Biology 101 Chapter 4

Cells as the Basic Unit of Life

 

The Cell Theory

Major Contributors:

Galileo = first observations made with a microscope

 

Robert Hooke = first to observe small compartments in dead plant tissue, coined the term "cell"

 

Antony van Leeuwenhoek = first to observe living, mobile cells and bacteria

 

Robert Brown = first to observe the nucleus

 

Rudolf Virchow = every new cell comes from a pre-existing cell

 

Schleiden and Schwann = plants and animals are composed of cells and cell products

 

Tenements of the Cell Theory:

1)  All organisms are composed of one or more cells.

2)  The cell is the smallest unit having the properties of life.

3)  The continuity of life arises directly from the growth and division of single cells.

 

Cell size and cell function: Surface area to volume ratio!

-        The larger the ratio, the better off the cell!

-        Impact of surface area to metabolism

What is the largest cell in the human body?  The smallest?

Cell Structures and Their Functions

All cells are placed in one of 2 classes:

 

        Prokaryotic = lack a nucleus (bacteria)

 

Eukaryotic = have a nucleus (protists, fungi, plants,

and animals)

 

PROKARYOTIC CELLS

       very, very small

       very simple structure

 

Parts:

A)  Plasma (cell) membrane = encloses cytoplasm of cell

 

B)  Nucleoid Region = where DNA is at (not a nucleus)

 

C)  Ribosomes = assembles proteins with info from DNA

 

D)  Bacterial Cell Wall = a rigid outer layer that surrounds

      the cell membrane, protects the cell, maintains shape

 

E)  Capsule = a sticky outer layer over cell wall

 

F)  Pili and Fimbriae = numerous short projections that

      help with adherence

 

G)  Prokaryotic Flagella = longer projections that help with

      motility

 

H)  Plasmids = extra-chromosomal pieces of DNA

 

 

 

EUKARYOTIC CELLS

       have a nucleus

       very, very large

       complex internal organization

       compartmentalized

       membrane bound organelles

 

Organelle = "small organ", membrane enclosed structures found inside the cell, each for a specialized function.  All chemical activities of the cell occur within organelles.

 

Benefits of Organelles:

1)  Separate environments for chemical reactions

2)  Increased membrane surface area

 

Eukaryotic Cells Broken Up into 3 Regions:

1. Cell Membrane

2. Cytoplasm (cytosol and organelles)

3. Nucleus

 

Organelles:

1.   Nucleus *

2.   Endoplasmic Reticulum (ER, smooth and rough)

3.   Golgi Apparatus (or Body)

4.   Vesicles (lysosomes and peroxisomes)

5.   Mitochondria

6.   Chloroplasts (only in plants)

7.   Storage Vacuole (mainly in plants)

8.   Centriolus (only in animal cells)

 

Other Structures:

1.   Ribosomes

2.   Cell Wall (in plants)*

3.   Cell Membrane

4.   Cytoskeleton

a.    Microtubules

b.   Microfilaments

c.    Intermediate Filaments

5.   Flagella and Cilia (mainly in animals)

6.   Nucleolus

 

 

The Nucleus

 

       Cell's genetic control center

       Double membrane

       Nucleoplasm

       Nuclear envelope

       Nuclear pores

       Chromatin = DNA + associated proteins

       Nucleolus = internal structure of nucleus, site of ribosome assembly

       Chromatin vs. Chromosome

 

The Cytomembrane System

       Function: internal transport, importing and exporting of cell

       3 parts:

1.   ER

2.   Golgi Apparatus

3.   Vesicles

 

Endoplasmic Reticulum

       Single, continuous membrane

       Pipes, tubes and tunnels in cell

       Continuous with nuclear envelope

       Superhighway of the cell

       2 kinds: Rough ER + Smooth ER

Rough ER

-        Flattened connected sacs

-        Studded, or covered, with ribosomes

-        Major site of protein synthesis

-        Synthesis of new membrane

 

Smooth ER

-        Lacks ribosomes

-        Continuous with rough ER

-        Functions:

1.   Transport

2.   Synthesis of lipids

3.   detoxification

4.   Storage of calcium ions

 

 

Golgi Apparatus

 

       Stack of flattened, pancake looking sacs located near cell membrane

       Handles export and import of material for cell

       Not continuous with ER, NOT physically connected

       Functions:

1.   Storage, packaging, sorting and final touches and modification of proteins before exportation

2.   The UPS of the cell

 

Vesicles

 

       General, short term transport, some storage, single membrane

       3 special types:

 

Transport Vesicles

1)  Used to transport material from ER to Golgi Apparatus

2)  Transport of finished product from Golgi to Cell Membrane for export (process reversed for import)

 

Lysosomes

1)  Contain digestive (hydrolytic) enzymes

2)  Breakdown cell's food and wastes

 

Peroxisomes

1)  Breakdown lipids

2)  Detox alcohols and hydrogen peroxide

 

 

Vacuoles

 

       Very large, single membrane sacs

       Functions:

1.   Work with lysosomes for digestion

2.   Storage of food and water

3.   Stores wastes, excess water

4.   Turgor pressure in plants

Ex. Large Central Vacuole of plants

 

 

 

Mitochondria

 

       Found in all eukaryotic cells

       Carry out cellular respiration to produce energy for the cell

       Cell's "power house"

       Composed of 2 membranes

       Cristae = folds of inner membrane, site of energy production

       Matrix = fluid inside mitochondria

 

 

Chloroplasts

 

       Found only in green plant cells and algae

       Site of photosynthesis

       Contain the pigment chlorophyll

       Composed of 3 membranes

       Grana = stacks of discs of inner membrane, actual site of photosynthesis

       Stroma = fluid inside chloroplast

 

 

Centriolus

 

       Also referred to as basal bodies and MTOCs

       Composed of two centrioles in a membrane

       Used for anchoring, microtubule growth

       Centrioles also used in cell reproduction

 

 

Structures Based on Microtubules

 

The Cytoskeleton

 

       Framework of protein fibers inside cell

       Support and movement (dynamic)

       Composed of:

1.   Microfilaments = thinnest (actin)

2.   Intermediate filaments = (composition varies)

3.   Microtubules = thickest (tubulin)

 

Cilia & Flagella

 

       Used in locomotion

1.   Cilia = numerous, very short

2.   Flagella = few, very long

 

       "9 + 2" arrangement of microtubules

       9 outer pairs

       2 single central

 

 

Plant Cell Wall

 

       Surrounds the cell external to cell membrane

       Very stiff, rigid structure

       Supports cell, gives it shape, protects it

       Composed of a complex sugar called cellulose

       Note: some protistans and all fungi also have a cell wall

 

 

COMPOSITE ANIMAL CELL

 

 

 

 

COMPOSITE PLANT CELL

 

 

 

 

Some notes on microscopes:

Stereomicroscopes (dissecting)

Compound light microscopes

Scanning Electron Microscope (SEM)

Tunneling Electron Microscope (TEM)

Scanning-Tunneling Electron Microscope (STM)

 

Drawbacks on electron microscopes