Cells: INTRODUCTION
I. Overview
• Prokaryotic vs. Eukaryotic cells
– A. Prokaryotic Cells
• 1. Small, 1-10 micrometers in diameter
• 2. Lack membrane-enclosed organelles
• B. Eukaryotic cells (all organisms other
than bacteria)
– 1. Relatively large- 10-100 um in diameter
•
Size limited by SA/Volume ratio
– 2. Contain membrane-enclosed nucleii and
other membranous organelles in their
cytoplasm
II. The Nucleus and Ribosomes
• A. The Nucleus contains a cell’s genetic
library
– 1. DNA is organized with protein (histone)
into thin fibers of chromatin
– 2. Chromatin coils into thick chromosomes in
dividing cells.
– 3. Nucleoli are inside the nucleus and are the
sites of ribosome synthesis.
• B. Ribosomes- small organelles in all
cells
– 1. The site of protein synthesis
III. The Endomembrane System
• A. Endoplasmic reticulum (ER)
– ER is a network of cisternae (Membraneenclosed compartments)
– 1. Smooth ER- lacks ribosomes
• A. Synthesizes steroids, metabolizes
carbohydrates, stores calcium in muscle cells, and
detoxifies poisons (i.e. alcohol) in liver cells
• 2. Rough ER- contains bound ribosomes
– a. Produces cell membranes
– b. Produces secretory proteins that are
released from the ER in transport vesicles
• B. Golgi apparatus- assembles, sorts and
ships cell products
– 1. The Golgi stack receives secretory protein
from ER.
– 2. Proteins are modified, sorted and released
from the other end
• C. Lysosomes- digestive compartments
– 1. Membranous sacs of hydrolytic enzymes.
– 2. Recycle parts and/or digest food.
• Autophagy is the word for digesting cell parts
• D. Vacuoles- diverse functions in cell
maintenance.
1. Plant cells’ large, central vacuole stores
products, disposal of waste, helps cells to grow,
protects the cell and provides rigidity. (turgor)
IV. Other membranous organelles
• A. Mitochondria- the sites of cellular
respiration
• B. Chloroplasts- The sites of
photosynthesis
• C. Peroxisomes- generate and breakdown
hydrogen peroxide
V. Cytoskeleton
• A. Made of microtubules,
microfilaments, and intermediate
filaments.
– 1. Microtubules-grow from the centrosome
• a. Microtubules shape the cell, guide movement of
the organelles, and help separate chromosomes in
dividing cells.
• b. Cilia and flagella, made of microtubules, are
motile structures
• 2. Microfilaments- thin rods made of
actin. Used in muscle contraction and
amoeboid movement.
• 3. Intermediate filaments- support cell
shape and fix organelles in place.
VI. Cell surfaces and junctions
• A. Plant cells have cell walls (made of
cellulose fibers)
• B. Extracellular matrix (ECM)- in animal
cells ECM functions in support, adhesion,
movement, and regulation
• C. Intercellular junctions- help cells to
communicate and work together
– 1. Plant cells have plasmodesmata,
channels that pass through adjoining cell
walls
• 2. Animal cells have tight junction,
desmosomes, and gap junctions
– a. Tight junction – prevents leakage of
materials between cells
– b. Desmosomes – functions as an anchor
to connect cells together
– c. Gap junction – Allows passage of
material (or current) between cells
Plasma Membrane
• Phospholipid bilayer
• Fundamental organization of all biological
membranes
– Hydrophilic phosphate heads (polar)
– Hydrophobic lipid tails (non polar)
• Membranes are…
• Selectively permeable - they allow only
specific substances to travel across them
– Some travel passively (passive transport):
water, oxygen, carbon dioxide
(diffusion/osmosis)
– Some need a little help: glucose (facilitated
diffusion) FYI: still passive transport
• Some require energy to pass through
(active transport): Ions
• Ex: potassium/sodium/hydrogen
– It requires ATP (cellular energy) and membrane
proteins
– It moves items against their concentration
gradient!