Download DNA replication

DNA/RNA
&
Molecular Basis of Evolution
ASTR 1420
Lecture 4
Sections 5.2, 5.4
Organic Building Blocks
Cells
• All living organisms are
made of cells
• Adult human body have
10-50 trillion cells!
Typical Eukaryotic Cell
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 replication
o function of DNA (genes)  protein synthesis
• 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 stucture
 cell signaling, immune responses, etc.
DNA structure
http://www.youtube.com/watch?v=qy8dk5iS1f0
DNA replication
http://www.youtube.com/watch?v=hfZ8o9D1tu
s
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
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
• Glycogen: the carbohydrate that animals use
to store energy is a polymer made of glucose
molecule contains 22 atoms
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!
• a distinct portion of DNA strand representing
any single function (e.g., instruction for one
protein)
Genes
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 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?
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
• 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!
Codes for most amino acids really depend on
just two letters
 in the past, genetic codes were two letter
based…
Mutation
• Any change in the base
sequence of DNA
• Replicating the whole ~3 billion bases for
human DNA takes only a few hours
• About 1 replication error in billion chances
o
o
o
o
wrong base
deleted base
extra base
etc.
• Most of these errors have no effect
Why? about 95% of human DNA bases are “noncoding 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!
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 battery
o ATP : fully charged
o 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
Important Terms
• Common ancestor of all Earth Life
(chirality of amino acid, common
genetic code, and use of ATP
among all living organisms on
Earth)
•
•
•
•
amino acids / proteins
chirality
genes, genetic code
mutation
• Some non-DNA based life forms in
the beginning?
• DNA replication
Chapter/sections covered in this lecture : 5.2 & 5.4