Structure and Function of Cells 3 Structure and Function of Cells 1

Structure and Function of Cells OBJECTIVES Define the cell doctrine Relate cell structure to function List and describe a cell’s internal structure/function of organelles Describe plasma membrane Discuss how to transport material across the membrane Explain how cells use and transform matter and energy

Cell Doctrine All living things are composed of cells A single cell is the smallest unit that exhibits all of the characteristics of life All cells come only from preexisting cells

Cells Are Classified According to Their Internal Organization Prokaryotic Cells Plasma membrane No nucleus Cytoplasm: fluid within membrane No true organelles Eukaryotic Cells Plasma membrane Nucleus: membrane bound information center Cytoplasm: fluid within membrane Organelles: membrane bound structures with specialized functions All human cells are eukaryotic

A eukaryotic animal cell has a nucleus and numerous small Figure 3.1 Plasma membrane Cell wall Cytoplasm Organelles Nucleus A eukaryotic animal cell has a nucleus and numerous small organelles. The cytoplasm is enclosed by a flexible plasma membrane. Prokaryotic cells such as this bacterium have a rigid cell wall surrounding the plasma membrane. The genetic material is not surrounded by a membrane, and there are no organelles in the cell. The elongated bacterium in the center of the photo is about to divide in two, as its genetic material is concentrated at both ends of the cell. Figure 3.1 Eukaryotes versus prokaryotes. 5

Cell Structure Reflects Cell Function Figure 3.2 A portion of several muscle cells of the heart Nerve cells of the central nervous system – carry signals over distances Cell Structure Reflects Cell Function Figure 3.2 Human cells vary in shape. Red blood cells Cells lining a tubule of a kidney 6

Small cells have a higher surface to volume ratio Figure 3.3 Small cells have a higher surface to volume ratio High surface to volume ratio promotes efficiency in Acquisition of nutrients Disposal of wastes One large cell. Eight small cells. Cell with microvilli on one surface. Figure 3.3 Cell size and plasma membrane shape affect surface area and volume. Cells Remain Small to Stay Efficient 7

Plasma Membrane A semi-permeable lipid bilayer Phospholipids: has polar head and nonpolar tail Cholesterol: increases membrane strength Proteins: various function (e.g. transport, receptor) Carbohydrates: recognition Plasma membrabe is very important in cell homeostasis!!! Hydrophilic one layer of lipids Hydrophobic Hydrophilic one layer of lipids http://www.youtube.com/watch?v=Qqsf_UJcfBc

Extracellular environment Figure 3.5 Extracellular environment Carbohydrate groups Receptor protein Channel protein (always open) Gated channel Protein (closed position) Figure 3.5 The plasma membrane. Lipid bilayer Glycoprotein Phospholipid Transport protein Cytoskeleton filaments Cytoplasm Cholesterol 9

Molecules Cross the Plasma Membrane in Several Ways Passive transport—does not need energy Diffusion Osmosis Active transport—must use energy Transport in bulk Involves membranous vesicles to move larger substances Endocytosis Exocytosis

Passive Transport: Principles of Diffusion and Osmosis Passive transport: transports a substance without using energy Diffusion: movement of molecules from: High concentration  Low concentration “Down” the gradient Osmosis: the diffusion of water across a selectively permeable membrane Water moves from an area of low solute concentration to an area of high solute concentration

https://www.youtube.com/watch?v=prfMUwjobo8 Diffusion through Figure 3.8 Higher concentration Lower concentration Diffusion through the lipid layer. Lipid-soluble molecules such as O2 and CO2 diffuse freely through the plasma membrane. Diffusion through channels. Some polar and charged molecules diffuse through protein Channels. Water is a typical example. Facilitated transport. Certain molecules bind to a protein, triggering a change in protein shape that transports the molecule across the membrane. Glucose typically enters cells by this method. Figure 3.8 The three forms of passive transport. https://www.youtube.com/watch?v=prfMUwjobo8 12

Active Transport Requires Energy Active transport moves substances from an area of lower concentration to an area of higher concentration Transported substance moves against the concentration gradient Requires ATP as energy Example: sodium-potassium pump expels 3 Na+ ions imports 2 K+ ions uses ATP http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

Endocytosis and Exocytosis Move Materials in Bulk Used to move larger molecules Endocytosis: brings substances into the cell As substance enters, it is surrounded by a membrane forming a membrane-bound vesicle Exocytosis: expels substances from the cell Substance is contained within a membranous vesicle, which then fuses with the membrane, releasing the substance to the external environment

Endocytosis. In endocytosis, material is surrounded Figure 3.10 Extracellular environment Plasma membrane Cytoplasm Vesicle Endocytosis. In endocytosis, material is surrounded by the cell membrane and brought into the cell. Figure 3.10 Endocytosis and exocytosis. Exocytosis. In exocytosis, a membranous vesicle fuses with the plasma membrane, expelling its contents outside the cell. Photomicrograph showing various stages of endocytosis. 15

Tonicity Affects Cell Volume Tonicity: comparison of the concentration of solutes in two different fluids or environments Q: What happens to the cell in each case?

Nucleus Mitochondrion Lysosome Cytosol Peroxisome Centrioles Figure 3.14 Cytosol Semifluid gel material inside the cell Nucleus Information center for the cell. Contains DNA Peroxisome Destroys cellular toxic waste Centrioles Microtubular structures involved in cell division Cytoskeleton Structural framework of the cell Smooth endoplasmic reticulum Primary site of macro- molecule synthesis other than proteins Rough endoplasmic reticulum Primary site of protein synthesis by ribosomes Golgi apparatus Refines, packages, and ships macromolecular products Figure 3.14 A typical animal cell. Secretory vesicle Membrane-bound shipping container Ribosomes Site of protein synthesis Mitochondrion Produces energy for the cell Plasma membrane Controls movement of materials into and out of cell Lysosome Digests damaged organelles and cellular debris 17

The Nucleus Controls the Cell Function: Contains the genetic information of the cell Controls all of the activities of the cell Structural features: Double-layered nuclear membrane Nuclear pores Chromosomes/chromatin Nucleolus

Endoplasmic Reticulum (ER) Highly folded membranous network Two types of endoplasmic reticulum (ER) Rough ER Has ribosomes on surface- Protein manufacturing Smooth ER No ribosomes on surface- Lipid synthesis, including the synthesis of some hormones Rough ER Smooth ER

Ribosomes- site of protein synthesis Free: floating in cytoplasm These ribosomes synthesize proteins for use in the cell Bound: attached to endoplasmic reticulum These ribosomes synthesize proteins that will be exported from the cell

Golgi Apparatus: Refines, Packages, and Ships Protiens are modified & packaged into vesicles and shipped to other locations

Vesicles Peroxisomes Lysosomes Contain enzymes that detoxify wastes produced by the cell Lysosomes Contain digestive enzymes

Mitochondria Provide Energy “Power plant” of the cell Surrounded by a double membrane Site of cellular respiration Utilizes O2 Generates ATP

Fat and Glycogen: Sources of Energy Fat cells store Triglycerides Long-term energy storage Muscle and liver cells store glycogen Carbohydrate storage Short-term energy storage in animals

Structures for support and movement Cytoskeleton Microtubules: tiny hollow tubes of protein Microfilaments: thin solid fibers of protein Microtubules and microfilaments form framework that supports the cell Centrioles Short rod-like structures near nucleus Play important role in cell division

Structures for support and movement Cilia Short, many Found on cells lining airways Flagella Long, single Enable spermatozoa to swim Cilia and flagella have similar internal structure

Cells Use and Transform Matter and Energy Metabolism: sum of all chemical reactions in an organism Two types of metabolic pathways: Anabolism: Assembly of larger molecules from smaller ones Requires energy (ATP input) Catabolism: Larger molecules are broken down Releases energy (ATP output)

Glucose Provides the Cell with Energy Metabolic activities of a living cell require a lot of energy Energy in glucose is used to generate ATP One glucose molecule may yield 36 ATP In absence of glucose, fats, and protein can be catabolized to generate ATP

Glucose Provides the Cell with Energy Cellular respiration: the breakdown of glucose in the presence of oxygen to yield ATP Four stages of cellular respiration Glycolysis Preparatory step Citric acid cycle Electron transport system

Cellular respiration Cellular respiration: major catabolic pathway that provides energy (C6H12O6 + 6O2  6H2O + 6CO2 + energy) Glycolysis: glucose (C6H12O6) split into two pyruvates Pyruvate converted to 2acetyl-Co A (+ CO2 released) Citric acid (Krebs) cycle: acetyl-CoA broken into CO2 H ions and electrons from glucose used in electron transport system to provide energy to make ATP

Mitochondrion Electron transport chain and oxidative phosphorylation Figure 3.29a 2 NADH 2 ATP to shuttle electrons from NADH in cytosol to NADH within mitochondrion Mitochondrion 2 NADH 6 NADH 2 FADH2 Electron transport chain and oxidative phosphorylation Glycolysis 2 Acetyl CoA Citric acid cycle 2 Pyruvate Preparatory step Glucose 2 ATP  4 ATP  2 ATP  about 34 ATP to initiate glycolysis by substrate-level phosphorylation by oxidative phosphorylation Figure 3.29a Most of the ATP generated during cellular respiration is synthesized in the electron transport system. About 36 ATP Most of the ATP generated during cellular respiration is synthesized in the electron transport system. 31

Fats and Proteins Are Additional Energy Sources Glycogen (storage form of glucose) Can be rapidly catabolized to glucose which then participates in cellular respiration 1% of total energy reserves Fats: 78% of total energy reserves Triglycerides have twice the energy of carbohydrates Proteins: 21% of total energy reserves Have the same amount of energy as carbohydrates

Some Questions Compare and contrast prokaryotic and eukaryotic cells Why is the rough endoplasmic reticulum rough? What are lysosomes? Give their function. Which organelle converts the energy stored in food to ATP? Which cell part is important for transporting material & maintaining homeostasis within the cell? What cells/tissue are most likely to store glycogen? What cells/tissue store triglycerides? What term describes the combination of all catabolic and anabolic reactions?