Download 37000 genes

Astronomy 3040
Astrobiology
Spring_2016
Day-11
Cells: Basic Units of Life
Cells – microscopic units separated from the outside by
a “membrane.”

Basic structure of larger organisms.

Can have one cell organisms.
Life on Earth is Carbon-based - everywhere.

Molecules linked by chemical bonds.

Carbon molecules = organic

Carbon + Hydrogen = hydrocarbon
Silicon Based Life
Silicon and Carbon are the only elements that can form
4 bonds.

Significantly weaker than carbon bonds.
Fragile, especially in water.

Silicon does not normally form double bonds.
Limits the reactions and molecular structures.

Carbon can be in a gaseous state (CO2).
SiO2 is a solid.
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 (selffeeding, 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.