DNA/RNA&

Molecular Basis of Evolution

ASTR 1420

Lecture 4

Sections 5.2, 5.4

Organic Building Blocks

Cells

Typical Eukaryotic Cell

• All living organisms are made of cells

• Adult human body have 10-50 trillion cells!

Components of Cell

• Carbohydrates (= carbs) : providing energy to cells and make cellular structures sugars, starches, cellulose, etc.

• Lipids (aka fats) : store energy, make cell membranes

• Proteins : versatile, essential molecules of cells

• Nucleic acids : handling heritable information of cells – DNA and RNA

DNA Proteins• All Earth life have DNA, and DNA is the backbone of heredity.o Heredity DNA replicationo function of DNA (genes) protein synthesis

• What’s protein? o organic compound made of amino acids in a folded chaino essential part of organisms and participate in every process within cells

enzymes involved in matabolism make cell stucture cell signaling, immune responses, etc.

DNA structure http://www.youtube.com/watch?v=qy8dk5iS1f0

DNA replication http://www.youtube.com/watch?v=hfZ8o9D1tus

Protein synthesis http://www.youtube.com/watch?v=XO-2Z933AzM

RNA world?• In the beginning of Earth life, the very first life could not be based on DNA.

DNA is way too complicated to be created by mere “lucky” chemical reaction.

early life must have used a simpler molecule (e.g., RNA)or, DNA was introduced externally?!?

Although we do not expect DNA or RNA to appear in life on other worlds, molecules with similar function are well expected!

Amino Acids

• Most important monomer!• Basic building blocks of

proteins, nucleotides, and sugars

• Typically, few hundred amino acids form a protein polymer. There are about 70 different amino acids in the nature, but only ~20 are used in living organisms. A strand of amino acids, part of a protein

Monomer/Polymer• Glycogen: the carbohydrate that animals use

to store energy is a polymer made of glucose molecule contains 22 atoms

Most life forms consist of small number of simple molecule types called monomers, which can join together in a repetitive sequence to become larger and more complex molecules called polymers.

glucose

Chirality of Amino Acids

• Chirality (handedness)

For a given amino acid, there are two geometrical shapes:

left-handed & right-handed

• In non-biological environ: two types are equally found

• In living organisms: only left-handed amino acids are found! All Earth life forms were originated from an ancestral life using only left-handed

amino acids!

Genes• a distinct portion of DNA strand representing

any single function (e.g., instruction for one protein)

Species No. of genes

Virus 10

Mitochondria 40

Microbe 1,000

E coli 4,400

Human 27,000

Mouse 29,000

Rice 50,000

Small difference in genes• Different human raceso Any possible distinct genetic differences are now disappeared by inter-racial

breed.o Genetic difference b/w races < b/w two individuals from one race!

• Astrobiological Implication?o Small genetic difference huge difference (e.g., Chimpanzee vs. Human)

; Chimpanzee and human share 98% of the same genes

o Is advanced intelligence an inevitable evolutionary outcome?

Genetic code : a set of rules for reading DNA

Codes for most amino acids really depend on just two letters

in the past, genetic codes were two letter based…

• Genetic “words” consist of three DNA bases in a row. For the purpose of protein building, each word represents either a particular amino acid or “start reading” or “stop reading”.

• Genetic code is same for nearly ALL living organisms on Earth! common ancestor of all life on Earth!

Mutation• Replicating the whole ~3 billion bases for

human DNA takes only a few hours• About 1 replication error in billion chanceso wrong baseo deleted baseo extra base o etc.

• Most of these errors have no effectWhy? about 95% of human DNA bases are “non-

coding DNA”Most significant change is from “deleted base”.

• Due to this “error”, every individual living organism differ each other.

• Mutation = molecular engine of the evolutionary adaption!

• Any change in the base sequence of DNA

Sickle-cell disease

• Just one base change in one gene (Adenine Thymine)

• Most mutations are harmful, but occasional good mutations are being picked up by “natural selection”

Another evidence of the common ancestor• ATP (Adenosine TriPhosphate).

• Cells recyle ATP. • The ATP molecule gives up energy

when it splits into ADP and a phosphate group.

• ATP/ADP are like batteryo ATP : fully chargedo ADP : fully discharged

• There are many other possibilities of different molecular pairs (i.e., different batteries), but all Earth life use ATP as the energy reservoir.

common ancestor of all Earth life.

In summary…

Important Concepts• Common ancestor of all Earth Life

(chirality of amino acid, common genetic code, and use of ATP among all living organisms on Earth)

• Some non-DNA based life forms in the beginning?

• DNA replication

Important Terms• amino acids / proteins• chirality• genes, genetic code• mutation

Chapter/sections covered in this lecture : 5.2 & 5.4