ASTR-3040: Astrobiology

Day 11

The Nature of Life on Earth

Chapter 5

Homework - 4

Due Tues. Feb. 22

Chapter 5: 4, 6, 14, 20, 25, 27, 33, 37, 42, 47, 48, 49, 51

Molecular Components

Carbohydrates – energy sources Sugars and starches

Lipids – energy stores, barriers Fats

Nucleic Acids – DNA and RNA

Molecular Components Proteins – structure & chemistry

Structural materials

Enzymes – catalysts for reactions

Amino Acids (20 used in most life forms)

Left-handed in biological entities.

Major Groupings

Leeuwenhoek – 1674 – microscope

5 Kingdoms Plants

Animals

Protista

Monera

Fungi

Is there a biochemical classification?

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.

Domains of Life

Based on biochemistry and genetics:

Bacteria

Archaea

Eukarya

Tree of life.

Kingdom – Phylum – Class – Order – Family – Genus – Species

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.

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.

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)

Classification by Metabolism

To obtain energy:

1. Photosynthesis: sunlight

2. chemosynthesis: chemical energy Ingested food

Inorganic reactions

4 Metabolic Classifications

Based on energy and carbon acquisition.

1. Photoautotrophs

2. Chemoautotrophs

3. Photoheterotrophs

4. Chemoheterotrophs

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.

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.

DNA Structure

Double helix

DNA bases – 4 Adenine

Guanine

Thymine

Cytosine

Pair as AT & CG

Replication

Unzip & each strand acts as a template.

Use RNA in the rebuild process.

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)

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.

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.

Extreme Life - Extremophiles

Thermophiles – heat lovers

Hyperthermophiles Black smokers (350˚C)

Hot springs

Extreme Life - Extremophiles

Psychrophiles – cold lovers Antarctica ice pack (-20˚C)

Also very dry

Radiation hardened

Extreme Life - Extremophiles

Endoliths – within rocks Up to several km below ground

Endospores (resting) – found on moon Could these survive interplanetary journeys?