Lecture XVI: The origin of life & Intro to Biodiversity

Question 1

Steps that may have lead to the origin of the first simple unicellular organisms:

Answer 1

Abiotic synthesis of small organic molecules (monomers).
e.g. Amino acids & nucleotides.

Joining these small organic molecules into larger macromolecules (polymers).
e.g. Proteins and nucleic acids

Packaging these macromolecules within lipid membranes (Protocells).

Origin of self-replicating molecules within protocells.

Question 2

1. Monomer Formation

Answer 2

Primitive Soup Hypothesis by Oparin and Haldane 1920s

It was hypothesized that conditions on Earth were conducive to the formation of small organic molecules.

Requirements for the hypothesis:
No free oxygen available

A source of energy (volcanic eruption, thunder storm, meteor strike, radiation)

Chemical building blocks (water, ions, dissolved gases)

Question 3

2. Macromolecules from Monomers

Answer 3

Experiments have shown that polymers will form without help from enzymes if the temperature is high enough to drive the reaction.

Question 4

3. Packaging organic macromolecules into Protocells

Answer 4

Simple lipid bilayer membranes (vesicles) may have formed around the organic macromolecules.

This would have isolated the macromolecules, in essence creating the first intracellular environment.

Question 5

4.Self Replication

Answer 5

Living organisms need to be able to replicate themselves.

Genetic information was most likely encoded as RNA in the first living organisms.
Simpler structure: single strand instead of double.
RNA key to protein synthesis and also some RNA molecules can perform enzymatic functions.

Question 6

DNA thought to have evolved after RNA

Answer 6

As RNA sequences become longer they become less stable.

DNA is much more stable in structure than RNA.

Question 7

Stromatolites

Answer 7

Structures called Stromatolites which are believed to have been formed by the ancestors of cyanobacteria (photoautotrophic).

Oldest known fossils found (aprox. 3.5 billion years old)

Composed of alternating layers of ancestor of cyanobacteria and sediment.

Question 8

First Living Organisms: The Prokaryotes (Chemo/photo autoprophs)

Answer 8

The first prokaryotes were chemoautotrophic or photoautotrophic:

Chemoautotrophs
Carbon source: CO2
Energy source: Inorganic molecules

Photoautotrophs
Carbon source: CO2
Energy source: Light

Question 9

Photosynthesis evolved early

Answer 9

The first photosynthetic prokaryotes were the ancestors of Cyanobacteria

These first photoautotrophs are responsible for filling our atmosphere with free oxygen (product of photosynthesis), remember the fossils of stromatolites.

There was a rapid increase in atmospheric oxygen between 2.4 and 2.2 b.y.a.

Question 10

Oxygen Revolution

Answer 10

Rapid increase in atmospheric oxygen. Evidence can be found in sedimentary rocks dated to that time period that show oxidation of iron had occurred.

Question 11

Recall: Endosymbiont Theory

Answer 11

The evolution of eukaryotic cells is thought to have involved 2 endosymbiont events.
Aerobic bacteria -> mitochondria
Photsynthetic bacteria -> Chloroplasts

Question 12

Cambrian Explosion

Answer 12

Around 535 – 525 mya the diversity of animals increased dramatically as is shown by the abundance of fossil remains found.
Coincides with the origin of multicellular aquatic invertebrate Consumers.

Question 13

The move to land by multicellular life (fungi, plants and animals) ~500 mya

Answer 13

Up to this point, majority of life occurring in water/moist habitats. What helped living organisms colonize land?
formation of the ozone layer reducing harmful UV radiation from the sun.

evolution of traits that reduced their reliance on water, e.g. waxy cuticle, sperm protected in pollen grains, seeds, internal fertilization…. We will discuss these in our tour of biodiversity.

Question 14

Quantifying Biodiversity

Answer 14

Ways:

1. Genetic Diversity: Measure of the genetic variation of a population, species and up to the domain level.
2. Ecosystem Diversity: All the different kinds of ecosystems in a given area.
3. Species Diversity: All the different species found in a given area.

Question 15

1. Genetic Diversity

Answer 15

We can examine genetic diversity at many levels: population, species, and up to the 3 domains Archaea, Bacteria and Eukarya.

By comparing specific sequences of DNA between groups we can see how closely related they are.

It is important, however, to compare more than one specific genetic sequence between groups to more accurately reflect evolutionary history.

Question 16

2. Ecosystem Diversity

Answer 16

How many and what kind of ecosystems can be found in a given area.
When there are many different types of ecosystems in an area there will also be many different kinds of life forms present. Greater species diversity.

Question 17

3. Species Diversity

Answer 17

Quantifies the number of different species and their relative proportions within the community that they live.
The stability of an ecosystem increases with species diversity. i.e. the more different types of species that exist in an ecosystem the more stable that ecosystem will be.

Question 18

Ecological Roles

Answer 18

Producers
Autotrophic organisms
Make up the base of a food web by synthesizing organic molecules from which all other organisms will depend upon.

Consumers
Heterotrophic organisms
Must ingest producers or other consumers to acquire carbon and energy.

Decomposers
Heterotrophic organisms
Digest organic molecules left by living organisms and absorb the breakdown products to acquire carbon and energy.

Question 19

1. Bacteria (ecological roles)

Answer 19

Important ecological roles of bacteria include:

Producers
Decomposers
Nitrogen fixers
Mutual symbionts
Pathogens

Question 20

Bacteria as producers

Answer 20

Cyanobacteria are photoautotrophic performing photosynthesis to acquire energy from the sun. They are producers forming the base of aquatic food chains.
Not only do they provide the initial source of energy and nutrients to all organisms in aquatic ecosystems, they also contribute substantial amounts of oxygen into our atmosphere, a byproduct of photosynthesis.

Question 21

Bacteria as Decomposers

Answer 21

Many species of bacteria thrive as decomposers. They are chemoheterotrophic, acquiring their energy and carbon by breaking down large organic molecules in waste products from living organisms or dead organisms.
Decomposers play a very important ecological role as they free up nutrients such as nitrogen, and phosphorous tied up in organic molecules and make them available again to producers.

Question 22

Bacteria as nitrogen fixers

Answer 22

N2 → NH3
The atmosphere is full of nitrogen gas, but most living organisms cannot utilize it in this form. We depend on nitrogen fixing bacteria to convert it into a usable form.

Question 23

Bacteria as mutual symbionts

Answer 23

Some bacteria live inside other organisms in a mutual symbiotic relationship. Each member of the partnership gains something.
The human intestines are home to 500-1000 different species of bacteria. Most digest food residues that our intestines are unable to breakdown.

Question 24

Bacteria as Pathogens

Answer 24

Most bacteria are decomposers, or producers, but some bacteria are pathogenic.

Half of human diseases are caused by bacteria so we tend to assume that that is their major ecological role!

Question 25

Contents of Bacterial Cells

Answer 25

Nucleoid Region
Contains the main circular chromosome of the cell.

Plasmids
Small circular DNA molecules in the cytoplasm.
Can be exchanged between bacterial cells during conjugation (a form of sexual reproduction).

Ribosomes
Required for making proteins.
Much smaller and less dense than eukaryotic cell ribosomes.

Question 26

External Bacterial Cell Features

Answer 26

All bacteria have a Cell Wall that contains a substance called Peptidoglycan (sugar/protein cross-linked together) which maintains cell shape and protects the bacteria from the external environment.

Many bacteria also have a Capsule exterior to the cell wall that has a sticky texture which allows them to adhere to the substrate or to each other.

Certain bacteria have hairlike appendages called Fimbriae which help them adhere to surfaces.
e.g. Gonorrhea bacteria use fimbriae to attach to the mucous membranes of its host.

About 50% of prokaryotic cells are capable of moving themselves and the most common mode of locomotion is through flagella.

Pili are involved in cell movement and DNA transfer between cells.

Sex Pili are used to pull 2 bacterial cells closer together in order to transfer plasmids from one cell to the other during conjugation.

Question 27

Categorization of Cell walls.

Answer 27

bacteria can be placed into one of 2 groups based upon the structure of their cell wall
Gram+

Gram-

This becomes relevant to us since certain antibiotics are more effective against Gram+ bacteria than Gram- bacteria and vice versa.

Question 28

Gram +:

Answer 28

Cell wall composed of a very thick layer of peptidoglycan.

Question 29

Gram - :

Answer 29

Cell wall has a thin peptidoglycan layer! It also includes an outer lipopolysaccharide membrane exterior to the peptidoglycan layer.

Question 30

2. Archaea

Answer 30

Prokaryotic
Many live in extreme environments (volcanic springs, high salinity lakes and seas)
Some in marshes where they produce methane gas as a bi-product of their energy metabolism.
Some live in our GI tract and on our skin as mutualists.
Generally play an important role as producers and decomposers in their ecosystems.

Question 31

3. The EukaryotesThe Protists

Answer 31

There are no general characteristics for this group as it contains a diversity of organisms and is currently under revision! Polyphyletic origin

Most are unicellular and have the ability to reproduce sexually or asexually.

Nutritional modes are diverse as we saw in the lab: