Chapter 4- Cells

Organisms are composed of one to many microscopic cells

Unicellular

Multicellular

Multicellular organisms are composed of one or more types of tissues

Different types of tissues are grouped to form organs

The Two Major Types of Cells

The Three Domains of Life

Domain Bacteria Domain Archaea

•Prokaryotic cells

Domain Eukarya includes all of the eukaryotic organisms.

Domain Eukarya

Protists (multiple kingdoms) Kingdom Plantae

Kingdom Fungi Kingdom Animalia

•Eukaryotic cells

Diagram of a plant cell

All eukaryotic cells and prokaryotic cells have at least three components in common:

The plasma membrane

Prokaryotic flagella

Nucleoid region (DNA)

Ribosomes Plasma membrane

Cell wall

Capsule

Pili

The plasma membrane is composed of phospholipids, proteins, and

other materials.

The cytoplasm consists of the entire region of the cell between the nucleus and plasma membrane

Ribosomes, are composed of protein and RNA.

Cell Membrane Structure and Function

The membranes of cells are composed of:

•The lipids belong to a special category called phospholipids

The cell membrane is described as selectively permeable

because it allows free passage of some materials and not

others.

Hydrophilic head

Hydrophobic tail

Outside cell

Cytoplasm (inside cell)

(a) Phospholipid bilayer of membrane

Hydrophilic region of protein

Phospholipid bilayer

Hydrophobic region of protein

(b) Fluid mosaic model of membrane

The cytosol is the cellular fluid.

-Larger molecules and ions (molecules with an

electrical charge) do not pass through the cell

membrane without specific membrane transport

proteins.

-Very small, uncharged molecules can easily pass through the membrane

Selective membrane permeability is the basis for osmosis.

Osmosis and Water Balance in Cells

Osmosis is the diffusion of water across the cell

membrane in response to differences in concentrations of

solutes (dissolved substances) such as sugars or ions.

Diffusion

Water, like many substances, will move from where it is

more concentrated to where it is less concentrated.

If the concentration of solutes inside and outside the cell is the same, then the cell is

osmotically balanced.

If the solute concentration is lower outside a cell than inside,

Osmosis and Water Balance in Cells

Prokaryotes, protists, fungi, and plants have cell walls that limit

the increase of cell volume through the uptake of water.

If the concentration of solutes outside the cells is higher than inside, water leaves the cell and the cytoplasm shrinks.

Eukaryotic cells share some features that prokaryotes lack

All eukaryotic cells have a:

The nucleus is the major site of genetic information (DNA) storage in eukaryotic cells.

The nuclear envelope

Nuclei also contain nucleoli (nucleolus, sing.),

Ribosomes Chromatin Nuclear envelope

Nucleolus Pore

Eukaryotic nuclear DNA is combined with proteins to

form chromosomes.

•Many of the membranous organelles in the cell belong to the endomembrane system

The endoplasmic reticulum (ER)

Nuclear envelope

Ribosomes

Rough ER Smooth ER

Rough ER

•The “roughness” of the rough ER is due to ribosomes that

stud the outside of the ER membrane

Ribosomes

Small globular structures composed of protein and RNA

that generate proteins from amino acids.

Transport vesicle buds off

Ribosome Secretory protein inside transport vesicle

Protein

Rough ER

Polypeptide

1 2

3

4

After the rough ER synthesizes a molecule it packages

the molecule into transport vesicles

Smooth ER

lacks the surface ribosomes of rough ER Nuclear envelope

Ribosomes

Rough ER Smooth ER

The Golgi apparatus

Works in partnership with ER

The Golgi apparatus of a cell consists of 1 or more Golgi bodies.

The cytoskeleton consists of three major types of long, thin, protein fibers:

Flagella and Cilia

Eukaryotic flagella typically contain a pair of single microtubules, surrounded by a

cylinder of nine paired microtubules (9 + 2 arrangement).

Mitochondria

Peroxisomes

-surrounded by single membrane

Components of cell walls: Cellulose

Non-cellulose components of plant cell walls

Plant cell walls also contain other polysaccharides such as:

Plant cells are distinguished from most other eukaryotic cells by:

Plant cells

Hemicellulose is a polymer of glucose and other sugars.

Each mitochondrion is enclosed by an envelope

composed of an outer membrane and a highly folded

inner membrane.

Cellulose is a polymer of glucose units, but the glucose monomers are linked together in different orientation.

- the most abundant organic compound on Earth

Pectin

Primary and Secondary Plant Cell Walls

Plasmodesmata

Plant cells that are still growing have only a single cell walllayer, or primary cell wall.

Secondary cell walls

Lignin may be added to the walls of water-conducting

cells, so mature cell walls can no longer stretch.

Large ions and molecules can be transported between the cells.

Chloroplasts

Leaves and other green parts of plants contain organelles called

chloroplasts.

Plant cells are enclosed by an envelope composed of 2 membranes.

Other types of plastids

Central vacuole

Chromoplasts

Amyloplasts

Plant and algal cells contain from one to

many plastids per cell.

The watery stroma contains other enzymes for photosynthesis.

The more general term plastid is used to describe

Study outline for Chapter 4-Cells

--Understand cell membrane structure and function- What are membranes of cells composed of?

-Know the structure of phospholipid bilayer of a membrane

-Understand the concept of selectively permeable

-Know examples of what can pass easily through membranes and substances that will not pass without specific

membrane transport proteins

-Understand osmosis and water balance in cells

-Know terms-osmosis, diffusion, isotonic, hypotonic, hypertonic, contractile vacuole, plasmolysis

-Know the features that eukaryotic cells share but prokaryotes lack

-Know structure and function-nucleus, nuclear envelope, nucleolus, chromosomes

-Know the membranous organelles that belong to the endomembrane system-ER (rough and smooth), ribosomes,

Golgi apparatus, Golgi body, cisternae

-Know the three major types of fibers in the cytoskeleton-microtubules, microfilaments, intermediate filaments

-Understand flagella and cilia- 9 + 2 arrangement

-Know structure and function of mitochondria and peroxisomes

Plant cells are distinguished from most other eukaryotic cells by which 4 cellular features?

-Know functions of cellulose cell walls

-Understand the structure of cellulose

-Know the structure and function of non-cellulose components of plant cell walls: hemicellulose, pectin

-Know the difference between primary and secondary plant cell walls

-Understand the structure and function of plasmodesmata

-Understand structure and function of different types of plastids-chloroplast, chromoplast, leucoplast (amyloplast)

-Know terms-thylakoid, stroma

-Understand structure and function of central vacuole