Download Lectures 5-7 Study Guide

TA: Alberto Lopez
Adapted from Lauren Javier
FALL 2015
D4
Lectures 5-7 Study Guide
I have organized some terms and topics that I think are important. This does not mean that other topics
mentioned during lecture or in the book will not be tested. This guide is meant to clarify and emphasize
certain points, NOT to list everything you need to know. I will focus on tying things together across lectures,
and giving real-life examples of the biological principles that we are learning. Details that I include that I
think will be helpful, but that you don’t need to know, I will write in green. Questions to think about I will
write in blue.
Lecture 5: Single Cell Dynamics / Plasma Membrane
Eukaryotes vs. Prokaryotes
 “karyon” is Greek for “kernel”, a.k.a. nucleus  therefore, “prokaryotic” translates roughly to
“before the nucleus”. Prokaryotes don’t have nuclei.
Prokaryotic Cell
Eukaryotic Cell
Bacteria and Archaea
Protists, Fungi, Animal and Plant cells
Bound by a selective barrier, the plasma membrane
Inside cells have a semifluid, jellylike substance called cytosol which suspends subcellular components
Contains chromosomes (carry genes in the form of DNA)
Contains ribosomes (makes proteins)
Smaller in size (0.1-5 μm in diameter)
Larger in size (10-100 μm in diameter)
DNA is concentrated in the nucleoid (not membrane DNA is stored in the nucleus, bounded by a double
enclosed)
membrane
Cytosol lacks the variety of organelles seen in Cytosol contains a variety of organelles with
eukaryotic cells
specialized form and function
Plasma membrane structure
 Composition = phospholipid bilayer, embedded with…
a. Cholesterol: regulates fluidity. It sits between the fatty acid tails of phospholipids, separating
them enough that they don’t get too rigid, but also keeping them stuck together enough
that the membrane doesn’t get mushy. This is particularly important at extreme
temperatures. At moderate temperatures, cholesterol reduces membrane fluidity by
reducing phospholipid movement. At low temperatures it hinders solidification by
disrupting the regular packing of phospholipids. “fluidity buffer”
b. Proteins: transport molecules across the membrane (traffic regulation), act as receptors for
signal transduction, and attach to other cells or to the extracellular matrix.
i. Integral proteins: penetrate the hydrophobic interior of the lipid bilayer. Majority are
transmembrane proteins, spanning the membrane; contains a hydrophobic and
hydrophilic part.
ii. Peripheral proteins: are not embedded in the lipid bilayer but are loosely bound to
the surface of the membrane, often to exposed parts of integral proteins
c. Carbohydrates: act as “nametags” for a cell. Cells recognize each other by sensing what
kinds of carbohydrates are on each others’ surfaces. Carbohydrates are NOT receptors, but
they are RECOGNIZED BY receptors. For example, blood type (A / B / AB / O) is determined
by carbohydrates on the surfaces of red blood cells. If your immune system senses red blood
cells with different carbohydrates on their surfaces, it will attack. That’s why blood type
matching is so important.
 Fluid mosaic model:
d. “fluid” = NOT SOLID. Things within the membrane, like lipids and membrane proteins, are
constantly moving. Most of these movements are lateral (sideways). It is more than just an
Modified from materials prepared by Carley Karsten, 2013
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TA: Alberto Lopez
Adapted from Lauren Javier
FALL 2015

D4
envelope for the cell.
e. “mosaic” = made up of MANY DIFFERENT PARTS. Contains lipids, phospholipids, proteins,
glycoproteins, cholesterol, and more. It is more than simply a lipid bilayer.
Phospholipids = amphipathic = have hydrophilic heads and hydrophobic tails. This is essential for the
spontaneous assembly of phospholipid chains into cell-shaped structures: by forming a hollow
sphere with the lipid bilayer, the structure is most stable, because the hydrophobic regions are
protected from the aqueous environment.
Lecture 6: Membrane Trafficking: Passive and Active Transport
The plasma membrane is selectively permeable
 Small molecules, and some larger hydrophobic molecules, can pass directly across the membrane.
This does NOT require energy. Why is it easier for hydrophobic molecules to cross than it is for
hydrophilic molecules?
 Larger molecules, especially hydrophilic ones, require help crossing the membrane. Special channels
or transporters help with this, sometimes using energy and other times not.
 HUGE things, like other cells being taken in as prey, are usually transported in vesicles.
Transportation across the membrane
 PASSIVE TRANSPORT = diffusion and facilitated diffusion. Can use channels or carrier proteins.
Molecules move DOWN their concentration gradient.
 ACTIVE TRANSPORT = anything called a “pump” is likely an active transporter. Channels are never
used in active transport, but carrier proteins can be. Energy (usually in the form of ATP) is used to
move molecules AGAINST their concentration gradient.
 CO-TRANSPORT = how does glucose transport depend on activity of the sodium-potassium pump?
 BULK TRANSPORT = Exocytosis and Endocytosis
o Exocytosis: the cell secretes molecules outside of the cell (into the extracellular fluid) by the
fusion of vesicles with the plasma membrane
o Endocytosis: the cell takes in molecules and particulate matter by forming new vesicles from
the plasma membrane
 Phagocytosis “cellular eating”: used for HUGE molecules / other cells; pseudopodium
reaches out to engulf particles, then is pulled into the cell to become a food vacuole.
 Pinocytosis “cellular drinking”: NONSPECIFIC, constantly happening. Important for
recycling the membrane.
 Receptor-Mediated Endocytosis: very specific because receptors signal when to pull
things in. Very important for neurotransmission. This is what won the Nobel Prize in
Physiology or Medicine this past year! It’s a big deal!
Osmosis and water balance in cells: remember that an important principle in biology (as well as chemistry
and physics) is that nature is always more comfortable at equilibrium.
 So, if there is more water inside a cell than outside, the water will want to move OUT of the cell to
try to make things equal.
 Similarly, if there is more of a solute (for example, salt) inside a cell than outside, then the solute
will want to move OUT of the cell to make things equal. The problem with this is that many solutes
can’t easily cross the membrane… that’s why we will often see water move INTO the cell instead of
the solute moving OUT.
 TONICITY: the ability of a surrounding solution to cause a cell to gain or lose water. It depends on
the concentration of solutes that cannot cross the membrane relative to that outside the cell.
o Isotonic: “same” inside and outside. There will be no net movement of water across the
plasma membrane
o Hypertonic: “more” outside the cell. The cell will lose water, shrivel, and probably die
Modified from materials prepared by Carley Karsten, 2013
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TA: Alberto Lopez
Adapted from Lauren Javier
FALL 2015
D4
o Hypotonic: “less” outside the cell. Water will enter the cell faster than it leaves. Normal in
plant cells (turgid). For animals, the cells can swell and lyse.
Question: Say we have a cell with a high concentration of sodium ions (Na+) inside. What are two
different ways we could make Na+ move OUT of the cell?
Lecture 7: Cytoskeleton, Mitochondria, Chloroplasts, Extracellular Matrix
CYTOSKELETON: a network of fibers extending throughout the cytoplasm important for cell support and
motility
 Properties of ALL cytoskeletal fibers:
o Polymers: made up of strings of monomers
o Polarized: the two ends behave differently
o Dynamic: constantly adding and removing monomers from either end
 Summary of the three main cytoskeletal fibers:
Structure
Location
Microtubules
Tubulin dimers
(Hollow tubes)
Radiating out from
centrosome / MTOC
Microfilaments
Two intertwined
strands of actin
monomers
Throughout
cytoplasm
Intermediate
filaments
Fibrous proteins
supercoiled into
thick cables
Surrounding nucleus
(nuclear lamina)
Function
Cell shape and organization, transportation
over long distances (the “highways” of the
cell”
Particularly important for cell movement (cell
crawling), but also provides structural
support, muscle contraction, and helps with
transport over short distances
Maintenance of cell shape, resisting tension,
cell and nuclear anchorage, formation of
nuclear lamina

Motor proteins: “walk” along microtubule highways. Require energy (ATP).
o Kinesin  + end
o Dynein  - end
 “Structure  function”: the location of the various cytoskeletal fibers helps us to understand
what they do. Where are MF / MT / IF located, and why?
Extracellular matrix (ECM):
 Made up mostly of glycoproteins (especially collagen)
 Holds cells together
 Cells link to the ECM via proteins such as fibronectin and integrins… this is important for the cell to
communicate with its environment.
Modified from materials prepared by Carley Karsten, 2013
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