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MCB 450 > Class 10: Protein Synthesis > Flashcards

Class 10: Protein Synthesis Flashcards

1
Q

how does information flow from DNA - DNA - RNA

A

base-pairing

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2
Q

genetic code

A
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3
Q

missense mutation example

A

sick cell disease

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4
Q

nonsense mutation

A

hemoglobin mckees Rocks

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5
Q

diferent mutations

A
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6
Q

Cystic Fibrosis

A

phenylalanine is deleted in CFTR: ATP dependent transport protein functions as cAMP regulated chloride channel

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7
Q

CFTR

A

cystic fibrosis transmembrane conductance regulator

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8
Q

components required fir translation

A
  1. Amino Acids
  2. Transfer RNA(tRNA)
  3. Aminoacyl-tRNA synthetase
  4. mRNA
  5. Small and large ribosomal subunits
  6. Protein factors: initiation, elongation, and termination factors
  7. Energy: 2 ATP equivalents and 2 GTP: 4 high energy bonds
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9
Q

tRNA

A

(tRNA) molecules function as an adaptor molecule between a codon and an amino acid. There is at least one tRNA molecule for each amino acid.

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10
Q

Steps for tRNA

A

1) In a two-dimensional representation, all tRNA molecules appear as a cloverleaf pattern. In 3-D, it appears as a “L”
shape.

2) The amino acid–accepting region is the acceptor stem, which contains the 3’ CCA terminal region. Many of the nucleotides are involved in hydrogen bonds that
form stems and loops.

3) The amino acid is attached to a hydroxyl group of
adenosine in the CCA region of the acceptor stem.

4) The 5’ end is phosphorylated and the 5’ terminal residue is usually pG.

5) The anticodon is in a loop near the center of the sequence.

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11
Q

codon–anticodon interactions

A

Codons that differ in either of the first two nucleotides must be recognized by different tRNA.

  1. The first base of the anticodon determines the degree of wobble. If the first base is inosine, the anticodon can recognize three codons.
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12
Q

wobble hypothesis

A

The anticodon loop contains a sequence complimentary to the corresponding codon in a mRNA; some tRNAs can read more than one codon as first proposed by the “Wobble Hypothesis”.

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13
Q

2 activities of aminoacyl-tRNA synthetase

A
  1. synthetase activity
  2. editing activity

1) The amino acid is first activated by reacting with ATP to form aminoacyl-AMP
(adenylation)

2) The activated amino
acid is transferred
from aminoacyl-AMP
to tRNA to form
aminoacy-tRNA
(charged tRNA)

Fidelity of translation is
maintained by synthetase
(editing activity)

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14
Q

mupirocin

A

anti bacterial reagent

  • targets the bacterial iso-leucylaRS synthetic active site by reversibly blocking the li-AMP binding
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15
Q

3 binding sites on the ribosome

A
  1. The A (aminoacyl) site binds the incoming tRNA.
  2. The P (peptidyl) site binds the tRNA with the growing peptide chain.
  3. The E (exit) site binds the uncharged tRNA before it leaves the ribosome.
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16
Q

initiation in protein synthesis

A
  1. Binding of mRNA to 3‘end of 16s rRNA in 30s ribosomal subunit
  2. AUG initiation codon recognized by special tRNA (enter the P site)
  3. 50s subunit joins the 30s subunit to form 70s initiation complex
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17
Q

streptomycin

A

binds to the 30s subunit (small 16S rRNA) and interferes with the binding of fMet-tRNAf and thereby inhibits protein synthesis
initiation in bacteria

18
Q

Elongation in protein synthesis

A
  1. Elongation factors direct the binding of the appropriate tRNA to the codon in the empty A-site
  2. Peptidyltransferase transfers the amino acid (or peptide chain) from the P-site onto the amino acid at the A-site, and catalyzes peptide bond formation (a ribozyme)
  3. The ribosome moves a distance of three nucleotides along the mRNA in the 5’-3’ direction
  4. Steps 1, 2 and 3 are repeated until the growing peptide is complete.
19
Q

tetrcyclines

A

interact with small ribosomal subunits, blocking access of the aminooacyl-tRNA to the mRNA-ribosome complex (prokaryotes)

20
Q

Puromycin

A

sembles aminoacyl-tRNA
becomes incorporated into the growing
chain and releases uncompleted
polypeptide chains from the ribosome

21
Q

Chloramphenicol

A

inhibits prokaryotic
peptidyltransferas. High level:
Mitochondria protein synthesis.

22
Q

lindamycin and erythromycin

A

Bind
to a site on the 50s subunit of the bacterial
ribosome, thus inhibiting translocation
(prokaryotes)

23
Q

Diphtheria Toxin:

A

inactivate the
eukaryotic elongation factor, eEF-2,
thus preventing translocation
(eukaryotes)

24
Q

Ricin fatallly modifies ??

A

28S ribosomal RNA

25
Q

ricin

A

A. In cytosol, ricin A-chain inactivates ribosomes by depurination of 28S rRNA in 60S ribosomal subunit. a Ricin removes an adenine from position 4324 of α-sarcin/ricin loop of 28S rRNA by its N-glycosidase activity.

B. The adenine A4324 site before and after depurination by N-glycosidase activity of ricin A-chain

26
Q

Termination in protein synthesis

A
  1. Termination codon is at the A site.
  2. Release factors: RF-1: UAA, UAG; RF-2: UGA, UAA; RF-3:
    binds GTP; eRF (eukaryotic)
  3. Recycle of the ribosomal subunit, mRNA, tRNA and other factors
27
Q

antibiotic inhibitors and function

A
28
Q

diphtheria toxin

A

inactivates translocation inhibiting eEF-2 (eukaryotes)

29
Q

ricin

A

inactivates ribosome by depurination od 28S rRNA (peptidyltransferase) in 60S ribosomal subunit

30
Q

difference between pro and eukaryotes

A
31
Q

bacteria and eukaryotes differ in initiation

A

1) formation of preinitiation complex consisting of the 40S ribosome and Met-tRNA
in association with eIF-2.
2) Initiation factor eIF4E binds to the 5′ cap of the mRNA and facilitates binding
of PIC to the mRNA
3) The PIC binds to the 5′ end of mRNA and begins searching for an AUG codon
by moving step-by-step in the 3′ direction.
4) The 60S subunit is then added to form the 80S initiation complex.

32
Q

after synthesis proteins are delivered too?

A
  1. internal sites such as mitochondria, the nucleus (from free ribosome)
  2. the endoplasmic reticiulum, a process called protein targeting or protein sorting (from ER-bound ribosome)
33
Q

2 locations for protein synthesis by two types of ribosome

A

1) the protein is synthesized in the cytoplasm, and then the completed protein is delivered to its intracellular location post-translationally. (the nucleus, chloroplast, mitochondria, and peroxisomes ). (via free ribosome)

2) Protein directed through secretory pathway into the endoplasmic reticulum (ER) (secreted proteins, residents of the ER, the Golgi complex, lysosomes, and integral membrane proteins of these organelles and integral plasma-membrane proteins). (via ER-bound ribosome)

34
Q

protein synthesis on ER

A
  1. Translation of protein begins in the cytosol.
  2. As the signal peptide emerges from the ribosome, an SRP (signal-recognition particle) binds to it and to the ribosome and inhibits further synthesis of protein.
  3. SRP binds to its receptor in the RER membrane, docking the ribosome on the RER.
  4. The SRP is released and protein synthesis resumes.
  5. As the signal peptide moves through a pore into the RER, a signal peptidase removes the signal peptide.
  6. Synthesis of the nascent protein continues, and the completed protein is released into the lumen of the RER .
35
Q

argeting proteins

A

1) Proteins synthesized on the RER travel in vesicles to the cis face of the Golgi complex.
2) After the membranes fuse, proteins enter the Golgi complex and bud from the trans face of the Golgi complex in vesicles.
3) The vesicles may become lysosomes or secretory vesicles depending on their contents.
4) Secretory proteins are released from the cell when the secretory vesicles fuse with the cell membrane.
5) Proteins with hydrophobic regions embedded in the membrane of the secretory vesicles may become cell membrane proteins.

36
Q

translational regulation of ferritin synthesis

A

Production of ferritin is regulated at the level of mRNA by
iron regulatory proteins (IRPs), which bind to iron response elements
(IREs) on the 5’- (ferritin) untranslated regions of the mRNAs.

Binding of IRPs to the IRE of ferritin on the 5’ end of mRNA
inhibits the translation.

37
Q

postrranslational modification of proteins

A

A. Trimming
B. Covalent Modifications

38
Q

formation of human insulin from??

A

preproinsulin

39
Q

protein modifications

A
  1. Phosphorylation - (Tyr, Ser, Thr) Metabolic Regulation, Signal transduction, etc.
  2. Hydroxylation - (Proline) in collagen, Endoplasmic Reticulum
  3. Glycosylation – (O-linked as with Ser/Threo- OH or N-Linked as in asparagine)
  4. Other - biotinylation, farnesylation prenylation, ubiquitination etc.
40
Q

histone code hypothesis

A

proposes that specific combinations of modifications, as well as the order in which they occur, help determine chromatin configuration and influence transcription.

MCB 450 (11 decks)

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