CHAPTER 6

A Tour of the Cell

CH. 6 WARM-UP

1. What are the 2 main types of cells? Which Domains do they consist of?

2. List 3 ways that eukaryotes differ from prokaryotes.

CH. 6 WARM-UP

1. How is the size of a cell related to its function?

2. Name 5 organelles or cell structures and their function.

CH. 6 WARM-UP

Animal Cell Plant Cell

Compare and contrast Animal vs. Plant Cells

CH. 6 WARM-UP

What is the structure & function of:1. Microtubules2. Microfilaments3. Intermediate filaments

CH. 6 WARM-UP

What is the function of:1. Plasmodesmata2. Gap junctions3. Tight junctions4. Desmosomes

YOU MUST KNOW

Three differences between prokaryotic and eukaryotic cells.

The structure and function of organelles common to plant and animal cells.

The structure and function of organelles found only in plant cells or only in animal cells.

EARLY CONTRIBUTIONS• Robert Hooke - First person to see cells, he was

looking at cork and noted that he saw "a great many boxes. (1665)

• Anton van Leeuwenhoek - Observed living cells in pond water, which he called "animalcules" (1673)

• Theodore Schwann - zoologist who observed tissues of animals had cells (1839)

• Mattias Schleiden - botanist, observed tissues of plants contained cells ( 1845)

• Rudolf Virchow - also reported that every living thing is made of up vital units, known as cells. He predicted that cells come from other cells. (1850 )

THE CELL THEORY• 1. Every living

organism is made of one or more cells.

• 2. The cell is the basic unit of structure and function. It is the smallest unit that can perform life functions.

• 3. All cells arise from pre-existing cells. *Why is the Cell Theory

called a Theory and not a Fact?

THREE FEATURES OF CELLS

1.   Plasma (Cell) Membrane  -  serves as a barrier, regulates what enters and leaves the cell    * We go into much more detail in the next chapter on how this works*

 

2.  GENETIC MATERIAL

1. provides cellular "blueprint" that controls the functions of the cell

2. In the form of DNA (Deoxyribonucleic acid)

3. DNA is universal for all cells, an all living things - evidence of common ancestry

4. Chromatin is the complex of proteins and DNA, it condenses into chromosomes before cell division

*We will go into much greater detail in a later unit on GENETICS*

3. CYTOPLASM  (CYTOSOL)1.  Located within the plasma membrane

2. contains water, salts, and other chemicals

3. organelles float within this jelly-like substance

Microtubules and filaments support the inner structure of the cell

HOW WE STUDY CELLS

Biologists use microscopes and the tools of biochemistry to study cells

CELLS ARE ALWAYS SMALL,  HOW SMALL DEPENDS ON THE TYPE OF CELL

CELLS CAN COME IN A VARIETY OF SHAPES

Single Cheek Cell - at different illuminations

FIGURE 4.3

Size range of cells

Note that light microscopes can not magnify as well as electron microscopes

CELL SIZE AND SCALEhttp://learn.genetics.utah.edu/content/begin/cells/scale/

Scale of the Universe:

http://www.onemorelevel.com/game/scale_of_the_universe_2012

Cells must be small to maintain a large surface area to volume ratiosurface area to volume ratio

Large S.A. allows rates of chemical exchange between cell and environment

SURFACE AREA EXAMPLE (ANIMALANIMAL):

Small Intestine: highly folded surface to increase absorption of nutrientsVilliVilli: finger-like projections on SI wallMicrovilliMicrovilli: projections on each cell

FOLDS FOLDS VILLI VILLI MICROVILLI MICROVILLI

SURFACE AREA EXAMPLE (PLANTPLANT):

Root hairsRoot hairs: extensions of root epidermal cells; increase surface area for absorbing water and minerals

Light Microscopy (LM) vs. Electron Microscopy (EM)

COMPARISONS OF SCOPES

Visible light passes through specimen

Refracts light so specimen is magnified

Magnify up to 1000X Specimen can be

alive/moving Color

Focuses a beam of electrons through/onto specimen

Magnify up to 1,000,000 times

Specimen non-living and in vacuum

Black and white

Light Electron

ELECTRON MICROSCOPY

2-D Creates a flat image

with extreme detail Can enhance contrast

by staining atoms with heavy metal dyes

3-D Used for detailed study

of surface of specimen Gives great field of

depth

Transmission (TEM) Scanning (SEM)

2 TYPES OF CELLS:

1. Prokaryotes: Domain Bacteria & Archaea

2. Eukaryotes (Domain Eukarya): Protists, Fungi, Plants, Animals

A PROKARYOTIC CELL (BACTERIA)

PROKARYOTE CELLS

• no membrane bound nucleus, chromosomes grouped together in an area called the "nucleoid"

• no membrane bound organelles• smaller than eukaryotes• Include the domains Bacteria and Archaea

• have cell wall and cell membrane, some have a capsule on the outside

• ribosomes make protein• consist of bacteria and

archaebacteria• Appendages

include:  fimbriae/pili, flagella

*pili are usually longer and fewer than fimbriae, both function for attachment and recognition of host cells (or (sexual reproduction)

FIGURE 4.4A

E. coli

EUKARYOTES

• has a membrane bound nucleus• has membrane bound organelles in

cytoplasm• Organelles perform specific functions• much larger than prokaryotes

Organisms within the animal, plant and fungi kingdoms are all eukaryotes

PROKARYOTE VS. EUKARYOTE “before” “kernel” No nucleus DNA in a nucleoid Cytosol No organelles other

than ribosomes Small size Primitive i.e. Bacteria &

Archaea

“true” “kernel” Has nucleus and

nuclear envelope Cytosol Membrane-bound

organelles with specialized structure/function

Much larger in size More complex i.e. plant/animal cell

KNOW THIS CHART!

Characteristic Prokaryotic Cells Eukaryotic Cells

Plasma Membrane Yes Yes

Cytosol with organelles

Yes Yes

Ribosomes Yes Yes

Nucleus No Yes

Size 1 um- 10 um 10 um- 100 um

Internal membranes

No yes

CELL ORGANELLES

NUCLEUS Function: control center of cell Contains DNA Surrounded by double membrane (nuclear

envelope)Continuous with the rough ER

Nuclear pores: control what enters/leaves nucleus

Chromatin: complex of DNA + proteins; makes up chromosomes

Nucleolus: region where ribosomal subunits are formed

NUCLEUS Contains DNA Function: control center of cell Surrounded by double membrane (nuclear

envelope)Continuous with the rough ER

Nuclear pores: control what enters/leaves nucleus

Chromatin: complex of DNA + proteins; makes up chromosomes

Nucleolus: region where ribosomal subunits are formed

RIBOSOMES Function: protein synthesis Composed of rRNA + protein Large subunit + small subunit Types:

1. Free ribosomes: float in cytosol, produce proteins used within cell

2. Bound ribosomes: attached to ER, make proteins for export from cell

ENDOMEMBRANE SYSTEM:Regulates protein traffic & performs metabolic functions

ENDOPLASMIC RETICULUM (ER) Network of membranes and sacs Types:

1. Rough ER: ribosomes on surface Function: package proteins for secretion,

send transport vesicles to Golgi, make replacement membrane

2. Smooth ER: no ribosomes on surface Function: synthesize lipids, metabolize

carbs, detox drugs & poisons, store Ca2+

ENDOPLASMIC RETICULUM (ER)

GOLGI APPARATUS Function: synthesis & packaging of materials (small

molecules) for transport (in vesicles); produce lysosomes

Series of flattened membrane sacs (cisternae)Cis face: receives vesiclesTrans face: ships vesicles

LYSOSOMES Function: intracellular digestion; recycle cell’s

materials; programmed cell death (apoptosis) Contains hydrolytic enzymes

VACUOLES Function: storage of materials (food, water,

minerals, pigments, poisons) Membrane-bound vesicles Eg. food vacuoles, contractile vacuoles Plants: large central vacuole -- stores water,

ions

MITOCHONDRIA Function: site of cellular respiration Double membrane: outer and inner membrane Cristae: folds of inner membrane; contains

enzymes for ATP production; increased surface area to ATP made

Matrix: fluid-filled inner compartment

CHLOROPLASTS Function: site of photosynthesis Double membrane Thylakoid disks in stacks (grana); stroma

(fluid) Contains chlorophylls (pigments) for

capturing sunlight energy

ENDOSYMBIONT THEORY

Mitochondria & chloroplasts share similar origin

Prokaryotic cells engulfed by ancestors of eukaryotic cells

Evidence: Double-membrane

structureHave own ribosomes &

DNAReproduce

independently within cell

PROKARYOTE VS EUKARYOTE CELLSEndosymbiosis theory: 

All organelles seem to share many properties with bacteria. Lynn Margulis proposed endosymbiont hypothesis: that organelles derived from ancient colonization of large bacteria (became the eukaryotic cell) by smaller bacteria (became the mitochondria, chloroplast, etc.) Symbiosis = "living together". *Mitochondria & Chloroplasts have their own DNA

Animation at Microbiological Concepts

PEROXISOMES Functions: break down fatty acids; detox

alcohol Involves production of hydrogen peroxide

(H2O2)

CYTOSKELETON: NETWORK OF PROTEIN FIBERS Function: support, motility, regulate

biochemical activities

Microtubules MicrofilamentsIntermediate

Filaments

• Protein = tubulin• Largest fibers• Shape/support cell• Track for organelle

movement• Forms spindle for

mitosis/meiosis• Component of

cilia/flagella

• Protein = actin• Smallest fibers• Support cell on

smaller scale• Cell movement• Eg. ameboid

movement, cytoplasmic streaming, muscle cell contraction

• Intermediate size• Permanent fixtures• Maintain shape of

cell• Fix position of

organelles

3 TYPES OF CYTOSKELETON FIBERS:

Microtubules MicrofilamentsIntermediate

Filaments

3 TYPES OF CYTOSKELETON FIBERS:

Centrosomes: region from which microtubules growAlso called microtubule organizing centerAnimal cells contain centrioles

CILIA & FLAGELLA Flagella: long and few; propel through water Cilia: short and numerous; locomotion or move fluids Have “9+2 pattern” of microtubules

EXTRACELLULAR MATRIX (ECM) Outside plasma membrane Composed of glycoproteins (ex. collagen) Function: Strengthens tissues and transmits external

signals to cell

INTERCELLULAR JUNCTIONS (ANIMAL CELLS)

Tight junctions: 2 cells are fused to form watertight seal

Desmosomes: “rivets” that fasten cells into strong sheets

Gap junctions: channels through which ions, sugar, small molecules can pass

PLANT CELLS

Cell wall: protect plant, maintain shapeComposed of

cellulose Plasmodesmata:

channels between cells to allow passage of molecules

Plant Cells Only Animals Cells Only

Central vacuoles Lysosomes

Chloroplasts Centrioles

Cell wall of cellulose Flagella, cilia

PlasmodesmataDesmosomes, tight and gap junctions

Extracellular matrix (ECM)

Parts of plant & animal cell p 108-109

HARVARD CELL VIDEOhttp://multimedia.mcb.harvard.edu/anim_innerlife.html