BIOLOGY 1020

UNIT 3: A TOUR OF THE CELL

CHAPTER 4

READ P.54-71

Figure 4.1 shows

the size range of

cells compared

with objects both

larger and

smaller.

DEVELOPMENT OF THE CELL THEORY

• PEOPLE HAVE KNOWN ABOUT THE EXISTENCE OF CELLS FOR ONLY THE LAST 300 YRS OR SO

• EARLY MICROSCOPES ALLOWED SCIENTISTS TO DISCOVER WHAT WE NOW TAKE FOR GRANTED:

• ALL LIVING THINGS ARE MADE UP OF CELLS

• CELLS ARE FUNDAMENTAL UNITS OF LIFE

Paramecium

Onion skin cells

PARTS OF THE CELL

• Organelle - A membrane-bound

compartment or structure in a cell

that performs a special function.

• Eukaryotic cells are structurally

complex, and by definition are

organized, in part, by interior

compartments that are themselves

enclosed by lipid membranes that

resemble the outermost cell membrane.

The larger organelles, such as the

nucleus and vacuoles, are easily visible

with the light microscope.

SCIENTIST WHO HELPED THE CELL THEORY

• ROBERT HOOKE WRITES A BOOK, IN WHICH IT SHOWS ILLUSTRATIONS OF TREE BARK AS SEEN UNDER THE MICROSCOPE. THE DRAWING SHOWED COMPARTMENTS HE CALLED “CELLS”

• ANTONY VAN LEEUWENHOEK DESIGNED HIS OWN MICROSCOPE WITH A TINY SIMPLE LENS. HE REPORTED THAT HE SAW TINY “ANIMALCULES” OR TINY ORGANISMS THAT MOVED. THIS MARKED THE DISCOVERY OF BACTERIA, THE SIMPLEST OF ALL LIVING ORGANISMS. LEEUWENHOEK DEVELOPED MICROSCOPES THAT HAD THE CLEAREST QUALITY IMAGE AT THE TIME

Bark cells

Van Leeuwenhoek’s microscope

Van Leeuwenhoek

mastered lens

craft in his single-

lens scopes

(achieve

magnifications as

high as 500x with

little distortion).

• ROBERT BROWN OBSERVED CELLS FROM VARIOUS ORGANISMS ANDNOTICED THAT THEY ALL HAD A DARK REGION IN THEM. THIS DARK REGIONHAS RECENTLY BEEN CALLED THE NUCLEUS.

• MATTHIAS JACOB SCHLEIDEN, A BOTANIST, SAID THAT “ALL PLANTS AREMADE UP OF CELLS”.

• THEODOR SCHWANN WROTE THAT “ALL ANIMALS ARE MADE UP OF CELLS” AND THEN ADDED THAT “CELLS ARE ORGANISMS, AND ANIMALS AND PLANTSARE COLLECTIVES OF THESE ORGANISMS”.

• ALEXANDER CARL HENRICH BRAUN SAID “CELLS ARE THE BASIC UNIT OFLIFE.

• JUGO VON MOHL SAID THAT “PROTOPLASM IS THE LIVING SUBSTANCE OFTHE CELL” THEN ADDED THAT “CELLS ARE MADE UP OF PROTOPLASMENVELOPED BY A FLEXIBLE MEMBRANE”.

CELL THEORY

1. ALL LIVING ORGANISMS ARE MADE UP OF ONE OR MORE CELLS

2. CELLS ARE THE BASIC UNIT OF STRUCTURE AND FUNCTION IN ALL ORGANISMS

3. ALL CELLS ARE DERIVED FROM PRE-EXISTING CELLS (THIS MEANS THAT ALL CELLS HAD TO COME FROM OTHER CELLS)

ALL LIVING CELLS HAVE 4 COMMON COMPONENTS:

1. Cell Membrane

2. Cytoplasm

3. DNA

4. Ribosomes

1. CELL MEMBRANE

Outer boundary of the cell that separates the

internal contents of the cell from the external.

• Functions for protection

• Maintain internal balance – semi-permeable

as it allows materials in and out of the cell for

internal chemical reactions

• Found in plants and animals

FLUID MOSAIC MODEL OF CELL MEMBRANE

• The cell membrane controls movement in and out of the cell due

to its structure:

• Phospholipid bilayer

• Proteins

• Embedded carbohydrates

• Other lipids - cholesterol

Video -https://www.youtube.com/watch?v=jEY9Bie92aM

• It is “fluid” because the membrane is always changing its

permeability due to its needs (permeable, semi-permeable,

impermeable).

• Permeability is never static – allows different molecules and sizes to

enter and/or exit at suited times.

• Small molecules diffuse through phospholipid bilayer, larger

molecules and ions are able to get through membrane by way of the

larger proteins – they act as gatekeepers

2. CYTOPLASM

• Internal solution contained within the cell

• Made up 92% water – other 8% are solutes needed for chemical reactions

(ions, monomers, enzymes etc.)

• Functions – to cushion the cell and aid in transport of materials throughout

the cell

• Found in plants and animals

3. DNA – (DEOXYRIBOSE NUCLEIC ACID)

• Genetic molecule - but controls all activity of the cells including

reproduction.

• Directs the making of proteins

• Make RNA (messenger RNA) that gives messages to ribosomes in the

cytoplasm for building proteins eg. Enzymes needed for chemical

reactions.

• Found in plants and animals.

4. RIBOSOMES

• Tiny 2 part structure (2 part globular unit – large subunit attached to a

smaller subunit – like a typewriter – the mRNA threads the junction where

the subunits attach and the message is read) – so these small structures assist

in interpreting the code and building proteins. Helps in protein synthesis.

• Found throughout the cytoplasm and on rough endoplasmic reticulum.

• Found in both plants and animals.

VIDEO PARTS OF THE CELL

https://www.youtube.com/watch?v=URUJD5NEXC8

THERE ARE 2 MAIN TYPES OF CELLS

1. Prokaryotic Cells

• “Before the nucleus” – no membrane bound

organelles

• Simplest of all cell types – bacteria

• Single cellular – size from 1um- 10 um

• (micrometers 106 smaller than meter)

• NO nucleus – all genetic material is found

in a nucleoid region.

2. Eukaryotic Cells

• “True cells” – contain membrane bound organelles.

• Organelles work as a team to preform essential functions of the cell.

• Larger cells – 10-100 um

• Found in all protists, fungi, plants and animals

TOUR OF CELLS

• HTTPS://MEDIAPLAYER.PEARSONCMG.COM/ASSETS/LGR3YHSD1UCPKYG387FPJ7OH9ZV8LO

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MORE ORGANELLES

5. Nucleus

• brain or the control center of the cell

• Bound by a porous envelope (nuclear membrane) that

isolates cells DNA from the rest of the cell.

• Contains cell’s DNA – this region performs its own cellular reactions such

as DNA replication and RNA synthesis – makes ribosomes.

• 6. Endoplasmic Reticulum (ER)

• Both types are found together coming from the nuclear envelope and

spreads throughout the entire cell – delivering products where needed or

bring products to the golgi apparatus/body.

System of flattened membrane-bound sacs and tubes continuous with the outer membrane of the nuclear envelope that has two types of membranes……

Rough ER – has ribosomes and synthesizes proteins

Smooth ER – synthesizes phospholipids and packages macromolecules in vesicles for transport to other parts of the cell

• The ER

• produces an enormous variety of molecules,

• is connected to the nuclear envelope, and

• is composed of interconnected rough and smooth ER that have different structures and functions.

• Some products manufactured by rough ER are chemically modified and then packaged into transport vesicles, sacs made of membrane that bud off from the rough ER.

• Then these transport vesicles may be dispatched to other locations in the cell.

7. Golgi Apparatus or Golgi Body

• Flattened sacs that receive products from the ER to finish

processing and packaging products for “shipping”. LIKE THE FACTORY OF THE

CELL.

8. Lysosomes - contain enzymes for modifying proteins and lipids, package

finished products into bundles for transport to the cell membrane (for secretion out

of the cell). Garbage men of the cell. Most plant cells do not have these.

9. Vesicles – are simply a piece of golgi body membrane wrapped

around the product for export – these will fuse to the cell

membrane then expel its products outside the cell.

10. Mitochondrion

• Powerhouse of the cell. Designed for cellular respiration, a metabolic

pathway for the production of energy.

• Composed of a double membrane – inner membrane is highly folded

into cristae to increase its surface area to increase the rate of reaction!

• Found in both plants and animals.

11. Chloroplasts

• Like mitochondrion, it contains a double

membrane with a highly folded inner

membrane. This inner membrane is folded into

grana for maximum surface area.

• For metabolic pathway for photosynthesis. (eg.

Converting light energy into a usable form of

energy and producing glucose.)

• Fluid within the chloroplast is known as stroma.

• Found only in plants that photosynthesize.

12. Cytoskeleton

• A cellular skeleton found within the cytoplasm of the cells.

• Maintains cell shape, enabling cellular motion, internal transport

and cellular division.

• 3 types of cytoskeleton forms:

a. Actin filaments - small 7nanometer solid filaments found beneath cell

membrane that function to help cell change shape and important when

the cytoplasm splits to form two new cells.

b. Intermediate filaments – bit bigger 8-11 nm solid filaments – most stable

in terms of strength and function in maintaining the cell’s 3-D structure.

c. Microtubules – large hollow cylinders 25 nm that function in internal

transport of the cell, cellular movement (flagella and cilia), cellular

division (centrioles/centrosomes – only in animal cells) and the

production of new cells walls in plants

https://www.youtube.c

om/watch?v=H49P4m

eYyos

WHY CELLS NEED TO BE SMALL?

• The important point is that the surface area to the

volume ratio gets smaller as the cell gets larger. Thus, if

the cell grows beyond a certain limit, not enough

material will be able to cross the membrane fast enough

to accommodate the increased cellular volume.

• Cells are so little, so they can maximize their ratio of

surface area to volume. Smaller cells have a higher ratio

which allow more molecules and ions move across the

cell membrane per unit of cytoplasmic volume. Cells

are so small because they need to be able to get the

nutrients in and the waste out quickly.

1.

2.

2 TYPES OF ELECTRON MICROSCOPES

1. Transmission Electron Microscope – Need to thinly slice specimen

– gives a 2-D image

2. Scanning Electron Microscope – Need to coat specimen in a precious metal

so electrons can bounce off specimen.

- gives a 3-D image

Both microscopes use electrons and

electromagnets as a illuminations source to

focus specimens

3 and 4.

CELL SHAPES