Transcript CELLS: The Living Units BIO 200 Chp 3 The Living Units Cell Theory: • The cell is the basic structural and functional unit of life •

CELLS: The Living Units
BIO 200
Chp 3
The Living Units
Cell Theory:
• The cell is the basic structural and
functional unit of life
• Organismal activity depends on individual
and collective activity of cells
• Biochemical activities of cells are dictated
by subcellular structure
• Continuity of life has a cellular basis
Figure 3.1
Cell Structure
Cell Structure
• Plasma Membrane
• Separates intracellular fluids from
extracellular fluids
• Plays a dynamic role in cellular activity
• Glycocalyx (a glycoprotein) bordering the
cell that provides highly specific biological
markers by which cells recognize one
another
Plasma Membrane Structure
The Fluid Mosaic Model
Figure 3.3
Fluid Mosaic Model
• Double bi-layer of lipids with imbedded
proteins
• Forms the basic “fabric” of the cell
membrane
• Bi-layer consists of phospholipids,
cholesterol and glycolipids
– Hydrophilic – attracts water (polar head)
– Hydrophobic – repel water (nonpolar tails)
Cell Plasma Membrane
Functions of Membrane Proteins
• Transport
• Enzymatic activity
• Receptors for signal transduction
Cell Plasma Structure
• The plasma aims to maintain
homeostasis
• Lipid molecules of the by-layer move
freely
• Polar-nonpolarity interactions keeps
stability
• Microvilla – (hairs) increase the plasma
membrane surface
Plasma Membrane
Membrane Junctions – help to knit or
adhere cellular tissue (enzymes)
Tight junction – impermeable junction that
encircles the cell, prevents molecules from
passing through
Desmosome – anchoring junction scattered
along the sides of cells, aid in mechanical stress
Gap junction – a nexus that allows chemical
substances (electrical activity) to pass between
cells
Functions of Plasma Membrane
Membrane transport
• Cells are surrounded by extacelluar or
interstitial fluid
• Interstitial fluid is rich and nutritious
• Derives from the blood stream
• Ingredients: amino acids, sugars, fatty
acids, vitamins, hormones, salts, waste
products.
Functions of Plasma Membrane
Membrane transport
• Substances move continuously across the
plasma membrane
• It allows some substances to pass and
excludes others
• Selective barrier
Characteristics of
• Differential barrier
a healthy cell
• Permeable barrier
*Damage barriers will imbalance homeostasis
Passive Transport:
Diffusion
1. Simple diffusion – nonpolar and lipidsoluble substances
• Diffuse directly through the lipid bilayer
• Diffuse through channel proteins
• Molecules disperse evenly
Figure 3.6
Passive Transport
Diffusion
2. Facilitated diffusion
• Allows transport of glucose, amino acids,
and ions
• Transported substances bind carrier
proteins or pass through water-filled
protein channels
Passive Transport
Facilitated diffusion
2. Carrier Proteins
• Are integral transmembrane proteins
• Show specificity for certain polar
molecules like sugars and amino acids
• Molecules too large to pass so they are
carried through by transport receptor
carriers
Passive Transport
3. Diffussion through Osmosis
• Occurs when concentration of a solvent is
different on opposite sides of a membrane
• Diffusion of water across a semi-permeable
membrane
• Osmolarity – total concentration of solute
particles in a solution
• Tonicity – how a solution affects cell volume
Figure 3.7
Figure 3.8
Active Transport
• Uses ATP to move solutes across a
membrane
• Requires carrier proteins
• Types of Active Transport
– Primary active transport – hydrolysis of ATP
phosphorylates the transport protein causing
conformational change
– Secondary active transport – use of an exchange
pump (such as the Na+-K+ pump) indirectly to
drive the transport of other solutes
Figure 3.10
Vesicular Transport
• Transport of large particles and
macromolecules across plasma
membranes
• Exocytosis – moves substance from the
cell interior to the extracellular space
• Endocytosis – enables large particles and
macromolecules to enter the cell
Vesicular Transport
• Transcytosis – moving substances into,
across, and then out of a cell
• Vesicular trafficking – moving substances
from one area in the cell to another
• Phagocytosis – pseudopods engulf solids
and bring them into the cell’s interior
Figure 3.12
Figure 3.13a
Figure 3.13b
Membrane Potential
• Voltage (electrical potential) across a membrane
• Resting membrane potential – the point where
K+ potential is balanced by the membrane
potential
• range -50 to -100 millivolts (mV)
• Cells become polarized
• Results from Na+ and K+ concentration
gradients across the membrane
• Steady state – maintained by active transport of
ions
Cell Membrane
• Cell adhesion molecules - anchor cells to
the extracellular matrix, assist in
movement,
• Membrane Receptors - important in
immunity, regulates voltage in nerve and
muscle tissue and neurotransmitters
Cytoplasm
• Cytoplasm – material between plasma
membrane and the nucleus
• Cytosol – viscous semi-fluid, largely water with
dissolved protein, salts, sugars, and other
solutes
• Cytoplasmic organelles – metabolic machinery
of the cell
• Inclusions – chemical substances such as
glycosomes, glycogen granules, and pigment
Cytroplasmic
Organelles
Cytoplasmic Organelles
• Membranous - mitochondria, peroxisomes,
lysosomes, endoplasmic reticulum, and
Golgi apparatus
• Nonmembranous - cytoskeleton,
centrioles, and ribosomes
Mitochondrion
Figure 3.17
Mitochondria
• Double membrane structure with shelf-like
cristae
• Provide most of the cell’s ATP via aerobic
cellular respiration
• Contain their own DNA and RNA
Ribosomes
• Granules containing protein and rRNA
• Site of protein synthesis
• Free ribosomes synthesize soluble
proteins
• Membrane-bound ribosomes synthesize
proteins to be incorporated into
membranes
Endoplasmic Reticulum (ER)
• Interconnected tubes and parallel
membranes enclosing cristernae (cristae)
• Continuous with the nuclear membrane
• Two varieties – rough ER and smooth ER
Endoplasmic Reticulum (er)
Figure 3.18
Rough (ER)
• External surface studded with
ribosomes
• Manufactures all secreted proteins
• Responsible for the synthesis of
integral membrane proteins and
phospholipids for cell membranes
Smooth (ER)
• Looping tubule network
• Catalyzes the following reactions in various
organs of the body:
• Liver – lipid & cholesterol metabolism,
breakdown of glycogen, detoxification of drugs
• In the testes – synthesis steroid-based
hormones
• In the intestinal cells – absorption, synthesis, and
transport of fats
• In skeletal and cardiac muscle – storage and release of
calcium
Golgi Apparatus
• Stacked and flattened membranous sacs
• Functions in modification, concentration,
and packaging of proteins
• “Traffic director” for cellular protein
• Transport vesicles from the ER and are
received by Golgi apparatus
Golgi Apparatus
Figure 3.20
Lysosomes
• Spherical membranous bags containing
digestive enzymes
• Digest ingested bacteria, viruses, and
toxins
• Degrade nonfunctional organelles
• Breakdown glycogen and release thyroid
hormone
• Autolysis – self-digestion of the cell
Lysosomes
• Breakdown nonuseful tissue
• Breakdown bone to release Ca2+
• Secretory lysosomes are found in white
blood cells, immune cells, and
melanocytes
Lysosomes
Figure 3.22
The Endomembrane System
Figure 3.23
Endomembrane System
• System of organelles that function to:
• Produce, store, and export biological
molecules
• Degrade potentially harmful substances
• Contains the following system:
Nuclear envelope, smooth and rough ER,
lysosomes, vacuoles, transport vesicles, Golgi
apparatus, and the plasma membrane
Peroxisomes
“Peroxide bodies”
• Membranous sacs containing oxidases
and catalases
• Detoxify harmful or toxic substances
• Neutralize dangerous free radicals
• Free radicals – highly reactive chemicals
with unpaired electrons
Cytoskeleton
• The “skeleton” of the cell
• Dynamic, elaborate series of rods running
through the cytosol
• Consists of microtubules, microfilaments,
and intermediate filaments
Cytoskeleton
Microtubules
• Dynamic, hollow tubes made of the
spherical protein tubulin
• Determine the overall shape of the cell
and distribution of organelles
Microfilaments
Dynamic strands of protein Actin
• Attached to the cytoplasmic side of the
plasma membrane
• Braces and strengthens the cell surface
Cytoskeleton
• Intermediate Filaments
• Tough, insoluble protein fibers with high
tensile strength
• Resist pulling forces on the cell and help
form desmosomes
Pg 91
Centrioles
• Small barrel-shaped organelles located in
the centrosome near the nucleus
• Pinwheel array of nine triplets of
microtubules
• Organize mitotic spindle during mitosis
• Form the bases of cilia and flagella
– Whip-like, motile cellular extensions on
exposed surfaces of certain
cells
Cilia
– Move substances in one direction across cell
surfaces
Figure 3.26
Figure 3.27a
Cellular Motion
CELIA
• Cellular extensions that
provide motility in a
whiplike motion.
• Typically found in large
numbers
• Located in the exposed
surface of the cell
• Move substances in one
direction across cell
surface
Figure 3.27c
Cellular Motion
Flagella
• Projections are longer
• A single propulsive flagellum
• Movement is achieved by propelling itself
across the surface or environment
• Basal bodies in the centrioles form the
bases for ceia and flagella
Nucleus
•
•
•
•
The control center containing genetic
Largest cytoplasmic organelle - 5µm
Nuclear envelop –dbl membrane barrier
Nucleoli – DNA & RNA for genetic
synthesis
• Chromatin – threadlike coils that form
chromosomes in cell division. Genes
Figure 3.28
DNA
Replication
Figure 3.31b
Cell Growth and Reproduction
Cell Life Cycle
• Cell division – essential for growth and
tissue repair.
• Cells die and continuously reproduce
• Some reproduce faster than others (skin,
intestinal vs. liver).
• Some loose ability to divide @ maturation
(nervous tissue, skeletal muscle, heart, RBCs)
• The DNA replicates before cell division
Cell Growth and Reproduction
Cell Division - M Phase (Mitotic)
• 2 phases: Mitosis & Cytokinesis
• Phase 1: Mitosis – nuclear division
a)
b)
c)
d)
•
prophase
metaphase
Anaphase
telophase
Phases merge together
Cell Division - Mitosis
Phase 2 – Cytokinesis
• Cytokinesis - cytoplasmic division
• Cleavage furrow formed in late anaphase
by contractile ring
• Cytoplasm is pinched into two parts after
mitosis ends
• The forming of 2 daughter cells
Figure 3.32
Figure 3.32