Cell membranes including cell surface modifications, Lecture notes of Veterinary

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AP Biology

VAN 1

CELL MEMBRANE

DR S.G. OLUKOLE

DEPARTMENT OF VETERINARY ANATOMY

UNIVERSITY OF IBADAN, NIGERIA.

2017/2018 SESSION

AP Biology Discovery of Cells

Cells were discovered in 1665 by Robert

Hooke.

Early studies of cells were conducted by

• Mathias Schleiden (1838)
• Theodor Schwann (1839)

Schleiden and Schwann proposed the Cell

Theory.

AP Biology Characteristics of Cells  (^) Genetic material 

single circular molecule of DNA in

prokaryotes



double helix located in nucleus in eukaryotes

• nuclear envelope (double membrane)  (^) Cytoplasm: fills cell interior – 

sugars, amino acids,



proteins - organelles

 (^) Plasma membrane: encloses 

the cell – phospholipid bilayer

S. G. OLUKOLE^4

• AP Biology

AP Biology

Cell Membrane  (^) The plasma membrane separates the living cell from its nonliving surroundings.  (^) This thin barrier, 8 nm thick, controls traffic into and out of the cell.  (^) Like other membranes, the plasma membrane is selectively permeable, allowing some substances to cross more easily than others.  (^) The main macromolecules in membranes are lipids and proteins, but include some carbohydrates.

AP Biology The Cell Membrane

AP Biology Arranged as a Phospholipid bilayer polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads  (^) Serves as a cellular barrier / border H 2

sugar O

lipids

salt

waste

impermeable to polar molecules

AP Biology Cell membrane defines cell  (^) Cell membrane separates living cell from

aqueous environment



thin barrier = 8nm thick

 (^) Controls traffic in & out of the cell 

allows some substances to cross more

easily than others

 hydrophobic (nonpolar) vs. hydrophilic (polar)

AP Biology Cell membrane is more than lipids…  (^) Transmembrane proteins embedded in

phospholipid bilayer



create semi-permeabe channels

lipid bilayer

membrane

protein channels

in lipid bilyer membrane

AP Biology

Many Functions of Membrane Proteins

Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion “Antigen” “Channel” 15

AP Biology Types of Membrane Proteins

1. Adhesion proteins – hold to surface, cells
2. Recognition proteins – recognize “self”
3. Receptor proteins – receive messages
4. Enzymes – speed up reactions
5. Transport proteins (active and passive) active – require energy to transport passive – no energy required for transport

AP Biology Cell membrane must be more than lipids…  (^) In 1972, S.J. Singer & G. Nicolson

proposed that membrane proteins are

inserted into the phospholipid bilayer

It’s like a fluid…

It’s like a mosaic…

It’s the

Fluid Mosaic Model!

AP Biology Membrane carbohydrates  (^) Play a key role in cell-cell recognition 

ability of a cell to distinguish one cell

from another

 antigens



important in organ &

tissue development



basis for rejection of

foreign cells by

immune system

AP Biology Any Questions??