Chemistry to Biology Cells, RNA, & DNA ASTR 1420 Lecture 5 Sections 5.2 & 5.4

RNA based world In the beginning of Earth life, the first life could not be based on DNA because DNA is too complicated to be created by mere “lucky” chemical reactions. In the beginning of Earth life, the first life could not be based on DNA because DNA is too complicated to be created by mere “lucky” chemical reactions.  early life must have used a simpler molecule (e.g., RNA)  or, DNA was introduced externally?!?

Organic Building Blocks Six essential chemical elements for Earth Life Carbohydrates (= carbs) : providing energy to cells and make cellular structures  sugars, starches, cellulose, etc. Carbohydrates (= carbs) : providing energy to cells and make cellular structures  sugars, starches, cellulose, etc. Lipids (aka fats) : store energy, make cell membranes Lipids (aka fats) : store energy, make cell membranes Proteins : versatile, essential molecules of cells Proteins : versatile, essential molecules of cells Nucleic acids : handling heritable information of cells – DNA and RNA Nucleic acids : handling heritable information of cells – DNA and RNA

Cells All living organisms are made of cells All living organisms are made of cells Adult human body have trillion cells! Adult human body have trillion cells! Typical Eukaryotic Cell

Monomer/Polymer Glycogen: the carbohydrate that animals use to store energy is a polymer made of glucose molecule contains 22 atoms 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

Carboxyl group Amino group Amino Acids Most important monomer! Most important monomer! Basic building blocks of proteins, nucleotides, and sugars Basic building blocks of proteins, nucleotides, and sugars Different side chain (R) makes a different amino acid. Different side chain (R) makes a different amino acid. There are about 70 different amino acids in Nature There are about 70 different amino acids in Nature

Amino Acids : peptide bond to make a long chain Basic building blocks of proteins, nucleotides, and sugars Basic building blocks of proteins, nucleotides, and sugars R R

Typically, few hundred amino acids form a protein polymer. Typically, few hundred amino acids form a protein polymer. Out of ~70 amino acids, only 20 are used in Earth life!! Out of ~70 amino acids, only 20 are used in Earth life!! A strand of amino acids, part of a protein Amino Acids : peptide bond to make a long chain

Chirality of Amino Acids Chirality (handedness) Chirality (handedness) For a given amino acid, there are two geometrical types: left-handed & right-handed right-handed In non-biological environ: two types are equally found In living organisms: only left-handed amino acids are found! Why?  All Earth life forms were originated from a single ancestral life using only left-handed amino acids!?!

DNA  Proteins All Earth life have DNA, and DNA is the backbone of heredity. All Earth life have DNA, and DNA is the backbone of heredity. o Heredity  DNA replication o function of DNA (genes)  protein synthesis What’s protein? What’s protein? o organic compound made of amino acids in a folded chain o essential part of organisms and participate in every process within cells  enzymes involved in matabolism  make cell stuctures  cell signaling, immune responses, etc.

DNA structure

DNA replication s

Protein synthesis

Genes Part of DNA strand representing any single function (e.g., instruction for one protein) Part of DNA strand representing any single function (e.g., instruction for one protein) SpeciesNo. of genes Virus10 Mitochondria40 Microbe1,000 E coli4,400 Human27,000 Mouse29,000 Rice50,000

Genetic code Codes for most amino acids really depend on just two letters  in the past, genetic codes were two letter based… The set of rules for reading DNA. The set of rules for reading DNA. 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 “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! 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 Replicating the whole ~3 billion bases for human DNA takes only a few hours About 1 replication error in billion chances About 1 replication error in billion chances o wrong base o deleted base o extra base o etc. Most of these errors have no effect : Why? Most of these errors have no effect : Why? o about 95% of human DNA bases are “non- coding DNA” o Most significant change is from “deleted base”. Due to this “error”, every individual living organism differ each other. Due to this “error”, every individual living organism differ each other. Mutation = molecular engine of evolution! Mutation = molecular engine of evolution! Any change in the base sequence of DNA Any change in the base sequence of DNA Stumpy, a four-legged duckling at Warrawee Duck Farm, Copythorne, Hampshire, England (2007)

Sickle-cell disease Just one base change in one gene (Adenine  Thymine) Just one base change in one gene (Adenine  Thymine) Most mutations are harmful, but occasional good mutations are being picked up by “natural selection” Most mutations are harmful, but occasional good mutations are being picked up by “natural selection”

Another evidence of the common ancestor Cells need Energy to function The ATP molecule gives up energy when it splits into ADP and a phosphate group. ATP/ADP are like battery o ATP : fully charged o ADP : fully discharged Adenosine diphosphate

Another evidence of the common ancestor Cells recyle ATP. There are many other possibilities of different molecular pairs (i.e., different batteries), but all Earth life use ADP/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

Small difference in genes Different human races Different human races o 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? Astrobiological Implication? o Small genetic difference  big difference (e.g., Chimpanzee vs. Human) ; Chimpanzee and human share 98% of the same genes o Is advanced intelligence an inevitable evolutionary outcome?