Transcript Transmission electron microscopes (TEMs)

Quick Recap!!
You need to know this stuff for your exam!!!
Overview: The Fundamental Units of Life
“The Cell Theory”
• The modern tenets of the Cell Theory include:
1. all known living things are made up of cells.
2. the cell is structural & functional unit of all living
things.
3. all cells come from pre-existing cells by division.
(Spontaneous Generation does not occur).
4. cells contains hereditary information which is
passed from
cell to cell during cell division.
5. All cells are basically the same in chemical
composition.
6. all energy flow (metabolism & biochemistry) of
life occurs
within cells.
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To study cells, biologists use microscopes and
the tools of biochemistry
• Though usually too small to be seen by the
unaided eye, cells can be complex
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Microscopy
• Scientists use microscopes to visualize
cells too small to see with the naked eye
• In a light microscope (LM), visible light
passes through a specimen and then
through glass lenses, which magnify the
image
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• The quality of an image depends on
• Magnification, the ratio of an object’s image
size to its real size
• Resolution, the measure of the clarity of the
image, or the minimum distance of two
distinguishable points
• Contrast, visible differences in parts of the
sample
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• LMs can magnify effectively to about 1,000
times the size of the actual specimen
• Various techniques enhance contrast and
enable cell components to be stained or
labeled
• Most subcellular structures, including
organelles (membrane-enclosed
compartments), are too small to be resolved
by an LM
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
• Two basic types of electron microscopes
(EMs) are used to study subcellular structures
• Scanning electron microscopes (SEMs)
focus a beam of electrons onto the surface of a
specimen, providing images that look 3-D
• Transmission electron microscopes (TEMs)
focus a beam of electrons through a specimen
• TEMs are used mainly to study the internal
structure of cells
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• Robert Hooke- used a compound microscope to see
chambers within a cork and named them “cells”
• Schleiden and Swann- works states that all plant and
animals are made of cells.
Cell Structure
Chapter 6
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
animal cells
• How different cell types show difference in subcellular components
• How internal membranes or organelles contribute to cell function
• How cell size and shape affect the overall rate of nutrient intake and
waste elimination
Prokaryotes
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Found in the domains Bacteria and Archaea(single-celled microorganisms. )
Contain a single, circular chromosome in nucleoid region
Contain no membrane-bound organelles
Very small in comparison to eukaryotes
Interesting Facts
• Prokaryotes dominate the biosphere
• Collective mass outweighs all eukaryotes combined by at
least 10fold
• More prokaryotes inhabit a handful of fertile soil or in the
mouth or skin of a human than the total number of people
who have ever lived!
• Found wherever there is life
• Especially in extreme environments
• There are a hundred billion prokaryotes per milliliter of fluid
in the human colon.
Eukaryotes
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Belong to domain Eukarya, includes animals, plants, fungi, protists (mainly
unicellular animals and plants, that do not form tissues.)
Membrane bound nucleus containing linear chromosomes
Membrane-bound organelles
Much larger than prokaryotes
Plasma Membrane
Ribosomes
Membrane-bound
organelles
Nucleus
Size
Prokaryotes
Yes
Yes
No
Eukaryotes
Yes
Yes
Yes
No
1-10um
Yes
10-100um
The Nucleus
• Contains DNA
• Surrounded by a lipid bilayer (membrane) called the nuclear
envelope which is connected to the rough endoplasmic reticulum
and contains nuclear pores to allow things to enter and leave the
nucleus
• Nucleolus – region (not really a
structure) where rRNA combines
with proteins to form ribosomal
subunits
Ribosomes
• Composed of rRNA and protein – one large subunit and one small
• Sites of protein synthesis
• Can be free-floating or bound to endoplasmic reticulum
• Free-floating – produce proteins to be used in the cell
• Bound – produce proteins that will be exported out of the cell
Endoplasmic Reticulum
• Network or folded membranes and sacs – space between called
cisternal space
• Smooth– no ribosomes associated
• Metabolism of lipids and carbs
• Detoxification of drugs and poisons
• Rough – covered in ribosomes
• Ribosomes synthesize proteins
which are then wrapped in
vesicles made of the membrane
of the ER
Golgi Apparatus
• Stacks of flattened sacs of
membrane called cisternae
• Modifies, stores, and ships out
proteins
• Sacs are polar with cis side
receiving incoming proteins from
the RER and shipping them out
from the trans side
Camilo Golgi
Lysosomes
• Membrane-bound sacs of
hydrolytic enzymes to digest
unwanted or old molecules
and organelles in the cell
• Release to monomers
produced by their reactions
back in to the cell
• Enzymes involved require a
low pH to function, so if
lysosome breaks open, they do
not work
Peroxisomes
• Membrane-bound sacs
• Transfer hydrogen from
compounds to oxygen, forming
H2O2 (toxic to cell)
• Contains enzymes to break
down the H2O2
• Breaks down fatty acids so that
they can be used by the
mitochondria
• Detoxify substances (alcohol)
by transferring its hydrogen to
oxygen
Peroxisomes
• Membrane-bound sacs
• Transfer hydrogen from compounds to oxygen, forming H2O2 (toxic
to cell)
• Contains enzymes to break down the H2O2
• Breaks down fatty acids so that they can be used by the
mitochondria
• Detoxify substances (alcohol) by transferring its hydrogen to
oxygen
Vacuoles
• Membrane-bound sacs used for various reasons
• Contractile vacuoles in protists – contracts to expel water out of
the cell to prevent lysis in hypotonic environments
https://www.youtube.com/watch?v=pahUt0RCKYc
• Central vacuole in plants – can make up as much as 80% of a cell,
used for storage
Mitochondria
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Sites of cellular respiration – energy conversion from food to ATP
2 membranes – outer and inner
Cristae – folds of the inner membrane, increase surface area
Matrix – fluid filled inner compartment
Contains its own circular DNA and its own ribosomes
Chloroplasts
• Site of photosynthesis in plants – energy conversion from light to food
• Also contains its own circular DNA and ribosomes
• Double membrane structure
Endosymbiotic theory
• Mitochondria and chloroplasts have many characteristics of
prokaryotic cells – circular DNA, ribosomes
• Double membrane indicates they were engulfed by
another cell by endocytosis
• Eukaryotes arose from one prokaryote engulfing others
and the engulfed cells developing specialized functions
Cytoskeleton
• Network of protein fibers for support, motility, and regulation
• Microtubules – tubulin fibers, shape and support, tracks for
molecules to travel along, separate chromosomes during mitosis
and meiosis, form cilia and flagella
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Flagella – long tails to propel cells
Cilia – shorter and more numerous than flagella, can be used to move the
cell itself or to move things along outside the cell
Both in 9+2 pattern – 9 pairs of microtubules around a core of 2
microtubules
• Microfilaments – composed of actin, smaller than microtubules,
involved in muscle contractions
• Intermediate filaments – maintain shape, fix position of oragnelles
Centrosomes – near nucleus, region where where microtubules
grow
Centrioles – located within centrosomes, used during mitosis
and meiosis
Extracellular components
• Cell wall
• In plants, composed of cellulose, for shape and support
• Also in prokaryotes & fungi, composed of peptidoglycan & chitin
• Plasmodesmata – channels in cell walls between cells to allow
passage of materials from one cell to another
• Extracellular Matrix (ECM)
• Animal cells
• Composed of glycoproteins secreted by cell, mostly collagen
• Strengthens tissues, allows for transmittal of stimuli into the
cell
• Intercellular junctions (in
animal cells)
• Tight junctions – two
neighboring cells are fused
by their cell membranes
• Desmosomes – proteins
that link adjacent cells like
rivets, making strong
sheets
• Gap junctions – protein
channels connecting
adjacent cells so small
molecules can pass from
one to the next