toxic substances to hydrogen peroxide Hydrogen peroxide is broken down by catalase to produce water and oxygen

Vacuoles Membrane bound storage sacs More common in plants than animals Contents –Water –Food –wastes

Mitochondria Have their own DNA Bound by double membrane Has inner foldings (Cristae) that increase the internal surface area

Mitochondria Break down fuel molecules ( cellular respiration) –Glucose –Fatty acids Release energy –ATP

Mitochondria Function –make ATP energy from cellular respiration sugar + O 2  ATP fuels the work of life in both animal & plant cells ATP

Plants make energy two ways! Mitochondria –make energy from sugar + O 2 cellular respiration sugar + O 2  ATP Chloroplasts –make energy + sugar from sunlight photosynthesis sunlight + CO 2  ATP & sugar –ATP = active energy –sugar = stored energy »build leaves & roots & fruit out of the sugars ATP sugar ATP

Chloroplasts Solar energy capturing organelle

Photosynthesis Takes place in the chloroplast Makes cellular food – glucose

Mitochondria are in both cells!! animal cells plant cells mitochondria chloroplast

Cells need workers = proteins! Making proteins –to run daily life & growth, the cell must… read genes (DNA) build proteins –structural proteins (muscle fibers, hair, skin, claws) –enzymes (speed up chemical reactions) –signals (hormones) & receptors –organelles that do this work… nucleus ribosomes endoplasmic reticulum (ER) Golgi apparatus

DNA RNA ribosomes endoplasmic reticulum vesicle Golgi apparatus vesicle protein on its way! protein finished protein Making Proteins TO: nucleus

Cells need to make more cells! Making more cells –to replace, repair & grow, the cell must… copy their DNA make extra organelles divide the new DNA & new organelles between 2 new “daughter” cells –organelles that do this work… nucleus centrioles

Centrioles Function –help coordinate cell division only in animal cells Structure –one pair in each cell

Cell Summary Cells have 3 main jobs –make energy need food + O 2 cellular respiration & photosynthesis need to remove wastes –make proteins need instructions from DNA need to chain together amino acids & “finish” & “ship” the protein –make more cells need to copy DNA & divide it up to daughter cells Our organelles do all those jobs!

Plasma Membrane Contains cell contents Double layer of phospholipids & proteins

Phospholipids Polar –Hydrophylic head –Hydrophobic tail Interacts with water

Movement Across the Plasma Membrane A few molecules move freely –Water, Carbon dioxide, Ammonia, Oxygen Carrier proteins transport some molecules –Proteins embedded in lipid bilayer –Fluid mosaic model – describes fluid nature of a lipid bilayer with proteins

Molecule Movement & Cells Passive Transport Active Transport Endocytosis ( phagocytosis & pinocytosis) Exocytosis

Passive Transport No energy required Move due to gradient –differences in concentration, pressure, charge Move to equalize gradient –High moves toward low

Types of Passive Transport 1. Diffusion 2. Osmosis 3. Facilitated diffusion

Diffusion Molecules move to equalize concentration

Osmosis Special form of diffusion Fluid flows from lower solute concentration Often involves movement of water –Into cell –Out of cell

Solution Differences & Cells solvent + solute = solution Hypotonic –Solutes in cell more than outside –Outside solvent will flow into cell Isotonic –Solutes equal inside & out of cell Hypertonic –Solutes greater outside cell –Fluid will flow out of cell

Facilitated Diffusion Differentially permeable membrane Channels (are specific) help molecule or ions enter or leave the cell Channels usually are transport proteins (aquaporins facilitate the movement of water) No energy is used

Process of Facilitated Transport Protein binds with molecule Shape of protein changes Molecule moves across membrane

Active Transport Molecular movement Requires energy (against gradient) Example is sodium-potassium pump

Endocytosis Movement of large material –Particles –Organisms –Large molecules Movement is into cells Types of endocytosis – bulk-phase (nonspecific) – receptor-mediated (specific)

Process of Endocytosis Plasma membrane surrounds material Edges of membrane meet Membranes fuse to form vesicle

Forms of Endocytosis Phagocytosis – cell eating Pinocytosis – cell drinking

Exocytosis Reverse of endocytosis Cell discharges material

Exocytosis Vesicle moves to cell surface Membrane of vesicle fuses Materials expelled

Membrane Proteins 1. Channels or transporters –Move molecules in one direction 2. Receptors –Recognize certain chemicals

Membrane Proteins 3. Glycoproteins –Identify cell type 4. Enzymes –Catalyze production of substances

Review of Eukaryotic Cells