T2- M3&4 Flashcards
What happens to mRNA during translation
It is read and translated into the specific primary amino acids
What does translation require and consist of
- initiation
- elongation
- termination
- release factors
- synthetase enzymes
- transfer RNA
- rRNA and ribosomal proteins
What does tRNA do
Translate amino acids from a pool of cataclysmically situated amino acids into a growing polypeptide strand in ribosome
Is each tRNA identical
No
How long is each tRNA molecule
70-90 nucleotides
What type of bonding does tRNA have
Hydrogen bonding between nucleotide bases
What does tRNA allow the formation of
4 double helical segments and 3 characteristic loops
What shape does tRNA fold onto itself in
L shape 3D structure
What does the anticodon region of tRNA compliment
mRNA codon sequence
Direction of anticodons written
3’ to 5’
Direction of written mRNA
5’ to 3’
What is at the 3’ end of tRNA molecule
Amino acid attachment site made of single stranded CCA nucleotide
What is the point of attachment to amino acids in tRNA
Terminal A for molecule activation
What protein is tRNA activation carried out by
aminoacyl tRNA synthetases
What does the tRNA active site recognize
anticodon end and attachment site
How many aminoacyl synthetases for each amino acid
20
What happens when aminoacyl synthetases bind to active site of tRNA
Can catalyze covalent attachment of tRNA to amino acid using ATP hydrolysis
What is the result of aminoacyl attachment to tRNA
charged tRNA molecule and amino acid joins polypeptide
How many codons and amino acids does mRNA code for
64 codons and 20 amino acids
How many tRNA molecules are there and why
45 due to nature of pairing interactions
- can bind to more than one mRNA
Define wobble
Explains the redundancy of the genetic code
- great flexibility in pairing third nucleotide of codon to its tRNA anticodon
Where is translation in eukaryotes
In the ribosome in the cytoplasm
Where is translation in prokaryotes
Cytosol
When does initiation begin in eukaryotes
When the initiation complex forms towards the 5’ end cap of mRNA and scans for AUG
What type of mRNA do eukaryotes have
Single stranded monocistronic mRNA
Describe initiation in prokaryotes
Located at ribosome sites called “shine dalgarno sequences” located upstream of AUG
- because they do not have 5’ cap
What type of mRNA do prokaryotes have
Polycistronic- code for several polypeptides along open reading frames
Why can prokaryotes have open polycistronic mRNA
Have functionally similar genes grouped together- transcribed from one promoter
How is a functional ribosome formed
Small and large subunits attach to mRNA molecule
What is the first amino acid
Methionine
What recruits the small ribosomal subunit
The initiation factor binding to 5’ cap
When does the large subunit bind
When the AUG is encountered
What energy does initiation use
GTP hydrolysis
When are initiation factors released
Once the ribosomal initiation complex are complete
How are amino acids synthesized
Amino end to carboxyl end
What site is methionine in
P site of large ribosomal subunit
Where does charged tRNA enter and bind
A site
How many nucleotides are read at once
3
What happens once correct pairing is made
GTP is hydrolyzed and aminoacyl end of tRNA released
Why is there a change in ribosome after tRNA binds
Allows for peptidyl transferase reaction to occur
What is a peptidyl transferase reaction
Condensation reaction of peptide bond
- transfer of polypeptide chain onto tRNA in A site
what allows translocation of tRNA
GTP bound elongation factors
What happens once GTP reaches stop codon
GTP bound release factors bind to A site and catalyze hydrolysis of bond between terminal amino acid in polypeptide and tRNA in P site
What will enable the dissociation of translation complex
GTP hydrolysis
What did the work on “neurospora crassa” by Beadle and Tatum establish
The one gene, one enzyme hypothesis based on the fact that fungus can grow well on minimal medium
What were Beadle and Tatum interesting in finding
They wanted to know if genes were mutated and disrupted, if they could still produce arginine
What did Beadle and Tatum hypothesis
One gene codes for one enzyme responsible for a part of the metabolic pathway
How was the one gene one enzyme tested
Srb and Horowitz put radiation on fungus to see which of the three enzymes are needed for arginine synthesis
What did Srb and Horowitz conclude
For a mutant to grow on either ornithine or citrulline, it must be able to make arginine from either compound
What is a better name for one gene, one enzyme
One gene, one polypeptide
Describe the human genome
Represents the full number of proteins expressed by all the info in our DNA
How many protein encoding genes did the project determine
20-25 000
Why can a single gene code for multiple proteins
Due to RNA processing and post translational modifications
Where does information split in eukaroytes
Double membrane nuclear envelope
Where did the nuclear membrane evolve from
Single membrane ER
What does compartmentalization allow
Intricate control in cell respiration regulation
Where are translation prepared mRNA sent and why
From nucleus to cytosol for free or ER bound proteins to facilitate translation
How can our proteome change
Depending on developmental stages and in response to internal and external signals
How are signals detected in blood glucose increase
Beta cells in pancreas sensory responses
How will the pancreas respond to high blood glucose levels
Release insulin to produce response on target cells
Where can glucose be absorbed in the bloodstream
- In the mouth across epithelial surfaces (with small microvilli and capillaries)
- in microvilli of small intestines
Where is insulin regulated
At transcriptional and translational levels
Where is insulin produced
Dense ER of pancreas cells
How many coded polypeptide amino acids in insulin
110
How many functional insulin amino acids coded
51
How many alpha and beta amino acids in insulin
21 alpha, 30 beta
Who determined structure of functional insulin and how
Dorothy Hodgkin using x ray crystallography
Define preproinsulin
110 amino acid precursor of mature insulin gene
What does preproinsulin contain
N terminal sequence that interacts with SRP particles to move to lumen of ER
What happens to preproinsulin
It is cleaved and yields proinsulin
What does proinsulin do
Undergoes folding in addition to formation of 3 disulfide bonds
What does proinsulin require to form bonds
Chaperon proteins
Where does proinsulin go
From RER to Golgi
What is formed after proinsulin
Insulin dimers (with beta and alpha chains) and releases c chain
What happens to c and n chains after modifications
They can bind to insulin receptors of target cells
What are two types of modifications
Covalent attachment and degregation of other proteins
What are the three types of covalent attachment
Phosphorylation, methylation, acetylation
Define phosphorylation
Involves a phosphate group to serine, threonine or tyrosine amino acid residues
- reversible
Describe methylation
covalent addition of methyl group
Describe acetylation
Covalent addition of acetyl group
What happens once beta cells release insulin
Insulin effector molecules bind to receptors that are expressed on specific target tissues
What are receptors
Proteins that receive and interpret info from signaling molecules
What does the insulin protein bind to
Insulin receptors called “receptor kinases”
In what form do receptor kinases exist
Monomeric form
Why is there a conformational change in insulin receptor
Insulin signaling molecules bind to receptor which pair up and dimerize
What does insulin receptor activate
Cytoplasmic domains of receptor which act like kinase receptors
What do kinase proteins engage in
Phosphorylation of amino acids
What activates an intracellular response
Due to intracellular signal amplification, the extracellular insulin signal causes cytoplasmic proteins to activte
What does intracellular signal activate
Glucose transporter proteins at cell surface- abosorbs glucose
When are intracellular signals induced in insulin
Once insulin is bound to receptor and phosphorylation occurs
What proteins are needed for intracellular signals in insulin
transducer and amplifier proteins
What type of feedback is signal induction
Positive feedback
What type of feedback is signal termination
Negative
Why is double negative feedback important
As an inhibitor, provides fine control
which cells take up glucose and fatty acids and where is extra stored
fat cells take up glucose and fatty acids and extra is stored in form of triglycerides
Do skeletal muscle or liver cells store more glucose?
Skeletal muscle
are exons included or removed
included
are introns included or removed
removed
what happens if exons are removed
creates isoforms or different types of RNA from same transcript
How many exons in insulin gene
22
what do skeletal muscle have removed
exon 11 and introns
how is the affinity of insulin receptor in skeletal cell
higher due to the isoform
- higher response of glucose uptake
what is removed in liver cells
only the introns, exon 11 present
How is the affinity of insulin receptors in liver cells
low affinity to insulin
what type of signal does insulin act as?
effector
Is insulin process positive or negative feedback?
Negative
What happens if insulin protein incorrectly processed after translation
Cannot bind to receptor of sensor tissues
What happens if insulin protein incorrectly spliced
No ability to transport glucose proteins
What does deficiencies in insulin protein and receptor cause
Hyperglycemia and diabetes
