Cell Structure

Cell Structure
And Function
Why are cells small?
• Metabolism determines size.
• Adequate surface area for exchange of
materials.
• Surface-area-to-volume ratio.
• Volume grows faster then surface area.
• In larger cells, rates of exchange are
inadequate to maintain cell.
Prokaryotic Cells Vs.
Eukaryotic Cells
• Prokaryotic Cells- lack a membrane
bound nucleus, and they are small (110um in diameter).
• Eukaryotic Cells-have membrane bound
nucleus, and they are larger (10-100um
in diameter).
Prokaryotic Cells
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There are two groups:
Domain Bacteria
And
Domain Archaea
Plasma Membrane
• Regulates the movement of molecules.
Prokaryotic Cells
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Thylakoids
Chlorophyll
Cell wall-> polysaccharides & proteins.
Plasma membrane -> glycerol+hydrocarbons
DNA&RNA base similar to eukaryotes
They live in extreme habitats.
Prokaryotic ->Eukaryotic Cells
• Endosymbiotic Theory= Cells living with
in cells, in a mutually benificial
relationship. (Symbiosis:)).
• Organelles have own DNA
• Organelles divide independently of the
cell they live in.
• Double membrane.
Eukaryotic Cells
• Animal & Plant Cells
The Nucleus
• It is the command center.
• It has chromatin in it
-forms chromosomes
-DNA+RNA+protein
• Nucleolus:
-produces ribosomes
• Nuclear Envelope:
-Double membrane
Ribosomes: Protein Synthesis
• Occur in Cytoplasm or attached to
endoplasmicreticulum.
Rough Endoplasmicreticulum
• Rough ER
• Continuous with nuclear envelope
• Flattened saccules
• Ribosomes
• Synthesizes proteins
• Modifies proteins:
-adds sugar chains
-helps with folding
-forms transport vesicles
Smooth Endoplasmic
Reticulum
• Smooth ER
-continuous with rough endoplasmic reticulum
-tubular
-no ribosomes
-main functions:
1.)synthesizes lipids (including sex hormones)
2.) detoxifies drugs
-forms transport vesicles
Golgi
Apparatus
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-stack of curved or flattened saccules
-inner vs outer face
-main functions:
Modify ER products
Manufacture Macromolecules
Sort Products
Ship products to vesicles
Endomembrane System
• Consists of: Nuclear envelope
• -Endoplasmicreticulum
• -Golgi Appartus
• -Lysosomes
• -Vesicles
Importance:
• - enzymes in certain areas
• -vesicles move molecules around
Lysosomes
• Produced by Golgi Apparatus in animal
cells
• Low pH
• Digestive enzymes-> hydrolyze
macromolecules
• Apoptosis- cell death
Peroxisomes
• Vesicles that contain enzymes.
• Enzymes synthesized in cytoplasm( not
in ER)
• Produce H2O2 ( by product), then
water.
• In seedlings, convert fatty acid to sugars
• In liver, detoxify ETOH (jack daniels)
Energy Transformers of Cells
• Mitochondria:
Cellular respiration-> ATP
• Chloroplasts:
Photosynthesis->Carbohydrates
Vaculoles
• Store substances
• Plant cell central vacuole:
Cell support
Stores nutrients and waste products
Acts like lysosomes in animals
Pigments are stored
Plant cell growth
Mitochondria
• Cristae
Increase surface area (enzyme
attachment)
• Matrix contains enzymes->cellular
respiration.
Cytoskeleton
• What is it??
• Networks of fibers that run through the
cytoplasm.
• What does it do?
• Mechanical support
• Maintain cell shape
• Anchor organelles
• Enables cells to change shape
• Entire cell
• Organelles with in cell wall
Cell Membrane Structure and
Function
• Fluid Mosaic Model -1972 Singer and
Nicholson
• Plasma membrane is a mosaic of
protein molecules bobbing in a fluid
layer of phospholipids.
Regions of Integral Proteins
• Hydrophobic Regions: Not water
friendly
• Hydrophilic: Water lover
Functions of Cell Membrane
• Barrier between living contents &
surrounding environment.
• Regulates what goes in and out of cell
• It is selective
• It helps maintain homeostatic
environment.
Fluid mosaic model
• Proteins in membrane can be:
• -peripheral-> inside surface anchored
by cytoskeleton(structural role)
• -integral->imbedded in membrane but
can move laterally.
• Most proteins move laterally in
membrane.
Fluid Mosaic Model
• Carbohydrate Chains
• Glycolipid=phospholipid+carbohydrate
(sugar chain)
• Glycoprotein=protein+carbohydrate
(sugar chain).
• Asymmetry->
• Carbohydrate chain on outside surface
BLOOD TYPE BASED ON CARBOHYDRATE CHAINS A,B,O
Fluidity of Cell Membrane
• Body temperature->olive oil
• More unsaturated fatty acid residues,
greater fluidity.
• Cholesterol (animal cells) stiffens and
strengthens membrane
• Why is it good to be fluid?
• Proteins only function properly when
they can move
Channel Protein
• Allows particular molecules to cross cell
membrane freely.
• Cystic Fibrosis->faulty chloride channel
Carrier Protein
• Selectively interacts with a specific
molecular ion so that it can cross
plasma membrane.
• Obesity-> problem with sodiumpotassium transport
Enzymatic Protein
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Carry out metabolic reactions
Adenylate cyclase->ATP
Metabolism
Toxin of cholera bacteria disrupts
adenylate cyclase-> severe diarrhea
Permeability of Plasma
Membrane
• It is differentialy (selectively) permeable.
How do molecules cross
membrane?
• Passive Transport: DOES NOT
REQUIRE ATP!!!
• Active Transport: REQUIRES LOTS OF
ATP!!!!
What is Diffusion?
• Movement of molecules from a high
concentration to a lower concentration
until equilibrium is achieved.
• Movement down a concentration
gradient.
What is Osmosis?
• Diffusion of water across a differentially
permeable membrane due to
concentration differences.
• Solution=fluid(the solvent)
That contains a dissolved solid(the solute)
Transport Across
Membrane:passive transport
->diffusion
• Co2, O2,glycerol,water, alcohol
Diffuse across membrane
Transport across membrane:
passive transport-> facilitated
• Moves molecules from high
concentration to low concentration.
• Sugars and amino acids (non-lipid
soluble).
• Requires carrier protein
• No energy expenditure needed
• Are specific
• Undergo change in shape
Transport across membrane:
Active Transport
• Move molecules across concentration
gradient
• Requires energy (ATP)& carrier proteins
• Proteins are called Pumps
Active Transport: Exocytosis
• Secretion- moving out of cell
Active Transport: Endocytosis
• Endocytosis= taking substance into cell
by vesicle formation
Active Transport: Endocytosis
• Phagocytosis= cellular eating, engulfing
of large particles
• Pinocytosis= cellular drinking engulfing
of lliquid and small particles
• Receptor-Mediated Endocytosis=form
of pinocytosis that is specific, this si how
cells can bring in a bulk qty of
molecules.
Modification of Animal Cell:
Surface Extracelluar matrix
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ECM functions:
Support cell and influence behavior
Components:protein+polysacharides
Structural proteins=
Collagen and elastin->
Strength and resiliance
Adhesive proteins =
Fibronectins and laminins ->
Cell migration and communication
Modification of Plant Cell
Surface:Cell Wall
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Functions :
Protection
Maintain shape
Prevent excessive water uptake
Hold plant up
Cellulose+other
polysaccharides+proteins
Modification of Plant Cell Wall
Surface: Cell Wall
• Primary cell wall->young cell-> cellulose
+pollysaccharides)
• Middle Lamella->cement cells together
w/ pectin
• Secondary cell wall ->strength(lignin)
• Plasmodesmata-> cytoplasmic
connections
Metabolism: Energy and
Enzymes
• What is metabolism?
• All chemical reactions that occur in a
cell
What is energy?
• Capacity to do work and bring about
change
Different Kinds of Energy
• Kinetic=energy of motion
• Potential= stored energy
Why are we talking about
energy?
• 1.cells must acquire energy from
environment
• 2.cells can not make energy (energy
exists and can be transformed)
• 3in life energy transformations are
chemical
Different Kinds of Energy
• Food has potential energy-> Kinetic
energy
• Food= Chemical energy
• Energy flows it does not cycle
Laws of Thermodynamics
• 1st law of thermodynamics: law of
conservation of energy.
• Energy can not be created nor
destroyed but it can be changed from
one form to another
Laws of Thermodynamics
• 2nd Law of Thermodynamics:
• Energy can not be changed from one
form to another with out a loss of
useable energy
Law of Thermodynamics
• 2nd law (restated):
• Every energy transformation makes the
universe more disordered.
• Entropy is a measure of disorder or
randomness
Energy Transformation
• Heat is useable energy
• Heat is the energy of random molecular
motion
• Release of heat increases entropy in
the universe
Cells and Entropy
• Energy transformation occurs in cells
• 2nd law: energy transformation in cells
increases the total entropy in the
universe
• Cells can be ordered
• Cellular processes require input of
energy from outside cell-> SUN
Linking metabolism and
Entropy
• Chemical reactions occur
spontaneously if it increases entropy in
the universe
• Standard for spontaneity -> free energy
• Free energy= amount of energy
available to do work following chemical
reactions
Types of Chemical reactions
• Exergonic: energy out, energy released
spontaneously(-)
• Endergonic: energy in energy absorbed
not spontaneous (+)
Exergonic vs Endergonic
• Many cellular processes are
endergonic(ex. Protein synthesis)
• Endergonic reactions require input of
energy.
• Energy released by exergonic reactions
drive endergonic reactions=coupled
reactions
ATP:Energy for Cells
• Energy released during break down of
ATP ( exergonic reaction) it helps drive
cellular endergonic reactions
How does ATP perform the
work?
• Enzymes transfer phosphate group from
one ATP to glutamic acid->
phosphorylation
• Phosphorylated glutamic acid is reactive
(less stable)than original molecule.
• Ammonia displaces phosphate group ->
glutamine
Function of ATP
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ATP supplies energy for : Chemical Work
Synthesis macromolecules transport work
Pumpsubstances across plasma membrane
Mechanical work
Contract muscles, beat cilia, and flagella, etc.
Enzymes and metabolism
• Enzymes are catalytic proteins that
speed up rate of chemical reaction in a
cell by lowering activation energy (EA)
barrier.
• Ea is the initial investment of energy for
starting a reaction-> energy require to
break bonds in reactant molecules
Enzyme and activation Energy
• Enzymes lower the Ea barrier by
bringing the substrates in contact w/
each other. Critical bonds in substances
providing favorable microenvironment,
direct participation with chemical
reaction
• Substrates= reactants in an enzymatic
reaction
Induced Fit
• Between Enzyme and its Substrate
• Active Site: undergoes change in shape
to fit more snugly around substrate
Factors Affecting enzymatic
speed:
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Substrate Concentration
Temperature
Ph
Rate of reaction
Enzyme Concentration
Control of enzymatic Activity
• Enzyme cofactors
• Non protein helpers (organic or inorganic)that
assist in catalytic activity or enzymes
• Coenzyme= organic cofactor that assists
enzymes, may accept, or contribute atoms to
a reaction
• Vitamins are required for synthesis of
coenzymes
• Phosphorylation=kinases add phosphate
groups to enzyme to activate them
Control of Enzyme Activity
• Enzyme inhibition= active enzyme
prevented from combining with
substrate.
• Examples: competitive inhibition
• Noncompetitive inhibition
• ( we see this with sulfamide drugs)
Control of Enzyme Activity
• Specific type of non competitive
inhibition: Feedback inhibition=when the
end product binds to the first enzyme of
a pathway.
Photosynthesis
• Land plants
• Multicellular algae
• Cyanobacteria-(1st living orgs to evolve
on earth)
• Unicellular protists
• Other photosynthetic prokaryotes
Photosynthesis
• Is conversion of solar enery->chemical
energy
• Solar energy+co2+H2O->glucose+O2
• Solar
energy+6CO2+6H2O+C6H12O6+6O2
Photosynthesis Occurs In
• Chloroplasts
• Chlorophyll absorbs solar energy and is
found in membranes of the thylakoids
Solar Energy
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Electromagnetic Spectrum
Light is a form of electromagnetic energy
Electromagnetic energy travels in waves
The distance between waves is a wavelength
Photon=a discrete amount of light energy
Light absorption by
chloroplasts
• Chlorophyll absorbs mainly blue & red
light and transmits or reflects green light
Photon absorption by isolated
chlorophyll
• Electron boosted from ground state (
low energy)->
• Excited state ( high energy)
• Electron returns to ground state emitting
energy ( heat and flouresence)
Photon Absorption by
chlorophyll in chloroplasts
• Photo system= chlorophyl+other pigments
• Photosystem-> light harvesting unit
• Antenna molecules absorb photon energy
and pass to reaction center
• Chlorophyll a transfer electron to primary
electron acceptor
• Primary electron receptor traps high energy
electron in excited state
Overview of Photosynthesis
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Light reaction: in thylakoid membrane
Require light
Occur in thylakoid membrane
Solar energy absorbed by chlorophyll
Solar energy converted to chemical
energy ATP & NADPH
• Water split releasing O2
Overview of Photosynthesis
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Calvin Cycle reaction:
Does not require light directly
Occurs in stroma
Chemical energy (ATP, NADPH) is used
to reduce CO2 to carbohydrate
Light Reactions
• Step 1
• Photon absorbed in photosystem 2
• Chlorophyl and electrons become
excited
• Excited electrons trapped by primary
electron receptor
• “hole”left by electrons must be filled
Light Reaction
• Step2
• Water is split by an enzyme
• Electrons extracted from water fill
“hole”in chlorophyll A
• H+ stay w/in thylakoid space
• Oxygen released into atmosphere
Light reaction
• Step 3
• Excited electrons pass down through
the ETS (electron transport system)
• ETS composed of cytochromecomplex
• This is a series of redox reactions
• Step4
• Energy from ETS used to produce ATP
What is the Electron transport
systme?
• A series of membrane bound carriers that
transfer electrons from one carrier to another
• Each transfer results in the release of energy
• High energy electrons enter
• Low energy electrons exit
• Each carrier is reduced and then oxidized in
turn
Light reaction
• Step 5
• At end of ETS electrons fill “hole”in
chlorophyll A of photosystem1
• “hole”result of photon absorption by
photosystem 1
Light Reaction
• Step 6
• Excited electrons passed to enzyme
NADP+
• NADP+ accepts 2 electrons and 2 H+
• NADPH os an electron carrier molecule
• Nadph Carries high energy electrons
How is ATP Made?
• Thylakoid spae->H+ reservoir
• H+ from splitting of water molecules
• Energy from ETS is used to pump
across metabolism
• Diffusion of H+down concentration
gradients powers ATP synthase
• AtP synthase makes ATP through
chemiosmosis
Chemiosmosis
• Use of a H+ to drive ATP synthesis
Calvin Cycle Reaction
• For 1 sugar molecule to be produced
the cycle must take place 3 times
• It takes 3 molecules of carbon dioxide to
produce 1 molecule of sugar
Calvin cycle reaction
• Phase 1: Carbon Fixation
• Co2 incorporated into organic material
• Each co2 is attached to a 5 carbon sugar
(RUBP)
• Rubisco catalyzes this step (most abundant
protein in chloroplasts, earth)
• 6 carbon molecule is unstable-> breaks down
into two 3 carbon molecules (PGA)
Calvin Cycle
• Phase 2 REDUCTION
• Energy from ATP & electron from NADPH are
reused to reduce 6 molecules of PGA to 6
molecules of sugar PGAL
• 1 PGAL leaves cycle as sugar, sugar has
converted 3co2 to 1 sugar
• 6 ATP consumed, 6 NADPH consumed
• How many turns of the cycle are needed to
produce 1 molecule of glucose?
Calvin Cycle
• Phase 3 Regeneration of RUBP
• 5 molecules of pgal are rearranged to
form 3 molecules of RUBP with the help
of ATP for energy
• 3 ATP are consumed
Cellular Respiration
“redox reaction”
• Cellular respiration: takes place in
cytoplasm and mitochindrion.
• Chemical energy->chemical energy
• C6H12O6+6O2
• (oxi)
(reduc.)
• ->6CO2+6H2O+atp+heat
Molecules of Importance
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NAD+
Redox coenzyme
Accepts 2 electrons andH+->NADH
NADH carries high energy electrons to
ETS(electron transport system)
Molecules of Importance
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FAD
Redox coenzyme
Accepts 2 electrons and 2H+->FADH2
FADH2 carries high energy electrons to
ETS(electron transport system)
Molecules of importance
• ATP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Overview of cellular
respiration
• Four main reactions:
• Glycolysis-occurs in cytoplasm is split of
sugars in 1/2, pyruvate. Energy
Investment
• Transition reaction- link from cytoplasm
to mitochondrion
• Cytric Cycle
• Cellular Respiration
Glycolysis
• Occurs in Cytoplasm
• Glucose broke down into 2 pyruvate
molecules
• Energy Investment phase: active
glucose w/ 2 ATP
• Energy Pay Off phase: oxidation the
removal of H, production of NADH, ATP
• This makes 4 molecules of ATP
Glycolysis
• Aerobic environment(likes O2)->
pyruvate enters mitochondrion still has
lots of energy in them
• Anaerobic environment (no O2)->
Fermentation
Glycolysis
• Inputs: glucose 2NAD+
• 2 ATP
• 2ADP+2P
• Outputs: 2 Pyruvate
• 2NADH
• 2ATP net
How is ATP made in
Glycolysis?
• Enzymatic transfer of a phosphate
group from a high energy substrate to
ADP
Transition reaction
• Connects glycolysis to citric acid cycle
• Pyruvate ( charged molecule)enters
mitochondria via active transport
• Reaction occurs in the matrix:
• Pyruvate->acetyl Co A
• Occurs 2x per glucose molecule
Summary of Citric Acid Cycle
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Input
2acetyl groups
6NAD+
2FAD
2 ADP+2P
Output
4CO2
6 NADH
2FADH2
2ATP
made by substr. Phos
Circles 2 x to make 1 glucose molecule
Electron transport System
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Located in crisate of Mitochondrion
High energy electrons enter
Low energy electrons leave
O2 is final electron acceptor
As electrons pass down ETS energy is
captured and ATP is produced
• NADH->3ATP
• FADH2->2ATP
How is ATP made in ETS?
• Oxidative phosphorlation
• Produces ATP from energy released by
ETS
• H+ pumped into intermembrane space
• H+ flow down concentration gradient
into matrix
• ATP made by ATP synthase->
chemiosmosis
Energy yield from Glucose
breakdown
• 39% of available energy transferred
from glucose to ATP
• Rest is lost to heat
• Yield 36-38 ATP
Fermentation
• Alcohol Fermentation
• Pyruvate converted into ethanol
• Yeast-> beer, wine, and bread
Fermentation
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Lactic Acid Fermentation:
Pyruvate converted to Lactate
Bacteria and yeast-> cheese, yougurt
Muscle Cells!!!!!!
Fermentation
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Input
Glucose
2 ATP
2ADP+2P
output
2 lactate or
2alcohol&2CO2
2ATP net
Breakdown of other foods
• Carbohydrates & fats & proteins
• Can all be used as fuel for cellular
respiration
• Monomers of these molecules enter
glycolysis or CAC at various points
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