Cell Transport. Cell Membrane: Function: Maintain homeostasis. This is also called equilibrium. ...
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Transcript of Cell Transport. Cell Membrane: Function: Maintain homeostasis. This is also called equilibrium. ...
Cell Transport
Cell Membrane: Function:
Maintain homeostasis.This is also called equilibrium.
Allow passage of some molecules while preventing the passage of others This is called being “Selectively
permeable” or “semi-permeable”
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Small molecules and larger hydrophobic molecules move through easily.e.g. O2, CO2, H2O
Semipermeable Membrane
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Ions-hydrophilic molecules larger than water, and large molecules such as proteins do not/ cannot pass through the membrane without help.
Semipermeable Membrane
Membrane structure:• Composed of a
phospholipid bilayer Have a phosphate
head which is polar- does react with water
Have a fatty acid (lipid) tail that is non-polar- does not react with water
Together these make up the membrane
• The inside of the membrane is hydrophobic- which means it does not react with water
• The outside of the membrane is hydrophillic- which means it does react with water
•Contains proteins within its structure1.Integral proteins (transport proteins)-
which allow the passage of molecules too large to pass through the membrane without help
2.Peripheral proteins- aid in signaling for the cell to communicate with other cells
Concentration Gradient Concentration gradients occur
when there is a higher amount of solutes in one area of solution then in another. Molecules will tend to travel from
areas of high concentration to areas of lower concentrations
Passive transport Molecules flow with or down a
concentration gradient No energy required Two types:
Diffusion Ex. Osmosis
Facilitated Diffusion
Diffusion
Facilitated Diffusion Diffusion for
molecules that are not lipid soluble or are too large to pass through the membrane.
Carrier proteins change shape to aid these molecules across the membrane
No Energy Required.
Example: Glucose, Fructose
Osmosis Diffusion involving water moving from
high water concentration to low water concentration. Water can move freely across the
membrane No energy required.
Osmosis There are three different types of osmotic solutions:
Hypotonic isotonic Hypertonic
Hypotonic Solution Higher concentration
of solutes within the cell More free water
outside the cell Water moves into the
cell The cell becomes
swells or gets larger
Hypo Hippo- it gets big and swells.
Hypertonic Solution Higher concentration of
solute outside the cell More free water in the
cell Water moves out of the
cell Cell shrinks
Isotonic solution Solutions are equal
between the two areas
Water moves both directions to keep the solutions at an equilibrium.
What will happen to water in the cell?
Three Different Osmotic Solutions
Hypotonic- higher concentration of solutes in the cell
Hypertonic- higher concentration of solutes outside the cell
Isotonic – equal amount of solutes inside and outside the cell
Example- Plants: In a hypotonic solution plant cell’s
membrane is pushed against the cell wall Turgor Pressure
In a hypertonic solution a plant cell’s membrane will shrink within the cell wall Plasmolysis Causes wilting when plants
dehydrate
Turgor Pressure
Plant cell becomes engorged with water
Gives plant the stiffness in their stem
Plasmolysis Plant cell membrane shrinks from the cell
wall Causes plant to wilt.
Active Transport Molecules are transported against the
concentration gradient by proteins Requires energy (ATP) Example: Sodium-Potassium Pump
A protein that transfers Na+ and K+ ions up the gradient
Cell has a high Na+ concentration outside the cell and a high K+ concentration inside the cell
http://www.youtube.com/watch?v=GTHWig1vOnY
Active transport Enodcytosis: cells engulf
substances that are too large to enter the cell by passing through the cell membrane
Exocytosis: cellular wastes
are removed from sacs at the cell’s surface
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• Molecules are moved out of the cell by vesicles that fuse with the plasma membrane.
Exocytosis-
moving things out.
• This is how many hormones are secreted and how nerve cells communicate with one another.
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25ExocytosisExocytic vesicle immediately after fusion with plasma membrane.
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Large molecules move materials into the cell by one of three forms of endocytosis.
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Pinocytosis-Most common form of endocytosis.
Takes in dissolved molecules as a vesicle.
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Pinocytosis- Cell forms an
invagination Materials dissolve
in water to be brought into cell
Called “Cell Drinking”
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Example of Pinocytosis
pinocytic vesicles forming
mature transport vesicle
Transport across a capillary cell (blue).
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Receptor-Mediated Endocytosis
Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.
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Endocytosis – Phagocytosis
Used to engulf large particles such as food, bacteria, etc. into vesiclesCalled “Cell Eating”
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Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)
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So to review the three types of Endocytosis are:• Phagocytosis• Pinocytosis• Receptor mediated
Endocytosis.
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Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane.
Inside Cell Cell environment
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What are the three different types of active transport? Protein pumps (Na/K) Endocytosis Exocytosis
Cell Transport Passive transport: molecules
travel along/down/with the concentration gradient No energy required
Active Transport: molecules are transported against/up the concentration gradient energy required