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A22 Biology > DNA as the Gentic Code > Flashcards

DNA as the Gentic Code Flashcards

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1
Q

Gene

A

A sequence of nucleotide bases that determines the order of the amino acids in the polypeptide produced.

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2
Q

Gene mutation

A

A spontaneous change in the DNA molecule.

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3
Q

Describe the three-base (triplet) code

A

A sequence of three nucleotide bases codes for an amino acid. There are four bases arranged in groups of three so the number of different sequences is 64.

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4
Q

Describe the degenerate nature of the genetic code

A

Most amino acids have more than one triplet code, since there are more triplets than amino acids.

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5
Q

How many amino acids are there?

A

20

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6
Q

Describe the non-overlapping nature of the genetic code

A

The triplet codes are read separately, each base is only read once.

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7
Q

Explain why DNA does not act directly in protein synthesis

A

DNA is a very long molecule. It is too long to move out of the nucleus and into the cytoplasm. As well as that DNA is better protected in the nucleus than in the metabolically more volatile cytoplasm.

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8
Q

State three differences between mRNA and DNA

A
  1. mRNA is single stranded compared to DNA which has a double helix arrangement ( mRNA is also shorter than DNA)
  2. RNA has a ribose sugar in its phosphate backbone whereas DNA has a deoxyribose sugar
  3. the presence of uracil as a nitrogenous base which replaces thymine of DNA
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9
Q

Describe the process of transcription [4]

A
  • The enzyme DNA helicase unzips the two DNA strands by breaking the hydrogen bonds between bases causing the helix to unzip.
  • The enzyme RNA polymerase moves along the template strand linking free ribonucleotides to the now exposed nucleotides
  • This follows complementary base pairing rules
  • RNA polymerase joins adjacent mRNA nucleotides to each other by phosphodiester bonds
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10
Q

What is an exon?

A

A section of DNA that codes for a polypeptide.

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11
Q

What is an intron?

A

A section of DNA that has a number of functions but does not code for a protein or polypeptide directly.

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12
Q

How does transcription deal with intron sections of DNA?

A
  • The transcription process is able to bypass them

- The template DNA is copied as it is and the intron sections are subsequently removed.

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13
Q

What is functional mRNA?

A

RNA with the introns removed

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14
Q

Describe the process of translation[1]

A

Translation involves the ‘translation’ of the mRNA code into the polypeptide primary structure.

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15
Q

What is a codon?

A

A sequence of three bases on the mRNA that codes for a particular amino acid.

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16
Q

Describe the structure of tRNA

A

a small molecule consisting of 70-80 nucleotides. It is single stranded molecule twisted into a clover leaf shape.

17
Q

What are the two functional parts of the tRNA molecule?

A
  1. A sequence of three bases (anticodon) at one end that forms complementary base pairs with a mRNA codon.
  2. The exposed nucleotide section to which an amino acid can attach
18
Q

What is the role of tRNA?[2]

A
  1. Transport amino acids within the cytoplasm to the site of protein synthesis.
  2. Ensure that each mRNA codon codes for a particular amino acid. In effect, this means that as the protein is being built up, each amino acid will be aligned in sequence adjacent to its matching codon on the mRNA.
19
Q

Name the first codon-linking site

A

aminoacyl site

20
Q

Name the second codon-linking site

A

peptidyl site

21
Q

What is the base sequence of the start codon?

A

AUG

22
Q

What bond links the first two amino acids together to form a dipeptide?

A

Peptide bond

23
Q

Define epigentics

A

The study of heritable modifications of the genome that do not involve changes to the DNA base sequence.

24
Q

Name two ways epigenetic modifications occur

A
  • DNA methylation

- Histone modification

A22 Biology (1 decks)

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