CHAPTER 7 Cellular Structure and Function Chapter 7

CHAPTER 7 Cellular Structure and Function

Chapter 7. 1: Cellular Structure and Function

KWL What do you know about cells?

Observations Describe the shape of the cork What do you see in the cork cells? What is the function of cork in the cork oak tree?

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History of Cell Theory • • For centuries, scientists had no idea that the human body consisted of billions of cell Existence of cells was unknown until Robert Hooke

How He Did It? • • Made a simple microscope and looked at a piece of cork (the dead cells of oak bark) Observed small box-shaped structures and called them cells because they reminded him of the cells in which monks lived in a monastery

What is a Cell? The basic structural and functional unit of all living organisms aka: The smallest unit of life

Anton van Leeuwenhoek Built his own microscope Saw that cells were seen in all other living organisms

Cell Theory One of the fundamental ideas of modern biology • Includes three principles: 1. 2. 3. All living organisms are composed of one or more cells Cells are the basic unit of structure and organization of all living organisms Cells arise only from preexisting cells, with cells passing copies of their genetic material on to their daughter cells

Microscopes: A Review • Compound Light Microscopes • • Uses glass lenses and light to magnify an image Electron Microscopes • • Uses electrons to see objects in greater detail Can be seen in 3 -D now

What All Cells Have • All cells have a plasma membrane • • All cells have a number of functions in common: • • A boundary that helps control what enters and leaves the cell Have genetic material in some form that provides instructions for making substances that the cell needs Break down molecules to generate energy for metabolism

Two Types Eukaryotic Cells Prokaryotic Cells

Eukaryotic Cells Contains organelles � Specialized structures that carry out specific cell functions � Contain a nucleus and other organelles that are membrane-bound Nucleus is a distinct central organelle that contains the cell’s genetic material in the form of DNA

Prokaryotic Cells • • • Cells without a nucleus or other membranebound organelles Most unicellular organisms Ex: Bacteria Called Prokaryotes Believed to be similar to the first organisms on Earth

Chapter 7. 2: The Plasma Membrane

Finish KWL Chart

The Plasma Membrane The plasma membrane is responsible for homeostasis A thin, flexible boundary between a cell and its environment that allows some nutrients into the cell and allows waste and some products to leave the cell All prokaryotes and eukaryotes have a plasma membrane

Structure of the Plasma Membrane The plasma membrane is composed of a phospholipid bilayer � Two layers of phospholipids arranged tail-to-tail � Head is polar and hydrophilic � Tail is nonpolar and hydrophobic

Phospholipid Bilayer

Other components of plasma membrane Proteins � Transmit signals to inside of cell � Create tunnels to allow certain substances to enter and leave the cell Cholesterol Carbohydrates

Fluid Mosaic Model Phospholipids can move sideways within the membrane Other components, like proteins can also move among the phospholipids Because there are different substances in the plasma membrane, a pattern, or mosaic, is created on the surface Components are in constant motion, sliding past one another

Chapter 7. 3: Structures and Organelles

Cytoplasm Cytoplasm: Semifluid material inside the plasma membrane Prokaryotes: � All chemical processes of the cell take place directly in the cytoplasm Ex: Breaking down sugar to generate ATP Eukaryotes: � Organelles located in cytoplasm

Cytoskeleton Organelles do not float freely in a cell, but are supported by a structure within the cytoplasm —The cytoskeleton Cytoskeleton: Supporting network of long, thin protein fibers that form a framework for the cell and provide an anchor for the organelles inside the cells � Called microtubules and microfilaments Function in cell movement and other cellular activities

Centrioles Function in cell division In animal cells, a pair of centrioles organizes the microtubules guiding chromosomes in cell division

Summary Microtubules Thickest � Cell structure and cell motility (movement) � Made of tubulin � Intermediate Filaments Thinnest � Internal movement within the cell � Made of actin and myosin (in muscles) � Microfilaments Intermediate in size � More permanent in the cell � Made of keratin (protein) �

Nucleus Contains cell’s DNA � Stores information used to make proteins for cell growth, function, and reproduction Surrounded by a double membrane called the nuclear envelope � Similar to plasma membrane, but has pores that allow larger-sized substances to move in and out of the nucleus Chromatin, which is a complex of DNA attached to protein, is spread throughout the nucleus

Ribosomes Manufacture proteins Made of RNA and protein Not bound by a membrane The nucleolus within the nucleus is the site of ribosome production

Endoplasmic Reticulum A membrane system of folded sacs and interconnected channels that serve as the site for protein and lipid synthesis Pleats and folds provide a large surface where cellular functions can take place Rough ER � Ribosomes export attached and produce proteins for Smooth ER � Provides membrane surface where carbohydrates and lipids are synthesized (phospholipids) Ex: In liver, ER detoxifies harmful substances

Golgi Apparatus Flattened sack of membranes that modifies, sorts, and packages proteins into sacs called vesicles Vesicles fuse with cell’s plasma membrane to release proteins to the environment outside of the cell

Vacuoles Sac used to store food, enzymes, and other materials needed by a cell Membrane-bound Found in plant cells Animal cells usually do not contain vacuoles � If they do they are much smaller than plant cells

Lysosomes Vesicles that contain substances that digest excess or worn-out organelles and food particles Digest bacteria and viruses that have entered the cell Can fuse with vacuoles and dispense their enzymes into the vacuole, digesting the wastes inside

Centrioles Organelles made of microtubules that function during cell division Located in the cytoplasm of animal cells and most protists and usually near the nucleus

Mitochondria Energy generators Converts sugars into usable energy Have an outer membrane and a highly folded inner membrane that provides a large surface area for breaking bonds in sugar molecules Energy produced from breakage is stored in bonds of molecules and later used by the cell

Chloroplasts Plant cells and some eukaryotes In addition to mitochondria Organelles that capture light energy and convert it to chemical energy through a process called photosynthesis Inner membrane called thylakoids � Energy from sunlight is trapped by a pigment called chlorophyll Gives leaves and stems their green color

Cell Wall Plant cells Thick, rigid, mesh of fibers that surrounds the outside of the plasma membrane, protecting the cell and giving it support Allow plants to stand at various heights Made of a carbohydrate called cellulose, which gives walls its inflexible characteristics

Cilia and Flagella Both used for cell movements, cilia are found in stationary cells Usually found in Prokaryotic cells, but can also be in Eukaryotic cells

Chapter 7. 4: Cellular Transport

Diffusion The net movement of particles from an area of high concentration of particles to an area of low concentration No additional energy input is needed for this to occur because the particles are already in motion

Dynamic Equilibrium Given enough time, particles continue to mix and form a uniform mixture The particles continue to move randomly, but no further change in concentration will occur � This is called dynamic equilibrium

Factors that Affect Rate of Diffusion Concentration � When high, occurs more quickly because there are more particles that collide Temperature and Pressure � Increases, number of collisions increase, thus increasing rate of diffusion

Facilitated Diffusion Cells need certain ions and small molecules in addition to water � Ex: Chloride ions � Sugars Water can diffuse across the cellular membrane, but other substances cannot Facilitated diffusion: Uses transport proteins to move other ions and small molecules across the plasma membrane

Facilitated Diffusion Substances move into the cell through a waterfilled transport protein called a channel protein that opens and closes to allow the substances to diffuse through the plasma membrane Carrier protein (a transport protein) helps substances move across the membrane by changing shape No additional energy required for facilitated diffusion to occur

Osmosis: Diffusion of Water passes freely into and out of the cell through the plasma membrane Osmosis: The diffusion of water across a selectively permeable membrane Regulating the movement maintains homeostasis

How it Works Water molecules diffuse towards the side with the greater sugar concentration; as it moves, sugar concentration decreases This happens until dynamic equilibrium occurs � Concentration sides of solutions is the same on both

Isotonic Solution When a cell is in a solution that has the same concentration of water and solutes (ions, sugars, proteins, etc. ) as its cytoplasm � Iso- Equal � Water still moves through the plasma membrane, but it enters and leaves at the same rate � Cells retain normal shape � Most cells are in isotonic solutions Ex: Blood

Hypotonic Solutions If a cells is in a solution that has a lower concentration of solute � Hypo-Under � There is more water outside the cell, then inside � Osmotic pressure: Pressure generated as water flows through the plasma membrane Membrane swells (animal cells) If too much pressure, membrane might burst (animal cells)

Hypotonic Solutions Plant cells: Rigid cell wall supports the cells and do not burst because as pressure increases, vacuole fills with water, pushing plasma membrane against the cell wall Cell becomes firmer

Hypertonic Solutions The concentration of the solute outside the cell is higher than the inside � Hyper-Above � The net movement of water is out of the cell � Animal cells: Shrivel � Plant because of decreased pressure in the cells: Lose water, mainly from central vacuole Plasma membrane shrinks away from cell wall Wilting

Active Transport Move from a region of lower concentration to a region of higher concentration Requires energy Against a concentration gradient Occurs with the aid of carrier proteins, called pumps Helps cell maintain homeostasis

Transport of Large Particles Endocytosis � Process by which a cell surrounds a substance in the outside environment, enclosing the substance in a portion of the plasma membrane � Pinches off and leaves substance in cell--vacoule Exocytosis � Secretion of materials at the plasma membrane � Expel wastes and secrete substances, such as hormones produced by the cell Require energy