BIO 1A03 McMaster University Test 2 Review
Translation Cellular components are able to read the genetic message in mRNA and
translate the message into specific primary amino acid sequence of a protein
How does tRNA structure allow for SPECIFICTY in 1. Plays critical role in ENABLING the translation of the information
translation? 2. Each type of tRNA molecule is not identical and can translate a specific codon
into a specific amino acid
What is the structure of tRNA? - single RNA strand (70-90 nucleotide length)
- four double helical segments and three characteristic loops
How are the four double helical segments and three Formed due to the large degree of complementarity along stretches of tRNA
loops in tRNA molecules formed? which results in many stretches of hydrogen bonding between complementary
bases.
What are anticodons? In what direction are they Three-base sequence in a transfer RNA molecule base that pairs with a
conventionally written? complementary codon in mRNA
They are conventionally written in the 3' to 5' direction
What is at the 3' end on tRNA? There is a protruding amino acid attachment site made up of CCA nucleotide
sequence (terminal "A" is point of attachment for amino acid during tRNA
molecule activation)
How is the activation of a tRNA molecule with a specific Activation is carried out by a family of enzymes called aminoacyl tRNA
amino acid carried out? synthetase
True or False; Each enzyme is specific to the type of True - 20 aminoacyl tRNA synthetase
tRNA and corresponding amino acid it will bind.
How do aminoacyl tRNA synthetases work? The active site of the enzyme recognizes the anticodon end of the tRNA and the
region of the amino acid attachment site.
Once bound to active site, enzymes catalyze covalent attachment of tRNA
molecule to its amino acid (energy from ATP Hydrolysis)
Charged tRNA able to deliver amino acids to growing polypeptide chain.
What does correct translation require (in terms of codon Correct translation requires the correct PAIRING of tRNA anticodon with the
and anti-codon)? appropriate mRNA codon
How does codon-anticodon pairing occur? The 5' end of codon (mRNA) will bind with the 3' end of the anticodon (tRNA)
What is meant by the term wobble? What does it help to Greater flexibility for base pairing between third nucleotide of a codon and
explain? corresponding base of tRNA anticodon
Wobble helps explain the redundancy of genetic code
When does translation initiation in Eukaryotes occur? In eukaryotes, it occurs when a translational initiation complex forms towards the
5' cap of the mRNA and then scans the mRNA until an AUG start codon is
encountered
How does translation initiation in Prokaryotes occur? Since there are no 5' caps, translation initiation complex will assemble at one or
more ribosome binding sites called Shine-Dalgarno sequences (Located a few
bases upstream the translation start codon)
, BIO 1A03 McMaster University Test 2 Review
What is the unique ability of prokaryotic translation? Translation can occur along multiple regions of prokaryotic mRNA sequence
(think operons) - Allows prokaryotes to have specific open reading frames for more than one
protein along mRNA
Eukaryotic translation initiation requires what Two ribosomal subunits
components? mRNA
Charged tRNA
Initiation factors
Initiation factors Bind to 5' cap of mRNA which allows for the recruitment of the small ribosomal
subunit
Other initiation factors will bind to tRNA that is charged with methionine
The partially assembled small subunit and tRNA do what They will move along the mRNA in a 5' to 3' direction until AUG is encountered
once initiated? - When this occurs, large ribosomal subunit is able to bind to the rest of the
initiation complex using energy from GTP hydrolysis
What happens to initiation factors once translation is Initiation factors are released once translation is complete
complete?
How does translation start in the ribosome (not - Methionine located in peptidyl site of ribosome
initiation)? - As the ribosome translates the mRNA, each subsequent charged tRNA enters
or binds to aminoacyl (A) site
GTP-bound elongation factor Each incoming charged tRNA is delivered in association with these
When the correct codon-anticodon pairing is made, GTP is hydrolyzed and
aminoacyl end of tRNA is released from elongation factor
How are peptide bonds formed in translation? Once tRNA binds mRNA, a conformational change occurs that is induced in
ribosomal RNA that allows for peptidyl-transferase reaction to occur
The condensation reaction occurs as peptide bond and transfers amino acid to
growing polypeptide chain onto tRNA in A-site
When another tRNA binds the site, what happens? The E-site is ejected
How is translation terminated? Once ribosome reaches stop codon, GTP-bound release factors will bind A-site
and catalyze hydrolysis of bond between terminal amino acid in polypeptide and
tRNA in P-site
Further GTP hydrolysis will also enable the dissociation of the translation
complex
one gene-one enzyme hypothesis the function of a gene is to dictate the production of a specific enzyme
- Based on the fact that Neurospora can grow well on minimal medium
- They must have some enzymes produced by a specific gene that convert
simple substances into amino acids and vitamins necessary for growth
Neurospora are able to synthesize what? Able to synthesize arginine through metabolic pathway
What did Srb and Horowitz demonstrate? Each gene contains the information needed to make each enzyme
How did Srb and Horowitz test their hypothesis? - Performed genetic screen of radiation treated neurospora to determine if there
are specific enzymes produced in the metabolic buildup of arginine
- Radiation would lead to mutations so they conducted the genetic screen by
raising colonies of radiation treated cells on a medium that was supplemented
with nothing, ornithine, citrulline, or arginine added to medium
, BIO 1A03 McMaster University Test 2 Review
What was the result of Horowitz and Srb's experiment? 1. With supplemented arginine, fungus is able to undergo growth
2. Non-supplemented medium, fungus not able to grow
3. Orthinine and Citrulline only: Inhibition in growth
Identified 3 mutants: Arg 1 (grows in all), Arg 2 (Citrulline and arginine only), Arg
3 (arginine growth only)
What is the exception to the one-gene, one enzyme - 20-25,000 protein encoding genes in human genome
hypothesis? - Provided evidence that more than one protein can possibly be produced from a
single gene
- Alternative splicing + other mechanisms contribute to complexity of mRNA and
therefore protein
The Human Proteome The full number of proteins that are expressed by all the hereditary information in
our DNA. (20-25,000 protein encoding genes)
The complexity of our proteome relative to our genome is The great complexity is largely attributed to RNA processing and post
attributed to what? translational modifications
True or False, the composition of proteome can change True - Occurs in organisms developmental stage and in response to internal and
in response to various factors? external signals
How does a cells ability to detect changes in Changes serve as stimuli that will result in important cellular responses
environment benefit the cell?
What happens in your body after a meal? 1. Stimulus can include an increase in Blood glucose levels (regulated by
sensory responses in specialized islet cells of pancreas)
2. Will lead to a cascade of events that return blood glucose back to normal
What happens in the case of high blood glucose? The pancreas will modulate the synthesis and secretion of an increased amount
of its own signal, insulin
What is Insulin? Effector protein that is produced by pancreatic beta cells that is able to
communicate with and produce a response on target cells and lead to a
DECREASE in blood glucose levels
Why are microvilli cells in the small intestine important? They are intimately associated with small blood vessels and they absorb glucose
found in intestinal tract and absorbed glucose in transported through blood
vessels
True or False: Glucose metabolism is an important True! Insulin biosynthesis is regulated at both the transcriptional and translational
physiological event which leads to an increase in insulin levels.
gene transcription and mRNA translation
The functional insulin protein secreted from beta cells of Alpha chain: 21 amino acids
pancreas is made up of two chains totalling 51 amino Beta chain: 30 amino acids
acids. What is the difference between the chains?
Two chains form a dimer that makes up functional insulin protein
Preproinsulin 110 amino acid precursor to functional insulin (Insulin gene encodes it)
How do N-terminal sequences assist movement of Preproinsulin contains N-terminal signal sequences which interacts with signal
preproinsulin? recognition particles to facilitate translocation of preproinsulin into lumen of the
RER
How is proinsulin created? The processing of preproinsulin through cleavage of the signal sequence which
yields proinsulin
Translation Cellular components are able to read the genetic message in mRNA and
translate the message into specific primary amino acid sequence of a protein
How does tRNA structure allow for SPECIFICTY in 1. Plays critical role in ENABLING the translation of the information
translation? 2. Each type of tRNA molecule is not identical and can translate a specific codon
into a specific amino acid
What is the structure of tRNA? - single RNA strand (70-90 nucleotide length)
- four double helical segments and three characteristic loops
How are the four double helical segments and three Formed due to the large degree of complementarity along stretches of tRNA
loops in tRNA molecules formed? which results in many stretches of hydrogen bonding between complementary
bases.
What are anticodons? In what direction are they Three-base sequence in a transfer RNA molecule base that pairs with a
conventionally written? complementary codon in mRNA
They are conventionally written in the 3' to 5' direction
What is at the 3' end on tRNA? There is a protruding amino acid attachment site made up of CCA nucleotide
sequence (terminal "A" is point of attachment for amino acid during tRNA
molecule activation)
How is the activation of a tRNA molecule with a specific Activation is carried out by a family of enzymes called aminoacyl tRNA
amino acid carried out? synthetase
True or False; Each enzyme is specific to the type of True - 20 aminoacyl tRNA synthetase
tRNA and corresponding amino acid it will bind.
How do aminoacyl tRNA synthetases work? The active site of the enzyme recognizes the anticodon end of the tRNA and the
region of the amino acid attachment site.
Once bound to active site, enzymes catalyze covalent attachment of tRNA
molecule to its amino acid (energy from ATP Hydrolysis)
Charged tRNA able to deliver amino acids to growing polypeptide chain.
What does correct translation require (in terms of codon Correct translation requires the correct PAIRING of tRNA anticodon with the
and anti-codon)? appropriate mRNA codon
How does codon-anticodon pairing occur? The 5' end of codon (mRNA) will bind with the 3' end of the anticodon (tRNA)
What is meant by the term wobble? What does it help to Greater flexibility for base pairing between third nucleotide of a codon and
explain? corresponding base of tRNA anticodon
Wobble helps explain the redundancy of genetic code
When does translation initiation in Eukaryotes occur? In eukaryotes, it occurs when a translational initiation complex forms towards the
5' cap of the mRNA and then scans the mRNA until an AUG start codon is
encountered
How does translation initiation in Prokaryotes occur? Since there are no 5' caps, translation initiation complex will assemble at one or
more ribosome binding sites called Shine-Dalgarno sequences (Located a few
bases upstream the translation start codon)
, BIO 1A03 McMaster University Test 2 Review
What is the unique ability of prokaryotic translation? Translation can occur along multiple regions of prokaryotic mRNA sequence
(think operons) - Allows prokaryotes to have specific open reading frames for more than one
protein along mRNA
Eukaryotic translation initiation requires what Two ribosomal subunits
components? mRNA
Charged tRNA
Initiation factors
Initiation factors Bind to 5' cap of mRNA which allows for the recruitment of the small ribosomal
subunit
Other initiation factors will bind to tRNA that is charged with methionine
The partially assembled small subunit and tRNA do what They will move along the mRNA in a 5' to 3' direction until AUG is encountered
once initiated? - When this occurs, large ribosomal subunit is able to bind to the rest of the
initiation complex using energy from GTP hydrolysis
What happens to initiation factors once translation is Initiation factors are released once translation is complete
complete?
How does translation start in the ribosome (not - Methionine located in peptidyl site of ribosome
initiation)? - As the ribosome translates the mRNA, each subsequent charged tRNA enters
or binds to aminoacyl (A) site
GTP-bound elongation factor Each incoming charged tRNA is delivered in association with these
When the correct codon-anticodon pairing is made, GTP is hydrolyzed and
aminoacyl end of tRNA is released from elongation factor
How are peptide bonds formed in translation? Once tRNA binds mRNA, a conformational change occurs that is induced in
ribosomal RNA that allows for peptidyl-transferase reaction to occur
The condensation reaction occurs as peptide bond and transfers amino acid to
growing polypeptide chain onto tRNA in A-site
When another tRNA binds the site, what happens? The E-site is ejected
How is translation terminated? Once ribosome reaches stop codon, GTP-bound release factors will bind A-site
and catalyze hydrolysis of bond between terminal amino acid in polypeptide and
tRNA in P-site
Further GTP hydrolysis will also enable the dissociation of the translation
complex
one gene-one enzyme hypothesis the function of a gene is to dictate the production of a specific enzyme
- Based on the fact that Neurospora can grow well on minimal medium
- They must have some enzymes produced by a specific gene that convert
simple substances into amino acids and vitamins necessary for growth
Neurospora are able to synthesize what? Able to synthesize arginine through metabolic pathway
What did Srb and Horowitz demonstrate? Each gene contains the information needed to make each enzyme
How did Srb and Horowitz test their hypothesis? - Performed genetic screen of radiation treated neurospora to determine if there
are specific enzymes produced in the metabolic buildup of arginine
- Radiation would lead to mutations so they conducted the genetic screen by
raising colonies of radiation treated cells on a medium that was supplemented
with nothing, ornithine, citrulline, or arginine added to medium
, BIO 1A03 McMaster University Test 2 Review
What was the result of Horowitz and Srb's experiment? 1. With supplemented arginine, fungus is able to undergo growth
2. Non-supplemented medium, fungus not able to grow
3. Orthinine and Citrulline only: Inhibition in growth
Identified 3 mutants: Arg 1 (grows in all), Arg 2 (Citrulline and arginine only), Arg
3 (arginine growth only)
What is the exception to the one-gene, one enzyme - 20-25,000 protein encoding genes in human genome
hypothesis? - Provided evidence that more than one protein can possibly be produced from a
single gene
- Alternative splicing + other mechanisms contribute to complexity of mRNA and
therefore protein
The Human Proteome The full number of proteins that are expressed by all the hereditary information in
our DNA. (20-25,000 protein encoding genes)
The complexity of our proteome relative to our genome is The great complexity is largely attributed to RNA processing and post
attributed to what? translational modifications
True or False, the composition of proteome can change True - Occurs in organisms developmental stage and in response to internal and
in response to various factors? external signals
How does a cells ability to detect changes in Changes serve as stimuli that will result in important cellular responses
environment benefit the cell?
What happens in your body after a meal? 1. Stimulus can include an increase in Blood glucose levels (regulated by
sensory responses in specialized islet cells of pancreas)
2. Will lead to a cascade of events that return blood glucose back to normal
What happens in the case of high blood glucose? The pancreas will modulate the synthesis and secretion of an increased amount
of its own signal, insulin
What is Insulin? Effector protein that is produced by pancreatic beta cells that is able to
communicate with and produce a response on target cells and lead to a
DECREASE in blood glucose levels
Why are microvilli cells in the small intestine important? They are intimately associated with small blood vessels and they absorb glucose
found in intestinal tract and absorbed glucose in transported through blood
vessels
True or False: Glucose metabolism is an important True! Insulin biosynthesis is regulated at both the transcriptional and translational
physiological event which leads to an increase in insulin levels.
gene transcription and mRNA translation
The functional insulin protein secreted from beta cells of Alpha chain: 21 amino acids
pancreas is made up of two chains totalling 51 amino Beta chain: 30 amino acids
acids. What is the difference between the chains?
Two chains form a dimer that makes up functional insulin protein
Preproinsulin 110 amino acid precursor to functional insulin (Insulin gene encodes it)
How do N-terminal sequences assist movement of Preproinsulin contains N-terminal signal sequences which interacts with signal
preproinsulin? recognition particles to facilitate translocation of preproinsulin into lumen of the
RER
How is proinsulin created? The processing of preproinsulin through cleavage of the signal sequence which
yields proinsulin
