membrane structure

lipids (phospholipids)– amphipathic (polar and nonpolar regions)

proteins some carbohydrates

fluid mosaic model Overton, 1895

– membranes made of lipids– substances that dissolve in lipids enter cells more rapidly

than substances that don’t Langmuir, 1917

– made artificial membrane out of phospholipids Gorter & Grendel, 1925

– membrane lipids are phospholipids, 2 layers thick Darson-Danielli, 1935

– sandwich model (supported by first EM images) Singer & Nicolson

– proteins randomly dispersed fluid mosaic

fluid mosaic model

phospholipid bilayer

membrane structure

membrane carbohydrates

cell-cell recognition = cell’s ability to distinguish one type of neighboring cell from another

important for sorting of cells in embyro basis for rejection of cells by immune system usually branched oligosaccharides

– some are covalently bonded to lipids (glycolipids)– most are covalently bonded to proteins

(glycoproteins)– human blood groups have different

oligosaccharides (A, B, AB, O)

passive transport DIFFUSION

– result of intrinsic KE of molecules– tendency of molecules to spread out into available

space– area of [high] area of [low]– movement is due to concentration gradient

OSMOSIS– diffusion of water across a selectively permeable

membrane– hypertonic = higher concentration of solutes– hypotonic = lower concentration of solutes– isotonic = equal concentration of solutes– direction of osmosis is determined only by a

difference in total solute concentration

diffusion

osmosis

water balance of cells

a cell without walls can tolerate neither excessive uptake nor excessive loss of water– problem solved if isotonic environment is

maintained– animals in hypo- or hypertonic environments must

have a mechanism for osmoregulation

cell walls help maintain water balance in non-isotonic environments– wall expands to point, then becomes turgid– hypertonic environment plasmolysis

• PM pulls away from wall• usually lethal to plant cell

cell water balance

facilitated diffusion transport proteins aid movement of

polar and ionic substances across PM has many of the properties of an

enzyme– may have specific binding site– can become saturated– can be inhibited– don’t act as catalysts, but as physical

carriers

* aquaporins

* gated channels

facilitated diffusion

active transport

solutes are moved against concentration gradient

“uphill” = requires energy major factor in ability of cell to maintain

stable internal concentrations of all molecules

work performed by membrane proteins

active transport

all cells have voltages across their PM (known as membrane potential…usually ~ -50 to –200mV)– cytoplasm of cell is negative compared to

extracellular fluid (ECF) because of unequal distribution of anions and cations

membrane potential acts like a battery(energy source that affects traffic of all charged

substances across membrane) 2 forces drive the diffusion of ions

– chemical force– electrical force

Na-K pump actively contributes to membrane potential

electrogenic pump = generates voltage across a membrane (Ex. H+ pump)

Na+ – K+ pump

proton pump

cotransport

endocytosis

energy flow in ecosystems

CATABOLIC PROCESSES

FERMENTATION partial degradation of sugars in absence

of O2

CELLULAR RESPIRATION O2 consumed as reactant with organic

molecules

(mitochondria is site of these reactions)

CHEMICAL EQUATION(general)

organic + O2

compounds

CO2 + H2O + energy

*** Energy produced is ATP & heat

CHEMICAL EQUATION(classic)

C6H12O6 + O2

CO2 + H2O + energy

*** G = -686 kcal / mole

ATP triphosphate tail is chemical equivalent of a

loaded spring close packing of 3 negatively charged PO4

groups makes arrangement unstable cells utilize energy by transferring PO4 to

other compounds price of most cellular work is conversion of

ATP ADP + Pi

To keep working, the cell must regenerate its supply of ATP from ADP.

The transfer of electrons is part of the answer to how metabolic pathways yield energy.

OXIDATION = loss of electron REDUCTION = gain of electron

e- donor = reducing agent e- acceptor = oxidizing agent

NAD+ acts as an electron shuttle

Because oxygen is so electronegative, it is one of the most potent oxidizing agents.

C6H12O6 + O2

(RA) (OA)

CO2 + H2O + energy

food

NADH

ETC

oxygen

THE PROCESS

1. GLYCOLYSIS

(cytosol) 2. KREBS CYCLE

(mitochondrial matrix) 3. ELECTRON TRANSPORT CHAIN

(inner mitochondrial membrane)

overview of cellular respiration

GLYCOLYSIS = splitting of sugar

catabolic takes place in CYTOSOL

glucose 2 pyruvate

C-C-C-C-C-C C-C-C + C-C-C

occurs with or without O2

GLYCOLYSIS

10 steps, each with own enzyme INVESTMENT PHASE:

cell spends ATP to phosphorylate fuel molecules

PAYOFF PHASE:

ATP produced; NAD+ NADH

(reduced)

glycolysis: energy inputs and outputs

glycolysis: energy investment phase

glycolysis: energy payoff phase

KREBS CYCLE

if O2 is present, pyruvate enters mitochondria to complete oxidation

2 carbon enter, 2 different carbon exit as CO2

oxaloacetate is always regenerated most of the energy harvested is

conserved as NADH

(one step uses FAD2 instead of NAD+)

pyruvate acetyl CoA

KREBS CYCLE

KREBS CYCLE—summary

ELECTRON TRANSPORT CHAIN

collection of molecules embedded in the inner membranes of the mitochondria

folds of inner membrane (cristae) increase surface area

most components are protein decrease in free energy as e- move

down the chain MAKES NO ATP DIRECTLY

ELECTRON TRANSPORT CHAIN

ELECTRON TRANSPORT CHAIN

FUNCTION:

break large free energy decrease into a series of smaller steps that release energy in manageable amounts

CHEMIOSMOSIS

along inner mitochondrial membrane are many ATP synthase enzymes

H+ gradient drives oxidative phosphorylation

ETC functions to maintain H+ gradient (uses flow of e- to pump H+ across membrane, from matrix to intermembrane space)

CHEMIOSMOSIS

FLOW OF ENERGY

glucose NADH ETC chemiosmosis ATP

each NADH 3 ATP each FADH2 2 ATP

ESTIMATED TOTAL ATP = 38

EFFICIENCY = 40%

Oxidation of mole of glucose = 686 kcal

Phosphorylation of ADP ATP = 7.3 kcal / ATP

7.3 x 38EFFICIENCY = -----------------

686*** rest of energy lost as heat ***

FERMENTATION

MECHANISM FOR OXIDIZING ORGANIC FUEL AND GENERATING ATP IN THE ABSENCE OF O2

pyruvate is crossroads …

FERMENTATION

2 ATP are generated in glycolysis whether conditions are anaerobic or aerobic

fermentation is an extension of glycolysis that can generate ATP solely by substrate-level phosphorylation

ALCOHOL FERMENTATION

LACTIC ACID FERMENTATION

FACULTATIVE ANAEROBES

some organisms (mainly yeast & bacteria) can make enough ATP to survive using either fermentation or respiration

pyruvate acts as “fork in the road”

ROLE OF GLYCOLYSIS LIKELY HAS EVOLUTIONARY BASIS

glycolysis is the most widespread metabolic pathway among living things

occurs in cytosol

(organelles probably didn’t appear until ~ 2 billion years after the first prokaryotes)

molecules entering glycolysis

STARCH GLUCOSE

GLYCOGEN GLUCOSE

POLYSACCHARIDES GLUCOSE

PROTEINS AMINO ACIDS

FATS ACETYL CoA

REGULATION

STEP 3 OF GLYCOLYSIS IS IRREVERSIBLE

fructose-6-phosphate

phosphofructokinase (allosteric enzyme)

fructose-1,6-bisphosphate

Chapter 10: Photosynthesis

Photosynthesis…

…the conversion of light to chemical energy

auto – trophic = “self feed”

ultimate source of organic compounds

PRODUCERS

plants

multicellular alga

unicellular protist

cyanobacteria

hetero – troph = “other feed”

live on compounds produced by other organisms

CONSUMERS

subtle forms: decomposers, etc.

CHLOROPLASTS all plant parts have

chloroplasts, but they are most abundant in leaves

color comes from chlorophyll (or another pigment)

light energy absorbed drives the synthesis of food molecules

CHLOROPLASTSfound mainly in cells of

mesophyll(tissue in interior of leaf)

microscopic pores (stomata) control flow of gases

water is absorbed by roots

CHLOROPLASTSSTRUCTURE

double membraneFLUID = stromathylakoid = “coins”grana = “stacks”

CHLOROPLASTS

PHOTOSYNTHESIS EQUATION6CO2 + 12H2O + light energy

C6H12O6 + 6O2 + 6H2O

net equation would only show water as a reactant net equation is reverse of respiration

(both processes occur in plants)

PHOTOSYNTHESIS EQUATION

CO2 + H2O + light energy

CH2O + 6O2 (simplified form)

synthesis of carbohydrate one carbon at a time

PHOTOSYNTHESIS EQUATION The splitting of water was confirmed

using a radioactive source.

(1.)

CO2 + 2H2O CH2O + H2O + O2

(2.)

CO2 + 2H2O CH2O + H2O + O2

PHOTOSYNTHESIS EQUATION The splitting of water was confirmed

using a radioactive source.

(1.)

Water is the source of H in products.

(2.)

Water is responsible for the release of O2

electromagnetic spectrum

location and structure of chlorophyll

LIGHT REACTIONS

PIGMENTS:

absorb visible light black absorbs all wavelengths as light meets matter, it may be

reflected, transmitted, or absorbed

LIGHT REACTIONS

PIGMENTS:

spectrophotometer can measure ability of pigment to absorb various wavelengths

measure absorption vs. wavelength(absorption = fraction of light not transmitted or reflected)

LIGHT REACTIONS

PIGMENTS:

absorption spectrum underestimates effectiveness of certain wavelengths

only cholorphyll a can participate in light reactions, but other pigments can absorb light and transfer the energy to chlorophyll a

LIGHT REACTIONS

ACCESSORY PIGMENTS:

chlorophyll b—slight structural difference leads to different absorption spectrum

carotenoids—function of some seems to be photoprotection; instead of transmitting light to chlorphyll a, they absorb and dissipate excessive light that would otherwise damage chlorophyll a

absorption spectra

how a photosystem harvests light

noncyclic electron flow

CHEMIOSMOSIS Mitochondria: food (CE) ATP

H+ driven from innermembrane space to matrix (OUT IN)

Chloroplast: light chemical energy

H+ driven from thylakoid space to stroma(IN OUT)--ATP forms in stroma--pH in thylakoid space rapidly drops when

illuminated

chemiosmosis: mitochondria vs. chloroplasts

light reactions and chemiosmosis

Melvin Calvin

CALVIN CYCLE

similar to Krebs cycle in that starting material is regenerated

CARBON: enters as CO2, leaves as carbohydrate (G3P)

--requires 3 cycles

CALVIN CYCLE

METABOLIC ADAPTATIONS FOR PLANT SURVIVAL compromise between photosynthesis and

excessive water loss from the plant on a hot, dry day, most plants will close

stomata to conserve water– even with stomata partially closed, [CO2]

decreases in air spaces

– [O2] released from photosynthesis begins to increase

– under these conditions, photorespiration is favored

C3 PLANTS most plants use the Calvin cycle to fix C

into 3-C compounds – 3-C compound= 3-phosphoglycerate– rubisco is enzyme

Ex. rice, soy, wheat, bean produce less food when stomata close

on hot dry days

PHOTORESPIRATION photo = occurs in light respiration = consumes O2

rubisco can accept O2 instead of CO2

photorespiration decreases photosynthetic output by siphoning organic materials from the Calvin cycle– generates no ATP– produces no food

not known how process is beneficial (drains up to 50% of C from Calvin cycle in soy beans)

PHOTORESPIRATION conditions that lead to photorespiration:

– bright, hot, dry days– leads plants to close stomata

C4 and CAM pathways minimize water loss and photorespiration

C4 PLANTS preface Calvin cycle by forming 4-C

compounds Ex. corn, sugar cane have unique anatomy:

– bundle-sheath cells: arranged in tightly packed sheaths around leaf veins

• site of Calvin cycle in chloroplasts

– mesophyll cells: more loosely arranged around bundle-sheath cells

• CO2 incorporated into organic compounds

C4 PLANTS

C4 PLANTS[in mesophyll cells]

1. CO2 + PEP (3-C) oxaloacetate (4-C)

enzyme: PEP carboxylase

(has high affinity for CO2 compared to rubisco)

(can fix CO2 efficiently when rubisco can’t)

2. oxaloacetate (4-C) malate (4-C)

[in bundle-sheath cells]

3. malate (4-C) pyruvate (3-C) PEP

CAM PLANTS Ex. cactus, pineapple open stomata at night, close during the

day mesophyll cells use vacuoles to store

organic acids made during the night stomata close in the morning during the day, CO2 is released from

organic acids, allowing ATP and NADPH to run the Calvin cycle

C4 and CAM plants

photosynthesis overview