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Fundamentals Of Life Science > The Genetic Code > Flashcards

The Genetic Code Flashcards

1
Q

Define DNA replication

A

DNA is copied to make more DNA

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2
Q

Define transcription

A

DNA is used as a template to make RNA

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3
Q

Define translation

A

RNA is read and proteins are made

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4
Q

Where does transcription occur?

A

In the nucleus

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5
Q

Where does translation occur?

A

In the cytoplasm

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6
Q

What is the basic structure of an amino acid?

A 
NH3 (amino group)
Central carbon 
R group 
Hydrogen 
COOH (carboxyl group)
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7
Q

What joins two amino acids?

A

A peptide bond

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8
Q

Where does the peptide bond form?

A

Between the carboxylic group of one amino acid and the amino group of the next

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9
Q

What kind of code is the genetic code?

A

Triplet code

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10
Q

What does triplet code mean?

A

Three nucleotides specify one amino acid

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11
Q

What is another name for a triplet?

A

A codon

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12
Q

What is the start codon in all polypeptides?

A

Methionine

AUG

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13
Q

What are the three stop codons?

A

UAA
UAG
UGA

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14
Q

What does degenerate mean?

A

Usually there is more than one codon for an amino acid

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15
Q

What is an open reading frame?

A

A string of sense codons that start with the codon ATG and end with a stop codon at the 3’ end

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16
Q

What determines which reading frame is read?

A

The start codon

Also the largest possible protein is always made

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17
Q

How many possible reading frames are there?

A

6

3 in each direction

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18
Q

How many subunits make up a ribosome?

A

Two

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19
Q

What are the two subunits of a ribosome?

A

The small and large subunit

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20
Q

What kind of ribosome is involved in protein synthesis and mRNA?

A

An 80s ribosome

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21
Q

Describe the small subunit

A

40s
18s rRNA
30 ribosomal proteins

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22
Q

Describe the large subunit

A

60s
28s + 5.8s + 5s rRNA
50 ribosomal proteins
2 binding sites

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23
Q

What are the two binding sites present in the large subunit?

A

The P site

The A site

24
Q

What is the A site?

A

The aminoacetyl-tRNA binding site

25
Q

What is the P site?

A

The peptidyl-tRNA binding site

26
Q

What is the role of tRNA?

A

tRNA molecules carry the amino acids to the ribosomes to be assembled into polypeptide chains

27
Q

What does mRNA consist of?

A

Leader
Reading frame
Trailer

28
Q

What features do all tRNA molecules share?

A

Similar in size and shape

CCA at the 3’ end which amino acids bind to

29
Q

What is the anticodon?

A

The section of the tRNA molecule which during translation reads the matching codon on mRNA

30
Q

How is an amino acid added to a tRNA molecule?

A

The enzyme aminoacyl-tRNA synthetase

31
Q

What is the name of the process given to adding amino acids to tRNA

A

Aminoacylation

32
Q

How many aminoacyl-tRNA synthases are there?

A

As there are 20 amino acids, there are 20 aminoacyl-tRNA synthases

33
Q

Are aminoacyl-tRNA synthases dependent on the codon?

A

No

So when an amino acid has multiple codons it will still only have one aminoacyl-tRNA synthase

34
Q

Describe the role of ATP in aminoacylation

A

ATP binds to the amino acid once it has bound to the enzyme
Loses two phosphate groups to become AMP
AMP released
tRNA binds

35
Q

What is the first step of translation?

A

A small ribosomal subunit binds to mRNA at start codon region

36
Q

What attracts the large subunit?

A

Initiation factors
This completes the ribosome
The start codon occupies the P site

37
Q

What is elongation dependent on?

A

The appropriate aminoacyl-tRNA binding to the codon in the A site of the ribosome

38
Q

What happens when a stop codon is reached?

A

Polypeptide synthesis ends
Polypeptide released from tRNA
tRNA released from the ribosome
Ribosomal subunits separate

39
Q

How many ribosomes can be on a piece of mRNA at one time?

40
Q

Name three things that cause DNA mutation?

A

Substitution
Insertion
Deletion

41
Q

Name the three kinds of mutation

A

Silent
Missense
Nonsense

42
Q

Describe the steps of aminoacylation

A

Complemintary amino acid binds to a specific AtRNA active site.
ATP binds to the amino acid once it has bound to the enzyme after causing a change in shape of the enzyme
ATP Llses two phosphate groups to become AMP
AMP released exposing a second active site complimentary to the uncharged tRNA
tRNA binds to the enzyme
Once binding of the amino acid to the acceptor stem of tRNA molecule occurs, it is expelled from the enzyme.

43
Q

What is the structure of tRNA?

A

Single stranded.
Has an acceptor stem of CCA at the 3’ for amino acid binding
Anticodon loop is variable dependent on the amino acid at the acceptor stem.

44
Q

What are the 3 phases of translation?

A

Initiation
Elongation
Termination

45
Q

What happens during the initiation phase of translation?

A

A small ribosomal subunit binds to mRNA at start codon region allowing a tRNA carrying methionine to bind to the P site.
initiation complex of translation forms
The A site is free and the next 3 bases of the mRNA are read.
A charged tRNA carrying the sepcific amino acid will bind to the A site
A peptide bond forms between the adjacent amino acids
The tRNA in the P site becomes uncharged and leaves from the ribosome allowing the A site tRNA to move into the P site.

46
Q

What happens during the elongation phase of translation?

A

Elongation of the polypeptide begins as the appropriate charged tRNA molecule will bind to the A site
Peptide bonds form between the amino acids elongating the polypeptide
AS the peptide bonds for the P site tRNA moves off and the A site tRNA moves into the P site constantly making the A site free for more tRNAs to bind to.
This process repeats until a stop codon is identified.

47
Q

What happens during the termination phase of translation?

A

No anticodon on tRNA matches a stop codon
Nothing occupies the A site
Release factor binds to the stop codon
Peptidyl transferase is triggered releasing the polypeptide
Ribosomal subunits separate

48
Q

What are polysomes?

A

Where multiple ribosomes bind to the mRNA strand at any one time forming a polysome.

49
Q

What is a silent mutation?

A

Base substitution which has no effect on the encoded amino acid due to DNA being degenerate

50
Q

What is a missense mutation?

A

Base substitution encoding for a different amino acid.
This has a big influence on the protein folding and therefore its function.
This is less effected if the new amino acid is similar biochemically.

51
Q

What is a nonsense mutation?

A

Base substitution which encodes for a stop codon causing early recruitment of a release factor and therefore forms a shortened non-functional protein.

52
Q

What is an insertion mutation?

A

Addition of a base in the coding which will cause a frameshift if the insertion is not a multiple of 3 bases added.

53
Q

What is a deletion mutation?

A

Deletion of a base in the coding which will cause a frameshift if the insertion is not a multiple of 3 bases added.

54
Q

What is extensive missense?

A

Where a stop codon is deleted via a deletion mutation

55
Q

What is extensive nonsense?

A

Where a stop codon is added via an insertion mutation.

56
Q

Where must addition and deletion mutations occur?

A

Within the reading frame of the first methionine.

Fundamentals Of Life Science (26 decks)

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