DNA, RNA, & Flow of Genetic Information
DNA & RNA are long linear polymers, called nucleic acids.
Genetic information is stored in a sequence of 4 kinds of bases
along the chain, and is passed from one generation to the next
Chapter 5: Outline
5.1 A nucleic acid consists of 4 kinds of bases linked to a
sugar-phosphate backbone
5.2 A pair of nucleic acid chains with complimentary sequences
can form a double-helical structure
5.3 DNA is replicated by polymerases that take instructions from
templates
5.4 Gene expression is the transformation of DNA information into
functional molecules
5.5 Amino acids are encoded by groups of three bases starting
from a fixed point
5.6 Most eucaryotic genes are mosaics of introns & exons
Polymeric structure of nucleic acids
Linear polymers of covalent structures, built from similar units
Sequence of bases uniquely characterizes nucleic acids
Represents a form of linear information
Backbone is constant: repeating units of sugar-phosphate
Different pentose sugars in RNA & DNA
RNA
DNA
Sugar carbons
have prime
numbers, to
distinguish them
from atoms in
bases
TEST
Backbone of DNA & RNA
3’-to-5’ phosphodiester linkages
Sugar, red. Phosphate, blue
TEST
Purines & Pyrimidines
Note: ring atom #s RNA DNA
TEST
Sugar - base linkage
Nucleoside
RNA: adenosine, guanosine, cytidine, & uridine
DNA: deoxyadenosine, deoxyguanosine, deoxycytidine, & thymidine
Base above plane of
sugar, linkage is 
TEST
Nucleotides: monomeric units of nucleic acids
5’ nucleotide - most common 3’ nucleotide
Adenosine 5’-triphosphate
Deoxyguanosine
3’ monophosphate
Nucleotide: nucleoside joined to one or more phosphate groups
by an ester linkage
TEST
Adenosine 5’-triphosphate
Triphosphate linked to sugar C5’
Adenosine linked to sugar C1’
Base
Sugar
Acid
Basic Structure of Nucleic Acids
Monophosphate
Diphosphate
Triphosphate
Adenine
Guanine
Thymine
Cytosine
Uracil
Nucleoside (Adenosine)
Nucleotide (Adenosine monophosphate, AMP)
Purine
Pyrimidine
Ribose,
Deoxyribose
1’
2’3’
4’
5’
JuangRH(2004)BCbasics
Deoxyguanosine 3’-monophosphate
Structure of DNA chain
5’ end, phosphate attached 3’ end, free hydroxyl group
The Two Chains of DNA Are Antiparallel
5’pCpGpApTpCpGpApT-OH3’
5’ pApTpCpGpApTpCpG-OH 3’
5’ 3’
3’ 5’
Juang RH (2004) BCbasics
Large groove
Small groove
1 Twist = 10.5 bp
1
2
3
4
5
6
7
8
9
10
36 Å
CharacteristicsofDoubleHelix
3’
5’
5’
3’
Juang RH (2004) BCbasics
Watson and Crick base pairs
Essentially the
same shape
DNA polymerization reaction
By DNA polymerase
Step by step addition of deoxyribonucleotide units to a DNA chain
New DNA chain assembled directly on a preexisting DNA template
Primer & template required
Activated precursors required: dATP, dGTP, TTP, dCTP
Also required: Mg2+ ion
DNA replication, phosphodiester bridge
Nucleophilic attack by 3’ -hydroxyl group of primer on innermost
phosphorus atom of deoxynucleotide triphosphate (dNTP)
Hydrolysis of pyrophosphate (PPi) helps drive polymerization
Elongation proceeds, 5’ -to- 3’
Retroviruses reverse flow of information
Reverse transcriptase brought into cell by the virus (eg. HIV-1)
ssRNA
genome
Incorporated
into host DNA
Roles of RNA in gene expression
Messenger RNA: template for translation (protein synthesis)
Transfer RNA: carriers of activated AAs to ribosomes
(at least one kind for each of 20 AAs)
Ribosomal RNA: major component of ribosomes
(play structural and catalytic roles)
RNA polymerase
“claw” shape to hold DNA to be transcribed Mg2+ ion at
active site
Transcription reaction - RNA polymerase
Nucleophilic attack by 3’ hydroxyl group
Requirements: a template, activated precursors (NTPs), &
Divalent metal ion, Mg2+ or Mn2+
RNA polymerase: instructions from DNA templates
mRNA & DNA complementarity
mRNA sequence is the compliment of that of the DNA template
& is the same as that of the coding DNA strand, except for T in
place of U
Prokaryotic promoter
Consensus sequences centered at -10, & -35
Promoter sites specifically binds RNA polymerase,
& determine where transcription begins
Eukaryotic promoter
Consensus sequences centered at -25 & -75
Eukaryotic promoters are further stimulated by
enhancer sequences (can be at a distance of several kb from
start site on either its 5’ or 3’ side
Termination signal in E. coli
Sequence at 3’ end
of mRNA:
Hairpin loop
followed by a
string of uridines (U)
Alternatively,
transcription ended
by action of
Rho protein
mRNA modification in eukaryotes
(Less known about transcription termination in eukaryotes)
mRNA is modified after transcription
A “cap” structure is attached to 5’ end & a sequence of
adenylates, the poly(A) tail, is added to the 3’ end
Amino acid attached to tRNA
Amino acid esterified to
3’-hydroxyl group of
terminal adenosine of
tRNA
Amino acid is in an
activated form
Whole molecule is,
aminoacyl - tRNA
Aminoacyl - tRNA, symbolic diagram
The anticodon is the
template-recognition
site
1961, Crick & Brenner,
the genetic code:
3 nucleotides encode
an amino acid,
Code is nonoverlapping,
Code has no punctuation,
Code is degenerate,
(some AAs encoded by
more than one codon)
Genetic code, nonoverlapping
Genetic code, no punctuation
Sequence of bases is read in blocks of 3 bases from a fixed
starting point
Genetic code, degenerate (64 codons, 20 aas)
Trp & Met, one codon
each,
other 18 aas, two or
more codons,
Leu, Arg, & Ser, six
codons each,
Synonyms, codons
for same aa,
Synonyms differ in
last base,
3 stop codons,
designate translation
termination
Translation initiation: start codon
Initiator tRNA carries fMet
(formylmethionine) to
AUG (& sometimes GUG)
in prokaryotes, but initiation
is more complex
Messenger RNA is translated
into proteins on ribosomes,
large molecular complexes
of proteins & ribosomal RNA
Prokaryotic translation start
Eukaryotic translation start
Genitic code, universal, except…
Nearly but not absolutely universal
Ciliated protozoa read UAA & UAG as codons for aas
instead of stop signals. UGA is their only stop
Eukaryotic genes: mosaic of introns & exons
Exons (expressed sequences), blue
Introns (intervening sequences), brown
Detecting introns by EM
mRNA hybridized to corresponding genomic DNA
Single loop indicates gene is continuous
Splicing at consensus sequences
Introns excised by spliceosomes (assemblies of proteins &
small RNAs)
Exon shuffling
Shuffling expands genetic repertoire
Alternative splicing, 1st variation
Alternative splicing, 2nd variation
43
Biosynthesis of purine and pyrimidine nucleotides
• purine and pyrimidine basis from food are not
used
• Synthesis of purine and pyrimidine
nucleotides are coordinated
• all cells needs ribonucleosides,
deoxyribonucleosides and their phosphates
TEST
Precursore molecules
• 3 main compounds:
• tetrahydrofolate
• glutamine
• PRPP – 5-phosphoribosyl-1-
pyrophosphate
TEST
45
Importance of folic acid for biosynthesis of
NA bases
Folate
Green leafy vegetables,
liver, whole grains, yeast, k
N
N
O H
N
N
C H2 N
H2 N
C O N H C H
C H2
C H2
C O O C
O O -
H
Used form in human is tetrahydrofolate
46
(dihydro)folatereduktase
folate
N
N
OH
NH2N
CO NH CH
CH2
CH2
COO-
COO-
H
CH2 N
N
H
H
tetrahydrofolate
dihydrofolate
NADPH + H+
NADP
NADP
NADPH + H+
N
N
OH
NH2N
CO NH CH
CH2
CH2
COO-
COO-
H
CH2 N
N
H
Formation of
tetrahydrofolate
+
+
DEHYDOGENATION
47
Methotrexate (anticancer agent)
Inhibitors (dihydro)folatereductase:
NH2
H2N
CH2 N
CH3
C NH
O
C
COO-
H
CH2
CH2
COO-
N
N
Trimethoprim (bacteriostaticum)
N
N
NH2
H2N
OCH3
OCH3
OCH3
48
N
N
OH
NH2N
CO NH CH
CH2
CH2
COO-
COOCH2
N
N
H
CH2
N-5,N-10- methylen H4F – synthesis of thymin
N
N
OH
NH2N
CO NH CH
CH2
CH2
COO-
COOCH2
N
N
H
CHOH
N-10-formyl H4F – synthesis of purins
5 10
1
3
Using of tetrahydrofolate
Importance of glutamin for purine and
pyrimidine biosynthesis
CH COO
NH3
(CH2)2C -
+
O
NH2
- Donor of aminogroup
50
Glutmine antagonists inhibits synthesis of purines and
pyrimidines
CH2 CH
NH2
COOHOC
O
CH
N
N
azaserin
51
Necessary for synthesis:
Purine nucleotides
Pyrimidine nucleotides
NAD+, NADP+
PRPP - phosphorybosylphyridoxalphosphate
O
O
CH2OP
O
O
O-
OH
OH
P P
O
OO
O
-- O
O
-
52
Ribosa-5P + ATP  PRPP + AMP
PRPP-synthetase
Synthesis of PRPP
O
O
CH2OP
O
O
O-
OH
OH
P P
O
OO
O
-- O
O
-
ribose-5-phosphate
(pentose cycle),
activeted penthose
53
Differences in purine and pyrimidine synthesis
Purins
First PRPP…
Pyrimidins
First heterocycle ribose-P from
PRPP
O
O
CH2OP
O
O
O-
OH
OH
P P
O
OO
O
-- O
O
-
N
NO
O
COO
-
H
Synthesis - puzzle – one part to others.
Diffrence in the beginning :
–purines : first PRPP and than is form base
- Pyrimidines : first base and than ribosa-5-P from PRPP.
TEST
54
BIOSYNTESIS of PYRIMIDINS
N
O
H
O
12
3
4
5
6
N
Ribosa-P
glutamin
HCO3
•2.
aspartate
• 3. PRPP
COO-
Orotidinmono-P
Decarboxylation – uridin mono-P
Origin of atoms in pyrimidines
 karbamoyl-P•1.
TEST
55
CYTOPLASM
• 1 Glutamine + 2 ATP + HCO3

karbamoyl-P + glutamate + 2 ADP + Pi
• syntesis of karbamoyl -P
CO
NH2
O P
O
O
O-
Karbamoyl-P-synthetase
-energy, enzym karbamoylphosphatesynthetase II
Inhibition by UTP („inhibition by product“) and
aktivation by ATP.
56
H2N
CH
CH2
COO
COO
-
-
H2N
C O
P OO
O
-
-
Pi
C
N
CH
CH2
COOO
COO
NH2
H
-
H2
O
-
HN
C
N
CH
CH2
C
O
COO
O
-
H
HN
C
N
C
O
COO
O
-
H
O
O P
O
O
CH2
OP
O
O
O
O P
O
O
O
-
--
-
--
-
HN
C
N
C
O
COO
O
-
O
O
O
P O CH2
O
-
-
HN
C
N
C
O
O
O
O
O
P O CH2
O
CO2
karbamoylaspartate
dihydroorotate
orotate
Orotidinmono-P PRPP
Uridinmono-P
(UMP)
karbamoylP
aspartate
TEST
57
ATP
Biosyntesis of UTP and CTP
UMP
UDP 
ADP
ATP
ADP + P
glutamine
glutamate
CTP
ATP
ADP
UTP Uridin tri-P
cytidin tri-P
TEST
58
dTMP (methylation)
Methylation- H4F
N
N
O
O
CH3
CH2
OH
O
H
Methylen group in H4F is reduced to methyl dUMP
Deoxythymidintri-P
59
UDP  dUDP  dUMP TMP
Thymidylatesynthase
(enzym dependent on folate)
Dihydrofolatereduktas
e
Synthesis of TMP
Methylen –H4F H2F
serin
H4F
glycin
NADPH
NADP
Transport of methylene (
H4F …. H2F)
Anticancer drugs
TEST
60
N
N
OH
NH2N
CO NH CH
CH2
CH2
COO-
COOCH2
N
N
H
CH2
N
N
OH
NH2N
CO NH CH
CH2
CH2
COO-
COOCH2
NH
N
N
N
OH
NH2N
CO NH CH
CH2
CH2
COO-
COO-
H
CH2 N
N
H
H
NADPH + H+
NADP+
CH2
CH2-H4F
H2F
H4F
H
H
H
H
61
Dihydrofolate reductase - an objective antitumor
therapy.
Dihydrofolate reductase was the first enzyme for which focused antitumor
therapy.
The first-used inhibitor was aminopterin.
It binds to the enzyme 1000 times tighter than folate, acts as a competitive
inhibitor.
Currently used methotrexate and similar derivatives.
All drugs which affect the synthesis of purines and pyrimidines, deplete
rapidly dividing cells - but not only cancer cells but also cells in the bone
marrow and GI tract cells such as hair follicles.
62
thymidylate synthase
The administration of fluorouracil
organism conversion to
5-fluorodeoxyuridine monophosphate
Competitive inhibition
thymidylatesynthasy
The cytostatic effect of a drug
Thymidylate
synthase because it is blocked by
a competitive inhibitor, which in
effect prevents dTMP, resulting in
a slowdown (disabling) of cell
division.
TEST
63
2. Synthesis of pyrimidins by salvage pathway
Uracil
or
Cytosin
Ribosa-1-P
Pi
Uridin
or
Cytidin
Thymin
Deoxyribosa-1-P
Pi
Thymidin
1. nukleosides
64
•thymidin + ATP  TMP + ADP
•cytidin + ATP  CMP + ADP
•deoxycytidin + ATP  dCMP + ADP
•uridin + ATP  UMP + ADP
2. Kinase - phosphorylation
Salvage pathway – extrahepatal tissues
65
Regulation of biosyntesis of pyrimidins
• KarbamoylPsynthetase:
inhibition by UTP, purins nucleotides,
aktivation by PRPP
 Allosteric:
 dependence on cell cycle
KarbamoylP-synthetase in S phase is more
sensitive to activation by PRPP
66
Degradation of pyrimidins nucleotides
deaminatio
n
reduktio
n
-alanin
-aminoisobutyrate
Pyrimidins – to the simple compounds – urine
pyrimidine base, we are able in our body break down into simpler components
STEPS:
a) Release of P
b) Release of sugar
c) Degradation of pyimidin base
End products of cleavege of pyrimidines:
NH3, CO2, -alanin, ( -aminoisobutyrate)
Soluble metabolist – excretion by urine
TEST
67
Ribosa-5-P
3 glycin
HCO3
-
aspartate
formyl-H4F
glutamin
1 PRPP
formyl-H4F
2
4
6
7
8
Biosyntesis of purins
(multienzym complex)
Inosin-5-P (IMP)
5
cytoplasm
liver
N
HN
O
N
N
C
C
C
TEST
68
O
O P
O
O
CH2
OP
O
O
O
O P
O
O
O
-
--
-
O
CH2
OP
O
O
O NH2
-
-
O
CH2
OP
O
O
O NH
C O
CH2
NH3
-
-
O
CH2
OP
O
O
O NH
C O
CH2
NH CHO
-
-O
CH2
OP
O
O
O NH
C NH
CH2
NH CHO
-
-
N
N
O
O
O
P O CH2
O
H2N
-
-
N
N
O
O
O
P O CH2
O
H2N
OOC-
-
N
N
O
O
O
P O CH2
O
H2N
CO
H2N
-
N
N
O
O
O
P O CH2
O
NH
CO
H2N
OHC
-
O
O
O
P O CH2
O
-
N
N
O
N
N
H
H
Biosyntesis of IMP
Gln Glu
inosinmonophosphate
ATP, glycin
ADP
Formyl-
THFTHF
Glu Gln
H2O
CO2
asp
formylTHF
THF
H2O
phosphoribosylaminPRPP
Inosin-5-P (IMP)
TEST
69
N
N
O
N
N
H
ribosa-5-P
Inosin-5-P (IMP)
Initial substance for synthesis of other basis
aspartate, GTP
amination
AMP
oxidation aminati
on
GMP
Glutamin, ATP
XMP
xantosinmonoP
70
N
N
O
N
N
Ribosa
H
P
N
N
N
CH CH2COO
COO
N
N
Ribosa P
-
-
N
N
NH2
N
N
Ribosa P
N
N
O
O
N
N
RibosaH P
N
N
O
H2N N
N
RibosaH P
HH
Syntesis of AMP a GM
IMP
Asp
GTP
GDP + Pi fumarate
AMP
NAD+
NADH + H+ ATP AMP + PPi
XMP GMP
Gln Glu
71
Inhibitors of syntesis of purins (cytostatics)
• inhibitors dihydrofolate reductase
• analogy glutamin (azaserin)
• 6-merkaptopurin- inhibition of change IMP
to AMP and GMP
N
N
SH
N
N
H
merkaptopurin
72
Syntesis of purins by salvage pathway
Extrahepatal tissue
Purin + PRPP  purinnukleotidmonoP + PP
phosphoribosyltransferas
e
Recyclation of purins phosphoribosyltransferase
73
O
O
CH2OP
O
O
O-
OH
OH
P P
O
OO
O
-- O
O
-
phosphoribosyltransferase
AMP adeninphosphoribosyltransferase
74
Phosphoribosyltransferase deficiency causes
Lesch-Nyhan syndrome
hereditary disease
overproduction purine bases
accumulation of uric acid - DNA
mental retardation, self-mutilation
75
Syntesis of nukleotiddiP and triP
nukleosidmonoP
nukleotiddiP
nukleotidtriP
ATP
ADP
ATP
ADP
76
Regulation of biosyntesis of purins
• concentration of PRPP
Speed of
synthesis
Speed of
degradationSpeed of use
• inhibice PRPP-glutamylamidotransferase by AMP
and GMP (end products)
IMP
AMP
GMP
GMP

AMP

1.
2.
3.
77
2-deoxyribonucleotides
O
CH2O
OH OH
basePP
NucleotiddiP  2-deoxynucleotiddiP
reduction
thioredoxin,
thioredoxinreductase,
NADPH
H
Thioredoxinreductase - Se deoxygenati
on
78
ribonucleotidreduktase
Nukleotiddiphosphate 
deoxynucleotiddiphosphate
cofactor protein bound
79
Degradation of purines
AMP,GMP,
IMP,XMP
5-nukleotidase
guanosin, inosin,
xantosin + Pi
nukleosidphosphoryl
ase
Adenosin + Pi,
guanin,
hypoxantin,
xantin
+ riboso-1-P
adenosindeaminase
inosinnukleosidphosphoryla
se
Cleavage of P
liver
80
AMP,GMP,
IMP,XMP
5-nucleotidase
guanosin, inosin,
xantosin + Pi
nucleosidphosphoryl
ase
Adenosin + Pi,
guanin,
hypoxantin,
xantin
+ ribosa-1-P
adenosindeaminase
inosinnucleosidphosphoryla
se
81
adenosine deaminase deficiency
Enzyme deficiency leads to the accumulation of toxic deoxyadenosine,
which affects immunocompetent cells
One of the causes of severe combined immunodeficiency (severe
combined immunodeficiency disease-SCID).
82
hypoxantin xantin
Uric acids
xantinoxidase
guanin
guanase
end metabolit primate,
….. (400-600 mg /den)
Inhibition by
allopurinolem
Degradation of purins
TEST
83
Defects in metabolism of purins
gout
 increasing of production and decreasing of excretion of uric acid
 defect in salwa pathway
(deficit hypoxantin-guaninphosphoribosyltransferase) (HGPRT)
hypoxantin + PRPP  IMP + PP
 decrease of clearance in kidney
Keeping of crystals of UA in tissue
TEST
84
Allopurinol – competitive inhibitor xantinoxidasy
Gout: allopurinol inhibits the oxidation of hypoxanthine to
xanthine
hypoxanthine is more soluble and more readily excreted
N
N
OH
N
N
H
85
hypouricemia
xantinoxidasy deficit (excretion of
hypoxanthine and xanthine)
87
protein synthesis
88
Synthesis of proteins -
translations
Where: in cells containing nuclear DNA
Where cell: ribosomes (free or bound to the ER,
mitochondria)
prokaryotes: transcription, editing, transcript and translation
are spatially separated
eukaryotes: translation in progress to mature mRNA is
transported to the cytoplasm
89
Molecules which are necessary for protein
synthesis?
Amino acids
A number of enzymes
protein factors
ATP and GTP
The inorganic ions (Mg2 +, K +)
90
Effects of antibiotics on protein synthesis of prokaryotes
antibiotic effect
Streptomycin binds to the 30S ribosomal subunit, inhibits the formation of
initiation complex errors in reading the mRNA.
Tetracycline binds to the 30S ribosomal subunit and inhibits the binding of
aminoacyl-tRNA to A
Chloramphenicol binds to the 50S ribosomal subunit and inhibits
peptidyltransferasu
Erythromycin binds to the 50S ribosomal subunit and inhibits translocation
Puromycin Populated A-site of the ribosome, causing premature termination
91
Protein folding (folding)
The nascent polypeptide chain is transported through the
ribosome
Gradually getting out of a "protected" area of the
ribosome and set its spatial folding
Folding (folding) is mediated by specific proteins chaperones
(heat shock proteins)
Faults in composing - Alzheimer's disease, BSE,
cystic fibrosis ad.
TEST
92
Post-translational modification of
proteins
-Removing methionine residue
-Changing the length of the molecule (cleavage of the
polypeptide chain)
-glycosylation
-acetylation
-carboxylation
-methylation
-prenylation
- hydroxylation
-Sulfation ad.
TEST
93
Glykosylation of proteins
Glycoproteins
N-glycosidic O-glycosidic
They differ in carbohydrate synthesis method
94
Synthesis of N-glycoproteins
Synthesis of sugar components takes place outside the protein
The base is polyisoprene dolichol (see synthesis of cholesterol)
H-[CH2-C=CH-CH2]n-CH2-CH-CH2-CH2OH
CH3 CH3
n=18-20
Dolichol diphosphate as it is bound in the ER membrane, the terminal
phosphate is gradually adjoin the activated monosaccharides.
Ready oligosaccharide is transferred to a protein is bound via asparagine Nglycosidic
linkage. In plasma protein binding will take place finish
oligosaccharide component.
95
Glykosylation of dolichol
Dolichol-P
Dolichol-P-P-GlcNAc
Dolichol-P-P-GlcNAcGlcNAc
Dolichol-P-P-GlcNAc2Man9Glc3
…….AsnXSer……
GlcNAc2Man9Glc3
UDP-GlcNAc
UMP
UDP-GlcNAc
UDP
9 GDP-Man, 3 UDP-Glc
12 UDP
…….AsnXSer……
Dolichol-P-P
Enzyme
glycosyltransferase
96
The oligosaccharide precursor bound dolichol
glucose
mannose
N-acetylglukosamin
97
AsnXSer
Cotranslation glycosylation
dolichol
ER
cytoplasm
Finishing
glycoside
component in
GA
98
Synthesis of O-glycoproteins
Takes place in the ER and the Golgi
………ser…………….
OH UDP-monosach. UDP
………ser…………….
O-monosacharide
Activated monosaccharides are sequentially attached
O-glycosidic linkage
99
Transport of proteins to subcellular and
extracellular spaces (targeting)
Protein synthesis on free
ribosomes
Proteins remain in the
cytoplasm and are
transported into the
organelles (nucleus,
mitochondria). AK contain
a sequence which directs
the transport
Protein synthesis on the
RER
Transport into lysosomes,
ER, Golgi apparatus or the
membranes, secretion from a
cell
TEST
100
Transport of proteins synthesized on the RER
Membrane of
RER
The signal peptide (usually 15-30
AK hydrophobic N-terminus)
The signal-
recognizing
particle
SRPreceptor
Signal
peptidase
The cleaved
signal peptide
1.
2
.
3
4
5
6
101
Transport of proteins synthesized on the RER
1. The translation begins in the cytosol
2. Once the signal peptide leaves the ribosome, it binds to the signalrecognizing
particle (signal recognition particle-SRP). At the same time binds
the ribosome and inhibits further synthesis
3. SRP particle binds to SRP receptor in the RER membrane and attaches to
the ribosome RER
4. SRP is released and continues synthesis
5. Once the signal peptide penetrates the RER, signal peptidase deletes it
6. The synthesis of nascent protein and continues complete protein is released
into the RER
TEST
102
Transport of proteins synthesized on the RER
Lyzosoms
secretory
vesicles
Cis Golgi
Trans Golgi
103
1. Proteins synthesized on the RER are transported in the form of
vesicles of the cis-Golgi
2. Here is a sorting center - structural features determine where the
protein routing (sorting)
3. Some remain in the Golgi apparatus, while others are returned to the
RER
4. Another wander in the form vesicles in the trans Golgi delivery
5. Here are separating lysosomes and secretory vesicles
6. The contents of secretory vesicles is released extracellularly
7. Hydrophobic proteins embedded in the membranes of vesicles
become membrane proteins
Transport of proteins synthesized on the RER-cont.
104
Principles of intracellular sorting (sorting)
Example 1:
Proteins destined for lysosomes are labeled N-linked
oligosaccharide terminated with mannose-6-P
Prot-oligosacharidmannosa-6-P
"Address" is recognized
by specific membrane
receptors in the Golgi,
the protein is
incorporated into a
coated vesicle
klathrinem
105
Example 2:
Proteins destined for the ER to the carboxyl terminus of the
sequence Lys-Asp-Glu-Leu
Principles of intracellular sorting
lys-asp-glu-leu The proteins are
transported from the Golgi
back to the ER
106
Example posttranslational modifications: the synthesis of insulin
1
SH SH
HS
Cleavage of the peptide lead ER
Cleavage of carboxypeptidases
in the Golgi
preproinsuline
SH
Creating H-
bridges
C-peptide
Leading
peptide
Mr
= 11 500
23 AK
TEST