Chapter 7

A View of the Cell

Cell Theory• CD-ROM• Before microscopes, people thought

diseases were caused by curses and supernatural spirits– They had no idea microorganisms, such as

bacteria and viruses existed

• When the microscope was invented, scientists discovered cells exist

• Cells are the basic units of living organisms

Cell Theory• Anton van Leeuwenhoek (Dutch) used the

first simple light microscope in the 1600s – It had one lens (page 1064)

• Gradually, lenses got better

• Compound light microscopes use a series of lenses to magnify objects in steps– Can magnify up to 1500 times– The microscopes we use in the lab

Cell Theory• Robert Hooke (1600s, English) used a

compound light microscope to study cork, the dead cells of oak bark

• He saw small, geometric shapes that reminded him of the small rooms monks lived in called cells

• Cells are the basic units of all living things

Cell Theory

• Matthias Schleiden (1830s, German) discovered that all plants are made of cells

• Theodor Schwann (German) discovered that all animals are made of cells

• Rudolf Virchow discovered that all cells come from existing cells

• All these scientists (plus others) contributed ideas that are now summed up in what we call the cell theory

Cell Theory• All organisms are composed of one or

more cells.

• The cell is the basic unit of structure and organization of organisms.

• All cells come from preexisting cells.

Electron Microscopes

• Electron Microscopes let us see a much greater magnification than light microscopes– They use beams of

electrons to produce images

• Scanning Electron Microscope– Used for scanning

3-D surfaces

Electron Microscopes

• Transmission Electron Microscope– Used for

scanning interior structures of cell

Types of Cells• Organelles are small, specialized

structures within cells

– Many, but not all are surrounded by membranes

• Prokaryotes are organisms that do not have membrane-bound organelles (biology.arizona.edu)

– Kingdom Monera ( now split into Eubacteria & Archaebacteria)

• Eukaryotes are organisms that do have membrane-bound organelles

– Kingdoms Animalae, Plantae, Fungi, Protista

Types of Cells• Robert Brown (Scottish) observed that

eukaryotic cells have a prominent structure, the nucleus– the nucleus manages cellular functions

• Rudolf Virchow concluded that this prominent structure was responsible for cell division

Section 1 Review

• How has the history of microscopes influence the study of cells?

• What are the three parts of the cell theory?

• What is the difference between a light microscope and an electron microscope?

• What is the difference between a prokaryote and a eukaryote?

The Plasma Membrane• Cells must maintain proper conditions within itself to

function• The plasma membrane is a flexible boundary between

the cell and its environment– It allows a steady supply of nutrients into and out of the cell at

the appropriate levels

• The plasma membrane is selectively permeable – This means that it allows some molecules to pass through

while keeping others out.– Like a screen in a window

The Plasma Membrane• Phospholipids• The “head” is polar, or slightly charged

– It is hydrophilic (likes water)• The “tail” is nonpolar, or not charged

– It is hydrophobic (repels water)• The phospholipids arrange themselves form a

bi-layer with the fatty acid tails forming the interior and the heads facing the watery environments outside and inside the cell

Plasma Membrane

• The plasma membrane is called a phospholipid bilayer

• Arranged in this manner, a barrier is created that is water-soluble at its outer surfaces and water-insoluble in the middle

• Keeps out both water soluble and water insoluble molecules

Plasma Membrane

• The current model of the plasma membrane is called the fluid mosaic model.

• The phospholipids actually move around like a fluid.

• The other components of the membrane (proteins, carbohydrates, cholesterol, etc.) move around as well

Plasma Membrane

• Cholesterol helps to stabilize the phospholipids by preventing their fatty acid tails from sticking together

• Transport proteins move span the membrane and move needed substances or waste materials through the plasma membrane

• Other proteins and carbohydrates that stick out help cells to identify surface signals and other cells– These proteins play an important part in protecting

cells from infection

Section 2 Review

• What is a phospholipid?

• Why is the cell membrane a bilayer?

• What does polar and nonpolar mean?

• What are the specialized parts of the cell membrane?

• Why is the cell membrane referred to as fluid mosaic?

Cell Wall• Fairly rigid structure located

outside the plasma membrane of some cells that provides additional support and protection– Plants, fungus, most bacteria

• The cell wall is very porous, made of a tough mesh of fibers– Like framing of a house

Nucleus• Membrane-bound (called

nuclear envelope) organelle that contains the directions to make proteins

• Nuclear pores allow passage through the nuclear envelope

• Chromatin - uncondensed strands of DNA– When cell is dividing, DNA

condenses into chromosomes

• Nucleolus - organelle within the nucleus that make ribosomes

Organelles• Ribosomes are the sites where

the cell produces proteins according to the directions of DNA– One organelle without a

membrane • Cytoplasm is the clear,

gelatinous fluid inside the cell – Acts as a medium for things

to move around in the cell – “Organelles can’t fly”

Organelles • The endoplasmic reticulum (ER) is

arranged in a series of highly folded membranes suspended in the cytoplasm

• In general, ER is involved in the movement of materials throughout the cell

• Rough ER has ribosomes, which is where protein synthesis takes place

• Smooth ER has no ribosomes and is involved in numberous biochemical activities, including the production and storage of lipids

Organelles• The Golgi apparatus is a

flattened stack of tubular membranes that modifies the proteins

• The Golgi sorts proteins into packages and packs them into membrane-bound structures called vescicles for later transport (like UPS)

Organelles

• Vacuoles are membrane-bound compartments for temporary storage of materials– Store food,

enzymes, water, waste

– Plant cells have one very large vacuole

Organelles• Lysosomes are organelles

that contain digestive enzymes

• Digest old organelles, food, viruses, bacteria, etc.

• Can fuse with a vacuole to dump waste or give enzymes

• Lysosomes digest a tadpole’s tail

Organelles• Plastids are a group of

organelles used for storage– Named for the color or

pigment they contain

• Chloroplasts are organelles that capture light energy and convert it to chemical energy (photosynthesis occurs here) – Plastid containing chlorophyll,

which actually traps the light and gives plants green color

Organelles• Mitochondria are

membrane-bound organelles in plant and animal cells that transform stored chemical energy into a usable form for the cell (ATP)

• Has an outer and inner highly folded membrane – ATP produced on inner folds

Organelles• The cytoskeleton forms a framework for the

cell– A network of tiny rods and filaments

• Cytoskeleton is constantly changing its shape• Microtubules are thin, hollow cylinders made of

protein• Microfilaments are smaller, solid protein fibers • Give support for cell• Provide “highway system” for organelles to

move throughout cell

Organelles• Centrioles are organelles made up

of microtubules that play a part in cell division– In animals and most protists

• Cilia are short, numberous projections that look like hairs– Made of microtubules and help

organelles move and feed• Flagella are longer projections that

move in a whip-like motion– Made of microtublules - help

with movement– Cells usually only have 1 or 2

Animal Cell

Plant Cell

Section 3 Review1. How are highly-folded membranes an advantage for

the functions of cellular parts?2. Name an organelle that has highly-folded membranes.3. If a cell synthesizes large quantities of protein

molecules, which organelles might be numerous in that cell?

4. A cell’s digestive enzymes are enclosed in a membrane-bound organelle. How can these molecules function in the cell?

5. Compare and contrast the functions of a cell wall to the functions of a plasma membrane.

6. What are the functions of the cytoskeleton? 7. Why are mitochondria and chloroplasts referred to as

energy transporters?