basics

Question 1

what is the central dogma of biology?

Answer 1

it refers to the unidirectional flow of genetic information from DNA through mRNA to the protein, involving transcription & translation

Question 2

what is the definition of a gene?

Answer 2

a gene is defined as a unit of inheritance which contains a sequence of nucleotides that codes for the synthesis of a gene product

Question 3

what are the 2 main functional components of a gene?

Answer 3

1. the coding region

2. the promoter

Question 4

what is an exon?

Answer 4

it is a coding sequence, as it is a sequence of nucleotides that codes for a gene product

Question 5

what is an intron?

Answer 5

an intron is a non-coding sequence, as it is used to separate exons

Question 6

what does the promoter contain?

Answer 6

it contains non-coding nucleotide sequences

Question 7

what is the function of a promoter?

Answer 7

the promoter controls when & in what tissue a gene is transcribed

Question 8

what does the genetic code determine?

Answer 8

the genetic code determines the amino acid sequence of a polypeptide chain via transcription & translation

Question 9

where is the genetic code stored?

Answer 9

in a specific sequence of DNA nucleotides in the gene

Question 10

what happens to the genetic code during transcription?

Answer 10

the specific sequence of DNA nucleotides of the gene is copied into a specific sequence of nucleotides in the mRNA

Question 11

what happens to the mRNA in translation?

Answer 11

the mRNA sequence is decoded, giving rise to the amino acid sequence of the polypeptide chain

Question 12

what are the features of the genetic code that allows the 4 nucleotides of DNA to give rise to the 20 known amino acids?

Answer 12

1. it is a triplet code
2. it is degenerate
3. it is non-overlapping
4. it is punctuated
5. it is universal

Question 13

what does it mean when we say that the genetic code is degenerate?

Answer 13

it means that more than 1 codon can code for the same amino acid

Question 14

why do we say that the genetic code is non-overlapping?

Answer 14

this is because each nucleotide in the triplet code is only used once, and that the codons in the genetic code do not overlap when mRNA is read

Question 15

what does it mean when we say that the genetic code is punctuated?

Answer 15

• it means that there is a start codon, AUG, present to signal the initiation of translation of mRNA into a sequence of amino acids
• it also means that there are stop codons, UAG, UAA, UGA, present to act as ‘stop signals’ for the termination of translation

Question 16

why do we say that the genetic code is universal?

Answer 16

• this is because the same 3 bases code for the same amino acids in all organisms!!
• however, there are exceptions to the code in certain types of bacteria & single-cell eukaryotes

Question 17

why is the genetic code a triplet code?

Answer 17

• it is a triplet code because when the genetic code is a triplet code, 4^3 = 64 amino acids can be coded, which is more than 20
• and as there are only 20 amino acids to code, some triplets can be redundant

Question 18

explain what is it meant by the term ‘codon’. [2]

Answer 18

1. a codon is a triplet base on mRNA [0.5]
2. that codes for 1 amino acid [0.5]
3. it is also complementary to the template strand of DNA [0.5]
4. and a specific anti-codon of tRNA [0.5]

Question 19

explain what is it meant by the term ‘anti-codon’ [0.5]

Answer 19

1. an anti-codon is a specific set of triplet bases of a tRNA [1]
2. that determines the specific amino acid sequence that it carries [0.5]
3. it is also complementary to a specific anti-codon on the mRNA [0.5]