2.1.2k The Nature of the Genetic Code Flashcards

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1
Q

Structure of Amino acid on slide 2

A
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2
Q

What is a gene

A

A length of DNA that codes for a polypeptide or for a length of RNA that is involved in regulating gene expression

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3
Q

What do genes do

A
  • Each chromosome in a eukaryotic cell nucleus includes a molecule of DNA
  • On each chromosome there are specific lengths of the DNA called genes
  • Each gene contains a code that determines the sequence of amino acids in a particular protein or polypeptide
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4
Q

Size of genes

A

Some genes can be as short as 50-100 nucleotides in length, but most are thousands of nucleotides long

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5
Q

What is the code for DNA

A

The code for DNA is a triplet code in which 3 bases code for an amino acid. This is called a codon

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6
Q

What is a Triplet code/codon

A

The 3 nitrogenous bases read along the DNA strand that code for amino acids

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7
Q

How many different combinations of triplet codes are there

A

There are 20 different amino acids & 64 different combinations of triplet codes; therefore some triplets code for the same amino acid.
However, some amino acids only have 1 triplet cod (eg. methionine, tryptophan)

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8
Q

What is the advantage of having different codes for the same amino acid

A

Having diff codes for the same amino acid means a mutation may have no effect on the amino acid coded for

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9
Q

see slide 5 for examples of triplet code

A
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10
Q

The nature of the genetic code

A
  • Universal
  • Degenerate
  • Non-overlapping
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11
Q

The nature of the genetic code: UNIVERSAL

A

The genetic code is near UNIVERSAL, bc in almost all living organisms the same triplet of DNA bases codes for the same amino acid

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12
Q

The nature of the genetic code: DEGENERATE

A

The genetic code is described as DEGENERATE, bc for all amino acids (except methionine & tryptophan), there is more than one base triplet

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13
Q

The nature of the genetic code: NON-OVERLAPPING

A

The genetic code is NON-OVERLAPPING, & it is read starting from a fixed point in groups of 3 bases. If a base is added or deleted then it causes a frame shift, as every base triplet after that, & hence every amino acid coded for, is changed

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14
Q

see slide 7 for using the chart to find protein sequence from a DNA sequence

A
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15
Q

see slide 8-11 for exam qs + ms

A
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16
Q

EXAM Q: Enzymes have active sites in which specific substates fit precisely. Suggest how a genetic mutation may result in an enzyme becoming non-functional

A

A mutation in the DNA changes the triplet code, meaning different amino acids are incorporated into the protein/enzyme that the DNA codes for. If such a change affects the precise structure of the active site, a substrate may not be able to bind, rendering the enzyme non-functional

17
Q

EXAM Q: Explain why there are likely to be more differences, overall, between base sequences of DNA than between amino acid sequences of proteins

A

The triplet code for DNA is degenerative, there are 64 different triplets/codons but only 20 amino acids. Therefore, an amino acid can be coded for by more than one codon, so more opportunity for differences in DNA sequence than amino acid sequence