Cell Membrane Flashcards
2-Describe EM picture of cell membrane.
Two dark electron-dense lines enclosing a light electron-lucent band. Thus it is called trilaminar membrane or unit membrane.
• There is a fuzzy material found on the outer surface only, which represents the cell coat (glycocalyx).
1-Describe LM picture of cell membrane.
• It is very thin (7.5-10 nm).
• Can be demonstrated when stained with silver
(Ag) or PAS (magenta red).
Explain the trilaminar appearance of cell membrane.
• The dark staining lines are formed by hydrophilic heads of phospholipids which take osmic acid used in staining.
• The light band is formed by fatty acid acid tails which are hydrophobic and do not take osmic acid.
Describe the Protein component in cell membrane.
about 50% w/w, present in two forms:
• a) Peripheral proteins:
• Small molecules
• a non-continuous layer
• outside the lipid bilayer.
• loosely attached to both surfaces of the cell membrane.
• b) Integral proteins:
– Embedded in the lipid bilayer.
– Some extend across the membrane from side to side ( mulipass transmembrane proteins).
5-Describe Lipid component of cell membrane.
Lipid : consists of phospholipids and cholesterol .
• Phospholipid molecules: arranged into 2 layers (lipid bilayer).
– Each molecule has:
• head:
– Is charged,
– Polar.
– hydrophilic,
– directed towards aqueous solutions.
• tail of fatty acids:
– Is non-charged
– Non polar.
– hydrophobic
– directed inwards away from aqueous solutions, so directed to the center facing each other.
• Cholesterol molecules:
– among the hydrophobic fatty acids,
– restricting their movement
– and modulating fluidity of membrane components.
-Describe carbohydrate component of cell membrane.
Carbohydrate: at the external surface formed of:
• a) Glycoproteins: oligosaccharide chains linked to protein molecules.
• b) Glycolipids: oligosaccharides linked to phospholipid molecules.
• Cell coat (glycocalyx):
• Formed of molecules of glycoproteins & glycolipids
• on the external surface of cell membrane.
• It includes receptors for drugs, hormones, bacteria and viruses.
What do the following refer to
1-Fluid mosaic
2-Membrane trafficking
The fluid mosaic model refers to:
• Fluid nature of lipids.
• Appearace of protein molecules as mosaic in the fluid bilayer.
Membrane trafficing includes membrane movements and recycling developing in endo- and exocytosis.
Define membrane trafficing and describe its mechanism.
Membrane trafficing includes membrane movements and recycling developing in endo- and exocytosis.
a)
Endocytosis: Bulk uptake of substances subdivided according to the nature of the substances into:
Phagocytosis (cell eating):
– – –
Macrophages and neutrophils
engulfing bacteria, protozoa, damaged cells, and unneeded extracellular constituents.
When a bacterium becomes bound to the surface of a macrophage, cytoplasmic processes extend and fuse, enclosing the bacterium in an intracellular phagosome.
Pinocytosis (cell drinking):
Small membrane invaginations enclose extracellular fluid forming intracellular pinocytic vesicles.
Receptor-mediated endocytosis:
Receptors for specific molecules, such as protein hormones and growth factors are integral proteins at the cell membrane.
Binding of the hormone to its receptor causes receptors to accumulate in coated pits.
The cytoplasmic surface of the pit is coated by clathrin protein.
The coated pit invaginates and pinches off, forming a coated vesicle that carries the hormone and its receptor into the cell.
b)Exocytosis: A membranous cytoplasmic vesicle fuses with the cell membrane to release its content into the extracellular space. The vesicular membrane will be added to the plasma membrane.
Describe vesicular transport.
Answer is of endocytosis and exocytosis.
-List/enumerate functions of cell coat.
– Cell protection.
– Cell identification.
– Cell immunity.
– Cell adhesion.
– Receptor functions.
Describe how transport takes place through cell membrane with reference to examples.
1-Simple diffusion: passively down a concentration gradient. water, ions and dissolved gases
2-Facilitated diffusion: passively down a concentration gradient
Substances which do not dissolve in fat need channels (integral transmembrane proteins) or carrier to enter the cell e.g. glucose & amino acids.
3-Active transport: Against a concentration gradient. Needs energy,
e.g. Na+/K+ pump.
4-Bulk transport:Endocytosis and exocytosis.see before
List active and passive processes in transport through cell membrane with reference to examples.
– Passive: simple diffusion and facilitated diffusion.
– Active:active transport, endocytosis(3)
&exocytosis.
• Give examples for each of the 7
-List the functions of cell membrane.
– Transport.7
– Functions of the coat.5
– Transmission of nerve impulse in nerve cell and
muscle.
– Modifications of cell membrane:
• Microvilli: in intestine to increase surface area for absorption.
• Cilia: move particles above the cell membrane in one direction as in fallopian tube.
• Flagella:as in tail of sperm to move the sperm. • Stereocilia: long microvilli.
-List the steps in receptor mediated endocytosis.
• Receptors for specific molecules, such as protein hormones and growth factors are integral proteins at the cell membrane.
• Binding of the hormone to its receptor causes receptors to accumulate in coated pits.
• The cytoplasmic surface of the pit is coated by clathrin protein.
• The coated pit invaginates and pinches off, forming a coated vesicle that carries the hormone and its receptor into the ce
Suggest why the patient my show features of hormone deficiency as Growth hormone although pituitary gland is producing this hormone efficiently.
Absence of receptors in cell membrane/coat; preventing the hormone to enter into the target cells by receptor mediated endocytosis
