Transcript Lecture 11 Ch.3 Cellular basic of life

Lecture 13
Plasma membrane
pages 63-68
Plasma Membrane
• Separates intracellular fluids from extracellular
fluids
• Plays a dynamic role in cellular activity
• Glycocalyx is a glycoprotein area abutting the
cell that provides highly specific biological
markers by which cells recognize one another
Morphology
Extracellular fluid (ECF) = fluid
outside the cell
Plasma Membrane (cell membrane) =
• Membrane composed of proteins & lipids that
surrounds the cell
•Composition and function vary from region to
region
Intracellular fluid (ICF), (cytosol, cytoplasm) =
•Clear gel inside the cell
•Organelles and cytoskeleton suspended within
Morphology
Intracellular face = side of
the membrane that faces
the cytoplasm
Extracellular face = side of
the membrane that faces the
outside
Fluid Mosaic Model
• Double bilayer of lipids with imbedded,
dispersed proteins
• Bilayer consists of phospholipids, cholesterol,
and glycolipids
– Glycolipids are lipids with bound carbohydrate
– Phospholipids have hydrophobic and hydrophilic
bipoles
Fluid Mosaic Model
Figure 3.3
The Cell
Cell Membrane
Glycocalyx
Extensions
4.5 The structure of membranes correlates with their
functions
• The plasma membrane controls the movement
of molecules into and out of the cell, a trait
called selective permeability
– The structure of the membrane with its component
molecules is responsible for this characteristic
– Membranes are made of lipids, proteins, and some
carbohydrate, but the most abundant lipids are
phospholipids
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Composition
• 98% of all membrane molecules are lipids
• 2% of all membrane molecules are proteins
Lipids
• 75% are phospholipids
Head
– Amphiphilic
– Create a bilayer
• Head
– Hydrophilic
– Contain phosphate
– Face the water on either side of
the membrane
Tails
Hydrophilic head
Phosphate
group
Symbol
Hydrophobic tails
Outside cell
Hydrophilic
heads
Hydrophobic
region of
protein
Hydrophobic
tails
Inside cell
Proteins
Hydrophilic
region of
protein
4.5 The structure of membranes correlates with their
functions
• Phospholipids form a two-layer sheet called a
phospholipid bilayer
– Hydrophilic heads face outward, and hydrophobic
tails point inward
– Thus, hydrophilic heads are exposed to water, while
hydrophobic tails are shielded from water
• Proteins are attached to the surface, and some
are embedded into the phospholipid bilayer
Copyright © 2009 Pearson Education, Inc.
Lipids
• 20% of membrane lipids are cholesterol
molecules
– Found among tails
– Low conc. – hold phospholipids still resulting in
a stiffened membrane in areas
– High conc. – can prevent close packing of
phospholipids thus increasing membrane
fluidity
Lipids
• 5% of membrane lipids – glycolipids
– Phospholipids with a short carbohydrate chain on
the extracellular face of the membrane
– Form the glycocalyx – carbohydrate coating on the
cell surface with multiple functions
Glycocalyx
Glycocalyx
Glycocalyx
•
•
•
•
External to the plasma membrane
“fuzzy coat” of glycolipids and glycoproteins
Present on all animal cells
Identification tag for cells
Glycocalyx purposes
• Protection
– Cushions
– protects from physical & chemical injury to the
plasma membrane
• Cell Adhesion
– Binds cells together
Membrane Proteins
• Only 2% of the molecules in the plasma
membrane
HOWEVER
• These proteins are larger than lipids ~ 50% of
membrane weight
Types Proteins
• Transmembrane – pass thru the membrane
– Hydrophilic regions in the cytoplasm and
extracellular fluid
– Hydrophobic regions in contact with the lipid
membrane
– Free floating or anchored to the cytoskeleton
Types Proteins
• Peripheral – do not enter the membrane, but
adhere to the surface
– Tend to be tethered to the cytoskeleton and in
association to a transmembrane
Types of Proteins
• Integral – enter the phospholipid bilayer, but
DO NOT cross it completely
Functions of these Cell Membrane
Proteins
Functions of Membrane Proteins
• Transport
• Enzymatic activity
• Receptors for signal
transduction
Figure 3.4.1
Functions of Membrane Proteins
• Intercellular adhesion
• Cell-cell recognition
• Attachment to
cytoskeleton and
extracellular matrix
Figure 3.4.2
Membrane Junctions
• Tight junction – impermeable junction that
encircles the cell
• Desmosome – anchoring junction scattered
along the sides of cells
• Gap junction – a nexus that allows chemical
substances to pass between cells
Membrane Junctions: Tight Junction
Figure 3.5a
Membrane Junctions: Desmosome
Figure 3.5b
Membrane Junctions: Gap Junction
Figure 3.5c
Tight junctions can bind cells together into leakproof
sheets – bladder, digestive tract
Anchoring junctions link animal cells into strong tissues –
heart, skin
Gap junctions allow substances to flow from cell to cell –
ions to trigger heart contractions
Tight junctions
Anchoring junction
Gap junctions
Figure 4.18B
Extracellular matrix
Space between cells
Plasma membranes of adjacent cells
Thank you