Chapter Seven

A View of the Cell

Cellular Organization

• Cell

• Tissue – group of cells functioning together.

• Organ – group of tissues functioning together.

• Organ System – group of organs functioning together.

• Organism – group of organ systems functioning together.

The History of the Cell

• The Cell

– The basic unit of an organism

– Discovery made possible by the invention of the microscope

Microscopes and Cells

• 1600’s.

–Anton van Leeuwenhoek first described living cells as seen through a simple

microscope.

Microscopes and Cells

• Robert Hooke used the first compound microscope to view thinly sliced cork cells.

•Compound scopes use a series of lenses to magnify in steps.

•Hooke was the first to use the term “cell”.

Microscopes and Cells • 1830’s.

– Mathias Schleiden identified the first plant cells and concluded that all plants made of cells.

- Theodor Schwann made the same conclusion about animal cells.

Cell Theory:

• All organisms are made up of one or more cells.

• The cell is the basic unit of organization of all organisms.

• All cells come from other cells all ready in existence.

Two Basic Cell Types

1) Prokaryote

– Lacks internal compartments.

– No true nucleus.

– Most are single-celled (unicellular) organisms.

– Examples: bacteria

Two Basic Cell Types

2) Eukaryote

– Has several internal structures (organelles).

– True nucleus.

– Either unicellular or multicellular. unicellular example: yeast

multicellular examples: plants and animals

bacteria cells Types of cells

animal cells plant cells

Prokaryote - no organelles

Eukaryotes -organelles

Cell Rap

Cell size comparison

Bacterial cell

Animal cell

micron = micrometer = 1/1,000,000 meter

diameter of human hair = ~20 microns

most bacteria

1-10 microns

eukaryotic cells

10-100 microns

The Functions of Eukaryotic Cell Parts

1. Boundaries

2. Controls

3. Assembly

4. Transport

5. Storage

6. Energy Transformers

7. Support

8. Locomotion

9. Cell Division

Cell video clip Cell Song

Boundaries

Plasma Membrane

• Serves as a boundary between the cell and its external environment.

• Allows materials to pass in and out of the cell. Fluid mosaic model

Boundaries Cell Wall

• Surrounds the plasma membrane of the cells of plants, bacteria, and fungi.

• Plant cell walls contain cellulose while fungi cell walls contain chitin.

Controls Nucleus

• Regulates cell function.

• Surrounded by a double-layered membrane (nuclear enveloped) with large pores that allow materials to pass in and out of the nucleus.

• Contains chromatin – long tangles of DNA.

Controls Nucleolus

•Found in the nucleus and responsible for ribosome production. (Ribosomes are the sites of protein production.)

Assembly

Cytoplasm •The jelly-like material that surrounds the organelles.

Transport

Endoplasmic reticulum • Folded membrane that acts as the cell’s delivery system.

• Smooth E.R. contains enzymes for lipid synthesis.

• Rough E.R. is studded with ribosomes for protein synthesis.

Transport

Golgi apparatus

(or Golgi body) • A series of flattened sacs where newly made lipids and proteins from the E.R. are repackaged and shipped to the plasma membrane.

:

Storage

Vacuoles and Vessicles

•A sac of fluid surrounded by a membrane used to store food, fluid, or waste products.

Storage Lysosomes

• Contain a digestive enzyme.

• Can fuse with vacuoles to digest food, or can digest worn cell parts.

• Also known as “suicide sacs” because they can also destroy the whole cell.

Energy Transformers

Mitochondria • Produce the energy for

the cell.

• Also known as the “powerhouse of the cell”.

• Has a highly folded inner membrane (cristae).

Energy Transformers

Chloroplasts

• Found in plant cells and some protists.

• Transforms light energy into chemical energy which is stored in food molecules.

• Contain chlorophyll – a green pigment that traps light energy and gives plants their green color.

Support Cytoskeleton

• A network of thin, fibrous materials that act as a scaffold and support the organelles.

• Microtubules – hollow filaments of protein.

• Microfilaments – solid filaments of protein.

Locomotion Cilia • Short, numerous, hair-like projections from the plasma membrane.

• Move with a coordinated beating action.

Locomotion Flagella

•Longer, less numerous projections from the plasma membrane.

•Move with a whiplike action.

Cell Division Centrioles

– made of protein.

– play a role in the splitting of the cell into two cells.

– found in animal and fungi cells.

Composite Animal Cell

Composite Animal Cell

Movement Across the Membrane

• Establishes Homeostasis

• Occurs through channel proteins

• Can be active or passive

– Passive does not require energy

– Active does require energy

Passive Transport: Diffusion

• Particles in a solution move constantly

• Particles tend to move from an area of high concentration to low concentration

• When concentration is equal everywhere, it has reached equilibrium

• Substances diffuse across membranes without requiring the cell to use energy (passive transport)

Diffusion HIGH concentration LOW concentration

Passive Transport: Osmosis

• If a substance can diffuse across a membrane, the membrane is said to be permeable to it and impermeable if it can't diffuse across it

• Water diffuses easily

• Osmosis is the diffusion of water across a selectively permeable membrane from an area of high concentration to low concentration

Osmosis • The direction of osmosis is determined

by comparing total solute concentrations

– HYPERTONIC - more solute, less water

– ISOTONIC - equal solute, equal water

– HYPOTONIC - less solute, more water

hypotonic hypertonic

freshwater balanced saltwater

Managing water balance

Cell survival depends on balancing water uptake & loss

The Phospholipid Bilayer is a Semipermeable Membrane

• The phospholipid bilayer is – Nonpolar – Has hydrophilic edges and hydrophobic

center

• What molecules can get through directly? – Nonpolar molecules: fats & other lipids

Diffusion through phospholipid bilayer

inside cell

outside cell

lipid salt

aa H2O sugar

NH3

What molecules can NOT get through directly?

polar molecules

H2O

ions (charged)

salts, ammonia

large molecules

starches, proteins

Semipermeable

Passive Transport-Facilitated Diffusion

Cell membranes have protein channels that act like carriers, making it easier for certain molecules to cross. They "facilitate" the diffusion of molecules.

There are hundreds of different channels that only allow certain molecules to come through.

Passive Transport-Facilitated Diffusion

It will only occur if there is a higher concentration on one side of the membrane. It doesn't require energy. It's passive transport.

Active Transport

“The Doorman”

Change in Shape of Protein

• Cells may need to move molecules against concentration gradient – conformational shape change transports solute from

one side of membrane to other – protein “pump” – “costs” energy = ATP

ATP

LOW

HIGH

How about large molecules?

• Moving large molecules into & out of cell through vesicles & vacuoles

How about large molecules?

• ENDOCYTOSIS: into the cell – 2 types 1. phagocytosis = “cellular eating”

2. pinocytosis = “cellular drinking”

• EXOCYTOSIS: out of the cell

exocytosis

Endocytosis

phagocytosis

pinocytosis

receptor-mediated endocytosis

fuse with lysosome for digestion

non-specific process

triggered by molecular signal

Getting through cell membrane summary

• Passive Transport – Simple diffusion

• diffusion of nonpolar, hydrophobic molecules – lipids – HIGH LOW concentration gradient

– Facilitated transport • diffusion of polar, hydrophilic molecules • through a protein channel

– HIGH LOW concentration gradient

• Active transport – diffusion against concentration gradient

• LOW HIGH

– uses a protein pump – requires ATP ATP

Cell Membrane

• Cell membrane establishes homeostasis for the cell by controlling what passes in and out of the cell.

• HOW? 1. PHOSPHOLIPID BILAYER creates a

barrier

2. Protein channels that allow polar substances through

3. Glyco-proteins are name tags

Phospholipid Bilayer

Glycoprotein

Integral Proteins

Peripheral Proteins