Nutrient Assimilation - Taking Up the Right Stuff. Each Fundamental Process of Life

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1 Absorption Ingestion Photosynthesis Each Fundamental Process of Life Unity of Life Universal physical and chemical principles Diversity of Life places design constraints on provides certain opportunities for Organismal strategies and/or 1. We ll use clickers today 2. Circulation systems HW due on Friday Unique Gas Exchange and Circulatory Systems in Different Multicellular Lineages Common genomic toolkit from LUCAC Ecological roles provides molecular solutions for can evolve for selection pressures Nutrient Assimilation - Taking Up the Right Stuff Different cells, tissues, & organs Nutrient Assimilation - Taking Up the Right Stuff Absorption Ingestion Photosynthesis No specializations for gas exchange and circulation in unicellular organisms - passive diffusion only Independent origins of gas exchange and/or circulatory systems in various multicellular animal and plant lineages Physicochemical constraints (Fick s Law and HagenPoiseuille equation) operating on convergent structures Deep molecular homologies underlie all nutritional strategies 1

2 Nutrient assimilation - Unity of Life Definition - the uptake of non-gaseous molecules from the environment into the cell Common features with gas exchange - 1) Transmembrane process dependent on surface area 2) Passive diffusion down chemical (concentration) gradients for a few molecules (such as water), but not true for most nutrient molecules at most times Big Steps in the Origin of Life Origin of information processing/replication system Origin of metabolism for generating small organic molecules and larger polymers Origin of bioenergetics Origin of lipid membranes defining the boundary of life the challenge of impermeable membranes C & R 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/excretion Evolved in pre-lucac organisms. F Fig 6.8 Gases - high permeability -> do not require transport proteins Nutrients - low permeability -> require selective transport proteins amino acids 2

3 Basic Mechanisms of Solute Transport - F. Fig (Simple) Simple diffusion - passive movement of molecules through the lipid membrane or a protein channel (also called a uniporter) Facilitated diffusion - passive movement of molecules across the membrane that is facilitated by a carrier/transporter Active transport - ATP-dependent movement of molecules across the membrane that is performed by a pump How do membranes perform active transport? ATP-dependent pump generates an electrochemical gradient a gradient of concentration ( chemical ) and charge ( electro ) across the membrane. Typical ions: H +,, K + ATP Electrochemical gradient F. Fig Some examples: 1) Gas exchange regulation - stomates in plants 2) Nutrient assimilation - digestive tracts in animals mycelia in fungi roots in vascular plants 3) Osmoregulation many organisms 4) Excretion - kidneys in vertebrates 5) Transport - sucrose transport in plants 6) Electrical signaling - excitable membranes Reminder: H + electrochemical gradients can drive ATP synthesis F-type ATP synthases/atpases Reverse process - ATP hydrolysis can generate H + or electrochemical gradients P-type ATPases F. Fig /K + pump Freeman Fig F. Fig F. Fig General class of F-type ATPases, including ATP synthases (H + gradients ATP) across the membranes of bacteria, mitochondria, and plastids during photosynthesis and respiration P-type ATPases (or ATP-dependent cation pumps) ATP cation electrochemical gradient For example, H + pump, /K + pump, and Ca 2+ pump operating across outer cell or ER membranes 3

4 Reverse process - ATP hydrolysis can generate H + electrochemical gradients V-type ATPases Unity of nutrient assimilation at molecular level 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 H + pump operating across many eukaryotic organelles (e.g., lysosomes, contractile vacuoles, and plant vacuoles) Similar structure and some homologous subunits as the F-type ATP synthase, but it runs in reverse Proton pump (all organisms) C & R Fig Alberts et al. Fig /K + pump (animals only) Step 2. H + electrochemical gradients can drive nutrient uptake in all organisms - Fig Alterative Step 2. electrochemical gradients can also drive nutrient uptake in animals 3 Na + Molecules cations (+) sugars cations (+) using these amino acids transporters anions (-) 2 K + Molecules cations (+) sugars cations (+) using these amino acids transporters anions (-) 4

5 Evolution of transport proteins Active transport ATPases are able to directly couple ATP hydrolysis to the transport of most molecules across biological membranes. Different transport proteins use H+ or Na+ electrochemical gradients as the energy source for carrying out the transport of most molecules. Both are true. Neither are true. Summary - unity of nutrient assimilation at the molecular level Bacteria Archaea Eukarya Last common ancestor or ancestral community Phylogenetic tree of H+/Na+ antiporter Many transporters of ions and other small molecules display considerable sequence and structural homology throughout the 3 domains -> deep evolutionary roots near the origin of life 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. Diversity of nutrient assimilation at the organismal level Universal features of nutrient assimilation in all organisms 1) Transmembrane transport depends on ATP-dependent pumps 2) These pumps establish H+ or Na+ electrochemical gradients for carrying out nutrient uptake 3) Selective transporters use these EC gradients to move nutrients into the organism. 4) Deep molecular homologies unify all nutritional (and osmoregulatory) strategies Important factors 1) Phylogeny 2) Nutritional strategy 3) Food source 4) Solute concentration 5) Metabolic rate 6) Organismal size 5

6 Nutrient assimilation (absorption) - fungi F Fig Nutrient assimilation (absorption) - fungi Well-adapted for absorption rapid growth hydrolytic exoenzymes high surface area P-type H+ pump, selective transporters C & R Fig. 31.2d C & R Fig Mycorrhizae - fungus roots Ion assimilation (photosynthesis) - plants Carnivorous fungus Nutrient assimilation (ingestion) - amoeba Pseudopodium engulfs small organisms or food particles via phagocytosis. Food vacuole fuses with lysosome containing hydrolytic enzymes Nutrients absorbed across lysosome membrane via active transport (V-type H+ pump, plus transporters) F Fig F Fig Roots are specialized for water and ion uptake Thin root hairs develop 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 and F Fig

7 Nutrient assimilation (ingestion) - ciliate Some animal cells are also capable of phagocytosis F Fig 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 of food vacuoles are expelled at anal pore C & R Fig For example, human macrophages ( big eaters ) use fibril-like pseudopodia to capture invading bacteria prior to phagocytosis Vertebrate small intestine Proteins and carbohydrates Broken down by enzymes into amino acids and sugars /K + ATPases establish EC gradients Transport proteins e.g., / amino acid (e.g., lysine) or /glucose cotransporters More in Monday s lecture Vertebrate small intestine Higher [ ], variable [glucose] diffusion cotransports glucose Lower [ ] due to /K + pump; Higher [glucose] due to /glucose cotransporter Glu diffuses down its conc gradient Lower [glucose] Fig Fig

8 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 enzyme(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. 8