Chapter7

Looking at cells

Where does cork come from?

• The bark of an oak tree that grows in Spain and Portugal

• The bark is dead• All that is left are the

cell walls enclosing air

Microscopes reveal cell structure

• Robert Hooke , an English scientist, invented the microscope in the 1600’s to view cork

• He named the “little boxes” he saw, “cells”

Anton van Leeuwenhoek

• 10 years after Hooke’s findings

• Used a microscope to view pond water

• He named the single-celled organisms he discovered “animalcules”

The Cell Theory

• All living things are made of cells

• Cells are the basic units of structure and function in organisms

• All cells arise from existing cells

Measuring the size of cell structures

• Measurements are in metric units

• International System of Measurements (SI)

• Based on powers of 10• Micrometers are one-

millionth of a meter ( the size of a bacterial cell)

Cells must be small

• Lower surface area to volume ratio = inability to move substances across the membrane in large enough numbers

• Higher surface area to volume ratio = greater ability to exchange substances

Small is good! Big is bad!

Common features of all cells

• Cell membrane

• Cytoplasm

• Cytoskeleton

• Ribosomes

• Genetic material

Prokaryotes do not contain internal compartments

• No nucleus

• Smaller

• Ex: bacteria

Characteristics of bacteria• Prokaryotes

• All have a cell wall surrounding the cell membrane

• Some have flagella for movement

• DNA is circular instead of linear

• Some have a capsule for clinging

Eukaryotic cells are organized

• Have a nucleus

• Have other membrane enclosed organelles

• Some have flagella or cilia for movement

Eukaryotes

• Larger

• More complex

• Many are highly specialized

• Plants, animals, fungi, and many protists

Cell Organization

• Two divisions:– Nucleus- eukaryotes only– Cytoplasm- fluid portion of the cell outside the

nucleus• Eukaryotes and prokaryotes

Organelles

• Specialized structures

• “Little organs”

Nucleus• Controls cell functions

• Surrounded by a double membrane with nuclear pores

• Contains DNA wound around proteins

• Wind up into chromosomes before division takes place

Nucleus

• Nucleolus- where ribosomes are made

• Nuclear pores- allow materials in and out

Vacuoles

• Large, saclike, membrane-enclosed structures that store materials such as water, salts, proteins, and carbohydrates

Vacuoles

• Plants- large central vacuole, helps keep leaves and flowers rigid

• Found in some unicellular organisms and animals– Contractile vacuole in paramecium

Vesicles

• In almost all eukaryotic cells

• Used for storage and movement

Lysosomes

• Small organelle filled with enzymes

• Digest old organelles, cellular “junk,” lipids, proteins, and carbohydrates

• Type of vesicle, found in animal and some plant cells

Ribosomes

• Made of RNA and protein

• Produce proteins

• Found in the cytoplasm (free) and rough ER (attached)

Endoplasmic Reticulum (ER)• A system of internal membranes that moves

proteins and other substances through the cell• Rough ER- has ribosomes on the surface that

create exported proteins • Smooth ER- no ribosomes, makes lipids for the

cell membrane – Detoxifies drugs

Golgi Apparatus

• Stack of flattened sacs

• Modifies, sorts, and packages proteins made from the rough ER

• Sent into or out of the cell

Sources of Energy

• Mitochondria- animal and plant cells

• Chloroplasts- plant cells

Chloroplasts

• Converts sunlight into food energy in a process called photosynthesis

• Double membrane

• Contains a green pigment called chlorophyll

Mitochondria

• In eukaryotic cells

• Power plant of the cells

• Converts food energy into smaller units the cell can more easily use

• Double membrane

Mitochondria

• Inherited only from your mother

• A way to trace the maternal lines of animals

Endosymbiotic Theory

• Chloroplasts and mitochondria have their own DNA and double membranes

• Theory states:– These may have been independent

organisms at one time– Create their own energy– May have been beneficial once absorbed and

found to be beneficial

Unique features of plant cells

• Cell wall -surrounds the cell membrane, supports and protects the cell

• Chloroplasts- green structures that absorb sunlight and produce glucose

• Central vacuole- stores water and other substances, when full makes a cell rigid

Cytoskeleton

• Network of protein filaments

• Gives cells their shape and internal organization– Helps to transport materials inside the cell

• Protein filaments– Microtubules– Microfilaments

Microfilaments

• Threadlike structures made of protein called actin

• Make up a tough flexible framework that helps support the cell

• Help cells move– Amoebas- assemble and disassemble to help

them move

Microtubules

• Hollow structures

• Made of protein tubulin

• Maintains cell shape

• Centrioles– Makes spindle during mitosis to separate

chromosomes

Microtubules

• Make up cilia and flagella– Used for swimming

• Arranged in a 9+2 pattern

• Small bridges between aid in movement

Cell Boundries

• Cell wall

• Cell membrane

Cell Wall

• Prokaryotes, plants, algae, fungi– Animal cells do not

• Outside the cell membrane

• Strong supporting layer

• Porous- allows water, carbon dioxide and oxygen to pass through

Cell Membrane

• Protects and supports cell

• Regulates what enters and leaves

• Phospholipid bilayer- to layers of lipids