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Questions
How does RNA polymerase work and what does it make?
How does it know where to start and stop?
How does a ribosome work and what does it make?
How does it know where to start and stop?
If the DNA in every cell in your body is the
same why don't your adipose (fat)
cells secrete epinephrine?
If the DNA contains all of the information why doesn't
the ribosome just 'read' it?
Why have intermediate steps?
Looking at RNA ECB2 7.1
Making a cytosolic protein:
Step 1--transcribe
Genes encode proteins
Why use an RNA step?
Major steps in process: Initiation, Elongation and Termination
animation
Initiation
DNA-RNA interactions
DNA
Template strand
Complementary RNA strand
DNA/RNA
Hybrid
Watching
Transcription
EBC2 7.2
Adapted from Life; Purves 6thed
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf
http://www.johnkyrk.com/DNAtranscription.html
Check out
Translation: Converting the blueprint into
a working model
36”
72’
Grade P red oak, inlay mahaog
Nucleotides to proteins: Step II
Questions:
Are cytosolic and integral membrane proteins transcribed
the same way?
Are they translated the same way?
Three basic steps
Initiation
Elongation
Termination
From nucleotides to amino acids---How?
Fig 4-26
Two adaptors used: tRNA and amino acyl tRNA-synthetases
*Codons, Anticodons, and Wobble
*‘Charging’ of tRNA
*Basepairing with a tRNA
Fig 4-28
*Using Inosine w/ A, U, or C
Fig4-26
Fig 4-28
That Degenerate Genetic code
# codons > # tRNAs > # aminoacids
CCAGAGCAGACUGCUUAGCUUCAUCCCACGAACGGGAG
P Q E S QR T L AL STOPS L F H I P P T R N T GG ?
R
A D C L A
S S H E R
E
How did they figure out the genetic code?
Strings of identical nucleotides
Nirenberg
IFs
Players?
mRNA
Initiation factors
5’
Met
3’
Small subunit of ribosome
AAAAAAAA
Initiator tRNA
Once initiation complex forms large subunit of ribosome is recruited
How does the complex know where to start translating?
In Bacteria?
In eukaryotes?
Elongation CBI 6.4 Translation
Players?
mRNA
Aminoacyl- tRNAs
Elongation factors
P
site
E site
A site
Ribosome
Requires GTP hydrolysis
Results in peptide bond formation
Chain grows from N to C
Termination
Players?
mRNA
Termination factors
Ribosome
How does it work?
Why does the chain end?
Fig 4-40
The Protein
What happens to the protein?
Folding
Sorting
What happens to the mRNA, the ribosomes & the tRNA?
Reuse
Polysomes
Translation, Bipolar Disorder, and ……
What does this have to do with bipolar disorder?
Nobel Prize for Medicine 2000:
Dopamine as a neurotransmitter and its role in brain dysfunctions
(Dopamine is the catecholamine implicated in bipolar disorder)
Biaxial Theory ‘Most simply, manic states are here understood as the
clinical expression, at one point in time, of excessive synaptic
neurochemical capacity within the primary affective system, and
depressive states as the clinical expression of neurotransmitter
depletion’
Askland and Parsons (2006)
Tale of 2 proteins--a stretched metaphor
Protein 1: Many neurotransmitters are amino acids,
amino acid derivatives (like dopamine),
or short peptides
Neuropeptides synthesized in cytosol sorted/packaged
into vesicles for use. (as is dopamine- but not through translation)
Protein 2: Neurotransmitter receptors are proteins.
Synthesized in cytosol, inserted into ER membrane
and sent to proper location on plasma membrane
Broad Hypothesis: Perhaps Bipolar is a result of problem(s)
Getting the transmitters or the receptors to the right place at
the right time. (neurochemical part of biaxial theory)
Broad Idea: Perhaps Bipolar is a result of
problem(s) getting the transmitters or the
receptors to the right place at the right time?
How do we study this?--- examine what ‘should’ happen and
look for changes from that ‘standard’
How does neurotransmitter packaging occur?
Synaptic vesicles
What are they?
Vesicles are membrane spheres
Neurotransmitters are polar
How do they get in?