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Molecular Genetics > Translation > Flashcards

Translation Flashcards

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Biology 101 flashcards
1
Q

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

A

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

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2
Q

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?

A

The anticodon of tRNA interacts with codon of mRNA

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3
Q

The Wobble hypothesis accounts for what phenomenon?

A

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

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4
Q

What are the 4 characteristics of genetic code?

A

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

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5
Q

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

A

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

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6
Q

What is a frameshift mutation?

A

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

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7
Q

Which type of mutation is known to cause Sickel Cell Anemia

A

Missense mutation

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

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8
Q

What are the 3 steps of Translation?

A

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

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9
Q

What type of template is used in Translation?

A

mRNA

prokaryotic mRNA is has several coding regions (polycistronic)

Eukaryotic mRNA only codes for one polypeptide chain (monocistronic)

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10
Q

How are ATP and GTP used in translation?

A

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

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11
Q

What is the aminoacyl-tRNA responsible for?

A

specificity and proofreading and high fidelity translation

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12
Q

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

A

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

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13
Q

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?

A

Positions it on the 30S subunit

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14
Q

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

A

cap structure

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15
Q

What is the anitcodon to UCA?

A

UGA

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16
Q

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

A

P site

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17
Q

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

A

A site

18
Q

Describe the translational-inhibitory effect of Streptomycin

A

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

19
Q

Describe the translational-inhibitory mechanism of Tetracyclines

A

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

20
Q

What is the function of peptidyl transferase?

A

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

21
Q

Describe the translational-inhibitory mechansim of Chloramphenicol

A

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

22
Q

Describe the translational-inhibitory mechansim of antibiotics Clindamycin and Erythromycin

A

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

23
Q

Describe the translational-inhibitory mechanism of Diptheria toxin

A

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

24
Q

Describe the translational-inhibitory mechanism of ricin

A

Inhibits eukaryotic trranslation by removing adenine from 28S rRNA

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

25
Q

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

A

Release factors bind to “A” site of ribosome

Peptidyl transferase hydrolyzes bond between peptide and tRNA

26
Q

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?

A

Prevent non-specific folding

Heat shock proteins

27
Q

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

A

Disulfide bond between cystein residues

Protein disulfide isomerase (PDI)

28
Q

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

A

Polyubiquitination

29
Q

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

A

Loss of function mutations

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

30
Q

Nuclear proteins have

A

Nuclear localization signal

31
Q

Mitochondrial proteins have

A

Mitochondrial entry signal

32
Q

What is the fate of proteins produced on the ER?

A

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)

33
Q

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?

A

Serine

Threonine

Tyrosine

34
Q

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

A

Lysine

Arginine

35
Q

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

A

Proline

Lysine

36
Q

Carboxylation

A

Blood coagulation

37
Q

Attachment of fatty acids

A

anchoring of protein to membrane

38
Q

Glycosylation

A

Serine

Threonine

Asparagine

residues of membrane or secreted proteins

39
Q

Biotinylation

A

Regulation of carboxylases via Lysine residue

40
Q

What are 4 examples of activation via proteolytic cleavage?

A

zymogens (stomach–>pancrease) via enteropeptidase

Blood clotting cascade

Procollagen–>Collagen

Apoptosis => mediated by caspases (procaspases–>caspases)

41
Q

Postranslational modifications increase

A

Proteomic diversity

Molecular Genetics (7 decks)

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