Chapter 7 Cell Structure & Function

Scientists & Discoveries Early 1600’s (Holland): 1st microscope was constructed Anton van Leeuwenhoek (1600’s) used single lens as a microscope to study and very carefully draw tiny living organisms (1665) English physicist Robert Hooke used light microscope to study thin slices of plants- saw cork had many tiny chambers he called “cells” like monastery cells

cells= the basic units for all forms of life (1838) Matthias Schleiden - concluded all plants made of cells (1839) Theodor Schwann - animals made of cells (1855) Rudolf Virchow -studied cell reproduction; 5yrs research concluded with: “Where a cell exists, there must have been a preexisting cell…”

The Cell Theory All living things are composed of cells Cells are the basic units of structure and function in living things New cells are created from existing cells

Basic Cell Structures Cells usually 5-50 micrometers Smallest: 0.2 micrometers Largest: (amoeba Chaos chaos) 1000 micrometers All cells have a cell membrane and cytoplasm Cell membrane: thin flexible barrier around a cell

Cytoplasm: material inside the cell membrane Many cells also have cell wall (strong layer around cell membrane Cell membranes & cell walls support & protect cells while allowing them to interact with their environment Some cells also have a nucleus (a large structure that stores the cells genetic information & controls the cells activities)

Prokaryotes vs. Eukaryotes Cells are divided into 2 categories: 1.Prokaryotes 2.Eukaryotes *divided into these 2 categories to separate cells that contain a nucleus and organelles (eukaryotes) and those that do not (prokaryotes)

Prokaryotes Usually smaller & simpler than eukaryotes Contain cell membranes & cytoplasm DO NOT have nuclei All bacteria are prokaryotes - examples: Escherichia coli (intestines), Staphylococcus aureus (skin infections)

Prokaryotes Carry out all activities that define life (grow, reproduce, respond to their environment, & some even move)

Eukaryotes CONTAIN nuclei, cell membrane, cytoplasm, & dozens of other specialized structures that perform special functions (organelles) Some are single celled organisms, but most make up multicellular organisms All plants, animals, fungi, and many microorganisms are eukaryotes

Eukaryotes

review 1.What 3 statements describe cell theory? 2. What is the main characteristic that distinguishes prokaryotes and eukaryotes? 3. Name 2 structures that all cells have.

Section 2: Cell Structures A. Cytoplasm- refers to the region outside the nucleus but inside the cell membrane Also called the plasma membrane Bi-layer phospholipids that regulates what enters and leaves the cell

B. Cell Wall *main function=provide support & protection for the cell *located outside cell membrane *made of cellulose (a carbohydrate fiber) & protein *found in plants, algae, fungi & nearly all eukaryotes (not animal cells)

C. Nucleus *controls most of the cell processes & contains hereditary information of DNA *chromatin-granular material in the nucleus that consists of DNA bound to protein *chromosomes- condensed chromatin that consists of genetic information that is to be passed on during cell division

(Nucleus contd.) *Nucleolus-small, dense region where assembly of ribosomes begins *Nuclear envelope- double-membrane layer that surrounds the nucleus. It contains many nuclear pores that allow material to move in/out of the nucleus

D. Cytoskeleton *network of protein filaments that help the cell to maintain its shape, also involved in cell movement *microtubules-hollow tubes of protein, can serve as “tracks” along which organelles move *microfilaments-long, thin fibers that function in the movement & support of cells

E. Organelles in the cytoplasm Ribosomes -small particles made of RNA & protein -produce proteins following coded instructions from the nucleus Endoplasmic Reticulum (ER)- organelle in which components of the cell membrane are assembled & some proteins are modified (rough E.R.-have ribosomes attached to the surface) -figure 7-8

Golgi Apparatus-enzymes in the Golgi Apparatus attach carbohydrates & lipids to proteins Lysosomes-small organelles filled with enzymes that break down lipids, carbohydrates, & proteins from food into particles that can be used by the rest of the cell (also break down organelles)

Vacuoles- sac-like structures that store materials like water, salts, proteins & carbohydrates (figure 7-10) Chloroplast-found in plants (figure 7-11) -use energy from sunlight to make energy rich molecules in a process known as photosynthesis -have a double membrane

Mitochondria- use energy from food to make high energy compounds that the cell can use to power growth, development, & movement (figure 7-12) -have a double membrane -found in nearly all eukaryotic cells

F. Organelle DNA Chloroplasts and mitochondria contain some of their own genetic information in the form of DNA These small DNA molecules contain information that is essential for them to function Mitochondria and chloroplasts could have once been prokaryotic cells that were engulfed by eukaryotic cells & formed a symbiotic relationship

Section 2 Review 1.What is the function of the ER, Golgi Apparatus, chloroplast, mitochondria? 2.What does the cell wall provide for the cell? 3.Describe the role of the nucleus in the cell. 4.What are the 2 functions of the cytoskeleton? 5.How is the cell like a factory?

Section 3: Movement through the Membrane The cell membrane regulates what enters & leaves the cell & also provides protection & support (figure 7-15) -lipid bilayer–a double layered membrane formed when certain kinds of lipids are dissolved in water -embedded proteins-forms channels & pumps that help move materials across the membrane -carbohydrate chains-attach to proteins & aids in chemical identification to allow cells to ID one another

Cell Membrane

Diffusion : tendency of molecules to move from an area of high concentration to an area of lower concentration to reach equilibrium (figure 7-16) -causes many substances to move across the cell membrane but does not require the cell to use energy -concentration=mass of solute/volume of solution

Osmosis : diffusion of water through a selectively permeable membrane (fig 7-17) -selectively permeable= some substances can pass through but others cannot -isotonic-same strength solution on both sides -hypertonic-more solutes in solution than in cell (water leaves cell to make it even) -hypotonic-more solutes in cell than in solution (water enters to make it even)

Osmosis exerts pressure known as osmotic pressure on the hypertonic side of the selectively permeable membrane. -osmotic pressure can cause a cell to shrink or burst (figure 7-18)

Facilitated Diffusion : the process of protein channels allowing a pathway for certain molecules to cross the membrane (figure 7-19) -100’s of different protein channels have been found that allow ions, sugars & salts to cross the membrane

Active Transport : requires energy to move molecules across a cell membrane against a concentration difference. The materials move from an area of lower concentration to an area of higher concentration (figure 7-20)-often compared to a pump

Endocytosis : the process of taking large particles into the cell by means of infoldings or pockets of the cell membrane that form vacuoles

Phagocytosis : process of taking large particles into the cell by endocytosis. Extensions of the cytoplasm surround & engulf the large particles.

Exocytosis : membrane of the vacuole surrounding material fuses with the cell membrane, forcing the contents out of the cell

Review 1.What processes are made possible by the cell membrane? 2.How does diffusion affect cells? 3.Describe how water moves during osmosis. 4.What is the basic structure of a cell membrane? 5.How does active transport differ from diffusion?