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lecture 16 Flashcards

(21 cards)

1
Q

what are the features of aa?
how are they joined?

A

alpha carbon, NH3 group, carboxyl group

-peptide bond between carboxyl group of one + NH3 group of another

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2
Q

how many aa are non polar, polar, basic and acidic?

A

np: 10–can form h bonds

p: 5–can participate in forming H bonds

acidic: 2

basic: 3

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3
Q

where and how does polypeptide assembly occur?
what is the N and C terminal?

A

in ribosome

-ribosomes bind mRNA and allow for mRNA codon pairing with tRNA anticodon, which determines what aa is added to the poly peptide
- in 5—> 3 direction

N is at 5’ end of mRNA
C is at 3’ end of mRNA

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4
Q

what 2 segments of mRNA that do not undergo translation?

A

5 UTR –helps initiate translation
3 UTR—–termination

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5
Q

what are the 4 levels of polypeptide structure?

A

primary— sequence, via peptide bonds

secondary— a helices and b sheet, via H bonds

tertiary–3d shape of polypeptide

quaternary— shape produced by combinations of polypeptides (2 or more)

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6
Q

what are the 3 essential tasks that ribosomes do in all domains of life?
what type of enzyme is the ribosome?

A

bind mRNA and identify start codon

allow base pairing of mRNA codons + tRNA anticodons

catalyze peptide bond formation between aa-

is a ribozyme, performed via rRNA

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7
Q

what are the 3 regions that the large and small subunits of the ribosome make up?
what does each one specifically have?

A

P site: holds tRNA where polypeptide is attached

A site: binds a new tRNA carrying the next aa to be added to the polypeptide

E site: where tRNA exit after their aa has been added to the polypeptide

—-small subunit has a place for initial binding of mRNA, scans mRNA to find start then binds

—large has peptide transferase activity – catalyze peptide bonds

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8
Q

what is the structure of the eukaryotic ribosome?
prokaryotic?

A

80s ribsome

60s subunit: 28s, 5.8s, 5s rRNA—49 proteins
40s: 18s rRNA–33 proteins

prokaryotic: 70s

50s: 23s, 5s– 31 ribosomal proteins
30s: 16s–21 ribosomal proteins

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9
Q

what is aminoacyl tRNA snythetase?

A

enzyme recognizes both aa and tRNA, 20 of them so specific for each aa

-catalyzes bond between carboxyl of aa and 3’ OH of Adenine

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10
Q

how is translation initiated in prokaryotes?

A

1) 30s small subunit + IF3 binds–> looks for start codon

2) once found, preinitiation complex forms (16srRNA, 30s, mRNA) —>then binds to Shine Dalgarno sequence (purine rich) upstream of the start codon

3) initiator tRNA + 50s large subunit binds to start codon, remains in P site–> IF is released

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11
Q

how does translation initiation in eukaryotes work?

A

1) preintiation complex 40s small subunit + eIF forms

2) initiation complex forms when small subunit binds 5’ cap—>then looks for start codon

3) start codon is found, 60s subunit is recruited + initiator tRNA binds–> eIFs are released

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12
Q

what does it mean that prokaryotes are polycistronic and eukaryotes are monocistronic?

A

polycistronic: multiple Shino dalgarno sequences–> many translatin initiation sites, so multiple peptides

monocistronic: 5’ cap is the only ribosome entry site, so one peptide

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13
Q

how does translation elongation work, step 1 ,2, 3?

A

1) entry of second tRNA into the A site helped by Ef (elongation factors)

  • fMet is already in the P site

2) peptide bond is formed between Met + new aa–> met is released from P site ( uncharged) and the dipeptide is in A site

3) the dipeptide is moved into the P site & the uncharged tRNA from the P site was moved to the E site to leave–> new peptide is ready to come in the A site

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14
Q

how does translation termination work?

A

1) stop codon enter the A site of the ribosome ( they have no tRNA)

2) since stop codons have no tRNA, RF bind the stop codon in the A site

3) RF allow for the polypeptide to be released from tRNA in the P site

4) tRNA and mRNA separate from ribosome AND ribosome disassembles into small & large subunit

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15
Q

what allows for bacteria to have coupled transcription and translation?
why are both of these processes not coupled in. eukaryotes?

A

no nucleus, so happen in the same general area

-transcription is in the nucleus , where the transcript is processed
-translation is in the cytoplasm after mature mRNA is capped

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16
Q

what are features of the genetic code?

A

no overlaps

almost universal-except in ciliates & in mitochondria

triplet code

degenerate— more than one codon can specifiy a specific amino acid

3 stop codons + 1 start codon

17
Q

what are isoaccepting tRNAs?

A

tRNA with different anti codon sequences that carry the same codon

this is why there are 64 codons that only code for 20 aa

18
Q

what is codon bias and 3rd base wobble theory?

A

it shows the frequency of synonymous codons

-flexible base paring on the 3’ end of codon and 5’ end of anticodon

19
Q

the production of functional proteins is not complete until?
what is signal hypothesis?

A

polypeptides are folder into their tertiary or quatanary structure

removal of 1 or more aa from the polypeptide is the most common form of postransltional polypeptide processing –> ex is fMet, is not functional!

—15-20 aa at the N terminus tells the polypeptide where to be transported, usually to the ER

20
Q

how did Crick and Brenner prove that the genetic code is triplet?

A

–used proflavin to create FCO mutations in rII via inserting or deleting base pairs

used insertions

21
Q

how did Nirenberg, Matthaei and Khorana assign codons to aa?

A

made artificial mRNA using U to decipher the genetic code

devised in virto