Download A new organelle: Magnetosomes

A new organelle: Magnetosomes
•  Why? This may simplify
aquatic searches for the
correct depth by keeping the
cell in the same direction…
like a sea anchor
•  Organelles that contain
magnetic iron particles
•  They are aligned in a linear
array and with partial
membranes
•  Magnetosomes help cells to
keep their orientation to the
magnetic field of the earth
Wednesday, January 11th, 2017
Class 7 Learning Goals
The Endomembrane System and Cell Movement
•  After this class, you should be able to:
–  Trace the path of transport and development for a protein or lipid
moving through the endomembrane system.
–  Explain the dynamic nature of cytoskeletal elements
–  Analyze and identify errors in a description of cellular movement
Organelle
Cellular Role
Nucleus
(Covered in great depth in 355)
Lysosome
Peroxisome
Vacuole
Mitochondria
(Covered in depth in Week 5)
Chloroplast
(Covered in great depth in 220)
Rough ER
Smooth ER
Golgi Apparatus
Ribosomes
(Covered in depth next week)
Cytoskeleton
Plasma membrane
(Covered in depth yesterday)
Specialized
components
Microenvironment
Clicker Question #9
The nucleus is the organelle in which DNA is stored
and used.
Which is most likely about the chemical
microenvironment of the nucleus in most cells?
The nuclear microenvironment:
1.  Contains all of the proteins in a cell because the
protein-building instructions are located therein
2.  Has a diversity of mutation-causing chemicals
3.  Allows import of DNA
4.  Is relatively protective against mutation-causing
rays and chemicals
Problem:
Some proteins need to be in the plasma membrane
Some proteins need to be sent outside the cell
…but proteins are far too big to go through even one
side of the plasma membrane…
The EndoMembrane System:
The protein & lipid factory
•  Comprised of
– the rough ER,
– the smooth ER, and
– the Golgi apparatus,
•  The EMS is the primary system
for protein and lipid synthesis.
This system allows
production, processing and
transport of specific and
diverse molecules.
Nucleus
EMS Organelles: The Rough ER
A Protein Synthesis and Processing Complex
• 
• 
• 
• 
The rough ER is contiguous
with the nuclear membrane
New proteins are directly
inserted into the ER
Microenvironment: noncytoplasmic molecular
Lumen of
conditions for protein folding
rough ER
After processing, proteins are
transported to other destinations Ribosomes
on outside
by controlled vesicle budding
Free ribosomes
in cytoplasm
Clicker Question #4
Many functional proteins are translated in the
cytoplasm with no need for the Endomembrane
System.
What is a good reason to use the EMS?
1. 
2. 
3. 
4. 
5. 
To make proteins that are delivered to a specific
organelle
To make proteins that are delivered to the plasma
membrane
To make proteins that fold differently than they would if
they were translated in the cytoplasm
To make proteins with lipid modifications
All of these are good reasons to use the EMS for
translation
EMS Organelles: Smooth ER
A Lipid-Handling Center and Storage Site
•  The smooth ER is the major
processing zone for lipids
•  Smooth ER lacks ribosomes,
naturally
•  ER hosts non-cytoplasmic
molecular conditions and
specialized enzymes
•  After processing, lipids are
transported to other
destinations by controlled
vesicle budding
Smooth endoplasmic reticulum
Lumen of
smooth ER
EMS Organelles: The Golgi Apparatus
A Site of Protein Processing
The cis face is oriented
towards the rough ER
• 
• 
• 
• 
A site for carbohydrate
modification of proteins
Packaging and transport to
cellular locations with
vesicles
Formed by a series of
stacked flat membranous
sacs called cisternae.
Receives products from
the rough ER and sends
finished products to the
cell surface in vesicles.
The trans face is oriented
away from the rough ER
Golgi apparatus
cis face
Vesicle
Lumen
Cisternae
Vesicles
trans face
Golgi Video
Clicker Question #5
What is a reasonably hypothesis about the microenvironment
of the Smooth Endoplasmic Reticulum?
1.  It is more hydrophobic than the rest of the cell
2.  It would be worse for protection of nucleic acids
than the microenvironment in the nucleus
3.  It is good for breaking down protein
4.  It is the same as the cytoplasm.
Organelles: The Cytoskeleton
•  The cytoskeleton is a complex
network of fibers that helps
maintain cell shape by providing
structural support.
•  The cytoskeleton is dynamic; it
changes to alter the cell’s shape,
to transport materials in the cell, or
to move the cell itself.
•  The three types of cytoskeletal
elements are
–  actin filaments,
–  intermediate filaments, and
–  microtubules.
Raven & Singer, 7th Edition
Organelles:
Cytoskeletal building
Peer Instruction
•  The smallest cytoskeletal elements are
actin filaments, also known as microfilaments.
•  Actin filaments form by polymerization of individual actin molecules.
the ‘-’ end
the ‘+’ end
‘actin polymerase’
‘actin depolymerase’
• 
How does this filament move to the right?
You have:
Peer Instruction
a cytoskeletal filament
a motor protein
a vesicle
a plasma membrane around the cell
Draw the answers:
How does your cell move part of the plasma membrane?
How does your cell move a vesicle towards an organelle?
Video: Cell crawling
1. ‘Crawling’
time 1
time 2
nucleus
Peer Instruction
time 3
nucleus
2. ‘Chasing’
nucleus
nucleus
target
3. ‘Contraction’
nucleus
nucleus
Clicker Question #1
Which would be a problem for a single-celled
organism if all depolymerases were inactivated?
1. 
2. 
3. 
4. 
5. 
6. 
All cell movement would be stopped
Cells could extend towards a goal, but rarely reach it
Cells would run out of actin monomers
Cells could not sense target molecules
Cells would not be able to undergo meiosis
No new actin polymers would be formed
Clicker Question #2
nucleus
This cell is changing
direction to move towards
a green ‘prey’ cell.
Which answer is FALSE?
1)  The cell has membrane proteins.
2)  The ‘prey’ is losing molecules into the
environment.
3)  Actin is polymerizing.
4)  The cell is anticipating the destination of the ‘prey’.
Clicker Question #3
time 1
time 3
nucleus
nucleus
Which answer is true about the location marked:
1) 
2) 
3) 
4) 
There are no actin polymerase enzymes here.
There are active actin polymerase enzymes here.
There are inactive polymerase enzymes here.
Actin polymerases found here may be
allosterically regulated.
?
Clicker Question #3
Which would be a problem for a single-celled
organism if all depolymerases were inactivated?
1. 
2. 
3. 
4. 
5. 
6. 
All cell movement would be stopped
Cells could extend towards a goal, but rarely reach it
Cells would run out of actin monomers
Cells could not sense target molecules
Cells would not be able to undergo meiosis
No new actin polymers would be formed
Key Concepts
• 
• 
• 
• 
• 
• 
• 
Why do you expect amino acid side chains on the outside of an integral
membrane protein (but within the bilayer) to be hydrophobic?
Explain the matches between three possible transport situations…
–  facilitated diffusion, active transport, and passive diffusion
…and three cellular situations
–  a need for extreme rapid transport, intake of a common large molecule,
letting a rare waste molecule out of the cell
What specialized enzymes would you expect in a mitochondrion? In the Rough
ER? What microenvironment is unique to the nucleus? To the peroxisome?
Imagine:
–  1) a lipid destined to become part of the plasma membrane, and
–  2) a protein that will be released outside of the cell.
•  Describe the differences in the pathways taken by each molecule.
Where or when does each pathway utilize the joining of lipid membranes?
What would happen to a crawling cell that instantly lost all actin polymerization
enzymes? Be as specific as possible.
Where is energy used in the movement of a single cell?
Bonus question: Where does the energy come from to move Golgi
vacuoles to different parts of the cell? There are two very different answers…