Lecture 9
Some notes about entropy
Molecular Biology continued
How does genetics help us to find interesting objects and find relationships between them?
There will be NO LECTURE on Tue, March 3
TSHG
The Gibbs free energy:
STHG
0 BAG
The process A→B will go spontaneously if
WkS ln
W = multiplicity of microscopic degrees of freedom (# of microstates)
B
A
B
AT
CpdT
T
dQS
Classical definition(from analysis of steam machines)
Statistical definition
0T
dQ
A
B
The ENTROPY
k – Boltzmann constant
V
P
T
dQdS
dQ – heat imparted to the system by the surroundings
t
i
ii ppk
S
1
ln
1 2 3 4 5 1 2 3 4 5 1 2 3 4 5
S = maxS = min
n
lattice position
Show this!
WkS ln
p – probabilities of states
What if microstates are occupied unequally? How to write the entropy?
pdVdTCdQ V
Classical property of entropy:
dVV
R
T
dTC
T
dQdS V
dVV
RTdTCdQ V
RTpV
for a mole of ideal gas:
integrating
VRTCS V lnln
1
2
1
221 lnln
V
VR
T
TCS
V
or
( = integration constant)
2
1
1
2 lnlnC
CR
V
VRS
At constant T and n
V
nC
so, entropy logarithmically depends on concentration
1
2
1
2 lnlnV
VR
T
TCS V
If perfect Watson-Crick pairing was strictly enforced, then every organism should have no less than 61 different tRNAs. Many creatures get away with a considerably smaller variety because of the ‘promiscuity’ or ‘wobble’ at the third position in many codons.
Phe codons UUU and UUC (5’-3’) can both be recognized by the tRNA that has GAA (5’-3’) anticodon
T. thermofilus 70S ribosome (M. Yusupov et al., 2001)
Low-resolution (EM) model of E. coli 70S ribosome
The assembly of a functional ribosome starts with initiation factors elF6 and elF3
Methionyl-tRNAiMet recognizes the AUG start codon before mRNA is loaded
There are two types of Met tRNA: Initiation tRNA can bind only to the P siteMet tRNA used in synthesis can bind to A site and than translocate
E site P site A site
Peptyidyl transferase reaction
Translocation
Binding of incoming amino acyl tRNA
Termination is assisted by RFs(release factors)
UAA – stop codon
Circular structure of mRNA increases the translation efficiency
The replication fork: leading strand and lagging strand
LargeT = helicase
Pol = priming DNA polymerase
Pol = DNA polymerase
PCNA - displaces Pol
Why GENETICS? (Chapter 5)
X X
In Haploid organisms complementig genes can be expressed on extra-chromosomal elements (plasmids), i.e. “in trans”
Diploid organisms
Generation of temperature-sensitive mutations
Tes
ting
mut
ants
for
com
plem
enta
tion
and
sort
ing
them
into
com
plem
enta
tion
grou
ps
