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