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88 Cards in this Set

  • Front
  • Back
translation occurs in the ... in association with ...
cytoplasm

ribosomes
translation is the ... step in protein synthesis and overall gene expression. (... is the first step)
2nd

transcription
the ... is the set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells.
genetic code
protein alphabet consists of # characters
20
nucleic acid alphabet consists of only # characters
4
combinations of 3 nucleotides that encodes for a specific amino acid
codons
there are # possible codons

most amino acids have #-# possible codons

... and ... have only one codon

3 codons do not enconde for an amino acid. These are called ... codons, which signal the end of translation
64
2-4
methionine and tryptophan
stop
each codon specifies # AA
1
some AA are specified by more than one possible codon, called the ... code
degenerate
When an AA has more than one codon, the codons usually vary in the # base, which allows for ... to occur
3rd
wobble
The code is almost universal among all living organisms. The big exception is the genetic code used to translate human ... and ...
mitochondrial RNA and proteins
The code is read beginning from the ... end of mRNA at a specific ... (AUG) and ending at a ... (UAA, UAG, UGA) near the ... end of mRNA
5'
start codon
stop codon
3'
a change in a single nucleotide in the DNA results in a ... in the mRNA sequence (changing a codon), which could result in an abnormal amino acid sequence
single change
other mutations (insertions, deletions, frameshift mutations) can cause the ... on the mRNA to shift, causing major changes in protein structure and function.
reading frame
there are # possible reading frames for mRNA
3
the 3 components that must come together for translation to occur are ...
mRNA
tRNA
ribosome
what contains the genetic code?
mRNA
what transports the appropriate amino acid
tRNA
what is the translator that brings the nucleotide language and amino acid language together to form a protein?
ribosome
ribosomes consist of ... and ...

the ... and ... subunits associate only during translation

They bring together ... and specific ... molecules that are "charged with an amino acid"
protein and rRNA

large and small

mRNA and tRNA
in prokaryotes, the large subunit is ... and the small ones are ... and ...
70S
30S 50S
in eukaryotes, the large subunit is ... and the small ones are ... and ...
80S
40S 60S
the 60S subunit is transported by a G protein-dependent transporter called ...
Nmd3p
once within the ... or ..., the ribosomal subunits specifically associate with each other to help guide the translational process
cytoplasm or RER
what is a small RNA chain (73-93 nucleotides long) that transfers a specific amino acid to a growing polypeptide chain within a ribosome?
transfer RNA (tRNA)
what serves as an adaptor, or connector between the mRNA and the AA?

Each type of this can be attached to only one type of AA and only one codon on mRNA (highly specific)
tRNA
the 5' end of the tRNA nucleotide strand usually ends with a ...
G
the 3' end of the tRNA usually consists of the nucleotide sequence ...
CCA-3'
amino acids are attached to tRNA at the ... end
3'
in the 3-D structure of tRNA, you will find a ... loop near the 5' end, a ... loop near the 3' end, and an ... loop in the middle.
D
T
anticodon
tRNA contains a triplet sequence called the ... that can base pair to the corresponding 3 base codon on mRNA
anticodon
what is this?
non-standard base pairing in the 3rd position of the codon.
the wobble phenomenon
what is this?
-Can hydrogen bond to more than one base in the corresponding codon position.
-One of the many modified bases in tRNA and is especially promiscuous in base pairing.
-can bind with A, U, or C.
-gives flexibility when it comes to translation.
inosine
... can pair with uracil (in addition to C)
Guanosine
tRNA that has an amino acid covalently attached to its 3’-end is called an … and is said to be …
Aminoacyl-tRNA
“charged”
What is the enzyme that is needed to attach an amino acid to its tRNA?

It uses an anticodon of tRNA as a recognition site for attachment of amino acid.

It requires energy (ATP)
Aminoacyl-tRNA synthase
What is the initiator tRNA?
Methionyl-tRNAi ^(met)
The first step in initiation involves … for translation
Preparing the tRNA
Methionyl-tRNAi met forms a pre-initiation complex with … and …
Eukaryotic initiation factor 2 (eIF2)
Small (40S) ribosomal subunit
The second step in initiation involves … for translation
Preparation of mRNA
What are the 2 important mRNA initiation factors and where do they bind?
-cap binding protein (CBP) or eIF4E
-poly-A binding protein (PABP)
-5’ cap
What is this?
-binds 3’-poly-A tail of mRNA
-helps to circularize some mRNAs prior to binding ribosome
-either favors or inhibits initiation
Poly-A binding protein (PABP)
Steps 3-5 of initiation involves …
Bringing mRNA into the ribosome
Step 3: The cap recognition complex targets mRNA to the …
(bringing the tRNA and mRNA together)
Pre-initiation complex
Step 4: the small unit ribosome scans along mRNA for the … (AUG)
Start codon
Step 5: when … (initiator tRNA) base pairs with AUG codon, … hydrolyzes GTP and initiation factors are released
Met-tRNA
eIF2
Steps 6-7 of initiation involves preparing the …
Ribosome
Step 6: … dissociate from small ribosomal subunit and are recycled for further rounds of translation
Initiation factors
Step 7: … (along with both mRNA and Met-tRNA) binds to …
Small ribosomal subunit
Large ribosomal subunit
What are the 3 binding sites that are available once the ribosome is complete?
P-site (peptidyl)
A-site (aminoacyl)
E-site (exit)
The initiation phase of translation is regulated by what 2 proteins?
-eIF2 protein (required for formation of the pre-initiation complex)
-eIF4E (mRNA cap binding protein)
If …, eIF2 does not bind to tRNAmet and translation does not occur. It can become this and inactivated during times of cellular stress, such as starvation, heat, and viral infections.
Phosphorylated
The eIF4E initiation factor only becomes activated when it … from the 4E-binding protein.
… (a hormone that stimulates protein synthesis[anabolic]) stimulates phosphorylation of the 4E-binding protein, which releases and … eIF4E allowing it to bind to mRNA and initiate translation
Dissociates
Insulin
activates
What is the major regulator of the initiation step? (the rate limiting step)
eIF2
The translation defect, Leukoencephalopathy with Vanishing White Matter (VWM) involves:
-chronic-progressive inherited …, usually occurring during childhood
-rapid deterioration of white matter (myelin) following … or minor … (tissue damage)
-inherited mutations within 2 subunits of the … translation initiation factor resulting in inactivation
Degenerative brain disease
Febrile infections or minor head trauma
eIF2B
Do prokaryotic and eukaryotic translation differ?
Only in the initiation phase
What are the 5 ways in which prokaryotic (bacterial) initiation of translation differs from eukaryotic?
-ribosomes : 70S (30S+50S)
-formylated Met-tRNA
-only 3 initiation factors needed (IF-1, IF-2, IF-3)
-mRNA is not “capped”
-Shine-Dalgarno sequence is used to recognize the start codon and initiate translation
What are the 3 sites in the 80S ribosome complex?
-P site
-A site
-E site
What site is this?
-where Met-tRNAi met is initially bound and where the growing peptide chain is located
P site
What is the site where new incoming activated tRNAs bind initially?
A site
What is the site where tRNAs exit the ribosome after they have transferred their amino acid to the growing peptide chain?
E site
What is the first step of elongation?
Binding of aminoacyl-tRNA to the A Site on the ribosome
During the first step of elongation:
-incoming aminoacyl-tRNA first combines with elongation factor … + GTP
EF1α
During the first step of elongation:
-aminoacyl-tRNA-EF1α-GTP complex binds to A site, where GTP is … and EF1α-GDP … from the tRNA
Hydrolyzed
Dissociates
During the 1st step of elongation:
… of the A site to ensure that each tRNA anticodon matches mRNA codon
Proofreading
The second step of elongation is …
The formation of peptide bonds
During the 2nd step of elongation:

-amino acid on tRNA in the … site forms peptide bond with amino acid on tRNA in … site

-catalyzed by … (part of the rRNA of the large ribosomal subunit)
A
P

Peptidyltransferase
The third step of elongation is…
Translocation
Translocation involves …
-complexes bind with GTP and binds ribosome
-binding causes … in ribosome that moves mRNA and paired tRNA
-uncharged tRNA moves from P site to the E site and is released from ribosome
Elongation factor (EF2)
Conformational change
Termination of translation:
-3 steps of elongation repeated until … moves into the A site
-… (a specific protein) binds to ribosome when a … is encountered on the mRNA, causing … to hydrolyze bond between peptide chain and tRNA
-nascent peptide is realsed from the ribosome
Stop codon
Release factor
stop codon
peptidyltransferase
What is this?
-resembles both transfer and messenger RNA. Stops translation of defective mRNA.
tmRNA
-Formation of each aminoacyl-tRNA requires # high-energy phosphate bonds in the form of ATP
-formation of the pre-initiation complex requires hydrolysis of …
-during elongation, as each amino acid is added to the growing peptide chain, 2 GTP’s are hydrolyzed (one with …, one with …)
2
GTP
EF1, EF2
What is this?
-a complex of many ribosomes simultaneously translating a single mRNA
-ribosomes every # nucleotides
-one mRNA guides synthesis of several copies of its protein product
Polysomes
100
What are these?
-macrolides
-tetracycline
-aminoglycosides
Antibiotics that target prokaryotic initiation and ribosomal units
MELAS (stands for mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Stroke-like episodes)
-involves defective mitochondrial …
-defects include impaired termination, impaired pre-tRNA processing, decreased stability and aminoacylation, and abnormal tRNA conformation
-commonly leads to a decreased steady-state level of normal aminoacylated tRNA, which in turn leads to …
-symptoms: seizures, stroke-like episodes, autonomic dysfunction, headache
-some symptoms mimic Herpes Simplex Encephalitis (HSE)
-defining feature: … or … lactic acid levels are typically high
tRNA Leu
reduced protein synthesis
plasma or CSF
Hypertension and other cardiovascular diseases
-mutations found in one family involving …
-abnormal mitochondrial proteins normally containing …
-overall effect: high blood …, low blood …
-mitochondrial tRNA for isoleucine
-isoleucine
-pressure, magnesium levels
What are 2 examples of mutations in mitochondrial tRNA?
-MELAS
-Hypertension and other cardiovascular diseases
What are 3 examples of diseases caused by premature termination codons in mRNA (PTC mutations)
-Duchenne muscular dystrophy
-cystic fibrosis
-cancer
# of all inherited diseases result from premature termination codon (PTC) mutations
1/3
What disease is this?
-most common X-linked fatal genetic disease
-10-20% of patients carry a nonsense mutation resulting in premature translation termination of the dystrophin protein in muscle cells
-absence of dystrophin permits excess calcium to penetrate the sarcolemma
Duchenne muscular dystrophy
Cystic fibrosis
-2-5% of patients have … mutations in the cystic fibrosis transmembrane regulator (CFTR) gene
Nonsense
What disease is this?
-PTC mutations in tumor-suppressor genes
Cancer
What are 2 major therapeutic approaches to overcome nonsense PTC mutations?
Gene therapy
Pharmacological
Which treatment of PTC mutations is the treatment of choice due to the potential for targeted repair?
Gene therapy
Which treatment approach of PTC mutations can modify gene expression and block nonsense-mediated mRNA destruction, without correcting the underlying gene defect?
Pharmacological
What is this?
-a group of antibiotics that are classically used against certain types of bacteria.
-alters the conformation of rRNA, inducing codon misreading that causes either incorporation of an erroneous amino acid (mis-incorporation) at a sense codon or failure of recognition of the stop codon, leading to translational read-through rather than chain termination
Aminoglycosides
In prokaryotes, aminoglycosides binds to … rRNA, inducing conformational alignment in the ribosomal decoding center despite codon/anticodon mismatch.
-enables UAA codon to be paried with CUU or GUU tRNA anticodon, promoting polypeptide chain … with glutamate or glutamine
16S
elongation
What is the only process in translation in which energy is not needed?
Termination