1. The fundamental of chemical physiology and of embryology is
to understand why tissue cells do not all express, all the time,
all the potentialities inherit in their genome
JACOB AND MONOD
DR.RITTU CHANDEL
MD BIOCHEMISTRY (2ND YEAR)
DEPARTMENT OF BIOCHEMISTRY
GRANT MEDICAL COLLEGE
MUMBAI
06-08-13

2. – functional unit of DNA
 Genome – total genetic information contained in
cell
 Gene expression – multistep process resulting in
production of functional gene product
 Gene
regulation
prokaryotes
eukaryotes
Level
Transcription
DNA level
Transcription
Post transcription
Translation
Post translation
process
fluctuates
irreversible

3.  It
is absolutely essential for growth,
development, differentiation and very
existence of an organism
 It answers to if, how much and when
particular gene product is made
 Rapidly adjusts ( half life of mRNA is low)
eg. Insulin synthesized by pancreatic cell
although nuclei of all cells contain insulin
gene

4. 
Housekeeping or constitutive genes – encode
products required for basic cellular function
Continually expressed
eg. Enzymes of TCA cycle
Induction – increase the expression of particular
product
eg. Lac operon
Repression – decreases the expression of particular
product
eg. Tryptophan operon

5. 
Cistron – smallest unit of genetic expression
one cistron – one subunit

Operon – linear array of coordinately controlled genes,turned
on and off as a unit

Promoters – sequences that are important for transcription
most common – rich in adenine and thymine ( TATA box )
other – GC box, CAA
regulatory sequence – regulates transcription
embedded in NCR of genome
cis acting – when they influence expression of gene
on same chromosome

10. sugar
Lac operon
Glucose
Lactose
Glucose and lactose
Off ( negatively regulated)
On ( positively regulated)
Off ( negatively regulated)

11. Nucleotide sequences of regulatory site shows a nearly perfect inverted
repeat, indicating that DNA in this region has an approximately two fold
axis of symmetry
Symmetry matching is a reccuring theme in DNA- protein
interactions

12.  Recognize
specific DNA sequences

13.  DNA
binding unit comes from protein lac
repressor
 Alpha helix from each monomer of protein
is inserted into the major groove of DNA,
where amino acid side chains make
specific contacts with exposed edges of
base pairs

14. These interactions allow the lac repressor to bind more tightly
to the specific site than to the wide range of other sites present
in E.coli genome

15. common to many prokaryotic DNA –
BINDING PROTEINS
 Pair of alpha helices separated by tight
turn
 2nd of these two helices is recognition
helix
 Residues of 1st helix participate in contacts
with DNA backbone
 exception- methionine repressor
 Is

16. Eg. Heme synthesis
regulated by repression of ALA synthase

17. p
p
o
l
a
trpe
trpd
trpb
trpc
trpa

21.  Genome
larger
 Nucleosome – complex of DNA and
histones
Not organized in operons
 Transcription and translation are
uncoupled
 Many different cell types present in most
eukaryotes

22.  1.Gene
amplification
Eg- in fruitfly
in resistance to methotrexate

24.  DNA
methylases are base and sequence
specific
 Prevents transcription
 Heavily methylated – genes not expressed
 5 azacytidine is inhibitor of methylases
 Housekeeping genes rarely methylated
 Requirment

25.  Chemical
modification
 Most important in preventing transcription
 Plays a role in maintenance of inactive
chromatin
 Eg – barr body

globin genes in non – erythroid cells

26.  One
gene is switched off while a closely
related gene takes up its function
 Hb synthesis
epsilon – zeta (embryo)
alpha – gamma (6th month)
alpha – beta (after birth)
Immunoglobin synthesis IgM to IgG

27.  At
2 levels
1.chromosomal packaging
Accessibility of transcription
2.individual gene regulation

29.  Requirement
for gene expression
 Chromatin structure is modulated through
covalent modifications of histone tails
 Histone acetyltransferase (HAT)

32.  Enhancer
works by facilitating the binding of
basic transcriptional complex to promoter
works when oriented in any direction
exert positive influence on
transcription even when separated by
1000s of bp from promoters

33.  Transcription
factors
Transcription
factors
enhancer
Transcription
factors
Transcription
factors
promoter
Transcription
factors

34.  Regulated
by signals eg. Hormones
 Properties
1.redundant
2.acts synergestically
Have one functional domain for DNA binding
and one for transcription activation
Can be classified according to structure of
their DNA binding domains

35.  Similar
to prokaryotic helix turn helix
 Recognizes asymetric DNA sequences

36. 2 cysteine and two histidine residues
seperated by 12 amino acids
Cysteine residues are seperated by 2
amino acids
Histidine residues seperated by 3 amino
acids
Loop that interacts with the major
groove of DNA

37. 2 polypeptides join to form Y shaped dimer
whose arms can interact with major groove of
DNA
Stem – leucine zipper
Pair of long alpha helices
1st part – basic, makes contacts responsible
for DNA recognition site
2nd part - forms coiled coil structure with its
partner

38. BINDING MOTIF
ORGANISM
REGULATORY
PROTEIN
HELIX TURN HELIX
E.coli
Lac repressor
ZINC FINGER
Mammals
Steroid receptor family
LEUCINE ZIPPER
Mammals
CRE binding protein

39.  Alternartive
splicing
varied products are produced
average human genome is thought to
code for 3 different proteins depending on
exons retained in splicing
calcitonin gene
1.In thyroid gland
2.In neurons

40.  May
operate in nucleus or cytoplasm
 Nucleus – hnRNA are produced which is
not processed to mRNA
 Cytoplasm
vary considerably in their half lives

41.  Initiation
factors are involved
 Action of initiation factor inhibited when
phosphorylated by protein kinase
 Eg. Reticulocytes – no nuclei, must
regulate synthesis of globin at translational
level
When heme is high, globin is produced
heme prevents phosphorylation of initiation
factors

42.  Modifications
like folding, enzymatic
clevage or bond formation
 Proinsulin -------------------- insulin
 Protein
degradation

43.  SATYANARYAN
 VASUDEVAN
 PANKAJA
NAIK
 LIPPINCOTT
 MARKS
 HARPER
 VOET
 STRYER
THANK YOU