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Crisitna Botello-Godoy
Period #4
Membranes
1. What does selective permeability mean and why is that important to cells?
Cells have a selective permeability membrane meaning that it only allows certain
substances to go in or out of the cell; mostly dependent on the molecules size. It is important for
cells because it allows substance to stay within the cell such and limits the intake of dangerous
substances inside the cell and allows the diffusion out of the cell of waste and such.
2. What is an amphipathic molecule?
An amphipathic molecule has both a hydrophilic region and a hydrophobic region meaning it
has both polar and non polar regions such as phospholipids.
3. How is the fluidity of cell’s membrane maintained?
The fluidity of a cell is affected by various factors including temperature. The membrane is
held together through hydrophobic interactions which are rather weak. As the temperature
decreases the fluidity of the membrane remains until the temperature drops solidifying. The
temperature at which this occurs depends on the types of lipids the membrane is composed
of. The Fluidity of the membrane will remain if unsaturated hydrocarbon tails of
phospholipids have kinks keeping the molecules from packing together. Cholesterol is a
temperature buffer used to maintain the fluidity of the cell as well. At warm temperatures
cholesterol decreases fluidity by restraining the movement of phosolipids (it gets between
them) while in low temperature it prevents the membrane from solidifying by also hindering
between the phospholipids. This also makes the temperature to solidify to lower.
4. Label the diagram below – for each structure – briefly list it’s function:
extracellular matrix – connect cells one to another, connective tissue.
carbohydrate – the part in the glycolipid or glycoprotein that bind to the other
carbohydrates for cell to cell recognition.
glycoprotein – carbohydrates through covalent bond attach to proteins; cell to cell
recognition
Microfilaments of Cytoskeleton- attach to proteins on the membrane to aid in the
support/shape of the cell.
cytoskeleton – structural support for the cell
cholesterol – helps with fluidity
Peripheral Protein- not enabled on the lipid layer at all lose; exposes lose parts of integral
proteins .performs regular activities of proteins. Enzymatic etc.
glycolipid – carbohydrates attach to lipids such as this one, to aid in cell to cell recognition
integral protein – go though the hydrophobic core of the membrane and performs regular
jobs of proteins. Such as transport, enzymatic activity etc.
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5. List the six broad functions of membrane proteins.
Transport, enzymatic activity, signal transduction, cell to cell recognition, intercellular
joining, attachment to the cytoskeleton and extracellular matrix
6. How do glycolipids and glycoprotein help in cell to cell recognition?
The carbonate part of either the glycolipid or glycoprotein act as the identification factor
in cell to cell recognition b y binding to the carbonate chain on the other glycolipid or
glycoprotein.
7. Why is membrane sidedness an important concept in cell biology?
Don’t quite understand this one.? Aha./
8. What is diffusion and how does a concentration gradient relate to passive
transport?
Diffusion is the movement of substances from high to low concentrations to reach
equilibrium. The concentration gradient allows such substances to diffuse in or out by
making the molecules go down its concentration gradient. In passive transport the molecules
do not use energy (ATP) to diffuse in or out, the concentration gradient itself serves as an
energy source.
9. Why is free water concentration the “driving” force in osmosis?
Free water concentration is the “driving” force in osmosis because water will diffuse from
the region with a lower solute concentration through a selectively preamble membrane to the
area of higher solute concentration until both regions have an equal solute concentration
10. Why is water balance different for cells that have walls as compared to cells
without walls?
Cells that do have ridged walls can tolerate excessive uptake and loss of water compared to
those that don’t.
11.
Animal cell:
Hypotonic: too much water has diffused inside the cell, and it “burst”
Isotonic solution: there is an equilibrium, there is a net movement of water, the water moves at the same rate in both
directions.
Hypertonic: the cell is hypotonic and water will diffuse out.
Plant cell:
Hypotonic: water diffuses inside reaching a point where the cell it turgid or very firm. Healthy for most plant cells.
Isotonic: the cell becomes “flaccid” and there is no net tenden for water to enter
Hypertonic: water diffuses out of cell
12. What is the relationship between ion channels, gated channels and facilitated
diffusion.
Facilated diffusion is aided by channels in the membrane that facilitate the transport of
molecules. An example of such is ion channels that allows the diffusion of ions from low to
high concentrations. Some ion channels are gated channels meaning that they open or close.
Allowing or preventing the passing of ions. These gated channels are stimulated either
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through a chemical or electrically to open and close. If chemical there is two substances
going through the channel one that’s the one transported and one that tells it to close (or
Open)
13. How is ATP specifically used in active transport?
In active transport energy is used to transport substances, many times against their
concentration gradient. For example ATP is used as it induces the protein to change its
confirmation hence translocation a solute bound to the protein across the membrane. This is
done when ATP transfers it terminal phosphate group directly to the transport protein
14.Define and contrast the following terms: membrane potential, electrochemical
gradient, electrogenic pump and proton pump
Membrane potential: the voltage across the membrane. It aids in diffusion preferring the
entrance of cations inside the cell and the exist of anions. it ranges from about -50 to -500 the
negative sign indicates the cell is negative compared to the outside (this would be the
electrical simulator?)
The electrochemical gradient is the combination of both chemical and electrical forces
enacting on the ion “ The electogenic pump is a transport protein that generates voltage
across the membrane while the proton pump is a sort of electrogenic pump.
15. What is cotransport and why is an advantage in living systems?
Cocntransport is when energey is being used to transport something down a concentration
gradient as well as another substance up a gradient (so two thingd) it is an advantage in
living systems since it requires less energy to two things.
16. What is a ligand? A ligand is a molecule that binds to the receptor site of another
molecule
17. Contrast the following terms: phagocytosis, pinocytosis and receptor-mediated
endocytosis.
In Phygocytosis the substance(food) going in into the cell is engulfed by having the
plasma membrane wrap pseudopodia’s around the ssubstance on both sides, resulting in
enclosing it. This is big enough to be considered a vacuole. The vacuole then fuses with
a lysome containing hydrolytic enzymes and the particle is digested. In Pinocytosis the
cell “gulps” small particles. It lets the particle go into the plasma membrane then
pinching in the end to make a vesicle . in pinicytosis the particles it carries aren’t specific.
In receptor-mediated endoyotosis is much more efficient and has a coat of proteins
surrounding the vesicle. The vesicles have proteins with receptor sites that are specific to
the the substance being taken in.
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