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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
X4
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
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
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