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63 Cards in this Set

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  • Back

What is the central dogma of molecular biology?

DNA --> RNA --> proteins

What is the genetic code?

It is a degenerate, unambiguous, non-overlapping and almost always universal.

*its the chart that matches up amino acids with codons, would be provided to us on the test

What do stop codons do?

They stop translation of mRNA

What are the three stop codons?




What is the only start codon?

AUG (Methionine)

What two amino acids only have one codon each?

Met and Trp

*The other 18 amino acids have multiple codons

What is the third base position of the codon called and why?

It is called the wobble. This is because the base pairs can wobble between amino acids. For example, G can pair with U, and U C or A can pair with the unusual base hypoxanthine (I) found in tRNA.

How many tRNAs are required to translate the genetic code?

*fewer than 61 tRNAs are required

*this is due to the wobble between the codon and anticodon

Three of the four codons for alanine can pair with...

...a single tRNA that contains the anticodon 5' IGC 3'

How many possible codon combinations are there?

64 possible combinations, 3 are stop codons, 61 sets remaining

How many different possible reading frames of mRNA are there?


What sets the reading frame for translation of a protein from the mRNA?

The start codon, AUG, near the 5' end of the mRNA

How are codons read?

In linear order, starting with AUG

*the other potential reading frames are not used because they would give proteins with different amino acid sequences

Which terminal is on the 5' end? The 3' end?

*n-terminal: 5' end

*c-terminal: 3' end

What is the relationship of mRNA's codon to tRNA's anticodon?

The tRNA contains an amino acid at it's 3' end that corresponds to the codon on mRNA with which the anti-codon of the tRNA can base pair.

What are two characteristics of codon-anticodon pairing?



(the anticodon in tRNA is antiparallel and complementary to the codon translated in mRNA)

Does the wobble position need to be paired?

No, the third position (wobble) of the codon does NOT always need to be paired with the anticodon

What is a point mutation?

a single base change

What is a silent mutation?

a change that specifies the same amino acid

*new codon specifies same amino acid

What is a miss-sense mutation?

a change that specifies a different amino acid

*new codon specifies different amino acid, variable effects (sickle cell anemia mutation)

What is a nonsense mutation?

a change that produces a stop codon

*new codon is a stop codon, usually non-functional

What is an insertion mutation?

an addition of one or more bases

What is a deletion mutation?

a loss of one or more bases

What type of mutation causes sickle cell?

point mutation (miss-sense)

What type of mutation can cause a frameshift? Describe what happens.

Insertion of a single nucleotide causes the reading frame to shift. The amino acid sequence of the protein translated from mRNA is different after the point of insertion.

What can happen to nucleotides that are deleted or inserted?

Similar to a frameshift, if the number of nucleotides deleted or inserted is not a multiple of 3.

How is mutation defined?

A permanent and inheritable. It can cause genetic diseases.

What are the 4 types of point mutations?





How is frameshift mutation defined?

A deletion or addition of base, usually non-functional

What are large segment deletion mutations?

*cause loss of function

*example is alpha-thalassemia

What are mutations in splice sites?


*Tay-Sachs disease

*Gaucher disease

What is triplet repeat expansion?

*longer and unstable protein is produced

*coding region: Huntington disease and spinobulbar muscular atrophy

*non-coding region: fragile X syndrome and myotonic dystrophy

*you could determine this from an anticipated pedigree

In the formation of amino-acyl-tRNA, each type of amino acid is activated by what?

A different amino-acyl tRNA synthetase.

What does amino-acyl tRNA synthetase transfer?

*It transfers the activated amino acid to the 3' end of the correct tRNA by formation of an ester bond that links the amino acid to the tRNA.

What has self checking functions?

tRNA synthetase

The amino acid is first activated by reacting with what? What happens to the amino acid then?


*the amino acid is then transferred from the amino-acyl-AMP to tRNA

The formation of the ester bond that links the amino acid to the tRNA by an amino-acyl-tRNA synthetase requires what? How many steps is the process?

*it requires energy

*it occurs in two steps

What are the two steps of the ester bond formation linking the amino acid to the tRNA?

1. Amino acid is activated in the first step when its carboxyl group reacts with ATP to form an enzyme (amino-acyl-AMP complex and pyrophosphate).

2. The cleavage of an ATP bond in the reaction provides energy, the subsequent cleavage of pyrophosphate helps to drive the reaction by removing one of the products.

In the second step of the ester bond formation, the activated amino acid is transferred from what position to what position?

It is transferred from the 3' hydroxyl group to the 2' hydroxyl group

What do all tRNAs have added after transcription?

They all have a CCA added to the 3' end after transcription

The energy in the amino-acyl-tRNA ester bond is used for what after the ester bond is formed?

It is used in the formation of a peptide bond during the process of protein synthesis

Are amino-acyl-tRNA syntheses specific? If so, what are they specific for?

*Yes, they are specific

*They are each specific for one tRNA, which it recognizes by binding the sequences of nucleotides called the recognition sites

What can sometimes happen with anticodons?

The anticodon can sometimes be a recognition site--true for human tRNAs, yeast, and E. coli.

What is the attachment point on tRNA?

The CCA sequence on the 3' end is the attachment point for the amino acid.

What are the three phases of translation?




What happens during initiation?

Often rate limiting, "regulated" step. It is where the small and large ribosomal subunits bind RNA.

What happens during elongation?

Actual protein synthesis from N to C terminal. This is where the ribosome translocates along mRNA.

What happens during termination?

Terminates at stop sites and releases ribosomal subunits from mRNA

What essential components are needed for the activation of amino acids?

*20 amino acids

*20 amino-acyl-tRNA synthetases

*32 or more tRNAs



What essential components are needed for initiation?


*N-formylmethionyl tRNA

*initiation codon in mRNA (AUG)

*30S ribosomal subunit

*50S ribosomal subunit

*initiation factors



What essential components are needed for elongation?

*functional 70S ribosome

*amino-acyl-tRNAs specified by codons

*elongation factors



What essential components are needed for termination and ribosome recycling?

*termination codon in mRNA

*release factors

*elongation factors

*initiation factors

What essential components are needed for filing and post-translational processing?

Specific enzymes, cofactors, other components for removal of initiating residues and signal sequences, additional proteolytic processing, modification of terminal residues, and attachment of acutely, phosphoric, methyl, carboxyl, carbohydrate, or prosthetic groups

What are the basic steps of the process of translation?

*A tRNA has donated its amino acid to the growing polypeptide chain, it is released from the mRNA

*A new amino-acyl-tRNA binds to the correct codon in the mRNA to donate its amino acid to the growing polypeptide chain

What is the reading direction of mRNA during translation?

5' to 3'

From left to right, what are the three sites of protein synthesis?


*E= ejection

*P= peptidyl

*A= amino-acyl

What does eIF stand for?

eukaryotic initiation factor

The formation of the first peptide bond occurs in what site?

The A site

Subsequent formation of a peptide bond occurs in what site?

The A site

What contains the growing polypeptide chain?

The peptidyl-tRNA

Describe in more detail the elongation of a polypeptide chain (translation).

1. Binding of valyl-tRNA to the A site

2. Formation of a peptide bond

3. Translocation

4. Ejection of the free tRNA

*after step 4, step 1 is repeated using amino-acyl-tRNA for the new codon in the A site

*these 4 steps keep repeating until termination

In the first round of elongation, the amino acid on the tRNA in the A site forms...

...a peptide bond with the methionine on the tRNA in the P site.

stopped at slide 20

stopped at slide 20