LECTURE 21
Wednesday 3/29/17
CELL MEMBRANES
•
are simple unicellular organisms
without a nucleus or membrane-enclosed organelles.
•
are cells containing membrane-enclosed
organelles, particularly a nucleus.
• An
is a specialized structure within a cell
that performs a specific function.
• The roles of membrane include:
• external cell membrane functions as a selective barrier
between the living cell and its environment;
• internal membranes surround some organelles, creating
cellular compartments that have separate organization and
functions.
CELL MEMBRANES (continued)
MEMBRANE STRUCTURE
• Most membranes
• The lipids in membranes are
• Lipids are organized in a lipid
with
hydrophobic (long carbon chain) portions inside and hydrophilic
(polar groups) exposed to the water environment.
• When a lipid bilayer is broken and the tails are exposed to
water, the resulting repulsion causes the bilayer to reform and
the break seals spontaneously.
FLUID MOSAIC MODEL OF
MEMBRANE STRUCTURE
MEMBRANE STRUCTURE (continued)
• Membrane lipids usually contain unsaturated fatty acid
chains.
• They fit into bilayers more loosely than saturated fatty
acids.
•
• Proteins
• Lipid molecules
•
are a broad class of compounds that have the
same structural feature:
STEROIDS (continued)
•
• the most abundant steroid in the human body.
• an essential component of cell membranes.
• a precursor of other important steroids.
• synthesized by liver and present in foods.
• A strong correlation exists between cholesterol blood levels
and atherosclerosis (hardening of arteries).
STEROIDS (continued)
•
is yellowish-brown or green, produced by
the liver, stored in the gallbladder, and emptied into the
intestine.
• Bile salts emulsify lipids in the intestine by breaking apart
lipid globules.
• The increased surface area allows lipids to be more
easily hydrolyzed.
STEROIDS (continued)
• Bile salts emulsify cholesterol found in the bile.
• Gallstones (80% cholesterol, colored by bile pigments)
form when:
• the cholesterol level in bile is
• the concentration of bile salts is
STEROIDS (continued)
• The passage of a gallstone:
• causes excruciating pain.
• can allow stones to lodge in the duct and prevent bile from
passing into the duodenum and prevents fats from being
digested normally.
• The result is great pain, feeling nauseated and ill, skin
taking on yellow color as bile pigments are absorbed
into the blood, and stool becoming gray-colored
because of the lack of excreted bile pigments.
• Both the gallbladder and the stones can be surgically
removed.
STEROID HORMONES
• A hormone is a chemical messenger secreted by specific
glands and carried through the blood to a target tissue, where it
triggers a particular response.
• There are two major categories of steroid hormones:
ADRENOCORTICOID HORMONES
• Adrenocorticoid hormones are produced by the adrenal
glands.
• The two classes of adrenocorticoid hormones are:
• mineralocorticoids, which regulate the concentration of
ions in bodily fluids.
• Example: Aldosterone, which increases absorption of
Na+ and Cl• glucocorticoids, which enhance
carbohydrate metabolism.
• Example: Cortisol, which
increases glucose
and glycogen concentrations
in the body and has powerful
anti-inflammatory effects
in the body
SEX HORMONES
• Androgens are
• Estrogen and progesterone are