Assimilation - Taking Up the Right Stuff Each Fundamental Process of Life Absorption Ingestion Unity of Life Diversity of Life

places design Universal physical constraints on Ecological roles and chemical provides certain principles opportunities for Organismal and/or strategies provides molecular Common genomic solutions for selectionpressures toolkit from LUCAC Different cells, 1. We’ll use clickers today can evolve for tissues, & organs 2. Circulation systems HW due on Friday

Unique and Circulatory Systems Nutrient Assimilation - Taking Up the Right Stuff in Different Multicellular Lineages Absorption Ingestion Photosynthesis

1. No specializations for gas exchange and circulation in unicellular organisms - passive diffusion only 2. Independent origins of gas exchange and/or circulatory systems in various multicellular animal and lineages 3. Physicochemical constraints (Fick’s Law and Hagen- Poiseuille equation) operating on convergent structures

Deep molecular homologies underlie all nutritional strategies

1 Nutrient assimilation - Unity of Life Big Steps in the Origin of Life

Definition - the uptake of non-gaseous molecules from the • Origin of information processing/replication system environment into the • Origin of for generating small organic molecules and larger polymers Common features with gas exchange - • Origin of bioenergetics 1) Transmembrane process dependent on surface area 2) Passive diffusion down chemical (concentration) gradients • Origin of lipid membranes defining the boundary of for a few molecules (such as ), but not true for most life – the challenge of impermeable membranes nutrient molecules at most times

C & R 26.12

Gas exchange vs. nutrient assimilation/osmoregulation Nutrient assimilation and osmoregulatory/excretory systems exhibit deep molecular homologies

• Homologous transport proteins operating in modern organisms • Carry out nutrient assimilation and osmoregulation/ • Evolved in pre-LUCAC organisms.

F Fig 6.8 amino acids Gases - high permeability -> do not require transport proteins - low permeability -> require selective transport proteins

2 Basic Mechanisms of Solute Transport - F. Fig. 6.29 How do membranes perform active transport? (Simple) ATP-dependent pump generates an electrochemical gradient – a gradient of concentration (“chemical”) and charge (“electro”) across the membrane. Typical ions: H+, Na+, K+ ATP Electrochemical gradient F. Fig. 6.22 Some examples: 1) Gas exchange regulation - stomates in 2) Nutrient assimilation - digestive tracts in animals mycelia in fungi Simple diffusion - passive movement of molecules through the lipid membrane in vascular plants or a channel (also called a uniporter) 3) Osmoregulation – many organisms Facilitated diffusion - passive movement of molecules across the membrane 4) Excretion - kidneys in vertebrates that is facilitated by a carrier/transporter 5) Transport - sucrose transport in plants 6) Electrical signaling - excitable membranes Active transport - ATP-dependent movement of molecules across the membrane that is performed by a pump

Reminder: H+ electrochemical gradients can drive Reverse process - ATP hydrolysis can generate H+ or Na+ ATP synthesis – F-type ATP synthases/ATPases electrochemical gradients – P-type ATPases F. Fig. 6.28

Freeman Fig. 6.29 Na+/K+ pump

F. Fig. 9.24 F. Fig. 9.25 P-type ATPases (or ATP-dependent cation pumps) General class of F-type ATPases, including ATP synthases ATP cation electrochemical gradient (H+ gradients ATP) across the membranes of , mitochondria, and plastids during photosynthesis and For example, H+ pump, Na+/K+ pump, and Ca2+ pump http://www.pump.ruhr-uni-bochum.de operating across outer cell or ER membranes

3 + Reverse process - ATP hydrolysis can generate H Unity of nutrient assimilation at molecular level – electrochemical gradients – V-type ATPases active transport moves solutes against their gradients Step 1. Ion pumps use ATP energy to generate electrochemical gradients (i. e., voltage and concentration gradients) across cell membranes.

electron microscopic images V-type ATPases (or ATP-dependent H+ pumps) ATP H+ electrochemical gradient C & R Fig. 8.17 Alberts et al. Fig. 11.13 • H+ pump operating across many eukaryotic organelles (e.g., lysosomes, contractile vacuoles, and plant vacuoles) Proton pump (all organisms) Na+/K+ pump (animals only) • Similar structure and some homologous subunitshttp://www.pump.ruhr-uni-bochum.de as the F-type ATP synthase, but it runs in reverse •

Step 2. H+ electrochemical gradients can drive Alterative Step 2. Na+ electrochemical gradients nutrient uptake in all organisms - Fig. 37.23 can also drive nutrient uptake in animals

+ + + Na + Na Na + Na + Na 3 Na+ Na Na+ Na+

+ Na

+ Na Na+ 2 K+ Molecules cations (+) sugars cations (+) Molecules cations (+) sugars cations (+) using these amino acids using these amino acids transporters anions (-) transporters anions (-)

4 Evolution of transport proteins Active transport Bacteria Archaea Eukarya

1. ATPases are able to directly couple ATP hydrolysis to the transport of most molecules across biological membranes. Last common ancestor or ancestral community Phylogenetic tree of 2. Different transport proteins use H+ H+/Na+ antiporter or Na+ electrochemical gradients as the energy source for carrying out Many transporters of ions and other small molecules display the transport of most molecules. considerable sequence and structural homology throughout the 3 domains -> deep evolutionary roots near the origin of life 3. Both are true. 4. Neither are true. Some workers argue for very few ancestral transport genes - a few ion and organic-molecule transporters that diversified to give rise to over 1,000 transport genes in some eukaryotes.

Summary - unity of nutrient assimilation at Diversity of nutrient assimilation at the molecular level the organismal level Universal features of nutrient assimilation in all organisms - 1) Transmembrane transport depends on ATP-dependent pumps Important factors - 2) These pumps establish H+ or Na+ electrochemical gradients for 1) Phylogeny carrying out nutrient uptake 2) Nutritional strategy 3) Selective transporters use these EC gradients to move nutrients into the organism. 3) source 4) Deep molecular homologies unify all nutritional (and 4) Solute concentration osmoregulatory) strategies 5) Metabolic rate 6) Organismal size

5 Nutrient assimilation (absorption) - fungi Nutrient assimilation (absorption) - fungi

Well-adapted for absorption • rapid growth • hydrolytic exoenzymes • high surface area • P-type H+ pump, • selective transporters F Fig. 30.6

C & R Fig. 31.2d C & R Fig. 37.14

Mycorrhizae - “fungus roots” Carnivorous fungus

Ion assimilation (photosynthesis) - plants Nutrient assimilation (ingestion) - amoeba

• Pseudopodium engulfs small organisms or food particles via phagocytosis. • Food vacuole fuses with lysosome containing hydrolytic • Nutrients absorbed across lysosome membrane via active transport (V-type H+ pump, plus transporters) F Fig. 38.9 F Fig. 36.2 Roots are specialized for Thin hairs develop water and ion uptake near growing root tip

Plants use homologous ATP-dependent H+ pumps to establish H+ electrochemical gradient, which transporters use to move ions into root cells. C & R Fig. 8.19 and F Fig. 28.15

6 Nutrient assimilation (ingestion) - ciliate Some animal cells are also capable of phagocytosis

• Cilia in oral groove move bacteria and other food to mouth • Food is engulfed via phagocytosis, and food vacuoles merge with lysosomes • Food vacuoles move toward apex and then toward base

• Undigested contents C & R Fig. 43.3 of food vacuoles are expelled at anal pore For example, human macrophages (“big eaters”) use fibril-like F Fig. 28.12 pseudopodia to capture invading bacteria prior to phagocytosis

Vertebrate Vertebrate small intestine

Proteins and Higher [Na+], variable [glucose]  Broken down by enzymes into Na+ diffusion cotransports glucose amino acids and sugars + + +  Na+/K+ ATPases establish Lower [Na ] due to Na /K pump; EC gradients Higher [glucose] due to +  Transport proteins – e.g., Na /glucose cotransporter Na+/amino acid (e.g., lysine) Glu diffuses down its conc gradient or Na+/glucose cotransporters  More in Monday’s lecture Lower [glucose]

Fig. 43.16 Fig. 43.16

7 Study questions- Learning Objectives 1. Explain why nutrient assimilation in all organisms exhibits deep molecular homologies. 2. Explain why nutrient assimilation occurs in different structures in various multicellular lineages. 3. Describe the membrane(s) and the (s) responsible for converting electrochemical gradients into high-energy phosphate bonds of ATP. 4. Do the same for the reverse conversion of high-energy phosphate bonds of ATP into electrochemical gradients. 5. Describe the different transporters which use the energy in an electrochemical gradient to move ions or polar organic molecules across a membrane. 6. Describe the different structural adaptations associated with nutrient assimilation in a fungus, amoeba, ciliate, plant root, and vertebrate small intestine.

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