WHAT IS LIFE?
What is life?
• condition that distinguishes organisms from inorganic objects
• life forms are able to act on their own behalf to support their own existence, and to reproduce themselves
• Every living thing is cellular either a single-celled or a multi-cellular creature membrane – bound contains a full set of instructions necessary for its
operation, reproduction
Viruses
• Not cellular, and are therefore described as "biological entities" rather than organisms.
• Grow as intracellular parasites after invading cells.
• Viruses are reproduced and can evolve; however, they contain no metabolic machinery of their own, so they use that of the host cell to reproduce.
• Without a host cell, viruses are merely inert, complicated particles which do nothing.
The T-4 Bacteriophage virus is about to attack the bacterium.
The virus injects its genetic material into the bacterium.
The bacterium explodes after it is forced to make copies of the virus
The action of viruses
Smallpox -
(Edward
Jenner in
1796)
Poliomyelitis
- (Jonas
Salk, 1955)
Hepatitis Ebola Virus Hanta Virus
Measles Rabies Chicken pox Common
Cold Influenza
HIV Mumps
Here's what an actual population of E. coli bacteria looks like as it is wiped out by T4 bacteriophage
The action of viruses
Examples of viruses
Figure 2-29 Molecular Biology of the Cell (© Garland Science 2008)
• All living matter is composed of
H2O
inorganic ions
small molecules
macromolecules
The chemicals of life
H20 and life • Cells ~70% water
– involved in almost all chemical rxns
• Life has evolved around special water properties – highly polar, therefore will
dissolve other polar compounds
• Biomolecules’ structures
arise from interaction with water – Forms covalent and
noncovalent interactions
Biological molecules
• Life on earth is carbon – based: biological molecules consist primarily of carbon bonded to carbon
carbon bonded to other molecules
• Carbon can form up to 4 covalent bonds.
• Carbon may be bonded to functional groups with specific properties
Biological macromolecules
• Simplest organic molecules = Hydrocarbons; consist of carbon, hydrogen
Covalent bonds store considerable energy.
Make good fuels
Biomolecules
• Biomolecules are typically large molecules (polymers) constructed from smaller subunits (monomers)
• Biomolecules built up, broken down via water interactions
Biomolecules
• Biochemistry requires understanding the structure, function of cellular components of biomolecules
Proteins
Carbohydrates
Lipids
nucleic acids
Figure 2-30 Molecular Biology of the Cell (© Garland Science 2008)
Functional groups
• Specific groups of atoms attached to carbon backbones
• Have definite chemical properties • Found in the various biomolecules
Proteins – amines, carboxylic acid Nucleic acids – phosphoric esters, hydroxyl groups Lipids – alkanes, carboxylic acid Carbohydrates – alcohols, aldehydes, ketones
• Rxns of biomolecules = rxns of their functional groups determine how molecule will interact with other
molecules
Proteins
• contain an amino group (-NH2), a carboxyl group (-COOH) and an H atom, all bonded to a central carbon atom
• Formed from 20 different monomers (amino acids)
• most abundant, functionally versatile biomolecule
Proteins derived from amino acids
• A protein is composed of one or more long chains of amino acids linked by peptide bonds
Figure 2-47 Molecular Biology of the Cell (© Garland Science 2008)
Enzyme activity
Enzymes = biological catalysts
Enzymes
Nucleic Acids
• Responsible for storage, transfer of genetic information
• 2 types: 1. Deoxyribonucleic
Acid (DNA) Encodes information
used to assemble proteins
2. Ribonucleic Acid (RNA) Reads DNA-encoded
information to direct protein synthesis
The molecular design of life
Carbohydrates
• Also known as sugars
• Molecules with a 1:2:1 ratio of C, H, O
empirical formula: (CH2O)n
examples: sugars, starch, glucose
• Since C – H covalent bonds hold much energy, carbohydrates are good energy storage molecules
The structure of glucose, a simple sugar
Functions of carbohydrates
energy stores, fuels, and metabolic intermediates
structural framework of RNA and DNA
structural elements in the cell walls of bacteria and plants
linked to many proteins and lipids
participate in biological transport, cell-cell recognition
Classification of carbohydrates
• Monosaccharides – e.g., glucose, fructose
• Oligosaccharides – Di, tri, tetra, penta, up to 9 or 10 monosacchs
– e.g., lactose, sucrose
• Polysaccharides or glycans – Homopolysaccharides-starch, glycogen, cellulose
– Heteropolysaccharides
– Complex carbohydrates
• Starch = nutritional reservoir in plants; makes up >50% of carbohydrates ingested by humans
• These chains are broken down into individual glucose molecules and used to generate energy
• Consumption of excess carbohydrates leads to conversion into glycogen or fats for future use.
Effect of decreased blood glucose
Structural carbohydrates
• Cellulose – found in plants
• Chitin – found in arthropods
and fungi
Lipids
• biomolecules that are insoluble in H2O but soluble in organic solvents
• Examples of lipids:
Fats (triglycerides)
Phospholipids
Steroids
• Variety of biological roles: Fuel molecules/Energy store
Membrane components
Signal molecules
Lipids
Triglycerides
• store twice as much energy as carbohydrates
• May be saturated or unsaturated Saturated fats - all internal carbon atoms are bonded to at
least two hydrogen atoms; maximum # of H
Unsaturated fats - at least one double bond between successive carbon atoms
Fatty acids/Triglycerides
• animal fats are usually saturated fats
solid at room temperature
• plant fats (oils) are usually unsaturated
liquid at room temperature
Phospholipids
• Main component of biological membranes
• Membranes usually exist as lipid bilayer
Polar head groups in contact with H2O
Nonpolar tail lies in interior
The watery interior of cells is surrounded by the plasma membrane, a two-layered shell of phospholipids
Phospholipids
Steroid hormones are derived from cholesterol
Metabolism of dietary fuels
• In humans, catabolism of carbohydrates, fats, and proteins for energy = important aspect of nutrition
provide energy to maintain body functions during rest and all forms of physical activity
• most diets provide >> required amt of calories
Carbohydrates, fats consumed in excess of nutritional requirements converted to storage forms
Carbohydrates → glycogen
Lipids → triglycerides
How did life start?
Origin of life hypotheses
1. Special creation supernatural or divine
origin
2. Extraterrestrial origin (panspermia) e.g., comets
3. Spontaneous origin life originated from
inanimate materials Abiotic evolution
Conditions on early Earth
• primitive atmosphere not conducive to life
Earth’s surface temperature probably hotter than today
• Early atmosphere often referred to as a reducing atmosphere
No free oxygen (O2)
• Contained free hydrogen (H2) and saturated hydrides (CH4, NH3 and H2O)
• Energy for chemical reactions between these gases could come from electric discharge in storms or solar energy (no ozone layer)
Geophysical Stage Chemical Stage Biological Stage
How did the earth’s crust and atmosphere look like when life originated?
How can the building blocks of life (nucleotides, amino acids) be synthesized? These blocks may (partially) have been different from modern blocks.
How did the building blocks organize into living organisms?
Reasonably well understood
Poorly understood
Stages of prebiotic evolution
Life began~ 3.5 bya
Stage 1: Abiotic synthesis of organic molecules such as proteins, amino acids and nucleotides
Origin of life
• Glucose, ribose, deoxyribose and other sugars form from formaldehyde (CH2O) when exposed to UV radiation
• Adenine forms from hydrogen cyanide (HCN) and was probably the first base to form
The Miller-Urey experiment
• Conducted in 1953 by Stanley L. Miller and Harold C. Urey at the University of Chicago
• Performed to test Oparin and Haldane's hypothesis:
Conditions on the primitive Earth favored chemical reactions that synthesized organic compounds from inorganic precursors
• simulated hypothetical conditions present on the early Earth – tested for the occurrence of chemical evolution
The Miller-Urey experiment
Miller-Urey experiment: results
After 1 week, the following were observed:
1. As much as 10-15% of the carbon within the system was now in the form of organic compounds.
2. 2% of the carbon had formed amino acids.
3. Sugars, lipids, and some of the building blocks for nucleic acids were also formed.
4. Nucleic acids (DNA, RNA) themselves were not formed.
Miller-Urey experiment: conclusions
• experiments cannot reproduce the exact conditions on the primitive Earth reconstructed atmosphere was probably wrong
experiment had never been repeated with a more accurate mixture
• Showed that the basic building blocks for the large macromolecules can be synthesized in vitro from inorganic compounds
Stage 2: joining of small molecules (monomers) into large molecules
Origin of life
From monomers to polymers
• Amino acids combined to form polypeptides
could have occurred when dry or highly concentrated monomers are heated
• Condensation reactions take place forming phosphodiester bonds form between nucleotides
Formation of polynucleotides
Stage 3: origin of self-replicating molecules that eventually made inheritance possible
Origin of life
What was the first biomolecule?
Proteins
easier to polymerize proteins than nucleotides
Nucleic acids
special conditions in the soup enabled replication without proteins?
Both?
What is the first biomolecule?
• DNA needed to make proteins
• Proteins needed to make DNA
• “RNA world” theory proposes that RNA = 1st biomolecule Since RNA can be used
to store genetic info, but may also contain catalytic properties
Figure 6-110 Molecular Biology of the Cell (© Garland Science 2008)
• Metabolism-first proponents argue that simple metal catalysts, as opposed to advanced protein-based enzymes, may have created a soup of organic building blocks that could have given rise to the other biomolecules
What was the first biomolecule?
• Authors created nucleic acid precursors starting with just hydrogen cyanide (HCN), hydrogen sulfide (H2S), and ultraviolet (UV) light
HCN abundant in comets; H2S common in early earth
• Conditions that produce nucleic acid precursors also create the starting materials needed to make amino acids and lipids
• Results suggest that a single set of reactions could have given rise to most of life’s building blocks simultaneously
Membranes defined the first cell
• The phospholipids form lipid bilayers when they are surrounded by water
• Formed 1st organism: anaerobes
Fed off organic molecules in the oceans
Utilized CO2, released O2
Cell-like microspheres can be formed by agitating proteins and lipids in a liquid medium
• By 2 billion years ago free oxygen was appearing in the atmosphere due to the activity of cyanobacteria
photosynthetic bacteria
able to produce free oxygen
What were the earliest organisms like?
• Photosynthesis increased the amount of oxygen in the atmosphere Led to development of aerobic organisms
• The oldest eukaryotic fossils are ~2 billion years old symbiotic community of prokaryotes living within larger
prokaryotes (Endosymbiosis theory)
led to development of membrane – enclosed organelles
Endosymbiont theory
Some organisms acquired membrane-enclosed organelles from engulfed bacteria
The oldest fossils of multicellular organisms are ~1.2 billion years old
Clock analogy for some key events in evolutionary history
How many species are there?
• Estimates of the total number of living species range from 10 to 100 million.
• Actual number likely around 13 – 14 million – most are insects, microscopic life forms in tropical
regions
• About 1.75 million have been given scientific names.
• We may never know how many there are Many will become extinct before being counted, described
Classifying living things
• Until the 20th century, most biologists considered all living things to be either a plant or an animal
• By the 1970s, the 5 Kingdom system, which accomodates fungi, protists, and bacteria became accepted as the model by which all living things could be classified
• Current model = domain system, which classifies organisms according to evolutionary history
includes a 3rd life form: the Archaea
The 5 – kingdom classification scheme
Archaea: distinct fom prokaryotes and eukaryotes
• Archaea have an independent evolutionary history from bacteria thought to have split from Bacteria 2 bya
• show many differences in their biochemistry from other forms of life
• may be the only organisms that can live in extreme habitats
Methanogens (produce methane CH3) extreme halophiles (salt-loving) extreme thermophiles (heat-loving)
The 3 – domain classification scheme
Did life arise on another planet?
• Various space missions have aimed to answer the question: Did life exist on Mars in the past or present?
• Could Mars be used to tell us more about the evolution of both Earth and our solar system?
First photograph ever taken from the surface of Mars. Viking 1 Lander July 20, 1976. Primary objectives of the Viking missions - obtain high-resolution images of the Martian surface, - characterize the atmosphere and surface - search for evidence of life on Mars http://grin.hq.nasa.gov/ABSTRACTS/GPN-2003-00061.html
Mission to Mars
• ..\..\youtube downloads\NASA Mars Rover Landing_ Curiosity Lands, Beams Back Pictures of Mars Surface.mp4
• Curiosity was designed to assess whether Mars ever had an environment able to support small life forms, e.g., bacteria – In other words, to determine the planet's
"habitability“
• Carries a gas chromatograph, mass spectrometer and laser spectrometer instruments will look for telltale isotopes, gases and
elements, especially methane and other carbon compounds
Mission to Mars
“The landing site of the Mars rover Curiosity was once covered with
fast-moving and possibly waist-high water that could have possibly
supported life, NASA scientists announced Thursday.”
Star Tribune Sept 28, 2012
..\1st sem 2014 - 2015\Curiosity Rover Report (6_24_2014)_
Curiosity Completes Its First Martian Year.mp4
Mars One mission: a one-way trip to the red planet in 2024
• The Mars One project aims to establish a human colony on the red planet by 2025
• ~20,000 applied to be part of the team (including several Filipinos!)
• However, has been recently reported as poorly planned, doomed to failure and could endanger the future of science
..\1st sem 2014 - 2015\The Great Debate - What is Life_.mp4
NatSci 50 reporting topics
1. Life outside earth: does it exist?
2. Unusual adaptations
3. Extinct/threatened species
4. Genealogy testing using DNA analysis
5. Mitochondrial Eve, Y chromosome Adam
6. Bioinformatics
7. Common misconceptions in genetics and heredity
8. Synthetic biology