Download Cell Structure and Function

General Cell Biology
and
Physiology
Rut Beyene
P3
Objectives
• By the end of the lecture students should know
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Cellular organization and theory
Plasma membrane composition
Membrane permeability and cellular transport
The sodium/potassium pump
Organelle structure and function
Different cell types
Epithelial cell classification
Cellular Organization
Principles of Cell Theory
• All living things are made of cells
• Smallest living unit of structure and
function of all organisms is the cell
• All cells arise from preexisting cells
Cell Size
Characteristics of All Cells
• Plasma membrane – flexible outer boundary
• Cytoplasm – intracellular fluid w/ organelles
• Nucleus – control center
Plasma Membrane
• Bimolecular layer of lipids and proteins in
a constantly changing fluid mosaic
• Plays a dynamic role in cellular activity
• Separates intracellular fluid (ICF) from
extracellular fluid (ECF)
– Interstitial fluid (IF) = ECF that surrounds cells
Plasma Membrane
• Contains cell contents
• Double layer of phospholipids & proteins
Membrane Lipids
• 75% phospholipids (lipid bilayer)
– Phosphate heads: polar and hydrophilic
– Fatty acid tails: nonpolar and hydrophobic
• 20% cholesterol
– Increases membrane stability and fluidity
• 5% glycolipids
– Lipids with polar sugar groups on outer membrane
surface
Phospholipids
• Polar
– Hydrophylic head
– Hydrophobic tail
• Interacts with water
Membrane Proteins
1. Channels or transporters
– Move molecules in one direction
2. Receptors
– Recognize certain chemicals for signal
transduction
Membrane Proteins
3. Glycoproteins
– Identify cell type
4. Enzymes
– Catalyze production of substances
Membrane Junctions
• There are three types of membrane
junctions found between cells
– Tight Junctions
– Desmosomes
– Gap Junctions
Tight Junctions
• Prevent fluids and most molecules from
moving between cells.
• Tight junctions between adjacent
epithelial cells lining the digestive tract
keep digestive enzymes and
microorganisms in the intestine from
seeping into the bloodstream.
Desmosomes
• “Rivets” or “spot-welds” that anchor
cells together.
• Abundant in tissues subjected to great
mechanical stress, such as skin and
heart muscle.
Gap Junctions
• Transmembrane proteins form pores
that allow small molecules to pass from
cell to cell.
• For spread of ions between cardiac or
smooth muscle cells.
Molecule Movement & Cells
• Passive Transport
• Active Transport
Passive Transport
• No energy required
• Move due to gradient
– differences in concentration, pressure, charge
• Move to equalize gradient
– High moves toward low
Types of Passive Transport
1. Diffusion
2. Osmosis
3. Facilitated diffusion
Diffusion
• Molecules move to equalize concentration
Osmosis
• Special form of diffusion
• Fluid flows from lower solute concentration
• Often involves movement of water
– Into cell
– Out of cell
Osmosis
Solution Differences & Cells
• solvent + solute = solution
• Hypotonic
– Solutes in cell more than outside
– Outside solvent will flow into cell
• Isotonic
– Solutes equal inside & out of cell
• Hypertonic
– Solutes greater outside cell
– Fluid will flow out of cell
Cell Tonicity
Facilitated Diffusion
• Channels are specific and help
molecule or ions enter or leave the cell
• Channels usually are transport proteins
• No energy is used
Process of Facilitated Transport
• Protein binds with molecule
• Shape of protein changes
• Molecule moves across membrane
Active Transport
• Requires carrier proteins, solute pumps
and ATP
• Moves solutes against a concentration
gradient
• Types of active transport:
– Primary active transport
– Secondary active transport
Primary Active Transport
• Molecular movement against gradient
• Example is sodium-potassium pump
Primary Active Transport
• Sodium-potassium pump (Na+-K+ ATPase)
– Located in all plasma membranes
– Involved in primary and secondary active transport of
nutrients and ions
– Maintains electrochemical gradients essential for
functions of muscle and nerve tissues
Secondary Active Transport
• Depends on an ion gradient created by
primary active transport
• Energy stored in ionic gradients is used
indirectly to drive transport of other solutes
Vesicular Transport
• Transport of large particles across plasma
membranes
– Endocytosis—transport into cell
– Exocytosis—transport out of cell
– Transcytosis—transport into, across, and then
out of cell
Process of Endocytosis
• Plasma membrane surrounds material
• Edges of membrane meet
• Membranes fuse to form vesicle
Exocytosis
• Reverse of endocytosis
• Cell discharges material
Cytoplasm
• Viscous fluid containing organelles
• components of cytoplasm
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Interconnected filaments & fibers
Fluid = cytosol
Organelles (not nucleus)
storage substances
Membranous Organelles
• Functional components within cytoplasm
• Bound by membranes
Nucleus
• Control center of cell
• Contains
– Chromosomes
– Nucleolus
Nuclear Envelope
• Separates nucleus from rest of cell
• Double membrane
• Has pores
DNA
• Hereditary material
• Chromosomes
– DNA
– Protiens
– Form for cell division
• Chromatin
Nucleolus
• Most cells have 2 or more
• Directs synthesis of RNA
• Forms ribosomes
Endoplasmic Reticulum
• Helps move substances within cells
• Network of interconnected membranes
• Two types
– Rough endoplasmic reticulum
– Smooth endoplasmic reticulum
Rough Endoplasmic Reticulum
• Ribosomes attached to surface
– Manufacture protiens
– Not all ribosomes attached to rough ER
• May modify proteins from ribosomes
Smooth Endoplasmic Reticulum
• No attached ribosomes
• Has enzymes that help build molecules
– Carbohydrates
– Lipids
Golgi Apparatus
• Involved in synthesis of plant cell wall
• Packaging & shipping station of cell
Golgi Apparatus Function
1. Molecules come in vesicles
2. Vesicles fuse with Golgi membrane
3. Molecules may be modified by Golgi
Golgi Apparatus Function
4. Molecules pinched-off in separate vesicle
5. Vesicle leaves Golgi apparatus
6. Vesicles may combine with plasma
membrane to secrete contents
Lysosomes
• Spherical membranous sacs containing
digestive enzymes
– Acid hydrolase
• Functions
– Aid in cell renewal
– Break down old cell parts
– Digests invaders (bacteria, viruses, toxins)
Peroxisome
• Spherical membranous sacs containing
oxidases and catalases
• Function
– Neutralize free radicals
– Converts radicals to hydrogen peroxide
– Hydrogen peroxide converted to water by
catalase enzymes
Mitochondria
• Have their own DNA
• Bound by double membrane
Mitochondria
• Break down fuel molecules (cellular respiration)
– Glucose
– Fatty acids
• Release energy
– ATP
Cytoskeleton
• Rod like structures found throughout the
cytosol for cellular support and movement
• Three types of rods in the cytoskeleton
– Microfilaments
– Intermediate filaments
– Microtubules
Microfilaments
• Dynamic actin strands
attached to cytoplasmic
side of plasma
membrane
• Involved in cell motility,
change in shape,
endocytosis and
exocytosis
Microfilaments
Strands made of spherical
protein subunits called actins
Actin subunit
7 nm
Microfilaments form the blue network
surrounding the pink nucleus in this
photo.
Intermediate Filaments
• Tough, insoluble
ropelike protein fibers
Intermediate filaments
Tough, insoluble protein fibers
constructed like woven ropes
Fibrous subunits
• Resist pulling forces
on the cell and attach
to desmosomes
10 nm
Intermediate filaments form the purple
batlike network in this photo.
Microtubules
Microtubules
• Dynamic hollow
tubes
• Most radiate from
centrosome
• Determine overall
shape of cell and
distribution of
organelles
Hollow tubes of spherical protein
subunits called tubulins
Tubulin subunits
25 nm
Microtubules appear as gold networks
surrounding the cells’ pink nuclei in
this photo.
Centrosome
• “Cell center” near
nucleus
• Generates microtubules;
organizes mitotic spindle
• Contains centrioles:
Small tube formed by
microtubules
Cellular Extensions
• Depending on the type of cell, there are
structures that extend outside the cell and
have varying functions
– Flagella
– Cilia
– Microvilli
Flagella
• Whip like structure that aides in the motility
and propulsion of cells.
• Contains microtubules and motor
molecules
• Requires ATP
Cilia
• Hair like projection on certain cells that
help move substances across cell
surfaces
• Contain microtubules and motor molecules
• Requires ATP
Microvilli
• Finger like projections of the plasma
membrane
• Increase the surface area for absorption
• Found mostly in the small intestine
Cell Types
• There are four main categories of tissues
– Epithelial cells: lining of hollow organs
– Muscle cells: contractility
– Nerve cells: communication
– Connective tissue: structural support
Epithelial Cell Classification
• By number of cell layers
– Simple: one cell thick
– Stratified: multiple cells thick
• By the shape of the cell
– Squamous: flat
– Cuboid: cube
– Columnar: column
Types of Epithelia
• Simple squamous
– Lining of all blood
vessel
Artery
Types of Epithelia
• Simple cuboidal
– Thyroid follicles
Types of Epithelia
• Simple columnar
– Small intestine
Types of Epithelia
• Stratified squamous
– Epidermis
– Esophagus
Non-keratinized
Keratinized
Keratinized Stratified Squamous
Epidermis
Non-Keratinized Stratified
Squamous
Esophagus
Types of Epithelia
• Stratified columnar
– Sublingual duct
Types of Epithelia
• Pseudostratified columnar
– Respiratory system