Download BIOL1040 OBJECTIVES

BIOL1040 OBJECTIVES
MODULE 1: PRINCIPLES OF CELL FUNCTION
LECTURE 1: CELL MEMBRANE STRUCTURE & FUNCTION
1) Describe the structural elements of cell membranes and their functions
Cell membranes are composed of four different types of molecules: phospholipids, cholesterol, proteins
and carbohydrates.
Molecule
Structure
Function
Phospholipids
 Amphipathic- hydrophilic head,
hydrophobic tail
 Head contains phosphate group
 Tails contains two strings are
hydrocarbons
 Arranged to form lipid bilayer
Most important property of lipid
bilayer is that
it is a highly
impermeable
structure
Cholesterol
 Composed of four rings of hydrogen
and carbon atoms
 Hydrophobic- found among tails
Fluidity buffer: reduces
membrane fluidity at moderate
temperatures by reducing
phospholipid movement. At low
temperatures it hinders
solidification by disrupting the
regular packing of phospholipids.
Proteins
 Composed of amino acids which
make polypeptide chains
Membrane proteins have six
main functions. Include
transport, acting as receptors
and enzymes. They determine
most of the membranes
functions.
FLUID MOSAIC MODEL
 In the fluid mosaic model the membrane is a fluid structure with a “mosaic” of various proteins
embedded in or attached to a bilayer or phospholipids.
 Lateral movement (side-by-side) of phospholipids occurs 107 times per second however, flipflopping is rare because in order to do so the hydrophilic head must cross the hydrophobic
interior of the membrane (once a month)
 Unsaturated hydrocarbon (C=C) tails prevent packing due to the kink in the tail, enhancing
fluidity
 Saturated hydrocarbon (C-C) tails pack together, increasing viscosity
THE SLIDING FILAMENT MODEL OF MUSCLE CONTRACTION
Myosins head is bound to ATP and is in its lowenergy configuration.
ATP is hydrolyzed to ADP and inorganic
phosphate. It is converted to its high-energy
form
The myosin head binds to actin, forming a
crossbridge. Pulls thin filament to center of
sarcomere
Crossbridge is broken when a new molecule of
ATP binds to myosin head
 The filaments do not
change length when the
sarcomere shortens. The
thin and thick filaments
slide past each other,
increasing their overlap
 The myosin filaments
have heads that bind and
pull actin rapidly
 Each myosin has a long
“tail” region and a
globular “head” region
 Calcium ions and
regulatory proteins bound
to actin play crucial roles
in both muscle cell contraction and relaxation
o Tropomyosin (regulatory protein) and the troponin complex are bound to
actin strands
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Acetylcholine (neurotransmitter) released at synaptic terminal diffuses
across synaptic cleft and binds to receptor proteins on muscle fiber’s
plasma membrane
Action potential is propagated along plasma membrane and down T
tubules
Action potential triggers release of calcium ions from sarcoplasmic
reticulum
Calcium ions bind to troponin in thin filament; myosin binding sites
exposed
Cycles of myosin cross bridge formation and breakdown coupled with
ATP hydrolysis, slide thin filament
Cytosolic calcium ions removed by active transport into SR after action
potential ends
Tropomyosin blockage of myosin binding sites is restored; contraction
ends, and muscle fiber relaxes
1) Make the link between cellular level events and how these relate to gross force production and
movement
 Two basic mechanisms by which the nervous system produces graded contractions of whole
muscles (1) by varying the number of muscle fibers that contract and (2) by varying the rate at
which muscle fibers are stimulated (mechanical summation)
o Force increases as more motor neurons controlling the muscle are activated
(recruitment)
 Tropic hormones are hormones that activate another endocrine gland to produce other
hormones
 Non-tropic hormones are hormones that target non-endocrine tissues
 Growth hormone has tropic and non-tropic effects. It exerts diverse metabolic effects to raise
blood glucose (non-tropic) and acts on the liver to release insulin-like growth factors (tropic)
Example: ADH (ANTIDIURETIC HORMONE AKA VASOPRESSIN)
 Stimulus: osmolarity of blood increases due to body losing water via sweating
 Osmoreceptors in hypothalamus detect changes in blood osmolarity stimulating the release of
ADH
 ADH enters bloodstream and acts on target cell in the kidney tubules
 ADH makes epithelium more permeable to waterincreased renal absorption of water (retain
as much water as possible)reduces urine volumemake urine more concentrated
 Mechanism via action of aquaporins
 Hypothalamus also increases feeling of thirst
 Drinking water decreases blood osmolarity
1) Rationalize how hormones mediate the short-term and long-term responses to stress
 Adrenal medulla secretes epinephrine and norepinephrine (short term)
 Adrenal cortex secretes mineralocorticoids and glucocorticoids (long term)
Stress is the stimulus and is detected by the hypothalamus which sends nervous impulse via spinal cord
to the adrenal medulla. The release of catecholamines (adrenaline and noradrenaline) acts on alphaadrenoreceptors and beta-adrenoreceptors in target tissues. Adrenaline that binds to beta-receptors in
liver cells causes an increase in blood glucose levels while adrenaline that binds to beta-receptors in
smooth muscle cells in the wall of blood vessels that supply skeletal muscle causes blood vessels to
dilate, increasing flow to skeletal muscle. Adrenaline that binds to alpha-receptors in the smooth
muscle cells in wall of blood vessels that supplies intestines causes blood vessels to constrict.
Short term effects
Long term effects
Effects of epinephrine and norepinephrine
Effects of
mineralocorticoids
 Retention of
sodium ions
and water by
kidneys
 Increased
blood volume
and blood
pressure
 Glycogen broken down to glucose,
increase in blood glucose
 Increases blood pressure
 Increased breathing rate
 Increased metabolic rate
 Change in blood flow patterns leading
to increased alertness and decreased
digestive, excretory, and reproductive
system activity
Effects of
glucocorticoids
 Proteins and fats
broken down and
converted to
glucose,
increased blood
glucose
 Possible
suppression of
immune system