astr-3040: astrobiology day 11 the nature of life on earth chapter 5
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ASTR-3040: Astrobiology
Day 11
The Nature of Life on Earth
Chapter 5
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Homework - 4
Due Tues. Feb. 22
Chapter 5: 4, 6, 14, 20, 25, 27, 33, 37, 42, 47, 48, 49, 51
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Molecular Components
Carbohydrates – energy sources Sugars and starches
Lipids – energy stores, barriers Fats
Nucleic Acids – DNA and RNA
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Molecular Components Proteins – structure & chemistry
Structural materials
Enzymes – catalysts for reactions
Amino Acids (20 used in most life forms)
Left-handed in biological entities.
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Major Groupings
Leeuwenhoek – 1674 – microscope
5 Kingdoms Plants
Animals
Protista
Monera
Fungi
Is there a biochemical classification?
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Microscopic Life Plants and Animals are different
Cell walls (plants)
Cell Nucleus Prokaryotes
Eukaryotes
All prokaryotes are
single celled. They
lack a cell nucleus.
Eukaryotes – single or multi-celled.
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Domains of Life
Based on biochemistry and genetics:
Bacteria
Archaea
Eukarya
Tree of life.
Kingdom – Phylum – Class – Order – Family – Genus – Species
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The Tree of Life
Extremely valuable organizational tool.
3 key ideas 1. Domains based on biochemistry & genetics is
fundamentally different from the older KPCOFGS based on structural & physiological differences.
2. New and fundamentally different view of microbes - lipid structure of cell membranes.
3. True diversity almost entirely in microbes.
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Metabolism: Chemistry of Life
Metabolic needs: 1. Source of raw materials.
2. Source of energy.
ATP: adenosine triphosphate Used by every living cell for internal energy.
Outside energy needed only to produce ATP.
Carbon sources – form basic materials.
Energy sources – run the metabolism.
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Classification by Metabolism
To obtain carbon:
1. Heterotrophs: Consume preexisting organic compounds (i.e. eating).
2. Autotrophs: Direct uptake from the environment (self-feeding, plants)
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Classification by Metabolism
To obtain energy:
1. Photosynthesis: sunlight
2. chemosynthesis: chemical energy Ingested food
Inorganic reactions
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4 Metabolic Classifications
Based on energy and carbon acquisition.
1. Photoautotrophs
2. Chemoautotrophs
3. Photoheterotrophs
4. Chemoheterotrophs
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Liquid Water on Earth
All living cells on Earth depend on liquid water because metabolism requires:
1. Organic chemicals are readily available for reactions.
2. A means of transporting chemicals to and within cells; waste products away.
3. Water plays a role in many of the reactions.
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DNA and Heredity
3 key features of life on Earth 1. structural units – cells
2. metabolic processes – energy production
3. owner's manual – data storage for how a cell is constructed, how it works, and how to build another one, and pass it on to the next generation - heredity.
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DNA Structure
Double helix
DNA bases – 4 Adenine
Guanine
Thymine
Cytosine
Pair as AT & CG
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Replication
Unzip & each strand acts as a template.
Use RNA in the rebuild process.
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Genome Humans have ~3 X 10^9 bases
46 chromosomes (23 pairs)
Sequences for individual instructions are called genes.
Most of DNA is “noncoding” (junk 95%)
Complete sequence – genome.
Some bacteria – 10^5 bases, few 10^2 genes
Humans – 20,000 – 25,000 genes
Rice – 37,000 genes (smaller DNA sequence)
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Genetic Code
Words consist of 3 DNA bases.
Sequence has a start and stop word.
Used to build proteins.
Redundancy (64 codes, 20 amino acids)
Most amino acids are coded with the first 2 base letters only (16). Does this give a clue to evolution of complex organisms?
Nearly all living organisms have mostly similar genetic code.
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RNA
Uses ACG & Uracil
mRNA – transcription (carries the instr.)
tRNA – transfer (gathers the AAs)
rRNA – backbone of building structure.
Mutations - <1:10^9, but can have dramatic consequences.
Provide the basis for evolution.
Genetic Engineering.
RNA was probable precursor.
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Extreme Life - Extremophiles
Thermophiles – heat lovers
Hyperthermophiles Black smokers (350˚C)
Hot springs
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Extreme Life - Extremophiles
Psychrophiles – cold lovers Antarctica ice pack (-20˚C)
Also very dry
Radiation hardened
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Extreme Life - Extremophiles
Endoliths – within rocks Up to several km below ground
Endospores (resting) – found on moon Could these survive interplanetary journeys?