THE CELL SURFACE
MEMBRANE: STRUCTURE
AND FUNCTION
by shamah ruzande
INTRODUCTION
• The cell surface membrane (plasma membrane) is a selectively permeable
barrier.
• It controls substance movement in and out of the cell.
• Plays a role in cell signalling, transport, and protection
• This presentation covers its structure and its function
STRUCTURE:THE FLUID MOSAIC
MODEL
• Phospholipid bilayer- forms the
basic structure
• Proteins- channel, carrier and
receptor proteins
• Cholesterol- stabilizes membrane
fluidity
• Glycoproteins and Glycolipids-
involved in cell recognition and
signaling
Phospholipid Bilayer
• Hydrophilic heads face outward,
interacting with water
• Hydrophobic tails face inward,
repelling water
• Creates a barrier that controls entry
and exit of substances
Proteins in the Membrane
• Integral proteins: embedded across
the bilayer, help in transport
(channels and carriers)
• Peripheral proteins: attached to the
surface, used for cell signaling and
recognition
Other Components
• Cholesterol: maintains fluidity and stability
• Glycoproteins and Glycolipids: used for cell recognition and communication
This Photo by Unknown Author is licensed under CC BY
Selective Permeability
• The membrane controls movement of substances
• Small, non-polar molecules (e.g., oxygen, CO2) pass through easily
• Large or charged molecules (e.g. glucose, ions) need proteins to enter
WHAT CAN PASS
WHAT CANNOT PASS
Oxygen, carbon dioxide – diffuse freely
Proteins, polysaccharides – too big
H2O, ethanol – via osmosis or aquaporins
Charged molecules and ions – repelled by
hydrophobic core
Steroid hormones – dissolve in the membrane
Hydrophilic molecules – without transport
Ions (sodium, e.g.) – require channel or carriers
proteins
Glucose, amino amino acids – transported via
facilitated diffusion or active transport
DEFINITIONS
• CELL SIGNALING- the process by which cells communicate with each other
by sending and receiving chemical signals
• CELL RECOGNITION – a biological process that allows cells to identify each
other and foreign material in the body
• CELL-TO-CELL ADHESION- the process by which cells physically connect and
stick to each other through specialized proteins on their cell membranes,
forming crucial junctions that are essential for building and maintaining
multicellular tissues within an organism, like skin or epithelium, by allowing
them to function as a cohesive unit
• BARRIER BETWEEN CYTOPLASM AND EXTERNAL ENVIROMENT – site for
enzyme catalyzed reaction
FUNCTIONS: TRANSPORT ACROSS THE
MEMBRANE
• Passive Transport (no energy required)
• Diffusion
• Facilitated diffusion (via channel/carrier proteins)
• Osmosis
• Active Transport (requires ATP)
• Uses carrier proteins to pump substances against the gradient
DIFFUSION
FACILLITATED DIFFUSION
OSMOSIS
ACTIVE TRANSPORT
FUNCTION: BULK TRANSPORT
(ENDOCYTOSIS AND EXOCYTOSIS)
• Endocytosis: bringing materials into the cell (phagocytosis and pinocytosis)
• Exocytosis: releasing materials out of the cell
SUMMARY AND CONCLUSION:
• The cell membrane’s structure enables it to carry out important functions
• The Fluid Mosaic Model explains membrane flexibility and function
• Selective permeable and transport mechanisms regulate what enters/exits the cell
WHAT WOULD HAPPEN IF A CELL LOST
ITS MEMBRANE?
References
• Znotes
• Google
• Cambridge AS Biology Syllabus (code:9700)
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