Download i. cell membrane

CELL STRUCTURE AND FUNCTION
I.
CELL MEMBRANE
A. Components
1. Phospholipids
a) Hydrophilic heads and hydrophobic tails
2. Proteins
a) Integral and peripheral membrane proteins
B. Fluid-Mosaic model
1. A lipid bilayer with many different proteins imbedded that acts as a two-dimensional
fluid
a) At least 50 different proteins associated with a cell membrane
b) Proteins and lipids drift laterally
(1) Do not flip-flop
c) Saturated lipids cause the membrane to be more rigid; unsaturated fatty acids
increase the fluidity
(1) Cholesterol stabilizes the membrane at higher temperatures and prevents it from getting too
rigid at cooler temperatures
C. Synthesis
1. New lipid is made at the smooth endoplasmic reticulum
D. Functions of membrane proteins
1. Cell recognition proteins
a) For unique for cell identity
2. Channel proteins
a) Allows molecules to move across the membrane
3. Carrier proteins
a) Combine with a particular substance to move it across the membrane
4. Receptor proteins
a) Binds to a specific molecule (hormones) due to its shape
5. Enzymatic proteins
a) Carries out a specific metabolic reaction
E. Transport of small molecules
1. Simple diffusion
a) Small, hydrophobic molecules like oxygen can diffuse through the lipid bilayer
b) This takes not energy
(1) Cannot concentrate molecules
c) No transport protein needed
2. Facilitated diffusion
a) Molecules cross the membrane using transport proteins that do not use energy
(1) Cannot concentrate molecules
3. Active Transport
a) Molecule cross the membrane using transport proteins that do use energy
(1) Can concentrate molecules
F. Endocytosis and Exocytosis
1. Endocytosis
a) Cell membrane forms a vesicle around a substance to be taken into the cell
(1) Requires energy
b) Phagocytosis
(1) Large, particulate (non-soluble) material is taken into the cell by forming a vesicle
c) Pinocytosis
(1) Soluble molecules the size of proteins and viruses are taken into the cell by forming a vesicle
2. Exocytosis
a) Intracellular vesicles formed by the Golgi apparatus transports cell products out of
the cell when the vesicle fuses with the cell membrane
II. EUKARYOTIC CELL ORGANELLES
A. Nucleus
1. Nuclear envelope
a) Double membrane with nuclear pores
B. Ribosomes
1. Composed of 2 subunits, each containing rRNA and protein
2. Ribosomes, which may be free or attached to the endoplasmic reticulum, are the site
of protein synthesis
C. Rough endoplasmic reticulum
1. Ribosomes are attached to tubular canals
2. Produces proteins for export out of the cell or membrane proteins via Golgi apparatus
D. Smooth endoplasmic reticulum
1. Lipid synthesis and steroid hormone production
E. Golgi apparatus
1. Structure
a) Stacks of flattened saccules, similar to hollow pancakes
b) Inner (cis) face directed toward the nucleus and ER while outer (trans) face is
directed toward cell membrane
2. Function
a) Packages, stores, modifies, and distributes molecules produced by the ER
F. Vacuoles
1. Large membranous sac, found more prominently in plant cells
2. Storage areas for water, sugars, salts, pigments, toxic substances
G. Lysosomes
1. Structure
a) Vesicles formed by the Golgi apparatus that contain hydrolytic enzymes to digest
macromolecules
2. Function
a) Intracellular digestion when material (large molecules, bacteria) in vesicles fuse
with lysosome
H. Mitochondria
1. Structure
a) A double membrane organelle with the inner membrane forming shelves called
cristae, which project into the matrix
2. Function
a) Called the powerhouse of the cell, they produce ATP for cellular energy via
aerobic cellular respiration
I.
Chloroplasts
1. Structure
a) Double membrane organelle that contains thylakoids (flattened sacs) piled up into
stacks (grana) and stroma (fluid-filled space about the grana)
2. Function
a) To carry on photosynthesis in which carbon dioxide, water, and radiant energy is
used to produce glucose and oxygen
J. Cytoskeleton
1. Function
a) Helps maintain the cell's shape and allows the cell and its organelles to move
K. Cilia and flagella
1. Structure
a) Hairlike extensions of the cell that have a 9 + 2 pattern of microtubule doublets,
which slide along one another
b) Cilia are shorter than flagella.
2. Function
a) Cilia cause movement in single-celled paramecia but in humans they are
responsible for moving substances past cells
b) Flagella cause male sperm cells to move
L. Cell walls
1. Eubacteria - peptidoglycan
2. Protist - varied
3. Fungi - chitin
4. Plants - cellulose
III. CELLULAR COMPARISONS
A. Prokaryotic versus eukaryotic
1. Prokaryotic cells
a) Includes bacteria
b) Lack most organelles and a nuclear envelope
2. Eukaryotic cells
a) Have many organelles and a nuclear envelope
B. Plant versus animal
1. Plants have a cell wall, large vacuoles, and chloroplasts