Download 3 DNA Function Transcription Translation

Making the Big Connection
How can we be sure that DNA is really the
stuff that encodes genetic information ?
After all DNA is really just a big sugar, isnt
it?. (Not!)
 DNA isn’t nearly complex enough to store
genetic information.
 Only proteins are versatile enough to be
able to store something as complex as
hereditary information.
 I’m sorry but I just don’t come from green
puss running out of an infection .

The Landmark Experiments

Fred Griffith
 Transforming
Principle of Pneumococcus
(Whole Oganism Approach)

Avery, MacLeod and McCarty
 Transforming
Principle of Pneumococcus
(Chemical Breakdown Approach)

Barbara McClintock
 Jumping

Genes in Corn
Hershey and Chase
 The
final nail in the coffin - The Blender Test
Fred Griffith
Avery, MacLeod
and McCarty
Hershey and
Chase
The Griffith Experiments 1928
Pneumococcus
is a kind of bacterium
that can cause death.
Pneumococcus comes in two varieties.
Avirulent
“II-R” - Rough Colonies, Not
sugar coated
Virulent “III-S” - Smooth Colonies, Sugar
coated
II-R
vs. III-S strains are gentically
different.
Type III-S bacteria
are pathogenic.
Injection into mice
results in pneumonia
and death.
Is this expected?
Type II-R bacteria are
not pathogenic.
Injection into mice
results in no
pathology.
Is this expected?
Type III-S bacteria are
pathogenic.
Heat killed bacteria
should not be deadly.
Injection into mice
does not result in any
pathology.
Is this expected?
Type III-S bacteria
are pathogenic.
Type II-R bacteria
are not pathogenic.
Injection into mice of
living II-R and dead
III-S results in
pneumonia and
death.
Is this expected?
The Avery, MacLeod and McCarty
Experiments (Hello Reductionism!)
Pneumococcus
is a kind of bacterium
that can cause death.
Pneumococcus comes in two varieties.
Avirulent
“II-R” - Rough Colonies, Not
sugar coated
Virulent “III-S” - Smooth Colonies, Sugar
coated
II-R
vs. III-S strains are genetically
different.
Type II-R bacteria
form rough colonies.
Type II-R bacteria
placed on agar will
grow to form rough
colonies.
Is this expected?
Type III-S bacteria
form smooth
colonies.
Dead bacteria don’t
grow on agar or
anything else.
Is this expected?
Type II-R bacteria
form rough colonies.
Type III-S bacteria
form smooth
colonies.
Mixing type II-R
bacteria with DNA
from dead III-S
produced smooth
colonies
Say what ?!
Type II-R bacteria
form rough colonies.
Type III-S bacteria
form smooth
colonies.
Mixing type II-R
bacteria with DNA
from dead III-S
produced smooth
colonies; protease
doesn’t stop this.
What does this mean?
Type II-R bacteria
form rough colonies.
Type III-S bacteria
form smooth
colonies.
Mixing type II-R
bacteria with DNA
from dead III-S
produced smooth
colonies; RNase
doesn’t stop this.
What does this mean?
Type II-R bacteria
form rough colonies.
Type III-S bacteria
form smooth
colonies.
Mixing type II-R
bacteria with DNA
from dead III-S
produced smooth
colonies; DNase
stops this.
What does this mean?
Human Genetic Traits
Clinodactyly (curved little finger)
Albinism
Human Genetic Traits
Progeria (Genetic Lethal)
Hairy Ears (Y-Chromosome)
Proteins



Composition: C, H, O, and sometimes S and N.
Examples: Egg Whites, Hair, Hemoglobin,
Insulin, Collagen, Antibodies...........
Significance:
 Reaction
catalysts (i.e. , they facilitate chemical
reactions)
 Transportation / storage of small molecules / ions.
 Coordinated motion (e.g., muscle action)
 Mechanical support (e.g., strengthen skin and bone)
 Immune Protection (e.g., antibodies)
 Regulate ion movement (e.g., nerve impulses)
Protein Secondary Structure
Secondary Structure
(a helix and b pleated sheet)
Kuru
Neurodegenerative
disease characterized
by ataxia / dementia
Brain Section
Tertiary
Structure
The structure of the Staphylococcus aureus
alpha-hemolysin pore determined to 1.9 A
resolution. Alpha-hemolysin is a water-soluble
protein toxin that can self-assemble into a
transmembrane pore of defined structure.
Shown is the side-view of the assembly, as it
would span the membrane. Within the
mushroom-shaped homo-oligomeric heptamer
is a solvent-filled channel, 100 A in length, that
runs along the sevenfold axis and ranges from
14 A to 46 A in diameter.
Quaternary
Structure
Staphylococcus
aureus
Hemolysin heptamer
Quaternary
Structure
S. aureus
Hemolysin
heptamer
Factors that Impact Protein Function
The Central (and almost correct) Dogma
DNA (Genes )
Make an mRNA copy
of the information
contained in the DNA
Transcription
RNA (mRNA)
Information stored in
mRNA is used to
direct the construction
of proteins.
Translation
Proteins (cell labor)
The Master Molecule
The Power Behind
DNA
The a and The W
RNA
Ribonucleic Acid - RNA



The Nucleic Acid Jezabelle
Functional Forms:

Messenger RNA (mRNA)

Transfer RNA (tRNA)

Ribosomal RNA (rRNA)
Significance:

Medium of genetic communication (mRNA is the voice of DNA)
Molecular shipping service (tRNA transports amino acids for protein
manufacture)
Molecular industrialist (rRNA manufactures proteins)

Non-protein enzyme (ribozyme)

Excise/Rewrite Genetic Information

Chromosome Maintenance

Information Storage Molecule

Possibly the oldest self-replicating biomolecule.


RNA Structure

RNA is not a
regular double
helix. RNA
structure almost
always involves
folding of the
RNA upon itself.
mRNA: the voice of DNA

DNA, itself, cannot direct protein production

RNA is a cheap, disposable copy of the DNA
information except that "U" replaces "T".

mRNA contains information on:
 1)
where to start protein construction
 2)
how to construct the protein (the amino
acid sequence)
 3)
where to stop protein construction
 4)
time before mRNA self-destruction
mRNA
mRNA contains
all instructions
that are required
for the assembly
of a functional
protein.
tRNA: FedEx of Protein
Production

Amino acids are the building blocks of proteins

The protein manufacturing facilities
(ribosomes) do not have a stock of amino acids
but rely on a "Just-in-Time" delivery system.

Each of sixty-one different tRNAs are specific
for only one of twenty different amino acids.

tRNAs have a dual job:
 1)
they pick up amino acids (one at a time) and
deliver them to the protein factories (ribosomes)
 2)
they participate in protein construction by
interfacing with the mRNA on the assembly line
tRNA - Transfer RNA
tRNA:
squashed
like a bug
tRNA:
the 3D
beauty
rRNA: Protein Production by Ford



Amino acids are assembled into proteins at
ribosomes.
The ribosomes are built from a combination of
up to 82 proteins and as many as 4 ribosomal
RNAs (rRNA).
Ribosomes participate in protein manufacturing
in two ways:
 1)
by providing a site for mRNA to interface with
tRNAs carrying amino acids
 2) by gluing the amino acids together to form a chain
(protein) according to the instructions of the mRNA.
rRNA - Ribosomal RNA/Ribosome
rRNA - Ribosomal RNA/Ribosome
The Central (and almost correct) Dogma
DNA (Genes )
Make an mRNA copy
of the information
contained in the DNA
Transcription
RNA (mRNA)
Information stored in
mRNA is used to
direct the construction
of proteins.
Translation
Proteins (cell labor)
Transcription: Making an RNA copy of DNA.

DNA: Double
Stranded

DNA strands
separate to
allow an RNA
copy to be
made.

Single strand
mRNA is the
final product
Transcription: Making an RNA copy of DNA.
Synthesis of
mRNA does
not change the
original DNA
sequence in
any way.
Transcription: Making an RNA copy of DNA.
The DNA can be
copied over and
over each time
it necessary to
produce a given
protein.
Cracking the Genetic Code
There are twenty amino acids. How many DNA
letters (GATC) code for a single amino acid?
There are a total of 16 possible two-letter
combinations (42).
GG
AG
UG
CG
GA
AA
UA
CA
GU
AU
UU
CU
GC
AC
UC
CC
There are a total of 64 possible three-letter
combinations (43).
Magic mRNA Decoder Ring
Initiation of Translation
Ribosome
Step
Large Subunit
Shine-Delgarno
Sequence
M
Methionine
tRNA at “P” site
Empty “A” site
 mRNA
UA C
A UA GG A G GA C GA A AA UG UA U U G G C CA GA A G U U
~
P
#1 in protein
synthesis is
assembly of an
mRNA / Ribosome
initiation complex.
This requires:
OH
binds to a
docking site on the
ribosome (ShineDelgarno sequence)
 Methionine
Small Subunit
is the first
amino acid in almost
all proteins.
Elongation of the Protein
Ribosome
M
K
tRNA carrying the
amino acid lysine (K)
enters the “A” site
UUU
UA C
A UA GG A G GA U GA A AC UG UA U U G G C C A GA A G U U
tRNA exits
through to get
another amino
acid (M)
P
mRNA
Ribosome
M
K
A bond is formed between amino
acids “M” and “K”. This releases the
tRNA from “M”
The ribosome then moves
forward and to shift the tRNA
with amino acids “MK” to the
“P” site
UA C U U U
A UA G G A G GA U G A A AC U G U A U U G G C C A GA A G U U
P
m RNA
~
OH
~
OH
Termination of a
Newly Made Protein
Ribosome
M
K
V
V
I
F
UA G
A UA GG A GGA U C U A AC UG UA U U G G C C A GA A G U U
Ribosome
Large
Subunit
M
K
Ribosomes stall
at termination
codons until the
translation
complex falls
apart.
P
mRNA
F
The translation complex
disengages in preparation for
the next round of synthesis
I
Ribosome
Small Subunit
A UA GG A G GA U C T A A C UG UA U U G G C C A GA A G U U
P
mRNA
~
OH
~
OH
Transcription and Translation
DNA
5’GGG TAT CGA ATT TTT CAT TGG CTG GGC 3’
3’CCC ATA GCT TAA AAA GTA ACC GAC CCG 5’
RNA
5’GGG UAU CGA AUU UUU CAU UGG CUG GGC 3’
Protein
G
Y
R
I
F
H
W
L
G