DNA replication

triteritzyBiotechnology

Dec 14, 2012 (4 years and 10 months ago)

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DNA/RNA

&

Evolution toward Technology

ASTR 1420


Lecture 4


Sections 5.2, 5.4, 6.5, 12.2

Today’s lecture

Molecular basis of evolutionary adaptation

RNA world?



Evolution of Human

Evolution toward technology

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

Amino Acids


Most important monomer!


Basic building blocks of
proteins,

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

Chirality

of

Amino Acids


Chirality

(handedness)











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




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


Part 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

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.


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 chances

o
wrong base

o
deleted base

o
extra base

o
etc.


Most of these errors have no effect

Why? 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 evolution!


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”

RNA based world?


In the beginning of Earth life, such 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 to appear in life on other
worlds, molecules with similar
function are well expected!


Another evidence of common ancestor


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.

Human Evolution

Evolution of Human


Traits of tree life transformed to good human skills

o
Grabbing branches





dexterous hands

o
Swinging among branches



depth perception













good hand
-
eye coordination

o
Good parental cares for youngsters



Primates : having hands, hand
-
like feet, forward
-
facing eyes



Common myth:



Apes





Human

Humanoid



Numerous hominid species




no “missing link” in human evolution



Toumai

Cultural &
Technological
Evolution


Dramatic changes


cultural evolution : via transmission of
accumulated knowledge



Cultural evolution

o
is far more important than natural evolution..

o
accelerates over time



Beginning a new trend?


Technological evolution
:

increased technology


new discoveries


more
advanced technologies






Active Evolution:

o
genetic engineering

o
modern medicine

o
not limited by Darwinian evolution anymore…


During the past 40,000
years, we did not make
any significant
evolutionary changes…


Is
intelligence
inevitable
?


“No”

o
biology might be common…

o
we (human) are the only one with Technology
in the Universe (or at best, extremely rare)

o
over 3.5
Gyr

of life, only 200 years of
technology

o
our existence is due to some chance events


evolutionary stress from Snowball Earth or
mass extinction impacts…


no mammal domination if there was no
asteroid impact 65
Myr

ago.


“Yes”

o
evolutionary pressure for intelligence

(lions and gazelles)

o
even if there was no human, other
technological species might have emerged
instead.

o
Convergent evolution


intelligence


Convergent
Evolution


Dolphins and Sharks

streamlined “torpedo
-
shape” body form


greater speed for better survival to catch preys



Eye
-
sights

o
most multi
-
cellular animals can “see”

o
eyes evolved independently 8+ times!



Flights

o
bats, birds, pterodactyls, some insects…



Sonar (echolocation)

o
whales/dolphins, bats

acquisition of the same
biological trait in unrelated
lineages


natural
selection often produces
analogous adaptations.

Bioluminescence


It has evolved independently at
least 40 times!


E. A.
Widder

(Science, 2010, 328, 704)


Bioluminescence has resulted from some
intriguing evolutionary adaptations.

(A)
In the deep
-

sea anglerfish
Linophryne

coronata
, bioluminescence from the
esca

is
bacterial in origin, whereas that from the chin
barbel

is an unidentified intrinsic chemistry.

(B)
In the octopus
Stauroteuthis

syrtensis
, its
suckers are
photophores
.

(C)
In the tunicate
Pyro
-

soma
atlanticum
,
luminescence originates from
pu
-

tative

bacterial
endosymbionts
.

Extra credit…


All crabs look quite similar… but DNA
information tells us that they are
from many different ancestors (from
shrimps, lobsters, etc.). Crablike body
and walking must be an outcome of
the convergent evolution.


What’s the benefits of these traits?

Woodpecker’s
Niche


Convergence evolution is very common on
Earth


By the same reasoning, convergence should
exist among alien life.

Really?


digging holes in live woods

o
dependable food sources : year
-
round insects &
sap


no need to migrate

o
stable housing : constant temperature &
humidity, protection from rain, wind, predators



Woodpecker’s adaptations

1.
strong, straight, chisel
-
like bill

2.
perching vertically on bark (stiff tail, strong
muscle, long curved toes)

3.
long extensible tongue (no need to drill
another hole after one insect’s burrow)

4.
tough skins to withstand insect bites and
stresses from pounding



Woodpecker Niche


Woodpeckers started their evolution about
50
Myrs

ago.



All modern woodpeckers are all closely
related



woodpecking

has evolved only
once!”



Is
woodpecking

so hard?

No


there are a handful (at least) other
birds have somewhat similar traits, but
none comparable to woodpecker’s


Some obviously valuable adaptations have
not happened

o
digesting cellulose effectively

o
growing one’s own food (photosynthesizing
animal) for example.


Convergence is not universal and not all chances are seized!



Measuring
Intelligence


Encephalization

Quotient
(EQ) =
the ratio of the actual
brain mass to the expected
brain mass of a typical animal
that size



Human : 7


Chimpanzee : 3


Dolphins : 2.5
-
4.5


Hippo : 0.27


Raptors : 5.5


Troodons

: 5.8


Evolution of
Intelligence


A trend toward increasing intelligence?



Factors encouraging intelligence


high, effective metabolism (2% body weight
uses ¼ of energy)


long period of parental care (to pass down
knowledge)


Natural selection on intelligence

o
less vigilant gazelle


prey to a lion

o

increases

intelligence of the whole gazelles


less smart lions can’t get meals


increased intelligence for both.



intelligence comes with a cost

o
high metabolism and handling heavy head.

If only for survival, for given limited resources, other capabilities are equally
good?

faster running, better fighting, etc.

Pass down accumulated knowledge to next generation!

Technology:
inevitable?


A pathway from higher brainpower
to
science and technology seems apparent…



For technology, there are some other needed
traits (e.g., dexterous hands)

o
dolphins : with intelligence and social structure.



need to manipulate complex tools!!



Even for advanced civilizations, do they head
toward interstellar radio communications or
space travels?


What about the Woodpecker’s niche?

Need to find an evidence of alien technology on other habitable worlds!

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


Cultural evolution


Technological evolution


Woodpecker’s niche


Important Terms


amino acids / proteins


chirality


genes, genetic code


mutation



Convergent evolution


Encephalization

Quotient


Chapter/sections covered in this lecture :
5.2, 5.4, 6.5
& 12.2