Lecture 3. What is Life? The Hallmarks of (Earth) Life.

reading: Chapter 3

What is Life?

We only know one kind of life - Earth life

Distinguishing life from non-lifecat vs. car

cat vs. a flame

cat vs. a crystal

What are the characteristics that separate life from non-life?

a flame in zero gravity

sugar

a flame inEarth’s gravity

What is Life?, cont.

We mostly rely upon the saying “we know it when we see it”.

We have, so far, not been able to define life. (Definition likewater IS H2O).

This may be a problem when we go to search for life elsewhere.We may not recognize it as life or easily distinguish it from non-life.

6 Key Properties of Life

1. Has Order/Structure• earth life is cellular• boundary separates the cell from the environment• structure/order within the cell• order is NECESSARY for life, but order by itself is NOT SUFFICIENT

for life (a dead cell has order but not life)

2. Reproduction• living organisms reproduce their own kind• sometimes this is a simple process• sometimes it is a very complex process

animals give live birth, plants use male and female flowers

6 Key Properties of Life, cont.

3. Growth and Development• living organisms grow in a controlled manner• (growth ≠ reproduction)• living organisms change/develop in a controlled manner• process is controlled by heredity - traits passed on to

the next generation in a precise manner• growth and development necessary, but not sufficient for life

4. Energy Utilization• cells need fuel• make waste products• harness the energy gained to create

order/structure, carry out reproduction, growth and development

6 Key Properties of Life, cont.

5. Response to the Environment• must interact with the environment• must interact with each other• adapt to SHORT-TERM changes in environment

grow a winter coat, alter your preferred energy source,hibernate

• movement

6. Evolutionary Adaptation• adapt to LONG-TERM changes in environment• adaptation must be heritable, passed onto next generation

in a controlled manner

Darwin’s Theory of Evolution

Origin of Species published 1859.“survival of the fittest”

1. Overproduction and the struggle for survival• resources (food, water, energy) are always limiting• there is always competition for resources

2. Individuals vary• mutations are always occurring• some have better traits than others

3. Survival of the fittest• individuals better able to obtain resources survive and reproduce• next generation will have better traits than previous generations• natural selection/adaptation

over time, advantageous traits are selected for and win.

Darwin’s Theory of Evolution, cont.

Darwin didn’t understand the mechanisms behind natural selection(discoveries in molecular biology & genetics much later).

This doesn’t invalidate his theory.

(Copernicus came up with the correct model for the solar system,but he didn’t understand concept of gravity.)

Spent almost 30 years collecting evidence to support his theory. Galapagos finches - 13 species, each adapted to different

microenvironments and lifestyles.artificial selection - breeding of domesticated plants & animals

can cause profound changes in a few thousand years.antibiotic resistance catastrophe in hospitals.

The 6 Key Properties of Life, revisited

Car Flame Crystal Virus

1. Order/Structure Y Y Y Y

2. Reproduction N Y Y Y

3. Growth/Development N Y Y Y

4. Energy Utilization Y Y N N

5. Response to the Environment Y/N Y Y N

6. Evolutionary Adaptation N N Y Y

The 6 Key Properties of Life, revisited

1. Order/structure2. Reproduction3. Growth/development4. Energy utilization5. Response to the environment6. Evolutionary adaptation

• All living things have to have ALL 6 of these traits.• One alone/five are not sufficient to constitute life.• Non-living things typically lack one or many of these traits.

Not only do all organisms have cells, all cells have similar structures.

The biochemistry of Earth cells is very similar:•all life is carbon based•all life made of the biogenic elements C, H, N, O, P, S

make up 96% of the atoms in cells•all have DNA and RNA•all make RNA the same way•all make proteins the same way using DNA and RNA and other proteins•Earth life is all fundamentally the same - it all shares a common

ancestor

Earth Life Goes Beyond the 6 Key Traits

Why Carbon?•C is abundant•can form bonds with lots of other elements (e.g., H, N, O, P, S)•can form a variety of C-C bonds

single (C-C), double (C=C), triple bonds (CC)•C is versatile

- forms rings- chains- networks- one atom bonds with up to 4 other atoms

•organic molecules contain C and H in addition to other atoms.

Silicon, Si:•Si is abundant•can also have 4 bonds at once•bonds are weaker than C•highly insoluble in water•doesn’t form double or triple bonds or chains, rings, networks•limited in its reactivity

Molecular Components of Earth Life

All components made from complex organic molecules

Carbohydrates:general structure CH2Oare sugarsmonomers: glucosepolymers (repeating units): lactose, cellulose, starch

Lipids:form cell membranes/barriers to the environmentoil and water -> oil dropletsfatty acid (fat + COOH)glycerol (simple sugar)

Proteins

Play structural roles: cell walls, collagen in our skin, fingernailsPlay catalytic roles: enzymes, catalyze the reactions needed for lifeAre polymers of amino acids - amino (contains NH2) acids (contains COOH)Are >70 amino acids in the universe.But only 20 amino acids are found in Earth life.

Valine

Phenylalanine

Glycine

Handedness

Complex organic compounds like amino acids have two flavorsthat are mirror images of each other (handedness).

Amino acids produced by non-living processes contain an equal mixture of left- (L-) and right-handed (D-) forms.

Amino acids produced by living processes contain the left-handed (L-) version!

Similarly, carbohydrates made by Earth life contain right-handed(D-) sugars.

Another hint that all of Earth life is related by a common ancestor.

Cells are chemical machines.Chemical reactions are carried out by proteins/enzymes.Catalysts make a chemical reaction “go” MUCH faster.

Cells make a variety of complex structures from raw materials.biosynthesis builds up those complex structures

Requires energy in the form of ATP(adenosine triphosphate).

Cells make ATP, then consume it during biosynthesis.

Again, evidence all Earth life had a common ancestor.

Similar Metabolism

Water

Chemical reactions occur in solution (dissolved in water).Allows substrates and wastes to be transported in and out of the cell.Is a reactant or product in many chemical reactions.Makes up most of the cell.When water disappears, cells die.

Water must be liquid (not boiling, not solid ice).

Nucleic Acids

DNA, deoxyribonucleic acid:Hereditary material of the cell.Holds the operating instructions for the cell.Double-stranded, so is easily duplicated

and passed to next generation.Information contained in the sequence of

bases: AGTTGTGCA binds to T, C binds to GSequence carries information to make proteins.Both strands match up and zip together.Can unzip, a copy of each is made.

RNA ribonucleic acid:Similar DNA, role is to help make proteins.Some RNAs catalyze reactions in protein synthesis (rRNA in the ribosome).Others make transient copies of genes, carry instructions for making a

protein (mRNA).

Mutations (changes) in the DNA can lead to changes in the protein.

phosphate

phosphate

phosphate

phosphate

sugar

sugar

sugar

bases:

sugar

Lecture 4. Big bang, nucleosynthesis, the lives and deaths of stars.

reading: Chapter 1