the ultrastructure of cells (1.2) - sammons...
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The Ultrastructure of Cells (1.2)IB Diploma Biology
Explain why cells with different functions have different structures.• Cells have different organelles depending on
the primary function of the cell type.
– This allows cells to specialize for a specific task which can lead to increased complexity of the entire organism.
Identify Ultrastructures Visible in a micrograph of a eukaryotic cell
Nucleus
Look for nuclear membrane and the nucleolus
http://images.wellcome.ac.uk/
Rough Endoplasmic Reticulum
Smooth Endoplasmic Reticulum
“Spot” the
difference?
Endoplasmic
Reticulum
The ‘spots’ are the
difference!
The Rough
Endoplasmic Reticulum
is peppered with
ribosomes that give it
the rough appearance
Proteins synthesized
here are secreted
Smooth ER is site of lipid
production
Cell Membrane Vs Cell Wall
http://commons.wikimedia.org/wiki/File:C_Golgi.jpg
http://commons.wikimedia.org/wiki/File:Golgi_in_the_cytoplasm_of_a_macrophage_in_the_alveolus_(lung)_-_TEM.jpg
I shall name it………The internal reticular
apparatus!!Pretty catchy… no?*
*Everybody
thought that was
a terrible name,
so they called it
the Golgi
apparatus
instead
Camillo
Golgi Look for stacks of membrane, typically
further from the nucleus
The Golgi Apparatus is a
flattened stack of membranes
responsible for the packaging
and delivery of proteins
Lysosomes are simple, membrane-bound organelles full of
enzymes that digest engulfed bacteria and viruses and
large molecules for recycling.
Small clear-ish sac, hard to
distinguish from vesicles unless
contents are visible.
Mitochondria in mammalian lung cells
The Mitochondrion (pl. Mitochondria)
• The ‘power house’ of the cell
• Has a smooth outer membrane and
a folded inner membrane
• Where aerobic respiration occurs
Free Ribosomes:
• 80s sized in
eukaryotes (v. 70s
size in prokaryotes)
• Proteins
synthesized for
use within the cell
(i.e. enzymes used
in the cytoplasm)
Vacuoles & Vesicles:• Animal cells sometimes have small vacuoles for digestion
• Unicellular organisms have contractile vacuoles for expelling water
• Plant cells have large vacuoles that hold water and food
• Vesicles are small clear lipid sacs used for transport
Chloroplasts
• Site of Photosynthesis in Plant Cells
• Stacks of Thylakoids
Centrioles & Microtubules:
• Centrioles are bundles of
microtubules found in Animal Cells
• Microtubules separate
chromosomes in cell division and
make-up cilia and flagella
S1.2.3 Interpret electron micrographs to identify organelles and deduce the function of
specialized cells.
S1.2.3 Interpret electron micrographs to identify organelles and deduce the function of
specialized cells.
Identify the labeled structures in this liver cell TEM image.
Source: http://www.udel.edu/biology/Wags/histopage/empage/empage.htm
What can you
see?
Given a micrograph of a cell, deduce the function of the cell based on the
structures present.
Cells will have specialized shapes given their function. For example:
• Small intestine villus cell: microvilli increase surface area absorption
• Many mitochondria for
fueling active transport.
• Exocrine gland cells of the
Pancreas secrete digestive
enzymes into small intestine
• Enzymes are proteins, so
these cells must produce
proteins in large quantities
• Organelles involved:• Rough ER
• Vesicles
• Golgi Apparatus
• Plasma membrane
Hormone secreting cell: many vesicles holding
the hormones until secretion.
• Palisade mesophyll cells
carry out most of the
photosynthesis in plant cells
• Organelles involved:• Chloroplasts
• Mitochondria
• Large Vacuole
Photosynthetic plant cell: chloroplasts for
performing photosynthesis
DRAWINGS
● Look at the following three electron micrographs carefully and examine the significant features that will be included in the drawing.
● DRAW ONLY WHAT YOU SEE!! Do not include what you think you should see. ● All drawings must be done in pencil ONLY. ● Drawings must be large and clear so that features can be easily distinguished. Use
at least ½ page for each drawing.● No more than two drawings should be on a single page of unlined white paper. ● Always use distinct, single lines when drawing. ● All drawings must have the following indicated:
o Title (give a full, clear and concise title that explains what is being illustrated) o Magnification (indicate the magnification at which the specimen was drawn) o Labels (each label line must be straight and should not overlap with other
label lines; all labels must be to one side and aligned in a vertical column)o Scale (always include a scale bar indicating the length or width of the
specimen drawn)
Drawing sample 1: “Typical Homo sapiens
Pancreas Beta Cell”
1. Observe the cells in the
micrograph image.
2. Draw a single cell on
unlined white paper.
3. Title the drawing.
4. Label structures (note:
darkest circles are secretory vesicles that
will secrete insulin out of the cell and into
the bloodstream).
5. Add a scale bar to
indicate that the cell is
10 um long. (Source)
6. Calculate the drawing
magnification.
Drawing sample 2: “Typical Zea mays Leaf
Cell”
1. Observe the cell in the
micrograph image.
2. Draw a single cell on
unlined white paper.
3. Title the drawing.
4. Label structures
5. Add a scale bar to
indicate the length of
the cell.
6. Calculate the drawing
magnification.
Drawing sample 3: Typical Plant Cell
1. Observe the cells in the
micrograph image.
2. Draw a single cell on
unlined white paper.
3. Title the drawing.
4. Label structures
5. Calculate size if
magnification is 1800x.
Endomembrane System
WHAT IS A SYSTEM?
Inside membraneMultiple
parts working together
with shared function
“A system of membranes inside
the cell membrane”
Endomembrane System
Membranes within the eukaryotic cell that work together to modify, process and ship molecules around and out of the cell.
List adjectives to describe a membrane.
Endomembrane System
Membranes within the eukaryotic cell that work together to modify, process and ship molecules around and out of the cell.
FLUID
MOSAIC
Like a bubble
Phospholipid bilayer
Semipermeable
Endomembrane System
• All made of phospholipid bilayer
• Includes:– Nuclear envelope
– Rough ER
– Smooth ER
– Transport vesicles
– Golgi apparatus
– Secretory vesicles
– Lysosomes
– Vacuole
proteins
transportvesicle
Golgiapparatus
vesicle
smooth ER
rough ER
nuclear porenucleus
ribosome
cellmembrane protein secreted
cytoplasm
The Endomembrane System
production of mRNA
from DNA in nucleus
mRNA out of nucleus
through nuclear pore
DNA
NucleusmRNA
nuclearmembrane
mRNA
nuclear pore
3. Packaging (protein into a
vesicle)
2. Translation (mRNA – protein)
1. Transcription (DNA – RNA)
• Using RNA code, a protein is
synthesized on a ribosome
and transported in channels of
the ER.
• Protein is packaged into
transport vesicles …
Endoplasmic Reticulum
• Function
– processes proteins
– manufactures membrane
• Structure
– membrane connected to nuclear envelope & extends throughout cell
Types of ER
rough smooth
4. Transport (protein in vesicle moves to
Golgi)
Protein is packaged into
transport vesicles and … travels
to the Golgi along the
cytoskeleton “track”
5. Modify (Golgi changes or adds to the
protein)
Vesicle fuses with the Golgi and
protein is modified as it passes
through.
Golgi Apparatus
transport vesicles
secretoryvesicles
• Function
– finishes, sorts, tags & ships products
• like “UPS shipping department”
– ships products in vesicles
• membrane sacs
• “UPS trucks”
Details of cis-trans
cisterna are not
required
6. Secrete (vesicle moves protein towards cell
membrane)
Completed protein is packaged
into secretory vesicles for
release from the cell or stored in
vesicle or lysosome if used
inside the cell.
Vesicle transport
7. Exocytosis (vesicle fuses with the cell
membrane, releases protein)
Vesicle fuses with the cell
membrane and protein is
released
Concept Check:
What has happened to the size of the membrane when a vesicle releases its protein contents to the outside of the cell?
Draw a picture to illustrate.
http://www.stolaf.edu/people/giannini/flashanimat/cellstructures/endomembrane%20protein%20synthesis.swf
Where did it come from?
The hypothesis is that eukaryotes evolved from prokaryotes.
In the early prokaryotic cells, there was an infolding of the plasma membrane into the cytoplasm.
The infolded membrane began to specialize for particular tasks.
This would explain why the endomembrane system is a phospholipid bilayer, just like the cell membrane.
Origin of Eukaryotic Cells
• Earth is 4.6 byo
• Life originated 3.5–4.0 bya
• Prokaryotes dominated earth for about 1by
Cyanobacteria•A type of prokaryote with much infolding of the cell membrane
•Capable of performing photosynthesis, which releases oxygen into the atmosphere
Cyanobacterium heterocyst
Oxygen atmosphere• Oxygen begins to accumulate 2.7 bya
• evidence in banded iron in rocks (rusting)
• makes aerobic respiration possible
• nearly all are aerobic,
–they depend on free oxygen to carry out their metabolic processes
• Accordingly, they could not have evolved before at least some free oxygen was present in the atmosphere
Eukaryotes
Two processes are thought to have led to the origin of eukaryotes….
1. Infoldings of the prokaryotic cell membrane
2. Endosymbiosis
Development of internal membranes• create internal micro-environments
(“compartments”)
• advantage = increase efficiency
infolding of theplasma membrane
DNA
cell wall
plasmamembrane
Prokaryoticcell
Prokaryotic ancestor of eukaryotic cells
Eukaryoticcell
endoplasmicreticulum (ER)
nuclear envelope*note double membrane
nucleus
plasma membrane
~2 bya
Check: Given what you know about infolding and the cell membrane as
a phospholipid bilayer:
• Why is the nuclear membrane a DOUBLE membrane (two layers of bilayer)
REMEMBER: Two processes are thought to have led to the origin of
eukaryotes….
1. Infoldings of the prokaryotic cell membrane
2. Endosymbiosis
Endosymbiosis
Ancestral eukaryotic cell
Eukaryotic cellwith mitochondrion
internal membrane
systemaerobic bacterium mitochondrion
Endosymbiosis
• FIRST early eukaryotic cells engulfed aerobic bacteriabut did not digest them
• Led to the origin of mitochondria
• Mutually beneficial relationship
mitochondrion
chloroplast
Eukaryotic cell with
chloroplast & mitochondrion
Endosymbiosis
Endosymbiosis
• THEN early eukaryotic cells engulfed
photosynthetic bacteria
but did not digest them• Led to origin of chloroplasts
• mutually beneficial relationship
Eukaryoticcell with mitochondrion
• In this relationship one cell lived within the other, which is a special type of symbiosis called endosymbiosis
• in some cases of a symbiotic relationship, one symbiont cannot live independently of the other
• This may have been the case early symbiotic prokaryotes that became increasingly interdependent until the unit could exist only as a whole
Endosymbiosis
A model of the origin of eukaryotes
Theory of Endosymbiosis
Lynn MargulisHow is the word “theory” in science
different than the use of the word theory in
every day language?
Both mitochondria & chloroplasts
– Resemble bacterial structure
–Are found in membranous envelopes (like a cell membrane)
–are the same approximate size as prokaryotes
–have 70s ribosomes
Structural Evidence
Both mitochondria & chloroplasts
–have circular naked DNA
–DNA shares common sequences with modern prokaryotes
Genetic Evidence
Both mitochondria & chloroplasts
–move freely within the cell
–reproduce independently from the cell through binary fission
–are inhibited by antibiotics
Functional Evidence
Where Did Organelles Come From ?
• Membranous infoldings
– Nucleus
– ER
– Golgi
– Lysosomes
– Vesicles
• Endosymbiosis
– Mitochondria
– Chloroplasts
Membrane infolding
Endosymbiotic theory
Bibliography / Acknowledgments
Jason de
Nys
Chris
Paine
