Chapter 4:  Cell Structure and Function

 

I.  Cell: smallest unit of living matter

            A.  Cell history

                        1.  Antonie von Leeuwenhoek (1632-1723) looked at

                            "animalicules", unicellular cells

 

                                    a.  His researches opened up an entire world of microscopic

                                          life to the awareness of scientists.

 

                                    b.  Allowed the discovery of bacteria, free-living and parasitic

                                    microscopic protists, sperm cells, blood cells, microscopic

                                    nematodes and rotifers, and much more. His researches

                                    opened up an entire world of microscopic life to the

                                    awareness of scientists.

 

                                    c.  Antonie van Leeuwenhoek would not tell anyone how he

                                    built his microscopes. It was over 100 years after

                                    Leeuwenhoek's death before anyone could manufacture a

                                    microscope that could match or surpass the magnifying

                                     quality of the microscopes he built.

 

                        2.  Robert Hooke, confirmed Leeuwenhoek's observations-

                            Saw tiny chambers in cork that looked like monastery,cells and

                            thus used the word "cell" to describe these chambers.

 

                        3.  1830's Matthias Schleiden said all plants are made of cells

 

                        4.  1830's Theodor Schwann said all animals are made of cells

 

            B.  Cell theory:

                        1.  All organisms are made up of cells

 

                        2.  The cell is the basic structural and functional unit of life

                        3.  New cells come from pre-existing cells

            C.  Small size has a larger surface area/volume ratio for exchange of

                 materials from the surface

 

  

II.  Microscopes

 

            A.  Bright field light microscope--light rays pass through specimen are brought

                into focus by a set of glass lens, and the resulting image is then observed by the

                human eye.l

 

            B.  Transmission electron microscope- electrons passing through a specimen are

                  brought into focus by magnetic lens,

 

                        1.  Resulting images projected onto a fluorescent screen or photographic film

 

            C.  Scanning electron Microscope-a narrow beam of electrons is scanned over the

                  surface of the specimen which is coated with a thin metal layer.

 

                        1.  The metal gives off secondary electrons that are collected by a detector to

                             provide an image on a television screen.

 

                        2:  Permits development of three-dimensional images.

 

III.  Prokaryotic cells: bacteria, cyanobacteria (blue-green algae)

 

Outer boundary

1.  Cell wall: may have a capsule and/or gelatinous slime layer flagella, some have fimbriae to attach to surfaces

 

 

 

2.  Plasma membrane: regulates passage of materials into/out of cell

 

 

Cytoplasm

1.  Cytosol: semifluid medium with enzymes

 

 

 

2.  Ribosomes: coordinate synthesis of proteins in the cell

 

 

 

3.  Thylakoids: membranes with light sensitive pigments; found in cyanobacteria

 

 

Nucleoid

1.  Chromosome: single circular, not membrane bound

 

 

 

IV.  Eukaryotic cells: "true nucleus", larger, plant and animal cells

 

            A.  Properties

           

Outer boundary

 

 

 

Plasma membrane

Phospholipid bilayer with embedded proteins

 

 

 

 

Cell wall

Plants: contain cellulose, for support and protection of plant cells

 

 

 

Cytoplasm

Cytosol

A semifluid medium that contains organelles

 

 

 

 

Organelles

1.  Small bodies in the cell

 

 

2.  Have a specific structure and function

 

 

3.  Compartmentalize the cell

 

 

 

 

            B.  Specific Organelles

 

Nucleus

"Control center", stores genetic information

 

 

 

 

 

1.  Chromatin

Network of threadlike strands of DNA

 

 

 

 

2.  Chromosomes:

Condensed DNA and protein, seen during cell division

 

 

 

 

3.  Nucleolus

Concentrated area of chromatin, where ribosomal RNA is produced and joins with proteins to form ribosome parts

 

 

 

 

4.  Nuclear envelope

Double membrane with pores

 

 

 

 

 

 

Ribosome

rRNA and proteins, used for protein synthesis, found free in the cytoplasm or attached to ER

 

 

 

 

 

 

 

Endoplasmic reticulum (ER)

System of membranous channels and saccules continuous with the outer membrane of the nuclear envelope.

 

 

 

 

 

1.  Rough ER

Has ribosomes, used for protein synthesis

 

 

 

 

2.  Smooth ER

Makes phospholipids, hormones, and detoxifies drugs, forms vesicles for transport of large molecules

 

 

 

 

 

 

Golgi Apparatus

Process, package and distributes molecules

 

 

 

 

 

1.  Saccules

(Stack of pancakes) contains enzymes to modify proteins and lipids

 

 

 

 

2.  Secretory Vesicles

Products packaged in vessicles that secrete products external to the cell membrane

 

 

 

 

Lysosomes

1. Vessicles with digestive enzymes

 

 

2.  Used for intracellular digestion

 

 

3.  Tay-sach's disease: don't have necessary enzymes, die young

 

 

 

 

 

 

Peroxisome

1.  Has enzymes for oxidizing organic molecules with the formation of hydrogen peroxide which is subsequently broken down into water and oxygen

 

 

 

 

 

2.  Detoxifying cellular poisons such as alcohol

 

 

 

 

 

 

 

Vacuoles and Small Vesicles

1.  Membranous sac used for storage

 

 

2.  Plants have large vacuoles filled with fluid for support

 

 

 

 

 

 

 

Mitochondria

1.  "Powerhouse" where cellular respiration occurs

 

 

2.  Produce ATP

 

 

3.  Surrounded by a double membrane

 

 

4.  Can divide

 

 

 

 

 

Cristae

Inner membrane foldings or shelves which penetrate inner matrix

 

 

 

 

Matrix

1.  Inner space, is a semifluid,

 

 

2.  Has DNA, ribosomes and enzymes that break down sugars

 

 

 

 

 

 

Chloroplasts

1.  Plastid where photosynthesis takes place

 

 

2.  Surrounded by a double membrane

 

 

 

 

 

Thylakoids

Flattened sacs made of membranes

 

 

 

 

Grana

Stack of thylakoids

 

 

 

 

Stroma

1.  Fluid-filled space around the thylakoids,

 

 

2.  Contains DNA, ribosomes, and enzymes that make carbohydrates

 

Cytoskeleton

protein filaments that give cells structure

 

 

 

 

 

Thin filaments

actin for movement

 

 

 

 

Thick filaments

myosin combines with actin for muscle contractions

 

 

 

 

Intermediate filaments

may support the nuclear envelope, plasma membrane or form cell-to-cell junctions, ex) keratin in skin

 

 

 

 

Microtubules

small hollow tubes made of tubulin

 

 

 

 

Centrosome

maintain shape of cell, acts as tracks for organelle movement, ex) kinesin

 

 

 

 

Centrioles

 

 

(Microtubial Organizing Center)-used during animal cell division to move chromosomes apart by spindle fibers

 

 

 

 

Basal bodies

control the movement of cilia or flagella, 9 + 2 pattern of microtubules

 

 

 

 

Cilia

small "hairs" that "beat" together

 

 

 

 

Flagella

longer than cilia, move like a whip or oar

 

 

 

 

 V.  Margulis' Endosymbiotic Theory:

 

            A.            Theory

 

                        1.  Mitochondria and chloroplasts originated from

                             prokaryotes that were taken up by a larger cell and

                             remained functional and heritable.

 

            B.            Evidence

 

                        1.  Mitochondria and chloroplasts are the same size as bacteria and

                             similar in structure

                        2.  Bound by a double membrane-outer membrane cell vesicle?

                        3.  Have DNA, in the form of a circular loop, and can divide

                        4.  Have their own ribosomes and make their own protein

 

                        5.  Ribosomal RNA similar to bacterial rRNA

 

VI.  Comparison of plant and animal cells

 

            A.  Plant cells:  cell walls, chloroplasts

            B.  Animal cells:  centrioles