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3) Genetics > Chapter 11: From DNA to Proteins: Translation > Flashcards

Chapter 11: From DNA to Proteins: Translation Flashcards

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Biology 101 flashcards
1
Q

Give examples of proteins serving a biological function.

A
  • Spider webs are made of proteins

- Glow of jellyfish is caused by GFP (protein)

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2
Q

What other molecule may have biological functions?

A

Some RNA molecules

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3
Q

What does the genetic code consist of?

A

64 codons

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4
Q

Does the genetic code apply for all organisms?

A
  • Most organisms (universal code)

- However, there are exceptions

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5
Q

Which categories of genomes possess exceptions in terms of the genetic code?

A
  • Bacterial DNA
  • Mitochondrial DNA
  • Nuclear DNA
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6
Q

What four groups do amino acids contain linked to their central carbon?

A
  • Amino group (+H3N)
  • Hydrogen (H)
  • Carboxyl (COO-)
  • Radical (side chain)
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7
Q

What links amino acids together?

A

Formation of a peptide bond, which releases a water molecule

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8
Q

What is the primary structure of a protein?

A

The sequence of amino acids, joined by peptide bonds

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9
Q

What is the secondary structure of a protein?

A

Interactions between amino acid side chains cause folding (ex: alpha-helix)

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10
Q

What is the tertiary structure of a protein?

A

Secondary structure folds further

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11
Q

What is the quaternary structure of a protein?

A

Two or more polypeptide chains associate

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12
Q

What dictates the function of a protein?

A

Its structure

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13
Q

What was the method to determine what amino acids are specified by codons composed of only one type of base (ex: UUU)?

A
  • A single amino acid was marked with radioactivity, while the others were not
  • The homopolymer (UUU) is added to the tube and translation takes place
  • The protein was filtered, and checked for radioactivity
  • Only a single protein (phenylalanine) was radioactive
  • UUU = phenylalanine
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14
Q

How did Nirenberg and Leder further determine which amino acids are specified by codons?

A
  • Synthetic mRNA with one codon was added to charged tRNAs and ribosome in a cell-free system
  • Mixture was passed through a filter
  • tRNAs paired with ribosome-bound mRNA stuck in the filter, whereas unbound tRNAs passed through it
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15
Q

The third nucleotide differs between codons coding for a single amino acid. What does that tell us?

A
  • tRNA detects mostly the first two nucleotides

- The third one is “less” important

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16
Q

Why may 64 codons be covered by between 20 and 50 tRNAs?

A

As certain tRNAs may detect more than one codon combination

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17
Q

What is the Wobble position?

A
  • Occurs at the third nucleotide in the pairing between a codon and an anticodon
  • Non-conventional pairing, which results in a weak interaction
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18
Q

What explains why there is no need for a single tRNA molecule for a specific codon?

A

The Wobble position

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19
Q

What is the key to specificity between an amino acid and its tRNA?

A
  • Aminoacyl-tRNA synthetase

- A cell has 20 different aminoacy-tRNA synthetase, one for each of the 20 amino acids

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20
Q

Each tRNA is specific to how many amino acids?

A

A single amino acid

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21
Q

What is the function of aminoacyl-tRNA synthetase?

A

Attaches the carboxyl group of the amino acid to the hydroxyl group of the 2’ or 3’ carbon of the final nucleotide at the end of tRNA

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22
Q

What is tRNA charging?

A

The attachment of a tRNA to its appropriate amino acid

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23
Q

Where does translation being?

A

At the start codon (AUG)

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24
Q

How does the charge of tRNA alter through translation?

A
  • Charged tRNA (with amino acid) binds to the transcript
  • Amino acid is released
  • Uncharged tRNA leaves the complex
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25
Q

What moves during translation: the ribosome or the mRNA?

A

The ribosome moves along the mRNA

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26
Q

Where are proteins largely synthesized?

A

In the cytoplasm, as ribosomes are mostly contained within the cytoplasm

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27
Q

What are the major steps to the translation process?

A
  • tRNA charging
  • Initiation
  • Elongation
  • Termination
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28
Q

Is the initiation of translation the same between Prokaryotes and Eukaryotes?

A

No, they differ

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29
Q

Which organisms possess the Shine-Dalgarno consensus sequence? Which possess the Kozak sequence? Are they the same?

A
  • Shine-Dalgarno: Prokaryotes
  • Kozak: Eukaryotes
  • They are DIFFERENT
30
Q

What is the function of the Shine-Dalgarno consensus sequence?

A
  • Found in mRNA
  • The small subunit of the ribosome in bacteria detects the sequence, and signals the local assembly of the ribosomal complex
31
Q

What does the small ribosomal subunit recognize in Eukaroytes? What occurs?

A
  • The cap at the 5’ ends of mRNA

- They detect the feature and assemble

32
Q

What is found in the middle of the Kozak sequence?

A

The start codon

33
Q

What is the function of the Kozak sequence?

A
  • Signals where the start codon (AUG) is in the transcript
  • Does NOT signal where the ribosome should assemble
  • AUG codons may be found in various locations, but the Kozak sequence signals which one is required for the initiation of translation
34
Q

How does the poly(A) tail of Eukaryotic mRNA play a role in the initiation of translation?

A
  • Proteins that attach to the poly(A) tail interact with cap-binding proteins
  • Enhance the binding of the ribosome to the 5’ end of the mRNA
35
Q

What are the three sites of elongation?

A
  • A (aminoacyl site)
  • P (peptidyl site)
  • E (exit site)
36
Q

What occurs at the A site?

A

Anticodon on the charged tRNA pairs with the codon on mRNA

37
Q

What occurs at the P site?

A

Formation of a peptide bond releases the amino acid from its tRNA

38
Q

What occurs at the E site?

A

Uncharged tRNA exits to the cytoplasm, where it can be recharged

39
Q

What happens when a stop codon is read by a tRNA?

A
  • The codon is recognized by a release factor, which bind to the ribosome
  • Causes a conformational change within the ribosome, causing it to detach from the mRNA, releasing the completed polypeptide
40
Q

What components are necessary for the binding of amino acid to tRNA?

A
  • Amino acids
  • tRNAs
  • Aminoacyl-tRNA synthetase
  • ATP
41
Q

What components are necessary for initiation of translation?

A
  • mRNA
  • Ribosomal subunits
  • Initiation factors
42
Q

What components are necessary for initiation of elongation?

A
  • Charged tRNAs

- Elongation factors

43
Q

What components are necessary for termination?

A

Release factors

44
Q

Why may transcription and translation occur simultaneously in Prokaryotes?

A
  • Because they do not possess organelles

- The DNA is available for both mechanisms

45
Q

How many ribosomes may treat an mRNA molecule simultaneously in Prokaryotes?

A

Several

46
Q

How many ribosomes may treat an mRNA molecule simultaneously in Eukaryotes?

A

Several

47
Q

Why may transcription and translation never occur simultaneously in Eukaryotes?

A

Because they are physically separated

48
Q

What determines the secondary and tertiary structures of a protein?

A

The amino acid sequence (primary structure) of a protein

49
Q

A codon is
A) One of three nucleotides that encode an amino acid
B) Three nucleotides that encode an amino acid
C) Three amino acids that encode a nucleotide
D) One of four bases in DNA

A

B) Three nucleotides that encode an amino acid

50
Q

How many sense codons do we possess?

A
  • 61 sense codons
  • 3 stop codons
  • 64 codons total
51
Q

What does the degeneracy of the genetic code mean?

A

Amino acids may be specified by more than one codon

52
Q

Which amino acids are only encoded by a single codon?

A
  • Tryptophan

- Methionine

53
Q

What is the important consequence of the wobble position?

A

It allows some tRNAs to pair with more than one codon on an mRNA

54
Q

Through wobble, a single _________ can pair with more than one _________.
A) codon, anticodon
B) group of three nucleotides in DNA, codon in mRNA
C) tRNA, amino acid
D) anticodon, codon

A

D) anticodon, codon

55
Q

The genetic code is generally considered to be (overlapping/non-overlapping).

A

non-overlapping

56
Q

What is a reading frame? How many potential reading frames does any sequence of nucleotides possess?

A
  • Each different way of reading the sequence

- Any sequence of nucleotides has three potential reading frames

57
Q

How is the correct reading frame established?

A

Set by the initiation codon (start codon)

58
Q

What does the initiation codon encode in bacterial cells? What about in eukaryotic cells?

A
  • Bacteria: N-formylmethionine

- Eukaryotes: unformylated methionine

59
Q

No tRNAs have anticodons that pair with __________.

A

termination codons

60
Q

What are isoaccepting tRNAs?

A

tRNAs with different anticodons that accept the same amino acid

61
Q 
Amino acids bind to which part of the tRNA?
A) anticodon
B) codon
C) 3' end
D) 5' end
A

C) 3’ end

62
Q

What are the components necessary for protein synthesis at the initiation stage of translation?

A

1) mRNA
2) Small and large subunits of the ribosome
3) Initiation factors
4) Initiator tRNA with fMet
5) GTP

63
Q

During the initiation of translation in bacteria, the small ribosomal subunit binds to which consensus sequence?

A

The Shine-Dalgarno sequence

64
Q

What site does the initiator tRNA immediately occupy? What site do all other tRNAs first enter?

A
  • P site

- A site

65
Q

What are the three steps of elongation?

A

1) Charged RNA binds to the A site
2) Formation of a peptide bonds between the AA that are attached to tRNAs in the P and A sites
3) Translocation: movement of the ribosome down the mRNA in the 5’ –> 3’ direction

66
Q

What is the progress of each tRNA through the ribosome in the course of elongation?

A
  • A site
  • P site
  • E site
  • Cytoplasm
67
Q 
In elongation, the creation of peptide bonds between amino acids is catalyzed by
A) rRNA
B) protein in the small subunit
C) protein in the large subunit
D) tRNA
A

A) rRNA

68
Q

Where is the termination codon located in the mRNA?

A

In the 3’ untranslated region

69
Q

How does the stability of mRNA differ in bacteria and eukaryotic cells?

A
  • Bacteria mRNA is short-lived

- mRNA in eukaryotic cells can last for hours or days due to the 5’ cap and 3’poly(A) tail

70
Q

What is a polyribosome?

A

mRNA with several ribosomes attached

71
Q

In polyribosomes, the polypeptides associated with which ribosomes will be the longest?
A) Those at the 5’ end of mRNA
B) Those at the 3’ end of mRNA
C) Those in the middle of mRNA
D) All polypeptides will be the same length

A

B) Those at the 3’ end of mRNA

72
Q

Do the initiation and termination codons specify an amino acid? If so, which ones?

A
  • The initiation codon in bacteria encodes N-
    formylmethionine. In eukaryotes, it encodes methionine.
  • Termination codons do not specify amino acids.

3) Genetics (16 decks)

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