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Genetics Test 3 > Lecture 26 > Flashcards

Lecture 26 Flashcards

1
Q

How many amino acids are there?

A

20

each has a different radical group

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2
Q

Describe the structure of an amino acid.

A

a carbon bound to…

  • H
  • amino group
  • carboxyl group
  • radical group
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3
Q

type of bond joining the amino acids

A

peptide

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4
Q

what is the protein’s primary structure

A

the amino acid sequence

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5
Q

secondary structure of protein

A

the chain of amino acids folds on itself

  • alpha helix
  • beta pleated sheet
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6
Q

tertiary structure of protein

A

the secondary structure folds further

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7
Q

quaternary structure of protein

A

joining of multiple subunits

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8
Q

Proteins are produced during…

A

translation

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9
Q

triplet code

A

the idea that 3 nucleotides on mRNA are used to specify 1 amino acid

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10
Q

Why did early researchers devise the triplet code?

A

Knowing there were many amino acids, this is the only way the 4 bases could produce the enough amino acids

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11
Q

Francis Crick

A
  • proposed that the code would be read in a nonoverlapping manner
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12
Q

Brenner and Crick

A

established that a codon consists of 3 non-overlapping nts

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13
Q

Nirenberg and Mattaei

A
  • first to determine that a specific RNA sequence coded for a specific amino acid
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14
Q

Nonoverlapping

A

need a 3 letter codon to provide for all 20 amino acids

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15
Q

Nirenberg and Mattaei experiment

A
  • used a cell tree extract to provide miscellaneous molecules needed for translation and added an RNA molecule that contained uracil and all 20 amino acids
  • made different amino acids radioactive in 20 different tubes with 14C
  • allowed protein to be produced and checked if radioactive
  • since mRNA contained only Uracil, the codons would be UUU repeating over and over
  • polyUUU only produced in phenylalanine
  • repeated fr polyC, polyA, did not work with polG

determined coding sequence for 3 codons

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16
Q

Triplet Binding Assay

A
  • Nirenberg and Leder

- used to deduce the rest of the genetic code

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17
Q

Triplet Binding Assay process

A
  • charged tRNA, ribosome, and trinucleotide bind and do not go through filter
    1. set up 20 reaction tubes for each possible codon with different radioactive amino acid with trinucleotide, ribosome, and charged tRNAs
    2. allow binding
    3. filter out unbound amino acids
    4. check if radioactive

only had radioactivity on filter paper when the trinucleotide was the codon for that amino acid

encoded 61 of 64 codons using this technique

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18
Q

The code is…

A
  • unambiguous
  • degenerate
  • containing stop/stop punctuation
  • without internal punctuation
  • almost universal
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19
Q

unambiguous

A

a specific codon always codes for a specific amino acid

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20
Q

degenerate

A

there is more than one codon that codes for the same amino acid

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21
Q

stop codons

A

UAAA
UAG
UGA

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22
Q

start codon

A

AUG

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23
Q

no internal punctuation

A

mRNA is read beginning with the start codon without skipping any bases

24
Q

almost universal

A

the code is almost always the same

25
How many amino acids have exactly 1 codon?
2 | met and trp
26
How many amino acids have exactly 4 codons?
5
27
What is the highest number of codons for one amino acid?
6 in leucine, arginine, serine
28
Is there a pattern to the degeneracy of the code?
yes the first two bases are more important than the last
29
wobble hypothesis
due to wobble in the anticodon, a single tRNA can pair with more than one codon
30
inosine
facilitates the wobble hypothesis inosine is a base in tRNA and when present is in the 1st anticodon position. It can pair with uracil, adenine, and cytosine
31
ex of inosine in the wobble
Codons: GGU, GGC, and GGA CCI will pair with all three
32
The codons that can bind to a tRNA with inosine must...
all code for the same amino acid ex cannot code for tyrosine as only UAU and UAC code tyrosine while UAA is a stop codon
33
wobble in the anticodon
- an anticodon containing guanine in the 5' position binds with 2 different codons ex. AGG may bind with both UCC and UCU
34
steps of translation
1. charging the tRNA 2. initiation 3. elongation 4. termination
35
charging the tRNA means...
joining the amino acid to the tRNA at the 3' end
36
initiation means...
the ribosome assembles on the mRNA and translation starts
37
elongation means...
the continued addition of amino acids to the growing peptide chain
38
termination means...
the stop of translation and release of the protein
39
enzyme that conducts the reaction to charge the tRNA
aminoacyl synthetase
40
Describe charging the tRNA
1. the specific aminoacyl synthetase binds with its specific amino acid in the presence of ATP 2. with magnesium as a cofactor, the Ppi is released and AMP is joined to the carboxyl of the amino acid 3. the specific tRNA enters and displaces AMP 4. this releases the AMP and joins the carboxyl end of the amino acid to the 3' end of the tRNA 5. the charged tRNA is then released from the enzyme
41
describe initiation
building a ribosome - shine-Dalgarno sequence on the mRNA base pairs to a complementary sequence in the 16S rRNA - the charged tRNA binds so that the anticodons binds to the AUG start codon on the mRNA forming the 30S initiation complex - the large subunit of the ribosome binds to form the 70S initiation complex
42
ribosome sites
there are 3 sites that can hold tRNA - A or aminoacyl - P or peptidyl - E or exit
43
where is the tRNA in the ribosome
the P site
44
where is the start codon in the ribosome
the P site
45
Describe elongation
1. the start codon is in the P site and the next codon in the A site 2. a tRNA with the correct anticodon and amino acid comes to the A site 3. the 23S rRNA in the large subunit acts as a ribozyme to form the peptide bond between the two amino acid 4. immediately after the dipeptide sits in the A site 5. translocation of the ribosome occurs setting the dipeptide on the P site and freeing the A site for the next tRNA 6. this continues until a stop codon sits on the A site
46
peptidyl transferase activity
- conducted by the 23S rRNA of the large subunit | - forms hydrogen bond between the amino acid at the P and A sites on the ribosome
47
ribozyme
when an RNA molecule acts to conduct an enzymatic function
48
reaction occurring to form the dipeptide in elongation
carboxyl end of the exisiting peptide is joined to the amino end of the incoming amino acid produced from amino to carboxyl ends
49
translocation of the ribosome requires...
elongation factor G and GTP
50
describe termination
1. stop codon arrives at A site 2. release factor binds to stop codon 3. the protein is released from the P site 4. GTP converts to GDP and all other componenet dissociate
51
polysomes
multiple ribosomes translating the same mRNA simultaneously in prokaryotes, transcription and translation can occur simultaneously since DNA isn't in nucleus
52
Differences in eukaryotic initiation of translation
- cap and poly a tail impact initiation - elongation and termination are similar but with more and different EFs and TFs - it is not polycistronic
53
Kozac sequence
- surrounds the start codon in eukaryotic mRNA 5' - ACCAUGG - 3'
54
Role of cap in eukaryotic translation
1. small subunit of ribosome, initiation factors, and charged initiator tRNA recognize and bind to the cap 2. the initiation complex moves down the mRNA until it finds the first start codon
55
Role of poly A tail in eukaryotic translation
- it interacts with proteins that bind the 5' cap to enhance ribosomal binding by forming closed loop structure

Genetics Test 3 (7 decks)

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