Astronomy190 - Topics in Astronomy

Astronomy and Astrobiology

Lecture 8 : Biology II

Ty Robinson

Questions of the Day

• How are prokaryotes and eukaryotes different? Similar?

• How do we use metabolism to classify organisms?

• What are extremophiles?

Structure of the Cell • cell membrane

– semi-permeable

• nucleus– genetic

material– “command

center”

• cytoplasm and organelles– mitochodria– chloroplasts

Prokaryotes and Eukaryotes The two major cell

types are discriminated by whether or not they have a cell nucleus that walls off genetic material from the rest of the cell. – eukaryotes have a

cell nucleus• amoebas, plants,

animals

– prokaryotes don’t • E. coli, salmonella

The Three Domains of Life

• The prokaryote classification was split into bacteria and archaea

• Most of life’s diversity is found in the microscopic realm.

Metabolism

• Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. – involves breaking down molecules as well as

building them

• Fundamentally, metabolism required a carbon source and an energy source.

Classifying Life via Metabolism

• astrobiologist classify life into four major categories based on metabolic sources– i.e. how life gets its carbon and energy.

• carbon sources: others or environment.– heterotrophs eat other life to gain their carbon– autotrophs take carbon from the environment (CO2)

• energy sources: light or chemicals– sunlight - (photo)– food, organic compounds - (chemo)– inorganic compounds (no carbon) - (chemo)

The Limits of Life• life’s basic requirements are energy, building blocks

(including carbon) and water– these can be found even in extreme environments where

temperature, pH, salt levels, water availability, “poisons” and radiation levels are typically hostile to most kinds of life

– organisms that thrive or require these extreme environments are called “extremophiles” (lovers of the extremes).

– Hyperthermophiles - “extreme heat lovers” (grow at 80-120C)– Psychrophiles - “cold lovers” (grow better at 15C to -20C)– Halophiles - “salt lovers” (need salinity 4X the ocean’s)– Endolith - “inside the rock” (grows inside rocks)– Piezophile - “pressure lover” (grows at 500-1100 bars)– Xerophile - “dry lover” (grows in extremely dry conditions)

Hydrothermal Vents• deep ocean volcanism

releases hot water, rocks and dissolved minerals– water released can be > 350C

(660F) but extreme pressure keeps it liquid.

– black smokers (vents) are inhabited by Archaea which can survive up to 113C or 121C depending on the species

– chemoautotrophs– hyperthermophiles– function best at higher

temperatures and they are poisoned by O2.

Questions of the Day

• How are prokaryotes and eukaryotes different? Similar?

• How do we use metabolism to classify organisms?

• What are extremophiles?

Quiz

1 - What six characteristics do a reasonable job of defining life? Can you think of something that meets most of these requirements but isn’t alive?

2 - What would be the likely sources of energy and carbon for an organism that lives at the bottom of Europa’s ocean? What would we call this type of organism?

3 - What is one thing you did not understand from today’s lecture?