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The Cell
The stuff that has been boring you for
years!
(Brought to you by the people who make learning
mandatory so that we can keep our jobs and have
summer off!)
Cytoskeleton
 Structural support for motility and
regulation
 Allows cell to change shape
 mechanically transmits signals
from surface to interior
 constructed from three types of
fibers
microtubules (thick)
 microfilaments(thin)

 Intermediate fibers
Microtubules
 Found in Eukaryotic Cells, hollow,
straight, constructed of globular
protein called tubulin, reinforce
cell shape
 Tracks for organelle movement by
motor molecules
 Separate chromosomes during cell
division
 Centrosomes, centrioles, cilia,
flagella
Centrosomes and Centrioles
 Centriole: pair of cylindrical
structures located in centrososme,
composes of nine sets of triplet
microtubules arranged in a ring,
replicate during division
Cilia and Flagella
 May propel, or draw fluid across
membrane
 extension of plasma membrane
with core of microtubules, 9 + 2
pattern, identical to centrioles,
anchored by basal body
 Use ATP to power dynein
movement
Microfilaments
 Solid rods of globular protein
(actin) wound into helix
 Provide cellular support, bear
tension, aide in muscle contraction
(myosin), cytoplasmic streaming,
and localized contraction for the
cleavage furrow during cell
division
Intermediate filaments
 Composed of Keratin, more
permanent the microtubules and
microfilaments
 Bear tension, framework for
cytoskeleton, fix organelle position
(nucleus)
Membrane Structure
 Plasma membrane is boundary
btwn living and nonliving, 8nm
thick, controls chemical traffic,
selectively permeable
 Made of amphipathic
phospholipids, means hydrophilic
and hyrdrophobic region present
Fluid Mosaic Membrane
 Membrane held together by weak
hydrophobic interactions
 lipids and proteins drift w/in membrane
 must be fluid to work properly,
moderated by cholesterol
 membrane less fluid at warmer T
by restraining movement of
phospholipids
 at low T, prevent packing of
phoshpolipids
 Membrane is a mosiac of diff
proteins embedded an dispersed in
a phoshp. Bilayer
Integral proteins: transmembrane,
 peripheral proteins: attached to
mem.surface,
 Distinct directional orientation


Carbs on exterior, proteins also have
directional orientation
Cell-Cell Recognition
 Basis for:
 sorting of embryo’s cells into tissues
and organs
 rejection of foreign cells by immune
system
 Recognize by carbs
 branched oligosaccharides bonded
covalently to lipids and proteins
Cell Communication
 Communicating cells may be close
or far apart, communicate by local
regulators or hormones
 Three stages of cell signaling :
Reception
 Transduction
 Response

Signal Reception
 Chemical signals bind to specific
receptors (receptor protein)
Signal molecules complement to
specific region or receptor protein
 signal behaves as ligand (small
molecule to large molecule)
 Signal receptors are plasma mem.
proteins

Signal Transduction Pathways
 Pathways relay signals from
receptors to cellular responses

Chain of reactions
 Information is passed along,
passes along info not molecule

second messengers; Cyclic AMP,
Ca ions
Cellular Responses to Signals
 In response to signal, cell may
regulate activity in cyto or
transcription in nucleus
 Pathways amplify and specify
responses
cAMP: few to many
 target cells with receptor bind to
specific signaling molecule

Regulation of Cell Cycle
 Controlled by a clock Internal and external cues
regulate
Chemical-nutrients, growth
factors
 Physical-density-dependent
inhibition

 Cancer cells have escaped from
cycle controls
Cancer
 Do not stop due to density inhibition
 Make growth factors themselves, is
abnormal signal
 Divide indefinitely as long as nutrients
are available, normal 20-50 times
 Stop dividing at random points
 Immune system normally recognizes
 If avoid regulation, from tumor,
unregulated mass of normal tissue
 Benign tumor: remain at this original
site and can be completely removed
 Malignant tumor: invasive, impair
normal function of organs, cancer
Properties of Malignant tumors
 Anomalous cell cycle,
 Unusual chromosome #
 Lost attachment to neighboring
cells, may cause separation from
original tumor
 Migrating cells invade other parts
of body, form more tumors
 Spread is call metastasis
Metabolism and Energy of Life
 Metabolism: Totality of organism’s
chemical processes
 Catabolic Paths: release E by breaking
down
 Anabolic Paths: consume E to build
complex from simple
ATP
 Powers cellular work by coupling
exergonic to endergonic rxns


Ex: net loss of free energy
En: E requiring that get net gain of E
 Drives mechanical, transport, and
chemical work in cells
 works by transferring phosphate group
Enzymes
 Speed up and control biochemical and
metabolic rxns by lowering energy
barriers
 Catalyst: accelerates rxn w/o being
changed, so used over and over
 Enzymes: biological catalysts made of
proteins
Enzymes are Substrate Specific
 Depends on enzymes 3D shape
 Substrate: substance an enzyme acts
on and makes more reactive
 Active Site: restricted region of an
enzyme molecule which binds to
substrate, changes its shape in response
to substrate, called induced fit
Active Site, catalytic center
 Hold two or more reactants in proper
position for they may react
 Active site conducive to particular type
of rxn
 the higher substrate [ ], the faster the
reaction, up to a limit
Cell’s Physical & Chemical env. Affects
Enzyme activity
 T and pH effect rate




Increasing T, increase rate until reach
denature point of enzyme and cells
optimal in humans: 35o to 40oC
optimal pH is 6-8
some work best in extreme pH, like
pepsin (digestive) at pH of 2
 Cofactors: small nonprotein molecules
required for catalysis
 Enzyme Inhibitors: some reversible
(weak bonds), or irreversible
(covalent)


Competitive: resemble normal substrate,
block active site,
Noncompetitive: bond to other enzyme
site, cause enzyme to change shape so
active site cannot bond, metabolic
poisons
Control of Metabolism
 Metabolic pathways are regulate by
controlling enzyme activity
 Allosteric regulation:
 Feedback inhibition
 Cooperativity:
 Location of enzymes orders
metabolism
Allosteric Regulation
 Uses site other than active site
 2 Conformations: catalytically active,
and inactive
 Binding stabilizes active conformation
 Makes it more or less reactive to
substrate
Feedback Inhibition
 Regulation of metabolic pathway by its
end product, which inhibits an enzyme
within the pathway
 Prevents cell from wasting chemical
resources
Cooperativity
 Substrate molecules may enhance
enzyme activity
 substrate binding to active site induces
substrate binding at other sub-unit
active site