CH 4: Evolutionary Origin of Cells and Their General Features

Bio 1134 - Lesson Learning Objectives

*Recall the Cell Theory

• Is credited to both Schleiden and Schwann with contributions Virchow

• Has three parts:

  1. All living are organisms composed of one or more cells.

  2. Cells are the smallest units of life. The smallest living units of all living organisms.

  3. New cells come only from pre-existing cells by cell division. They only arise by division of a previously existing cell (mitosis).

*State the features shared by all cells.

• Biochemical: composed/made of carbohydrates, proteins, lipids, and nucleic acids (DNA & RNA)

• Structural: have a plasma membrane, cytoplasm, genetic material, and ribosomes

• Metabolic: obtain energy from their environment, convert that energy to the energy of ATP (adenosine triphosphate) for energy requiring cellular processes

What can cells do?

Cells can grow, transform energy, respond to the environment, and reproduce; and have order. A population of unicellular organisms can evolve.

*Repeated Information: Macromolecules are ______.

Polymers

*What are the main polymers?

Proteins, Nucleic acids, lipids, carbohydrates

*What are the monomers (subunits) of the main polymers?

• Proteins - amino acids

• Nucleic acids - Nucleotides (A, T, C, & G)

• Lipids - fatty acids and glycerol

• Carbohydrates - monosaccharides (glucose, fructose, galactose)

*What do you need to make cells?

Phospholipids, nucleic acids, proteins, carbohydrates (all polymers) (organic) to make up cells

• Also need water, potassium, sodium, phosphorus, carbon, nitrogen (inorganic) to make up cell

*What are the steps for how cells are formed?

1. Cell membrane

2. Cytoplasm (inside membrane)

3. RNA/DNA is developed after cytoplasm is enclosed

*What is the origin of cells/life on earth?

Cells formed in Earth’s ancient, reducing (anoxic - very low oxygen levels) atmosphere. Originated 3.75+ BYA

• Oxygen breaks things down (oxidation)

• Molecules will build in an environment with little oxygen

• Earth’s ancient world has built molecules due to little oxygen

*What is the first step hypothesizing the origin of cells in Earth’s ancient, reducing atmosphere?

• Research hypothesizes why the biochemical and structural similarities of cells exist.

  1. Synthesis organic monomers (reducing atmosphere hypothesis, extraterrestrial hypothesis, and deep-sea vent hypothesis)

Explain the 3 different hypotheses of where the synthesis of organic monomers came from. (#1)

1. Reducing atmosphere hypothesis -

   • Urey-Miller Experiments

     • built a closed system to fake early earth that had

       • water (like early ocean)

       • the gases they thought were in early earth’s atmosphere (methane, ammonia, hydrogen)

       • they heated the water (like ocean evaporation) and sent electric sparks through the gases (like meteors or lightning)

       • after a week, they checked and found that in the water amino acids had formed

   • Earth had no oxygen, it was hot, and volcanoes everywhere

   • the atmosphere was made up of gases like methane (ch4), ammonia (nh3), hydrogen (h2), and water vapor (h20)

   • this atmosphere is called an reducing atmosphere because it gives electrons (electrodes) to chemical reactions

   • Hypothesis says that, with energy from things like lightning, volcanoes, or meteors, simple gases could turn into more complex organic molecules like amino acids, the building blocks of proteins

Explain the 3 different hypotheses of where the synthesis of organic monomers came from. (#2)

2. Extraterrestrial hypothesis -

   • aka “Organic Molecules Came from Space” idea

   • hypothesis suggests that the building blocks of life didn’t form on Earth at all, but instead, they came from outer space

   • scientists believe that some of these space rocks (meteors/asteroids) carried organic molecules (like amino acids and other carbon-based compounds)

   • when these rocks crashed into earth, they could have delivered those molecules to our planet

   • these molecules could have then mixed with Earth’s environment and helped kickstart life

   • This hypothesis has gained the most evidence over the years

Explain the 3 different hypotheses of where the synthesis of organic monomers came from. (#3)

3. Deep-sea vent hypothesis -

   • aka hydrothermal vent hypothesis

   • Hypothesis says that life may have started at the bottom of the ocean, near hydrothermal vents (are like underwater volcanoes - cracks in the earth’s crust that shoots out hot, mineral-rich water)

   • vents are super-hot and full of chemical energy and minerals

   • even though there is no sunlight, bacteria and other tiny life forms can survive by using chemical reactions for energy instead of photosynthesis

   • heat and minerals around these vents were said to form from simple molecules to complex and organic molecules

*What is the second step hypothesizing the origin of cells in Earth’s ancient, reducing atmosphere?

2. Synthesis of organic polymers on clay catalyst

   • This step comes after the formation of organic monomers (like amino acids and nucleotides)

   • polymers = chains of monomers stuck together (like lego structure) (ex: RNA or DNA) (due to dehydration synthesis)

   • Clay particles have a charged surface that allows them to attract and hold onto monomers

   • when monomers stick to the clay, they are close together, which increases the chance they will link up to form polymers (ex: amino acid chain builds proteins)

   • Clay acts as a catalyst - it helps the reaction happen faster without being charged itself (acts as a helper letting the building blocks of life snap together more easily)

*What is the third step hypothesizing the origin of cells in Earth’s ancient, reducing atmosphere?

3. Formation of precells (protobionts) that possessed a selectively permeable membrane and had the ability to divide. Polymers enclosed by a boundary.

   • Step where molecules start looking like real, living cells

   • Precells are tiny bubbles or droplets made of molecules surrounded by a membrane-like structure

     • Inside these bubbles (selectively permeable sacs) important molecules (like proteins or RNA) were protected and organized

   • Precells with a selectively permeable membrane controlled what molecules could enter and leave

     • Important polymers like RNA or proteins were trapped inside the membrane, where they could interact more and kickstart chemical reactions to support life

   • Precells had the ability to divide or reproduce by absorbing molecules from their environment

     • eventually they could split apart and divide into two daughter sacs

   • Some people believe the protobionts may have been liposomes (vesicles surrounded by a phospholipid bilayer)

*What is the fourth step hypothesizing the origin of cells in Earth’s ancient, reducing atmosphere?

4. Origin of self-replicating molecules (RNA, chemical selection and evolution)

   • How molecules learned to copy themselves. and why RNA is believed to have come first.

     • RNA is more versatile than DNA and can store information like DNA and also act like and enzyme (called ribozyme) to help chemical reactions happen.

   • 1st step of chemical selection: mutation - some versions of RNA were better at replicating, or more stable, being more likely to survive and make more copies of themselves

   • Overtime this led to chemical evolution - a for of natural selection at the molecular level (the 2nd step of chemical selection)

*Connect the four steps of hypothesizing to the origin of prokaryotes.

• There are two categories of prokaryotic organisms: bacteria and archaea

• Prokaryote is a simple, single-celled organism that: has a cell membrane, has DNA or RNA genetic material, has no nucleus or organelles (the first true life form)

  1. Formation of Organic Monomers:

     • these monomers are needed to make proteins and genetic material - both of which prokaryotes have

     • monomers are the basic building blocks of life

  2. Formation of Organic Polymers (on clay surfaces):

     • Prokaryotes use proteins to run their cells and RNA/DNA to store and pass on genetic info

     • this step builds those components

  3. Formation of Precells (Protobionts)

     • Precells are the structural blueprint of a prokaryotic cells: enclosed, organized, and separated from the environment

  4. Origin of Self-Replicating Molecules (RNA):

     • This step gives the precells the ability to pass on traits and evolve, just like modern cells do

• Once all these steps came together it became a structure with a membrane, molecules that can replicate, the ability to use reactions to grow and divide

*Contrast prokaryotic and eukaryotic cells.

• Prokaryotes:

  • do not have membrane-bound nucleus or membrane-bound organelles

  • are unicellular

• Eukaryotes:

  • have membrane-bound nucleus and membrane-bound organelles

  • are unicellular and multicellular

What is the oldest and most numerous organisms on Earth?

Prokaryotes - member of Domain Archaea and Domain Bacteria

What organism is the most diverse organisms on Earth?

Eukaryotic - Domain Eukarya: kingdoms Protista, plantae, fungi, and animalia)

• Eukaryotic cells (protist, plant, fungi, and animal cells) share many organelles, such as the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, and mitochondria

*Differentiate plant and animal cells.

• Plant cells:

  • have chloroplasts and central vacuoles

  • plant and fungal cells also have cell walls

• Animal Cells:

  • animal cells have none of these features

  • however both plant and animal cells have a mitochondira for ATP

*Explain the features and function of the cytosol.

• The region of a eukaryotic cell that is outside the organelles but inside the plasma membrane (the jelly-like fluid inside a cell) (like the soup that everything floats in)

  • fills the space between the cell membrane and the organelles

  • together with the organelles it makes up the cytoplasm

• Cytosol features:

  • consists of the cytoplasm (the fluid part + organelles) (site of metabolic reactions)

    • the cytosol itself is the liquid portion

    • it is the site of many metabolic reactions (chemical processes that keep the cell alive)

      • ex: breaking down glucose for energy, building proteins

  • consists of cytoskeleton (structures involved in cell shape, structure, and movement)

• Cytosol functions:

  • metabolic reactions - sum of the chemical reactions by which cells produce the material and utilize the energy necessary to sustain life (*)

  • cytoskeleton provides shape, organization, and movement

    • a network of protein filaments that acts like the cell’s skeleton + highway system

    • maintains cell shape, provides support, helps with movement of the cell itself (like in amoebas)

    • moves organelles around inside (like conveyor belts in a factory)

*Understand the structure and role of the nucleus in eukaryotic cells.

• The nucleus of eukaryotic cells houses DNA (genome) packaged as chromosomes

• The nucleus is involved in gene expression (protein synthesis) and ribosome subunit assembly

  • Ribosomes are responsible for protein synthesis in both prokaryotes and eukaryotes

*State the organelles of the endomembrane system in eukaryotic cells and explain the function of each.

• Eukaryotic cells have endomembrane systems and protein sorting organelles that play critical roles in protein synthesis and sorting.

  • endomembrane system is eukaryotic cell that have a set of organelles that work together to make, sort, and transport proteins

  • key organelles in protein synthesis/sorting are: nucleus, rough ER, Golgi apparatus, vesicles, plasma membrane

*State the semiautonomous organelles of eukaryotic cells and explain the origin of each.

• the semiautonomous organelles: mitochondria and chloroplasts

  • semiautonomous organelles arose by endosymbiosis: appropriate size, replicate asexually, DNA, inner membranes, machinery of protein synthesis

  • mitochondria - powerhouse of the cell, site of cellular respiration (makes ATP)

    • all eukaryotic cells make ATP by cellular respiration in mitochondria

  • chloroplasts - site of photosynthesis (makes sugars using sunlight)

    • the chemical reactions of photosynthesis occur in plant and algal chloroplasts

*Recall the biochemical and structural evidence supporting the endosymbiotic origins of mitochondria and chloroplasts.

• Mitochondria and chloroplasts were once free-living prokaryotes.

  • this fact is supported by morphological and biochemical evidence including the size, structure, asexual mode of reproduction, and gene expression of mitochondria and chloroplasts

• Mitochondria originated from endosymbiotic proteobacteria

• Chloroplasts originated from endosymbiotic cyanobacteria