Dr. Yost - Exam 1 Lecture Notes - Chapter 21 PDF

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Dr. Robert Yost lecture notes for exam 1 of BIOL-K 103. These notes provide exact details as to what material is present on his exams. The book is unnecessary to purchase. He never changes his exams. ...

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Chapter 21: The Origin and Evolutionary History of Life 1Learning Objectives 1.

Describe the formation of organic molecules under the conditions believed to have existed on early Earth. This will include: describing examples of reactive surfaces comparing and contrasting the prebiotic soup and iron-sulfur world hypotheses (knowledge/comprehension)

2.

Describe the Miller-Urey experimental model and explain how it could be used to investigate the synthesis of organic molecules. This will include: understanding the prebiotic soup hypothesis, how the experiment was conducted, and the results obtained (knowledge/comprehension/application)

3.

Define the terms anaerobe, aerobe, heterotroph, and autotroph. (knowledge)

4a. Describe the formation of protobionts. 4b. Compare and contrast microspheres and coacervates, which are two types of protobionts. 4c. Describe how protobionts are similar to, as well as different from, eukaryotic cells. (knowledge/comprehension/application) 5. Compare and contrast the major hypotheses related to the evolution of cellular metabolism and regulation. They are the RNA first, DNA first, metabolism first hypotheses, and the DNA/RNA/Protein model. (knowledge/comprehension/application) 6. Describe the transformation in energy conversion when organisms transitioned from an anaerobic to an aerobic environment (knowledge/comprehension) 7a. Compare and contrast how the autogenesis (endomembranous) and serial endosymbiosis theories are related to the evolution of cellular organelles. 7b. Discuss evidence used to support that some organelles arose from an endosymbiotic relationship with eubacteria (knowledge/comprehension/application)

Some key words Autotroph an organism capable of producing its own organic compounds from inorganic materials (photosynthesis for example) Coacervate a specific type of protobiont containing enzymes used for more complex synthesis Endomembranous theory single membrane organelles originated by budding off the internal surface of the plasma membrane Endosymbiont an organism that lives in or on another Endosymbiosis theory double membrane organelles arose from a symbiotic relationship in which the endosymbiont lving inside the cell lost its autonomy and became incorporated as an organelle within that cell Heterotroph an organism not capable of producing its own organic molecules from inorganic materials (will be a consumer) Microsphere one type of protobiont; produced by adding water to abiotically formed polypeptides Protobiont a vesicle of abiotically produced polymers Stromatolite a column of prokaryote cells that become fossilized (living stromatolites are extremely rare)

Chapter 21: The Origin and Evolutionary History of Life I. Environment and evolution of organic molecules Gases present in primitive atmosphere carbon dioxide (CO2) water vapor (H2O) carbon monoxide (CO) nitrogen (N2) ammonia (NH3) [limited] hydrogen sulfide (H2S) methane (CH4) [limited] II. Four requirements for chemical evolution A. Little or no free oxygen so atmosphere was reducing environment B. Energy source was lightning, cosmic and ultraviolet radiation C. Chemical building blocks including water, dissolved inorganic molecules and atmospheric gases were present D. Time

I. Formation of organic molecules A. Reactive surfaces 1. Pyrite – fool’s gold 2. Clay - charged surfaces - ions (Zn + Fe) – catalysts - enzyme-like - attract monomers that spontaneously polymerize

This will include: understanding the prebiotic soup hypothesis, how the experiment was conducted, and the results obtained (knowledge/comprehension/application)

B. Prebiotic soup hypothesis – organic molecules near Earth’s surface (water) “sea of organic soup” B. Iron-sulfur hypothesis 1. Organic precursors formed near thermal vents energy rich molecules and precursors of biological molecules 2. Communities there today: tube worms & other organisms Slide 4

I. Miller-Urey experiments: Prebiotic soup hypothesis A. Conditions meant to mimic primitive Earth - heat source, lightning (spark chamber), rain (condenser) time – inorganic to organic B. Results All 20 amino acids, bases for RNA and DNA, lipids, ATP, etc. based upon what is in the mixture that is used

I. Terms related to primitive Earth’s environment A. Anaerobic: absence of O2 B. Aerobe: requires O2 C. Heterotroph: ingests already formed organic/inorganic material (use what’s available)  Anaerobic heterotrophs are predicted first found D. Autotroph: makes own organic/inorganic molecules  photosynthesis I. Requirements preceding origin of cells and life A. Abiotic production of nucleotides and amino acids: prior to appearance of cells B. Polymerization leading to DNA, RNA, and proteins C. Two types of microspheres formed 1. Protobionts: precursor to cell; not necessarily a coacervate 2. Coacervates: type of protobiont D. Membrane enclosed polymers [coacervates] evolved cellular properties 1. Self-replication___________________________________________________________ 2. Inheritance________________________________________________________________

Slide 7 I. Microspheres as Precursors to cells: protobionts and coacervates A. Protobionts: abiotically produced 1. What are they?: nonliving microsphere; evolved into cells by way of coacervates 2. Structurally what do they do?: separate internal and external environments  Protobiont are not coacervate 3. Functionally what is similar to cells? a. excitability: electrochemical gradient; slight charge difference (charges/ions coming in and out) o If we change the gradient, it will respond (excitability) o Concentration b. osmotically active: respond to osmotic and chemical changes in environment c. simple chemical reactions: d. division: binary fission (protists) o large soap bubble splitting in two 5. What protobionts lack a. no DNA to establish lineage b. not self-replicating Protobiont -> Coacervate -> Cells

B. Coacervates leading to first cells 1. What are coacervates? : Specialized protobiont (microsphere), organic molecules are trapped inside [“protected environment”] 2. What can they do?  If enzymes and reactants trapped inside get directed product formation beginnings of cellular reactions Protobiont vs Coacervate  Coacervate has active chemical processes  Protobionts are inactive (hollow) – can have ions – no real biological activity

Brooker Biology pg 460-61

I. Molecules necessary for cellular metabolism A. Metabolism-first hypothesis – benefits of chemical reactions A role for coacervates 1. Intrasphere organization _____________________________________________________________________ 2. Energy source ______________________________________________________________________ Slide 12 4. RNA and DNA synthesis: already known they can form spontaneously on clay; proteins [enzyme] first would allow organized and directed synthesis of RNA and DNA  Most likely, RNA came first: o Single stranded o Could more easily than DNA, reflect the environment

B. RNA-first hypothesis 1. Self-replicating RNA arose first: ribozymes; RNA replication and eventually chemical reactions in cells 2. Role for proteins: later, independent enzymes catalyzed reactions 3. Information storage: RNA can store info in its sequence

Other supporting factors for RNA 1. Single strand sequence more “easily” replicated 2. Stability of base sequence depends upon environment 3. Can assume a variety of shapes based upon sequence

4. Can get different sequences due to synthesis errors 5. Have been able to synthesize different RNAs in lab

C. DNA involvement in cellular processes 1. Initial DNA synthesis: RNA replicated a duplicate strand; DNA made from RNA via reverse transcriptase 2. Positives for evolution of DNA: double stranded, info stability, fewer mutations than RNA, genetic storage

3. Negative for DNA synthesis first: no enzymatic properties; selection occurred for cells both with RNA and DNA D. Transition from RNA/DNA/protein to DNA/RNA/protein world DNA → RNA → protein Summary DNA became the information storage molecule RNA remained involved in protein synthesis Protein enzymes catalyzed most cell reactions Selection occurred for cells with both DNA and RNA

The first cells A. Heterotrophs: rely on preformed molecules; consumed spontaneously-formed organic molecule B. Anaerobic environment C. Energy source fermentation (anaerobic)

I. Biological evolution began with the first cells A. Stromatolites: minute layers of fossils that are mineralized dead cells living under new cells 1. Microfossils 2. Minute layers of prokaryotic cells (Cyanobacteria) 3. Fossil evidence of early cells 3.5 bya 4. Some still living B. Cyanobacteria

These organisms were most likely the source of the first free oxygen in the atmosphere

II. The transition from heterotroph to autotroph A. Switch from fermentation to photosynthesis: eventually organisms that obtained energy from other sources like photosynthesis evolved and survived (autotroph). Mutations likely responsible for transition B. Splitting molecules other than water Perhaps splitting water-rich molecules like H2S releasing sulfur

C. Role of cyanobacteria and photosynthesis: first organisms to obtain H2 electrons by splitting water. Photosynthesis resulted in O2 released as a gas (ox-redox possible) and O2 levels increased in ocean and atmosphere

Objective 7: 7a. Compare and contrast how the autogenesis (endomembranous) and serial endosymbiosis theories are related to the evolution of cellular organelles. 7b. Discuss evidence used to support that some organelles arose from an endosymbiotic relationship with eubacteria (knowledge/comprehension/application)

Origin of organelles A. Autogenesis [endomembranous] theory: single membrane organelles; inward budding of plasma membrane

Serial endosymbiosis: one organisms that is different than other; those two will live in or on one

another; once free-living prokaryote engulfs and lost independent existence; double membrane  Organelles ; chloroplast; photosynthetic bacteria engulfed by heterotrophic cells  Mitochondria – aerobic bacteria initially engulfed by anaerobic

Origin of organelles Evidence supporting prokaryotic origin of come cellular organelles

A. Size : similar B. Genetic analysis: mitochondria derived from bacterium similar to modern alphaproteobacterial that synthesize ATP via oxidative phophorylation C. Enzymes and transport systems : similar to those associated w/ bacterial membranes

D. Replication: binary fission or splitting; similar to bacteria E. Antibiotics : organelle activities harmed by antibiotics effective against bacteria...