BILD 3 Lecture 11 Notes - Origin of Life PDF

BILD 3: Lecture 11 (Notes) The Origin Of Cellular Life ○ Cells are the BASIC UNIT of life. ○ All cellular life consists of CELLS, the BASIC units, which are composed of a SET of attributes: Metabolism Growth...

BILD 3: Lecture 11 (Notes) The Origin Of Cellular Life ○ Cells are the BASIC UNIT of life. ○ All cellular life consists of CELLS, the BASIC units, which are composed of a SET of attributes: Metabolism Growth Differentiation Communication Evolution The Origin Of Life ○ About 3.8-4 BILLION YEARS AGO, CELLULAR LIFE appeared on Earth. Some microbial fossil records DO exist, largely in fossilized MATS in AUSTRALIA and SOUTH AFRICA. The ROD-SHAPED BACTERIA that is found in South Africa and Australia are the OLDEST FOSSILS that we have. The Clock ○ 0: Origin of EARTH (4.6 BYA) ○ 2 PM: Original of CELLULAR LIFE (4 BYA) ○ 4-5 PM: Origin of CYANOBACTERIA (3 BYA) ○ 7 PM: Modern EUKARYOTES (2 BYA) ○ 11th Hour/Present: Humans (100,000 YEARS) The Origin Of The First Cell ○ Life began with RNA (Single-Celled Strand of DNA) This was the FIRST MOLECULE to appear. During PRIMORDIAL EARTH, it was not a very DIVERSE/PLEASANT planet. There was a bit of WATER/LOTS OF HEAT on the planet more than 3 billion years ago. Most of the water was EVAPORATED, and there was LOTS OF LIGHTNING.  ○ DR. UREY found HYDROGEN, CO2, AMMONIA, METHANE, and a LITTLE WATER. Different compounds were being made through these elements: CYANIDE, ALDEHYDES, and KETONES. These were combined with the LIGHTNING and ENERGY on Earth at the time. This led to the production of AMINO ACIDS/PURINES/SUGARS/PRYIMIDINES. This then made POLYMERS. The DNA Process ○ ADENINE is one of the 4 nitrogenous bases present in NUCLEIC ACIDS. This was present in a HIGH CONCENTRATION in prebiotic soup. It originated from the CONVERSION of HCN. This formed a TETRAMER, which reacted with FORMAMIDINE, and produced ALCN. ○ TETRAMER: Four molecules of CYANIDE bound together. ALCN = ADENINE. ○ After seeing the formation of ADENINE, Miller and Urey were able to witness the development of GUANINE. ADENINE = FIRST NITROGENOUS BASE FOUND! ○ The development of COMPLEX ORGANIC MOLECULES that were produced by RANDOM CHEMISTRY led to the development of RNA. Clay-Bentonite ○ In prebiotic soup, CLAY helps the POLYMERIZATION of nucleotides and FORMATION of other complex organic molecules. Through tests in the lab, scientists found that in the presence of CLAY, all of the NUCLEOTIDES can form a LONG STRUCTURE. I-METHYLADENINE easily polymerizes in the presence of BENTONITE, producing up to 40 NUCLEOTIDES. ○ Clay played an essential role in the EVOLUTION OF LIFE because it had a ROLE in the origin of ANCIENT MEMBRANES and helped to form POLYMERS.  The Origin Of Life ○ It started with the BIOLOGICAL BUILDING BLOCKS. Amino Acids, Nucleotides, Sugars RNA World ○ The first living entity was much more SIMPLER than modern cells, even the SIMPLEST we know. A single molecule of RNA (or PRE-RNA) could REPLICATE ITSELF and METABOLIZE chemicals. ○ Some RNA molecules can CATALYZE reactions These are known as RIBOZYMES, a combination of RIBONUCLEIC ACID and ENZYMES. ○ RNA could serve the DUAL purpose of storing GENETIC INFORMATION and CATALYZING REACTIONS. The Sequence ○ Complex Organic Molecules Produced by RANDOM CHEMISTRY —> RNA —> PROTEINS —> DNA Cells & Cell Membrane ○ All cells must have a cell MEMBRANE to count as a cell. This membrane must protect the CELL from the OUTSIDE. It will decide what can go IN and what will go OUT. ○ A single LIPID LAYER known as a MICELLE might have been an EARLY plasma membrane FORM. The presence of those ENVELOPES was able to CREATE a way of separating the INSIDE CONTENT from the OUTSIDE world. This could have formed a CRUDE WAY of separating INTERIOR contents from the EXTERNAL environment. The RNA World Hypothesis ○ A membrane FORMED around the RNA.  This RNA was able to SELF-REPLICATE itself, and then it was SURROUNDED by a MEMBRANE. There was a PHYSICAL SEPARATION that protected the RNA from the OUTSIDE. ○ PROTEINS were synthesized using information from RNA. RNA gave rise to DNA to store GENETIC INFORMATION. Proteins were the ones who now became able to perform CATALYTIC REACTIONS. DNA was the LAST ONE to appear. LUCA: The last PRIMORDIAL CELL from which ALL OF THE DIFFERENT CELLS originated. Origin Of Membranes ○ Early replicating polymers could have become ENCLOSED in lipid envelopes. Bentonite FACILITATES the conversion of LIPIDS into VESICLES. It helped in forming the LONG STRUCTURES but also with the CONVERSION PROCESS. Clay then becomes ENTRAPPED in the vesicles, bringing any RNA embedded in the CLAY PARTICLES. Formation of ENCAPSULATED STRUCTURES protected the genome from DEGRADATION. LUCA: Last Universal Common Ancestor ○ This was the FIRST CELL from which ALL LIFE ON EARTH is believed to have DESCENDED. SIMPLE metabolism RNA GENETIC material PRIMITIVE ribosome and protein BIOSYNTHETIC APPARATUS Transcriptional MACHINERY GENETIC code Why DNA? ○ Cells today use DOUBLE-STRANDED DNA, not SINGLE-STRAND RNA, to store GENETIC INFORMATION.  dsDNA provides a BACKUP COPY of the genetic information in case of a PROBLEM. The change between DNA and RNA exists because DNA is MORE STABLE than RNA. RNA initially existed because it is SINGLE STRAND and it is MUCH EASIER. ○ However, due to DNA’s DOUBLE-STRANDED formation, it provides a BACKUP COPY. Molecular Evolution Order ○ Based on the ORIGIN OF LIFE, molecules originated in the order of: RNA —> Protein —> DNA Central Dogma ○ DNA is transcribed into a WORKING COPY of MESSENGER RNA (mRNA). mRNA is then translated into the PROTEINS needed to make a cell WORK. Other forms of RNA (tRNA and rRNA) are ALSO IMPORTANT. These will show the VERSATILITY of RNA molecules for LIFE PROCESSES. Vertical Vs. Horizontal Gene Transfer ○ Vertical: When a cell divides, it will replicate its DNA and then, the DNA will be passed to a COPY of it. The mother cell DIVIDES and the two daughter cells get a COPY of the DNA. ○ Horizontal: Genetic information can be PASSED to other cells, and they do NOT need to be the SAME. It is just exchanged to other cells that are PRESENT, and it is the exchange of GENETIC INFORMATION.  It is the EXCHANGE of DNA between DIFFERENT CELLS. These types of exchanges are what gave rise to PROKARYOTES, BACTERIA, and ARCHAEA. Subsurface Origin Hypothesis ○ Life originated at HYDROTHERMAL SPRINGS on the OCEAN FLOOR. The conditions would have been MORE STABLE. ○ In the BOTTOM of the ocean, there are HOLES, and from those holes, HOT WATER comes out. They are 2 KM DEEP at the bottom of the ocean, and there are DIFFERENT TYPES OF VENTS. ○ Steady and abundant supplies of ENERGY would have been AVAILABLE at these sites. ○ “BLACK SMOKER” VENTS are organic compounds that are UNSTABLE in extreme heat. ALKALINE VENTS will release water with HIGH pH and WARM WATER. The water that comes out of these is NOT THAT HOT, and it has a HIGH pH. ○ With this WARM WATER, there are a LOT of COMPOUNDS that come out from here. ○ In those small HOLES, there is probably everything that occurred on LAND in HERE. This created a DIFFERENT GRADIENT, which allows it to be a DIFFERENT ACIDITY LEVEL that was more SUITABLE for the origin of life. When Did Cellular Metabolism Evolve? ○ In the beginning, OXYGEN was NOT PRESENT on Earth. Some microorganisms, such as ARCHAEA, are REMNANTS of a PRIMORDIAL METABOLISM in very HARSH conditions (Hot Springs). Archaea are a GROUP OF ORGANISMS that live in EXTREME environments and can live in HOT WATER. Early Life On Earth ○ Earth was ANOXIC Metabolism: Doing things INSIDE of the cells, such as BREAKING DOWN FOOD and ABSORBING NUTRIENTS. The metabolism of PRIMITIVE CELLS was exclusively ANAEROBIC and likely CHEMOLITHOTROPHIC. ○ Anaerobic: NO OXYGEN ○ Chemolithtrohpic: USE INORGANIC COMPOUNDS FOR ENERGY.  ○ At some point, there was a MEMBRANE that was using PHOSPHOLIPIDS. ATPase in OUR CELLS now undergoes AEROBIC RESPIRATION, and a lot of energy is made in the MITOCHONDRIA. It will take advantage of the ELECTRON TRANSPORT CHAIN, which is what generates MOST of our ATP. Primitive ATPase uses HYDROGEN SULFIDE, but there is still an ELECTRON TRANSPORT CHAIN of some sort. Great Oxidation Event ○ Around 2.7 BYA, CYANOBACTERIA developed a PHOTOSYSTEM that could use WATER instead of H2S, which allowed them to generate OXYGEN. There was a BACTERIUM that helped in the development of CYANOBACTERIA. They are green because they can PHOTOSYNTHESIZE. Instead of using HYDROGEN SULFIDE, they ended up using WATER, which created the GREAT POLLUTION EVENT. Around 2.4 BYA, the GREAT OXIDATION EVENT occurred and OXYGEN LEVELS continued to rise. Oxygen went from 0% to 21-22%, which came from the cyanobacteria using WATER to photosynthesize. ○ The cells BEFORE THEM were able to survive WITHOUT oxygen. ○ Aerobic Respiration exists because our cells need to BREAK IT DOWN for WATER. Prokaryotes Vs. Eukaryotes ○ Prokaryotes: Bacteria and Archaea with NO NUCLEUS Pro-Karyon = BEFORE NUCLEUS ○ Eukaryotes: Cell WITH a Nucleus Eu-Karyon = WITH NUCLEUS Endosymbiotic Theory ○ Organelles, such as MITOCHONDRIA and CHLOROPLASTS, originated from a relationship of ENDOSYMBIOSIS. An ancestral BACTERIUM was EATEN/ENGULFED by an ancestral EUKARYOTE. It lost its ability to live INDEPENDENTLY, and that ended up evolving into an MITOCHONDRION and CHLOROPLAST.  ○ It is said that EUKARYOTIC CELLS exist because a LARGER CELL engulfs a SMALLER CELL. The cyanobacteria were now a PART of the LARGER CELL, and that is how it became an MITOCHONDRIA. ○ However, there was also ANOTHER endosymbiotic event where the cell engulfed ANOTHER BACTERIA that was able to PHOTOSYNTHESIZE. They were able to form the CHLOROPLAST that is seen in cells today. This theory explains how LARGER CELLS engulfed SMALLER CELLS, which is what was able to use OXYGEN. ○ That engulfing process is what became the MITOCHONDRIA. ○ Then, the SEPARATE EVENT for PLANTS is what created the CHLOROPLAST. Evidence For Endosymbiotic Theory ○ DNA within the mitochondria can be used to determine ANCESTRY. ○ Mitochondria RESEMBLE bacteria in SIZE and SHAPE. Mitochondria contain CIRCULAR DNA and reproduce INDEPENDENTLY of their HOST CELLS. ○ Mitochondria have a mechanism of PROTEIN SYNTHESIS similar to bacteria. The same ANTIBIOTICS that inhibit protein synthesis in RIBOSOMES in BACTERIA will also inhibit it in MITOCHONDRIA. ○ rRNA GENE ANALYSIS provided the CONFIRMATION to this theory. Mitochondria ○ During FERTILIZATION, DNA from the BIOLOGICAL FATHER and from the BIOLOGICAL MOTHER form a ZYGOTE. However, the mitochondria only come from the MOTHER, and it is ONLY INHERITED from them. Mitochondria DO NOT MIX during Fertilization. ○ The sperm can only give the DNA within the NUCLEUS, but the MITOCHONDRIA comes from the egg. Mitochondria & Evolution ○ Due to their INHERITANCE, mitochondria are important in EVOLUTION STUDIES (mtDNA). All humans descend from a COMMON ANCESTOR, MITOCHONDRIAL EVE, and she lived in the EAST AFRICAN RIFT.