Cell Structure And Function. Why are cells small? Metabolism determines size. Adequate surface area...

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 (1-10um in diameter).

• Eukaryotic Cells-have membrane bound nucleus, and they are larger (10-100um in diameter).

Prokaryotic Cells

• There are two groups:

• Domain Bacteria

• And

• Domain Archaea

Plasma Membrane

• Regulates the movement of molecules.

Prokaryotic Cells

• 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

GolgiApparatus

• -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 sodium-potassium transport

Enzymatic Protein

• 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

• 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

• 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

• 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:

• 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

• 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

• 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

• 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

• NAD+

• Redox coenzyme

• Accepts 2 electrons andH+->NADH

• NADH carries high energy electrons to ETS(electron transport system)

Molecules of Importance

• 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

• Input Output

• 2acetyl groups 4CO2

• 6NAD+ 6 NADH

• 2FAD 2FADH2

• 2 ADP+2P 2ATP

• made by substr. Phos

• Circles 2 x to make 1 glucose molecule

Electron transport System

• 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

• Lactic Acid Fermentation:

• Pyruvate converted to Lactate

• Bacteria and yeast-> cheese, yougurt

• Muscle Cells!!!!!!

Fermentation

• Input output

• Glucose 2 lactate or

• 2 ATP 2alcohol&2CO2

• 2ADP+2P 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