Translation

Question 1

Translation is the biochemical synthesis of proteins. How is this done?

Answer 1

The translation of sequences of nucleotide in mRNA into the sequence of amino acids in polypeptide

Question 2

In translation the AAs are unable to bind directly to the codon so tRNA functions as an adaptor molecule between the two sequences. How does this work?

Answer 2

The anticodon of tRNA interacts with codon of mRNA

Question 3

The Wobble hypothesis accounts for what phenomenon?

Answer 3

Why multiple codons code for one amino acid One tRNA can recognize more than one codon due to less precise base pairing –> Therefore fewer than 61 tRNAs are required for efficient translation

Question 4

What are the 4 characteristics of genetic code?

Answer 4

Specificity => specific codon always codes for same AA Universality => specificity of genetic code has be conserved from very early stages of evolution (exception in mitochondria) Redundancy => given AA may have more than one triplet for it (Arg/Ser = 6 codons) Non-overlapping and commaless => Code is read from fixed starting point as continues sequence of bases three at a time

Question 5

A point mutation occurs when 1 base is altered. List and descirbe the 6 point mutations:

Answer 5

Silent: changed codon may code for same AA (no consequences)

Missense: changed codon codes for different AA

Nonsense: Changed codon codes for STOP codon

Insertions, deletions, and frameshift mutations

Question 6

What is a frameshift mutation?

Answer 6

Occurs when the number of inserted or deleted nucleotides is not a multiple of 3

Question 7

Which type of mutation is known to cause Sickel Cell Anemia

Answer 7

Missense mutation

*in the sickle cell gene, GTG (Val) replaces the normal GAG (Glu)*

Question 8

What are the 3 steps of Translation?

Answer 8

Initiaion- Recognition of mRNA by small ribosomal subunit and formation of initiation complex

Elongation- Repeated addition of AAs to a growing polypeptide

Termination- Stop codon leads to the release of complete polypeptide; dissociation of ribosome from mRNA

Question 9

What type of template is used in Translation?

Answer 9

mRNA

prokaryotic mRNA is has several coding regions (polycistronic)

Eukaryotic mRNA only codes for one polypeptide chain (monocistronic)

Question 10

How are ATP and GTP used in translation?

Answer 10

ATP: used to attach AA to tRNA

GTP: used for binding of aminoacyl-tRNA to A site and for translocation step

*additional ATP and GTP are used in initation and termination steps

Question 11

What is the aminoacyl-tRNA responsible for?

Answer 11

specificity and proofreading and high fidelity translation

Question 12

A ribosome has 3 sites where tRNA molecules bind or exit. List and define these sites:

Answer 12

A site: binds incoming aminoacyl-tRNA and specifies next AA to be added

P site: occupied by peptidyl-tRNA; this tRNA carries synthesized peptide

E site: occupied by empty tRNA as it is about to exit

Question 13

In eukaryotes, 16S ribosomal RNA (rRNA) contains the sequence which is complementary to the shine-delgarno sequence in mRNA. What does binding of these 2 sequences do to the mRNA position?

Answer 13

Positions it on the 30S subunit

Question 14

In eukaryotes the 40S subunit binds to the what of mRNA?

Answer 14

cap structure

Question 15

What is the anitcodon to UCA?

Answer 15

UGA

Question 16

During the iniation step of tranlsation the tRNA binds to which site?

Answer 16

P site

Question 17

After initiation, the tRNA binds to which site for the duration of translation?

Answer 17

A site

Question 18

Describe the translational-inhibitory effect of Streptomycin

Answer 18

Binds the 30S subunit and distorts its structure, interferring with initiation of protein synthesis

Question 19

Describe the translational-inhibitory mechanism of Tetracyclines

Answer 19

Interact with small ribosomal subunits, blocking access of aminoacyl-tRNA to the mRNA-ribosome complex

Question 20

What is the function of peptidyl transferase?

Answer 20

A component of the 50S ribosomal subunit, transfers the amino acid from the P-site onto the amino acid at the A-site, and catalyzes peptide bond formation

Question 21

Describe the translational-inhibitory mechansim of Chloramphenicol

Answer 21

Inhibits prokaryotic peptidyl transferase; high levels may also inhibit mitochondrial protein synthesis

Question 22

Describe the translational-inhibitory mechansim of antibiotics Clindamycin and Erythromycin

Answer 22

Bind irreversibly to a site on the 50S subunit of the bacterial ribosome, thus inhibiting translocation

Question 23

Describe the translational-inhibitory mechanism of Diptheria toxin

Answer 23

Inactivates (ADP-ribosylates) the eukaryotic elongation factor, eEF-2, thus preventing translocation

Question 24

Describe the translational-inhibitory mechanism of ricin

Answer 24

Inhibits eukaryotic trranslation by removing adenine from 28S rRNA

–> This modification inhibits ability of large ribosomal subunit to bind elongation factors

Question 25

Elongation is signified by the movement of STOP codon to an "A" site triggering what series of events?

Answer 25

Release factors bind to "A" site of ribosome Peptidyl transferase hydrolyzes bond between peptide and tRNA

Question 26

Once the polypeptide is released from the ribosome, chaperones bind to the polypeptide in order to do what? What family of proteins do these chaperones belong to?

Answer 26

Prevent non-specific folding Heat shock proteins

Question 27

In addition to heat shock proteins, another important step in proper protein folding is formation of what bond? What enzyme is responsible for this?

Answer 27

Disulfide bond between cystein residues Protein disulfide isomerase (PDI)

Question 28

What is the process utilized in order to label misfolded proteins for degradation?

Answer 28

Polyubiquitination

Question 29

What are the two ways in which protein misfolding materializes as a disease?

Answer 29

Loss of function mutations Gain of function mechanisms =\> mutations that cause a toxic novel function, dominant negative mutations and amyloid accumulation (neurodegenerative)

Question 30

Nuclear proteins have

Answer 30

Nuclear localization signal

Question 31

Mitochondrial proteins have

Answer 31

Mitochondrial entry signal

Question 32

What is the fate of proteins produced on the ER?

Answer 32

Lysosomes- peptides, nucleic acids, carbs, lipids Secretory vesicles- gastric acid, digestive enzymes, lung surfactant, sebum Extracellular vesicles- protein and nucleic acids (can be considered another type of cell signaling)

Question 33

On the list of covalent modifications of polypeptides (either during or after their synthesis) is phosphorylation (or dephosphorylation). What are the three amino acids which are the only 3 that will bind a phosphate group?

Answer 33

Serine Threonine Tyrosine

Question 34

Methylation of histones is inlvolved in the regulation of transcription (transcriptional activation). What are the two AAs that accept methyl groups?

Answer 34

Lysine Arginine

Question 35

In order to stabilize collagen there is the process of hydroxylation. What 2 AAs will accept a hydroxyl group?

Answer 35

Proline Lysine

Question 36

Carboxylation

Answer 36

Blood coagulation

Question 37

Attachment of fatty acids

Answer 37

anchoring of protein to membrane

Question 38

Glycosylation

Answer 38

Serine Threonine Asparagine residues of membrane or secreted proteins

Question 39

Biotinylation

Answer 39

Regulation of carboxylases via Lysine residue

Question 40

What are 4 examples of activation via proteolytic cleavage?

Answer 40

zymogens (stomach--\>pancrease) via enteropeptidase Blood clotting cascade Procollagen--\>Collagen Apoptosis =\> mediated by caspases (procaspases--\>caspases)

Question 41

Postranslational modifications increase

Answer 41

Proteomic diversity