honors biology ch. 5 Notes Membranes

honors biology
ch. 5 Notes
Membranes
MEMBRANE STRUCTURE AND FUNCTION
5.1 Fluid Mosaic model of the plasma membrane
“Fluid” The molecules can migrate through the layer that they are
in but they will very seldom flip-flop.
“Mosaic” The pattern or collection of molecules (phospholipids
and proteins) that makes up the plasma membrane.
5.1 Describe the diverse functions of membrane
proteins
50 different types of proteins found in RBC’s.
Six Functions:
1. Support: (see graphic)
a. integrins give the membrane a stronger
framework.
b. Span the membrane and attach to the
cytoskeleton on the inside and the
extracellular matrix (ECM) on the outside
2. cell-cell recognition: (see graphic)
a. glycoproteins (sugar-protein)
b. glycolipids (sugar-phospholipid)
c. “glyco” or sugar acts as ID tags
i. embryo sorts cells into tissues and
organs
ii. immune system to recognize and
reject foreign cells like bacteria
3. intercellular junctions:
4. enzymes (see below)
5. signal transduction (see below)
6. transport (see below)
5.1 Relate the structure of phospholipid molecules to the
structure and properties of cell membranes.
Selective Permeability: Membranes allow some substances to
cross more easily than others.
Molecules that can move across plasma membrane are soluble
in lipid (phospholipid tails are hydrophobic-“like dissolves
like.”)
Molecules that Move across easily
Molecules that need proteins to get
Small, nonpolar molecules
across membrane
Small polar (water)
Larger, nonpolar
charged
Mrs. Loyd
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5.2 Explain how the properties of phospholipids
spontaneously form membranes.
•
One of the first organic molecules to form on early Earth
•
Spontaneously self-assemble into simple membrane
“bubbles”
•
without help from DNA
•
“membrane-bound sacs” surrounding beneficial
chemistry (protobiont) was important stepping stone to
first cell.
•
Hydrophilic heads “love” water inside and outside cell
•
Hydrophobic tails “fear” water and huddle together
•
“Like dissolves like”
5.3 Define diffusion and describe the process of passive
transport.
Diffusion: Particles spread out evenly in an available space,
from high concentration to low due to thermal motion (heat).
NEVER requires energy.
Passive Transport: The diffusion of a molecule across a
membrane from high to low concentration or down its
concentration gradient.
Small, nonpolar molecules like O2 and CO2 diffuse easily.
Small, polar water diffuses easily.
Large, polar molecules and ions can diffuse across using a
transport protein (facilitated diffusion).
Passive
Active
H→L
L→H
No energy
Uses Energy
Examples:
Diffusion
endocytosis
•
osmosis
exocytosis
Facilitated
Na+/K+ pump
Diffusion-Glucose
5.4 Explain how osmosis can be defined as the diffusion of
water across a membrane.
•
Osmosis is a special case of diffusion, it is specifically
for water.
•
It is defined as water moving across a membrane from
H→L concentration.
•
Predicting how water will move across a membrane will
be your main challenge in this chapter.
5.5 Distinguish between hypertonic, hypotonic, and
isotonic solutions.
Hyper = “over” like “hyperactive”
Hypo = “under” like “hypodermic needle”
Iso = “same” like “isosceles triangle”
Tonic = solute
These terms are relative. We will always be comparing one
side of a membrane to the other side. (outside a cell vs.
inside the cell.)
Mrs. Loyd
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STEPS in determining the
direction of osmosis
Latin Solute
English Solute
English Water
Place your L,
then H→L
Decide if water is
entering or leaving
the cell
(Draw a PICTURE!)
Determine the results
Determine what will happen
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hypertonic
“over” salty
“under” watery
H→L
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5.5 Explain how animal and plants cells change when placed
into hypertonic or hypotonic solutions.
Complete your “Osmosis Worksheet” to practice.
5.6 - 5.8 Compare the processes of facilitated diffusion and
active transport.
Facilitated Diffusion:
•
uses a protein embedded in the membrane to facilitate,
or help, a substance diffuse across the membrane.
•
Example: Glucose has its own protein in the cell
membrane for this purpose.
•
It is diffusion, so the sugar moves from H→L
concentration of sugar.
Active Transport:
•
USES ENERGY
•
L→H Moves molecules against their concentration
gradient.
•
Examples:
o endocytosis
o exocytosis
o Na+/K+ pump
5.9 Distinguish between exocytosis, endocytosis,
phagocytosis, pinocytosis, and receptor-mediated
endocytosis.
Use animations
Mrs. Loyd
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